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Sample records for fracture mechanics sensitivity

  1. Fracture Mechanics

    International Nuclear Information System (INIS)

    Jang, Dong Il; Jeong, Gyeong Seop; Han, Min Gu

    1992-08-01

    This book introduces basic theory and analytical solution of fracture mechanics, linear fracture mechanics, non-linear fracture mechanics, dynamic fracture mechanics, environmental fracture and fatigue fracture, application on design fracture mechanics, application on analysis of structural safety, engineering approach method on fracture mechanics, stochastic fracture mechanics, numerical analysis code and fracture toughness test and fracture toughness data. It gives descriptions of fracture mechanics to theory and analysis from application of engineering.

  2. Fracture Mechanics

    CERN Document Server

    Zehnder, Alan T

    2012-01-01

    Fracture mechanics is a vast and growing field. This book develops the basic elements needed for both fracture research and engineering practice. The emphasis is on continuum mechanics models for energy flows and crack-tip stress- and deformation fields in elastic and elastic-plastic materials. In addition to a brief discussion of computational fracture methods, the text includes practical sections on fracture criteria, fracture toughness testing, and methods for measuring stress intensity factors and energy release rates. Class-tested at Cornell, this book is designed for students, researchers and practitioners interested in understanding and contributing to a diverse and vital field of knowledge. Alan Zehnder joined the faculty at Cornell University in 1988. Since then he has served in a number of leadership roles including Chair of the Department of Theoretical and Applied Mechanics, and Director of the Sibley School of Mechanical and Aerospace Engineering.  He teaches applied mechanics and his research t...

  3. Fracture mechanics

    CERN Document Server

    Perez, Nestor

    2017-01-01

    The second edition of this textbook includes a refined presentation of concepts in each chapter, additional examples; new problems and sections, such as conformal mapping and mechanical behavior of wood; while retaining all the features of the original book. The material included in this book is based upon the development of analytical and numerical procedures pertinent to particular fields of linear elastic fracture mechanics (LEFM) and plastic fracture mechanics (PFM), including mixed-mode-loading interaction. The mathematical approach undertaken herein is coupled with a brief review of several fracture theories available in cited references, along with many color images and figures. Dynamic fracture mechanics is included through the field of fatigue and Charpy impact testing. Explains computational and engineering approaches for solving crack-related problems using straightforward mathematics that facilitate comprehension of the physical meaning of crack growth processes; Expands computational understandin...

  4. Fracture Mechanics of Concrete

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    This special issue of S¯adhan¯a is rightly dedicated to the fracture mechanics of concrete. In particular, the size effect is highlighted. As appropriately pointed out in the first inter- national conference on fracture mechanics of concrete structures, FraMCos-I, organized by Z P Ba˘zant, at Breckenridge, Colorado in 1992, ...

  5. Classical fracture mechanics methods

    International Nuclear Information System (INIS)

    Schwalbe, K.H.; Heerens, J.; Landes, J.D.

    2007-01-01

    Comprehensive Structural Integrity is a reference work which covers all activities involved in the assurance of structural integrity. It provides engineers and scientists with an unparalleled depth of knowledge in the disciplines involved. The new online Volume 11 is dedicated to the mechanical characteristics of materials. This paper contains the chapter 11.02 of this volume and is structured as follows: Test techniques; Analysis; Fracture behavior; Fracture toughness tests for nonmetals

  6. Elastic plastic fracture mechanics

    International Nuclear Information System (INIS)

    Simpson, L.A.

    1978-07-01

    The application of linear elastic fracture mechanics (LEFM) to crack stability in brittle structures is now well understood and widely applied. However, in many structural materials, crack propagation is accompanied by considerable crack-tip plasticity which invalidates the use of LEFM. Thus, present day research in fracture mechanics is aimed at developing parameters for predicting crack propagation under elastic-plastic conditions. These include critical crack-opening-displacement methods, the J integral and R-curve techniques. This report provides an introduction to these concepts and gives some examples of their applications. (author)

  7. Fracture mechanics and parapsychology

    Science.gov (United States)

    Cherepanov, G. P.

    2010-08-01

    The problem of postcritical deformation of materials beyond the ultimate strength is considered a division of fracture mechanics. A simple example is used to show the relationship between this problem and parapsychology, which studies phenomena and processes where the causality principle fails. It is shown that the concept of postcritical deformation leads to problems with no solution

  8. Fracture mechanics and microstructures

    International Nuclear Information System (INIS)

    Gee, M.G.; Morrell, R.

    1986-01-01

    The influence of microstructure on defects in ceramics, and the consequences of their presence for the application of fracture mechanics theories are reviewed. The complexities of microstructures, especially the multiphase nature, the crystallographic anisotropy and the resultant anisotropic physical properties, and the variation of microstructure and surface finish from point to point in real components, all lead to considerable uncertainties in the actual performance of any particular component. It is concluded that although the concepts of fracture mechanics have been and will continue to be most useful for the qualitative explanation of fracture phenomena, the usefulness as a predictive tool with respect to most existing types of material is limited by the interrelation between material microstructure and mechanical properties. At present, the only method of eliminating components with unsatisfactory mechanical properties is to proof-test them, despite the fact that proof-testing itself is limited in ability to cope with changes to the component in service. The aim of the manufacturer must be to improve quality and consistency within individual components, from component to component, and from batch to batch. The aim of the fracture specialist must be to study longer-term properties to improve the accuracy of behaviour predictions with a stronger data base. Materials development needs to concentrate on obtaining defect-free materials that can be translated into more-reliable products, using our present understanding of the influence of microstructure on strength and toughness

  9. Phase Field Fracture Mechanics.

    Energy Technology Data Exchange (ETDEWEB)

    Robertson, Brett Anthony [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2015-11-01

    For this assignment, a newer technique of fracture mechanics using a phase field approach, will be examined and compared with experimental data for a bend test and a tension test. The software being used is Sierra Solid Mechanics, an implicit/explicit finite element code developed at Sandia National Labs in Albuquerque, New Mexico. The bend test experimental data was also obtained at Sandia Labs while the tension test data was found in a report online from Purdue University.

  10. Fracture Mechanics of Concrete

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    Going back in the memory pipeline, it was M F Kaplan1 (in 1961) who tried to obtain the fracture toughness of concrete. It was observed ... of cracks. The next question is how to bring the size effect into codes of practice on the design of reinforced concrete structures, since large structures like dams, nuclear reactors, very tall.

  11. Fracture Mechanics of Concrete

    DEFF Research Database (Denmark)

    Ulfkjær, Jens Peder

    Since analytical methods are very time consuming different analytical models have been developed. Three methods for plain concrete are presented, where one of the methods is developed by the author. The method is based on three different fracture models. Also two models applicable for lightly reinforced...... with a description of the different types of size effects. Three examples which discuss the two terms 'size effect' and 'brittleness' and the importance of a stiff test rig. Finally some brittleness numbers are defined. Chapter 3 In chapter 3 the most well-known numerical methods which use the fictitious crack...... to describe fracture in concrete are presented. Two of the methods are combined into a power method which is stable for all brittleness numbers and which is able of calculating the entire load-displacement curve even for very ductile beams. This method is used extensively in the rest of the thesis. Chapter 4...

  12. Probabilistic application of fracture mechanics

    International Nuclear Information System (INIS)

    Dufresne, J.

    1981-04-01

    The different methods used to evaluate the rupture probability of a pressure vessel are reviewed. Data collection and processing of all parameters necessary for fracture mechanics evaluation are presented with particular attention to the size distribution of defects in actual vessels. Physical process is followed during crack growth and unstable propagation, using LEFM (Linear Elastic Fracture Mechanism) and plastic instability. Results show that the final failure probability for a PWR pressure vessel is 3.5 10 -8 , and is due essentially to LOCAs for any break size. The weakest point is the internal side of the belt line

  13. Fracture mechanics model of fragmentation

    International Nuclear Information System (INIS)

    Glenn, L.A.; Gommerstadt, B.Y.; Chudnovsky, A.

    1986-01-01

    A model of the fragmentation process is developed, based on the theory of linear elastic fracture mechanics, which predicts the average fragment size as a function of strain rate and material properties. This approach permits a unification of previous results, yielding Griffith's solution in the low-strain-rate limit and Grady's solution at high strain rates

  14. Continuum damage and fracture mechanics

    CERN Document Server

    Öchsner, Andreas

    2016-01-01

    This textbook offers readers an introduction to damage and fracture mechanics, equipping them to grasp the basic ideas of the presented approaches to modeling in applied mechanics. In the first part, the book reviews and expands on the classical theory of elastic and elasto-plastic material behavior. A solid understanding of these two topics is the essential prerequisite to advancing to damage and fracture mechanics. Thus, the second part of this course provides an introduction to the treatment of damage and fractures in the context of applied mechanics. Wherever possible, the one-dimensional case is first introduced and then generalized in a following step. This departs somewhat from the more classical approach, where first the most general case is derived and then simplified to special cases. In general, the required mathematics background is kept to a minimum.   Tutorials are included at the end of each chapter, presenting the major steps for the solution and offering valuable tips and tricks. The supplem...

  15. Deformation and fracture mechanics of engineering materials

    National Research Council Canada - National Science Library

    Hertzberg, Richard W; Vinci, Richard Paul; Hertzberg, Jason L

    2012-01-01

    "Hertzberg's 5th edition of Deformation & Fracture Mechanics of Engineering Materials offers several new features including a greater number and variety of homework problems using more computational software...

  16. Recent trends in fracture and damage mechanics

    CERN Document Server

    Zybell, Lutz

    2016-01-01

    This book covers a wide range of topics in fracture and damage mechanics. It presents historical perspectives as well as recent innovative developments, presented by peer reviewed contributions from internationally acknowledged authors.  The volume deals with the modeling of fracture and damage in smart materials, current industrial applications of fracture mechanics, and it explores advances in fracture testing methods. In addition, readers will discover trends in the field of local approach to fracture and approaches using analytical mechanics. Scholars in the fields of materials science, engineering and computational science will value this volume which is dedicated to Meinhard Kuna on the occasion of his 65th birthday in 2015. This book incorporates the proceedings of an international symposium that was organized to honor Meinhard Kuna’s contributions to the field of theoretical and applied fracture and damage mechanics.

  17. Intermetallic alloys: Deformation, mechanical and fracture behaviour

    International Nuclear Information System (INIS)

    Dogan, B.

    1988-01-01

    The state of the art in intermetallic alloys development with particular emphasis on deformation, mechanical and fracture behaviour is documented. This review paper is prepared to lay the ground stones for a future work on mechanical property characterization and fracture behaviour of intermetallic alloys at GKSS. (orig.)

  18. Fracture mechanics in pavement design

    CSIR Research Space (South Africa)

    Denneman, E

    2009-07-01

    Full Text Available MODELLING FRACTURE IN PAVEMENT MATERIALS The cohesive crack approach can be incorporated in finite element method (FEM) to simulate fracture in pavement materials. In this paper an embedded discontinuity method (EDM) based on the work by Sancho et al... through elements, in other words, independent of nodal positions and element boundaries. The EDM was used for the numerical simulation of two examples of fracture tests on road materials from the literature. The model is applied to reproduce...

  19. Fracture mechanics of piezoelectric and ferroelectric solids

    CERN Document Server

    Fang, Daining

    2013-01-01

    Fracture Mechanics of Piezoelectric and Ferroelectric Solids presents a systematic and comprehensive coverage of the fracture mechanics of piezoelectric/ferroelectric materials, which includes the theoretical analysis, numerical computations and experimental observations. The main emphasis is placed on the mechanics description of various crack problems such static, dynamic and interface fractures as well as the physical explanations for the mechanism of electrically induced fracture. The book is intended for postgraduate students, researchers and engineers in the fields of solid mechanics, applied physics, material science and mechanical engineering. Dr. Daining Fang is a professor at the School of Aerospace, Tsinghua University, China; Dr. Jinxi Liu is a professor at the Department of Engineering Mechanics, Shijiazhuang Railway Institute, China.

  20. Physical fracture properties (fracture surfaces as information sources; crackgrowth and fracture mechanisms; exemples of cracks)

    International Nuclear Information System (INIS)

    Meny, Lucienne.

    1979-06-01

    Fracture surfaces are considered as a useful source of informations: an introduction to fractography is presented; the fracture surface may be observed through X ray microanalysis, and other physical methods such as Auger electron spectroscopy or secundary ion emission. The mechanisms of macroscopic and microscopic crackgrowth and fracture are described, in the case of unstable fracture (cleavage, ductile with shear, intergranular brittleness) and of progressive crack propagation (creep, fatigue). Exemples of cracks are presented in the last chapter [fr

  1. Mechanisms of hydraulic fracturing in cohesive soil

    Directory of Open Access Journals (Sweden)

    Jun-jie Wang

    2009-12-01

    Full Text Available Hydraulic fracturing in the soil core of earth-rockfill dams is a common problem affecting the safety of the dams. Based on fracture tests, a new criterion for hydraulic fracturing in cohesive soil was suggested. Using this criterion, the mechanisms of hydraulic fracturing in cubic soil specimens were investigated. The results indicate that the propagation of the crack in a cubic specimen under water pressure occurs in a mixed mode I-II if the crack face is not perpendicular to any of the principal stresses, and the crack most likely to propagate is the one that is perpendicular to the minor principal stress and propagates in mode I.

  2. Mechanical Behaviour of Materials Volume II Fracture Mechanics and Damage

    CERN Document Server

    François, Dominique; Zaoui, André

    2013-01-01

    Designing new structural materials, extending lifetimes and guarding against fracture in service are among the preoccupations of engineers, and to deal with these they need to have command of the mechanics of material behaviour. This ought to reflect in the training of students. In this respect, the first volume of this work deals with elastic, elastoplastic, elastoviscoplastic and viscoelastic behaviours; this second volume continues with fracture mechanics and damage, and with contact mechanics, friction and wear. As in Volume I, the treatment links the active mechanisms on the microscopic scale and the laws of macroscopic behaviour. Chapter I is an introduction to the various damage phenomena. Chapter II gives the essential of fracture mechanics. Chapter III is devoted to brittle fracture, chapter IV to ductile fracture and chapter V to the brittle-ductile transition. Chapter VI is a survey of fatigue damage. Chapter VII is devoted to hydogen embrittlement and to environment assisted cracking, chapter VIII...

  3. Fractures and Rock Mechanics, Phase 1

    DEFF Research Database (Denmark)

    Havmøller, Ole; Krogsbøll, Anette

    1997-01-01

    The main objectives of the project are to combine geological description of fractures, chalk types and rock mechanical properties, and to investigate whether the chosen outcrops can be used as analogues to reservoir chalks. Five chalk types, representing two outcrop localities: Stevns...... and Hillerslev, and three reservoir zones: Tyra Maastrictian, Valhall Tor and Valhall Hod are investigated. Different test types are applied in small and large scale in order to investigate the influence on stiffness and strength from natural and induced fractures, stylolites, bedding planes and healed fractures...

  4. Integration of NDE Reliability and Fracture Mechanics

    Energy Technology Data Exchange (ETDEWEB)

    Becker, F. L.; Doctor, S. R.; Heas!er, P. G.; Morris, C. J.; Pitman, S. G.; Selby, G. P.; Simonen, F. A.

    1981-03-01

    The Pacific Northwest Laboratory is conducting a four-phase program for measuring and evaluating the effectiveness and reliability of in-service inspection (lSI} performed on the primary system piping welds of commercial light water reactors (LWRs). Phase I of the program is complete. A survey was made of the state of practice for ultrasonic rsr of LWR primary system piping welds. Fracture mechanics calculations were made to establish required nondestrutive testing sensitivities. In general, it was found that fatigue flaws less than 25% of wall thickness would not grow to failure within an inspection interval of 10 years. However, in some cases failure could occur considerably faster. Statistical methods for predicting and measuring the effectiveness and reliability of lSI were developed and will be applied in the "Round Robin Inspections" of Phase II. Methods were also developed for the production of flaws typical of those found in service. Samples fabricated by these methods wilI be used in Phase II to test inspection effectiveness and reliability. Measurements were made of the influence of flaw characteristics {i.e., roughness, tightness, and orientation) on inspection reliability. These measurernents, as well as the predictions of a statistical model for inspection reliability, indicate that current reporting and recording sensitivities are inadequate.

  5. Development in fracture mechanics and failure assessment

    International Nuclear Information System (INIS)

    Chell, G.G.

    1978-01-01

    Application of the theories of fracture mechanics can help avoid the type of catastrophic failure that has occurred in structures, eg the failure, whilst undergoing a routine test, of a turbogenerator for Hinkly Point power station. The development is described for a procedure for summarising the salient features of fracture theory as applied to steel structures. This is achieved by the introduction of a relatively simple failure assessment diagram which may be used by unspecialised staff. (author)

  6. Application of microstatistical fracture mechanics to dynamic fracture problems

    International Nuclear Information System (INIS)

    Shockey, D.A.; Curran, D.R.; Seaman, L.

    1983-01-01

    This chapter presents a microstatistical treatment of shear bands. Describes the microstatistical fracture mechanics (MSFM) approach by illustrating its use in the case of shock-induced ductile voids in steel. Shows that the microstatistical approach merges with the continuum approach. Computes the behavior of a macrocrack propagating in a DCB specimen by using MSFM and the data generated in the shock wave experiments. Discusses shockwave-induced ductile fractures; plate impact experiments; data analysis; progress in MSFM and required research efforts; and macrocrack propagation. Points out that although continuum treatments have the advantage of simplicity and low cost, the more complex and expensive MSFM treatment may be the only viable approach when detailed information is needed such as size, velocity, and trajectory distributions of fragments ejected from a plate of armor steel after impact

  7. Geometry, mechanics and transmissivity of rock fractures

    International Nuclear Information System (INIS)

    Lanaro, F.

    2001-04-01

    This thesis work investigates methods and tools for characterising, testing and modelling the behaviour of rock fractures. Using a 3D-laser-scanning technique, the topography of the surfaces and their position with respect to one another are measured. From the fracture topography, fracture roughness, angularity and aperture are quantified; the major features used for characterisation. The standard deviations for the asperity heights, surface slopes and aperture are determined. These statistical parameters usually increase/decrease according to power laws of the sampling size, and sometimes reach a sill beyond which they become constant. Also the number of contact spots with a certain area decreases according to a power-law function of the area. These power-law relations reveal the self affine fractal nature of roughness and aperture. Roughness is 'persistent' while aperture varies between 'persistent' and 'anti-persistent' probably depending on the degree of match of the fracture walls. The fractal models for roughness, aperture and contact area are used to develop a constitutive model, based on contact mechanics, for describing the fracture normal and shear deformability. The experimental testing results of normal deformability are simulated well by the model whereas fracture shear deformability is not as well modelled. The model predicts well fracture dilation but is too stiff compared to rock samples. A mathematical description of the aperture pattern during shearing is also formulated. The mean value and covariance of the aperture in shearing is calculated and verifies reported observations. The aperture map of samples is inserted in a numerical program for flow calculation. The 'integral transform method' is used for solving the Reynolds' equation; it transforms the fracture transmissivity pattern into a frequency-based function. This closely resembles the power laws that describe fractals. This function can be described directly from the fractal properties of

  8. Fractures and Rock Mechanics, Phase 1

    DEFF Research Database (Denmark)

    Krogsbøll, Anette; Jakobsen, Finn; Madsen, Lena

    1997-01-01

    The main objective of the project is to combine geological descriptions of fractures, chalk types and rock mechanical properties in order to investigate whether the chosen outcrops can be used as analogues to reservoir chalks. This report deals with 1) geological descriptions of outcrop locality...

  9. Role of fracture mechanics in modern technology

    International Nuclear Information System (INIS)

    Sih, G.C.

    1987-01-01

    The conference served as a forum not only for reviewing past concepts and technologies but it provided an opportunity for many of the designers, engineers and scientists to come forth with more advanced ideas so that fracture mechanics application can be broadened and employed more effectively to avoid unexpected failures that are annoying, costly and destructive of credibility of the engineering community in general

  10. Fracture Mechanisms in Steel Castings

    Directory of Open Access Journals (Sweden)

    Stradomski Z.

    2013-09-01

    Full Text Available The investigations were inspired with the problem of cracking of steel castings during the production process. A single mechanism of decohesion - the intergranular one - occurs in the case of hot cracking, while a variety of structural factors is decisive for hot cracking initiation, depending on chemical composition of the cast steel. The low-carbon and low-alloyed steel castings crack due to the presence of the type II sulphides, the cause of cracking of the high-carbon tool cast steels is the net of secondary cementite and/or ledeburite precipitated along the boundaries of solidified grains. Also the brittle phosphor and carbide eutectics precipitated in the final stage solidification are responsible for cracking of castings made of Hadfield steel. The examination of mechanical properties at 1050°C revealed low or very low strength of high-carbon cast steels.

  11. Computational simulation methods for composite fracture mechanics

    Science.gov (United States)

    Murthy, Pappu L. N.

    1988-01-01

    Structural integrity, durability, and damage tolerance of advanced composites are assessed by studying damage initiation at various scales (micro, macro, and global) and accumulation and growth leading to global failure, quantitatively and qualitatively. In addition, various fracture toughness parameters associated with a typical damage and its growth must be determined. Computational structural analysis codes to aid the composite design engineer in performing these tasks were developed. CODSTRAN (COmposite Durability STRuctural ANalysis) is used to qualitatively and quantitatively assess the progressive damage occurring in composite structures due to mechanical and environmental loads. Next, methods are covered that are currently being developed and used at Lewis to predict interlaminar fracture toughness and related parameters of fiber composites given a prescribed damage. The general purpose finite element code MSC/NASTRAN was used to simulate the interlaminar fracture and the associated individual as well as mixed-mode strain energy release rates in fiber composites.

  12. Mechanical dispersion in fractured crystalline rock systems

    International Nuclear Information System (INIS)

    Lafleur, D.W.; Raven, K.G.

    1986-12-01

    This report compiles and evaluates the hydrogeologic parameters describing the flow of groundwater and transport of solutes in fractured crystalline rocks. This report describes the processes of mechanical dispersion in fractured crystalline rocks, and compiles and evaluates the dispersion parameters determined from both laboratory and field tracer experiments. The compiled data show that extrapolation of the reliable test results performed over intermediate scales (10's of m and 10's to 100's of hours) to larger spatial and temporal scales required for performance assessment of a nuclear waste repository in crystalline rock is not justified. The reliable measures of longitudinal dispersivity of fractured crystalline rock are found to range between 0.4 and 7.8 m

  13. Fracture mechanics of collagen fibrils

    DEFF Research Database (Denmark)

    Svensson, Rene B; Mulder, Hindrik; Kovanen, Vuokko

    2013-01-01

    technique to measure the mechanical behavior of individual collagen fibrils loaded to failure. Fibrils from human patellar tendons, rat-tail tendons (RTTs), NaBH₄ reduced RTTs, and tail tendons of Zucker diabetic fat rats were tested. We found a characteristic three-phase stress-strain behavior in the human...... and the plateau continued until failure. The importance of cross-link lability was investigated by NaBH₄ reduction of the rat-tail fibrils, which did not alter their behavior. These findings shed light on the function of cross-links at the fibril level, but further studies will be required to establish...

  14. 3-D description of fracture surfaces and stress-sensitivity analysis for naturally fractured reservoirs

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, S.Q.; Jioa, D.; Meng, Y.F.; Fan, Y.

    1997-08-01

    Three kinds of reservoir cores (limestone, sandstone, and shale with natural fractures) were used to study the effect of morphology of fracture surfaces on stress sensitivity. The cores, obtained from the reservoirs with depths of 2170 to 2300 m, have fractures which are mated on a large scale, but unmated on a fine scale. A specially designed photoelectric scanner with a computer was used to describe the topography of the fracture surfaces. Then, theoretical analysis of the fracture closure was carried out based on the fracture topography generated. The scanning results show that the asperity has almost normal distributions for all three types of samples. For the tested samples, the fracture closure predicted by the elastic-contact theory is different from the laboratory measurements because plastic deformation of the aspirates plays an important role under the testing range of normal stresses. In this work, the traditionally used elastic-contact theory has been modified to better predict the stress sensitivity of reservoir fractures. Analysis shows that the standard deviation of the probability density function of asperity distribution has a great effect on the fracture closure rate.

  15. Fracture mechanics evaluation of heavy welded structures

    International Nuclear Information System (INIS)

    Sprung, I.; Ericksson, C.W.; Zilberstein, V.A.

    1982-01-01

    This paper describes some applications of nondestructive examination (NDE) and engineering fracture mechanics to evaluation of flaws in heavy welded structures. The paper discusses not only widely recognized linear elastic fracture mechanics (LEFM) analysis, but also methods of the elastic-plastic fracture mechanics (EPFM), such as COD, J-integral, and Failure Assessment Diagram. Examples are given to highlight the importance of interaction between specialists providing input and the specialists performing the analysis. The paper points out that the critical parameters for as-welded structures when calculated by these methods are conservative since they are based on two pessimistic assumptions: that the magnitude of residual stress is always at the yield strength level, and that the residual stress always acts in the same direction as the applied (mechanical) stress. The suggestion is made that it would be prudent to use the COD or the FAD design curves for a conservative design. The appendix examines a J-design curve modified to include residual stresses

  16. Fracture Mechanisms and Strengthening of Slab Lasers

    Science.gov (United States)

    Marion, John E.

    1987-04-01

    The fracture mechanisms of slab lasers are examined and the critical defects, induced during optical fabrication, are identified. A rationale for determining an appropriate operating stress for the slab laser is outlined, based on Weibull statistics, and this method is experimentally assessed in full-sized slab fracture tests. Techniques for achieving strong slabs are then examined. We determine that strengthening by subsurface damage minimization has the highest potential for strengthening, but that slab durability must also be enhanced in order for the slab to remain strong in practice. Good chemical durability is achieved by the use of water-proof overcoats. Good mechanical durability is achieved by the use of compressive surface layers. The compressive surface layers prevent the deterioration in slab strength from physical damage to the slab surface.

  17. Fracture mechanics of ceramics. Vol. 8. Microstructure, methods, design, and fatigue

    International Nuclear Information System (INIS)

    Bradt, R.C.; Evans, A.G.; Hasselman, D.P.H.; Lange, F.F.

    1986-01-01

    This paper presents information on the following topics: fracture mechanics and microstructures; non-lubricated sliding wear of Al 2 O 3 , PSZ and SiC; mixed-mode fracture of ceramics; some fracture properties of alumina-containing electrical porcelains; transformation toughening in the Al 2 O 3 -Cr 2 O 3 /ZrO 2 -HfO 2 system; strength toughness relationships for transformation toughened ceramics; tensile strength and notch sensitivity of Mg-PSZ; fracture mechanisms in lead zirconate titanate ceramics; loading-unloading techniques for determining fracture parameters of brittle materials utilizing four-point bend, chevron-notched specimens; application of the potential drop technique to the fracture mechanics of ceramics; ceramics-to-metal bonding from a fracture mechanics perspective; observed changes in fracture strength following laser irradiation and ion beam mixing of Ni overlayers on sintered alpha-SiC; crack growth in single-crystal silicon; a fracture mechanics and non-destructive evaluation investigation of the subcritical-fracture process in rock; slow crack growth in sintered silicon nitride; uniaxial tensile fatigue testing of sintered silicon carbide under cyclic temperature change; and effect of surface corrosion on glass fracture

  18. The radiation swelling effect on fracture properties and fracture mechanisms of irradiated austenitic steels. Part I. Ductility and fracture toughness

    Energy Technology Data Exchange (ETDEWEB)

    Margolin, B., E-mail: mail@crism.ru; Sorokin, A.; Shvetsova, V.; Minkin, A.; Potapova, V.; Smirnov, V.

    2016-11-15

    The radiation swelling effect on the fracture properties of irradiated austenitic steels under static loading has been studied and analyzed from the mechanical and physical viewpoints. Experimental data on the stress-strain curves, fracture strain, fracture toughness and fracture mechanisms have been represented for austenitic steel of 18Cr-10Ni-Ti grade (Russian analog of AISI 321 steel) irradiated up to neutron dose of 150 dpa with various swelling. Some phenomena in mechanical behaviour of irradiated austenitic steels have been revealed and explained as follows: a sharp decrease of fracture toughness with swelling growth; untypical large increase of fracture toughness with decrease of the test temperature; some increase of fracture toughness after preliminary cyclic loading. Role of channel deformation and channel fracture has been clarified in the properties of irradiated austenitic steel and different tendencies to channel deformation have been shown and explained for the same austenitic steel irradiated at different temperatures and neutron doses.

  19. Introduction into technical application of fracture mechanics. 3. rev. ed.

    International Nuclear Information System (INIS)

    Heckel, K.

    1991-01-01

    Technical components made out of metal material are liable to be defective. Cracks are the most dangerous defects. Based on fracture mechanics methods were developed which permit to estimate the proveness of cracks to intrate fracture. The present book is restricted to the standardised methods of fracture mechanics. Theoretical foundations of various concepts aspect under the fracture mechanics are given. Experimental methods of determining material characteristics of fracture mechanics are explained in detail as a profound knowledge of testing criteria is necessary in order to be able to a characteristic to a component. This book contains the latest level of standardised methods of fracture mechanics. It is meant for advanced students and engineers working in practice. Some fully calculated examples are used as an introduction into the thinking of fracture mechanics. (orig./MM) [de

  20. Micro- and macroapproaches in fracture mechanics for interpreting brittle fracture and fatigue crack growth

    International Nuclear Information System (INIS)

    Ekobori, T.; Konosu, S.; Ekobori, A.

    1980-01-01

    Classified are models of the crack growth mechanism, and in the framework of the fracture mechanics suggested are combined micro- and macroapproaches to interpreting the criterion of the brittle fracture and fatigue crack growth as fracture typical examples, when temporal processes are important or unimportant. Under the brittle fracture conditions the crack propagation criterion is shown to be brought with the high accuracy to a form analogous to one of the crack propagation in a linear fracture mechanics although it is expressed with micro- and macrostructures. Obtained is a good agreement between theoretical and experimental data

  1. Sensitivity of the fracture probability in a reactor vessel to variations in data

    International Nuclear Information System (INIS)

    Nilsson, Fred; Palm, S.

    1980-05-01

    The report discusses the sensitivity of the fracture probability of a reactor vessel. The main problem has been to find relevant input data to the statistical model. The model is based on the linear elastic fracture mechanics. The probability of fracture toughness, of non-detection and of the initial distribution of defects is taken into cinsideration. The loads and fatigue data are considered as deterministic. The probability of fracture for all welds was calculated to P 0 sub (b tot) (T) = 8.34 x 10 -8 , where T is the service life of the vessel. The study discusses relative deviations when varying input data. The value of P 0 sub (b tot) is found to increase fast during the first four years and it remains constant afterwards. The sensitivity analysis shows that P sub (b tot) is very sensitive to input data for fracture toughness and for the distribution in initial defects. In the case of detectability the probability of fracture is inversely proportional to the probability of detection of cracks in the interval 10 to 15 mm. (G.B.)

  2. Sensitivity Analysis of the Bone Fracture Risk Model

    Science.gov (United States)

    Lewandowski, Beth; Myers, Jerry; Sibonga, Jean Diane

    2017-01-01

    Introduction: The probability of bone fracture during and after spaceflight is quantified to aid in mission planning, to determine required astronaut fitness standards and training requirements and to inform countermeasure research and design. Probability is quantified with a probabilistic modeling approach where distributions of model parameter values, instead of single deterministic values, capture the parameter variability within the astronaut population and fracture predictions are probability distributions with a mean value and an associated uncertainty. Because of this uncertainty, the model in its current state cannot discern an effect of countermeasures on fracture probability, for example between use and non-use of bisphosphonates or between spaceflight exercise performed with the Advanced Resistive Exercise Device (ARED) or on devices prior to installation of ARED on the International Space Station. This is thought to be due to the inability to measure key contributors to bone strength, for example, geometry and volumetric distributions of bone mass, with areal bone mineral density (BMD) measurement techniques. To further the applicability of model, we performed a parameter sensitivity study aimed at identifying those parameter uncertainties that most effect the model forecasts in order to determine what areas of the model needed enhancements for reducing uncertainty. Methods: The bone fracture risk model (BFxRM), originally published in (Nelson et al) is a probabilistic model that can assess the risk of astronaut bone fracture. This is accomplished by utilizing biomechanical models to assess the applied loads; utilizing models of spaceflight BMD loss in at-risk skeletal locations; quantifying bone strength through a relationship between areal BMD and bone failure load; and relating fracture risk index (FRI), the ratio of applied load to bone strength, to fracture probability. There are many factors associated with these calculations including

  3. Three-dimensional effects in fracture mechanics

    International Nuclear Information System (INIS)

    Benitez, F.G.

    1991-01-01

    An overall view of the pioneering theories and works, which enlighten the three-dimensional nature of fracture mechanics during the last years is given. the main aim is not an exhaustive reviewing but the displaying of the last developments on this scientific field in a natural way. This work attempts to envisage the limits of disregarding the three-dimensional behaviour in theories, analyses and experiments. Moreover, it tries to draw attention on the scant fervour, although increasing, this three-dimensional nature of fracture has among the scientific community. Finally, a constructive discussion is presented on the use of two-dimensional solutions in the analysis of geometries which bear a three-dimensional configuration. the static two-dimensional solutions and its applications fields are reviewed. also, the static three-dimensional solutions, wherein a comparative analysis with elastoplastic and elastostatic solutions are presented. to end up, the dynamic three-dimensional solutions are compared to the asymptotic two-dimensional ones under the practical applications point of view. (author)

  4. Compressive Fracture of Brittle Geomaterial: Fractal Features of Compression-Induced Fracture Surfaces and Failure Mechanism

    Directory of Open Access Journals (Sweden)

    L. Ren

    2014-01-01

    Full Text Available Compressive fracture is one of the most common failure patterns in geotechnical engineering. For better understanding of the local failure mechanism of compressive fractures of brittle geomaterials, three compressive fracture tests were conducted on sandstone. Edge cracked semicircular bend specimens were used and, consequently, fresh and unfilled compressive fracture surfaces were obtained. A laser profilometer was employed to measure the topography of each rough fracture surface, followed by fractal analysis of the irregularities of the obtained compression-induced fracture surfaces using the cubic cover method. To carry out a contrastive analysis with the results of compressive fracture tests, three tension mode fracture tests were also conducted and the fractal features of the obtained fracture surfaces were determined. The obtained average result of the fractal dimensions of the compression-induced surfaces was 2.070, whereas the average result was 2.067 for the tension-induced fracture surfaces. No remarkable differences between the fractal dimensions of the compression-induced and tension-induced fracture surfaces may indicate that compressive fracture may occur, at least on the investigative scale of this work, in a similar manner to tension fracture.

  5. Fracture mechanics performance of UF6 containers

    International Nuclear Information System (INIS)

    Gonzalez, M.E.; Iorio, A.F.; Crespi, J.C.

    1993-01-01

    The main purpose of this work was to determine the fracture mechanics performance of UF 6 transport cylinders type ANSI N14.1.30B, which was made from ASTM A 516 Grade 70 steel. It was assumed an internal surface axial crack subjected to stresses due to service, proof and transport accident loads. The KUMAR-GERMAN-SHIH elastoplastic methodology gave adequate results for crack depth estimation. The results validate the leak-before-break criteria for service and proof conditions but not for accident ones. In the last case a non-destructive examination must be done in order to assure the absence of defects larger than one third of the cylinder wall thickness. (Author)

  6. Numerical modelling in non linear fracture mechanics

    Directory of Open Access Journals (Sweden)

    Viggo Tvergaard

    2007-07-01

    Full Text Available Some numerical studies of crack propagation are based on using constitutive models that accountfor damage evolution in the material. When a critical damage value has been reached in a materialpoint, it is natural to assume that this point has no more carrying capacity, as is done numerically in the elementvanish technique. In the present review this procedure is illustrated for micromechanically based materialmodels, such as a ductile failure model that accounts for the nucleation and growth of voids to coalescence, and a model for intergranular creep failure with diffusive growth of grain boundary cavities leading to micro-crack formation. The procedure is also illustrated for low cycle fatigue, based on continuum damage mechanics. In addition, the possibility of crack growth predictions for elastic-plastic solids using cohesive zone models to represent the fracture process is discussed.

  7. Mechanical stratigraphic controls on natural fracture spacing and penetration

    Science.gov (United States)

    McGinnis, Ronald N.; Ferrill, David A.; Morris, Alan P.; Smart, Kevin J.; Lehrmann, Daniel

    2017-02-01

    Fine-grained low permeability sedimentary rocks, such as shale and mudrock, have drawn attention as unconventional hydrocarbon reservoirs. Fracturing - both natural and induced - is extremely important for increasing permeability in otherwise low-permeability rock. We analyze natural extension fracture networks within a complete measured outcrop section of the Ernst Member of the Boquillas Formation in Big Bend National Park, west Texas. Results of bed-center, dip-parallel scanline surveys demonstrate nearly identical fracture strikes and slight variation in dip between mudrock, chalk, and limestone beds. Fracture spacing tends to increase proportional to bed thickness in limestone and chalk beds; however, dramatic differences in fracture spacing are observed in mudrock. A direct relationship is observed between fracture spacing/thickness ratio and rock competence. Vertical fracture penetrations measured from the middle of chalk and limestone beds generally extend to and often beyond bed boundaries into the vertically adjacent mudrock beds. In contrast, fractures in the mudrock beds rarely penetrate beyond the bed boundaries into the adjacent carbonate beds. Consequently, natural bed-perpendicular fracture connectivity through the mechanically layered sequence generally is poor. Fracture connectivity strongly influences permeability architecture, and fracture prediction should consider thin bed-scale control on fracture heights and the strong lithologic control on fracture spacing.

  8. Influence of temperature on fracture mechanisms of magnesium composites

    Energy Technology Data Exchange (ETDEWEB)

    Gaertnerova, V.; Jaeger, A.; Trojanova, Z. [Dept. of Metal Physics, Charles Univ., Praha (Czech Republic); Chalupova, M. [Dept. of Materials Engineering, Univ. of Zilina, Zilina (Slovakia)

    2005-07-01

    Magnesium alloy AZ91 (9% Al, 1% Zn, 0.2% Mn in wt.%) with different reinforcements has been used to study fracture mechanisms and crack development. SiC particles and/or Saffil fibres were used as the reinforcement. Fracture surfaces of specimens prepared by impact tests in the temperature range from room temperature to 300 C were investigated by scanning electron microscope (SEM). Possible mechanisms of fracture are discussed in the relation to the test temperature. (orig.)

  9. Finnie's notes on fracture mechanics fundamental and practical lessons

    CERN Document Server

    Dharan, C K H; Finnie, Iain

    2016-01-01

    This textbook consists primarily of notes by Iain Finnie who taught a popular course on fracture mechanics at the University of California at Berkeley. It presents a comprehensive and detailed exposition of fracture, the fundamentals of fracture mechanics and procedures for the safe design of engineering components made from metal alloys, brittle materials like glasses and ceramics, and composites. Interesting and practical problems are listed at the end of most chapters to give the student practice in applying the theory. A solutions manual is provided to the instructor. The text presents a unified perspective of fracture with a strong fundamental foundation and practical applications. In addition to its role as a text, this reference would be invaluable for the practicing engineer who is involved in the design and evaluation of components that are fracture critical. This book also: Presents details of derivations of the basic equations of fracture mechanics and the historical context of the development of f...

  10. Complexity: a new paradigm for fracture mechanics

    Directory of Open Access Journals (Sweden)

    S. Puzzi

    2009-10-01

    Full Text Available The so-called Complexity Sciences are a topic of fast growing interest inside the scientific community. Actually, researchers did not come to a definition of complexity, since it manifests itself in so many different ways [1]. This field itself is not a single discipline, but rather a heterogeneous amalgam of different techniques of mathematics and science. In fact, under the label of Complexity Sciences we comprehend a large variety of approaches: nonlinear dynamics, deterministic chaos theory, nonequilibrium thermodynamics, fractal geometry, intermediate asymptotics, complete and incomplete similarity, renormalization group theory, catastrophe theory, self-organized criticality, neural networks, cellular automata, fuzzy logic, etc. Aim of this paper is at providing insight into the role of complexity in the field of Materials Science and Fracture Mechanics [2-3]. The presented examples will be concerned with the snap-back instabilities in the structural behaviour of composite structures (Carpinteri [4-6], the occurrence of fractal patterns and selfsimilarity in material damage and deformation of heterogeneous materials, and the apparent scaling on the nominal mechanical properties of disordered materials (Carpinteri [7,8]. Further examples will deal with criticality in the acoustic emissions of damaged structures and with scaling in the time-to-failure (Carpinteri et al. [9]. Eventually, results on the transition towards chaos in the dynamics of cracked beams will be reported (Carpinteri and Pugno [10,11].

  11. Sedimentary facies control on mechanical and fracture stratigraphy in turbidites

    NARCIS (Netherlands)

    Ogata, Kei; Storti, Fabrizio; Balsamo, Fabrizio; Tinterri, Roberto; Bedogni, Enrico; Fetter, Marcos; Gomes, Leonardo; Hatushika, Raphael

    2017-01-01

    Natural fracture networks exert a first-order control on the exploitation of resources such as aquifers, hydrocarbons, and geothermal reservoirs, and on environmental issues like underground gas storage and waste disposal. Fractures and the mechanical stratigraphy of layered sequences have been

  12. Mechanical behavior and essential work of fracture of starch-based blown films

    Science.gov (United States)

    Nottez, M.; Chaki, S.; Soulestin, J.; Lacrampe, M. F.; Krawczak, P.

    2015-05-01

    A fracture mechanics approach (Essential Work of Fracture, EWF) was applied to assess the toughness of novel partly starch-grafted polyolefin blown films, compared to that of a neat polyethylene reference. Tests were performed on double-end notched samples. The digital image correlation method was used to monitor the deformation field around the notch. Regular tensile and tear tests were also carried out. The specific essential work of fracture is a characteristic which is much more sensitive to materials structural modifications than the tensile or tear properties.

  13. Fracture mechanics as judgement criterion in reference publications

    International Nuclear Information System (INIS)

    Bartholome, G.

    1976-01-01

    Fracture mechanics is applied in particular in ship and aeroplane construction, in astronautics, and in nuclear engineering. Around 1950, the high quality demands in nuclear engineering led to the first regulation for brittle-fracture-safe operation of thick-walled nuclear pressure vessels. These regulations are based on the brittle-fracture-plan (NDT concept). For reactor engineering this plan is applied in a simplified way, the so-called modified PORSE-diagram. The permissible operational stresses must be out of the range of brittle fracture margin which is defined by the NDT temperature extension limit. (RW) [de

  14. Fracture mechanics and statistical mechanics of reinforced elastomeric blends

    CERN Document Server

    Heinrich, Gert; Kaliske, Michael; Klüppel, Manfred; Schneider, Konrad; Vilgis, Thomas

    2013-01-01

    Elastomers are found in many applications ranging from technology to daily life applications for example in tires, drive systems, sealings and print rollers. Dynamical operation conditions put extremely high demands on the performance and stability of these materials and their elastic and flow properties can be easily adjusted by simple manipulations on their elastic and viscous properties. However, the required service life suffers often from material damage as a result of wear processes such as abrasion and wear fatigue, mostly caused by crack formation and propagation. This book covers interdisciplinary research between physics, physical chemistry, material sciences and engineering of elastomers within the range from nanometres to millimetres and connects these aspects with the constitutive material properties. The different chapters describe reliable lifetime and durability predictions based on new fracture mechanical testing concepts and advanced material-theoretical methods which are finally implemented...

  15. Baroreflex sensitivity: mechanisms and measurement

    OpenAIRE

    Swenne, C. A.

    2012-01-01

    This article is a brief review of baroreflex physiology, the definition and functional meaning of baroreflex sensitivity, and the methods used to measure baroreflex sensitivity. The arterial baroreflex is important for haemodynamic stability and for cardioprotection, and it has convincingly been demonstrated that baroreflex sensitivity, even when assessed with different methods, has a strong prognostic value. Development of new baroreflex assessing procedures is still ongoing, with a focus on...

  16. Use of probability with linear elastic fracture mechanics in studying brittle fracture in pressure vessels

    International Nuclear Information System (INIS)

    Jouris, G.M.; Shaffer, D.H.

    1978-01-01

    One phase is considered in the development of statistical methodology for a fracture mechanics analysis of the failure of nuclear steam supply system components, in particular that of brittle fracture in the beltline region of the pressure vessel resulting from various transients. It introduces a probability structure into the deterministic linear elastic fracture mechanics calculations. The resulting estimates of probability of brittle fracture reflect not only variation due to heterogeneity of vessel material but also uncertainties in the effect of embrittlement of the vessel steel due to neutron irradiation. Using importance sampling in conjunction with Monte Carlo simulation it was estimated that, for the operational transients considered, the probability of brittle fracture conditional on the presence of an Appendix G (ASME Code.Sn13) flaw is less than 2 x 10sup(-10). (author)

  17. Fracture Mechanics Prediction of Fatigue Life of Aluminum Highway Bridges

    DEFF Research Database (Denmark)

    Rom, Søren; Agerskov, Henning

    2015-01-01

    Fracture mechanics prediction of the fatigue life of aluminum highway bridges under random loading is studied. The fatigue life of welded joints has been determined from fracture mechanics analyses and the results obtained have been compared with results from experimental investigations. The fati......Fracture mechanics prediction of the fatigue life of aluminum highway bridges under random loading is studied. The fatigue life of welded joints has been determined from fracture mechanics analyses and the results obtained have been compared with results from experimental investigations...... against fatigue in aluminum bridges, may give results which are unconservative. Furthermore, it was in both investigations found that the validity of the results obtained from Miner's rule will depend on the distribution of the load history in tension and compression....

  18. Associations of early premenopausal fractures with subsequent fractures vary by sites and mechanisms of fractures.

    Science.gov (United States)

    Honkanen, R; Tuppurainen, M; Kroger, H; Alhava, E; Puntila, E

    1997-04-01

    In a retrospective population-based study we assessed whether and how self-reported former fractures sustained at the ages of 20-34 are associated with subsequent fractures sustained at the ages of 35-57. The 12,162 women who responded to fracture questions of the baseline postal enquiry (in 1989) of the Kuopio Osteoporosis Study, Finland formed the study population. They reported 589 former and 2092 subsequent fractures. The hazard ratio (HR), with 95% confidence interval (CI), of a subsequent fracture was 1.9 (1.6-2.3) in women with the history of a former fracture compared with women without such a history. A former low-energy wrist fracture was related to subsequent low-energy wrist [HR = 3.7 (2.0-6.8)] and high-energy nonwrist [HR = 2.4 (1.3-4.4)] fractures, whereas former high-energy nonwrist fractures were related only to subsequent high-energy nonwrist [HR = 2.8 (1.9-4.1)] but not to low-energy wrist [HR = 0.7 (0.3-1.8)] fractures. The analysis of bone mineral density (BMD) data of a subsample of premenopausal women who underwent dual x-ray absorptiometry (DXA) during 1989-91 revealed that those with a wrist fracture due to a fall on the same level at the age of 20-34 recorded 6.5% lower spinal (P = 0.140) and 10.5% lower femoral (P = 0.026) BMD than nonfractured women, whereas the corresponding differences for women with a former nonwrist fracture due to high-energy trauma were -1.8% (P = 0.721) and -2.4% (P = 0. 616), respectively. Our results suggest that an early premenopausal, low-energy wrist fracture is an indicator of low peak BMD which predisposes to subsequent fractures in general, whereas early high-energy fractures are mainly indicators of other and more specific extraskeletal factors which mainly predispose to same types of subsequent fractures only.

  19. Fracture mechanics of the cell wall of Chara corallina.

    Science.gov (United States)

    Toole, G A; Gunning, P A; Parker, M L; Smith, A C; Waldron, K W

    2001-03-01

    Previous mechanical studies using algae have concentrated on cell extension and growth using creep-type experiments, but there appears to be no published study of their failure properties. The mechanical strength of single large internode cell walls (up to 2 mm diameter and 100 mm in length) of the charophyte (giant alga) Chara corallina was determined by dissecting cells to give sheets of cell wall, which were then notched and fractured under tension. Tensile tests, using a range of notch sizes, were conducted on cell walls of varying age and maturity to establish their notch sensitivity and to investigate the propagation of cracks in plant cell walls. The thickness and stiffness of the walls increased with age whereas their strength was little affected. The strength of unnotched walls was estimated as 47+/-13 MPa, comparable to that of some grasses but an order of magnitude higher than that published for model bacterial cellulose composite walls. The strength was notch-sensitive and the critical stress intensity factor K1c was estimated to be 0.63+/-0.19 MNm(-3/2), comparable to published values for grasses.

  20. Fracture mechanics for delamination problems in composite materials

    Science.gov (United States)

    Wang, S. S.

    1983-01-01

    A fracture mechanics approach to the well-known delamination problem in composite materials is presented. Based on the theory of anisotropic laminate elasticity and interlaminar fracture mechanics concepts, the composite delamination problem is formulated and solved. The exact order of the delamination crack-tip stress singularity is determined. Asymptotic stress and displacement fields for an interlaminar crack are obtained. Fracture mechanics parameters such as mixed-mode stress intensity factors, KI, KII, KIII, and the energy release rate, G, for composite delamination problems are defined. To illustrate the fundamental nature of the delamination crack behavior, solutions for edge-delaminated graphite-epoxy composites under uniform axial extension are presented. Effects of fiber orientation, ply thickness, and delamination length on the interlaminar fracture are examined.

  1. Pattern and Trauma Mechanisms of Paediatric Long Bone Fractures ...

    African Journals Online (AJOL)

    Background: There are few reports on trauma mechanisms in children in Nigeria. Knowledge of the pattern of injuries and trauma mechanisms should help formulate injury prevention measures. The objective of this study was to determine the pattern and trauma mechanisms in children with long bone fractures managed in ...

  2. Colloid retention mechanisms in single, saturated, variable-aperture fractures.

    Science.gov (United States)

    Rodrigues, S N; Dickson, S E; Qu, J

    2013-01-01

    The characterization of fractured aquifers is commonly limited to the methodologies developed for unconsolidated porous media aquifers, which results in many uncertainties. Recent work indicates that fractured rocks remove more particulates than they are conventionally credited for. This research was designed to quantify the number of Escherichia coli RS2-GFP retained in single, saturated, variable-aperture fractures extracted from the natural environment. Conservative solute and E. coli RS2-GFP tracer experiments were used to elucidate the relationships between dominant retention mechanisms, aperture field characteristics, and flow rate. A non-destructive method of determining a surrogate measure of a coefficient of variation (COV(S)) for each fracture was used to better understand the transport behaviour of E. coli RS2-GFP. The results from this research all point to the importance of aperture field characterization in understanding the fate and transport of contaminants in fractured aquifers. The mean aperture was a very important characteristic in determining particulate recovery, so were matrix properties, COV(s), and flow rate. It was also determined that attachment is a much more significant retention mechanism than straining under the conditions employed in this research. Finally, it was demonstrated that the dominant retention mechanism in a fracture varies depending on the specific discharge. An improved understanding of the mechanisms that influence the fate and transport of contaminants through fractures will lead to the development of better tools and methodologies for the characterization of fractured aquifers, as well as the ability to manipulate the relevant mechanisms to increase or decrease retention, depending on the application. Copyright © 2012 Elsevier Ltd. All rights reserved.

  3. Application of simulation techniques in the probabilistic fracture mechanics

    International Nuclear Information System (INIS)

    De Ruyter van Steveninck, J.L.

    1995-03-01

    The Monte Carlo simulation is applied on a model of the fracture mechanics in order to assess the applicability of this simulation technique in the probabilistic fracture mechanics. By means of the fracture mechanics model the brittle fracture of a steel container or pipe with defects can be predicted. By means of the Monte Carlo simulation also the uncertainty regarding failures can be determined. Based on the variations in the toughness of the fracture and the defect dimensions the distribution of the chance of failure is determined. Also attention is paid to the impact of dependency between uncertain variables. Furthermore, the influence of the applied distributions of the uncertain variables and non-destructive survey on the chance of failure is analyzed. The Monte Carlo simulation results agree quite well with the results of other methods from the probabilistic fracture mechanics. If an analytic expression can be found for the chance of failure, it is possible to determine the variation of the chance of failure, next to an estimation of the chance of failure. It also appears that the dependency between the uncertain variables has a large impact on the chance of failure. It is also concluded from the simulation that the chance of failure strongly depends on the crack depth, and therefore of the distribution of the crack depth. 15 figs., 7 tabs., 12 refs

  4. Interaction of hydraulic and buckling mechanisms in blowout fractures.

    Science.gov (United States)

    Nagasao, Tomohisa; Miyamoto, Junpei; Jiang, Hua; Tamaki, Tamotsu; Kaneko, Tsuyoshi

    2010-04-01

    The etiology of blowout fractures is generally attributed to 2 mechanisms--increase in the pressure of the orbital contents (the hydraulic mechanism) and direct transmission of impacts on the orbital walls (the buckling mechanism). The present study aims to elucidate whether or not an interaction exists between these 2 mechanisms. We performed a simulation experiment using 10 Computer-Aided-Design skull models. We applied destructive energy to the orbits of the 10 models in 3 different ways. First, to simulate pure hydraulic mechanism, energy was applied solely on the internal walls of the orbit. Second, to simulate pure buckling mechanism, energy was applied solely on the inferior rim of the orbit. Third, to simulate the combined effect of the hydraulic and buckling mechanisms, energy was applied both on the internal wall of the orbit and inferior rim of the orbit. After applying the energy, we calculated the areas of the regions where fracture occurred in the models. Thereafter, we compared the areas among the 3 energy application patterns. When the hydraulic and buckling mechanisms work simultaneously, fracture occurs on wider areas of the orbital walls than when each of these mechanisms works separately. The hydraulic and buckling mechanisms interact, enhancing each other's effect. This information should be taken into consideration when we examine patients in whom blowout fracture is suspected.

  5. Inelastic material behavior and fracture mechanics a variational approach

    CERN Document Server

    Bruno, L

    1999-01-01

    A variational principle is presented, which relates the macroscopic fracture response of a mechanical component to its microscopic, inelastic material behavior. The principle allows a comparison between the crack driving force, expressed by the J-integral, and an integral expression of the fracture resistance. On this basis, the critical values of J are calculated for a Griffith crack under mixed- mode loading. The preliminary check with data available in literature shows a fairly good agreement. (8 refs).

  6. Single-well tracer push-pull test sensitivity w. r. to fracture aperture and spacing

    Science.gov (United States)

    Ghergut, I.; Behrens, H.; Karmakar, S.; Sauter, M.

    2012-04-01

    Dealing with a parallel-fracture system of infinite lateral extension, four characteristic regimes of tracer signal sensitivity w. r. to fracture aperture and w. r. to fracture spacing s (whose reciprocal defines fracture density, or the fluid-rock interface area per volume) can be identified during the pull phase of a single-well push-pull test, also depending upon the ratio between push-phase duration Tpush and a characteristic time scale Ts (defined by s2 / D = Ts , with D denoting the tracer's effective diffusion coefficient): early-time regime: tracer signals are sensitive w. r. to fracture aperture, but insensitive w. r. to fracture spacing; sensitivity w. r. to fracture aperture first increases, then decreases with Tpush / Ts (thus there will be an optimum in terms of to Tpush / Ts , at early pull times); mid-time regime: tracer signals are sensitive w. r. to fracture spacing, but insensitive w. r. to fracture aperture; sensitivity w. r. to fracture spacing increases with Tpush / Ts ; late-time regime: with increasing pull duration, tracer signals become increasingly insensitive w. r. to fracture spacing, while regaining sensitivity w. r. to fracture aperture; 'very late'-time regime: sensitivity w. r. to fracture aperture becomes independent upon Tpush / Ts . From these different regimes, some recommendations can be derived regarding the design and dimensioning of dual-tracer single-well push-pull tests for the specific purposes of geothermal reservoir characterization, using conservative solutes and heat as tracers. Acknowledgement: This study is funded by MWK Niedersachsen (Lower-Saxony's Science and Culture Ministry) and by Baker Hughes (Celle) within task unit 'G6' of the Collaborative Research Project 'gebo' (Geothermal Energy and High-Performance Drilling).

  7. Toughness of carbon nanotubes conforms to classic fracture mechanics.

    Science.gov (United States)

    Yang, Lin; Greenfeld, Israel; Wagner, H Daniel

    2016-02-01

    Defects in crystalline structure are commonly believed to degrade the ideal strength of carbon nanotubes. However, the fracture mechanisms induced by such defects, as well as the validity of solid mechanics theories at the nanoscale, are still under debate. We show that the fracture toughness of single-walled nanotubes (SWNTs) conforms to the classic theory of fracture mechanics, even for the smallest possible vacancy defect (~2 Å). By simulating tension of SWNTs containing common types of defects, we demonstrate how stress concentration at the defect boundary leads to brittle (unstable) fracturing at a relatively low strain, degrading the ideal strength of SWNTs by up to 60%. We find that, owing to the SWNT's truss-like structure, defects at this scale are not sharp and stress concentrations are finite and low. Moreover, stress concentration, a geometric property at the macroscale, is interrelated with the SWNT fracture toughness, a material property. The resulting SWNT fracture toughness is 2.7 MPa m(0.5), typical of moderately brittle materials and applicable also to graphene.

  8. Sensitization to Corrosion as Initiator of Fatigue Fracture in Compressor Blades

    Directory of Open Access Journals (Sweden)

    Vladimír CIHAL

    2011-06-01

    Full Text Available Certain failures of stainless steels interpreted purely in terms of fracture mechanisms may in fact be closely associated with previous damage caused by localized corrosion. The closeness of the link between fatigue and corrosion is documented by the case history of compressor blades made of grade 14Cr17Ni2 (X14CrNi17-2 stainless steel. Fatigue fracturing observed in areas near the blade root tended to follow intergranular pathways, indicating that some additional mechanism other than fatigue might be involved. This suspicion was confirmed by electrochemical potentiokinetic reactivation (EPR measurements in situ, which revealed sensitization to intergranular corrosion. It has been found that at the transition between the blade root and the blade proper the surfaces had been ground and polished too vigorously, heating the subcutaneous layers to within the danger zone of 400-600°C. Preferential integranular attack in these locations was the initiation mechanism that provoked a subsequent failure of the blades by fatigue fracture.

  9. Application of fracture mechanics to fatigue in pressure vessels

    International Nuclear Information System (INIS)

    Ghavami, K.

    1982-01-01

    The methods of application of fracture mechanics to predict fatigue crack propagation in welded structures and pressure vessels are described with the following objectives: i) To identify the effect of different variables such as crack tip plasticity, free surface, finite plate thickness, stress concentration and type of the structure, on the magnitude of stress intensity factor K in Welded joint. ii) To demonstrate the use of fracture mechanics for analysing fatigue crack propagation data. iii) To show how a law of fatigue crack propagation based on fracure mechanics, may be used to predict fatigue behavior of welded structures such as pressure vessel. (Author) [pt

  10. Primer: Fracture mechanics in the nuclear power industry

    International Nuclear Information System (INIS)

    Wessel, E.T.; Server, W.L.; Kennedy, E.L.

    1990-01-01

    This Primer is intended to familiarize utility engineers with the fracture mechanics technology and to provide the basis for a working knowledge of the subject. It is directed towards all the engineering disciplines that are involved either directly or indirectly with the structural reliability of electrical power generation equipment and systems. These engineering disciplines include such areas as: design and stress analysis, metallurgy and materials, nondestructive inspection and quality control, structural analysis and reliability engineering, chemical engineering and water chemistry control, and architectural engineering. This Primer does not provide a comprehensive, in-depth treatment of all the detailed aspects involved in fracture mechanics. It does, however, provide sufficient information and a common vocabulary that should enable engineers to: read and converse intelligently about the subject, understand and utilize ASME Codes and Regulatory Guides involving fracture mechanics, absorb technical information presented and discussed at various technical meetings, and begin to apply this technology towards actual engineering problems encountered in the course of their work. Example problems are provided to further enhance an understanding of fracture mechanics. Also, Appendix A describes fracture mechanics computer codes available through EPRI to analyze rotors, reactor pressure vessels and piping

  11. Thermo-hydro-mechanical behavior of fractured rock mass

    International Nuclear Information System (INIS)

    Coste, F.

    1997-12-01

    The purpose of this research is to model Thermo-Hydro-Mechanical behavior of fractured rock mass regarding a nuclear waste re-depository. For this, a methodology of modeling was proposed and was applied to a real underground site (EDF site at Nouvelle Romanche). This methodology consists, in a first step, to determine hydraulic and mechanical REV. Beyond the greatest of these REV, development of a finite element code allows to model all the fractures in an explicit manner. The homogenized mechanical properties are determined in drained and undrained boundary conditions by simulating triaxial tests that represent rock mass subject to loading. These simulations allow to study the evolution of hydraulic and mechanical properties as a function of stress state. Drained and undrained boundary conditions enable to discuss the validity of assimilation of a fractured rock mass to a porous medium. The simulations lead to a better understanding of the behavior of the fractured rock masses and allow to show the dominant role of the shear behavior of the fractures on the hydraulic and mechanical homogenized properties. From a thermal point of view, as long as conduction is dominant, thermal properties of the rock mass are almost the same as those the intact rock. (author)

  12. Substance P spinal signaling induces glial activation and nociceptive sensitization after fracture

    OpenAIRE

    Li, Wen-Wu; Guo, Tian-Zhi; Shi, Xiaoyou; Sun, Yuan; Wei, Tzuping; Clark, David J; Kingery, Wade S

    2015-01-01

    Tibia fracture in rodents induces substance P (SP)-dependent keratinocyte activation and inflammatory changes in the hindlimb, similar to those seen in complex regional pain syndrome (CRPS). In animal pain models spinal glial cell activation results in nociceptive sensitization. This study tested the hypothesis that limb fracture triggers afferent C-fiber SP release in the dorsal horn, resulting in chronic glia activation and central sensitization. At 4 weeks after tibia fracture and casting ...

  13. Relationship between trauma mechanism and etiology on mandibular fracture patterns

    Directory of Open Access Journals (Sweden)

    Fakhrurrazi Fakhrurrazi

    2010-03-01

    Full Text Available Background: Mandibular fracture occurs more commonly than maxillary fracture because of its prominent position and its arrow arch like bone anatomy. Many factors may cause mandibular fracture. Motorcycle accident is the main etiology of mandibular fracture in the world. Based on the literature, 43% mandibular fractures are caused by motorcycle accident, 34% by violence, 7% by accident at work, 7% by fall, 4% by sports and the others were caused by various things. Purpose: The purpose of this study was to know the relation between the etiology and mechanisms of trauma and the patterns of mandibular fracture at Hasan Sadikin Hospital, Bandung, from January 2006 to October 2007. Method: The study was taken on patients with mandibular fractures who came to Hasan Sadikin Hospital Bandung. The data were taken retrospectively by documenting the etiologies of mandibular fracture, the mechanisms of fracture, and the location of mandibular fracture. The data were analyzed with Chi Square statistic test. Result: The result showed that There were 83 mandibular fractures. The mandibular fracture more commonly attacks men about 77%, and women about 22.9%. Mandibular fracture occurs more often between the age group of 21-30 years old, about 31 people (37.3%. Mandibular fracture was mostles often caused by motorcycle accident, affecting about 71 people (85.5%. Parasymphysis fracture is the most common fracture location among mandibular fracture cases, about 47 people (56.6%. Conclusion: It can be concluded that there is no significant relationship between the etiology and mechanisms of trauma and the pattern of mandibular fracture.Latar belakang: Fraktur mandibula lebih sering terjadi dibandingkan dengan fraktur maksilla karenaposisinya yang lebihprominen dan bentuk anatomi tulang seperti busur panah. Banyak faktor yang dapat menyebabkan terjadinya fraktur mandibula. Kecelakaan kendaraan bermotor merupakan etiologi utama penyebab fraktur mandibula di dunia

  14. Fracture mechanisms in biopolymer films using coupling of mechanical analysis and high speed visualization technique

    NARCIS (Netherlands)

    Paes, S.S.; Yakimets, I.; Wellner, N.; Hill, S.E.; Wilson, R.H.; Mitchell, J.R.

    2010-01-01

    The aim of this study was to provide a detailed description of the fracture mechanisms in three different biopolymer thin materials: gelatin, hydroxypropyl cellulose (HPC) and cassava starch films. That was achieved by using a combination of fracture mechanics methodology and in situ visualization

  15. Theoretical Analysis of the Mechanism of Fracture Network Propagation with Stimulated Reservoir Volume (SRV) Fracturing in Tight Oil Reservoirs.

    Science.gov (United States)

    Su, Yuliang; Ren, Long; Meng, Fankun; Xu, Chen; Wang, Wendong

    2015-01-01

    Stimulated reservoir volume (SRV) fracturing in tight oil reservoirs often induces complex fracture-network growth, which has a fundamentally different formation mechanism from traditional planar bi-winged fracturing. To reveal the mechanism of fracture network propagation, this paper employs a modified displacement discontinuity method (DDM), mechanical mechanism analysis and initiation and propagation criteria for the theoretical model of fracture network propagation and its derivation. A reasonable solution of the theoretical model for a tight oil reservoir is obtained and verified by a numerical discrete method. Through theoretical calculation and computer programming, the variation rules of formation stress fields, hydraulic fracture propagation patterns (FPP) and branch fracture propagation angles and pressures are analyzed. The results show that during the process of fracture propagation, the initial orientation of the principal stress deflects, and the stress fields at the fracture tips change dramatically in the region surrounding the fracture. Whether the ideal fracture network can be produced depends on the geological conditions and on the engineering treatments. This study has both theoretical significance and practical application value by contributing to a better understanding of fracture network propagation mechanisms in unconventional oil/gas reservoirs and to the improvement of the science and design efficiency of reservoir fracturing.

  16. Theoretical Analysis of the Mechanism of Fracture Network Propagation with Stimulated Reservoir Volume (SRV Fracturing in Tight Oil Reservoirs.

    Directory of Open Access Journals (Sweden)

    Yuliang Su

    Full Text Available Stimulated reservoir volume (SRV fracturing in tight oil reservoirs often induces complex fracture-network growth, which has a fundamentally different formation mechanism from traditional planar bi-winged fracturing. To reveal the mechanism of fracture network propagation, this paper employs a modified displacement discontinuity method (DDM, mechanical mechanism analysis and initiation and propagation criteria for the theoretical model of fracture network propagation and its derivation. A reasonable solution of the theoretical model for a tight oil reservoir is obtained and verified by a numerical discrete method. Through theoretical calculation and computer programming, the variation rules of formation stress fields, hydraulic fracture propagation patterns (FPP and branch fracture propagation angles and pressures are analyzed. The results show that during the process of fracture propagation, the initial orientation of the principal stress deflects, and the stress fields at the fracture tips change dramatically in the region surrounding the fracture. Whether the ideal fracture network can be produced depends on the geological conditions and on the engineering treatments. This study has both theoretical significance and practical application value by contributing to a better understanding of fracture network propagation mechanisms in unconventional oil/gas reservoirs and to the improvement of the science and design efficiency of reservoir fracturing.

  17. The hydro-mechanical modeling of the fractured media; Modelisation hydromecanique des milieux fractures

    Energy Technology Data Exchange (ETDEWEB)

    Kadiri, I

    2002-10-15

    The hydro-mechanical modeling of the fractured media is quite complex. Simplifications are necessary for the modeling of such media, but, not always justified, Only permeable fractures are often considered. The rest of the network is approximated by an equivalent continuous medium. Even if we suppose that this approach is validated, the hydraulic and mechanical properties of the fractures and of the continuous medium are seldom known. Calibrations are necessary for the determination of these properties. Until now, one does not know very well the nature of measurements which must be carried out in order to carry on a modeling in discontinuous medium, nor elements of enough robust validation for this kind of modeling. For a better understanding of the hydro-mechanical phenomena in fractured media, two different sites have been selected for the work. The first is the site of Grimsel in Switzerland in which an underground laboratory is located at approximately 400 m of depth. The FEBEX experiment aims at the in-situ study of the consecutive phenomena due to the installation of a heat source representative of radioactive waste in the last 17 meters of the FEBEX tunnel in the laboratory of Grimsel. Only, the modeling of the hydro-mechanical of the excavation was model. The modeling of the Febex enabled us to establish a methodology of calibration of the hydraulic properties in the discontinuous media. However, this kind of study on such complex sites does not make possible to answer all the questions which arise on the hydro-mechanical behavior of the fractured media. We thus carried out modeling on an other site, smaller than the fist one and more accessible. The experimental site of Coaraze, in the Maritime Alps, is mainly constituted of limestone and fractures. Then the variation of water pressure along fractures is governed by the opening/closure sequence of a water gate. Normal displacement as well as the pore pressure along these fractures are recorded, and then

  18. The hydro-mechanical modeling of the fractured media

    International Nuclear Information System (INIS)

    Kadiri, I.

    2002-10-01

    The hydro-mechanical modeling of the fractured media is quite complex. Simplifications are necessary for the modeling of such media, but, not always justified, Only permeable fractures are often considered. The rest of the network is approximated by an equivalent continuous medium. Even if we suppose that this approach is validated, the hydraulic and mechanical properties of the fractures and of the continuous medium are seldom known. Calibrations are necessary for the determination of these properties. Until now, one does not know very well the nature of measurements which must be carried out in order to carry on a modeling in discontinuous medium, nor elements of enough robust validation for this kind of modeling. For a better understanding of the hydro-mechanical phenomena in fractured media, two different sites have been selected for the work. The first is the site of Grimsel in Switzerland in which an underground laboratory is located at approximately 400 m of depth. The FEBEX experiment aims at the in-situ study of the consecutive phenomena due to the installation of a heat source representative of radioactive waste in the last 17 meters of the FEBEX tunnel in the laboratory of Grimsel. Only, the modeling of the hydro-mechanical of the excavation was model. The modeling of the Febex enabled us to establish a methodology of calibration of the hydraulic properties in the discontinuous media. However, this kind of study on such complex sites does not make possible to answer all the questions which arise on the hydro-mechanical behavior of the fractured media. We thus carried out modeling on an other site, smaller than the fist one and more accessible. The experimental site of Coaraze, in the Maritime Alps, is mainly constituted of limestone and fractures. Then the variation of water pressure along fractures is governed by the opening/closure sequence of a water gate. Normal displacement as well as the pore pressure along these fractures are recorded, and then

  19. Relating Cohesive Zone Model to Linear Elastic Fracture Mechanics

    Science.gov (United States)

    Wang, John T.

    2010-01-01

    The conditions required for a cohesive zone model (CZM) to predict a failure load of a cracked structure similar to that obtained by a linear elastic fracture mechanics (LEFM) analysis are investigated in this paper. This study clarifies why many different phenomenological cohesive laws can produce similar fracture predictions. Analytical results for five cohesive zone models are obtained, using five different cohesive laws that have the same cohesive work rate (CWR-area under the traction-separation curve) but different maximum tractions. The effect of the maximum traction on the predicted cohesive zone length and the remote applied load at fracture is presented. Similar to the small scale yielding condition for an LEFM analysis to be valid. the cohesive zone length also needs to be much smaller than the crack length. This is a necessary condition for a CZM to obtain a fracture prediction equivalent to an LEFM result.

  20. Computational aspects of nonlinear fracture mechanics

    International Nuclear Information System (INIS)

    Brocks, W.; Cornec, A.; Scheider, I.

    2003-01-01

    The following contribution will essentially restrict to the application of the von Mises theory of incremental plasticity to cracked specimens and components. In particular, the classical parameters of EPFM, J and CTOD, as well as subsequently proposed parameters such as energy dissipation rate and crack-tip opening angle (CTOA) and the related computational aspects will be discussed. Some remarks follow on the 'local approach to fracture' which is based on continuum field quantities, namely stresses and strains, and the damage models of Gurson (1977) and Rousselier (1987), which have now found increasing application, will be briefly addressed in Section 3.03.4. The numerical modeling of decohesion and separation phenomena by 'cohesive elements' will be presented in Section 3.03.5. (orig.)

  1. Mechanical transport in two-dimensional networks of fractures

    International Nuclear Information System (INIS)

    Endo, H.K.

    1984-04-01

    The objectives of this research are to evaluate directional mechanical transport parameters for anisotropic fracture systems, and to determine if fracture systems behave like equivalent porous media. The tracer experiments used to measure directional tortuosity, longitudinal geometric dispersivity, and hydraulic effective porosity are conducted with a uniform flow field and measurements are made from the fluid flowing within a test section where linear length of travel is constant. Since fluid flow and mechanical transport are coupled processes, the directional variations of specific discharge and hydraulic effective porosity are measured in regions with constant hydraulic gradients to evaluate porous medium equivalence for the two processes, respectively. If the fracture region behaves like an equivalent porous medium, the system has the following stable properties: (1) specific discharge is uniform in any direction and can be predicted from a permeability tensor; and (2) hydraulic effective porosity is directionally stable. Fracture systems with two parallel sets of continuous fractures satisfy criterion 1. However, in these systems hydraulic effective porosity is directionally dependent, and thus, criterion 2 is violated. Thus, for some fracture systems, fluid flow can be predicted using porous media assumptions, but it may not be possible to predict transport using porous media assumptions. Two discontinuous fracture systems were studied which satisfied both criteria. Hydraulic effective porosity for both systems has a value between rock effective porosity and total porosity. A length-density analysis (LDS) of Canadian fracture data shows that porous media equivalence for fluid flow and transport is likely when systems have narrow aperture distributions. 54 references, 90 figures, 7 tables

  2. Evaluation of fracture mechanics analyses used in RPV integrity assessment regarding brittle fracture

    International Nuclear Information System (INIS)

    Moinereau, D.; Faidy, C.; Valeta, M.P.; Bhandari, S.; Guichard, D.

    1997-01-01

    Electricite de France has conducted during these last years some experimental and numerical research programmes in order to evaluate fracture mechanics analyses used in nuclear reactor pressure vessels structural integrity assessment, regarding the risk of brittle fracture. These programmes included cleavage fracture tests on large scale cladded specimens containing subclad flaws with their interpretations by 2D and 3D numerical computations, and validation of finite element codes for pressurized thermal shocks analyses. Four cladded specimens made of ferritic steel A508 C13 with stainless steel cladding, and containing shallow subclad flaws, have been tested in four point bending at very low temperature in order to obtain cleavage failure. The specimen failure was obtained in each case in base metal by cleavage fracture. These tests have been interpreted by two-dimensional and three-dimensional finite element computations using different fracture mechanics approaches (elastic analysis with specific plasticity corrections, elastic-plastic analysis, local approach to cleavage fracture). The failure of specimens are conservatively predicted by different analyses. The comparison between the elastic analyses and elastic-plastic analyses shows the conservatism of specific plasticity corrections used in French RPV elastic analyses. Numerous finite element calculations have also been performed between EDF, CEA and Framatome in order to compare and validate several fracture mechanics post processors implemented in finite element programmes used in pressurized thermal shock analyses. This work includes two-dimensional numerical computations on specimens with different geometries and loadings. The comparisons show a rather good agreement on main results, allowing to validate the finite element codes and their post-processors. (author). 11 refs, 24 figs, 3 tabs

  3. Integration of nondstructive examination reliability and fracture mechanics

    International Nuclear Information System (INIS)

    Doctor, S.R.; Bates, D.J.; Collins, H.D.; Good, M.S.; Hartzog, H.R.; Heasler, P.G.; Mart, G.A.; Simonen, F.A.; Spanner, J.C.; Taylor, T.T.

    1985-01-01

    A multi-year program on the Integration of Nondestructive Examination and Fracture Mechanics (NDE/FM) has been funded by the USNRC at the Pacific Northwest Laboratory. Many activities are being pursued under this program. This paper highlights some of the activities: input to the NRC Pipe Crack Task Group, an evaluation of manual ultrasonic testing of centrifugally cast stainless steel, interaction matrix, advanced UT technique evaluation, qualification document, evaluation of crack characterization techniques, international NDE reliability work, siamese imaging technique for imaging planar-type radial defects in reactor piping, fracture mechanics analysis for PTS-type flaws and piping reliability, and a position paper on piping ISI. (orig./HP)

  4. Fracture mechanism of coronal teenage dentin

    Science.gov (United States)

    Panfilov, P. E.; Kabanova, A. V.; Borodin, I. N.; Guo, J.; Zang, Z.

    2017-10-01

    The structure of coronal teenage dentin and the development of cracks in it are studied on microand nanolevels. The material is found to fail according to a ductile mechanism on a microlelvel and according to a ductile-brittle mechanism on a nanoscale. This behavior is similar to the failure of a polyethylene film and rubber, when significant elastic and irreversible deformation precedes crack growth. The viscoelastic behavior can be considered as the reaction of dentin to an applied mechanical load.

  5. Finite elements in fracture mechanics theory, numerics, applications

    CERN Document Server

    Kuna, Meinhard

    2013-01-01

    Fracture mechanics has established itself as an important discipline of growing interest to those working to assess the safety, reliability and service life of engineering structures and materials. In order to calculate the loading situation at cracks and defects, nowadays numerical techniques like finite element method (FEM) have become indispensable tools for a broad range of applications. The present monograph provides an introduction to the essential concepts of fracture mechanics, its main goal being to procure the special techniques for FEM analysis of crack problems, which have to date only been mastered by experts. All kinds of static, dynamic and fatigue fracture problems are treated in two- and three-dimensional elastic and plastic structural components. The usage of the various solution techniques is demonstrated by means of sample problems selected from practical engineering case studies. The primary target group includes graduate students, researchers in academia and engineers in practice.

  6. Nonlinear Fracture Mechanics and Plasticity of the Split Cylinder Test

    DEFF Research Database (Denmark)

    Olesen, John Forbes; Østergaard, Lennart; Stang, Henrik

    2006-01-01

    The split cylinder testis subjected to an analysis combining nonlinear fracture mechanics and plasticity. The fictitious crack model is applied for the analysis of splitting tensile fracture, and the Mohr-Coulomb yield criterion is adopted for modelling the compressive crushing/sliding failure. Two...... demonstrates the influence of varying geometry or constitutive properties. For a split cylinder test in load control it is shown how the ultimate load is either plasticity dominated or fracture mechanics dominated. The transition between the two modes is related to changes in geometry or constitutive...... properties. This implies that the linear elastic interpretation of the ultimate splitting force in term of the uniaxial tensile strength of the material is only valid for special situations, e.g. for very large cylinders. Furthermore, the numerical analysis suggests that the split cylinder test is not well...

  7. Fracture mechanics evaluation for at typical PWR primary coolant pipe

    Energy Technology Data Exchange (ETDEWEB)

    Tanaka, T. [Kansai Electric Power Company, Osaka (Japan); Shimizu, S.; Ogata, Y. [Mitsubishi Heavy Industries, Ltd., Kobe (Japan)

    1997-04-01

    For the primary coolant piping of PWRs in Japan, cast duplex stainless steel which is excellent in terms of strength, corrosion resistance, and weldability has conventionally been used. The cast duplex stainless steel contains the ferrite phase in the austenite matrix and thermal aging after long term service is known to change its material characteristics. It is considered appropriate to apply the methodology of elastic plastic fracture mechanics for an evaluation of the integrity of the primary coolant piping after thermal aging. Therefore we evaluated the integrity of the primary coolant piping for an initial PWR plant in Japan by means of elastic plastic fracture mechanics. The evaluation results show that the crack will not grow into an unstable fracture and the integrity of the piping will be secured, even when such through wall crack length is assumed to equal the fatigue crack growth length for a service period of up to 60 years.

  8. Comparative study of fracture mechanical test methods for concrete

    DEFF Research Database (Denmark)

    Østergaard, Lennart; Olesen, John Forbes

    2004-01-01

    and the interpretation, i.e. the analysis needed to extract the stress-crack opening relationship, the fracture energy etc. Experiments are carried out with each test configuration using mature, high performance concrete. The results show that the UTT is a highly complicated test, which only under very well controlled...... circumstances will yield the true fracture mechanical properties. It is also shown that both the three point bending test and the WST are well-suited substitutes for the uniaxial tension test.......This paper describes and compares three different fracture mechanical test methods; the uniaxial tension test (UTT), the three point bending test (TPBT) and the wedge splitting test (WST). Potentials and problems with the test methods will be described with regard to the experiment...

  9. The fluid mechanics of channel fracturing flows: experiment

    Science.gov (United States)

    Rashedi, Ahmadreza; Tucker, Zachery; Ovarlez, Guillaume; Hormozi, Sarah

    2017-11-01

    We show our preliminary experimental results on the role of fluid mechanics in channel fracturing flows, particularly yield stress fracturing fluids. Recent trends in the oil industry have included the use of cyclic pumping of a proppant slurry interspersed with a yield stress fracturing fluid, which is found to increase wells productivity, if particles disperse in a certain fashion. Our experimental study aims to investigate the physical mechanisms responsible for dispersing the particles (proppant) within a yield stress carrier fluid, and to measure the dispersion of proppant slugs in various fracturing regimes. To this end we have designed and built a unique experimental setup that resembles a fracture configuration coupled with a particle image/tracking velocimetry setup operating at micro to macro dimensions. Moreover, we have designed optically engineered suspensions of complex fluids with tunable yield stress and consistency, well controlled density match-mismatch properties and refractive indices for both X-rays and visible lights. We present our experimental system and preliminary results. NSF (Grant No. CBET-1554044- CAREER), ACS PRF (Grant No. 55661-DNI9).

  10. Draft fracture mechanics code case for American Society of Mechanical Engineers NUPACK rules

    Energy Technology Data Exchange (ETDEWEB)

    McConnell, P.; Sorenson, K. [Sandia National Labs., Albuquerque (United States); Nickell, R. [Applied Science and Technology, Poway (United States); Saegusa, T. [Central Research Inst. for Electric Power Industry, Abiko (Japan)

    2004-07-01

    The containment boundaries of most spent-fuel casks certified for use in the United States by the Nuclear Regulatory Commission are constructed with stainless steel, a material that is ductile in an engineering sense at all temperatures and for which, therefore, fracture mechanics principles are not relevant for the containment application. Ferritic materials may fail in a nonductile manner at sufficiently low temperatures, so fracture mechanics principles may be applied to preclude nonductile fracture. Because of the need to transport and store spent nuclear fuel safely in all types of climatic conditions, these vessels have regulatory lowest service temperatures that range down to -40 C (-40 F) for transport application. Such low service temperatures represent a severe challenge in terms of fracture toughness to many ferritic materials. Linear-elastic and elastic-plastic fracture mechanics principles provide a methodology for evaluating ferritic materials under such conditions.

  11. Hydrogen Embrittlement - Loading Rate Effects in Fracture Mechanics Testing

    NARCIS (Netherlands)

    Koers, R.W.J.; Krom, A.H.M.; Bakker, A.

    2001-01-01

    The fitness for purpose methodology is more and more used in the oil and gas industry to evaluate the significance of pre-existing flaws and material deficiencies with regard to the suitability of continued operation of equipment. In this methodology, traditional fracture mechanics is integrated

  12. Effects of fibre content on mechanical properties and fracture ...

    Indian Academy of Sciences (India)

    2016-08-26

    Aug 26, 2016 ... Geopolymer matrix composites reinforced with different volume fractions of short carbon fibres (Cf/geopolymer composites) were prepared and the mechanical properties, fracture behaviour and microstructure of as-prepared composites were studied and correlated with fibre content. The results show that ...

  13. Fracture mechanics applied to the machining of brittle materials

    Energy Technology Data Exchange (ETDEWEB)

    Hiatt, G.D.; Strenkowski, J.S.

    1988-12-01

    Research has begun on incorporating fracture mechanics into a model of the orthogonal cutting of brittle materials. Residual stresses are calculated for the machined material by a combination of Eulerian and Lagrangian finite element models and then used in the calculation of stress intensity factors by the Green`s Function Method.

  14. The model of mechanisms of materials resistance to fracture

    International Nuclear Information System (INIS)

    Tyugashov, P.F.

    1994-01-01

    A description is made for shear, break-up and combined fracture mechanisms. The potentiality of the model proposed is demonstrated on study of load-elongation diagram for titanium alloy type VT3-1. Comparison of calculation result to with available experimental data confirms the validity of assumptions about materials behaviour under creep conditions. 3 refs., 3 tabs

  15. Effects of fibre content on mechanical properties and fracture ...

    Indian Academy of Sciences (India)

    Administrator

    Abstract. Geopolymer matrix composites reinforced with different volume fractions of short carbon fibres. (Cf /geopolymer composites) were prepared and the mechanical properties, fracture behaviour and micro- structure of as-prepared composites were studied and correlated with fibre content. The results show that.

  16. Fracture Mechanics of an Elastic Softening Material like Concrete

    NARCIS (Netherlands)

    Reinhardt, H.W.

    1984-01-01

    Concrete is modelled as a linear elastic softening material and introduced into fracture mechanics. A discrete crack is considered with softening zones at the crack tips. Following the approach of Dugdale/Barenblatt, closing stresses are applied to the crack faces in the softening zone. The stresses

  17. Use of fracture mechanics in the US industry

    Energy Technology Data Exchange (ETDEWEB)

    Landes, J.D. [GKSS-Forschungszentrum Geesthacht GmbH (Germany). Inst. fuer Materialforschung

    2001-07-01

    The modern fracture mechanics technology began in the US in the 1960's. It was developed in response to failure problems that could not be explained by current technology. Some segments of the US industry were quick to embrace this new technology. The period of 1960 to middle 1980's marked a time of active fracture mechanics research in the US industry. From this various codes and assessment procedures have been developed to apply the fracture mechanics approach to evaluate the safety and reliability of critical structural components. This report discusses the US industry use of fracture mechanics. It considers the historical developments, some of the fracture mechanics tools that are available and present practices. Several different industry segments that have used the fracture mechanics approach are considered. These include aerospace, military, power generation, petrochemical and pipelines, metal producers, and construction/transportation. Their current use of the fracture mechanics methods involves the implementation of codes and procedures, the development of software packages, the use of outside consulting groups and some in-house research efforts. (orig.) [German] Die Entwicklung der modernen Bruchmechanik in den USA begann in den 1960er Jahren im Zusammenhang mit einer Reihe von Versagensfaellen, die auf konventionelle Weise nicht erklaert werden konnten. Die neuen Ansaetze wurden von einigen Branchen schnell aufgegriffen und weiterentwickelt. Die Periode von 1960 bis in die Mitte der 1980er Jahre markiert eine Zeit intensiver Forschungsarbeit in der amerikanischen Industrie. Eine Reihe von Codes und Vorschriften zur Bewertung der Sicherheit und Zuverlaessigkeit gefaehrdeter Strukturen hat ihren Ursprung in dieser Zeit. Der vorliegende Aufsatz thematisiert die Anwendung bruchmechanischer Methoden in der Industrie der USA anhand historischer Aspekte, des heute verfuegbaren Instrumentariums der Bauteilbewertung und der gaengigen Praxis bei der

  18. Application of Fracture-Mechanics Approach to Gas Pipelines

    Czech Academy of Sciences Publication Activity Database

    Gajdoš, Lubomír; Šperl, Martin

    VII, č. 73 (2011), s. 480-487 ISSN 2010-376X R&D Projects: GA ČR(CZ) GAP105/10/2052; GA ČR(CZ) GPP105/10/P555 Grant - others:GAMPO(CZ) FT-TA5/076 Program:FT Institutional research plan: CEZ:AV0Z20710524 Keywords : axial crack * fracture-mechanics * J integral * pipeline wall Subject RIV: JL - Materials Fatigue, Friction Mechanics

  19. The fracture properties and toughening mechanisms of bone and dentin

    Science.gov (United States)

    Koester, Kurt John

    The mechanical properties of bone and dentin and in particular their fracture properties, are the subject of intense research. The relevance of these properties is increasing as our population ages and fracture incidence impacts the lives of a greater portion of the population. A robust framework is needed to understand the fracture properties of bone and dentin to guide researchers as they attempt to characterize the effects of aging, disease, and pharmaceutical treatments on the properties of these mineralized tissues. In the present work, this framework is provided and applied to human bone, human dentin, and animal bone. In situ electron microscopy was also used to identify the salient toughening mechanisms in bone and dentin. It was found that bone and dentin are extrinsically toughened materials and consequently their fracture properties are best characterized utilizing a crack-growth resistance approach. A description of the different mechanical measurements commonly employed when using small animal models (rats and mice) to evaluate the influence of drug therapies on bone fragility is provided. A study where these properties were measured for a large population of wild-type rats and mice was also conducted. Given my findings, it was determined that for the most complete understanding of small animal bone it was necessary to measure strength and toughness. Strength measurements probe the flaw distribution and toughness measurements to evaluate the resistance to facture in the presence of a single dominant worst-case flaw.

  20. Sensitivity filtering from a continuum mechanics perspective

    DEFF Research Database (Denmark)

    Sigmund, Ole; Maute, Kurt

    2012-01-01

    In topology optimization filtering is a popular approach for preventing numerical instabilities. This short note shows that the well-known sensitivity filtering technique, that prevents checkerboards and ensures mesh-independent designs in density-based topology optimization, is equivalent to min...... to minimizing compliance for nonlocal elasticity problems known from continuum mechanics. Hence, the note resolves the long-standing quest for finding an explanation and physical motivation for the sensitivity filter....

  1. Hydraulic Fracture Extending into Network in Shale: Reviewing Influence Factors and Their Mechanism

    Science.gov (United States)

    Ren, Lan; Zhao, Jinzhou; Hu, Yongquan

    2014-01-01

    Hydraulic fracture in shale reservoir presents complex network propagation, which has essential difference with traditional plane biwing fracture at forming mechanism. Based on the research results of experiments, field fracturing practice, theory analysis, and numerical simulation, the influence factors and their mechanism of hydraulic fracture extending into network in shale have been systematically analyzed and discussed. Research results show that the fracture propagation in shale reservoir is influenced by the geological and the engineering factors, which includes rock mineral composition, rock mechanical properties, horizontal stress field, natural fractures, treating net pressure, fracturing fluid viscosity, and fracturing scale. This study has important theoretical value and practical significance to understand fracture network propagation mechanism in shale reservoir and contributes to improving the science and efficiency of shale reservoir fracturing design. PMID:25032240

  2. Hydraulic fracture extending into network in shale: reviewing influence factors and their mechanism.

    Science.gov (United States)

    Ren, Lan; Zhao, Jinzhou; Hu, Yongquan

    2014-01-01

    Hydraulic fracture in shale reservoir presents complex network propagation, which has essential difference with traditional plane biwing fracture at forming mechanism. Based on the research results of experiments, field fracturing practice, theory analysis, and numerical simulation, the influence factors and their mechanism of hydraulic fracture extending into network in shale have been systematically analyzed and discussed. Research results show that the fracture propagation in shale reservoir is influenced by the geological and the engineering factors, which includes rock mineral composition, rock mechanical properties, horizontal stress field, natural fractures, treating net pressure, fracturing fluid viscosity, and fracturing scale. This study has important theoretical value and practical significance to understand fracture network propagation mechanism in shale reservoir and contributes to improving the science and efficiency of shale reservoir fracturing design.

  3. Fracture mechanical analysis of operational damaged piping

    International Nuclear Information System (INIS)

    Azodi, D.

    1987-01-01

    A series of crack arrest experiments by means of transverse wedge-loaded compact specimen was simulated numerically to verify the dynamic J-integral formulation, for applications in brittle and ductile regions as well as for two- and three-dimensional geometries. The transverse wedge-loaded compact crack arrest test is a widely used small scale test to evaluate the crack arrest toughness of nuclear pressure vessel steels. In this test method the crack attains a high velocity after initiation, then decelerates to a low velocity prior to arrest. The opening displacement remains constant during the crack propagation. Crack extension and the opening displacement behaviour were measured using a sensitive time scale. Regarding material toughness two entirely different kind of steels, HFX 760 (brittle) and 20 MnMoNi 55 (ductile) were considered. The testing temperature was the room temperature. The numerical analyses were performed by an extended version of the finite element code ADINA. Crack propagation was simulated by 'node shift and fixity release' procedure. Discussions in this report are, among others, directed to the: Numerical stability of different J-integral contours during the fast crack propagation and comparison between the static approach, dynamic finite element analyses and experimental results for crack initiation toughness and arrest toughness. The numerical simulation results and experimental data were in close agreement. The achieved results confirm that the dynamic J-integral formulation is able to describe the rapid crack propagation and the crack arrest in steel components sufficiently. (orig.) [de

  4. Cyclic Fracture Toughness of Railway Axle and Mechanisms of its Fatigue Fracture

    Directory of Open Access Journals (Sweden)

    Sorochak Andriy

    2015-06-01

    Full Text Available The main regularities in fatigue fracture of the railway axle material - the OSL steel - are found in this paper. Micromechanisms of fatigue crack propagation are described and systematized, and a physical-mechanical interpretation of the relief morphology at different stages of crack propagation is proposed for fatigue cracks in specimens cut out of the surface, internal and central layers of the axle.

  5. Early Age Fracture Mechanics and Cracking of Concrete

    DEFF Research Database (Denmark)

    Østergaard, Lennart

    2003-01-01

    . The reasons are the increased autogenous deformation, the high rate of heat evolution and a higher brittleness of these concretes. Due to these adverse mechanisms the interest in the full description of the behavior of early age concrete has increased dramatically in the last two or three decades. Almost all...... the governing material parameters have undergone intensive research and the body of knowledge provides today a basis for calculation of the stress evolution and thus, repre- sents a tool for prediction of whether cracking will occur or not. However, the experimental investigation and the modelling of the early...... the fictitious crack model and the aim has been experimentally to determine the fracture mechanical properties related to this model. The results provide interesting and important insight into the development of the fracture properties in early age. It is found that the characteristic length has moments of low...

  6. Therapeutic ultrasound in fracture healing: The mechanism of osteoinduction

    Directory of Open Access Journals (Sweden)

    John P

    2008-01-01

    Full Text Available Background: Ultrasound has been used therapeutically for accelerating fracture healing since many years. However, the controversy on the exact mechanism of osteoinduction still continues. In this study, we try to bring out the exact biomolecular mechanism by which ultrasound induces fracture healing. Materials and Methods: The study was conducted in two phases: animal experiments and clinical study. In the first phase, we induced fractures on the left tibia of Wistar strain rats under anaesthesia. They were divided into two groups. One of the groups was given low-intensity, pulsed ultrasound (30 MW/cm 2 20 min a day for 10 days. Tissue samples and radiographs were taken weekly for 3 weeks from both the groups. In the second phase of our study, ten patients with fractures of the distal end of the radius (ten fractures were included. Five of these were treated as cases, and five were treated as controls. Ultrasound was given 30 MW/cm 2 for 20 min every day for 2 weeks. The patients were assessed radiologically and sonologically before and after ultrasound therapy. Tissue samples were studied with thymidine incorporation test with and without adding various neurotransmitter combinations. Results: Radiological findings revealed that there was an increased callus formation in the ultrasound group. At the cellular level, there was an increased thymidine incorporation in the ultrasound group. When various neurotransmitters were added to the cells, there was an increased thymidine incorporation in the ultrasound group. In the second phase of the study, radiological and sonological assessments showed that there was an increased callus formation in the ultrasound group. In cytological study, thymidine incorporation was found to be increased in the ultrasound group. Conclusions: The results of animal and clinical studies demonstrated an early and increased callus formation in the ultrasound group. Cytological studies revealed increased thymidine

  7. State-of-the-art report on piping fracture mechanics

    International Nuclear Information System (INIS)

    Wilkowski, G.M.; Olson, R.J.; Scott, P.M.

    1998-01-01

    This report is an in-depth summary of the state-of-the-art in nuclear piping fracture mechanics. It represents the culmination of 20 years of work done primarily in the US, but also attempts to include important aspects from other international efforts. Although the focus of this work was for the nuclear industry, the technology is also applicable in many cases to fossil plants, petrochemical/refinery plants, and the oil and gas industry. In compiling this detailed summary report, all of the equations and details of the analysis procedure or experimental results are not necessarily included. Rather, the report describes the important aspects and limitations, tells the reader where he can go for further information, and more importantly, describes the accuracy of the models. Nevertheless, the report still contains over 150 equations and over 400 references. The main sections of this report describe: (1) the evolution of piping fracture mechanics history relative to the developments of the nuclear industry, (2) technical developments in stress analyses, material property aspects, and fracture mechanics analyses, (3) unresolved issues and technically evolving areas, and (4) a summary of conclusions of major developments to date

  8. State-of-the-art report on piping fracture mechanics

    Energy Technology Data Exchange (ETDEWEB)

    Wilkowski, G.M.; Olson, R.J.; Scott, P.M. [Battelle, Columbus, OH (United States)

    1998-01-01

    This report is an in-depth summary of the state-of-the-art in nuclear piping fracture mechanics. It represents the culmination of 20 years of work done primarily in the US, but also attempts to include important aspects from other international efforts. Although the focus of this work was for the nuclear industry, the technology is also applicable in many cases to fossil plants, petrochemical/refinery plants, and the oil and gas industry. In compiling this detailed summary report, all of the equations and details of the analysis procedure or experimental results are not necessarily included. Rather, the report describes the important aspects and limitations, tells the reader where he can go for further information, and more importantly, describes the accuracy of the models. Nevertheless, the report still contains over 150 equations and over 400 references. The main sections of this report describe: (1) the evolution of piping fracture mechanics history relative to the developments of the nuclear industry, (2) technical developments in stress analyses, material property aspects, and fracture mechanics analyses, (3) unresolved issues and technically evolving areas, and (4) a summary of conclusions of major developments to date.

  9. 35. Conference of the DVM Working Group on Fracture Processes: Advances in fracture and damage mechanics - simulation methods of fracture mechanics

    International Nuclear Information System (INIS)

    2003-01-01

    Subjects of the meeting were: Simulation of fatigue crack growth in real strucures using FEA (M. Fulland, Paderborn); Modelling of ductile crack growth (W. Brocks, Geesthacht); Advances in non-local modelling of ductile damage (F. Reusch et al., Berlin, Dortmund); Fracture mechanics of ceramics (D. Munz, Karlsruhe); From materials testing to vehicle crash testing (J.G. Blauel, Freiburg); Analytical simulation of crack growth in thin-walled structures (U. Zerbst, Geesthacht); The influence of intrinsic stresses on fatigue crack growth (C. Dalle Donne etc., Cologne, Dortmund, Pisa, and M. Sander, Paderborn); Fracture mechanical strength calculation in case of mixed mode loads on cracks (H.A. Richard, Paderborn); Numeric simulation of intrinsic stresses during welding (C. Veneziano, Freiburg); New research fields of the Fraunhofer-Institut fuer Werkstoffmechanik (P. Gumbsch, Head of the Institute, Freiburg); Modern developments and advances in fracture and damage mechanics; Numeric and experimental simulation of crack propagation and damage processes; Exemplary damage cases; Fracture mechanics in product development; Failure characteristics of lightweight constructional materials and joints [de

  10. Microstructure-Sensitive Investigation of Fracture Using Acoustic Emission Coupled With Electron Microscopy

    Science.gov (United States)

    Wisner, Brian; Cabal, Mike; Vanniamparambiland, Prashanth A.; Leser, William; Hochhalter, Jacob; Kontsos, Antonios

    2015-01-01

    A novel technique using Scanning Electron Microscopy (SEM) in conjunction with Acoustic Emission (AE) monitoring is proposed to investigate microstructure-sensitive fatigue and fracture of metals. The coupling between quasi in situ microscopy with actual in situ nondestructive evaluation falls into the ICME framework and the idea of quantitative data-driven characterization of material behavior. To validate the use of AE monitoring inside the SEM chamber, Aluminum 2024-B sharp notch specimen were tested both inside and outside the microscope using a small scale mechanical testing device. Subsequently, the same type of specimen was tested inside the SEM chamber. Load data were correlated with both AE information and observations of microcracks around grain boundaries as well as secondary cracks, voids, and slip bands. The preliminary results are in excellent agreement with similar findings at the mesoscale. Extensions of the application of this novel technique are discussed.

  11. Fracture mechanics evaluation of similar and dissimilar welded fracture specimens under plane-strain

    Energy Technology Data Exchange (ETDEWEB)

    Khan, I.A.; Bhasin, V.; Chattopadhyay, J.; Vaze, K.K.; Ghosh, A.K.; Kushwaha, H.S. (Reactor Safety Division, Bhabha Atomic Research Centre, Mumbai (India)), e-mail: imran@barc.gov.in

    2009-07-01

    The classical Upper bound approach of limit analysis is based on the assumption of rigid blocks of deformation that moves between the lines of tangential displacement discontinuity. This assumption leads to considerable simplification but often at the cost of higher estimates of the actual load. Moreover, in many cases, it does not give a correct shape of the plastic field. In order to overcome these limitations a Modified Upper Bound approach (MUB) was proposed by Khan and Ghosh. The proposed approach is basically an energetic approach but unlike the classical upper bound approach it is capable of including the presence of statically governed stress field. In this presentation various applications of this recently proposed MUB approach in the area of fracture mechanics evaluation of similar and dissimilar welded fracture specimens are discussed

  12. Technical report on micro-mechanical versus conventional modelling in non-linear fracture mechanics

    International Nuclear Information System (INIS)

    2001-07-01

    While conventional fracture mechanics is capable of predicting crack growth behaviour if sufficient experimental observations are available, micro-mechanical modelling can both increase the accuracy of these predictions and model phenomena that are inaccessible by the conventional theory such as the ductile-cleavage temperature transition. A common argument against micro-mechanical modelling is that it is too complicated for use in routine engineering applications. This is both a computational and an educational problem. That micro-mechanical modelling is unnecessarily complicated is certainly true in many situations. The on-going development of micro-mechanical models, computational algorithms and computer speed will however most probably diminish the computational problem rather rapidly. Compare for instance the rate of development of computational methods for structural analysis. Meanwhile micro-mechanical modelling may serve as a tool by which more simplified engineering methods can be validated. The process of receiving a wide acceptance of the new methods is probably much slower. This involves many steps. First the research community must be in reasonable agreement on the methods and their use. Then the methods have to be implemented into computer software and into code procedures. The development and acceptance of conventional fracture mechanics may serve as an historical example of the time required before a new methodology has received a wide usage. The CSNI Working Group on Integrity and Ageing (IAGE) decided to carry out a report on micro-mechanical modeling to promote this promising and valuable technique. The report presents a comparison with non-linear fracture mechanics and highlights key aspects that could lead to a better knowledge and accurate predictions. Content: - 1. Introduction; - 2. Concepts of non-linear fracture mechanics with point crack tip modelling; - 3. Micro-mechanical models for cleavage fracture; - 4, Micro-mechanical modelling of

  13. Principles of fracture mechanics applications in nuclear power plants

    International Nuclear Information System (INIS)

    Acker, D.

    1995-05-01

    Fracture mechanics is widely used in nuclear plants safety assessment and remaining life evaluation. Methods of flow assessment in nuclear components are at an advanced stage of development and are suitable for general application in light water reactors and liquid metal cooled reactors. Following the first Saclay International Seminar on Structural Integrity (SISSI), hold in October 1991 and devoted to fracture in austenitic steels components, the second SISSI convened in April 1994 the European specialists to review the flaw assessment guides in application or in development in their countries, to discuss supporting research and development validation programs, application experience on the nuclear power plants and consequences on the components design. The seminar is sponsored by the CEA, Electricite de France, Framatome and the European Union D.G. XI. (J.S.)

  14. Probabilistic fracture mechanics applied for lbb case study: international benchmark

    International Nuclear Information System (INIS)

    Radu, V.

    2015-01-01

    An application of probabilistic fracture mechanics to evaluate the structural integrity for a case study chosen from experimental Mock-ups of FP7 STYLE project is described. The reliability model for probabilistic structural integrity, focused on the assessment of TWC in the pipe weld under complex loading (bending moment and residual stress) has been setup. The basic model is the model of fracture for through-wall cracked pipe under elastic-plastic conditions. The corresponding structural reliability approach is developed with the probabilities of failure associated with maximum load for crack initiation, net-section collapse but also the evaluation the instability loads. The probabilities of failure for a through-wall crack in a pipe subject to pure bending are evaluated by using crude Monte Carlo simulations. The results from the international benchmark are presented for the mentioned case in the context of ageing and lifetime management of pressure boundary/pressure circuit component. (authors)

  15. An efficient hydro-mechanical model for coupled multi-porosity and discrete fracture porous media

    Science.gov (United States)

    Yan, Xia; Huang, Zhaoqin; Yao, Jun; Li, Yang; Fan, Dongyan; Zhang, Kai

    2018-02-01

    In this paper, a numerical model is developed for coupled analysis of deforming fractured porous media with multiscale fractures. In this model, the macro-fractures are modeled explicitly by the embedded discrete fracture model, and the supporting effects of fluid and fillings in these fractures are represented explicitly in the geomechanics model. On the other hand, matrix and micro-fractures are modeled by a multi-porosity model, which aims to accurately describe the transient matrix-fracture fluid exchange process. A stabilized extended finite element method scheme is developed based on the polynomial pressure projection technique to address the displacement oscillation along macro-fracture boundaries. After that, the mixed space discretization and modified fixed stress sequential implicit methods based on non-matching grids are applied to solve the coupling model. Finally, we demonstrate the accuracy and application of the proposed method to capture the coupled hydro-mechanical impacts of multiscale fractures on fractured porous media.

  16. Survival Predictions of Ceramic Crowns Using Statistical Fracture Mechanics.

    Science.gov (United States)

    Nasrin, S; Katsube, N; Seghi, R R; Rokhlin, S I

    2017-05-01

    This work establishes a survival probability methodology for interface-initiated fatigue failures of monolithic ceramic crowns under simulated masticatory loading. A complete 3-dimensional (3D) finite element analysis model of a minimally reduced molar crown was developed using commercially available hardware and software. Estimates of material surface flaw distributions and fatigue parameters for 3 reinforced glass-ceramics (fluormica [FM], leucite [LR], and lithium disilicate [LD]) and a dense sintered yttrium-stabilized zirconia (YZ) were obtained from the literature and incorporated into the model. Utilizing the proposed fracture mechanics-based model, crown survival probability as a function of loading cycles was obtained from simulations performed on the 4 ceramic materials utilizing identical crown geometries and loading conditions. The weaker ceramic materials (FM and LR) resulted in lower survival rates than the more recently developed higher-strength ceramic materials (LD and YZ). The simulated 10-y survival rate of crowns fabricated from YZ was only slightly better than those fabricated from LD. In addition, 2 of the model crown systems (FM and LD) were expanded to determine regional-dependent failure probabilities. This analysis predicted that the LD-based crowns were more likely to fail from fractures initiating from margin areas, whereas the FM-based crowns showed a slightly higher probability of failure from fractures initiating from the occlusal table below the contact areas. These 2 predicted fracture initiation locations have some agreement with reported fractographic analyses of failed crowns. In this model, we considered the maximum tensile stress tangential to the interfacial surface, as opposed to the more universally reported maximum principal stress, because it more directly impacts crack propagation. While the accuracy of these predictions needs to be experimentally verified, the model can provide a fundamental understanding of the

  17. Forecasts on service life by fracture mechanics methods

    International Nuclear Information System (INIS)

    Munz, D.

    1985-01-01

    The service life of many component parts can frequently be divided into the stages up to the formation of a crack and of crack propagation. This holds good of fatigue crack, stress corrosion crack, and also in many cases of creep. But often the crack propagation stage is the only one of interest for service life forecasts if cracks must be reckoned with already on putting parts into service. Cracks in welding constructions are typical examples. Crack- and -fracture mechanics deal with the laws underlying crack propagation and provide quantitative information on crack propagation behaviour. (orig./DG) [de

  18. Probabilistic/Fracture-Mechanics Model For Service Life

    Science.gov (United States)

    Watkins, T., Jr.; Annis, C. G., Jr.

    1991-01-01

    Computer program makes probabilistic estimates of lifetime of engine and components thereof. Developed to fill need for more accurate life-assessment technique that avoids errors in estimated lives and provides for statistical assessment of levels of risk created by engineering decisions in designing system. Implements mathematical model combining techniques of statistics, fatigue, fracture mechanics, nondestructive analysis, life-cycle cost analysis, and management of engine parts. Used to investigate effects of such engine-component life-controlling parameters as return-to-service intervals, stresses, capabilities for nondestructive evaluation, and qualities of materials.

  19. (Environmental and geophysical modeling, fracture mechanics, and boundary element methods)

    Energy Technology Data Exchange (ETDEWEB)

    Gray, L.J.

    1990-11-09

    Technical discussions at the various sites visited centered on application of boundary integral methods for environmental modeling, seismic analysis, and computational fracture mechanics in composite and smart'' materials. The traveler also attended the International Association for Boundary Element Methods Conference at Rome, Italy. While many aspects of boundary element theory and applications were discussed in the papers, the dominant topic was the analysis and application of hypersingular equations. This has been the focus of recent work by the author, and thus the conference was highly relevant to research at ORNL.

  20. Defect vectors and path integrals in fracture mechanics

    International Nuclear Information System (INIS)

    Roche, R.L.

    1979-01-01

    Several criteria have been proposed in Elastic Plastic Fracture Mechanics. One of the most interesting ones is the J 1 criterion where J 1 is a path integral surrounding the crack tip. Other path integrals (or surface integrals in 3D problems) can be used. But all these integrals are introduced on an elastic basis, though they are applied in plasticity. This paper shows that it is possible to introduce these integrals without any reference to the elastic behavior of the material. The method is based on the 'defect vector theory' which is an extension of the energy-momentum tensor theory. (orig.)

  1. Fracture mechanisms in multilayer phosphorene assemblies: from brittle to ductile.

    Science.gov (United States)

    Liu, Ning; Hong, Jiawang; Zeng, Xiaowei; Pidaparti, Ramana; Wang, Xianqiao

    2017-05-24

    The outstanding mechanical performance of nacre has stimulated numerous studies on the design of artificial nacres. Phosphorene, a new two-dimensional (2D) material, has a crystalline in-plane structure and non-bonded interaction between adjacent flakes. Therefore, multi-layer phosphorene assemblies (MLPs), in which phosphorene flakes are piled up in a staggered manner, may exhibit outstanding mechanical performance, especially exceptional toughness. Therefore, molecular dynamics simulations are performed to study the dependence of the mechanical properties on the overlap distance between adjacent phosphorene layers and the number of phosphorene flakes per layer. The results indicate that when the flake number is equal to 1, a transition of fracture patterns is observed by increasing the overlap distance, from a ductile failure controlled by interfacial friction to a brittle failure dominated by the breakage of covalent bonds inside phosphorene flakes. Moreover, the failure pattern can be tuned by changing the number of flakes in each phosphorene layer. The results imply that the ultimate strength follows a power law with the exponent -0.5 in terms of the flake number, which is in good agreement with our analytical model. Furthermore, the flake number in each phosphorene layer is optimized as 2 when the temperature is 1 K in order to potentially achieve both high toughness and strength. Moreover, our results regarding the relations between mechanical performance and overlap distance can be explained well using a shear-lag model. However, it should be pointed out that increasing the temperature of MLPs could cause the transition of fracture patterns from ductile to brittle. Therefore, the optimal flake number depends heavily on temperature to achieve both its outstanding strength and toughness. Overall, our findings unveil the fundamental mechanism at the nanoscale for MLPs as well as provide a method to design phosphorene-based structures with targeted properties

  2. Study of gas production from shale reservoirs with multi-stage hydraulic fracturing horizontal well considering multiple transport mechanisms.

    Directory of Open Access Journals (Sweden)

    Chaohua Guo

    Full Text Available Development of unconventional shale gas reservoirs (SGRs has been boosted by the advancements in two key technologies: horizontal drilling and multi-stage hydraulic fracturing. A large number of multi-stage fractured horizontal wells (MsFHW have been drilled to enhance reservoir production performance. Gas flow in SGRs is a multi-mechanism process, including: desorption, diffusion, and non-Darcy flow. The productivity of the SGRs with MsFHW is influenced by both reservoir conditions and hydraulic fracture properties. However, rare simulation work has been conducted for multi-stage hydraulic fractured SGRs. Most of them use well testing methods, which have too many unrealistic simplifications and assumptions. Also, no systematical work has been conducted considering all reasonable transport mechanisms. And there are very few works on sensitivity studies of uncertain parameters using real parameter ranges. Hence, a detailed and systematic study of reservoir simulation with MsFHW is still necessary. In this paper, a dual porosity model was constructed to estimate the effect of parameters on shale gas production with MsFHW. The simulation model was verified with the available field data from the Barnett Shale. The following mechanisms have been considered in this model: viscous flow, slip flow, Knudsen diffusion, and gas desorption. Langmuir isotherm was used to simulate the gas desorption process. Sensitivity analysis on SGRs' production performance with MsFHW has been conducted. Parameters influencing shale gas production were classified into two categories: reservoir parameters including matrix permeability, matrix porosity; and hydraulic fracture parameters including hydraulic fracture spacing, and fracture half-length. Typical ranges of matrix parameters have been reviewed. Sensitivity analysis have been conducted to analyze the effect of the above factors on the production performance of SGRs. Through comparison, it can be found that hydraulic

  3. Study of gas production from shale reservoirs with multi-stage hydraulic fracturing horizontal well considering multiple transport mechanisms.

    Science.gov (United States)

    Guo, Chaohua; Wei, Mingzhen; Liu, Hong

    2018-01-01

    Development of unconventional shale gas reservoirs (SGRs) has been boosted by the advancements in two key technologies: horizontal drilling and multi-stage hydraulic fracturing. A large number of multi-stage fractured horizontal wells (MsFHW) have been drilled to enhance reservoir production performance. Gas flow in SGRs is a multi-mechanism process, including: desorption, diffusion, and non-Darcy flow. The productivity of the SGRs with MsFHW is influenced by both reservoir conditions and hydraulic fracture properties. However, rare simulation work has been conducted for multi-stage hydraulic fractured SGRs. Most of them use well testing methods, which have too many unrealistic simplifications and assumptions. Also, no systematical work has been conducted considering all reasonable transport mechanisms. And there are very few works on sensitivity studies of uncertain parameters using real parameter ranges. Hence, a detailed and systematic study of reservoir simulation with MsFHW is still necessary. In this paper, a dual porosity model was constructed to estimate the effect of parameters on shale gas production with MsFHW. The simulation model was verified with the available field data from the Barnett Shale. The following mechanisms have been considered in this model: viscous flow, slip flow, Knudsen diffusion, and gas desorption. Langmuir isotherm was used to simulate the gas desorption process. Sensitivity analysis on SGRs' production performance with MsFHW has been conducted. Parameters influencing shale gas production were classified into two categories: reservoir parameters including matrix permeability, matrix porosity; and hydraulic fracture parameters including hydraulic fracture spacing, and fracture half-length. Typical ranges of matrix parameters have been reviewed. Sensitivity analysis have been conducted to analyze the effect of the above factors on the production performance of SGRs. Through comparison, it can be found that hydraulic fracture

  4. CT for diagnosing fractures of the undersurface of the talus and mechanism of injury

    Energy Technology Data Exchange (ETDEWEB)

    Okamoto, Hideaki; Shibata, Yoshimori; Nishi, Genzaburo; Tago, Kyoji; Tsuchiya, Daiji; Chiba, Takehiro; Okumura, Hisashi [Aichiken Koseiren Kainan Hospital, Yatomi (Japan); Ikeda, Takeshi; Wada, Ikuo

    2000-02-01

    Talus fractures whose fracture lines extend to the subtalar joint, except fractures of the neck and the body of the talus, are defined as fractures of the lower portion of the talus. It is difficult to make a correctly diagnosis of inferior fractures of the talus by plain radiography or tomography alone. The author encountered 12 cases of inferior fractures of the talus between 1989 and 1997, and CT imaging in 2 directions, in the horizontal and frontal plane, was useful in making the diagnosis. The correct diagnosis rate was 100%, and differentiation of the site and extent of the fractures was possible. Based on the CT findings, the fractures were classified into 8 types (fractures of the lateral process of the talus, fractures of the medial tubercle, fractures of the posterior process, and combinations of the above, and comminuted fractures). The mechanism of the injuries was also investigated, and the fractures of the lateral process of the talus seemed to have been caused by excessive eversion force on the ankle joint, with the lateral process becoming trapped between the fibula and the calcaneus. Medial tubercle fractures also seemed to be caused by forcible inversion of the ankle, with the tip of the medial malleous impacting and the medial tubercle being trapped between it and the sustentaculum tali. The comminuted fractures seem to have been caused by axial compression added to various of external forces. (K.H.)

  5. CT for diagnosing fractures of the undersurface of the talus and mechanism of injury

    International Nuclear Information System (INIS)

    Okamoto, Hideaki; Shibata, Yoshimori; Nishi, Genzaburo; Tago, Kyoji; Tsuchiya, Daiji; Chiba, Takehiro; Okumura, Hisashi; Ikeda, Takeshi; Wada, Ikuo

    2000-01-01

    Talus fractures whose fracture lines extend to the subtalar joint, except fractures of the neck and the body of the talus, are defined as fractures of the lower portion of the talus. It is difficult to make a correctly diagnosis of inferior fractures of the talus by plain radiography or tomography alone. The author encountered 12 cases of inferior fractures of the talus between 1989 and 1997, and CT imaging in 2 directions, in the horizontal and frontal plane, was useful in making the diagnosis. The correct diagnosis rate was 100%, and differentiation of the site and extent of the fractures was possible. Based on the CT findings, the fractures were classified into 8 types (fractures of the lateral process of the talus, fractures of the medial tubercle, fractures of the posterior process, and combinations of the above, and comminuted fractures). The mechanism of the injuries was also investigated, and the fractures of the lateral process of the talus seemed to have been caused by excessive eversion force on the ankle joint, with the lateral process becoming trapped between the fibula and the calcaneus. Medial tubercle fractures also seemed to be caused by forcible inversion of the ankle, with the tip of the medial malleous impacting and the medial tubercle being trapped between it and the sustentaculum tali. The comminuted fractures seem to have been caused by axial compression added to various of external forces. (K.H.)

  6. Application of fracture mechanics to weldments; Bruchmechanische Bewertung von Schweissverbindungen

    Energy Technology Data Exchange (ETDEWEB)

    Zerbst, U.; Kocak, M. [GKSS-Forschungszentrum Geesthacht GmbH (Germany). Inst. fuer Werkstofforschung; Huebner, P. [Technische Univ. Bergakademie Freiberg (Germany)

    2002-07-01

    Weldments have been a major topic of engineering fracture mechanics research for many years as it shows up in the immense number of scientific papers published recently. Part of this generated knowledge has already been implemented in some industrial codes and standards. The focussing on weldments has its own reason in the utmost importance of this class of components in many industrial fields, but also in its susceptibility to the formation of defects during manufacturing and cracks in service, which promotes the danger of component failure. The present report is addressed to designers and material testers to provide updated information on the present state-of-the-art of fracture mechanics application to weldments. (orig.) [German] Schweissverbindungen bilden seit vielen Jahren einen Schwerpunkt der anwendungsnahen bruchmechanischen Forschung, was seinen Niederschlag in einer nahezu unuebersehbaren Fuelle an wissenschaftlichen Publikationen findet. Ein Teil der Ergebnisse hat bereits Eingang in industrienahe bruchmechanische Bewertungsvorschriften gefunden. Die Konzentration auf Schweissverbindungen hat ihre Ursache in der immensen Bedeutung dieser Bauteilklasse fuer viele Gebiete der Volkswirtschaft, aber auch in ihrer besonderen Anfaelligkeit zur Rissbildung in der Fertigung und im Betrieb und damit hinsichtlich der Gefahr von Bauteilversagen. Der vorliegende Beitrag wendet sich an Konstrukteure und Werkstoffpruefer, die einen Einblick in den gegenwaertigen Stand der Ingenieurbruchmechanik an Schweissverbindungen gewinnen wollen. (orig.)

  7. Hot ductility and fracture mechanisms of a structural steel

    International Nuclear Information System (INIS)

    Calvo, J.; Cabrera, J. M.; Prado, J. M.

    2006-01-01

    The hot ductility of a structural steel produced from scrap recycling has been studied to determine the origin of the transverse cracks in the corners that appeared in some billets. Samples extracted both from a billet with transverse cracks and from a billet with no external damage were tested. To evaluate the influence of residual elements and inclusions, the steel was compared to another one impurity free. Reduction in area of the samples tensile tested to the fracture was taken as a measure of the hot ductility. The tests were carried out at temperatures ranging from 1000 degree centigree to 650 degree centigree and at a strain rate of 1.10-3 s-1. The fracture surfaces of the tested samples were observed by scanning electron microscopy in order to determine the embrittling mechanisms that could be acting. The steel with residuals and impurities exhibited lower ductility values for a wider temperature range than the clean steel. The embrittling mechanisms also changed as compared to the impurity free steel. (Author)

  8. Tibial Fractures in Alpine Skiing and Snowboarding in Finland: A Retrospective Study on Fracture Types and Injury Mechanisms in 363 Patients.

    Science.gov (United States)

    Stenroos, A; Pakarinen, H; Jalkanen, J; Mälkiä, T; Handolin, L

    2016-09-01

    Alpine skiing and snowboarding share the hazards of accidents accounting for tibial fractures. The aim of this study was to evaluate the fracture patterns and mechanisms of injury of tibial fractures taking place in downhill skiing and snowboarding. All patients with tibial fracture due to alpine skiing or snowboarding accident treated in four trauma centers next to the largest ski resorts in Finland were analyzed between 2006 and 2012. The hospital records were retrospectively reviewed for data collection: equipment used (skis or snowboard), age, gender, and mechanism of injury. Fractures were classified according to AO-classification. There were 342 skiing and 30 snowboarding related tibial fractures in 363 patients. Tibial shaft fracture was the most common fracture among skiers (n = 215, 63%), followed by proximal tibial fractures (n = 92, 27%). Snowboarders were most likely to suffer from proximal tibial fracture (13, 43%) or tibial shaft fracture (11, 37%). Snowboarders were also more likely than skiers to suffer complex AO type C fractures (23% vs 9%, p jumping (46%). The most important finding was the relatively high number of the tibial plateau fractures among adult skiers. The fracture patterns between snowboarding and skiing were different; the most common fracture type in skiers was spiral tibial shaft fracture compared to proximal tibial fractures in snowboarders. Children had more simple fractures than adults. © The Finnish Surgical Society 2016.

  9. Radionuclide migration through fractured rock for arbitrary-length decay chain: Analytical solution and global sensitivity analysis

    Science.gov (United States)

    Shahkarami, Pirouz; Liu, Longcheng; Moreno, Luis; Neretnieks, Ivars

    2015-01-01

    This study presents an analytical approach to simulate nuclide migration through a channel in a fracture accounting for an arbitrary-length decay chain. The nuclides are retarded as they diffuse in the porous rock matrix and stagnant zones in the fracture. The Laplace transform and similarity transform techniques are applied to solve the model. The analytical solution to the nuclide concentrations at the fracture outlet is governed by nine parameters representing different mechanisms acting on nuclide transport through a fracture, including diffusion into the rock matrices, diffusion into the stagnant water zone, chain decay and hydrodynamic dispersion. Furthermore, to assess how sensitive the results are to parameter uncertainties, the Sobol method is applied in variance-based global sensitivity analyses of the model output. The Sobol indices show how uncertainty in the model output is apportioned to the uncertainty in the model input. This method takes into account both direct effects and interaction effects between input parameters. The simulation results suggest that in the case of pulse injections, ignoring the effect of a stagnant water zone can lead to significant errors in the time of first arrival and the peak value of the nuclides. Likewise, neglecting the parent and modeling its daughter as a single stable species can result in a significant overestimation of the peak value of the daughter nuclide. It is also found that as the dispersion increases, the early arrival time and the peak time of the daughter decrease while the peak value increases. More importantly, the global sensitivity analysis reveals that for time periods greater than a few thousand years, the uncertainty of the model output is more sensitive to the values of the individual parameters than to the interaction between them. Moreover, if one tries to evaluate the true values of the input parameters at the same cost and effort, the determination of priorities should follow a certain

  10. Fracture mechanics of piezoelectric solids with interface cracks

    CERN Document Server

    Govorukha, Volodymyr; Loboda, Volodymyr; Lapusta, Yuri

    2017-01-01

    This book provides a comprehensive study of cracks situated at the interface of two piezoelectric materials. It discusses different electric boundary conditions along the crack faces, in particular the cases of electrically permeable, impermeable, partially permeable, and conducting cracks. The book also elaborates on a new technique for the determination of electromechanical fields at the tips of interface cracks in finite sized piezoceramic bodies of arbitrary shape under different load types. It solves scientific problems of solid mechanics in connection with the investigation of electromechanical fields in piezoceramic bodies with interface cracks, and develops calculation models and solution methods for plane fracture mechanical problems for piecewise homogeneous piezoceramic bodies with cracks at the interfaces. It discusses the “open” crack model, which leads to a physically unrealistic oscillating singularity at the crack tips, and the contact zone model for in-plane straight interface cracks betw...

  11. Model and mechanism of erosion fracture of refractories at high temperatures

    International Nuclear Information System (INIS)

    Abrajtis, R.J.

    1988-01-01

    A calculational technique to evaluate the refractory erosion resistance is proposed. It is shown that under erosion fracture due to breaking off flow erosion plasters are formed which cover all the fractured surface. The proposed model and mechanism of erosion fracture and erosion plaster stability allow one to perform evaluation calculations of erosion characteristics of refractiories based on zirconium dioxide

  12. An experimental investigation into the mechanics of dynamic fracture

    Science.gov (United States)

    Ravi-Chandar, K.

    behaviour. The crack branching process was found to be a continuous process arising out of propagation along a straight line. High speed photomicrographs of the branching process indicated the presence of a number of part-through attempted branches that interact with one another and finally the successful emergence of a few full fledged branches.The microscopic observations on the crack propagation and branching process leads to a new interpretation of dynamic fracture that attempts to qualitatively explain the constancy of the velocity of propagation, the terminal velocity and crack branching. The crack branching mechanism is a logical continuation of the mechanism for crack propagation.

  13. Sensitivities of biomechanical assessment methods for fracture healing of long bones.

    Science.gov (United States)

    Chen, G; Wu, F Y; Zhang, J Q; Zhong, G Q; Liu, F

    2015-07-01

    There is a controversy as to whether the biomechanical methods are feasible to assess fracture healing of long bones. This paper investigated the sensitivities of two biomechanical methods, torsion and bending, for assessing fracture healing of long bones; both a simplified beam model and finite element model of an artificial femur were employed. The results demonstrated that, in the initial healing stage, the whole-bone stiffness of the fractured bone is extremely sensitive to the variation of the callus stiffness at the fracture site; when the shear (or Young's) modulus of the callus reaches 15% that of the intact bone, the whole-bone stiffness rises up to 90% that of the intact bone. After that, the whole-bone torsional (or bending) stiffness increases slowly; it becomes less sensitive to the variation of the callus stiffness. These results imply that the whole-bone stiffness is of limited reliability to assess the healing quality particular at late stages of the healing process. The simplified model in this paper provided a theoretical framework to explain why the whole-bone stiffness is insensitive to the healing process of fractured long bones in the late stage of healing. The conclusions obtained from the simplified model were verified with the finite element simulations of the artificial femur. Copyright © 2015 IPEM. Published by Elsevier Ltd. All rights reserved.

  14. A three-dimensional coupled thermo-hydro-mechanical model for deformable fractured geothermal systems

    DEFF Research Database (Denmark)

    Salimzadeh, Saeed; Paluszny, Adriana; Nick, Hamidreza M.

    2018-01-01

    A fully coupled thermal-hydraulic-mechanical (THM) finite element model is presented for fractured geothermal reservoirs. Fractures are modelled as surface discontinuities within a three-dimensional matrix. Non-isothermal flow through the rock matrix and fractures are defined and coupled to a mec......A fully coupled thermal-hydraulic-mechanical (THM) finite element model is presented for fractured geothermal reservoirs. Fractures are modelled as surface discontinuities within a three-dimensional matrix. Non-isothermal flow through the rock matrix and fractures are defined and coupled....... The model has been validated against several analytical solutions, and applied to study the effects of the deformable fractures on the injection of cold water in fractured geothermal systems. Results show that the creation of flow channelling due to the thermal volumetric contraction of the rock matrix...

  15. Mechanisms of aspirin-sensitive asthma

    Directory of Open Access Journals (Sweden)

    Sun Ying

    2004-01-01

    Full Text Available It is now widely accepted that aspirin, along with other non-steroidal anti-inflammatory drugs (NSAIDs, may precipitate asthma attacks in a minority of susceptible individuals. The syndrome is part of a mucosal inflammatory disease that typically affects the nasal, as well as the bronchial, mucosa and sometimes the gut and skin also. Although the mucosal cellular infiltrate in aspirin-sensitive asthma and rhinitis resembles that of asthma and rhinitis in general, there is evidence of increased expression of asthma-relevant cytokines, such as interleukin-5 and granulocyte–macrophage colony stimulating factor, and a more intense infiltrate of mast cells and eosinophils. One key feature of aspirin-sensitive asthma is thought to be the overproduction of cysteinyl leukotrienes, principally by these local mast cells and eosinophils, but whether this represents a fundamental abnormality or is simply a consequence of greater numbers and activation of inflammatory cells is unclear. Genetic polymorphisms of the leukotriene C4 synthase gene, which result in elevated expression of this enzyme, may also play a role. In addition, overexpression of cysteinyl leukotriene receptors, particularly CysLT1, may contribute to an enhanced response of local inflammatory and structural cells to cysteinyl leukotrienes. Aspirin challenge in these patients is accompanied by acute further elevation of the already elevated baseline cysteinyl leukotriene synthesis, a phenomenon that is most closely related to the ability of aspirin and related NSAIDs to inhibit the cyclooxygenase enzyme COX-1. The reason for this is unknown, although it has been suggested that the COX-1 product prostaglandin E2 (PGE2 serves as a ‘brake’ to leukotriene synthesis and that somehow this mechanism is deficient in aspirin-sensitive asthmatics. A better understanding of the pathogenesis of aspirin-sensitive asthma will undoubtedly lead to better approaches to treatment. Aside from the use of

  16. Effects of Silicon on Mechanical Properties and Fracture Toughness of Heavy-Section Ductile Cast Iron

    Directory of Open Access Journals (Sweden)

    Liang Song

    2015-01-01

    Full Text Available The effects of silicon (Si on the mechanical properties and fracture toughness of heavy-section ductile cast iron were investigated to develop material for spent-nuclear-fuel containers. Two castings with different Si contents of 1.78 wt.% and 2.74 wt.% were prepared. Four positions in the castings from the edge to the center, with different solidification cooling rates, were chosen for microstructure observation and mechanical properties’ testing. Results show that the tensile strength, elongation, impact toughness and fracture toughness at different positions of the two castings decrease with the decrease in cooling rate. With an increase in Si content, the graphite morphology and the mechanical properties at the same position deteriorate. Decreasing cooling rate changes the impact fracture morphology from a mixed ductile-brittle fracture to a brittle fracture. The fracture morphology of fracture toughness is changed from ductile to brittle fracture. When the Si content exceeds 1.78 wt.%, the impact and fracture toughness fracture morphology transforms from ductile to brittle fracture. The in-situ scanning electronic microscope (SEM tensile experiments were first used to observe the dynamic tensile process. The influence of the vermicular and temper graphite on fracture formation of heavy section ductile iron was investigated.

  17. Wear resistance and fracture mechanics of WC-Co composites

    Energy Technology Data Exchange (ETDEWEB)

    Kaytbay, Saleh [Benha Univ. (Egypt). Dept. of Mechanical Engineering; El-Hadek, Medhat [Port-Said Univ. (Egypt). Dept. of Production and Mechanical Design

    2014-06-15

    Manufacturing of WC-Co composites using the electroless precipitation method at different sintering temperatures of 1 100, 1 250, 1 350 and 1 500 C was successfully achieved. The chemical composition of the investigated materials was 90 wt.% WC with 10 wt.% Co, and 80 wt.% WC with 20 wt.% Co. The specific density, densification, and Vickers microhardness measurements were found to increase with increased sintering temperature for both the WC-Co compositions. The composites of tungsten carbide with 10 wt.% Co had a higher specific density and Vickers microhardness measurements than those for the composites of tungsten carbide with 20 wt.% Co. Composites with WC-10 wt.% Co had better wear resistance. The stress-strain and transverse rupture strength increased monotonically with the increase in sintering temperatures, agreeing with the material hardness and wear resistance behavior. Fractographical scanning electron microscopy analysis of the fracture surface demonstrated a rough characteristic conical shape failure in the direction of the maximum shear stress. A proposed mechanism for the formation of the conical fracture surface under compression testing is presented. (orig.)

  18. Stress sensitivity in psychopathology: mechanisms and consequences.

    Science.gov (United States)

    Hammen, Constance

    2015-02-01

    The special section on "Stress Sensitivity in Psychopathology: Mechanisms and Consequences" presents an array of articles and results across samples of children, adolescents, and adults that are at once exciting for the field and challenging. The articles highlight an empirically and conceptually important topic in psychopathology- the role of stress. For many years, this topic was mainly a focus of depression research but has now widened to include relevance to a variety of forms of psychological disorders, as shown in this special section. In addition to the applications to many different disorders, our field of psychopathology is enriched by highlighting the remarkable range of naturalistic and experimental paradigms for studying stress processes in humans, and to learn about diverse conceptual models. The authors of the articles in this special section have given us much food for thought in their innovative studies, and their work provides fruitful guides for next steps. It is to be hoped that such work points to future integrative and collaborative studies, across levels of analyses, methods, and samples that will further elaborate on the associations between stress and psychopathology, as well as the mechanisms that have relevance to the advancement of knowledge of disorders and their treatment. (PsycINFO Database Record (c) 2015 APA, all rights reserved).

  19. The mechanical behaviour of hydraulic fractured, possibly saturated materials

    NARCIS (Netherlands)

    Visser, J.H.M.; Mier, J.G.M. van

    1998-01-01

    The influence of a fluid pressure load on the extensile fracturing of mortar and sandstone has been investigated. A fluid pressure in the (initiating) fracture stimulates both fracture initiation and propagation and may be as effective as a directly applied uniaxial tensile stress. The efficiency of

  20. Effect of hydro mechanical coupling on natural fracture network formation in sedimentary basins

    Science.gov (United States)

    Ouraga, Zady; Guy, Nicolas; Pouya, Amade

    2018-05-01

    In sedimentary basin context, numerous phenomena, depending on the geological time span, can result in natural fracture network formation. In this paper, fracture network and dynamic fracture spacing triggered by significant sedimentation rate are studied considering mode I fracture propagation using a coupled hydro-mechanical numerical methods. The focus is put on synthetic geological structure under a constant sedimentation rate on its top. This model contains vertical fracture network initially closed and homogeneously distributed. The fractures are modelled with cohesive zone model undergoing damage and the flow is described by Poiseuille's law. The effect of the behaviour of the rock is studied and the analysis leads to a pattern of fracture network and fracture spacing in the geological layer.

  1. Rheological Characteristics of Cement Grout and its Effect on Mechanical Properties of a Rock Fracture

    Science.gov (United States)

    Liu, Quansheng; Lei, Guangfeng; Peng, Xingxin; Lu, Chaobo; Wei, Lai

    2018-02-01

    Grouting reinforcement, which has an obvious strengthening effect on fractured rock mass, has been widely used in various fields in geotechnical engineering. The rheological properties of grout will greatly affect its diffusion radius in rock fractures, and the water-cement ratio is an important factor in determining the grouting flow patterns. The relationship between shear stress and shear rate which could reflect the grout rheological properties, the effects of water-cement ratio, and temperature on the rheological properties of grouting was studied in the laboratory. Besides, a new method for producing fractured rock specimens was proposed and solved the problem of producing natural fractured rock specimens. To investigate the influences of grouting on mechanical properties of a rock fracture, the fractured rock specimens made using the new method were reinforced by grouting on the independent designed grouting platform, and then normal and tangential mechanical tests were carried out on fractured rock specimens. The results showed that the mechanical properties of fractured rock mass are significantly improved by grouting, the peak shear strength and residual strength of rock fractures are greatly improved, and the resistance to deformation is enhanced after grouting. Normal forces affect the tangential behavior of the rock fracture, and the tangential stress strength increases with normal forces. The strength and stability of fractured rock mass are increased by grouting reinforcement.

  2. Effective Hydro-Mechanical Properties of Fluid-Saturated Fracture Networks

    Science.gov (United States)

    Pollmann, N.; Vinci, C.; Renner, J.; Steeb, H.

    2015-12-01

    Consideration of hydro-mechanical processes is essential for the characterization of liquid-resources as well as for many engineering applications. Furthermore, the modeling of seismic waves in fractured porous media finds application not only in geophysical exploration but also reservoir management. Fractures exhibit high-aspect-ratio geometries, i.e. they constitute thin and long hydraulic conduits. Motivated by this peculiar geometry, the investigation of the hydro-mechanically coupled processes is performed by means of a hybrid-dimensional modeling approach. The effective material behavior of domains including complex fracture patterns in a porous rock is assessed by investigating the fluid pressure and the solid displacement of the skeleton saturated by compressible fluids. Classical balance equations are combined with a Poiseuille-type flow in the dimensionally reduced fracture. In the porous surrounding rock, the classical Biot-theory is applied. For simple geometries, our findings show that two main fluid-flow processes occur, leak-off from fractures to the surrounding rock and fracture flow within and between the connected fractures. The separation of critical frequencies of the two flow processes is not straightforward, in particular for systems containing a large number of fractures. Our aim is to model three dimensional hydro-mechanically coupled processes within complex fracture patterns and in particular determine the frequency-dependent attenuation characteristics. Furthermore, the effect of asperities of the fracture surfaces on the fracture stiffness and on the hydraulic conductivity will be added to the approach.

  3. From fracture mechanics to damage mechanics: how to model structural deterioration

    International Nuclear Information System (INIS)

    Nicolet, S.; Lorentz, E.; Barbier, G.

    1998-01-01

    Modelling of structural deteriorations of thermo-mechanical origin is highly enhanced when using damage mechanics. Indeed, the latter offers both a fine description of the material behaviour and an ability to deal with any loading conditions, moving away the current limits of fracture mechanics. But new difficulties can arise, depending on the examined problem: if forecasts of rack initiation are well mastered, the study of crack propagation remains more complex and needs sophisticated modelizations, which are nevertheless on the point of being well understood too. (authors)

  4. Combined Isolated Laugier’s Fracture and Distal Radial Fracture: Management and Literature Review on the Mechanism of Injury

    Directory of Open Access Journals (Sweden)

    Walid Osman

    2016-01-01

    Full Text Available Introduction. Isolated fracture of the trochlea is an uncommon condition requiring a particular mechanism of injury. Its association with a distal radial fracture is rare. We aimed through this case report to identify the injury mechanism and to assess surgical outcomes. Case Presentation. We report a 26-year-old female who was admitted to our department for elbow trauma following an accidental fall on her outstretched right hand with her elbow extended and supinated. On examination, the right elbow was swollen with tenderness over the anteromedial aspect of the distal humerus. The elbow range was restricted. Standard radiographs showed an intra-articular half-moon-shaped fragment lying proximal and anterior to the distal humerus. There was a comminuted articular fracture of the distal radius with an anterior displacement. A computed tomography revealed an isolated shear fracture of the trochlea without any associated lesion of the elbow. The patient was surgically managed. Anatomical reduction was achieved and the fracture was fixed with 2 Kirschner wires. The distal radial fracture was treated by open reduction and plate fixation. The postoperative course was uneventful with a good recovery. Conclusion. Knowledge of such entity would be useful to indicate the suitable surgical management and eventually to obtain good functional outcomes.

  5. Microstructure, fracture and damage mechanisms in rare-earth doped silicon nitride ceramics

    Czech Academy of Sciences Publication Activity Database

    Tatarko, P.; Chlup, Zdeněk; Dusza, J.

    2011-01-01

    Roč. 465, - (2011), s. 93-96 ISSN 1013-9826. [MSMF-6: Materials Structure and Micromechanics of Fracture VI. Brno, 28.06.2010-30.06.2010] Institutional research plan: CEZ:AV0Z20410507 Keywords : rare-earth element * silicon nitride * composite * fracture * mechanical properties Subject RIV: JL - Materials Fatigue, Friction Mechanics

  6. Characterisation of Fracture Behaviour of Starch Gels Using Conventional Fracture Mechanics and Wire Cutting Tests

    Science.gov (United States)

    Gamonpilas, C.; Charalambides, M. N.; Williams, J. G.; Dooling, P. J.; Gibbon, S. R.

    2008-07-01

    The fracture behaviour of starch gels is investigated through experimental tests and finite element simulations. Both conventional fracture and wire cutting experiments were performed. The results from these two tests were consistent with the fracture toughness increasing with loading rate. In the FE analysis, a non-linear elastic constitutive relationship was used to model the starch gels and frictionless condition was assumed between the wire-starch gel contact interface. A failure criterion based on critical fracture strain was assumed. Predictions of the steady-state cutting force at various wire diameters were found to be in good agreement with the wire cutting data.

  7. Mechanical test and fractal analysis on anisotropic fracture of cortical bone

    Energy Technology Data Exchange (ETDEWEB)

    Yin, Dagang [State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044 (China); College of Aerospace Engineering, Chongqing University, Chongqing 400044 (China); Chen, Bin, E-mail: bchen@cqu.edu.cn [State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044 (China); College of Aerospace Engineering, Chongqing University, Chongqing 400044 (China); Ye, Wei [College of Aerospace Engineering, Chongqing University, Chongqing 400044 (China); Gou, Jihua [Department of Mechanical and Aerospace Engineering, University of Central Florida, Orlando, FL 32816 (United States); Fan, Jinghong [Division of Mechanical Engineering, Alfred University, Alfred, NY 14802 (United States)

    2015-12-01

    Highlights: • The mechanical properties of the cortical bone of fresh bovine femora along three different directions are tested through four-point bending experiments. • SEM observation shows that the roughness of the fracture surfaces of the three different directions of the bone are remarkably different. • The fractal dimensions of the different fracture surfaces of the bone are calculated by box-counting method in MATLAB. • The fracture energies of the different fracture directions are calculated based on their fractal models. - Abstract: The mechanical properties of the cortical bone of fresh bovine femora along three different directions are tested through four-point bending experiments. It is indicated that the fracture energy along the transversal direction of the bone is distinctly larger than those of the longitudinal and radial directions. The fracture surfaces of the three different directions are observed by scanning electron microscope (SEM). It is shown that the roughness of the fracture surface of the transversal direction is obviously larger than those of the fracture surfaces of the longitudinal and radial directions. It is also revealed that the osteons in the bone are perpendicular to the fracture surface of the transversal direction and parallel to the fracture surfaces of the longitudinal and radial directions. Based on these experimental results, the fractal dimensions of the fracture surfaces of different directions are calculated by box-counting method in MATLAB. The calculated results show that the fractal dimension of the fracture surface of the transversal direction is remarkably larger than those of the fracture surfaces of the longitudinal and radial directions. The fracture energies of different directions are also calculated based on their fractal models. It is denoted that the fracture energy of the transversal direction is remarkably larger than those of the longitudinal and radial directions. The calculated results are in

  8. Mechanical test and fractal analysis on anisotropic fracture of cortical bone

    International Nuclear Information System (INIS)

    Yin, Dagang; Chen, Bin; Ye, Wei; Gou, Jihua; Fan, Jinghong

    2015-01-01

    Highlights: • The mechanical properties of the cortical bone of fresh bovine femora along three different directions are tested through four-point bending experiments. • SEM observation shows that the roughness of the fracture surfaces of the three different directions of the bone are remarkably different. • The fractal dimensions of the different fracture surfaces of the bone are calculated by box-counting method in MATLAB. • The fracture energies of the different fracture directions are calculated based on their fractal models. - Abstract: The mechanical properties of the cortical bone of fresh bovine femora along three different directions are tested through four-point bending experiments. It is indicated that the fracture energy along the transversal direction of the bone is distinctly larger than those of the longitudinal and radial directions. The fracture surfaces of the three different directions are observed by scanning electron microscope (SEM). It is shown that the roughness of the fracture surface of the transversal direction is obviously larger than those of the fracture surfaces of the longitudinal and radial directions. It is also revealed that the osteons in the bone are perpendicular to the fracture surface of the transversal direction and parallel to the fracture surfaces of the longitudinal and radial directions. Based on these experimental results, the fractal dimensions of the fracture surfaces of different directions are calculated by box-counting method in MATLAB. The calculated results show that the fractal dimension of the fracture surface of the transversal direction is remarkably larger than those of the fracture surfaces of the longitudinal and radial directions. The fracture energies of different directions are also calculated based on their fractal models. It is denoted that the fracture energy of the transversal direction is remarkably larger than those of the longitudinal and radial directions. The calculated results are in

  9. Coupled hydro-mechanical simulations of discrete fluid-driven fracture propagation through fractured rock masses using a lattice modeling approach

    Science.gov (United States)

    Kim, K.; Rutqvist, J.; Birkholzer, J. T.

    2016-12-01

    Fluid-driven fractures are critically important in a number of geoengineering application, such as to increase the permeability of an oil/gas reservoir and stimulate the productivity. On the contrary, near the underground storage sites for radioactive wastes or carbon dioxide, the propagation of fractures induced by pressurized gas should be avoided to detain the pollutants. Numerous numerical models have been developed to reproduce the physical phenomena of the fluid-driven fractures and have better understanding of the fracturing mechanism. However, it is still challenging to explicitly model the fluid-driven fracture propagation because it involves tightly coupled hydro-mechanical behavior with a singularity at the crack tip and complex interactions with pre-existing discontinuities in heterogeneous rock masses. This study investigates hydraulic fracture propagation and formation of discrete fracture networks using a coupled hydro-mechanical simulation code, TOUGH-RBSN. The modeling tool combines a multiphase fluid flow and heat transport simulator, TOUGH2, with a geomechanical and fracture-damage model, called the rigid-body-spring network (RBSN). Fractures are modeled as discrete features, and hydrological properties (e.g., permeability, porosity) of fracture elements are evaluated by fracture opening and aperture changes calculated at time steps of the simulations. Modeling capabilities for hydraulic fracturing processes are presented through simulations of a virtual fractured reservoir consisting of multiple pre-existing natural fractures. Case studies are conducted by changing the reservoir configurations, such as confining stress condition (e.g., degree of stress anisotropy), the matrix permeability, and the viscosity of injected fluid. In the preliminary results, the stress field and the fluid pressure distribution are provided to demonstrate modeling of complex hydro-mechanical interactions between propagating fractures and pre-existing fractures. The

  10. Morphology Evolution on the Fracture Surface and Fracture Mechanisms of Multiphase Nanostructured ZrCu-Base Alloys

    Directory of Open Access Journals (Sweden)

    Feng Qiu

    2017-03-01

    Full Text Available A multiphase nanostructured ZrCu-base bulk alloy which showed a unique microstructure consisting of sub-micrometer scale Zr2Cu solid solution, nano-sized twinned plate-like ZrCu martensite (ZrCu (M, and retained ZrCu (B2 austenite was fabricated by copper mold casting. The observation of periodic morphology evolution on the fracture surface of the multiphase nanostructured ZrCu-base alloys has been reported, which suggested a fluctuant local stress intensity along the crack propagation. It is necessary to investigate the compressive deformation behavior and the fracture mechanism of the multiphase alloy and the relation to the unique microstructures. The results obtained in this study provide a better understanding of the deformation and fracture mechanisms of multiphase hybrid nanostructured ZrCu-based alloys and give guidance on how to improve the ductility/toughness of bulk ZrCu-based alloys.

  11. Isolated posterior malleolus fracture: A rare injury mechanism ...

    African Journals Online (AJOL)

    Sprain of the ankle is undoubtedly a common injury during athletic activity, and the sprain can be also associated with fracture of the ankle. Isolated posterior malleolus fracture is a very rare condition, which is usually missed. Here, we are presenting a 37 years old female patient, who suffered injury secondary pressing on ...

  12. Chemically- and mechanically-mediated influences on the transport and mechanical characteristics of rock fractures

    Energy Technology Data Exchange (ETDEWEB)

    Min, K.-B.; Rutqvist, J.; Elsworth, D.

    2009-02-01

    A model is presented to represent changes in the mechanical and transport characteristics of fractured rock that result from coupled mechanical and chemical effects. The specific influence is the elevation of dissolution rates on contacting asperities, which results in a stress- and temperature-dependent permanent closure. A model representing this pressure-dissolution-like behavior is adapted to define the threshold and resulting response in terms of fundamental thermodynamic properties of a contacting fracture. These relations are incorporated in a stress-stiffening model of fracture closure to define the stress- and temperature-dependency of aperture loss and behavior during stress and temperature cycling. These models compare well with laboratory and field experiments, representing both decoupled isobaric and isothermal responses. The model was applied to explore the impact of these responses on heated structures in rock. The result showed a reduction in ultimate induced stresses over the case where chemical effects were not incorporated, with permanent reduction in final stresses after cooling to ambient conditions. Similarly, permeabilities may be lower than they were in the case where chemical effects were not considered, with a net reduction apparent even after cooling to ambient temperature. These heretofore-neglected effects may have a correspondingly significant impact on the performance of heated structures in rock, such as repositories for the containment of radioactive wastes.

  13. Investigation of Mechanical Properties and Fracture Simulation of Solution-Treated AA 5754

    Science.gov (United States)

    Kumar, Pankaj; Singh, Akhilendra

    2017-10-01

    In this work, mechanical properties and fracture toughness of as-received and solution-treated aluminum alloy 5754 (AA 5754) are experimentally evaluated. Solution heat treatment of the alloy is performed at 530 °C for 2 h, and then, quenching is done in water. Yield strength, ultimate tensile strength, impact toughness, hardness, fatigue life, brittle fracture toughness (K_{Ic} ) and ductile fracture toughness (J_{Ic} ) are evaluated for as-received and solution-treated alloy. Extended finite element method has been used for the simulation of tensile and fracture behavior of material. Heaviside function and asymptotic crack tip enrichment functions are used for modelling of the crack in the geometry. Ramberg-Osgood material model coupled with fracture energy is used to simulate the crack propagation. Fracture surfaces obtained from various mechanical tests are characterized by scanning electron microscopy.

  14. In situ grain fracture mechanics during uniaxial compaction of granular solids

    Science.gov (United States)

    Hurley, R. C.; Lind, J.; Pagan, D. C.; Akin, M. C.; Herbold, E. B.

    2018-03-01

    Grain fracture and crushing are known to influence the macroscopic mechanical behavior of granular materials and be influenced by factors such as grain composition, morphology, and microstructure. In this paper, we investigate grain fracture and crushing by combining synchrotron x-ray computed tomography and three-dimensional x-ray diffraction to study two granular samples undergoing uniaxial compaction. Our measurements provide details of grain kinematics, contacts, average intra-granular stresses, inter-particle forces, and intra-grain crystal and fracture plane orientations. Our analyses elucidate the complex nature of fracture and crushing, showing that: (1) the average stress states of grains prior to fracture vary widely in their relation to global and local trends; (2) fractured grains experience inter-particle forces and stored energies that are statistically higher than intact grains prior to fracture; (3) fracture plane orientations are primarily controlled by average intra-granular stress and contact fabric rather than the orientation of the crystal lattice; (4) the creation of new surfaces during fracture accounts for a very small portion of the energy dissipated during compaction; (5) mixing brittle and ductile grain materials alters the grain-scale fracture response. The results highlight an application of combined x-ray measurements for non-destructive in situ analysis of granular solids and provide details about grain fracture that have important implications for theory and modeling.

  15. Defect forces, defect couples and path integrals in fracture mechanics

    International Nuclear Information System (INIS)

    Roche, R.L.

    1979-07-01

    In this work, it is shown that the path integrals can be introduced without any reference to the material behavior. The method is based on the definition in a continuous medium of a set of vectors and couples having the dimension of a force or a moment. More precisely, definitions are given of volume defect forces, surface defect forces, volume defect couples, and surface defect couples. This is done with the help of the stress working variation of a particule moving through the solid. The most important result is: the resultant of all the defect forces included in a volume V is the J integral on the surface surrounding V and the moment resultant is the L integral. So these integrals are defined without any assumption on the material constitutive equation. Another result is the material form of the virtual work principle - defect forces are acting like conventional forces in the conventional principles of virtual work. This lead to the introduction of the energy momentum tensor and of the associated couple stress. Application of this method is made to fracture mechanics in studying the defect forces distribution around a crack [fr

  16. Fracture Mechanics Analyses for Interface Crack Problems - A Review

    Science.gov (United States)

    Krueger, Ronald; Shivakumar, Kunigal; Raju, Ivatury S.

    2013-01-01

    Recent developments in fracture mechanics analyses of the interfacial crack problem are reviewed. The intent of the review is to renew the awareness of the oscillatory singularity at the crack tip of a bimaterial interface and the problems that occur when calculating mode mixity using numerical methods such as the finite element method in conjunction with the virtual crack closure technique. Established approaches to overcome the nonconvergence issue of the individual mode strain energy release rates are reviewed. In the recent literature many attempts to overcome the nonconvergence issue have been developed. Among the many approaches found only a few methods hold the promise of providing practical solutions. These are the resin interlayer method, the method that chooses the crack tip element size greater than the oscillation zone, the crack tip element method that is based on plate theory and the crack surface displacement extrapolation method. Each of the methods is validated on a very limited set of simple interface crack problems. However, their utility for a wide range of interfacial crack problems is yet to be established.

  17. Sensitivity analysis of a discrete fracture network model for performance assessment of Aberg

    International Nuclear Information System (INIS)

    Outters, N.; Shuttle, D.

    2000-12-01

    This report presents a sensitivity analysis of pathway simulations in a DFN model. The DFN model consists of two sets of stochastic fractures at different scales and the canister locations of a hypothetical repository layout. The hydrogeological base case model is defined by constant head boundary conditions on the edges of a 2000 x 2000 x 1000 m 3 block. The pathway analysis carried out by the program PAWorks provides pathway parameters (pathway length, pathway width, transport aperture, reactive surface area, pathway transmissivity), canister statistics (average number of pathways per canister, percentage of canister locations with pathways) and visualisation of pathways. The project provided the following results from the alternative cases: Case 1: Model with a 100 m thick fracture network at the repository scale instead of 50 m in the base case. The model is little sensitive to the increase of the thickness of the local fracture network. Case 2: Model including fracture networks where the mean size and size standard deviation is twice the ones used in the base case. The travel times to the biosphere is slightly shortened by increasing the fracture diameter. Case 3: Two models with alternative hydraulic boundary conditions: two different flux boundary conditions are tested instead of head boundary conditions in the base case. The advective travel time is shortened by changing the boundary conditions in both alternative cases; in some cases it is reduced to less than a year. Case 4: Study of alternative pathway search algorithms: the pathway search is here based on minimum travel time. The pathway search algorithm of PAWorks based on minimum travel time gives much more optimistic results than the base case where the maximum flow rate was used. The mean travel time is about 5000 years. Due to editorial reasons only a subset of all this information is treated in this report

  18. Understanding cracking failures of coatings: A fracture mechanics approach

    Science.gov (United States)

    Kim, Sung-Ryong

    A fracture mechanics analysis of coating (paint) cracking was developed. A strain energy release rate (G(sub c)) expression due to the formation of a new crack in a coating was derived for bending and tension loadings in terms of the moduli, thicknesses, Poisson's ratios, load, residual strain, etc. Four-point bending and instrumented impact tests were used to determine the in-situ fracture toughness of coatings as functions of increasing baking (drying) time. The system used was a thin coating layer on a thick substrate layer. The substrates included steel, aluminum, polycarbonate, acrylonitrile-butadiene-styrene (ABS), and Noryl. The coatings included newly developed automotive paints. The four-point bending configuration promoted nice transversed multiple coating cracks on both steel and polymeric substrates. The crosslinked type automotive coatings on steel substrates showed big cracks without microcracks. When theoretical predictions for energy release rate were compared to experimental data for coating/steel substrate samples with multiple cracking, the agreement was good. Crosslinked type coatings on polymeric substrates showed more cracks than theory predicted and the G(sub c)'s were high. Solvent evaporation type coatings on polymeric substrates showed clean multiple cracking and the G(sub c)'s were higher than those obtained by tension analysis of tension experiments with the same substrates. All the polymeric samples showed surface embrittlement after long baking times using four-point bending tests. The most apparent surface embrittlement was observed in the acrylonitrile-butadiene-styrene (ABS) substrate system. The impact properties of coatings as a function of baking time were also investigated. These experiments were performed using an instrumented impact tester. There was a rapid decrease in G(sub c) at short baking times and convergence to a constant value at long baking times. The surface embrittlement conditions and an embrittlement toughness

  19. Effect of sensitization on the mechanical properties of type 304 L stainless steel

    International Nuclear Information System (INIS)

    Vargas Mendoza, L.F.

    1990-01-01

    The sensitization is a corrosion cause that it has studied broadly in the austenitic steels; however its relations don't knowed very well, into the sensitization and the steel's mechanical properties. Wherefore, the objectives of this work was to study the mechanical properties, in tension of austenitic steel with different levels of sensitization. The material utilized was a 304 L steel of standard composition AISI. The samples were sensitized at 450, 650 and 850 Centigrade degree, by short expositions, following by a temper in water. After this treatment, the tension test tubes were carried to rupture at low deformation velocity. The sensitization was evaluated by the method of Akashi EPR cyclic polarization. The sensitization distribution was analyzed by optical metallography in color and the fracture surface were studied by sweeping electronic microscopy. The distribution and length of the carbides were the factor that control the mechanic behavior of materials. At 450 Centigrade, the border of the grain its founded free of carbides, also for the longest times of exposition, but the particles are presented as fine precipitates in the grain interior, with this is increased the mechanical properties by the internal interactions of hardness or oldness types. At 650 Centigrade the frontiers show a dense distribution of fine carbides. These precipitates are interacting with the borders grain, increasing lightly the mechanical properties of steel. At 850 Centigrade, were formed discontinued carbides that not affect the mechanical behavior, but whether the fracture; the resistance is reduced and the ductility is increased although to impose the thermic effect of treatment. (Author)

  20. Failure conditions from push out tests of a steel-concrete joint: fracture mechanics approach

    Czech Academy of Sciences Publication Activity Database

    Klusák, Jan; Seitl, Stanislav; De Corte, W.; Helincks, P.; Boel, V.; De Schutter, G.

    488-489, - (2012), s. 710-713 ISSN 1013-9826. [International Conference on Fracture and Damage Mechanics - FDM 2011 /10./. Dubrovník, 19.09.2011-21.09.2011] R&D Projects: GA ČR GAP108/10/2049 Institutional research plan: CEZ:AV0Z20410507 Keywords : Push out test * generalized linear elastic fracture mechanics * bi-material notch Subject RIV: JL - Materials Fatigue, Friction Mechanics

  1. Mechanical and fracture properties of a self-compacting version of ...

    Indian Academy of Sciences (India)

    B S Al-Azzawi

    The method of the production of CARDIFRC and its mechanical and fracture properties were reported in a series .... All constituents used in UHPFRC based on CARDIFRC. Mix II were locally available. .... tri-linear approximation is closer to how the local fracture energy varies as the crack grows from a notched specimen.

  2. comparison of elastic-plastic FE method and engineering method for RPV fracture mechanics analysis

    International Nuclear Information System (INIS)

    Sun Yingxue; Zheng Bin; Zhang Fenggang

    2009-01-01

    This paper described the FE analysis of elastic-plastic fracture mechanics for a crack in RPV belt line using ABAQUS code. It calculated and evaluated the stress intensity factor and J integral of crack under PTS transients. The result is also compared with that by engineering analysis method. It shows that the results using engineering analysis method is a little larger than the results using FE analysis of 3D elastic-plastic fracture mechanics, thus the engineering analysis method is conservative than the elastic-plastic fracture mechanics method. (authors)

  3. An extension of fracture mechanics/technology to larger and smaller cracks/defects.

    Science.gov (United States)

    Abé, Hiroyuki

    2009-01-01

    Fracture mechanics/technology is a key science and technology for the design and integrity assessment of the engineering structures. However, the conventional fracture mechanics has mostly targeted a limited size of cracks/defects, say of from several hundred microns to several tens of centimeters. The author and his group has tried to extend that limited size and establish a new version of fracture technology for very large cracks used in geothermal energy extraction and for very small cracks/defects or damage often appearing in the combination of mechanical and electronic components of engineering structures. Those new versions are reviewed in this paper.

  4. An extension of fracture mechanics/technology to larger and smaller cracks/defects

    Science.gov (United States)

    Abé, Hiroyuki

    2009-01-01

    Fracture mechanics/technology is a key science and technology for the design and integrity assessment of the engineering structures. However, the conventional fracture mechanics has mostly targeted a limited size of cracks/defects, say of from several hundred microns to several tens of centimeters. The author and his group has tried to extend that limited size and establish a new version of fracture technology for very large cracks used in geothermal energy extraction and for very small cracks/defects or damage often appearing in the combination of mechanical and electronic components of engineering structures. Those new versions are reviewed in this paper. PMID:19907123

  5. Neural and psychosocial mechanisms of pain sensitivity in fibromyalgia.

    Science.gov (United States)

    English, Brian

    2014-06-01

    Fibromyalgia is a chronic musculoskeletal pain disorder that affects an estimated 5 million adults in the U.S. The hallmark is burning, searing, tingling, shooting, stabbing, deep aching, or sharp pain. Fibromyalgia is generally considered to be a "central sensitivity syndrome" where central sensitization is regarded as the cause of pain in its own right. Nonetheless, the case continues to be made that all central and spatially distributed peripheral components of fibromyalgia pain would fade if the peripheral generators could be silenced. Although neural mechanisms are clearly important in pain sensitivity, cognitive and social mechanisms also need to be considered. The aim of this review is to examine four mechanisms responsible for heightened pain sensitivity in fibromyalgia: peripheral sensitization, central sensitization, cognitive-emotional sensitization, and interpersonal sensitization. The purpose of framing the review in terms of pain sensitivity in fibromyalgia is to highlight that different mechanisms of sensitization are appropriately regarded as intervening variables when it comes to understanding individual differences in the experience of pain. The paper concludes by considering the implications of the findings of the review for explanations of fibromyalgia pain by nurses working in multidisciplinary teams. The trend appears to be able to explain the cause of fibromyalgia pain in terms of sensitization per se. The recommended alternative is to explain fibromyalgia pain in terms of changes in pain sensitivity and the role of underlying neural and psychosocial mechanisms. Copyright © 2014 American Society for Pain Management Nursing. Published by Elsevier Inc. All rights reserved.

  6. Thermo-hydro-mechanical simulation of a 3D fractured porous rock: preliminary study of coupled matrix-fracture hydraulics

    International Nuclear Information System (INIS)

    Canamon, I.; Javier Elorza, F.; Ababou, R.

    2007-01-01

    We present a problem involving the modeling of coupled flow and elastic strain in a 3D fractured porous rock, which requires prior homogenization (up-scaling) of the fractured medium into an equivalent Darcian anisotropic continuum. The governing equations form a system of PDE's (Partial Differential Equations) and, depending on the case being considered, this system may involve two different types of 'couplings' (in a real system, both couplings (1) and (2) generally take place): 1) Hydraulic coupling in a single (no exchange) or in a dual matrix-fracture continuum (exchange); 2) Thermo-Hydro-Mechanical interactions between fluid flow, pressure, elastic stress, strain, and temperature. We present here a preliminary model and simulation results with FEMLAB R , for the hydraulic problem with anisotropic heterogeneous coefficients. The model is based on data collected at an instrumented granitic site (FEBEX project) for studying a hypothetical nuclear waste repository at the Grimsel Test Site in the Swiss Alps. (authors)

  7. Analysis of seismic sources for different mechanisms of fracture growth for microseismic monitoring applications

    International Nuclear Information System (INIS)

    Duchkov, A. A.; Stefanov, Yu. P.

    2015-01-01

    We have developed and illustrated an approach for geomechanic modeling of elastic wave generation (microsiesmic event occurrence) during incremental fracture growth. We then derived properties of effective point seismic sources (radiation patterns) approximating obtained wavefields. These results establish connection between geomechanic models of hydraulic fracturing and microseismic monitoring. Thus, the results of the moment tensor inversion of microseismic data can be related to different geomechanic scenarios of hydraulic fracture growth. In future, the results can be used for calibrating hydrofrac models. We carried out a series of numerical simulations and made some observations about wave generation during fracture growth. In particular when the growing fracture hits pre-existing crack then it generates much stronger microseismic event compared to fracture growth in homogeneous medium (radiation pattern is very close to the theoretical dipole-type source mechanism)

  8. Fracture mechanics evaluation of some LOFT blowdown system and primary coolant coldleg welds

    International Nuclear Information System (INIS)

    Nagata, P.K.

    1978-01-01

    Fracture mechanics evaluations were performed for three welds in the LOFT blowdown system and one weld in the LOFT primary coolant system. Because the applied stress is not known, a sensitivity analysis was run. The assumed initial defect size was one that had a small probability of being missed; applied stresses of 68.9, 137.8, 206.7, and 344.8 MPa were used. It was found that at the lowest stress (68.9 MPa or 10 ksi) the number of cycles from the initial size to rupture was over 6 x 10 6 . The current calculations indicate that with the worst crack configuration--depth-to-length ratio (a/2c) of 0.10--about 1000 cycles with a peak stress of 227.5 MPa (33 ksi) will be needed to propagate the 0.5 x 5.1 cm (0.2 x 2.0 in.) crack to failure

  9. The radiation swelling effect on fracture properties and fracture mechanisms of irradiated austenitic steels. Part II. Fatigue crack growth rate

    Energy Technology Data Exchange (ETDEWEB)

    Margolin, B., E-mail: margolinbz@yandex.ru; Minkin, A.; Smirnov, V.; Sorokin, A.; Shvetsova, V.; Potapova, V.

    2016-11-15

    The experimental data on the fatigue crack growth rate (FCGR) have been obtained for austenitic steel of 18Cr-10Ni-Ti grade (Russian analog of AISI 321 steel) irradiated up to neutron dose of 150 dpa with various radiation swelling. The performed study of the fracture mechanisms for cracked specimens under cyclic loading has explained why radiation swelling affects weakly FCGR unlike its effect on fracture toughness. Mechanical modeling of fatigue crack growth has been carried out and the dependencies for prediction of FCGR in irradiated austenitic steel with and with no swelling are proposed and verified with the obtained experimental results. As input data for these dependencies, FCGR for unirradiated steel and the tensile mechanical properties for unirradiated and irradiated steels are used.

  10. Tensile properties and fracture mechanism of IN-100 superalloy in high temperature range

    Directory of Open Access Journals (Sweden)

    Milan T. Jovanović

    2017-06-01

    Full Text Available Tensile properties and fracture mechanism of a polycrystalline IN-100 superalloy have been investigated in the range from room temperature to 900°C. Optical microscopy (OM and transmission electron microscopy (TEM applying replica technique were used for microstructural investigation, whereas scanning electron microscopy (SEM was utilized for fracture study. High temperature tensile tests were carried out in vacuumed chamber. Results show that strength increases up to 700°C, and then sharply decreases with further increase in temperature. Elongation increases very slowly (6-7.5% till 500°C, then decreases to 4.5% at 900°C. Change in elongation may be ascribed to a change of fracture mechanism. Appearance of a great number of microvoids prevails up to 500°C resulting in a slow increase of elongation, whereas above this temperature elongation decrease is correlated with intergranular crystallographic fracture and fracture of carbides.

  11. Continuum and micro-mechanics treatment of constraint in fracture

    International Nuclear Information System (INIS)

    Dodds, R.H. Jr.; Shih, C.F.

    1993-01-01

    This paper explores the fundamental concepts of the J-Q description of crack-tip fields, the fracture toughness locus and micromechanics approaches to predict the variability of macroscopic fracture toughness with constraint under elastic-plastic conditions. While these concepts derived from plane-strain considerations, initial applications in fully 3-D geometries are very promising. Computational results are presented for a surface cracked plate containing a 6:1 semi-elliptical, a=t/4 flaw subjected to remote uniaxial and biaxial tension. Crack-tip stress fields consistent with the J-Q theory are demonstrated to exist at each location along the crack front. The micromechanics model employs the J-Q description of crack-front stresses to interpret fracture toughness values measured on laboratory specimens for fracture assessment of the surface cracked plate. The computational results suggest only a minor effect of the biaxial loading on the crack tip stress fields and, consequently, on the propensity for fracture relative to the uniaxial loading. 45 refs., 19 figs., 3 tabs

  12. Numerical Modeling and Investigation of Fluid-Driven Fracture Propagation in Reservoirs Based on a Modified Fluid-Mechanically Coupled Model in Two-Dimensional Particle Flow Code

    Directory of Open Access Journals (Sweden)

    Jian Zhou

    2016-09-01

    Full Text Available Hydraulic fracturing is a useful tool for enhancing rock mass permeability for shale gas development, enhanced geothermal systems, and geological carbon sequestration by the high-pressure injection of a fracturing fluid into tight reservoir rocks. Although significant advances have been made in hydraulic fracturing theory, experiments, and numerical modeling, when it comes to the complexity of geological conditions knowledge is still limited. Mechanisms of fluid injection-induced fracture initiation and propagation should be better understood to take full advantage of hydraulic fracturing. This paper presents the development and application of discrete particle modeling based on two-dimensional particle flow code (PFC2D. Firstly, it is shown that the modeled value of the breakdown pressure for the hydraulic fracturing process is approximately equal to analytically calculated values under varied in situ stress conditions. Furthermore, a series of simulations for hydraulic fracturing in competent rock was performed to examine the influence of the in situ stress ratio, fluid injection rate, and fluid viscosity on the borehole pressure history, the geometry of hydraulic fractures, and the pore-pressure field, respectively. It was found that the hydraulic fractures in an isotropic medium always propagate parallel to the orientation of the maximum principal stress. When a high fluid injection rate is used, higher breakdown pressure is needed for fracture propagation and complex geometries of fractures can develop. When a low viscosity fluid is used, fluid can more easily penetrate from the borehole into the surrounding rock, which causes a reduction of the effective stress and leads to a lower breakdown pressure. Moreover, the geometry of the fractures is not particularly sensitive to the fluid viscosity in the approximate isotropic model.

  13. Fracture mechanics analyses of the slip-side joggle regions of wing-leading-edge panels

    Directory of Open Access Journals (Sweden)

    Kyongchan Song

    2011-01-01

    Full Text Available The Space Shuttle wing-leading edge consists of panels that are made of reinforced carbon-carbon. Coating spallation was observed near the slip-side region of the panels that experience extreme heating. To understand this phenomenon, a root-cause investigation was conducted. As part of that investigation, fracture mechanics analyses of the slip-side joggle regions of the hot panels were conducted. This paper presents an overview of the fracture mechanics analyses.

  14. Generalized linear elastic fracture mechanics: an application to a crack touching the bimaterial interface

    Czech Academy of Sciences Publication Activity Database

    Náhlík, Luboš; Šestáková, L.; Hutař, Pavel; Knésl, Zdeněk

    2011-01-01

    Roč. 452-453, - (2011), s. 445-448 ISSN 1013-9826 R&D Projects: GA AV ČR(CZ) KJB200410803; GA ČR GA101/09/1821 Institutional research plan: CEZ:AV0Z20410507 Keywords : generalized stress intensity factor * bimaterial interface * composite materials * strain energy density factor * fracture criterion * generalized linear elastic fracture mechanics Subject RIV: JL - Materials Fatigue, Friction Mechanics

  15. Fracture Mechanics Analyses of the Slip-Side Joggle Regions of Wing-Leading-Edge Panels

    Science.gov (United States)

    Raju, Ivatury S.; Knight, Norman F., Jr.; Song, Kyongchan; Phillips, Dawn R.

    2011-01-01

    The Space Shuttle wing-leading edge consists of panels that are made of reinforced carbon-carbon. Coating spallation was observed near the slip-side region of the panels that experience extreme heating. To understand this phenomenon, a root-cause investigation was conducted. As part of that investigation, fracture mechanics analyses of the slip-side joggle regions of the hot panels were conducted. This paper presents an overview of the fracture mechanics analyses.

  16. Mechanical properties and fracture behaviour of defective phosphorene nanotubes under uniaxial tension

    Science.gov (United States)

    Liu, Ping; Pei, Qing-Xiang; Huang, Wei; Zhang, Yong-Wei

    2017-12-01

    The easy formation of vacancy defects and the asymmetry in the two sublayers of phosphorene nanotubes (PNTs) may result in brand new mechanical properties and failure behaviour. Herein, we investigate the mechanical properties and fracture behaviour of defective PNTs under uniaxial tension using molecular dynamics simulations. Our simulation results show that atomic vacancies cause local stress concentration and thus significantly reduce the fracture strength and fracture strain of PNTs. More specifically, a 1% defect concentration is able to reduce the fracture strength and fracture strain by as much as 50% and 66%, respectively. Interestingly, the reduction in the mechanical properties is found to depend on the defect location: a defect located in the outer sublayer has a stronger effect than one located in the inner layer, especially for PNTs with a small diameter. Temperature is also found to strongly influence the mechanical properties of both defect-free and defective PNTs. When the temperature is increased from 0 K to 400 K, the fracture strength and fracture strain of defective PNTs with a defect concentration of 1% are reduced further by 71% and 61%, respectively. These findings are of great importance for the structural design of PNTs as building blocks in nanodevices.

  17. Integrity of the osteocyte bone cell network in osteoporotic fracture: Implications for mechanical load adaptation

    International Nuclear Information System (INIS)

    Kuliwaba, J S; Truong, L; Codrington, J D; Fazzalari, N L

    2010-01-01

    The human skeleton has the ability to modify its material composition and structure to accommodate loads through adaptive modelling and remodelling. The osteocyte cell network is now considered to be central to the regulation of skeletal homeostasis; however, very little is known of the integrity of the osteocyte cell network in osteoporotic fragility fracture. This study was designed to characterise osteocyte morphology, the extent of osteocyte cell apoptosis and expression of sclerostin protein (a negative regulator of bone formation) in trabecular bone from the intertrochanteric region of the proximal femur, for postmenopausal women with fragility hip fracture compared to age-matched women who had not sustained fragility fracture. Osteocyte morphology (osteocyte, empty lacunar, and total lacunar densities) and the degree of osteocyte apoptosis (percent caspase-3 positive osteocyte lacunae) were similar between the fracture patients and non-fracture women. The fragility hip fracture patients had a lower proportion of sclerostin-positive osteocyte lacunae in comparison to sclerostin-negative osteocyte lacunae, in contrast to similar percent sclerostin-positive/sclerostin-negative lacunae for non-fracture women. The unexpected finding of decreased sclerostin expression in trabecular bone osteocytes from fracture cases may be indicative of elevated bone turnover and under-mineralisation, characteristic of postmenopausal osteoporosis. Further, altered osteocytic expression of sclerostin may be involved in the mechano-responsiveness of bone. Optimal function of the osteocyte cell network is likely to be a critical determinant of bone strength, acting via mechanical load adaptation, and thus contributing to osteoporotic fracture risk.

  18. Integrity of the osteocyte bone cell network in osteoporotic fracture: Implications for mechanical load adaptation

    Science.gov (United States)

    Kuliwaba, J. S.; Truong, L.; Codrington, J. D.; Fazzalari, N. L.

    2010-06-01

    The human skeleton has the ability to modify its material composition and structure to accommodate loads through adaptive modelling and remodelling. The osteocyte cell network is now considered to be central to the regulation of skeletal homeostasis; however, very little is known of the integrity of the osteocyte cell network in osteoporotic fragility fracture. This study was designed to characterise osteocyte morphology, the extent of osteocyte cell apoptosis and expression of sclerostin protein (a negative regulator of bone formation) in trabecular bone from the intertrochanteric region of the proximal femur, for postmenopausal women with fragility hip fracture compared to age-matched women who had not sustained fragility fracture. Osteocyte morphology (osteocyte, empty lacunar, and total lacunar densities) and the degree of osteocyte apoptosis (percent caspase-3 positive osteocyte lacunae) were similar between the fracture patients and non-fracture women. The fragility hip fracture patients had a lower proportion of sclerostin-positive osteocyte lacunae in comparison to sclerostin-negative osteocyte lacunae, in contrast to similar percent sclerostin-positive/sclerostin-negative lacunae for non-fracture women. The unexpected finding of decreased sclerostin expression in trabecular bone osteocytes from fracture cases may be indicative of elevated bone turnover and under-mineralisation, characteristic of postmenopausal osteoporosis. Further, altered osteocytic expression of sclerostin may be involved in the mechano-responsiveness of bone. Optimal function of the osteocyte cell network is likely to be a critical determinant of bone strength, acting via mechanical load adaptation, and thus contributing to osteoporotic fracture risk.

  19. A Modified TSD Specimen for Fracture Toughness Characterization – Fracture Mechanics Analysis and Design

    DEFF Research Database (Denmark)

    Berggreen, Christian; Carlsson, Leif A.

    2010-01-01

    The tilted sandwich debond (TSD) specimen has been recognized as a viable candidate for characterization of the face/core fracture resistance. Analysis, however, shows that the range of phase angles that can be realized by altering the tilt angle and other parameters of the test is quite limited....

  20. Fracture simulation of restored teeth using a continuum damage mechanics failure model.

    Science.gov (United States)

    Li, Haiyan; Li, Jianying; Zou, Zhenmin; Fok, Alex Siu-Lun

    2011-07-01

    The aim of this paper is to validate the use of a finite-element (FE) based continuum damage mechanics (CDM) failure model to simulate the debonding and fracture of restored teeth. Fracture testing of plastic model teeth, with or without a standard Class-II MOD (mesial-occusal-distal) restoration, was carried out to investigate their fracture behavior. In parallel, 2D FE models of the teeth are constructed and analyzed using the commercial FE software ABAQUS. A CDM failure model, implemented into ABAQUS via the user element subroutine (UEL), is used to simulate the debonding and/or final fracture of the model teeth under a compressive load. The material parameters needed for the CDM model to simulate fracture are obtained through separate mechanical tests. The predicted results are then compared with the experimental data of the fracture tests to validate the failure model. The failure processes of the intact and restored model teeth are successfully reproduced by the simulation. However, the fracture parameters obtained from testing small specimens need to be adjusted to account for the size effect. The results indicate that the CDM model is a viable model for the prediction of debonding and fracture in dental restorations. Copyright © 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  1. Finite element analysis of surface cracks in the Wilkins Ice Shelf using fracture mechanics

    Science.gov (United States)

    Plate, Carolin; Müller, Ralf; Gross, Dietmar; Humbert, Angelika; Braun, Matthias

    2010-05-01

    Ice shelves, located between the warming atmosphere and the ocean, are sensitive elements of the climate system. The Wilkins Ice Shelf is situated in the south-western part of the Antarctic Peninsula, a well known hot spot of global warming. Recent break-up events exemplified the potential of disintegration of the ice shelf. A multi interdisciplinary project consisting of remote sensing, modeling of the ice dynamics and fracture mechanics intends to improve the understanding of the impacts of temperature increase on ice shelf stability. As a part of this project the aim of this presentation is to demonstrate the fracture mechanical approach using finite elements and configurational forces. For fracture mechanical purposes the material behavior of ice is treated as a brittle solid, and linear fracture mechanics is used. Crucial to all methods in linear fracture mechanics is the evaluation of the stress intensity factor K which is a measure for the load concentration at the crack tip and which depends on the geometry of the body and on the applied loading. The computed value of K can be compared to the critical stress intensity factor Kc, a material property obtained from experimental examinations, to judge whether a crack will propagate. One very effective procedure to obtain the stress intensity factor takes advantage of configurational forces, which can be easily obtained in the finite element analysis. An initial investigation is based on a 2-dimensional analysis of a single crack with a mode-I load type using a static plane strain model in the finite element analysis software COMSOL and additional routines to compute and evaluate the configurational forces. Analytical solutions of simple geometry and load cases are called on in comparison. The application to the Wilkins Ice Shelf follows by using material parameters, geometries and loading situations, which are obtained from literature values, remote sensing data analysis and modeling of the ice dynamics

  2. Fracture Mechanics Analysis of a Modified TSD Specimen

    DEFF Research Database (Denmark)

    Berggreen, Christian; Carlsson, Leif A.

    2008-01-01

    The Tilted Sandwich Debond (TSD) specimen has been recognized as a viable candidate for characterization of the face/core fracture resistance. Analysis, however, shows that the range of phase angles that can be realized by altering the tilt angle is quite limited. A parametric study however shows...

  3. The WST method, a fracture mechanics test method for FRC

    DEFF Research Database (Denmark)

    Lofgren, I.; Stang, Henrik; Olesen, John Forbes

    2008-01-01

    The applicability of the wedge-splitting test method (WST), for determining fracture properties of fibre-reinforced concrete, is discussed. Experimental results, using the WST method, are compared with results from uniaxial tension tests (UTT) and three-point bending tests (3PBT) for five differe...

  4. Mechanical properties and fracture toughness of rail steels and thermite welds at low temperature

    Science.gov (United States)

    Wang, Yuan-qing; Zhou, Hui; Shi, Yong-jiu; Feng, Bao-rui

    2012-05-01

    Brittle fracture occurs frequently in rails and thermite welded joints, which intimidates the security and reliability of railway service. Railways in cold regions, such as Qinghai-Tibet Railway, make the problem of brittle fracture in rails even worse. A series of tests such as uniaxial tensile tests, Charpy impact tests, and three-point bending tests were carried out at low temperature to investigate the mechanical properties and fracture toughness of U71Mn and U75V rail steels and their thermite welds. Fracture micromechanisms were analyzed by scanning electron microscopy (SEM) on the fracture surfaces of the tested specimens. The ductility indices (percentage elongation after fracture and percentage reduction of area) and the toughness indices (Charpy impact energy A k and plane-strain fracture toughness K IC) of the two kinds of rail steels and the corresponding thermite welds all decrease as the temperature decreases. The thermite welds are more critical to fracture than the rail steel base metals, as indicated by a higher yield-to-ultimate ratio and a much lower Charpy impact energy. U71Mn rail steel is relatively higher in toughness than U75V, as demonstrated by larger A k and K IC values. Therefore, U71Mn rail steel and the corresponding thermite weld are recommended in railway construction and maintenance in cold regions.

  5. Pseudoarthrosis following proximal humeral fractures: A possible mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Rooney, P.J.; Cockshott, W.P.

    1986-01-01

    A small series of four patients with pseudarthrosis of the proximal humeral shaft is reported. These patients all had restricted movement of the shoulder joint prior to the trauma, three as a result of rheumatoid arthritis and one due a surgical fusion of the glenohumeral joint. It is suggested that pseudarthrosis is more likely under these circumstances and that pursuit of union of the fracture in such patients may not always be necessary.

  6. Future trends in fracture mechanics: theory and applications

    International Nuclear Information System (INIS)

    Hosbons, R.R.

    1978-05-01

    A brief description of the current methods available for the analysis of fracture in ductile materials is given. Crack-opening displacement, R-curves and J-integrals are discussed and their future incorporation into structural codes assessed. The current areas of research which will probably influence code making bodies are also described. Emphasis is made on J-integral theory and a description of its limitations and extensions. Numerical techniques for calculating J for complicated structure are outlined. (author)

  7. Application of linear-elastic fracture mechanics concepts to ferritic spent fuel shipping casks

    International Nuclear Information System (INIS)

    McConnell, P.; Wullaert, R.A.; Trujillo, A.

    1983-01-01

    A linear-elastic fracture mechanics analysis is an appropriate methodology for the fail-safe design of spent fuel shipping containers. It provides a quantitative basis by which to assess the margin of safety inherent to a particular cask. Required inputs are the maximum stresses to be expected from a nine-meter drop, the largest flaw size that may be expected to exist in the cask (based upon capabilities of NDE), and the fracture toughness of the cask material. It was analytically, and conservatively, demonstrated using linear-elastic fracture mechanics procedures that two typical shipping cask designs, constructed of candidate ferritic steel and nodular cast iron materials, can withstand a nine-meter drop. No crack initiation would occur even should a flaw of a size well above the detectability limit of conventional NDE exist in the cask. The fracture toughness of even relatively low toughness ferritic materials is sufficient to ensure the structural integrity of these casks

  8. Correlation of AO and Lauge-Hansen classification systems for ankle fractures to the mechanism of injury.

    Science.gov (United States)

    Rodriguez, Edward K; Kwon, John Y; Herder, Lindsay M; Appleton, Paul T

    2013-11-01

    Our aim was to assess whether the Lauge-Hansen (LH) and the Muller AO classification systems for ankle fractures radiographically correlate with in vivo injuries based on observed mechanism of injury. Videos of potential study candidates were reviewed on YouTube.com. Individuals were recruited for participation if the video could be classified by injury mechanism with a high likelihood of sustaining an ankle fracture. Corresponding injury radiographs were obtained. Injury mechanism was classified using the LH system as supination/external rotation (SER), supination/adduction (SAD), pronation/external rotation (PER), or pronation/abduction (PAB). Corresponding radiographs were classified by the LH system and the AO system. Thirty injury videos with their corresponding radiographs were collected. Of the video clips reviewed, 16 had SAD mechanisms and 14 had PER mechanisms. There were 26 ankle fractures, 3 nonfractures, and 1 subtalar dislocation. Twelve fractures with SAD mechanisms had corresponding SAD fracture patterns. Five PER mechanisms had PER fracture patterns. Eight PER mechanisms had SER fracture patterns and 1 had SAD fracture pattern. When the AO classification was used, all 12 SAD type injuries had a 44A type fracture, whereas the 14 PER injuries resulted in nine 44B fractures, two 44C fractures, and three 43A fractures. When injury video clips of ankle fractures were matched to their corresponding radiographs, the LH system was 65% (17/26) consistent in predicting fracture patterns from the deforming injury mechanism. When the AO classification system was used, consistency was 81% (21/26). The AO classification, despite its development as a purely radiographic system, correlated with in vivo injuries, as based on observed mechanism of injury, more closely than did the LH system. Level IV, case series.

  9. State of the Art Report on Fracture Mechanics (Fracture in the Creep Range). Volume 3: Appendices H - M

    International Nuclear Information System (INIS)

    Ellison, E.G.; Musicco, G.G.; Pineau, A.

    1988-01-01

    A CEC State of the Art Report on Fracture Mechanics for Fast Breeder Reactors (Fracture below the Creep Range) has recently been published by Bhandari and coworkers (1984). There has also been a compilation of Creep Crack Growth Data from Germany, France and the U.K. for 304 and 316 stainles steel by Lloyd et al (1984). The present Report provides considerably more data and analytical techniques taken from Worldwide sources on creep crack initiation and propagation. Since the subject is moving quickly there is an emphasis on the most recent work; indeed research studies as yet unpublished are also included. The total Report is in 3 volumes. Volume 3 contains the most important and up-to-date information in some detail in Appendices H to M; this provides a sound base for the Report and for future workers

  10. Experimental and theoretical fracture mechanics applied to volcanic conduits and domes

    Science.gov (United States)

    Sammonds, P.; Matthews, C.; Kilburn, C.; Smith, R.; Tuffen, H.; Meredith, P.

    2008-12-01

    We present an integrated modelling and experimental approach to magma deformation and fracture, which we attempt to validate against field observations of seismicity. The importance of fracture processes in magma ascent dynamics and lava dome growth and collapse are apparent from the associated seismicity. Our laboratory experiments have shown that brittle fracture of magma can occur at high temperature and stress conditions prevalent in the shallow volcanic system. Here, we use a fracture mechanics approach to model seismicity preceding volcanic eruptions. Starting with the fracture mechanics concept of a crack in an elastic body, we model crack growth around the volcanic conduit through the processes of crack interactions, leading either to the propagation and linkage of cracks, or crack avoidance and the inhibition of crack propagation. The nature of that interaction is governed by the temperature and plasticity of the magma. We find that fracture mechanics rules can account for the style of seismicity preceding eruptions. We have derived the changes in seismic b-value predicted by the model and interpret these in terms of the style of fracturing, fluid flow and heat transport. We compare our model with results from our laboratory experiments where we have deformed lava at high temperatures under triaxial stresses. These experiments were conducted in dry and water saturated conditions at effective pressures up to 10 MPa, temperatures up to 1000°C and strain rates from 10-4 s-1 to 10-6 s-1. The behaviour of these magmas was largely brittle under these conditions. We monitored the acoustic emission emitted and calculate the change in micro-seismic b-value with deformation. These we find are in accord with volcano seismicity and our fracture mechanics model.

  11. Mechanical and mathematical models of multi-stage horizontal fracturing strings and their application

    Directory of Open Access Journals (Sweden)

    Zhanghua Lian

    2015-03-01

    Full Text Available Multi-stage SRV fracturing in horizontal wells is a new technology developed at home and abroad in recent years to effectively develop shale gas or low-permeability reservoirs, but on the other hand makes the mechanical environment of fracturing strings more complicated at the same time. In view of this, based on the loading features of tubing strings during the multi-stage fracturing of a horizontal well, mechanical models were established for three working cases of multiple packer setting, open differential-pressure sliding sleeve, and open ball-injection sliding sleeve under a hold-down packer. Moreover, mathematical models were respectively built for the above three cases. According to the Lame formula and Von Mises stress calculation formula for the thick-walled cylinder in the theory of elastic mechanics, a mathematical model was also established to calculate the equivalent stress for tubing string safety evaluation when the fracturing string was under the combined action of inner pressure, external squeezing force and axial stress, and another mathematical model was built for the mechanical strength and safety evaluation of multi-stage fracturing strings. In addition, a practical software was developed for the mechanical safety evaluation of horizontal well multi-stage fracturing strings according to the mathematical model developed for the mechanical calculation of the multi-packer string in horizontal wells. The research results were applied and verified in a gas well of Tahe Oilfield in the Tarim Basin with excellent effects, providing a theoretical basis and a simple and reliable technical means for optimal design and safety evaluation of safe operational parameters of multi-stage fracturing strings in horizontal wells.

  12. Effect of strain rate and notch geometry on tensile properties and fracture mechanism of creep strength enhanced ferritic P91 steel

    Science.gov (United States)

    Pandey, Chandan; Mahapatra, M. M.; Kumar, Pradeep; Saini, N.

    2018-01-01

    Creep strength enhanced ferritic (CSEF) P91 steel were subjected to room temperature tensile test for quasi-static (less than 10-1/s) strain rate by using the Instron Vertical Tensile Testing Machine. Effect of different type of notch geometry, notch depth and angle on mechanical properties were also considered for different strain rate. In quasi-static rates, the P91 steel showed a positive strain rate sensitivity. On the basis of tensile data, fracture toughness of P91 steel was also calculated numerically. For 1 mm notch depth (constant strain rate), notch strength and fracture toughness were found to be increased with increase in notch angle from 45° to 60° while the maximum value attained in U-type notch. Notch angle and notch depth has found a minute effect on P91 steel strength and fracture toughness. The fracture surface morphology was studied by field emission scanning electron microscopy (FESEM).

  13. Fatigue crack growth and fracture mechanics analysis of a working roll surface layer material

    Directory of Open Access Journals (Sweden)

    M. Drobne

    2014-10-01

    Full Text Available Fatigue crack growth and fracture mechanics analysis of a working roll surface layer material is presented in this paper. The research is done on a hot strip mill working roll where High Chromium Steel is used for roll’s shell material. To obtain corresponding parameters, a rectangular single edge notched bend specimens – SENB, according to standard BS 7448, were used. The fatigue crack growth analysis was done on a resonant testing machine with use of special crack gauges, while for fracture mechanics parameters the electro–mechanical testing machine was used.

  14. A comparison of the fracture resistance of three machinable ceramics after thermal and mechanical fatigue.

    Science.gov (United States)

    Yang, Rui; Arola, Dwayne; Han, Zhihui; Zhang, Xiuyin

    2014-10-01

    Mechanical and thermal fatigue may affect ceramic restorations in the oral environment. The purpose of this study was to determine the influence of thermal and mechanical cycling on the fracture load and fracture patterns of 3 machinable ceramics. Seventy-two human third molar teeth were prepared for bonding ceramic specimens of Sirona CEREC Blocs, IPS e.maxCAD, or inCoris ZI meso blocks. The 24 specimens of each ceramic were divided into 4 groups (n=6), which underwent no preloading (control), thermocycling (5°C-55°C, 2000 cycles), mechanical cycling (10(5) cycles, 100 N), and thermocycling (5°C-55°C, 2000 cycles) plus mechanical cycling (10(5) cycles, 100 N). The specimens were subsequently loaded to failure, and both stereomicroscopy and scanning electron microscopy were used to investigate the fracture patterns. The data were analyzed with 2-way ANOVA and the Fisher exact probability test (α=.05). Mechanical and thermal cycling had a significant influence on the critical load to failure of the 3 ceramics. No significant difference was found between mechanical cycling for 10(5) times and thermocycling for 2000 times within the same ceramic. The specimens of inCoris ZI experienced significantly higher fracture loads for all the groups. The fracture patterns of the 3 machinable ceramics showed that failure mainly occurred at the cement-dentin interface. The effects of combined thermal and mechanical cycling on the fracture load of ceramics were more significant than any individual mode of cyclic fatigue. Overall, the inCoris ZI resisted thermal and mechanical fatigue better than the Sirona CEREC and IPS e.maxCAD. Copyright © 2014 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

  15. POSSIBLE MECHANISM OF DEVELOPMENT OF SALT SENSITIVE ESSENTIAL HYPERTENSION.

    Science.gov (United States)

    Kantaria, N; Pantsulaia, I; Andronikashvili, I; Simonia, G

    2016-09-01

    It has been known that salt-sensitivity of blood pressure is defined genetically as well as can be developed secondary to either decreased renal function or by influence of other environmental factors. The aim of the study was to evaluate the possible mechanism for the development of salt-sensitive essential hypertension in the population of Georgia. The Case-Control study included 185 subjects, 94 cases with Essential Hypertension stage I (JNC7) without prior antihypertensive treatment, and 91 controls. Salt-sensitivity test was used to divide both case and control groups into salt-sensitive (n=112) and salt-resistant (n=73) subgroups. Endogenous cardiotonic steroids, sodium and PRA were measured in blood and urine samples at the different sodium conditions. Determinations of circulating levels of endogenous sodium pump inhibitors and PRA were carried out using the ELISA and RIA methods. Descriptive statistics were used to analyze the data. Differences in variables between sodium conditions were assessed using paired t-tests. Salt-sensitivity was found in 60.5% of total population investigated, with higher frequency in females. Salt-sensitivity positively correlated with age in females (r=0.262, psalt-sensitivity r=0.334, psalt-sensitivity and PRA. Since no significant correlations were found between BMI and salt-sensitivity, we assume that BMI and salt-sensitivity should be discussed as different independent risk factors for the development of Essential Hypertension. Significant correlation was found between changes in GFR in salt-sensitive cases and controls phypertensive nephropathy in salt-sensitive individuals. At the high sodium condition Endogenous MBG and OU were high in salt-sensitive subjects compared to salt-resistant. These compounds decreased after low salt diet in salt-sensitive cases as well as controls but remained within the same level in salt-resistant individuals. MBG and OU levels positively correlated with SBP in salt-sensitive individuals but

  16. Numerical Analysis and Experimental Study of Hard Roofs in Fully Mechanized Mining Faces under Sleeve Fracturing

    Directory of Open Access Journals (Sweden)

    Zhitao Zheng

    2015-11-01

    Full Text Available Sudden falls of large-area hard roofs in a mined area release a large amount of elastic energy, generate dynamic loads, and cause disasters such as impact ground pressure and gas outbursts. To address these problems, in this study, the sleeve fracturing method (SFM was applied to weaken a hard roof. The numerical simulation software FLAC3D was used to develop three models based on an analysis of the SFM working mechanism. These models were applied to an analysis of the fracturing effects of various factors such as the borehole diameter, hole spacing, and sleeve pressure. Finally, the results of a simulation were validated using experiments with similar models. Our research indicated the following: (1 The crack propagation directions in the models were affected by the maximum principal stress and hole spacing. When the borehole diameter was fixed, the fracturing pressure increased with increasing hole spacing. In contrast, when the fracturing pressure was fixed, the fracturing range increased with increasing borehole diameter; (2 The most ideal fracturing effect was found at a fracturing pressure of 17.6 MPa in the model with a borehole diameter of 40 mm and hole spacing of 400 mm. The results showed that it is possible to regulate the falls of hard roofs using the SFM. This research may provide a theoretical basis for controlling hard roofs in mining.

  17. Mechanisms for Hysteresis in a Horizontal Unsaturated Fracture with Matric Imbibition

    Science.gov (United States)

    Fox, D. T.; Glass, R. J.

    2002-12-01

    Within porous media, macroscopic hysteretic pressure-saturation relations have long been thought to be the result of microscopic effects such as phase invasion within local `ink bottle' geometry, phase trapping or accessibility, and differences between solid-liquid-liquid contact angles for wetting and nonwetting invasion. Here we consider the mechanisms for hysteresis within a horizontal rough-walled fracture. An analogue horizontal rough-walled fracture (10 cm x 15 cm) was formed by placing a piece of transparent textured glass against a water saturated, flat porous plate. Water could enter and leave the fracture via the porous plate while air entered or left via the fracture edges. The evolution of wetted structure within the fracture was recorded with digital images taken through the transparent side as the tension in the porous plate was raised and lowered. Following a sequence of such invasion experiments, the porous plate was replaced with a piece of flat glass and the aperture field was measured using a light transmission technique. Analysis of digital images taken during displacement demonstrated that the macroscopic hysteresis in pressure-saturation curves resulted primarily from the underlying microscopic mechanisms of ink bottle and phase trapping accessibility. Additionally, we found the wetted structure within the fracture to become connected and form a satiated (0 tension) structure containing complex entrapped air structures (volumetric saturation ~0.5) thus greatly reducing permeability at 0 tension. The pressure at which this structure formed on wetting and fragmented on drainage also showed significant hysteresis.

  18. Effect of Water Saturation on the Fracture and Mechanical Properties of Sedimentary Rocks

    Science.gov (United States)

    Guha Roy, Debanjan; Singh, T. N.; Kodikara, J.; Das, Ratan

    2017-10-01

    Fracture and mechanical properties of the water saturated sedimentary rocks have been experimentally investigated in the present paper. Three types of sandstones and one type of shale were saturated in water for different periods of time. They were then tested for their index geomechanical properties such as Brazilian tensile strength (BTS), Young's modulus (YM), P-wave velocity and all pure and mixed-mode fracture toughness (FT). FT was measured using semicircular bend specimens in a three-point bend set-up. All the geomechanical and fracture properties of the saturated rocks were compared together to investigate their interrelations. Further, statistical methods were employed to measure the statistical significance of such relationships. Next, three types of fracture criteria were compared with the present experimental results. Results show that degree of saturation has significant effect on both the strength and fracture properties of sedimentary rock. A general decrease in the mechanical and fracture toughness was noticed with increasing saturation levels. But, t-test confirmed that FT, BTS, P-wave velocity and YM are strongly dependent on each other and linear relationships exist across all the saturation values. Calculation of the `degradation degree' (DD) appeared to be a difficult task for all types of sedimentary rocks. While in sandstone, both the BTS and mode-I FT overestimated the DD calculated by YM method, in shale BTS was found to give a closure value.

  19. Variate generation for probabilistic fracture mechanics and fitness-for-service studies

    International Nuclear Information System (INIS)

    Walker, J.R.

    1987-01-01

    Atomic Energy of Canada Limited is conducting studies in Probabilistic Fracture Mechanics. These studies are being conducted as part of a fitness-for-service programme in support of CANDU reactors. The Monte Carlo analyses, which form part of the Probabilistic Fracture Mechanics studies, require that variates can be sampled from probability density functions. Accurate pseudo-random numbers are necessary for accurate variate generation. This report details the principles of variate generation, and describes the production and testing of pseudo-random numbers. A new algorithm has been produced for the correct performance of the lattice test for the independence of pseudo-random numbers. Two new pseudo-random number generators have been produced. These generators have excellent randomness properties and can be made fully machine-independent. Versions, in FORTRAN, for VAX and CDC computers are given. Accurate and efficient algorithms for the generation of variates from the specialized probability density functions of Probabilistic Fracture Mechanics are given. 38 refs

  20. Hydraulic and mechanical properties of natural fractures in low-permeability rock

    International Nuclear Information System (INIS)

    Pyrack-Nolte, L.J.; Myer, L.R.; Cook, N.G.W.; Witherspoon, P.A.

    1987-01-01

    The results of a comprehensive laboratory study of the mechanical displacement, permeability, and void geometry of single rock fractures in a quartz monzonite are summarized and analyzed. A metal-injection technique was developed that provided quantitative data on the precise geometry of the void spaces between the fracture surfaces and the areas of contact at different stresses. At effective stresses of less than 20 MPa fluid flow was proportional to the mean fracture aperture raised to a power greater than 3. As stress was increased, contact area was increased and void spaces become interconnected by small tortuous channels that constitute the principal impediment to fluid flow. At effective stresses higher than 20 MPa, the mean fracture aperture continued to diminish with increasing stress, but this had little effect on flow because the small tortuous flow channels deformed little with increasing stress

  1. Vertebroplasty and Kyphoplasty Can Restore Normal Spine Mechanics following Osteoporotic Vertebral Fracture

    Science.gov (United States)

    Luo, Jin; Adams, Michael A.; Dolan, Patricia

    2010-01-01

    Osteoporotic vertebral fractures often lead to pain and disability. They can be successfully treated, and possibly prevented, by injecting cement into the vertebral body, a procedure known as vertebroplasty. Kyphoplasty is similar, except that an inflatable balloon is used to restore vertebral body height before cement is injected. These techniques are growing rapidly in popularity, and a great deal of recent research, reviewed in this paper, has examined their ability to restore normal mechanical function to fractured vertebrae. Fracture reduces the height and stiffness of a vertebral body, causing the spine to assume a kyphotic deformity, and transferring load bearing to the neural arch. Vertebroplasty and kyphoplasty are equally able to restore vertebral stiffness, and restore load sharing towards normal values, although kyphoplasty is better at restoring vertebral body height. Future research should optimise these techniques to individual patients in order to maximise their beneficial effects, while minimising the problems of cement leakage and adjacent level fracture. PMID:20981329

  2. Coupled hydrological-mechanical effects due to excavation of underground openings in unsaturated fractured rocks

    International Nuclear Information System (INIS)

    Montazer, P.

    1985-01-01

    One of the effects of excavating an underground opening in fractured rocks is a modification of the state of the stress in the rock mass in the vicinity of the opening. This effect causes changes in the geometry of the cross sections of the fracture planes, which in turn results in modification of the hydrologic properties of the fractures of the rock mass. The significance of the orientation of the fractures and their stiffness on the extent of the modification of the hydrologic properties as a result of excavation of underground openings is demonstrated. A conceptual model is presented to illustrate the complexity of the coupled hydrological-mechanical phenomena in the unsaturated zone. This conceptual model is used to develop an investigative program to assess the extent of the effect at a proposed repository site for storing high-level nuclear wastes

  3. Fracture mechanics in fiber reinforced composite materials, taking as examples B/A1 and CRFP

    Science.gov (United States)

    Peters, P. W. M.

    1982-01-01

    The validity of linear elastic fracture mechanics and other fracture criteria was investigated with laminates of boron fiber reinforced aluminum (R/A1) and of carbon fiber reinforced epoxide (CFRP). Cracks are assessed by fracture strength Kc or Kmax (critical or maximum value of the stress intensity factor). The Whitney and Nuismer point stress criterion and average stress criterion often show that Kmax of fiber composite materials increases with increasing crack length; however, for R/A1 and CFRP the curve showing fracture strength as a function of crack length is only applicable in a small domain. For R/A1, the reason is clearly the extension of the plastic zone (or the damage zone n the case of CFRP) which cannot be described with a stress intensity factor.

  4. Auxetic Mechanical Metamaterials to Enhance Sensitivity of Stretchable Strain Sensors.

    Science.gov (United States)

    Jiang, Ying; Liu, Zhiyuan; Matsuhisa, Naoji; Qi, Dianpeng; Leow, Wan Ru; Yang, Hui; Yu, Jiancan; Chen, Geng; Liu, Yaqing; Wan, Changjin; Liu, Zhuangjian; Chen, Xiaodong

    2018-03-01

    Stretchable strain sensors play a pivotal role in wearable devices, soft robotics, and Internet-of-Things, yet these viable applications, which require subtle strain detection under various strain, are often limited by low sensitivity. This inadequate sensitivity stems from the Poisson effect in conventional strain sensors, where stretched elastomer substrates expand in the longitudinal direction but compress transversely. In stretchable strain sensors, expansion separates the active materials and contributes to the sensitivity, while Poisson compression squeezes active materials together, and thus intrinsically limits the sensitivity. Alternatively, auxetic mechanical metamaterials undergo 2D expansion in both directions, due to their negative structural Poisson's ratio. Herein, it is demonstrated that such auxetic metamaterials can be incorporated into stretchable strain sensors to significantly enhance the sensitivity. Compared to conventional sensors, the sensitivity is greatly elevated with a 24-fold improvement. This sensitivity enhancement is due to the synergistic effect of reduced structural Poisson's ratio and strain concentration. Furthermore, microcracks are elongated as an underlying mechanism, verified by both experiments and numerical simulations. This strategy of employing auxetic metamaterials can be further applied to other stretchable strain sensors with different constituent materials. Moreover, it paves the way for utilizing mechanical metamaterials into a broader library of stretchable electronics. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Hydrogen assisted fracture of sensitized Type 304L austenitic stainless steel

    International Nuclear Information System (INIS)

    Caskey, G.R. Jr.

    1980-01-01

    Sensitized specimens of Type 304L stainless steel were tensile tested in atmospheres of hydrogen and helium at high pressure, and in air at ambient pressure. Comparison tensile tests were made with solution-annealed specimens of Type 304L stainless steel in the same atmosphere. When both specimens were tested in high-pressure hydrogen, the sensitized specimens had greater loss in ductility and increased tendency to intergranular fracture. For the sensitized specimens, plastic strain to failure (epsilon/sub p/ = 1n A 0 /A/sub f/) in hydrogen at 69 MPa was reduced by 60 to 70% in comparison to similar tests in helium. In addition, a notch with a stress concentration factor of about 3 reduced plastic strain an additional 50 to 60%. In all cases, the nominal tensile strength of Type 304L stainless steel was increased by the notch. There was no evidence of intergranular failure in notched specimens of solution-annealed Type 304L stainless steel tested in high-pressure hydrogen environments

  6. The mechanical benefit of medial support screws in locking plating of proximal humerus fractures.

    Directory of Open Access Journals (Sweden)

    Wen Zhang

    Full Text Available BACKGROUND: The purpose of this study was to evaluate the biomechanical advantages of medial support screws (MSSs in the locking proximal humeral plate for treating proximal humerus fractures. METHODS: Thirty synthetic left humeri were randomly divided into 3 subgroups to establish two-part surgical neck fracture models of proximal humerus. All fractures were fixed with a locking proximal humerus plate. Group A was fixed with medial cortical support and no MSSs; Group B was fixed with 3 MSSs but without medial cortical support; Group C was fixed with neither medial cortical support nor MSSs. Axial compression, torsional stiffness, shear stiffness, and failure tests were performed. RESULTS: Constructs with medial support from cortical bone showed statistically higher axial and shear stiffness than other subgroups examined (P<0.0001. When the proximal humerus was not supported by medial cortical bone, locking plating with medial support screws exhibited higher axial and torsional stiffness than locking plating without medial support screws (P ≤ 0.0207. Specimens with medial cortical bone failed primarily by fracture of the humeral shaft or humeral head. Specimens without medial cortical bone support failed primarily by significant plate bending at the fracture site followed by humeral head collapse or humeral head fracture. CONCLUSIONS: Anatomic reduction with medial cortical support was the stiffest construct after a simulated two-part fracture. Significant biomechanical benefits of MSSs in locking plating of proximal humerus fractures were identified. The reconstruction of the medial column support for proximal humerus fractures helps to enhance mechanical stability of the humeral head and prevent implant failure.

  7. Fracture mechanics of polymer mortar made with recycled raw materials

    Directory of Open Access Journals (Sweden)

    Marco Antonio Godoy Jurumenha

    2010-12-01

    Full Text Available The aim of this work is to show that industrial residues could be used in construction applications so that production costs as well as environmental protection can be improved. The fracture properties of polymer mortar manufactured with recycled materials are investigated to evaluate the materials behaviour to crack propagation. The residues used in this work were spent sand from foundry industry as aggregate, unsaturated polyester resin from polyethylene terephthalate (PET as matrix and polyester textile fibres from garment industry, producing an unique composite material fully from recycled components with low cost. The substitution of fresh by used foundry sand and the insertions of textile fibres contribute to a less brittle behaviour of polymer mortar.

  8. Deformation Mechanisms and Fracture of Ni-Based Metallic Glasses

    Directory of Open Access Journals (Sweden)

    Lesz S.

    2016-06-01

    Full Text Available The cracking of materials and fracture surface is of great practical and academic importance. Over the last few years the development of the fractography of crystalline alloys resulted in a useful tool for the prediction or failure analysis. Many attempts have been made to observe cracks using optical microscopy, X-ray topography and transmission electron microscopy (TEM. Of these techniques, the resolution of optical microscopy and X-ray topography is too poor. By contrast, the resolution of TEM is high enough for detailed information to be obtained. However, in order to apply TEM observations, a thin foil specimen must be prepared, and it is usually extremely difficult to prepare such a specimen from a pre-selected region containing a crack.

  9. Combining NDE and fracture mechanics by artifical intelligence expert systems techniques

    International Nuclear Information System (INIS)

    Mucciardi, A.N.; Riccardella, P.C.

    1986-01-01

    This paper reports on the development of a PC-based expert system for non-destructive evaluation. Software tools from the expert systems subfield of artificial intelligence are being used to combine both NDE and fracture mechanics algorithms into one, unified package. The system incorporates elements of computer-enhanced ultrasonic signal processing, featuring artificial intelligence learning capability, state-of-the-art fracture mechanics analytical tools, and all relevant metallurgical and design data necessary to emulate the decisions of the panel(s) of experts typically involved in generating and dispositioning NDE data

  10. Mechanisms Underlying Stress Fracture and the Influence of Sex and Race/Ethnicity

    Science.gov (United States)

    2017-10-01

    AWARD NUMBER: W81XWH-16-1-0652 TITLE: Mechanisms Underlying Stress Fracture and the Influence of Sex and Race/Ethnicity PRINCIPAL INVESTIGATOR...5a. CONTRACT NUMBER W81XWH-16-1-0652 Mechanisms Underlying Stress Fracture and the Influence of Sex and Race/Ethnicity 5b. GRANT NUMBER W81XWH...Email addresses: mbouxsei@bidmc.harvard.edu; scaksa@mgh.harvard.edu; serudolph@mgh.harvard.edu ; kpopp@mgh.harvard.edu E-Mail: 5f. WORK UNIT NUMBER 7

  11. Proceedings of the 20th meeting of the working group on fracture mechanisms

    International Nuclear Information System (INIS)

    1988-01-01

    This volume contains 41 contributions presented at the 20th meeting of the working group on fracture mechanisms. The contributions dealt with the following topics: 1.) mechanical and test fundamentals of crack initiating corrosion processes; 2.) crack formation in water and seawater; 3.) crack formation in the process industry; 4.) hydrogen-induced crack formation; 5.) stress and crack corrosion of rustproof cast alloys; 6.) corrosion-induced crack formation at high temperatures; 7.) experimental and numerical studies on fracture behaviour. 30 contributions were separately integrated in the data base 'ENERGY'. (MM) [de

  12. Validation of a fracture mechanics approach to nuclear transportation cask design through a drop test program

    International Nuclear Information System (INIS)

    Sorenson, K.B.

    1986-01-01

    Sandia National Laboratories (SNL), under contract to the Department of Energy, is conducting a research program to develop and validate a fracture mechanics approach to cask design. A series of drop tests of a transportation cask is planned for the summer of 1986 as the method for benchmarking and, thereby, validating the fracture mechanics approach. This paper presents the drop test plan and background leading to the development of the test plan including structural analyses, material characterization, and non-destructive evaluation (NDE) techniques necessary for defining the test plan properly

  13. An Overview of Innovative Strategies for Fracture Mechanics at NASA Langley Research Center

    Science.gov (United States)

    Ransom, Jonathan B.; Glaessgen, Edward H.; Ratcliffe, James G.

    2010-01-01

    Engineering fracture mechanics has played a vital role in the development and certification of virtually every aerospace vehicle that has been developed since the mid-20th century. NASA Langley Research Center s Durability, Damage Tolerance and Reliability Branch has contributed to the development and implementation of many fracture mechanics methods aimed at predicting and characterizing damage in both metallic and composite materials. This paper presents a selection of computational, analytical and experimental strategies that have been developed by the branch for assessing damage growth under monotonic and cyclic loading and for characterizing the damage tolerance of aerospace structures

  14. TRPA1 mediates mechanical sensitization in nociceptors during inflammation.

    Directory of Open Access Journals (Sweden)

    Richard C Lennertz

    Full Text Available Inflammation is a part of the body's natural response to tissue injury which initiates the healing process. Unfortunately, inflammation is frequently painful and leads to hypersensitivity to mechanical stimuli, which is difficult to treat clinically. While it is well established that altered sensory processing in the spinal cord contributes to mechanical hypersensitivity (central sensitization, it is still debated whether primary afferent neurons become sensitized to mechanical stimuli after tissue inflammation. We induced inflammation in C57BL/6 mice via intraplantar injection of Complete Freund's Adjuvant. Cutaneous C fibers exhibited increased action potential firing to suprathreshold mechanical stimuli. We found that abnormal responses to intense mechanical stimuli were completely suppressed by acute incubation of the receptive terminals with the TRPA1 inhibitor, HC-030031. Further, elevated responses were predominantly exhibited by a specific subgroup of C fibers, which we determined to be C-Mechano Cold sensitive fibers. Thus, in the presence of HC-030031, C fiber mechanical responses in inflamed mice were not different than responses in saline-injected controls. We also demonstrate that injection of the HC-030031 compound into the hind paw of inflamed mice alleviates behavioral mechanical hyperalgesia without affecting heat hyperalgesia. Further, we pharmacologically anesthetized the TRPA1-expressing fibers in vivo by co-injecting the membrane-impermeable sodium channel inhibitor QX-314 and the TRPA1 agonist cinnamaldehyde into the hind paw. This approach also alleviated behavioral mechanical hyperalgesia in inflamed mice but left heat hypersensitivity intact. Our findings indicate that C-Mechano Cold sensitive fibers exhibit enhanced firing to suprathreshold mechanical stimuli in a TRPA1-dependent manner during inflammation, and that input from these fibers drives mechanical hyperalgesia in inflamed mice.

  15. A numerical manifold method model for analyzing fully coupled hydro-mechanical processes in porous rock masses with discrete fractures

    Science.gov (United States)

    Hu, Mengsu; Rutqvist, Jonny; Wang, Yuan

    2017-04-01

    In this study, a numerical manifold method (NMM) model was developed for fully coupled analysis of hydro-mechanical (HM) processes in porous rock masses with discrete fractures. Using an NMM two-cover-mesh system of mathematical and physical covers, fractures are conveniently discretized by dividing the mathematical cover along fracture traces to physical cover, resulting in a discontinuous model on a non-conforming mesh. In this model, discrete fracture deformation (e.g. open and slip) and fracture fluid flow within a permeable and deformable porous rock matrix are rigorously considered. For porous rock, direct pore-volume coupling was modeled based on an energy-work scheme. For mechanical analysis of fractures, a fracture constitutive model for mechanically open states was introduced. For fluid flow in fractures, both along-fracture and normal-to-fracture fluid flow are modeled without introducing additional degrees of freedom. When the mechanical aperture of a fracture is changing, its hydraulic aperture and hydraulic conductivity is updated. At the same time, under the effect of coupled deformation and fluid flow, the contact state may dynamically change, and the corresponding contact constraint is updated each time step. Therefore, indirect coupling is realized under stringent considerations of coupled HM effects and fracture constitutive behavior transfer dynamically. To verify the new model, examples involving deformable porous media containing a single and two sets of fractures were designed, showing good accuracy. Last, the model was applied to analyze coupled HM behavior of fractured porous rock domains with complex fracture networks under effects of loading and injection.

  16. Accurate in vitro identification of fracture onset in bones: failure mechanism of the proximal human femur.

    Science.gov (United States)

    Juszczyk, Mateusz Maria; Cristofolini, Luca; Salvà, Marco; Zani, Lorenzo; Schileo, Enrico; Viceconti, Marco

    2013-01-04

    Bone fractures have extensively been investigated, especially for the proximal femur. While failure load can easily be recorded, and the fracture surface is readily accessible, identification of the point of fracture initiation is difficult. Accurate location of fracture initiation is extremely important to understand the multi-scale determinants of bone fracture. In this study, a recently developed technique based on electro-conductive lines was applied to the proximal femoral metaphysis to elucidate the fracture mechanism. Eight cadaveric femurs were prepared with 15-20 electro-conductive lines (crack-grid) covering the proximal region. The crack-grid was connected to a dedicated data-logger that monitored electrical continuity of each line at 700 kHz. High-speed videos (12,000 frames/s, 0.1-0.2 mm pixel size) of the destructive tests were acquired. Most crack-grid-lines failed in a time-span of 0.08-0.50 ms, which was comparable to that identified in the high-speed videos, and consistent with previous video recordings. However, on all specimens 1-3 crack-grid-lines failed significantly earlier (2-200 ms) than the majority of the crack-grid-lines. The first crack-grid-line to fail was always the closest one to the point of fracture initiation identified in the high-speed videos (superior-lateral neck region). Then the crack propagated simultaneously, at comparable velocity on the anterior and posterior sides of the neck. Such a failure pattern has never been observed before, as spatial resolution of the high-speed videos prevented from observing the initial opening of a crack. This mechanism (fracture onset, time-lag, followed by catastrophic failure) can be explained with a transfer of load to the internal trabecular structure caused by the initial fracture of the thin cortical shell. This study proves the suitability of the crack-grid method to investigate bone fractures associated to tensile stress. The crack-grid method enables significantly faster sampling

  17. An experimental analysis of fracture mechanisms by acoustic ...

    African Journals Online (AJOL)

    Afin d'analyser le comportement mécanique globale de l'assemblage, des essais de traction .... named as Groups A, B and C (Tab. 5). Table.1: Mechanical properties of epoxy matrix Vicotex 914. Table.2: Mechanical properties of fibers T300. Young. 's modul us. E. Poisson's ratio. Ν shear modulus. G. Tensile strength yield.

  18. Fracture Resistance Measurement Method for in situ Observation of Crack Mechanisms

    DEFF Research Database (Denmark)

    Sørensen, Bent F.; Horsewell, A.; Jørgensen, O.

    1998-01-01

    A special test fixture has been developed for fracture mechanical testing of brittle materials inside an environmental scanning electron microscope. The fixture loads a double cantilever beam specimen with pure bending moments and provides stable crack growth. Crack growth is detected by in situ...... observation and acoustic emission, As an example, crack growth in a cubic-phase yttria-stabilized zirconia is detected easily by in situ observation of the crack-tip region, Many fracture toughness measurements are obtained for each specimen, giving high confidence in the measured fracture toughness value......, In situ observation is useful for the study of toughening mechanisms and subcritical crack-growth behavior and to sort out erroneous measurements (e.g., due to crack branching)....

  19. Failure probability assessment of wall-thinned nuclear pipes using probabilistic fracture mechanics

    International Nuclear Information System (INIS)

    Lee, Sang-Min; Chang, Yoon-Suk; Choi, Jae-Boong; Kim, Young-Jin

    2006-01-01

    The integrity of nuclear piping system has to be maintained during operation. In order to maintain the integrity, reliable assessment procedures including fracture mechanics analysis, etc., are required. Up to now, this has been performed using conventional deterministic approaches even though there are many uncertainties to hinder a rational evaluation. In this respect, probabilistic approaches are considered as an appropriate method for piping system evaluation. The objectives of this paper are to estimate the failure probabilities of wall-thinned pipes in nuclear secondary systems and to propose limited operating conditions under different types of loadings. To do this, a probabilistic assessment program using reliability index and simulation techniques was developed and applied to evaluate failure probabilities of wall-thinned pipes subjected to internal pressure, bending moment and combined loading of them. The sensitivity analysis results as well as prototypal integrity assessment results showed a promising applicability of the probabilistic assessment program, necessity of practical evaluation reflecting combined loading condition and operation considering limited condition

  20. Economic evaluation of maintenance strategies for steam generator tubes using probabilistic fracture mechanics and financial method

    International Nuclear Information System (INIS)

    Sagisaka, Mitsuyuki; Isobe, Yoshihiro; Yoshimura, Shinobu; Yagawa, Genki

    2004-01-01

    As an application of probabilistic fracture mechanics (PFM) and a financial method, risk-benefit analyses were performed for the purpose of optimizing maintenance activities of steam generator (SG) tubes used in pressurized water reactors (PWRs). Parameters such as in-service inspection (ISI) detection accuracy, ISI interval, sampling inspection, replacement of SGs and stress corrosion cracking (SCC) allowance operation were selected for sensitivity analyses. In the analysis of the operation introducing maintenance criteria, the effect of quantitative accuracy of the inspection was also taken into account. Although the analyses were mainly conducted for SG tubes made of Inconel 600 mill anneal (MA) materials, the analyses were also performed for SCC-resistant materials with making assumptions on their crack initiation probabilities and crack propagation laws. To justify whether or not it is worth while implementing the selected maintenance strategies in terms of an economic point of view, net present value (NPV) was calculated as an index which is one of the most fundamental financial indices for decision-making based on the discounted cash flow (DCF) method. (author)

  1. Mechanical stimulation enhanced estrogen receptor expression and callus formation in diaphyseal long bone fracture healing in ovariectomy-induced osteoporotic rats.

    Science.gov (United States)

    Chow, S K H; Leung, K S; Qin, J; Guo, A; Sun, M; Qin, L; Cheung, W H

    2016-10-01

    . The enhancement of ER-α expression by mechanical stimulation was not likely to be related to the increased expression in osteoblastic cells but rather to the systemic enhancement in recruitment of ER-expressing progenitor cells through increased blood flow and neo-angiogenesis. This finding might explain the observed difference in mechanical sensitivity of osteoporotic fracture to mechanical stimulation.

  2. Large stable crack growth in fracture mechanics specimen

    International Nuclear Information System (INIS)

    Brock, W.; Fricke, S.; Veith, H.

    1992-01-01

    This is a report on the crack resistance behaviour of the STE 460 steel on CT 25 and CCT 25 samples with side notches according to the J concept, from the J-controlled area to a crack growth of about 8 mm. Numerical simulation of the ductile crack growth controlled by J R curves for EVZ models of the sample geometries make an analysis possible of how well the standards, guidelines and proposals for determining the remote field J integral from experimental data agree with the numerical calculation of J from the stresses and distortions for large crack growth. With the stress, distortion and deformation fields available from the simulation with fine elementing in the ligament, the J concept for large ductile crack growth expanded by the multi-axiality parameter h is explained and the behaviour of other fracture parameters such as the crack tip opening (CTOD) and the crack opening angle (CTOA) for large crack growth are shown. (orig./DG) [de

  3. An experimental analysis of fracture mechanisms by acoustic ...

    African Journals Online (AJOL)

    This work is focused on the study of the evolution of damage mode and failure mechanisms of woven composite bolted assembly carbon fiber/epoxy. In the present paper three configurations are studied [0°,45°,0°,45°], [0°,45°,0°,45°]s and [0°,45°,0°,45,0°]s. In order to analyze a global mechanical behavior of the assembly, ...

  4. Study on Notch Sensitivity of Fracture Properties of Concrete Containing Nano-SiO2 Particles and Fly Ash

    Directory of Open Access Journals (Sweden)

    Peng Zhang

    2013-01-01

    Full Text Available The fracture parameters and fracture relational curves of the concrete containing nano-SiO2 and fly ash with different relative notch depth of the notched beam specimens were measured by means of three-point bending method. The results indicate that the relative notch depth of the notched specimens has great effect on ac, KICini, KICun, GF, CMODc, and the fracture relational curves of the concrete containing nano-SiO2 and fly ash. There is a tendency of increase in ac and CMODc with the increase of relative notch depth, while KICini, KICun, and GF are decreasing gradually with the increase of relative notch depth of the notched beam specimens. Besides, when the relative notch depth increases from 0.2 to 0.5, the nonlinear stage of the curve becomes shorter and shorter, and the descent stage of the curve becomes sharper and sharper. The fracture parameters of ac, KICini, KICun, GF, and CMODc and the fracture curves are sensitive to the relative notch depth, while CTODc may be not sensitive to the relative notch depth of the specimens of the concrete containing nano-SiO2 and fly ash.

  5. An Analytical Model for Fatigue Life Prediction Based on Fracture Mechanics and Crack Closure

    DEFF Research Database (Denmark)

    Ibsø, Jan Behrend; Agerskov, Henning

    1996-01-01

    test specimens are compared with fatigue life predictions using a fracture mechanics approach. In the calculation of the fatigue life, the influence of the welding residual stresses and crack closure on the fatigue crack growth is considered. A description of the crack closure model for analytical...

  6. Structural Reliability of Ceramics at High Temperature: Mechanisms of Fracture and Fatigue Crack Growth

    Energy Technology Data Exchange (ETDEWEB)

    Reinhold H. Dauskardt

    2005-08-01

    Final report of our DOE funded research program. Aim of the research program was to provide a fundamental basis from which the mechanical reliability of layered structures may be understood, and to provide guidelines for the development of technologically relevant layered material structures with optimum resistance to fracture and subcritical debonding. Progress in the program to achieve these goals is described.

  7. What happens between pure hydraulic and buckling mechanisms of blowout fractures?

    Science.gov (United States)

    Nagasao, Tomohisa; Miyamoto, Junpei; Shimizu, Yusuke; Jiang, Hua; Nakajima, Tatsuo

    2010-06-01

    The present study aims to evaluate how the ratio of the hydraulic and buckling mechanisms affects blowout fracture patterns, when these two mechanisms work simultaneously. Three-dimensional computer-aided-design (CAD)models were generated simulating ten skulls. To simulate impact, 1.2J was applied on the orbital region of these models in four patterns. Pattern 1: All the energy works to cause the hydraulic effect. Pattern 2: Two-thirds of the energy works to cause the hydraulic effect; one-third of the energy works to cause the buckling effect. Pattern 3: One-third of the energy works to cause the hydraulic effect; two-thirds of the energy works to cause the buckling effect. Pattern 4: The entire energy quantum works to cause the buckling effect. Using the finite element method, the regions where fractures were theoretically expected to occur were calculated and were compared between the four patterns. More fracture damage occurred for Pattern 1 than Pattern 2, and for Pattern 3 than for Pattern 4. The hydraulic and buckling mechanisms interact with one another. When these two mechanisms are combined, the orbital walls tend to develop serious fractures. Copyright (c) 2009 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.

  8. An Analytical Model for Fatigue Life Prediction Based on Fracture Mechanics and Crack Closure

    DEFF Research Database (Denmark)

    Ibsø, Jan Behrend; Agerskov, Henning

    1996-01-01

    Fatigue in steel structures subjected to stochastic loading is studied. Of special interest is the problem of fatigue damage accumulation and in this connection, a comparison between experimental results and results obtained using fracture mechanics. Fatigue test results obtained for welded plate...

  9. Applications and limits of application of fracture mechanics methods in assessing the safety of components

    International Nuclear Information System (INIS)

    Stahlberg, R.

    1977-01-01

    On the basis of fracture mechanics calculations and experimental investigations, it is shown how cracks of different shape and location behave under given static and cyclic loads. In particular, component safety with regard to spontaneous failure and crack growth behaviour in different components are discussed. [de

  10. Mechanism and patterns of cervical spine fractures-dislocations in vertebral artery injury

    Directory of Open Access Journals (Sweden)

    Pankaj Gupta

    2012-01-01

    Full Text Available Purpose: To identify the fracture patterns and mechanism of injury, based on subaxial cervical spine injury classification system (SLIC, on non-contrast computed tomography (NCCT of cervical spine predictive of vertebral artery injury (VAI. Patients and Methods: We retrospectively analyzed cervical spine magnetic resonance imaging (MRI of 320 patients who were admitted with cervical spine injury in our level I regional trauma center over a period of two years (April 2010 to April 2012. Diagnosis of VAI was based on hyperintensity replacing the flow void on a T2-weighted axial image. NCCT images of the selected 43 patients with MRI diagnosis of VAI were then assessed for the pattern of injury. The cervical spinal injuries were classified into those involving the C1 and C2 and subaxial spine. For the latter, SLIC was used. Results: A total of 47 VAI were analyzed in 43 patients. Only one patient with VAI on MRI had no detectable abnormality on NCCT. C1 and C2 injuries were found in one and six patients respectively. In subaxial injuries, the most common mechanism of injury was distraction (37.5% with facet dislocation with or without fracture representing the most common pattern of injury (55%. C5 was the single most common affected vertebral level. Extension to foramen transversarium was present in 20 (42.5% cases. Conclusion: CT represents a robust screening tool for patients with VAI. VAI should be suspected in patients with facet dislocation with or without fractures, foramina transversarium fractures and C1-C3 fractures, especially type III odontoid fractures and distraction mechanism of injury.

  11. Time-dependent reliability sensitivity analysis of motion mechanisms

    International Nuclear Information System (INIS)

    Wei, Pengfei; Song, Jingwen; Lu, Zhenzhou; Yue, Zhufeng

    2016-01-01

    Reliability sensitivity analysis aims at identifying the source of structure/mechanism failure, and quantifying the effects of each random source or their distribution parameters on failure probability or reliability. In this paper, the time-dependent parametric reliability sensitivity (PRS) analysis as well as the global reliability sensitivity (GRS) analysis is introduced for the motion mechanisms. The PRS indices are defined as the partial derivatives of the time-dependent reliability w.r.t. the distribution parameters of each random input variable, and they quantify the effect of the small change of each distribution parameter on the time-dependent reliability. The GRS indices are defined for quantifying the individual, interaction and total contributions of the uncertainty in each random input variable to the time-dependent reliability. The envelope function method combined with the first order approximation of the motion error function is introduced for efficiently estimating the time-dependent PRS and GRS indices. Both the time-dependent PRS and GRS analysis techniques can be especially useful for reliability-based design. This significance of the proposed methods as well as the effectiveness of the envelope function method for estimating the time-dependent PRS and GRS indices are demonstrated with a four-bar mechanism and a car rack-and-pinion steering linkage. - Highlights: • Time-dependent parametric reliability sensitivity analysis is presented. • Time-dependent global reliability sensitivity analysis is presented for mechanisms. • The proposed method is especially useful for enhancing the kinematic reliability. • An envelope method is introduced for efficiently implementing the proposed methods. • The proposed method is demonstrated by two real planar mechanisms.

  12. Interlocking Friction Governs the Mechanical Fracture of Bilayer MoS2.

    Science.gov (United States)

    Jung, Gang Seob; Wang, Shanshan; Qin, Zhao; Martin-Martinez, Francisco J; Warner, Jamie H; Buehler, Markus J

    2018-04-24

    A molybdenum disulfide (MoS 2 ) layered system is a two-dimensional (2D) material, which is expected to provide the next generation of electronic devices together with graphene and other 2D materials. Due to its significance for future electronics applications, gaining a deep insight into the fundamental mechanisms upon MoS 2 fracture is crucial to prevent mechanical failure toward reliable applications. Here, we report direct experimental observation and atomic modeling of the complex failure behaviors of bilayer MoS 2 originating from highly variable interlayer frictions, elucidated with in situ transmission electron microscopy and large-scale reactive molecular dynamics simulations. Our results provide a systematic understanding of the effects that different stacking and loading conditions have on the failure mechanisms and crack-tip behaviors in the bilayer MoS 2 systems. Our findings unveil essential properties in fracture of this 2D material and provide mechanistic insight into its mechanical failure.

  13. Modelling of Debond and Crack Propagation in Sandwich Structures Using Fracture and Damage Mechanics

    DEFF Research Database (Denmark)

    Berggreen, C.; Simonsen, Bo Cerup; Toernqvist, Rikard

    2003-01-01

    Skin-core de-bonding or core crack propagation will often be dominating mechanisms in the collapse modes of sandwich structures. This paper presents two different methods for prediction of crack propagation in a sandwich structure: a fracture mechanics approach, where a new mode-mix method...... is presented, and a local damage mechanics approach. The paper presents a real-life application example, where the superstructure in a vessel pulls the skin off the sandwich deck. The calculations show almost unstable crack growth initially followed by a stabilization, and a nearly linear relation between...... lifting and crack length. A remarkably good agreement is found between the results of the fracture and damage mechanics approaches....

  14. Probabilistic Fracture Mechanics of Reactor Pressure Vessels with Populations of Flaws

    Energy Technology Data Exchange (ETDEWEB)

    Spencer, Benjamin [Idaho National Lab. (INL), Idaho Falls, ID (United States); Backman, Marie [Univ. of Tennessee, Knoxville, TN (United States); Williams, Paul [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Hoffman, William [Idaho National Lab. (INL), Idaho Falls, ID (United States); Alfonsi, Andrea [Idaho National Lab. (INL), Idaho Falls, ID (United States); Dickson, Terry [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Bass, B. Richard [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Klasky, Hilda [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2016-09-01

    This report documents recent progress in developing a tool that uses the Grizzly and RAVEN codes to perform probabilistic fracture mechanics analyses of reactor pressure vessels in light water reactor nuclear power plants. The Grizzly code is being developed with the goal of creating a general tool that can be applied to study a variety of degradation mechanisms in nuclear power plant components. Because of the central role of the reactor pressure vessel (RPV) in a nuclear power plant, particular emphasis is being placed on developing capabilities to model fracture in embrittled RPVs to aid in the process surrounding decision making relating to life extension of existing plants. A typical RPV contains a large population of pre-existing flaws introduced during the manufacturing process. The use of probabilistic techniques is necessary to assess the likelihood of crack initiation at one or more of these flaws during a transient event. This report documents development and initial testing of a capability to perform probabilistic fracture mechanics of large populations of flaws in RPVs using reduced order models to compute fracture parameters. The work documented here builds on prior efforts to perform probabilistic analyses of a single flaw with uncertain parameters, as well as earlier work to develop deterministic capabilities to model the thermo-mechanical response of the RPV under transient events, and compute fracture mechanics parameters at locations of pre-defined flaws. The capabilities developed as part of this work provide a foundation for future work, which will develop a platform that provides the flexibility needed to consider scenarios that cannot be addressed with the tools used in current practice.

  15. Study on the mechanism of seepage flow in the grouting for multiple fractured model

    International Nuclear Information System (INIS)

    Nishigaki, Makoto; Mikake, Shin-ichiro

    2002-01-01

    The purpose of study is to improve the grouting method for fractured rock masses. In this paper, the results on the fundamental phenomenon for grasping the properties of grouting injection and seepage flow are discussed. The case of grouting stage is studied about the multiple hydraulic fractured apertures in the injected borehole. So the theory on the mechanism is constructed, and experiment is executed in order to verify the availability of the theory. From the results, it is shown that Bernoulli's law is able to prove the behavior of the grouting. And the theoretical evaluation is executed on the experiential procedure of the grouting. (author)

  16. Microstructure, mechanical behaviour and fracture of pure tungsten wire after different heat treatments

    DEFF Research Database (Denmark)

    Zhao, P.; Riesch, J.; Höschen, T.

    2017-01-01

    treatments in terms of microstructure, mechanical behaviour and fracture mode. Recrystallization is already observed at a relatively low temperature of 1273 K due to the large driving force caused by a high dislocation density. Annealing for 30 min at 1900 K also leads to recrystallization, but causes......-edge-necking of individual grains on the fracture surface. While the wire recrystallized at 1900 K displays large, almost equiaxed grains with low aspect ratios as well as distinct brittle properties. Therefore, it is suggested that a high aspect ratio of the grains is important for the ductile behaviour of tungsten wire...

  17. The use of the J* integral for non-linear fracture mechanics

    International Nuclear Information System (INIS)

    Hellen, T.K.

    1976-09-01

    The Griffith energy balance criterion, first postulated over 50 years ago, is still the basis of linear elastic fracture mechanics. From this, accurate numerical methods for establishing stress intensity factors and energy release rates have been developed. One such method involves path independent contour integrals about the crack tip. An improved contour integral, designated J* is discussed, and shown to have distinct advantages over others in non-linear strain situations. A number of examples are shown including fractures in thermo-plastic and creep situations. (author)

  18. Deformation and Fracture Mechanisms of Bone and Nacre

    Science.gov (United States)

    Wang, Rizhi; Gupta, Himadri S.

    2011-08-01

    Bone and nacre are the most-known biological hard tissues to materials researchers. Although highly mineralized, both bone and nacre are amazingly tough and exhibit remarkable inelasticity, properties that are still beyond the reach of many modern ceramic materials. Very interestingly, the two hard tissues seem to have adopted totally different structural strategies for achieving mechanical robustness. Starting from a true nanocomposite of the mineralized collagen fibril and following up to seven levels of hierarchical organization, bone is built on a structure with extreme complexity. In contrast, nacre possesses a structure of surprising simplicity. Polygonal mineral tablets of micrometer size are carefully cemented together into a macroscopic wonder. A comparative analysis of the structure-property relations in bone and nacre helps us to unveil the underlying mechanisms of this puzzling phenomenon. In this review, we critically compare the various levels of structures and their mechanical contributions between bone and nacre, with a focus on inelasticity and the toughening process. We demonstrate that, although nacre and bone differ from each other in many aspects, they have adopted very similar deformation and toughening mechanisms.

  19. Generalised fracture mechanics approach to the interfacial failure analysis of a bonded steel-concrete joint

    Czech Academy of Sciences Publication Activity Database

    De Corte, W.; Helincks, P.; Boel, V.; Klusák, Jan; Seitl, Stanislav; De Schutter, G.

    2017-01-01

    Roč. 11, č. 42 (2017), s. 147-160 ISSN 1971-8993 R&D Projects: GA MŠk(CZ) LQ1601; GA ČR(CZ) GA16-18702S Institutional support: RVO:68081723 Keywords : Epoxy adhesive * Fracture mechanics * Interfacial properties * Numerical study * Push-out test * High performance concrete Subject RIV: JL - Materials Fatigue, Friction Mechanics OBOR OECD: Audio engineering, reliability analysis

  20. Generalised fracture mechanics approach to the interfacial failure analysis of a bonded steel-concrete joint

    Czech Academy of Sciences Publication Activity Database

    De Corte, W.; Helincks, P.; Boel, V.; Klusák, Jan; Seitl, Stanislav; De Schutter, G.

    2017-01-01

    Roč. 11, č. 42 (2017), s. 147-160 ISSN 1971-8993 R&D Projects: GA MŠk(CZ) LQ1601; GA ČR(CZ) GA16-18702S Institutional support: RVO:68081723 Keywords : Epoxy adhesive * Fracture mechanics * Interfacial properties * Numerical study * Push-out test * Steel-concrete joint Subject RIV: JL - Materials Fatigue, Friction Mechanics OBOR OECD: Audio engineering, reliability analysis

  1. Mechanical behavior and fracture characterization of the T91 martensitic steel in liquid sodium environment

    International Nuclear Information System (INIS)

    Hamdane, Ouadie

    2012-01-01

    The T91 martensitic steel is designed to constitute structural material of future sodium fast reactors of fourth generation, where it will be subjected to stresses in presence of liquid sodium. This study presents a qualitative and quantitative estimate of the sensitivity of T91 steel towards the phenomenon of liquid metal embrittlement. The effect of liquid sodium on T91 steel was studied and quantified according to the temperature and the cross head rate displacement, by using a set-up of Small Punch Test, three and four bending test, developed in laboratory. Mechanical tests in sodium environment are carried out inside a Plexiglas cell, conceived and developed at the laboratory. The atmosphere inside this cell is severely purified and controlled, in order to avoid on the one hand an explosive reaction of sodium with moisture, or an ignition with oxygen, and on the other hand to minimize the presence of impurities in liquid sodium used. The presence of sodium accelerates T91 steel fracture at low temperature, without modifying its ductile character. The T91 pre-immersion in sodium makes it possible to dissolve the protective layer of chromium oxide, and to obtain an intimate contact with the molten metal. However, pre-immersion generates a surface defects which cause a partial embrittlement by sodium. The hardening of T91 steel by heat treatment with a tempering temperature of 550 C (T91-TR550) causes a total embrittlement of steel in presence of sodium, with and without pre-immersion. The rupture of the T91-TR550 steel takes then place by intergranular de-cohesion, corresponding to the crack initiation phase, followed by laths de-cohesion, corresponding to the phase of propagation of these cracks. The mechanism suggested in this study is based on the intergranular penetration of sodium, supported by the presence of segregated impurities such phosphorus, and by the plastic deformation [fr

  2. The effect of inferomedial screw on postoperative shoulder function and mechanical alignment in proximal humerus fractures.

    Science.gov (United States)

    Erdoğan, Murat; Desteli, Engin Eren; İmren, Yunus; Üztürk, Ali; Kılıç, Mesut; Sezgin, Hicabi

    2014-10-01

    The aim of the study was to evaluate the clinical and radiologic results of locking plate fixation with or without inferomedial screw (IMS) in surgically treated proximal humerus fractures. Thirty-six patients with displaced proximal humerus fractures from two centers were operated using locking plate. All of the fractures were classified according to the Neer classification. In 18 of the cases, an additional IMS running through the medial curvature of the surgical neck was used. There was no significant difference among both groups in terms of height, gender, weight, and mechanism of injury. The fractures were evaluated according to the radiographic and functional findings during follow-up period of 14 months in average (range 8-32 months). At the end of first year, shoulder radiographs were received and shoulder examinations were performed using ASES scores. Humeral head-shaft angles were measured by true AP projections. Head-shaft angle measurements were categorized as varus if 145. Mean time for fracture healing was 18 weeks. Complete union was achieved in 35 patients by the end of 6 months. In one of the 18 displaced proximal humerus fractures of IMS (+) group, the head-shaft angle was measured to be <125, whereas six patients had varus deviation in IMS (-) group at follow-up (p < 0.05). Mean ASES scores of IMS (+) group and IMS (-) group were 58.21 ± 5.82 and 38.61 ± 3.44, respectively (p < 0.001). Use of inferomedial screw running through the medial curvature of surgical neck prevents varus deformity and improves functional outcome after surgical treatment for proximal humerus fractures.

  3. Humeral fracture in non-ambulant infants - a possible accidental mechanism

    International Nuclear Information System (INIS)

    Somers, John M.; Halliday, Katharine E.; Chapman, Stephen

    2014-01-01

    Humeral fracture in a non-ambulant infant younger than 1 year is suspicious for a non-accidental injury unless there is a credible accidental explanation. A previously unrecognised accidental mechanism was described in 1996 whereby a 5-month-old infant was rolled by a 3-year-old sibling from a prone to a supine position. To investigate the widely accepted view that an infant with limited mobility cannot sustain a fracture of the humerus by his or her own actions in the absence of the intervention of an external party. We present seven cases of non-ambulant infants between 4 and 7 months of age in whom an isolated humeral fracture was the only injury present. In each case the caregiver described the fracture occurring when the child rolled over, trapping the dependent arm, without the intervention of another party. There is no proof for this mechanism in the form of an independent witness or video recording. However, we propose that this mechanism is worthy of further consideration as a rare and unusual cause for the injury. Further study is required. (orig.)

  4. Humeral fracture in non-ambulant infants - a possible accidental mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Somers, John M.; Halliday, Katharine E. [Nottingham University Hospitals, Radiology Department, Nottingham (United Kingdom); Chapman, Stephen [Birmingham Children' s Hospital, Birmingham (United Kingdom)

    2014-10-15

    Humeral fracture in a non-ambulant infant younger than 1 year is suspicious for a non-accidental injury unless there is a credible accidental explanation. A previously unrecognised accidental mechanism was described in 1996 whereby a 5-month-old infant was rolled by a 3-year-old sibling from a prone to a supine position. To investigate the widely accepted view that an infant with limited mobility cannot sustain a fracture of the humerus by his or her own actions in the absence of the intervention of an external party. We present seven cases of non-ambulant infants between 4 and 7 months of age in whom an isolated humeral fracture was the only injury present. In each case the caregiver described the fracture occurring when the child rolled over, trapping the dependent arm, without the intervention of another party. There is no proof for this mechanism in the form of an independent witness or video recording. However, we propose that this mechanism is worthy of further consideration as a rare and unusual cause for the injury. Further study is required. (orig.)

  5. Flexible parallel implicit modelling of coupled thermal-hydraulic-mechanical processes in fractured rocks

    Science.gov (United States)

    Cacace, Mauro; Jacquey, Antoine B.

    2017-09-01

    Theory and numerical implementation describing groundwater flow and the transport of heat and solute mass in fully saturated fractured rocks with elasto-plastic mechanical feedbacks are developed. In our formulation, fractures are considered as being of lower dimension than the hosting deformable porous rock and we consider their hydraulic and mechanical apertures as scaling parameters to ensure continuous exchange of fluid mass and energy within the fracture-solid matrix system. The coupled system of equations is implemented in a new simulator code that makes use of a Galerkin finite-element technique. The code builds on a flexible, object-oriented numerical framework (MOOSE, Multiphysics Object Oriented Simulation Environment) which provides an extensive scalable parallel and implicit coupling to solve for the multiphysics problem. The governing equations of groundwater flow, heat and mass transport, and rock deformation are solved in a weak sense (either by classical Newton-Raphson or by free Jacobian inexact Newton-Krylow schemes) on an underlying unstructured mesh. Nonlinear feedbacks among the active processes are enforced by considering evolving fluid and rock properties depending on the thermo-hydro-mechanical state of the system and the local structure, i.e. degree of connectivity, of the fracture system. A suite of applications is presented to illustrate the flexibility and capability of the new simulator to address problems of increasing complexity and occurring at different spatial (from centimetres to tens of kilometres) and temporal scales (from minutes to hundreds of years).

  6. A MEMS resonant accelerometer with sensitivity enhancement and adjustment mechanisms

    International Nuclear Information System (INIS)

    Ding, Hong; Ju, Bing-Feng; Xie, Jin; Wang, Wen

    2017-01-01

    This paper proposes a resonant accelerometer with sensitivity enhancement and adjustment mechanisms based on microelectromechanical systems (MEMS). Different from conventional resonant accelerometers with sensitivity only enhanced by microleverage mechanisms, the proposed accelerometer utilizes a fishbone-shaped resonator as sensing element to enhance and adjust sensitivity. The fishbone-shaped resonator can realize the mode selection and frequency-tuning function according to the configuration of sensing and driving electrodes, so then different modes yields different sensitivities. Experimental results demonstrate that the mean differential sensitivities span from 12.44–61.00 Hz g −1 (Mode 1: 12.44 Hz g −1 ; Mode 2: 36.94 Hz g −1 ; Mode 3: 61.00 Hz g −1 ) and the average resonant frequencies are 116.47 kHz, 299.87 kHz and 548.35 kHz, respectively. Moreover, the preliminary tilt experiment verifies that this prototype has potential usage in tilt measurement. (paper)

  7. Fracture resistance curves and toughening mechanisms in polymer based dental composites

    DEFF Research Database (Denmark)

    De Souza, J.A.; Goutianos, Stergios; Skovgaard, M.

    2011-01-01

    The fracture resistance (R-curve behaviour) of two commercial dental composites (Filtek Z350® and Concept Advanced®) were studied using Double Cantilever Beam sandwich specimens loaded with pure bending moments to obtain stable crack growth. The experiments were conducted in an environmental...... displayed distinctly different R-curve behaviours. The difference was related to different toughening mechanisms as the two composites had markedly different microstructures. Contrary to common experience, the composite with the finer microstructure (smaller particles), the Concept Advanced®, showed...... significantly higher fracture resistance than the composite with the coarser microstructure. The fracture properties were related to the flexural strength of the dental composites. The method, thus, can provide useful insight into how the microstructure enhances toughness, which is necessary for the future...

  8. The mechanics of tessellations - bioinspired strategies for fracture resistance.

    Science.gov (United States)

    Fratzl, Peter; Kolednik, Otmar; Fischer, F Dieter; Dean, Mason N

    2016-01-21

    Faced with a comparatively limited palette of minerals and organic polymers as building materials, evolution has arrived repeatedly on structural solutions that rely on clever geometric arrangements to avoid mechanical trade-offs in stiffness, strength and flexibility. In this tutorial review, we highlight the concept of tessellation, a structural motif that involves periodic soft and hard elements arranged in series and that appears in a vast array of invertebrate and vertebrate animal biomaterials. We start from basic mechanics principles on the effects of material heterogeneities in hypothetical structures, to derive common concepts from a diversity of natural examples of one-, two- and three-dimensional tilings/layerings. We show that the tessellation of a hard, continuous surface - its atomization into discrete elements connected by a softer phase - can theoretically result in maximization of material toughness, with little expense to stiffness or strength. Moreover, the arrangement of soft/flexible and hard/stiff elements into particular geometries can permit surprising functions, such as signal filtering or 'stretch and catch' responses, where the constrained flexibility of systems allows a built-in safety mechanism for ensuring that both compressive and tensile loads are managed well. Our analysis unites examples ranging from exoskeletal materials (fish scales, arthropod cuticle, turtle shell) to endoskeletal materials (bone, shark cartilage, sponge spicules) to attachment devices (mussel byssal threads), from both invertebrate and vertebrate animals, while spotlighting success and potential for bio-inspired manmade applications.

  9. Phenomenological and mechanics aspects of nondestructive evaluation and characterization by sound and ultrasound of material and fracture properties

    Science.gov (United States)

    Fu, L. S. W.

    1982-01-01

    Developments in fracture mechanics and elastic wave theory enhance the understanding of many physical phenomena in a mathematical context. Available literature in the material, and fracture characterization by NDT, and the related mathematical methods in mechanics that provide fundamental underlying principles for its interpretation and evaluation are reviewed. Information on the energy release mechanism of defects and the interaction of microstructures within the material is basic in the formulation of the mechanics problems that supply guidance for nondestructive evaluation (NDE).

  10. Fracture Mechanics Analyses of Subsurface Defects in Reinforced Carbon-Carbon Joggles Subjected to Thermo-Mechanical Loads

    Science.gov (United States)

    Knight, Norman F., Jr.; Raju, Ivatury S.; Song, Kyongchan

    2011-01-01

    Coating spallation events have been observed along the slip-side joggle region of the Space Shuttle Orbiter wing-leading-edge panels. One potential contributor to the spallation event is a pressure build up within subsurface voids or defects due to volatiles or water vapor entrapped during fabrication, refurbishment, or normal operational use. The influence of entrapped pressure on the thermo-mechanical fracture-mechanics response of reinforced carbon-carbon with subsurface defects is studied. Plane-strain simulations with embedded subsurface defects are performed to characterize the fracture mechanics response for a given defect length when subjected to combined elevated-temperature and subsurface-defect pressure loadings to simulate the unvented defect condition. Various subsurface defect locations of a fixed-length substrate defect are examined for elevated temperature conditions. Fracture mechanics results suggest that entrapped pressure combined with local elevated temperatures have the potential to cause subsurface defect growth and possibly contribute to further material separation or even spallation. For this anomaly to occur, several unusual circumstances would be required making such an outcome unlikely but plausible.

  11. A study on rate sensitivity of elasto-plastic fracture toughness of TRIP steel evaluated by a small punch test

    Directory of Open Access Journals (Sweden)

    Shi L.

    2012-08-01

    Full Text Available TRIP steel indicates an excellent characteristic in energy absorption because of its high ductility and strength by strain-induced martensitic transformation (SIMT. Recently, some shock absorption members are being used for automotive industries. For good fuel consumption of the automobile, it would realize the weight reduction without decaying performance if TRIP steel can be applied to those members. It can be considered that the fracture toughness is an important factor to evaluate the performance. To evaluate fracture toughness locally at any point of a product of those members, small punch testing method is quite effective. In the present study, first, an impact small punch testing apparatus is established. In addition, elasto-plastic fracture toughness of TRIP steel under impact loading and its rate sensitivity tested at various deflection rates are challenged to evaluate.

  12. Effect of Temperature-Force Factors and Concentrator Shape on Impact Fracture Mechanisms of 17Mn1Si Steel

    Directory of Open Access Journals (Sweden)

    S. V. Panin

    2017-01-01

    Full Text Available The influence of the notch shape on the impact fracture of 17Mn1Si steel is investigated at different temperatures with the focus placed on the low-temperature behavior. An approach towards fracture characterization has been suggested based on the description of elastic-plastic deformation of impact loaded specimens on the stage of crack initiation and growth at ambient and lower temperatures. The analysis of the impact loading diagrams and fracture energy values for the pipe steel 17Mn1Si revealed the fracture mechanisms depending on the notch shape. It was found that the testing temperature reduction played a decisive role in plastic strain localization followed by dynamic fracture of the specimens with differently shaped notches. A classification of fracture macro- and microscopic mechanisms for differently notched specimens tested at different temperatures was proposed which enabled a self-consistent interpretation of impact test results.

  13. Sensitiveness of the Constant-Murley’s Shoulder and Quick DASH as an Outcome Measure for Midshaft Clavicle Fracture

    Directory of Open Access Journals (Sweden)

    R Magetsari

    2010-03-01

    Full Text Available BACKGROUND: Quick DASH and Constant-Murley’s Shoulder are two valid measuring tools for health status and are useful for patients with a wide variety of upper-extremity complaints; it is sufficiently sensitive to reveal even small changes in function. Objective: To evaluate the sensitivity of Quick DASH and Constant-Murley’s Shoulder as an outcome measurement for midshaft clavicle fracture. METHOD: The study population consisted of 64 patients with a diagnosis of midshaft clavicle fracture based on clinical and radiological criteria. Study design was that of a classic prospective cohort study with measurements at 3 and 6 months following the injury. Evaluation was based on effect size (ES and standardized response means (SRM. RESULT: Both Quick DASH and Constant-Murley’s Shoulder showed high sensitivity (ES: 0.711; SRM: 1.46 and ES: 0.628; SRM: 1.45, respectively. CONCLUSION: Quick DASH was more sensitive than Constant-Murley’s Shoulder in detecting clinical changes on midshaft clavicle fractures at 3 and 6 month following treatment.

  14. Bisphosphonates and Risk of Subtrochanteric, Femoral Shaft, and Atypical Femur Fracture: Sensitivity and Trim and Fill Studies

    Science.gov (United States)

    Liu, Jie; Zhang, Hong-xin; Lu, Xiong-xiong; Hu, Jia-jia

    2014-01-01

    Objective: This study carried out sensitivity analysis and trim-fill analysis between bisphosphonates and subtrochanteric, femoral shaft, and atypical femur fracture. Methods: A random-effects model was used finally. Sensitivity, trim and fill, and publication bias analyses were done. Results: Under a random-effects model (I2=87.535), the Z-value=5.672, p-value of test of nullBisphosphonate exposure was associated with an increased risk of atypical femur fracture (3.243 [95% CI 2.160–4.870]). When any study is removed, the remaining sensitivity analysis results are still significant. Trim and fill results show that two studies were missed. After filling them, a funnel plot of precision by log risk ratio was more symmetrical. Conclusion: This study suggests that (1) there is an increased risk of subtrochanteric, femoral shaft, and atypical femur fracture in bisphosphonate users; (2) any single study does not influence the total sensitivity; (3) two studies have been lost, theoretically. PMID:24205872

  15. Planar Porous Graphene Woven Fabric/Epoxy Composites with Exceptional Electrical, Mechanical Properties, and Fracture Toughness.

    Science.gov (United States)

    Liu, Xu; Sun, Xinying; Wang, Zhenyu; Shen, Xi; Wu, Ying; Kim, Jang-Kyo

    2015-09-30

    Planar interconnected graphene woven fabrics (GWFs) are prepared by template-based chemical vapor deposition and the GWFs are employed as multifunctional filler for epoxy-based composites. Apart from flexibility, transparency, lightweight, and high electrical conductivity, the GWFs have unique morphological features consisting of orthogonally interweaved, inherently percolated, hollow graphene tubes (GTs). The orthogonal GT structure means that the GWF/epoxy composites hold significant anisotropy in mechanical and fracture properties. The composites with 0.62 wt % graphene deliver a combination of excellent electrical and fracture properties: e.g., an electrical conductivity of ~0.18 S/cm; and fracture toughness of 1.67 and 1.78 MPa·m(1/2) when loaded along the 0° and 45° directions relative to the GT direction, respectively, equivalent to notable 57% and 67% rises compared to the solid epoxy. Unique fracture processes in GWF/epoxy composites are identified by in situ examinations, revealing crack tip blunting that occurs when the crack impinges GTs, especially those at 45° to the crack growth direction, as well as longitudinal tearing of hollow GTs as the two major toughening mechanisms.

  16. Exploring particulate retention mechanisms through visualization of E. coli transport through a single, saturated fracture

    Science.gov (United States)

    Burke, M. G.; Dickson, S. E.; Schutten, M.

    2011-12-01

    Groundwater is an extremely valuable resource; a large body of work has been conducted towards remediating, tracking and reducing its contamination. Even so, there are large gaps within the current understanding of groundwater flow and contaminant transport, particularly within fractured media. Fractured media has the ability transport contaminants over longer distances in less time relative to porous media. Furthermore, colloids display unique transport characteristics in comparison to dissolved constituents, including the fact that they typically exhibit earlier initial arrival times. Of particular concern to human health are pathogenic microorganisms, which often originate from fecal contamination. Escherichia coli is a common indicator for fecal contamination; some strains are pathogenic, causing acute illness and sometimes death, in humans. A comprehensive understanding of the transport and retention of E. coli in fractured media will improve our ability to accurately assess whether a site is at risk of becoming contaminated by pathogenic microorganisms. Therefore, the goal of this work is to expand our mechanistic understanding particulate retention, specifically E. coli, in fractures, and the influence of flow rate on these mechanisms. In order to achieve this goal, clear epoxy casts were fabricated of two dolomitic limestone fractures retrieved from a quarry in Guelph, Ontario. Each aperture field was characterized through hydraulic and tracer tests, and measured directly using the light transmission technique. E. coli RS2-GFP, which is a non-pathogenic strain of E. coli that has been tagged with a green fluorescent protein, was injected into the cast under three separate specific discharges ranging from 5 - 30 m/d. These experiments were conducted on an ultraviolet light source, and a high resolution charged-couple device (CCD) camera was employed to take photos at regular intervals in order to capture the dominant flow paths and the areas of retention

  17. Probabilistic Fracture Mechanics Analysis of Boling Water Reactor Vessel for Cool-Down and Low Temperature Over-Pressurization Transients

    Directory of Open Access Journals (Sweden)

    Jeong Soon Park

    2016-04-01

    Full Text Available The failure probabilities of the reactor pressure vessel (RPV for low temperature over-pressurization (LTOP and cool-down transients are calculated in this study. For the cool-down transient, a pressure–temperature limit curve is generated in accordance with Section XI, Appendix G of the American Society of Mechanical Engineers (ASME code, from which safety margin factors are deliberately removed for the probabilistic fracture mechanics analysis. Then, sensitivity analyses are conducted to understand the effects of some input parameters. For the LTOP transient, the failure of the RPV mostly occurs during the period of the abrupt pressure rise. For the cool-down transient, the decrease of the fracture toughness with temperature and time plays a main role in RPV failure at the end of the cool-down process. As expected, the failure probability increases with increasing fluence, Cu and Ni contents, and initial reference temperature-nil ductility transition (RTNDT. The effect of warm prestressing on the vessel failure probability for LTOP is not significant because most of the failures happen before the stress intensity factor reaches the peak value while its effect reduces the failure probability by more than one order of magnitude for the cool-down transient.

  18. The mechanics of delamination in fiber-reinforced composite materials. Part 2: Delamination behavior and fracture mechanics parameters

    Science.gov (United States)

    Wang, S. S.; Choi, I.

    1983-01-01

    Based on theories of laminate anisotropic elasticity and interlaminar fracture, the complete solution structure associated with a composite delamination is determined. Fracture mechanics parameters characterizing the interlaminar crack behavior are defined from asymptotic stress solutions for delaminations with different crack-tip deformation configurations. A numerical method employing singular finite elements is developed to study delaminations in fiber composites with any arbitrary combinations of lamination, material, geometric, and crack variables. The special finite elements include the exact delamination stress singularity in its formulation. The method is shown to be computationally accurate and efficient, and operationally simple. To illustrate the basic nature of composite delamination, solutions are shown for edge-delaminated (0/-0/-0/0) and (+ or - 0/+ or - 0/90/90 deg) graphite-epoxy systems under uniform axial extenstion. Three-dimensional crack-tip stress intensity factors, associated energy release rates, and delamination crack-closure are determined for each individual case. The basic mechanics and mechanisms of composite delamination are studied, and fundamental characteristics unique to recently proposed tests for interlaminar fracture toughness of fiber composite laminates are examined.

  19. The mechanics of delamination in fiber-reinforced composite materials. II - The delamination behavior and fracture mechanics parameters

    Science.gov (United States)

    Wang, S. S.; Choi, I.

    1983-01-01

    Based on theories of laminate anisotropic elasticity and interlaminar fracture, the complete solution structure associated with a composite delamination is determined. Fracture mechanics parameters characterizing the interlaminar crack behavior are defined from asymptotic stress solutions for delaminations with different crack-tip deformation configurations. A numerical method employing singular finite elements is developed to study delaminations in fiber composites with any arbitrary combinations of lamination, material, geometric, and crack variables. The special finite elements include the exact delamination stress singularity in its formulation. The method is shown to be computationally accurate and efficient, and operationally simple. To illustrate the basic nature of composite delamination, solutions are shown for edge-delaminated (0/-0/-0/0) and (+ or - 0/+ or - 0/90/90 deg) graphite-epoxy systems under uniform axial extension. Three-dimensional crack-tip stress intensity factors, associated energy release rates, and delamination crack-closure are determined for each individual case. The basic mechanics and mechanisms of composite delamination are studied, and fundamental characteristics unique to recently proposed tests for interlaminar fracture toughness of fiber composite laminates are examined. Previously announced in STAR as N84-13222

  20. Ipsilateral simultaneous fracture of the trochlea involving the lateral end clavicle and distal end radius: a rare combination and a unique mechanism of injury

    Directory of Open Access Journals (Sweden)

    Gupta RK

    2014-07-01

    Full Text Available 【Abstract】Isolated trochlea fracture in adults is a rare surgical entity as compared to its capitellar counterpart. It has been only mentioned sporadically in the literature as case reports. Fracture of the trochlea is accompanied by other elbow injuries like elbow dislocation, capitellum fracture, ulnar fracture and extraarticular condylar fracture. Here we report a unique case of isolated displaced trochlea fracture associated with fractures of the lateral end clavicle and the distal end radius. We propose a unique mechanism for this rare combination of injuries: typical triad of injury, i.e. fracture of the distal end radius with trochlea and fracture of the lateral end of the clavicle. Nonoperative treatment is recommended for undisplaced humeral trochlea fractures; but for displaced ones, anatomical reduction and internal fixation are essential to maintain the congruous trochleacoronoid articulation and hence to maintain the intrinsic stability of the elbow. Key words: Isolated trochlea fracture; Clavicle; Radius fractures

  1. Salt-Sensitive Hypertension: Perspectives on Intrarenal Mechanisms

    Science.gov (United States)

    Majid, Dewan S.A.; Prieto, Minolfa C.; Navar, L Gabriel

    2015-01-01

    Salt sensitive hypertension is characterized by increases in blood pressure in response to increases in dietary salt intake and is associated with an enhanced risk of cardiovascular and renal morbidity. Although researchers have sought for decades to understand how salt sensitivity develops in humans, the mechanisms responsible for the increases in blood pressure in response to high salt intake are complex and only partially understood. Until now, scientists have been unable to explain why some individuals are salt sensitive and others are salt resistant. Although a central role for the kidneys in the development of salt sensitivity and hypertension has been generally accepted, it is also recognized that hypertension is of multifactorial origin and a variety of factors can induce, or prevent, blood pressure responsiveness to the manipulation of salt intake. Excess salt intake in susceptible persons may also induce inappropriate central and sympathetic nervous system responses and increase the production of intrarenal angiotensin II, catecholamines and other factors such as oxidative stress and inflammatory cytokines. One key factor is the concomitant inappropriate or paradoxical activation of the intrarenal renin-angiotensin system, by high salt intake. This is reflected by the increases in urinary angiotensinogen during high salt intake in salt sensitive models. A complex interaction between neuroendocrine factors and the kidney may underlie the propensity for some individuals to retain salt and develop salt-dependent hypertension. In this review, we focus mainly on the renal contributions that provide the mechanistic link between chronic salt intake and the development of hypertension. PMID:26028244

  2. Fracture Mechanics Analyses of Reinforced Carbon-Carbon Wing-Leading-Edge Panels

    Science.gov (United States)

    Raju, Ivatury S.; Phillips, Dawn R.; Knight, Norman F., Jr.; Song, Kyongchan

    2010-01-01

    Fracture mechanics analyses of subsurface defects within the joggle regions of the Space Shuttle wing-leading-edge RCC panels are performed. A 2D plane strain idealized joggle finite element model is developed to study the fracture behavior of the panels for three distinct loading conditions - lift-off and ascent, on-orbit, and entry. For lift-off and ascent, an estimated bounding aerodynamic pressure load is used for the analyses, while for on-orbit and entry, thermo-mechanical analyses are performed using the extreme cold and hot temperatures experienced by the panels. In addition, a best estimate for the material stress-free temperature is used in the thermo-mechanical analyses. In the finite element models, the substrate and coating are modeled separately as two distinct materials. Subsurface defects are introduced at the coating-substrate interface and within the substrate. The objective of the fracture mechanics analyses is to evaluate the defect driving forces, which are characterized by the strain energy release rates, and determine if defects can become unstable for each of the loading conditions.

  3. Immobilization contributes to exaggerated neuropeptide signaling, inflammatory changes, and nociceptive sensitization after fracture in rats.

    Science.gov (United States)

    Guo, Tian-Zhi; Wei, Tzuping; Li, Wen-Wu; Li, Xiang-Qi; Clark, J David; Kingery, Wade S

    2014-10-01

    A tibia fracture cast immobilized for 4 weeks can induce exaggerated substance P and calcitonin gene-related peptide signaling and neuropeptide-dependent nociceptive and inflammatory changes in the hind limbs of rats similar to those seen in complex regional pain syndrome (CRPS). Four weeks of hind limb cast immobilization can also induce nociceptive and vascular changes resembling CRPS. To test our hypothesis that immobilization alone could cause exaggerated neuropeptide signaling and inflammatory changes, we tested 5 cohorts of rats: 1) controls; 2) tibia fracture and hind limb casted; 3) hind limb casted, no fracture; 4) tibia fracture with intramedullary pinning, no cast; and 5) tibia fracture with intramedullary pinning and hind limb casting. After 4 weeks, the casts were removed and hind limb allodynia, unweighting, warmth, edema, sciatic nerve neuropeptide content, cutaneous and spinal cord inflammatory mediator levels, and spinal c-Fos activation were measured. After fracture with casting, there was allodynia, unweighting, warmth, edema, increased sciatic nerve substance P and calcitonin gene-related peptide, increased skin neurokinin 1 receptors and keratinocyte proliferation, increased inflammatory mediator expression in the hind paw skin (tumor necrosis factor-α, interleukin [IL]-1β, IL-6, nerve growth factor) and cord (IL-1β, nerve growth factor), and increased spinal c-Fos activation. These same changes were observed after cast immobilization alone, except that spinal IL-1β levels were not increased. Treating cast-only rats with a neurokinin 1 receptor antagonist inhibited development of nociceptive and inflammatory changes. Four weeks after fracture with pinning, all nociceptive and vascular changes had resolved and there were no increases in neuropeptide signaling or inflammatory mediator expression. Collectively, these data indicate that immobilization alone increased neuropeptide signaling and caused nociceptive and inflammatory changes similar

  4. Fracture mechanics based design for radioactive material transport packagings -- Historical review

    International Nuclear Information System (INIS)

    Smith, J.A.; Salzbrenner, D.; Sorenson, K.; McConnell, P.

    1998-04-01

    The use of a fracture mechanics based design for the radioactive material transport (RAM) packagings has been the subject of extensive research for more than a decade. Sandia National Laboratories (SNL) has played an important role in the research and development of the application of this technology. Ductile iron has been internationally accepted as an exemplary material for the demonstration of a fracture mechanics based method of RAM packaging design and therefore is the subject of a large portion of the research discussed in this report. SNL's extensive research and development program, funded primarily by the U. S. Department of Energy's Office of Transportation, Energy Management and Analytical Services (EM-76) and in an auxiliary capacity, the office of Civilian Radioactive Waste Management, is summarized in this document along with a summary of the research conducted at other institutions throughout the world. In addition to the research and development work, code and standards development and regulatory positions are also discussed

  5. The application of fracture mechanics to the safety assessment of transport casks for radioactive materials

    International Nuclear Information System (INIS)

    Zencker, U.; Mueller, K.; Droste, B.; Roedel, R.; Voelzke, H.

    2004-01-01

    BAM is the German responsible authority for the mechanical and thermal design safety assessment of packages for the transport of radioactive materials. The assessment has to cover the brittle fracture safety proof of package components made of potentially brittle materials. This paper gives a survey of the regulatory and technical requirements for such an assessment according to BAM's new ''Guidelines for the Application of Ductile Cast Iron for Transport and Storage Casks for Radioactive Materials''. Based on these guidelines higher stresses than before can become permissible, but it is necessary to put more effort into the safety assessment procedure. The fundamentals of such a proof with the help of the methods of fracture mechanics are presented. The recommended procedure takes into account the guidelines of the IAEA Advisory Material which are based on the prevention of crack initiation. Examples of BAM's research and safety assessment practices are given. Recommendations for further developments towards package designs with higher acceptable stress levels will be concluded

  6. Mechanical Behavior and Fracture Properties of NiAl Intermetallic Alloy with Different Copper Contents

    Directory of Open Access Journals (Sweden)

    Tao-Hsing Chen

    2016-03-01

    Full Text Available The deformation behavior and fracture characteristics of NiAl intermetallic alloy containing 5~7 at% Cu are investigated at room temperature under strain rates ranging from 1 × 10−3 to 5 × 103 s−1. It is shown that the copper contents and strain rate both have a significant effect on the mechanical behavior of the NiAl alloy. Specifically, the flow stress increases with an increasing copper content and strain rate. Moreover, the ductility also improves as the copper content increases. The change in the mechanical response and fracture behavior of the NiAl alloy given a higher copper content is thought to be the result of the precipitation of β-phase (Ni,CuAl and γ'-phase (Ni,Cu3Al in the NiAl matrix.

  7. Nonlinear mechanical resonators for ultra-sensitive mass detection

    Energy Technology Data Exchange (ETDEWEB)

    Datskos, Panos G [ORNL; Lavrik, Nickolay V [ORNL

    2014-01-01

    The fundamental sensitivity limit of an appropriately scaled down mechanical resonator can approach one atomic mass unit when only thermal noise is present in the system. However, operation of such nanoscale mechanical resonators is very challenging due to minuteness of their oscillation amplitudes and presence of multiple noise sources in real experimental environments. In order to surmount these challenges, we use microscale cantilever resonators driven to large amplitudes, far beyond their nonlinear instability onset. Our experiments show that such a nonlinear cantilever resonator, described analytically as a Duffing oscillator, has mass sensing performance comparable to that of much smaller resonators operating in a linear regime. We demonstrate femtogram level mass sensing that relies on a bifurcation point tracking that does not require any complex readout means. Our approaches enable straightforward detection of mass changes that are near the fundamental limit imposed by thermo-mechanical fluctuations.

  8. Sensitizing mechanism and adsorption properties of dye-sensitized TiO sub 2 thin films

    CERN Document Server

    Hu Zhi Xue; Wang Kong Jia

    2002-01-01

    The dye-sensitized TiO sub 2 complex films were prepared by the dye coat onto TiO sub 2 surfaces, and the sensitizing mechanism and adsorption properties of the dye-sensitized TiO sub 2 complex films were investigated. The influence of the application conditions of dye adsorbed on TiO sub 2 films on the amount of dye adsorption was discussed. Experimental results show that the concentration, the temperature of dye solutions and the dipping time of TiO sub 2 films in the dye solutions have a significant influence on the amount of dye adsorption. Cell test indicates that the conversion efficiency of light to electricity increases with the amount of dye adsorption

  9. Fracture mechanics of pseudoelastic NiTi alloys: review of the research activities carried out at University of Calabria

    Directory of Open Access Journals (Sweden)

    E. Sgambitterra

    2013-01-01

    Full Text Available This paper reports a brief review of the research activities on fracture mechanics of nickel-titanium based shape memory alloys carried out at University of Calabria. In fact, this class of metallic alloys show a unusual fracture response due to the reversible stress-induced and thermally phase transition mechanisms occurring in the crack tip region as a consequence of the highly localized stresses. The paper illustrates the main results concerning numerical, analytical and experimental research activities carried out by using commercial NiTi based pseudoelastic alloys. Furthermore, the effect of several thermo-mechanical loading conditions on the fracture properties of NiTi alloys are illustrated.

  10. The effect of crack propagation mechanism on the fractal dimension of fracture surfaces in steels

    Czech Academy of Sciences Publication Activity Database

    Dlouhý, Ivo; Strnadel, B.

    2008-01-01

    Roč. 75, č. 3-4 (2008), s. 726-738 ISSN 0013-7944 R&D Projects: GA ČR(CZ) GA106/06/0646; GA AV ČR IAA200410502 Institutional research plan: CEZ:AV0Z20410507 Keywords : low-alloyed steel * fracture surface * fractography Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.713, year: 2008

  11. Non–double-couple mechanisms of microearthquakes induced by hydraulic fracturing

    Czech Academy of Sciences Publication Activity Database

    Šílený, Jan; Hill, D. P.; Eisner, L.; Cornet, F. H.

    2009-01-01

    Roč. 114, B8 (2009), B08307/1-B08307/15 ISSN 0148-0227 R&D Projects: GA AV ČR IAA300120502; GA ČR GA205/09/0724 Grant - others:EC(XE) MTKI-CT-2004-517242 Institutional research plan: CEZ:AV0Z30120515 Keywords : microearthquakes * source mechanisms * hydraulic fracturing Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 3.082, year: 2009

  12. A fracture mechanics study of tungsten failure under high heat flux loads

    International Nuclear Information System (INIS)

    Li, Muyuan

    2015-01-01

    The performance of fusion devices is highly dependent on plasma-facing components. Tungsten is the most promising candidate material for armors in plasma-facing components in ITER and DEMO. However, the brittleness of tungsten below the ductile-to-brittle transition temperature is very critical to the reliability of plasma-facing components. In this work, thermo-mechanical and fracture behaviors of tungsten are predicted numerically under fusion relevant thermal loadings.

  13. Deformation and Failure Mechanism of Roadway Sensitive to Stress Disturbance and Its Zonal Support Technology

    Directory of Open Access Journals (Sweden)

    Qiangling Yao

    2016-01-01

    Full Text Available The 6163 haulage roadway in the Qidong coal mine passes through a fault zone, which causes severe deformation in the surrounding rock, requiring repeated roadway repairs. Based on geological features in the fault area, we analyze the factors affecting roadway deformation and failure and propose the concept of roadway sensitive to stress disturbance (RSSD. We investigate the deformation and failure mechanism of the surrounding rocks of RSSD using field monitoring, theoretical analysis, and numerical simulation. The deformation of the surrounding rocks involves dilatation of shallow rocks and separation of deep rocks. Horizontal and longitudinal fissures evolve to bed separation and fracture zones; alternatively, fissures can evolve into fracture zones with new fissures extending to deeper rock. The fault affects the stress field of the surrounding rock to ~27 m radius. Its maximum impact is on the vertical stress of the rib rock mass and its minimum impact is on the vertical stress of the floor rock mass. Based on our results, we propose a zonal support system for a roadway passing through a fault. Engineering practice shows that the deformation of the surrounding rocks of the roadway can be effectively controlled to ensure normal and safe production in the mine.

  14. The microstructural, mechanical, and fracture properties of austenitic stainless steel alloyed with gallium

    Science.gov (United States)

    Kolman, D. G.; Bingert, J. F.; Field, R. D.

    2004-11-01

    The mechanical and fracture properties of austenitic stainless steels (SSs) alloyed with gallium require assessment in order to determine the likelihood of premature storage-container failure following Ga uptake. AISI 304 L SS was cast with 1, 3, 6, 9, and 12 wt pct Ga. Increased Ga concentration promoted duplex microstructure formation with the ferritic phase having a nearly identical composition to the austenitic phase. Room-temperature tests indicated that small additions of Ga (less than 3 wt pct) were beneficial to the mechanical behavior of 304 L SS but that 12 wt pct Ga resulted in a 95 pct loss in ductility. Small additions of Ga are beneficial to the cracking resistance of stainless steel. Elastic-plastic fracture mechanics analysis indicated that 3 wt pct Ga alloys showed the greatest resistance to crack initiation and propagation as measured by fatigue crack growth rate, fracture toughness, and tearing modulus. The 12 wt pct Ga alloys were least resistant to crack initiation and propagation and these alloys primarily failed by transgranular cleavage. It is hypothesized that Ga metal embrittlement is partially responsible for increased embrittlement.

  15. Flexible parallel implicit modelling of coupled thermal–hydraulic–mechanical processes in fractured rocks

    Directory of Open Access Journals (Sweden)

    M. Cacace

    2017-09-01

    Full Text Available Theory and numerical implementation describing groundwater flow and the transport of heat and solute mass in fully saturated fractured rocks with elasto-plastic mechanical feedbacks are developed. In our formulation, fractures are considered as being of lower dimension than the hosting deformable porous rock and we consider their hydraulic and mechanical apertures as scaling parameters to ensure continuous exchange of fluid mass and energy within the fracture–solid matrix system. The coupled system of equations is implemented in a new simulator code that makes use of a Galerkin finite-element technique. The code builds on a flexible, object-oriented numerical framework (MOOSE, Multiphysics Object Oriented Simulation Environment which provides an extensive scalable parallel and implicit coupling to solve for the multiphysics problem. The governing equations of groundwater flow, heat and mass transport, and rock deformation are solved in a weak sense (either by classical Newton–Raphson or by free Jacobian inexact Newton–Krylow schemes on an underlying unstructured mesh. Nonlinear feedbacks among the active processes are enforced by considering evolving fluid and rock properties depending on the thermo-hydro-mechanical state of the system and the local structure, i.e. degree of connectivity, of the fracture system. A suite of applications is presented to illustrate the flexibility and capability of the new simulator to address problems of increasing complexity and occurring at different spatial (from centimetres to tens of kilometres and temporal scales (from minutes to hundreds of years.

  16. Coupled hydro-thermo-mechanical modeling of hydraulic fracturing in quasi-brittle rocks using BPM-DEM

    Directory of Open Access Journals (Sweden)

    Ingrid Tomac

    2017-02-01

    Full Text Available This paper presents an improved understanding of coupled hydro-thermo-mechanical (HTM hydraulic fracturing of quasi-brittle rock using the bonded particle model (BPM within the discrete element method (DEM. BPM has been recently extended by the authors to account for coupled convective–conductive heat flow and transport, and to enable full hydro-thermal fluid–solid coupled modeling. The application of the work is on enhanced geothermal systems (EGSs, and hydraulic fracturing of hot dry rock (HDR is studied in terms of the impact of temperature difference between rock and a flowing fracturing fluid. Micro-mechanical investigation of temperature and fracturing fluid effects on hydraulic fracturing damage in rocks is presented. It was found that fracture is shorter with pronounced secondary microcracking along the main fracture for the case when the convective–conductive thermal heat exchange is considered. First, the convection heat exchange during low-viscosity fluid infiltration in permeable rock around the wellbore causes significant rock cooling, where a finger-like fluid infiltration was observed. Second, fluid infiltration inhibits pressure rise during pumping and delays fracture initiation and propagation. Additionally, thermal damage occurs in the whole area around the wellbore due to rock cooling and cold fluid infiltration. The size of a damaged area around the wellbore increases with decreasing fluid dynamic viscosity. Fluid and rock compressibility ratio was found to have significant effect on the fracture propagation velocity.

  17. fracture criterion

    Indian Academy of Sciences (India)

    Fracture in metallic glasses. What are the connections between nano- and micro- mechanisms and toughness? Metallic glasses are schizophrenic in the fracture sense. PDF Create! 5 Trial www.nuance.com ...

  18. EGS in sedimentary basins: sensitivity of early-flowback tracer signals to induced-fracture parameters

    Science.gov (United States)

    Karmakar, Shyamal; Ghergut, Julia; Sauter, Martin

    2015-04-01

    Artificial-fracture design, and fracture characterization during or following stimulation treatment is a central aspect of many EGS ('enhanced' or 'engineered' geothermal system) projects. During the creation or stimulation of an EGS, the injection of fluids, followed by flowback and production stages offers the opportunity for conducting various tracer tests in a single-well (SW) configuration, and given the typical operational and time limitations associated with such tests, along with the need to assess treatment success in real time, investigators mostly favour using short-time tracer-test data, rather than awaiting long-term 'tailings' of tracer signals. Late-time tracer signals from SW injection-flowback and production tests have mainly been used for the purpose of multiple-fracture inflow profiling in multi-layer reservoirs [1]. However, the potential of using SW short-term tracer signals for fracture characterization [2, 3] remained little explored as yet. Dealing with short-term flowback signals, we face a certain degree of parameter interplay, leading to ambiguity in fracture parameter inversion from the measured signal of a single tracer. This ambiguity can, to a certain extent, be overcome by - combining different sources of information (lithostratigraphy, and hydraulic monitoring) in order to constrain the variation range of hydrogeologic parameters (matrix and fracture permeability and porosity, fracture size), - using different types of tracers, such as conservative tracer pairs with contrasting diffusivity, or tracers pairs with contrasting sorptivity onto target surfaces. Fracture height is likely to be constrained by lithostratigraphy, while fracture length is supposed to be determinable from hydraulic monitoring (pressure recordings); the flowback rate can be assumed as a known (measurable) quantity during individual-fracture flowback. This leaves us with one or two unknown parameters to be determined from tracer signals: - the transport

  19. Comprehensive mechanisms for combustion chemistry: Experiment, modeling, and sensitivity analysis

    Energy Technology Data Exchange (ETDEWEB)

    Dryer, F.L.; Yetter, R.A. [Princeton Univ., NJ (United States)

    1993-12-01

    This research program is an integrated experimental/numerical effort to study pyrolysis and oxidation reactions and mechanisms for small-molecule hydrocarbon structures under conditions representative of combustion environments. The experimental aspects of the work are conducted in large diameter flow reactors, at pressures from one to twenty atmospheres, temperatures from 550 K to 1200 K, and with observed reaction times from 10{sup {minus}2} to 5 seconds. Gas sampling of stable reactant, intermediate, and product species concentrations provides not only substantial definition of the phenomenology of reaction mechanisms, but a significantly constrained set of kinetic information with negligible diffusive coupling. Analytical techniques used for detecting hydrocarbons and carbon oxides include gas chromatography (GC), and gas infrared (NDIR) and FTIR methods are utilized for continuous on-line sample detection of light absorption measurements of OH have also been performed in an atmospheric pressure flow reactor (APFR), and a variable pressure flow (VPFR) reactor is presently being instrumented to perform optical measurements of radicals and highly reactive molecular intermediates. The numerical aspects of the work utilize zero and one-dimensional pre-mixed, detailed kinetic studies, including path, elemental gradient sensitivity, and feature sensitivity analyses. The program emphasizes the use of hierarchical mechanistic construction to understand and develop detailed kinetic mechanisms. Numerical studies are utilized for guiding experimental parameter selections, for interpreting observations, for extending the predictive range of mechanism constructs, and to study the effects of diffusive transport coupling on reaction behavior in flames. Modeling using well defined and validated mechanisms for the CO/H{sub 2}/oxidant systems.

  20. Correlating Scatter in Fatigue Life with Fracture Mechanisms in Forged Ti-6242Si Alloy

    Science.gov (United States)

    Sinha, V.; Pilchak, A. L.; Jha, S. K.; Porter, W. J.; John, R.; Larsen, J. M.

    2018-04-01

    Unlike the quasi-static mechanical properties, such as strength and ductility, fatigue life can vary significantly (by an order of magnitude or more) for nominally identical material and test conditions in many materials, including Ti-alloys. This makes life prediction and management more challenging for components that are subjected to cyclic loading in service. The differences in fracture mechanisms can cause the scatter in fatigue life. In this study, the fatigue fracture mechanisms were investigated in a forged near- α titanium alloy, Ti-6Al-2Sn-4Zr-2Mo-0.1Si, which had been tested under a condition that resulted in life variations by more than an order of magnitude. The crack-initiation and small crack growth processes, including their contributions to fatigue life variability, were elucidated via quantitative characterization of fatigue fracture surfaces. Combining the results from quantitative tilt fractography and electron backscatter diffraction, crystallography of crack-initiating and neighboring facets on the fracture surface was determined. Cracks initiated on the surface for both the shortest and the longest life specimens. The facet plane in the crack-initiating grain was aligned with the basal plane of a primary α grain for both the specimens. The facet planes in grains neighboring the crack-initiating grain were also closely aligned with the basal plane for the shortest life specimen, whereas the facet planes in the neighboring grains were significantly misoriented from the basal plane for the longest life specimen. The difference in the extent of cracking along the basal plane can explain the difference in fatigue life of specimens at the opposite ends of scatter band.

  1. Progressive fracture in quartzite samples as a result of chemo-mechanical interactions

    Science.gov (United States)

    Voigtlaender, Anne; Leith, Kerry; Krautblatter, Michael

    2017-04-01

    Stress corrosion cracking reduces brittle fracture strength through the interaction of chemical and mechanical processes. In order to better understand the coupling of these processes in natural rock samples, we set up a long-term test in which six Alta-Quartzite samples (AQ 1-6, 300 x 30 x 70 mm) were brought to failure in stepped single edge notch bending (SENB) creep tests. Distilled water was introduced to the notch in four of these samples (AQ 1-2, 4-5), while reference samples remained dry. Samples were pre-loaded to 60% of their intact strength, as determined from preliminary short-term tests, to generate sharp initial cracks at the end of the saw-cut notch. They were then unloaded, before being re-loaded in steps of 5-10 % of the intact flexural strength starting at 0% for AQ1-3 and at 50% for AQ4-6. Strains were measured using electrical resistivity strain gages 2 mm below the notch. For comparable loading paths, measured strains were up to an order of magnitude higher in samples which had water introduced, and approached tertiary creep at 70-80% of the dry maximum load. Scanning electron microscopy of the fracture path of the 'wet notch' quartzite samples revealed various alterations in conformity with the stress field. Observations include etch pits aligned parallel to the principal stress direction, terrace dissolution in the plane of the principal tensile stress, as well as stress direction dependent contrast of highly to not corroded surface, following microstructural, e.g. foliation planes. These fracture features indicate the importance of coupled chemical and mechanical processes, particularly along grain boundaries, crystal planes and microstructural interfaces. Chemo-mechanical interactions are likely to facilitate progressive fracture of surface bedrocks in natural setting. Stress corrosion cracking is thus an important control on the promotion of rock slope failure, bedrock incision and building material damage.

  2. Computational implementation of the multi-mechanism deformation coupled fracture model for salt

    International Nuclear Information System (INIS)

    Koteras, J.R.; Munson, D.E.

    1996-01-01

    The Multi-Mechanism Deformation (M-D) model for creep in rock salt has been used in three-dimensional computations for the Waste Isolation Pilot Plant (WIPP), a potential waste, repository. These computational studies are relied upon to make key predictions about long-term behavior of the repository. Recently, the M-D model was extended to include creep-induced damage. The extended model, the Multi-Mechanism Deformation Coupled Fracture (MDCF) model, is considerably more complicated than the M-D model and required a different technology from that of the M-D model for a computational implementation

  3. Tracer SWIW tests in propped and un-propped fractures: parameter sensitivity issues, revisited

    Science.gov (United States)

    Ghergut, Julia; Behrens, Horst; Sauter, Martin

    2017-04-01

    -scale diffusion; (iii) attempt to determine both advective and non-advective transport parameters from one and the same conservative-tracer signal (relying on 'third-party' knowledge), or from twin signals of a so-called 'dual' tracer pair, e. g.: using tracers with contrasting reactivity and partitioning behavior to determine residual saturation in depleted oilfields (Tomich et al. 1973), or to determine advective parameters (Ghergut et al. 2014); using early-time signals of conservative and sorptive tracers for propped-fracture characterization (Karmakar et al. 2015); using mid-time signals of conservative tracers for a reservoir-borne inflow profiling in multi-frac systems (Ghergut et al. 2016), etc. The poster describes new uses of type-(iii) techniques for the specific purposes of shale-gas reservoir characterization, productivity monitoring, diagnostics and engineering of 're-frac' treatments, based on parameter sensitivity findings from German BMWi research project "TRENDS" (Federal Ministry for Economic Affairs and Energy, FKZ 0325515) and from the EU-H2020 project "FracRisk" (grant no. 640979).

  4. The Hydraulic Mechanism in the Orbital Blowout Fracture Because of a High-Pressure Air Gun Injury.

    Science.gov (United States)

    Kang, Seok Joo; Chung, Eui Han

    2015-10-01

    There are 2 predominant mechanisms that are used to explain the pathogenesis of orbital blowout fracture; these include hydraulic and buckling mechanisms. Still, however, its pathophysiology remains uncertain. To date, studies in this series have been conducted using dry skulls, cadavers, or animals. But few clinical studies have been conducted to examine whether the hydraulic mechanism is involved in the occurrence of pure orbital blowout fracture. The authors experienced a case of a 52-year-old man who had a pure medial blowout fracture after sustaining an eye injury because of a high-pressure air gun. Our case suggests that surgeons should be aware of the possibility that the hydraulic mechanism might be involved in the blowout fracture in patients presenting with complications, such as limitation of eye movement, diplopia, and enophthalmos.

  5. Coupled Thermo-Hydro-Mechanical-Chemical Modeling of Water Leak-Off Process during Hydraulic Fracturing in Shale Gas Reservoirs

    Directory of Open Access Journals (Sweden)

    Fei Wang

    2017-11-01

    Full Text Available The water leak-off during hydraulic fracturing in shale gas reservoirs is a complicated transport behavior involving thermal (T, hydrodynamic (H, mechanical (M and chemical (C processes. Although many leak-off models have been published, none of the models fully coupled the transient fluid flow modeling with heat transfer, chemical-potential equilibrium and natural-fracture dilation phenomena. In this paper, a coupled thermo-hydro-mechanical-chemical (THMC model based on non-equilibrium thermodynamics, hydrodynamics, thermo-poroelastic rock mechanics, and non-isothermal chemical-potential equations is presented to simulate the water leak-off process in shale gas reservoirs. The THMC model takes into account a triple-porosity medium, which includes hydraulic fractures, natural fractures and shale matrix. The leak-off simulation with the THMC model involves all the important processes in this triple-porosity medium, including: (1 water transport driven by hydraulic, capillary, chemical and thermal osmotic convections; (2 gas transport induced by both hydraulic pressure driven convection and adsorption; (3 heat transport driven by thermal convection and conduction; and (4 natural-fracture dilation considered as a thermo-poroelastic rock deformation. The fluid and heat transport, coupled with rock deformation, are described by a set of partial differential equations resulting from the conservation of mass, momentum, and energy. The semi-implicit finite-difference algorithm is proposed to solve these equations. The evolution of pressure, temperature, saturation and salinity profiles of hydraulic fractures, natural fractures and matrix is calculated, revealing the multi-field coupled water leak-off process in shale gas reservoirs. The influences of hydraulic pressure, natural-fracture dilation, chemical osmosis and thermal osmosis on water leak-off are investigated. Results from this study are expected to provide a better understanding of the

  6. A novel Lagrangian approach for the stable numerical simulation of fault and fracture mechanics

    Energy Technology Data Exchange (ETDEWEB)

    Franceschini, Andrea; Ferronato, Massimiliano, E-mail: massimiliano.ferronato@unipd.it; Janna, Carlo; Teatini, Pietro

    2016-06-01

    The simulation of the mechanics of geological faults and fractures is of paramount importance in several applications, such as ensuring the safety of the underground storage of wastes and hydrocarbons or predicting the possible seismicity triggered by the production and injection of subsurface fluids. However, the stable numerical modeling of ground ruptures is still an open issue. The present work introduces a novel formulation based on the use of the Lagrange multipliers to prescribe the constraints on the contact surfaces. The variational formulation is modified in order to take into account the frictional work along the activated fault portion according to the principle of maximum plastic dissipation. The numerical model, developed in the framework of the Finite Element method, provides stable solutions with a fast convergence of the non-linear problem. The stabilizing properties of the proposed model are emphasized with the aid of a realistic numerical example dealing with the generation of ground fractures due to groundwater withdrawal in arid regions. - Highlights: • A numerical model is developed for the simulation of fault and fracture mechanics. • The model is implemented in the framework of the Finite Element method and with the aid of Lagrange multipliers. • The proposed formulation introduces a new contribution due to the frictional work on the portion of activated fault. • The resulting algorithm is highly non-linear as the portion of activated fault is itself unknown. • The numerical solution is validated against analytical results and proves to be stable also in realistic applications.

  7. Long-term cumulative survival and mechanical complications of single-tooth Ankylos Implants: focus on the abutment neck fractures

    OpenAIRE

    Shim, Hye Won; Yang, Byoung-Eun

    2015-01-01

    PURPOSE To evaluate the cumulative survival rate (CSR) and mechanical complications of single-tooth Ankylos? implants. MATERIALS AND METHODS This was a retrospective clinical study that analyzed 450 single Ankylos? implants installed in 275 patients between December 2005 and December 2012. The main outcomes were survival results CSR and implant failure) and mechanical complications (screw loosening, fracture, and cumulative fracture rate [CFR]). The main outcomes were analyzed according to ag...

  8. Influences of Cutting Speed and Material Mechanical Properties on Chip Deformation and Fracture during High-Speed Cutting of Inconel 718.

    Science.gov (United States)

    Wang, Bing; Liu, Zhanqiang; Hou, Xin; Zhao, Jinfu

    2018-03-21

    The paper aims to investigate the influences of material constitutive and fracture parameters in addition to cutting speed on chip formation during high-speed cutting of Inconel 718. Finite element analyses for chip formation are conducted with Johnson-Cook constitutive and fracture models. Meanwhile, experiments of high-speed orthogonal cutting are performed to verify the simulation results with cutting speeds ranging from 50 m/min to 7000 m/min. The research indicates that the chip morphology transforms from serrated to fragmented at the cutting speed of 7000 m/min due to embrittlement of the workpiece material under ultra-high cutting speeds. The parameter of shear localization sensitivity is put forward to describe the influences of material mechanical properties on serrated chip formation. The results demonstrate that the effects of initial yield stress and thermal softening coefficient on chip shear localization are much more remarkable than the other constitutive parameters. For the material fracture parameters, the effects of initial fracture strain and exponential factor of stress state on chip shear localization are more much prominent. This paper provides guidance for controlling chip formation through the adjustment of material mechanical properties and the selection of appropriate cutting parameters.

  9. Additional Stress And Fracture Mechanics Analyses Of Pressurized Water Reactor Pressure Vessel Nozzles

    International Nuclear Information System (INIS)

    Walter, Matthew; Yin, Shengjun; Stevens, Gary; Sommerville, Daniel; Palm, Nathan; Heinecke, Carol

    2012-01-01

    In past years, the authors have undertaken various studies of nozzles in both boiling water reactors (BWRs) and pressurized water reactors (PWRs) located in the reactor pressure vessel (RPV) adjacent to the core beltline region. Those studies described stress and fracture mechanics analyses performed to assess various RPV nozzle geometries, which were selected based on their proximity to the core beltline region, i.e., those nozzle configurations that are located close enough to the core region such that they may receive sufficient fluence prior to end-of-life (EOL) to require evaluation of embrittlement as part of the RPV analyses associated with pressure-temperature (P-T) limits. In this paper, additional stress and fracture analyses are summarized that were performed for additional PWR nozzles with the following objectives: To expand the population of PWR nozzle configurations evaluated, which was limited in the previous work to just two nozzles (one inlet and one outlet nozzle). To model and understand differences in stress results obtained for an internal pressure load case using a two-dimensional (2-D) axi-symmetric finite element model (FEM) vs. a three-dimensional (3-D) FEM for these PWR nozzles. In particular, the ovalization (stress concentration) effect of two intersecting cylinders, which is typical of RPV nozzle configurations, was investigated. To investigate the applicability of previously recommended linear elastic fracture mechanics (LEFM) hand solutions for calculating the Mode I stress intensity factor for a postulated nozzle corner crack for pressure loading for these PWR nozzles. These analyses were performed to further expand earlier work completed to support potential revision and refinement of Title 10 to the U.S. Code of Federal Regulations (CFR), Part 50, Appendix G, Fracture Toughness Requirements, and are intended to supplement similar evaluation of nozzles presented at the 2008, 2009, and 2011 Pressure Vessels and Piping (PVP

  10. On improving the fracture toughness of a NiAl-based alloy by mechanical alloying

    Science.gov (United States)

    Kostrubanic, J.; Koss, D. A.; Locci, I. E.; Nathal, M.

    1991-01-01

    Mechanical alloying (MA) has been used to process the NiAl-based alloy Ni-35Al-20Fe, such that a fine-grain (about 2 microns) microstructure is obtained through the addition of 2 vol pct Y2O3 particles. When compared to a conventionally processed, coarse-grained (about 28 microns) Ni-35-20 alloy without the Y2O3 particles, the MA alloy exhibits two to three times higher fracture toughness values, despite a 50-percent increase in yield strength. Room-temperature K(O) values as high as 34 MPa sq rt m are observed, accompanied by a yield strength in excess of 1100 MPa. Fractography confirms a change in fracture characteristics of the fine-grained MA alloy.

  11. Trochanteric fractures. Classification and mechanical stability in McLaughlin, Ender and Richard osteosynthesis

    Energy Technology Data Exchange (ETDEWEB)

    Herrlin, K.; Stroemberg, T.; Lidgren, L.; Walloee, A.; Pettersson, H.

    Four hundred and thirty trochanteric factures operated upon with McLaughlin, Ender or Richard's osteosynthesis were divided into 6 different types based on their radiographic appearance before and immediately after reposition with special reference to the medial cortical support. A significant correlation was found between the fracture type and subsequent mechanical complications where types 1 and 2 gave less, and types 4 and 5 more complications. A comparison of the various osteosyntheses showed that Richard's had significantly fewer complications than either the Ender or McLaughlin types. For Richard's osteosynthesis alone no correlation to fracture type could be made because of the small number of complications in this group.

  12. A nonlocal continuum damage mechanics approach to simulation of creep fracture in ice sheets

    Science.gov (United States)

    Duddu, Ravindra; Waisman, Haim

    2013-06-01

    We present a Lagrangian finite element formulation aimed at modeling creep fracture in ice-sheets using nonlocal continuum damage mechanics. The proposed formulation is based on a thermo-viscoelastic constitutive model and a creep damage model for polycrystalline ice with different behavior in tension and compression. In this paper, mainly, we detail the nonlocal numerical implementation of the constitutive damage model into commercial finite element codes (e.g. Abaqus), wherein a procedure to handle the abrupt failure (rupture) of ice under tension is proposed. Then, we present numerical examples of creep fracture under four-point bending, uniaxial tension, and biaxial tension in order to illustrate the viability of the current approach. Finally, we present simulations of creep crack propagation in idealized rectangular ice slabs so as to estimate calving rates at low deformation rates. The examples presented demonstrate the mesh size and mesh directionality independence of the proposed nonlocal implementation.

  13. Probabilistic Fatigue Life Prediction of Bridge Cables Based on Multiscaling and Mesoscopic Fracture Mechanics

    Directory of Open Access Journals (Sweden)

    Zhongxiang Liu

    2016-04-01

    Full Text Available Fatigue fracture of bridge stay-cables is usually a multiscale process as the crack grows from micro-scale to macro-scale. Such a process, however, is highly uncertain. In order to make a rational prediction of the residual life of bridge cables, a probabilistic fatigue approach is proposed, based on a comprehensive vehicle load model, finite element analysis and multiscaling and mesoscopic fracture mechanics. Uncertainties in both material properties and external loads are considered. The proposed method is demonstrated through the fatigue life prediction of cables of the Runyang Cable-Stayed Bridge in China, and it is found that cables along the bridge spans may have significantly different fatigue lives, and due to the variability, some of them may have shorter lives than those as expected from the design.

  14. Superplastic Grade Titanium Alloy: Comparative Evaluation of Mechanical Properties, Microstructure, and Fracture Behavior

    Directory of Open Access Journals (Sweden)

    K. V. Sudhakar

    2016-01-01

    Full Text Available In this investigation, static fracture, microstructure, and the mechanical behavior of SP-700 alloy (a superplastic grade were evaluated and compared with two other titanium alloys. The comparisons were made in terms of suitably designed heat treatment cycles. The heat treatment cycles included annealing and a combination of solutionizing and aging treatments for all three alloys. Tensile properties were determined using MTS Landmark Servohydraulic Test System. Tensile tested samples’ fracture surfaces were investigated with LEO-VP SEM instrument. Ti-15-3-3-3 alloy exhibited relatively a higher combination of strength and ductility in comparison to the other two alloys. All three types of titanium alloys demonstrated a very good level of tensile strength and ductility suitable for applications in military and biomedical fields.

  15. Fracture mechanics parameters calculation for semielliptical underclad cracks postulated in the cylindrical part of the WWER pressure vessel

    International Nuclear Information System (INIS)

    Matkovskij, V.V.; Akbashev, I.F.

    2015-01-01

    The requirements of brittle fracture failure resistance are fulfilled if the cracks postulated in RPV structure remain stable within all project cases. This requirements are stated in terms of fracture mechanics parameters such as J-integral or stress intensity factor. The case of semielliptical underclad cracks postulated in a cylindrical part of WWER pressure vessel is investigated. The analytical solution for fracture mechanics parameters estimation along the crack front in the ferritic vessel was developed on the basis of finite element calculation results. The amplification of the elastic stress intensity factor with respect to effect of plasticity is introduced [ru

  16. Limited magnetic resonance imaging of the lumbar spine has high sensitivity for detection of acute fractures, infection, and malignancy

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Benjamin; Fintelmann, Florian J.; Kamath, Ravi S.; Kattapuram, Susan V.; Rosenthal, Daniel I. [Massachusetts General Hospital, Department of Radiology, Boston, MA (United States)

    2016-12-15

    The objective of this study is to determine how a limited protocol MR examination compares to a full conventional MR examination for the detection of non-degenerative pathology such as acute fracture, infection, and malignancy. A sample of 349 non-contrast MR exams was selected retrospectively containing a 3:1:1:1 distribution of negative/degenerative change only, acute fracture, infection, and malignancy. This resulted in an even distribution of pathology and non-pathology. A limited protocol MR exam was simulated by extracting T1-weighted sagittal and T2-weighted fat-saturated (or STIR) sagittal sequences from each exam and submitting them for blinded review by two experienced musculoskeletal radiologists. The exams were evaluated for the presence or absence of non-degenerative pathology. Interpretation of the limited exam was compared to the original report of the full examination. If either reader disagreed with the original report, the case was submitted for an unblinded adjudication process with the participation of a third musculoskeletal radiologist to establish a consensus diagnosis. There were five false negatives for a sensitivity of 96.9 % for the limited protocol MR exam. Infection in the psoas, paraspinal muscles, and sacroiliac joint, as well as acute fractures in transverse processes and sacrum were missed by one or more readers. No cases of malignancy were missed. Overall diagnostic accuracy was 96.0 % (335/349). MR imaging of the lumbar spine limited to sagittal T1-weighted and sagittal T2 fat-saturated (or STIR) sequences has high sensitivity for the detection of acute fracture, infection, or malignancy compared to a conventional MR examination. (orig.)

  17. Kinetics and fracture resistance of lithiated silicon nanostructure pairs controlled by their mechanical interaction

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Seok Woo; /Stanford U., Geballe Lab.; Lee, Hyun-Wook; /Stanford U., Materials Sci. Dept.; Ryu, Ill; /Brown U.; Nix, William D.; /Stanford U., Materials Sci. Dept.; Gao, Huajian; /Brown U.; Cui, Yi; /Stanford U., Materials Sci. Dept. /SLAC

    2015-06-01

    Following an explosion of studies of silicon as a negative electrode for Li-ion batteries, the anomalous volumetric changes and fracture of lithiated single Si particles have attracted significant attention in various fields, including mechanics. However, in real batteries, lithiation occurs simultaneously in clusters of Si in a confined medium. Hence, understanding how the individual Si structures interact during lithiation in a closed space is necessary. Herein, we demonstrate physical/mechanical interactions of swelling Si structures during lithiation using well-defined Si nanopillar pairs. Ex situ SEM and in situ TEM studies reveal that compressive stresses change the reaction kinetics so that preferential lithiation occurs at free surfaces when the pillars are mechanically clamped. Such mechanical interactions enhance the fracture resistance of This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under Contract No. DE-AC02-76SF00515. SLAC-PUB-16300 2 lithiated Si by lessening the tensile stress concentrations in Si structures. This study will contribute to improved design of Si structures at the electrode level for high performance Li-ion batteries.

  18. Application of probabilistic fracture mechanics to reactor pressure vessel safety assessment

    International Nuclear Information System (INIS)

    Venturini, V.; Pitner, P.

    1995-06-01

    Among all the components of a PWR (Pressurized Water Reactor) nuclear power plant, the reactor vessel is of major importance for safety. The integrity of this structure must be guaranteed in all circumstances, even in the case of the most severe accidents, and its mechanical state can be decisive for the lifetime of the plant. The brittle rupture would be the most important of all potential hazards if the irradiation effects were not consistent with predictions. The interest of having a reliable and precise method of evaluating the available safety margins and the integrity of this component led Electricite de France (EDF) to carry out a probabilistic fracture mechanics analysis. The probabilistic model developed by integration of the uncertainties in the usual fracture mechanics equations is presented. A special focus is made on the problem of coupling thermo-mechanical finite element calculations and reliability analysis. The use of a finite element code can be associated with prohibitive computation times when it is invoked numerous times during simulations sequences or complex iterative procedures. The response surface method is used. It provides an approximation of the response from a reduced number of original data. The global approach is illustrated on an example corresponding to a specific accidental transient. A validation of the obtained results is also carried out through the comparison with an equivalent model without coupling. (author)

  19. The Pellini test as a brittle fracture criterion for components and for the determination of the application limits of fracture mechanics

    International Nuclear Information System (INIS)

    Schulze, H.D.

    1976-01-01

    Linear-elastic fracture mechanics have made it possible to make the brittle behaviour of cracks in components accessible for a description. The concepts envisaging an extension to yield point mechanics as well, which would allow the behaviour of cracks with large plastic deformations at the tip of the crack to be described, are at present not perfected enough yet to be applied in practice. The Pellini concept with its semi-quantitative statements closes at present this gap. (orig./RW) [de

  20. Consideration on the Mechanism of Microwave Emission Due to Rock Fracture

    Science.gov (United States)

    Takano, Tadashi; Sugita, Seiji; Yoshida, Shingo; Maeda, Takashi

    2010-05-01

    Microwave emission due to rock fracture was found at 300 MHz, 2 GHz, and 22 GHz, and its power was calibrated in laboratory for the first time in the world. The observed waveform is impulsive, and contains correspondent frequency component inside the envelope at each frequency band. At such high frequencies, the electro-magnetic signal power can be calibrated as a radiating wave with high accuracy. Accordingly, it was verified that a substantial power is emitted. The microwave emission phenomena were also observed on occasions of hypervelocity impact, and esteemed as phenomena generally associated with material destruction. Earthquakes and volcanic activities are association with rock fractures so that the microwave is expected to be emitted. Actually, the e emission was confirmed by the data analysis of the brightness temperature obtained by a remote sensing satellite, which flew over great earthquakes of Wuenchan and Sumatra, and great volcanic eruptions of Reventador and Chanten. It is important to show the microwave emission during rock fracture in natural phenomena. Therefore, the field test to detect the microwave due to the collapse of a crater cliff was planned and persecuted at the volcano of Miyake-jima about 100 km south of Tokyo. Volcanic activity may be more convenient than an earthquake because of the known location and time. As a result, they observed the microwave emission which was strongly correlated with the cliff collapses. Despite of the above-mentioned phenomenological fruits, the reason of the microwave emission is not fixed yet. We have investigated the mechanism of the emission in consideration of the obtained data in rock fracture experiments so far and the study results on material destruction by hypervelocity impact. This paper presents the proposal of the hypothesis and resultant discussions. The microwave sensors may be useful to monitor natural hazards such as an earthquake or a volcanic eruption, because the microwave due to rock

  1. Application of probabilistic fracture mechanics to the reliability analysis of pressure-bearing reactor components

    International Nuclear Information System (INIS)

    Schmitt, W.; Roehrich, E.; Wellein, R.

    1977-01-01

    Since no failures in the primary reactor components have been reported so far, it is impossible to estimate the failure probability of those components just by means of statistics. Therefore the way of probabilistic fracture mechanics has been proposed. Here the material properties, the loads and the crack distributions are treated as statistical variables with certain distributions. From the distributions of these data probability density functions can be established for the loading of a component (e.g. the stress intensity factor) as well as for the resistance of this component (e.g. the fracture toughness). From these functions the failure probability for a given failure mode (e.g. brittle fracture) is easily obtained either by the application of direct integration procedures which are shortly reviewed here, or by the use of Monte Carlo techniques. The most important part of the concept is the collection of a sufficiently large amount of raw data from different sources (departments within the company or external). These data need to be processed so that they can be transformed into probability density functions. The method of data collection and processing in terms of histograms, plots of probability density functions etc, is described. The choice of the various types of distribution functions is discussed. As an example the derivation of the probability density function for cracks of a given size in a component is presented. (Auth.)

  2. Low-temperature embrittlement and fracture of metals with different crystal lattices – Dislocation mechanisms

    Directory of Open Access Journals (Sweden)

    V.M. Chernov

    2016-12-01

    Full Text Available The state of a low-temperature embrittlement (cold brittleness and dislocation mechanisms for formation of the temperature of a ductile-brittle transition and brittle fracture of metals (mono- and polycrystals with various crystal lattices (BCC, FCC, HCP are considered. The conditions for their formation connected with a stress-deformed state and strength (low temperature yield strength as well as the fracture breaking stress and mobility of dislocations in the top of a crack of the fractured metal are determined. These conditions can be met for BCC and some HCP metals in the initial state (without irradiation and after a low-temperature damaging (neutron irradiation. These conditions are not met for FCC and many HCP metals. In the process of the damaging (neutron irradiation such conditions are not met also and the state of low-temperature embrittlement of metals is absent (suppressed due to arising various radiation dynamic processes, which increase the mobility of dislocations and worsen the strength characteristics.

  3. Results of fracture-mechanical studies on the steel X6CrNi1811

    International Nuclear Information System (INIS)

    Tietje, H.; Cornec, A.; Schwalbe, K.H.

    1989-01-01

    Ductile breaking processes in partly and fully plastic material behaviour can be be characterized with the concepts of yield fracture mechanics. Various methods are available: 1) In the CTOD concept, the deformation at the crack tip (in particular, the crack-tip opening displacement δ 5 ) is seen as the criterion for material stress, and used as a fracture criterion. 2) The J integral can be used as a fracture parameter within certain ranges of validity; it describes the stress and displacement field ahead of the crack tip. It has been discovered that in a two-dimensional state of stress, an R curve shows a larger range of validity on a CTOD basis than on the basis of the J integral. In this study, these inter-connections are tested with the help of a material with a high degree of ductility and an extremely high crack resistance. To this end, measurements were performed with compact specimens (CT specimens) and with tensile test specimens (CCT specimens) from the austenitic steel X6CrNi1811 (material no. 1.4948), and the J-R and δ 5 -R curves were determined (δ 5 : crack-tip opening displacement with a measuring basis of 5 mm). (orig.) [de

  4. Colloid and radionuclide retention mechanisms in fractured rock under near-natural flow conditions

    International Nuclear Information System (INIS)

    Delos, A.; Schaefer, T.; Geckeis, H.; Guimera, J.; Carrera, J.; Fanghaenel, T.

    2005-01-01

    Full text of publication follows: Experiments in fractured host rock (Grimsel Test Site, GTS, Switzerland) revealed that the colloid relevance for actinide migration is high due to the specific geochemical groundwater conditions [1]. However, even under such conditions it is found that retention of colloids and colloid-borne actinides becomes significant under near-natural groundwater flow rates (1-10 m/a) [2]. Underlying mechanisms of colloid and radionuclide retention are not well understood up to now. The present study co-funded by the NoE ACTINET-6 focuses on (i) the kinetics of actinide-colloid interactions and (ii) the relevance of matrix diffusion as a competition process to other retention mechanisms which affect the actinides behavior in fractured rock systems such as the Grimsel granodiorite. Colloid migration is studied with well defined model colloids as e.g. fluorescence dyed carboxylated polystyrene particles, and natural colloids extracted from bentonite (FEBEX) and from fracture filling material (GTS). In order to study the influence of matrix porosity on actinides migration, those experiments are performed in columns of well defined geometry filled with microporous unmodified silica spheres, porous ceramic material and natural fracture filling material from the GTS. The behaviour of actinides (Pu(IV) and Am(III)) sorbed onto bentonite colloids is investigated in column and batch experiments. All experiments are performed under anoxic conditions. Colloid characterization methods used in this study include the combination of photon correlation spectroscopy (PCS), laser-induced breakdown detection (LIBD), fluorimetry and field flow fractionation (FFF). Experimental results and their application to the parametrisation of reactive colloid transport models are discussed. [1] Geckeis H, Schaefer T, Hauser W, Rabung T, Missana T, Degueldre C, Moeri A, Eikenberg J, Fierz T, Alexander WR (2004) Results of the Colloid and Radionuclide Retention experiment

  5. Application of probabilistic fracture mechanics to optimize the maintenance of PWR steam generator tubes

    International Nuclear Information System (INIS)

    Pitner, P.; Riffard, T.

    1993-09-01

    This paper describes the COMPROMIS code developed by Electricite de France (EDF) to optimize the tube bundle maintenance of steam generators (SG). The model, based on probabilistic fracture mechanics, makes it possible to quantify the influence of in-service inspections and maintenance work on the risk of an SG tube rupture, taking all significant parameters into account as random variables (initial defect size distribution, reliability of nondestructive detection and sizing, crack initiation and propagation, critical sizes, leak before risk of break, etc). (authors). 14 figs., 4 tabs., 12 refs

  6. Application of probabilistic fracture mechanics to estimate the risk of rupture of PWR steam generator tubes

    International Nuclear Information System (INIS)

    Pitner, P.; Riffard, T.; Granger, B.

    1992-01-01

    This paper describes the COMPROMIS code developed by Electricite de France (EDF) to optimize the tube bundle maintenance of steam generators. The model, based on probabilistic fracture mechanics, makes it possible to quantify the influence of in-service inspections and maintenance work on the risk of an SG tube rupture, taking all significant parameters into account as random variables (initial defect size distribution, reliability of non-destructive detection and sizing, crack initiation and propagation, critical sizes, leak before risk of break, etc.). (authors). 5 refs., 8 figs., 3 tabs

  7. The Fracture Mechanical Markov Chain Fatigue Model Compared with Empirical Data

    DEFF Research Database (Denmark)

    Gansted, L.; Brincker, Rune; Hansen, Lars Pilegaard

    The applicability of the FMF-model (Fracture Mechanical Markov Chain Fatigue Model) introduced in Gansted, L., R. Brincker and L. Pilegaard Hansen (1991) is tested by simulations and compared with empirical data. Two sets of data have been used, the Virkler data (aluminium alloy) and data...... established at the Laboratory of Structural Engineering at Aalborg University, the AUC-data, (mild steel). The model, which is based on the assumption, that the crack propagation process can be described by a discrete Space Markov theory, is applicable to constant as well as random loading. It is shown...

  8. Three-dimensional elastic--plastic stress and strain analyses for fracture mechanics: complex geometries

    Energy Technology Data Exchange (ETDEWEB)

    Bellucci, H.J.

    1975-11-01

    The report describes the continuation of research into capability for three-dimensional elastic-plastic stress and strain analysis for fracture mechanics. A computer program, MARC-3D, has been completed and was used to analyze a cylindrical pressure vessel with a nozzle insert. A method for generating crack tip elements was developed and a model was created for a cylindrical pressure vessel with a nozzle and an imbedded flaw at the inside nozzle corner. The MARC-3D program was again used to analyze this flawed model. Documentation for the use of the MARC-3D computer program has been included as an appendix.

  9. Fracture mechanics characterization of crack growth under creep and fatigue conditions

    International Nuclear Information System (INIS)

    Hollstein, T.; Kienzler, R.

    1987-01-01

    Based on theoretical considerations and experimental evidence, several concepts have been investigated to correlate crack growth under high-temperature conditions with material parameters of fracture mechanics, e.g., stress-intensity factor K, and line integrals J and C * . It could be shown for different materials that these parameters describe the behavior of cracks independent of geometry and loading conditions within certain limits of validity. The laboratory results then can be transferred to real structures for (residual) lifetime predictions or safety analyses (Incoloy 800H, Thermon 4972, 9% chromium steel). With 45 refs., 3 tabs., 56 figs [de

  10. Evaluation of the Fatigue Strength of Sintered Steel Based on Fracture Mechanics

    OpenAIRE

    加藤, 正名; 井上, 克己; 鄧, 鋼; 佐藤, 寿樹; 亀子, 峰雄

    1996-01-01

    This paper deals with an evaluation of the fatigue strength of sintered steel based on linear fracture mechanics. The fatigue crack growth is measured with bend test specimens of Fe-Cu-Cr sintered steel of various densities. From this result, the fatigue strengths of the specimens with initial length of crack a at the life N are calculated, and they are shown as N-S-A curves. A model, which has an initial crack at the surface but is homogeneous and has no internal flaws, is introduced to anal...

  11. Direct observation of fracture mechanisms in polymer-layered silicate nanocomposites

    Energy Technology Data Exchange (ETDEWEB)

    Manias, E.; Kramer, E.J.; Giannelis, E.P. [Cornell Univ., Ithaca, NY (United States). Dept. of Materials Science and Engineering; Han, W.J. [Motorola Korea, Seoul (Korea, Republic of); Jandt, K.D. [Univ. of Bristol (United Kingdom). Dept. of Oral and Dental Sciences

    1997-09-01

    Conventional three point bending and TEM techniques are employed to determine the fracture toughness and identify the failure mechanisms in model layered-silicate polymer nanocomposites. In their pristine form most of these layered mica-type silicates contain a hydrated layer of cations between the silicate planes and only certain polar polymers can be intercalated. On the other hand, one can modify these inorganic host lattices by tethering cationic surfactant molecules on the silicate surfaces and in this way a very broad range of polymers--from non-polar polystyrene (PS) to strongly polar nylon--can be intercalated in them.

  12. Materials characterization and fracture mechanics of a space grade dielectric silicone insulation

    Science.gov (United States)

    Abdel-Latif, A. I.; Tweedie, A. T.

    1982-01-01

    The present investigation is concerned with the DC 93-500 high voltage silicone insulation material employed to pot the gun and the collector end of a traveling wave tube (TWT) used on the Landsat D Satellite. The fracture mechanics behavior of the silicone resin was evaluated by measuring the slow crack velocity as a function of the opening mode of the stress intensity factor at +25 and -10 C, taking into account various uniaxial discrete strain values. It was found that the silicone resins slow crack growth is faster than that for a high voltage insulation polyurethane material at the same stress intensity factor value and room temperature.

  13. Integrity evaluation of power plant components by fracture mechanics and related techniques

    International Nuclear Information System (INIS)

    Mukherjee, B.; Vanderglas, M.L.; Davies, P.H.

    1982-01-01

    Power plant components can be subject to unexpected failures with serious consequences, unless careful attention is paid to minute crack defects and their possible growth. The Linear Elastic Fracture Mechanics approach to structural integrity evaluation, as it appears in the ASME Code, is discussed. Projects related to material data generation and the development of structural analysis methods to make the above method usable are described. Several integrity-related questions outside the scope of the Code guidelines are documented, concluding with comments on possible future developments

  14. Fracture mechanical analysis of relevant transients in the pressure vessel of Atucha I reactor

    International Nuclear Information System (INIS)

    Saavedra, Fernando M.

    2001-01-01

    The evolution of the applied stress intensity factor K I for 10 relevant transients of the nuclear power station Atucha I obtained from thermohydraulic data is analyzed according to the methodology proposed in Section XI of ASME Boiler and Pressure Vessel Code. Vast knowledge was thus obtained about basic concepts of fracture mechanics and its application to remanent life of nuclear components. Basic knowledge which commands the performance of nuclear power stations was also obtained, especially that related to the Atucha I utility [es

  15. Refinement and fracture mechanisms of as-cast QT700-6 alloy by alloying method

    Directory of Open Access Journals (Sweden)

    Min-qiang Gao

    2017-01-01

    Full Text Available The as-cast QT700-6 alloy was synthesized with addition of a certain amount of copper, nickel, niobium and stannum elements by alloying method in a medium frequency induction furnace, aiming at improving its strength and toughness. Microstructures of the as-cast QT700-6 alloy were observed using a scanning-electron microscope (SEM and the mechanical properties were investigated using a universal tensile test machine. Results indicate that the ratio of pearlite/ferrite is about 9:1 and the graphite size is less than 40 μm in diameter in the as-cast QT700-6 alloy. The predominant refinement mechanism is attributed to the formation of niobium carbides, which increases the heterogeneous nucleus and hinders the growth of graphite. Meanwhile, niobium carbides also exist around the grain boundaries, which improve the strength of the ductile iron. The tensile strength and elongation of the as-cast QT700-6 alloy reach over 700 MPa and 6%, respectively, when the addition amount of niobium is 0.8%. The addition of copper and nickel elements contributed to the decrease of eutectoid transformation temperature, resulting in the decrease of pearlite lamellar spacing (about 248 nm, which is also beneficial to enhancing the tensile strength. The main fracture mechanism is cleavage fracture with the appearance of a small amount of dimples.

  16. Mechanical Behavior and Fracture Toughness Evaluation of Multiphase Polymer Nanocomposites Using Impact and J-Integral via Locus Method

    Directory of Open Access Journals (Sweden)

    Bishnu P. Panda

    2013-01-01

    Full Text Available Fracture behaviors of fibrillar silicate clay (MMT filled thermoplastic polyolefin (TPO containing polypropylene (PP blended with ethylene-propylene-diene monomer (EPDM were systematically investigated using impact test method and J-integral by locus method. Drastic increase in impact strength is observed for all developed compositions and generally shows higher value for the selected phases containing dispersed nanoclay in PP matrix. A fracture mechanics approach has been adopted by mode I test, and the effects of specimen geometry have been investigated. Increase in interlaminar fracture energy value, Gc, and J-integral value, Jc, is marked as the crack propagated through the composite; that is, a rising “R-curve” is observed. Toughness measurements revealed that the fracture toughness increased with increasing clay content reaching maximum at 3 wt% of clay than pure PP. Moreover, enhancement of fracture toughness was more remarkable than that of stiffness. The fracture surfaces taken from different specimens were observed for exploring the fracture mechanisms using transmission electron microscopy (TEM revealed a strong particle-matrix adhesion.

  17. Study of mechanical properties and fracture mechanisms of synthetic fibers nylon-and-polyester type, used in engineering products

    International Nuclear Information System (INIS)

    Cardoso, Sergio Gomes

    2009-01-01

    Fibers are groups formed by molecular-chain-oriented filaments. Fibers play a fundamental role in human being's daily life and they can be found in several forms and geometries, such as filaments, yarns, beams, rope, fabric, composite, coatings, others. They are used in various segments such as civil, mechanical, electrical, electronics, military, naval, nautical, aviation, health, medicine, environment, communications, safety, space, others. Fibers are divided into two distinct classes: natural and chemical ones, which cover synthetic and man-made sub-classes. They can be produced from several materials, such as wool, cotton, rayon, flax, silk, rock, nylon, polyester, polyethylene, poly-propylene, aramid, glass, carbon, steel, ceramic, others. Globally, the participation of chemical fibers corresponds to approximately 59,9%, and the synthetic fiber polyester, the most used one, represents approximately 63% of the world market. Vital needs have led to the development of multi-function fibers and the focus has changed in the last 10 years with the use of nano technology for environmental responsibility and smart fibers. The study of mechanical properties and fracture mechanisms of fibers is of great relevance for characterization and understanding of causes as consequence of failures. For such reason, it was selected technical fabrics made of high performance synthetic fiber nylon-and-polyester type, used in engineered products such as tires, belts, hoses and pneumatic springs, which have been analyzed in each processing phase. Fiber samples were extracted after each processing phase to be analyzed, by traction destructive tests and scanning electron microscopy. The results of analysis of mechanical properties showed loss of resistance to temperature and multi axial stress during fiber processing phase. Through microscopy tests, it was possible to find contamination, surface stains, plastic deformations, scaling, variations in the fracture faces of the filaments and

  18. Analysis and modeling of coupled thermo-hydro-mechanical phenomena in 3D fractured media

    International Nuclear Information System (INIS)

    Canamon Valera, I.

    2006-11-01

    This doctoral research was conducted as part of a joint France-Spain co-tutelage PhD thesis in the framework of a bilateral agreement between two universities, the Institut National Polytechnique de Toulouse (INPT) and the Universidad Politecnica de Madrid (UPM). It concerns a problem of common interest at the national and international levels, namely, the disposal of radioactive waste in deep geological repositories. The present work is devoted, more precisely, to near-field hydrogeological aspects involving mass and heat transport phenomena. The first part of the work is devoted to a specific data interpretation problem (pressures, relative humidities, temperatures) in a multi-barrier experimental system at the scale of a few meters - the 'Mock-Up Test' of the FEBEX project, conducted in Spain. Over 500 time series are characterized in terms of spatial, temporal, and/or frequency/scale-based statistical analysis techniques. The time evolution and coupling of physical phenomena during the experiment are analyzed, and conclusions are drawn concerning the behavior and reliability of the sensors. The second part of the thesis develops in more detail the 3-Dimensional (3D) modeling of coupled Thermo-Hydro-Mechanical phenomena in a fractured porous rock, this time at the scale of a hundred meters, based on the data of the 'In-Situ Test' of the FEBEX project conducted at the Grimsel Test Site in the Swiss Alps. As a first step, a reconstruction of the 3D fracture network is obtained by Monte Carlo simulation, taking into account through optimization the geomorphological data collected around the FEBEX gallery. The heterogeneous distribution of traces observed on the cylindrical wall of the tunnel is fairly well reproduced in the simulated network. In a second step, we develop a method to estimate the equivalent permeability of a many-fractured block by extending the superposition method of Ababou et al. [1994] to the case where the permeability of the rock matrix is not

  19. Continuum Damage Mechanics A Continuum Mechanics Approach to the Analysis of Damage and Fracture

    CERN Document Server

    Murakami, Sumio

    2012-01-01

    Recent developments in engineering and technology have brought about serious and enlarged demands for reliability, safety and economy in wide range of fields such as aeronautics, nuclear engineering, civil and structural engineering, automotive and production industry.  This, in turn, has caused more interest in continuum damage mechanics and its engineering applications.   This book aims to give a concise overview of the current state of damage mechanics, and then to show the fascinating possibility of this promising branch of mechanics, and to provide researchers, engineers and graduate students with an intelligible and self-contained textbook.   The book consists of two parts and an appendix.  Part I  is concerned with the foundation of continuum damage mechanics.  Basic concepts of material damage and the mechanical representation of damage state of various kinds are described in Chapters 1 and 2.  In Chapters 3-5, irreversible thermodynamics, thermodynamic constitutive theory and its application ...

  20. Effect of strength mismatch on fracture mechanical behavior of NG-DMW

    International Nuclear Information System (INIS)

    Sarikka, T.; Brederholm, A.; Mouginot, R.; Saukkonen, T.; Ahonen, M.; Karjalainen-Roikonen, P.; Nevasmaa, P.; Haenninen, H.

    2015-01-01

    In modern pressurized water reactor (PWR) designs, dissimilar metal joints, e.g. reactor pressure vessel (RPV) safe-ends, are manufactured using a new weld design which takes advantage of narrow-gap (NG) welding technique. In addition to the new weld design, the filler metals have been changed from Alloys 82 and 182 to higher Cr containing Alloys 52 and 152 to ensure the structural integrity of the welds. In dissimilar metal welds (DMW), the mismatch in material properties between the two joined materials and their narrow local variation in different zones of the weld are of importance because the local strength mismatch state plays an important role in the fracture behavior of the weld. For the experimental determination of the local strength variations in a narrow-gap dissimilar metal weld (NG-DMW), a weld mock-up was manufactured using narrow-gap gas-tungsten arc welding (GTAW) method. The weld consisted of SA 508 pressure vessel steel with AISI 309L/308L cladding, AISI 304 piping steel, and Alloy 52 weld metal. The weld was characterized in two different heat treatment conditions, in as-welded condition and in post-weld heat treated (PWHT) condition. The microstructure of the weld mock-up was characterized using FEGSEM. The fusion zone (FZ) between the SA 508 pressure vessel steel and Alloy 52 weld metal was characterized using micro- and nano-hardness testing and the strength mismatch state of the FZ was determined with tensile testing using miniature-sized tensile testing specimens allowing the determination of the local tensile properties of the narrow weld zones near the fusion line (FL). The fracture mechanical testing was performed at room temperature to examine the effect of local strength mismatch on the fracture behavior and crack propagation. The results of the tensile tests revealed that Alloy 52 weld metal had close to equivalent strength with SA 508 base material and the highest strength mismatch existed between the SA 508 heat-affected zone (HAZ

  1. Mechanisms of recharge in a fractured porous rock aquifer in a semi-arid region

    Science.gov (United States)

    Manna, Ferdinando; Walton, Kenneth M.; Cherry, John A.; Parker, Beth L.

    2017-12-01

    Eleven porewater profiles in rock core from an upland exposed sandstone vadose zone in southern California, with thickness varying between 10 and 62 m, were analyzed for chloride (Cl) concentration to examine recharge mechanisms, estimate travel times in the vadose zone, assess spatial and temporal variability of recharge, and determine effects of land use changes on recharge. As a function of their location and the local terrain, the profiles were classified into four groups reflecting the range of site characteristics. Century- to millennium-average recharge varied from 4 to 23 mm y-1, corresponding to zone and in groundwater, the contribution of diffuse flow (estimated at 80%) and preferential flow (20%) to the total recharge was quantified. This model of dual porosity recharge was tested by simulating transient Cl transport along a physically based narrow column using a discrete fracture-matrix numerical model. Using a new approach based on partitioning both water and Cl between matrix and fracture flow, porewater was dated and vertical displacement rates estimated to range in the sandstone matrix from 3 to 19 cm y-1. Moreover, the temporal variability of recharge was estimated and, along each profile, past recharge rates calculated based on the sequence of Cl concentrations in the vadose zone. Recharge rates increased at specific times coincident with historical changes in land use. The consistency between the timing of land use modifications and changes in Cl concentration and the match between observed and simulated Cl concentration values in the vadose zone provide confidence in porewater age estimates, travel times, recharge estimates, and reconstruction of recharge histories. This study represents an advancement of the application of the chloride mass balance method to simultaneously determine recharge mechanisms and reconstruct location-specific recharge histories in fractured porous rock aquifers. The proposed approach can be applied worldwide at sites

  2. Strain rate effects on the mechanical properties and fracture mode of skeletal muscle

    Energy Technology Data Exchange (ETDEWEB)

    Shapiro, Michael; Tovar, Nick; Yoo, Daniel [Biomaterials and Biomimetics, New York University College of Dentistry (United States); Sobieraj, Micheal [Orthopedic Surgery, Hospital for Joint Diseases (United States); Gupta, Nikhil [Mechanical and Aerospace Engineering, NYU-Poly (United States); Branski, Ryan C. [Dept of Otolaryngology, New York University School of Medicine (United States); Coelho, Paulo G., E-mail: pc92@nyu.edu [Biomaterials and Biomimetics, New York University College of Dentistry (United States)

    2014-06-01

    The present study aimed to characterize the mechanical response of beagle sartorius muscle fibers under strain rates that increase logarithmically (0.1 mm/min, 1 mm/min and 10 mm/min), and provide an analysis of the fracture patterns of these tissues via scanning electron microscopy (SEM). Muscle tissue from dogs' sartorius was excised and test specimens were sectioned with a lancet into sections with nominal length, width, and thickness of 7, 2.5 and 0.6 mm, respectively. Trimming of the tissue was done so that the loading would be parallel to the direction of the muscle fiber. Samples were immediately tested following excision and failures were observed under the SEM. No statistically significant difference was observed in strength between the 0.1 mm/min (2.560 ± 0.37 MPa) and the 1 mm/min (2.702 ± 0.55 MPa) groups. However, the 10 mm/min group (1.545 ± 0.50 MPa) had a statistically significant lower strength than both the 1 mm/min group and the 0.1 mm/min group with p < 0.01 in both cases. At the 0.1 mm/min rate the primary fracture mechanism was that of a shear mode failure of the endomysium with a significant relative motion between fibers. At 1 mm/min this continues to be the predominant failure mode. At the 10 mm/min strain rate there is a significant change in the fracture pattern relative to other strain rates, where little to no evidence of endomysial shear failure nor of significant motion between fibers was detected.

  3. Effect of zirconia surface treatment on zirconia/veneer interfacial toughness evaluated by fracture mechanics method.

    Science.gov (United States)

    Wang, Gaoqi; Zhang, Song; Bian, Cuirong; Kong, Hui

    2014-07-01

    The aim of this study was to evaluate the effect of the airborne-particle abrasion and liner application on the interfacial toughness between veneering porcelain and zirconia core by means of a fracture mechanics test. Beam-shaped zirconia specimens were sectioned and divided into 4 groups according to different surface treatments as follows: Group C (control): no treatment; Group L: application of liner; Group A: airborne-particle abrasion with Al2O3 (sandblasting); and Group AL: airborne-particle abrasion and application of liner. The zirconia surfaces before and after sandblasting were observed and analyzed by SEM and white light interferometer. Specimens of each pretreated group were veneered with 3 core/veneer thickness ratios of 2:3, 1:1, and 3:2, corresponding to 3 phase angles respectively. Fracture mechanics test was performed on each specimen, the energy release rate G and phase angle ψ were calculated to characterize interfacial toughness. The experimental data were analyzed statistically using three-way ANOVA and the Tukey's HSD test. The surfaces of fractured specimens were examined by SEM and EDX. At each phase angle, the interfaces with no treatment had higher mean G values than that of other groups. All the specimens showed mixed failure mode with residual veneer or liner on the zirconia surfaces. The toughness of zirconia/veneer interface with no treatment is significantly higher than that of interfaces subjected to liner application and airborne-particle abrasion. Liner application and airborne-particle abrasion seem to reduce zirconia/veneer interfacial toughness. Therefore, the two surface treatment methods should be applied with caution. Copyright © 2014 Elsevier Ltd. All rights reserved.

  4. Study of gas production from shale reservoirs with multi-stage hydraulic fracturing horizontal well considering multiple transport mechanisms

    OpenAIRE

    Guo, Chaohua; Wei, Mingzhen; Liu, Hong

    2018-01-01

    Development of unconventional shale gas reservoirs (SGRs) has been boosted by the advancements in two key technologies: horizontal drilling and multi-stage hydraulic fracturing. A large number of multi-stage fractured horizontal wells (MsFHW) have been drilled to enhance reservoir production performance. Gas flow in SGRs is a multi-mechanism process, including: desorption, diffusion, and non-Darcy flow. The productivity of the SGRs with MsFHW is influenced by both reservoir conditions and hyd...

  5. Standard guide for evaluating data acquisition systems used in cyclic fatigue and fracture mechanics testing

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    1998-01-01

    1.1 This guide covers how to understand and minimize the errors associated with data acquisition in fatigue and fracture mechanics testing equipment. This guide is not intended to be used instead of certified traceable calibration or verification of data acquisition systems when such certification is required. It does not cover static load verification, for which the user is referred to the current revision of Practices E 4, or static extensometer verification, for which the user is referred to the current revision of Practice E 83. The user is also referred to Practice E 467. 1.2 The output of the fatigue and fracture mechanics data acquisition systems described in this guide is essentially a stream of digital data. Such digital data may be considered to be divided into two types- Basic Data, which are a sequence of digital samples of an equivalent analog waveform representing the output of transducers connected to the specimen under test, and Derived Data, which are digital values obtained from the Basic D...

  6. Mean load effect on fatigue of welded joints using structural stress and fracture mechanics approach

    International Nuclear Information System (INIS)

    Kim, Jong Sung; Kim, Cheol; Jin, Tae Eun; Dong, P.

    2006-01-01

    In order to ensure the structural integrity of nuclear welded structures during design life, the fatigue life has to be evaluated by fatigue analysis procedures presented in technical codes such as ASME B and PV Code Section III. However, existing fatigue analysis procedures do not explicitly consider the presence of welded joints. A new fatigue analysis procedure based on a structural stress/fracture mechanics approach has been recently developed in order to reduce conservatism by erasing uncertainty in the analysis procedure. A recent review of fatigue crack growth data under various mean loading conditions using the structural stress/fracture mechanics approach, does not consider the mean loading effect, revealed some significant discrepancies in fatigue crack growth curves according to the mean loading conditions. In this paper, we propose the use of the stress intensity factor range ΔK characterized with loading ratio R effects in terms of the structural stress. We demonstrate the effectiveness in characterizing fatigue crack growth and S-N behavior using the well-known data. It was identified that the S-N data under high mean loading could be consolidated in a master S-N curve for welded joints

  7. Reliability calculation of cracked components using probabilistic fracture mechanics and a Markovian approach

    International Nuclear Information System (INIS)

    Schmidt, T.

    1988-01-01

    The numerical reliability calculation of cracked construction components under cyclical fatigue stress can be done with the help of models of probabilistic fracture mechanics. An alternative to the Monte Carlo simulation method is examined; the alternative method is based on the description of failure processes with the help of a Markov process. The Markov method is traced back directly to the stochastic parameters of a two-dimensional fracture mechanics model, the effects of inspections and repairs also being considered. The probability of failure and expected failure frequency can be determined as time functions with the transition and conditional probabilities of the original or derived Markov process. For concrete calculation, an approximative Markov chain is designed which, under certain conditions, is capable of giving a sufficient approximation of the original Markov process and the reliability characteristics determined by it. The application of the MARKOV program code developed into an algorithm reveals sufficient conformity with the Monte Carlo reference results. The starting point of the investigation was the 'Deutsche Risikostudie B (DWR)' ('German Risk Study B (DWR)'), specifically, the reliability of the main coolant line. (orig./HP) [de

  8. Fracture mechanics study on stress corrosion cracking behavior under corrosive environment

    International Nuclear Information System (INIS)

    Fujii, Tomoyuki; Tohgo, Keiichiro; Shimamura, Yoshinobu; Ishizuka, Naohiro; Takanashi, Masahiro; Itabashi, Yu; Nakayama, Gen; Sakakibara, Yohei; Hirano, Takashi

    2013-01-01

    This paper deals with applicability of non-linear fracture mechanics to crack growth by stress corrosion cracking (SCC) under large-scale yielding and in a plastically deformed area. Crack growth test by compact tension specimen is carried out to evaluate crack growth rate under small-scale and large-scale yielding conditions. To evaluate the crack growth behavior from a crack initiated in a plastically deformed area, crack growth test is also carried out for a very short pre-crack in a plastically deformed four-point bending specimen. Conventional stress intensity factor (K) and equivalent stress intensity factor (K J ) defined by J integral are used as fracture mechanics parameters which characterize the crack growth rate. On da/dt-K diagram, a data band shows wide scatter, especially the crack growth rate in a plastically deformed area is higher than that under small-scale yielding condition. On the other hand, da/dt-K J diagram exhibits narrower scatter on a data band than da/dt-K diagram. The equivalent stress intensity factor is appropriate for characterization of crack growth rate by SCC under small-scale yielding through large scale yielding conditions and in a plastically deformed area. (author)

  9. The application of fracture mechanics to the safety assessment of transport casks for radioactive material

    International Nuclear Information System (INIS)

    Zencker, U.; Mueller, K.; Droste, B.; Roedel, R.; Voelzke, H.

    2004-01-01

    BAM is the responsible authority in Germany for the assessment of the mechanical and thermal design safety of packages for the transport of radioactive materials. The assessment has to cover the brittle fracture safety 'proof of package' for components made of potentially brittle materials. This paper gives a survey of the regulatory and technical requirements for such an assessment according to BAM's new 'Guidelines for the application of ductile cast iron for transport and storage casks for radioactive materials'. Based on these guidelines, higher stresses than before will be permissible, but it is necessary to put more effort into the safety assessment procedure. The fundamentals of such a proof using the methods of fracture mechanics are presented. The recommended procedure takes into account the guidelines of the IAEA's advisory material which are based on the prevention of crack initiation. Examples of BAM's research and safety assessment practices are given. Recommendations for further developments towards package designs with higher acceptable stress levels will conclude the paper. (author)

  10. Fracture mechanics based design for radioactive material transport packagings -- Historical review

    Energy Technology Data Exchange (ETDEWEB)

    Smith, J.A.; Salzbrenner, D.; Sorenson, K.; McConnell, P.

    1998-04-01

    The use of a fracture mechanics based design for the radioactive material transport (RAM) packagings has been the subject of extensive research for more than a decade. Sandia National Laboratories (SNL) has played an important role in the research and development of the application of this technology. Ductile iron has been internationally accepted as an exemplary material for the demonstration of a fracture mechanics based method of RAM packaging design and therefore is the subject of a large portion of the research discussed in this report. SNL`s extensive research and development program, funded primarily by the U. S. Department of Energy`s Office of Transportation, Energy Management and Analytical Services (EM-76) and in an auxiliary capacity, the office of Civilian Radioactive Waste Management, is summarized in this document along with a summary of the research conducted at other institutions throughout the world. In addition to the research and development work, code and standards development and regulatory positions are also discussed.

  11. Structure, thermal and fracture mechanical properties of benzoxazine-modified amine-cured DGEBA epoxy resins

    Directory of Open Access Journals (Sweden)

    2011-03-01

    Full Text Available First, traditional diamine hardeners of epoxy resins (EP were checked as potential accelerators for the benzoxazine (BOX homopolymerization. It was established that the acceleration effect depends on both the type and amount of the diamine compounds. In the follow-up work amine-curable diglycidyl ether bisphenol A (DGEBA type EP was modified with BOX keeping the EP/BOX ratio constant (75/25 wt.%. The amine hardeners, added in the EP in stoichiometric amounts, were of aliphatic and aromatic nature, viz. diethylenetriamine (DETA, 4,4'-diaminodiphenyl methane (DDM, and their 1/1 mixture. The thermal, viscoelastic, flexural and fracture mechanical properties of the EP/BOX hybrids were determined and compared to those of the reference EPs. Based on dynamic-mechanical thermal analysis and atomic force microscopy the formation of co-network between EP and BOX was concluded. Homopolymerized BOX was built in the network in nanoscaled inclusions and it was associated with internal antiplasticization. Incorporation of BOX improved the charring, enhanced the flexural modulus and strength, and reduced the glass transition of the parent EP. The fracture toughness and energy were not improved by hybridization with BOX.

  12. Long-term cumulative survival and mechanical complications of single-tooth Ankylos Implants: focus on the abutment neck fractures.

    Science.gov (United States)

    Shim, Hye Won; Yang, Byoung-Eun

    2015-12-01

    To evaluate the cumulative survival rate (CSR) and mechanical complications of single-tooth Ankylos® implants. This was a retrospective clinical study that analyzed 450 single Ankylos® implants installed in 275 patients between December 2005 and December 2012. The main outcomes were survival results CSR and implant failure) and mechanical complications (screw loosening, fracture, and cumulative fracture rate [CFR]). The main outcomes were analyzed according to age, sex, implant length or diameter, bone graft, arch, and position. The 8-year CSR was 96.9%. Thirteen (2.9%) implants failed because of early osseointegration failure in 3, marginal bone loss in 6, and abutment fracture in 4. Screw loosening occurred in 10 implants (2.2%), and 10 abutment fractures occurred. All abutment fractures were located in the neck, and concurrent screw fractures were observed. The CSR and rate of screw loosening did not differ significantly according to factors. The CFR was higher in middle-aged patients (5.3% vs 0.0% in younger and older patients); for teeth in a molar position (5.8% vs 0.0% for premolar or 1.1% for anterior position); and for larger-diameter implants (4.5% for 4.5 mm and 6.7% for 5.5 mm diameter vs 0.5% for 3.5 mm diameter) (all Ptooth restoration in Koreans. However, relatively frequent abutment fractures (2.2%) were observed and some fractures resulted in implant failures. Middle-aged patients, the molar position, and a large implant diameter were associated with a high incidence of abutment fracture.

  13. Proceedings of the Joint IAEA/CSNI Specialists' Meeting on Fracture Mechanics Verification by Large-Scale Testing

    International Nuclear Information System (INIS)

    1993-10-01

    This report provides the proceedings of a Specialists' Meeting on Fracture Mechanics Verification by Large-Scale Testing that was held in Oak Ridge, Tennessee, on October 23-25, 1992. The meeting was jointly sponsored by the International Atomic Energy Agency (IAEA) and the Nuclear Energy Agency (NEA) of the Organization for Economic Cooperation and Development. In particular, the International Working Group (IWG) on Life Management of Nuclear Power Plants (LMNPP) was the IAEA sponsor, and the Principal Working Group 3 (PWG-3) (Primary System Component Integrity) of the Committee for the Safety of Nuclear Installations (CSNI) was the NEA's sponsor. This meeting was preceded by two prior international activities that were designed to examine the state-of-the-art in fracture analysis capabilities and emphasized applications to the safety evaluation of nuclear power facilities. The first of those two activities was an IAEA Specialists' Meeting on Fracture Mechanics Verification by Large-Scale Testing that was held at the Staatliche Materialprufungsanstalt (MPA) in Stuttgart, Germany, on May 25-27, 1988; the proceedings of that meeting were published 1991.1 The second activity was the CSNI/PWG-3's Fracture Assessment Group's Project FALSIRE (Fracture Analyses of Large-Scale International Reference Experiments). The proceedings of the FALSIRE workshop that was held in Boston, Massachusetts, U.S.A., on May 8-10, 1990, was recently published by the Oak Ridge National Laboratory (ORNL). Those previous activities identified capabilities and shortcomings of various fracture analysis methods based on analyses of six available large-scale experiments. Different modes of fracture behavior, which ranged from brittle to ductile, were considered. In addition, geometry, size, constraint and multiaxial effects were considered. While generally good predictive capabilities were demonstrated for brittle fracture, issues were identified relative to predicting fracture behavior at higher

  14. Mechanics and upscaling of heavy oil bitumen recovery by steam-over-solvent injection in fractured reservoirs method

    Energy Technology Data Exchange (ETDEWEB)

    Singh, R.; Babadagli, T. [Alberta Univ., Edmonton, AB (Canada)

    2011-01-15

    This paper discussed a numerical modelling scheme applied to the steam-over-solvent injection in fractured reservoirs (SOS-FR) method for a single-matrix block. After modelling the process at the core scale, sensitivity tests were performed to determine the optimal injection conditions for efficient oil recovery and solvent retrieval. The basic mechanisms and physics of the process were described along with the amount of injectant and the time required for recovering target oil for field-scale application. In the physics of the recovery mechanism, gravity was found to have a substantial effect on oil recovery when the matrix was exposed to solvent. Special attention was paid to the solvent retrieval rate and amount in the third cycle and the permeability reduction caused by asphaltene precipitation in the solvent injection phase; the latter factor was observed to be substantially critical for the process. An upscaling analysis yielded an encouraging straight-line relationship between the time value to reach ultimate recovery and the matrix size with a non-integer exponent less than 2. 21 refs., 1 tab., 15 figs.

  15. A hybrid-dimensional approach for an efficient numerical modeling of the hydro-mechanics of fractures

    Science.gov (United States)

    Vinci, C.; Renner, J.; Steeb, H.

    2014-02-01

    Characterization of subsurface fluid flow requires accounting for hydro-mechanical coupling between fluid-pressure variations and rock deformation. Particularly, flow of a compressible fluid along compliant hydraulic conduits, such as joints, fractures, or faults, is strongly affected by the associated deformation of the surrounding rock. We investigated and compared two alternative numerical modeling approaches that describe the transient fluid-pressure distribution along a single deformable fracture embedded in a rock matrix. First, we analyzed the coupled hydro-mechanical problem within the framework of Biot's poroelastic equations. Second, in a hybrid-dimensional approach, deformation characteristics of the surrounding rock were combined with a one-dimensional approximation of the fluid-flow problem to account for the high aspect ratios of fractures and the associated numerical problems. A dimensional analysis of the governing equations reveals that the occurring physical phenomena strongly depend on the geometry of the hydraulic conduit and on the boundary conditions. For the analyzed geometries, hydro-mechanical coupling effects dominate and convection effects can be neglected. Numerical solutions for coupled hydro-mechanical phenomena were obtained and compared to field data to characterize the fractured rock in the vicinity of an injection borehole. Either approach captures convection, diffusion, and hydro-mechanical effects, yet the hybrid-dimensional approach is advantageous due to its applicability to problems involving high-aspect-ratio features. For such cases, the modeling of pumping tests by means of the hybrid-dimensional approach showed that the observed inverse-pressure responses are the result of the coupling between the fluid flow in the fracture and the rock deformation caused by fluid-pressure variations along the fracture. Storage capacity as a single parameter of a fracture is insufficient to address all aspects of the coupling.

  16. A predictive mechanical model for evaluating vertebral fracture probability in lumbar spine under different osteoporotic drug therapies.

    Science.gov (United States)

    López, E; Ibarz, E; Herrera, A; Puértolas, S; Gabarre, S; Más, Y; Mateo, J; Gil-Albarova, J; Gracia, L

    2016-07-01

    Osteoporotic vertebral fractures represent a major cause of disability, loss of quality of life and even mortality among the elderly population. Decisions on drug therapy are based on the assessment of risk factors for fracture from bone mineral density (BMD) measurements. A previously developed model, based on the Damage and Fracture Mechanics, was applied for the evaluation of the mechanical magnitudes involved in the fracture process from clinical BMD measurements. BMD evolution in untreated patients and in patients with seven different treatments was analyzed from clinical studies in order to compare the variation in the risk of fracture. The predictive model was applied in a finite element simulation of the whole lumbar spine, obtaining detailed maps of damage and fracture probability, identifying high-risk local zones at vertebral body. For every vertebra, strontium ranelate exhibits the highest decrease, whereas minimum decrease is achieved with oral ibandronate. All the treatments manifest similar trends for every vertebra. Conversely, for the natural BMD evolution, as bone stiffness decreases, the mechanical damage and fracture probability show a significant increase (as it occurs in the natural history of BMD). Vertebral walls and external areas of vertebral end plates are the zones at greatest risk, in coincidence with the typical locations of osteoporotic fractures, characterized by a vertebral crushing due to the collapse of vertebral walls. This methodology could be applied for an individual patient, in order to obtain the trends corresponding to different treatments, in identifying at-risk individuals in early stages of osteoporosis and might be helpful for treatment decisions. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

  17. Fracture mechanics in new designed power module under thermo-mechanical loads

    Directory of Open Access Journals (Sweden)

    Durand Camille

    2014-06-01

    Full Text Available Thermo-mechanically induced failure is a major reliability issue in the microelectronic industry. On this account, a new type of Assembly Interconnected Technology used to connect MOSFETs in power modules has been developed. The reliability is increased by using a copper clip soldered on the top side of the chip, avoiding the use of aluminium wire bonds, often responsible for the failure of the device. Thus the new designed MOSFET package does not follow the same failure mechanisms as standard modules. Thermal and power cycling tests were performed on these new packages and resulting failures were analyzed. Thermo-mechanical simulations including cracks in the aluminium metallization and intermetallics (IMC were performed using Finite Element Analysis in order to better understand crack propagation and module behaviour.

  18. Assessing the Effect of Natural and Induced Fractures on Long-Term CO2 Storage in the Northern Appalachian Basin Using Thermo-Hydro-Mechanical Modeling

    Science.gov (United States)

    Raziperchikolaee, S.; Kelley, M. E.; Main, J.

    2017-12-01

    Natural and induced fractures in a caprock could allow CO2 to migrate out of the intended storage reservoirs in the CO2 sequestration process. We evaluate, through the use of coupled hydro-mechanical numerical modeling, the effectiveness of the Cambrian-Ordovician caprock system in the northern Appalachian Basin for providing long-term containment of CO2 in the presence of existing and induced fractures. Resistivity image and acoustic image logs from wells in the study area were used characterize natural fractures in the caprock zone. The logs showed no compelling evidence of pervasive natural fracturing of the caprock; however, limited natural fractures occur in small isolated patches. Therefore, we modeled natural fractures as isolated features of limited size using the dual-porosity method. The modeling results show that the caprock is effective at preventing CO2 breakthrough in the presence of a natural fracture that partially penetrates the caprock; however, the caprock would be ineffective for containing CO2 if the fracture fully penetrates caprock. To assess induced fractures, coupled fluid-flow, geomechanical, and fracture mechanics modeling was conducted to model the effect of an induced fracture on the sealing integrity of the caprock. First, a fracture mechanics model was used to generate the injection-induced hydraulic fracture and calculate its dimensions (height, length, width). Then, a fluid-flow model was used to evaluate the impacts of the fracture on caprock sealing effectiveness. A significant observation is that the hydraulic fracture was confined to the reservoir (Rose Run sandstone) and did not extend upward into the caprock because the reservoir has the lower minimum horizontal stress. Our study shows that both natural and induced fractures can affect long term CO2 storage depending on size of natural fracture zone, geological and geomechanical properties of reservoir and caprock formations as well as injection parameters.

  19. Setting reinspection intervals for seam welded piping by use of probabilistic fracture mechanics and target reliability values

    International Nuclear Information System (INIS)

    Harris, D.O.; Dedhia, D.

    1995-01-01

    The purpose of this paper is to describe a procedure for the selection of a reinspection interval for defects found during an inspection. The procedure is based on probabilistic fracture mechanics calculations of the reliability of the component into the future and selection of an inspection time based on maintaining the target value reliability. The selection of a target value based on the risk of everyday activities is discussed. The procedure is applied to high temperature seam welded piping as an example, because the probabilistic fracture mechanics tools are relatively readily available and this is a problem of great current interest. The results obtained in the example problem indicate reinspection intervals much shorter than field experience would suggest. This indicates a conservatism in the fracture mechanics procedures and/or lack of accurate characterization of scatter in material properties due to lack of data. The general procedure should prove useful in the disposition of detected cracks in a wide variety of situations

  20. Dependence of the mechanical fracture energy of the polymeric composite material from the mixture of filler fractions

    Directory of Open Access Journals (Sweden)

    E. M. Nurullaev

    2015-01-01

    Full Text Available This paper for the first time presents an equation for calculating the mechanical fracture energy of the polymeric composite material (PCM with regard to the basic formulation parameters. By means of the developed computer program the authors calculated the mechanical fracture energy of the polymer binder of the 3D cross-linked plasticized elastomer filled with multifractional silica. The solution of the integral equation was implemented using the corresponding dependence of stress on relative elongation at uniaxial tension. Engineering application of the theory was considered with respect to asphalt road covering. The authors proposed a generalized dependence of ruptural deformation of the polymer binder from the effective concentration of chemical and physical (intermolecular bonds for calculating the mechanical fracture energy of available and advanced PCMs as filled elastomers.

  1. Development of inelastic constitutive model for type 304 stainless steel and its application to fracture mechanics analysis

    International Nuclear Information System (INIS)

    Takahashi, Yukio

    1993-01-01

    Inelastic deformation plays an important role in the structural integrity of components of liquid metal fast breeder reactors and its accurate assessment is strongly desirable for development of a reliable design procedure. A time-independent plastic constitutive model was developed for this purpose with an emphasis on temperature and temperature history-dependence of cyclic deformation behavior. This model was incorporated into a finite clement code for promoting its use in structural integrity assessment of components. A function of fracture mechanics analysis was also developed. This paper describes both the constitutive model and an example of fracture mechanics analysis. Methods for numerically estimating fracture mechanics parameters were given and their effectiveness was verified by application to a simple problem

  2. The effect of advanced ultrasonic forging on fatigue fracture mechanisms of welded Ti-6A1-4V alloy

    Science.gov (United States)

    Smirnova, A.; Pochivalov, Yu.; Panin, V.; Panin, S.; Eremin, A.; Gorbunov, A.

    2017-12-01

    The current study is devoted to application of advanced postwelding ultrasonic forging to joints formed by laser welding of Ti-6A1-4V alloy in order to enhance their mechanical properties and fatigue durability. Low cycle fatigue tests were performed via digital image correlation technique used to obtain strain fields and in situ characterization of deformation, crack growth and fracture. Fracture surfaces were studied by SEM analysis accompanied with calculation of fracture patterns percentage. The fatigue tests demonstrate the high increase in the number of cycles until fracture (from 17 000 to 32 000 cycles) which could be explained by high ductility of welded material after treatment. This leads to lower fatigue crack growth rate due to higher energy dissipation. The obtained effect is attributable only for small cracks on micro-/mesoscales and fails to play a significant role for macro cracks.

  3. Sensitivity and precision of adverse effects search filters in MEDLINE and EMBASE: a case study of fractures with thiazolidinediones.

    Science.gov (United States)

    Golder, Su; Loke, Yoon K

    2012-03-01

    Search filters have been developed in MEDLINE and EMBASE to help overcome the challenges of searching electronic databases for information on adverse effects. However, little evaluation of their effectiveness has been carried out. To measure the sensitivity and precision of available adverse effects search filters in MEDLINE and EMBASE. A case study systematic review of fracture related adverse effects associated with the use of thiazolidinediones was used. Twelve MEDLINE search strategies and three EMBASE search strategies were tested. Nineteen relevant references from MEDLINE and 24 from EMBASE were included in the review. Four search filters in MEDLINE achieved high sensitivity (95 or 100%) with an improved level of precision from searches without any adverse effects filter. High precision in MEDLINE could also be achieved (up to 53%) using search filters that rely on Medical Subject Headings. No search filter in EMBASE achieved high precision (all were under 5%) and the highest sensitivity in EMBASE was 83%. Adverse effects search filters appear to be effective in MEDLINE for achieving either high sensitivity or high precision. Search filters in EMBASE, however, do not appear as effective, particularly in improving precision. © 2011 The authors. Health Information and Libraries Journal © 2011 Health Libraries Group.

  4. Mechanical properties, fracture surface characterization, and microstructural analysis of six noble dental casting alloys.

    Science.gov (United States)

    Ucar, Yurdanur; Brantley, William A; Johnston, William M; Dasgupta, Tridib

    2011-06-01

    Because noble dental casting alloys for metal ceramic restorations have a wide range of mechanical properties, knowledge of these properties is needed for rational alloy selection in different clinical situations where cast metal restorations are indicated. The purpose of this study was to compare the mechanical properties and examine both the fracture and polished surfaces of 6 noble casting alloys that span many currently marketed systems. Five alloys were designed for metal ceramic restorations, and a sixth Type GPT has Type IV alloy for fixed prosthodontics (Maxigold KF) was included for comparison. Specimens (n=6) meeting dimensional requirements for ISO Standards 9693 and 8891 were loaded to failure in tension using a universal testing machine at a crosshead speed of 2 mm/min. Values of 0.1% and 0.2% yield strength, ultimate tensile strength, elastic modulus, and percentage elongation were obtained. Statistical comparisons of the alloy mechanical properties were made using 1-way ANOVA and the REGW multiple-range test (α=.05). Following fracture surface characterization using scanning electron microscopy (SEM), specimens were embedded in epoxy resin, polished, and again, examined with the SEM. When the multiple comparisons were considered, there were generally no significant differences in the elastic modulus, 0.1% and 0.2% offset yield strength, and ultimate tensile strength for the d.SIGN 91 (Au-Pd), d.SIGN 59 (Pd-Ag), Capricorn 15 (Pd-Ag-Au) and Maxigold KF (Au-Ag-Pd) alloys, except that the ultimate tensile strength was significantly lower (PAg-Pd alloys. Wide variation was found in percentage elongation, with the Pd-Ag and Pd-Ag-Au alloys having the highest values and the Au-Pd-Pt and Au-Ag-Pd alloys having the lowest values. Copyright © 2011 The Editorial Council of the Journal of Prosthetic Dentistry. Published by Mosby, Inc. All rights reserved.

  5. Characteristics of fracture during the approach process and wear mechanism of a silicon AFM tip

    International Nuclear Information System (INIS)

    Chung, Koo-Hyun; Lee, Yong-Ha; Kim, Dae-Eun

    2005-01-01

    The wear of an atomic force microscope (AFM) tip is one of the crucial issues in AFM as well as in other probe-based applications. In this work, wear tests under extremely low normal load using an AFM were conducted. Also, in order to understand the nature of silicon tip wear, the wear characteristics of crystal silicon and amorphous silicon oxide layer were investigated by a high-resolution transmission electron microscope (HRTEM). It was found that fracture of the tip readily occurred due to impact during the approach process. Experimental results showed that the impact should be below 0.1 nN s to avoid significant fracture of the tip. Also, it was observed that wear of the amorphous layer, formed at the end of the tip, occurred at the initial stage of the silicon tip damage process. Based on Archard's wear law, the wear coefficient of the amorphous layer was in the range of 0.009-0.014. As for the wear characteristics of the silicon tip, it was shown that wear occurred gradually under light normal load and the wear rate decreased with increase in the sliding distance. As for the wear mechanism of the silicon tip, oxidation wear was identified to be the most significant. It was shown that the degree of oxidation was higher under high normal load and in a nitrogen environment, oxidation of the silicon tip was reduced

  6. Influences of process parameters and microstructure on the fracture mechanisms of ODS steels

    Energy Technology Data Exchange (ETDEWEB)

    Rouffié, A.L., E-mail: anne-laure.rouffie@cea.fr [CEA, DEN, DANS, DMN, SRMA, Bât 453, F-91191 Gif-sur-Yvette (France); Wident, P.; Ziolek, L. [CEA, DEN, DANS, DMN, SRMA, Bât 453, F-91191 Gif-sur-Yvette (France); Delabrouille, F. [EDF – EDF R and D, Département MMC groupe Métallurgie, 77818 Moret sur Loing (France); Tanguy, B. [CEA, DEN, DANS, DMN, SEMI, Bât 625, F-91191 Gif-sur-Yvette (France); Crépin, J.; Pineau, A. [Mines ParisTech, Centre des Matériaux PM Fourt, UMR CNRS 7633, BP 87, 91003 Evry (France); Garat, V. [AREVA NP, 10 rue J. Récamier, 69006 Lyon (France); Fournier, B. [Manoir Industries, Metallurgy Dept., 12 rue des Ardennes, BP 8401 Pîtres, 27108 Val de Reuil Cedex (France)

    2013-02-15

    The present work investigates the impact response of three ODS steels containing 9%Cr and 14%Cr. These steels were produced by hot extrusion in the shapes of a rod and a plate. The 9%Cr ODS steel has a quasi-isotropic microstructure and is given as a reference material. In comparison, the 14%Cr ODS steel has a strong morphological and crystallographic texture given by the process route. The impact behaviour is anisotropic and the fracture energies are higher when the material is tested in the longitudinal direction compared to the transverse direction. Moreover, the 14%Cr ODS steel has a better impact behaviour when it is extruded in the shape of a rod rather than in the shape of a plate. This work focuses on the fracture mechanisms involved in the ductile to brittle transition regime and in the brittle regime of these materials. In the case of the 14%Cr ODS steel, the cleavage facets observed at very low temperature are much larger than the actual size of the grains. Packets of grains with less than 15° of internal misorientation were defined as effective grains for cleavage. In the transition range, the texture enhances intergranular delamination on the 14%Cr rod material. The occurrence of delamination consumes a lot of energy and tends to enhance scattering in impact energies.

  7. Length-scale and strain rate-dependent mechanism of defect formation and fracture in carbon nanotubes under tensile loading

    Science.gov (United States)

    Javvaji, Brahmanandam; Raha, S.; Mahapatra, D. Roy

    2017-02-01

    Electromagnetic and thermo-mechanical forces play a major role in nanotube-based materials and devices. Under high-energy electron transport or high current densities, carbon nanotubes fail via sequential fracture. The failure sequence is governed by certain length scale and flow of current. We report a unified phenomenological model derived from molecular dynamic simulation data, which successfully captures the important physics of the complex failure process. Length-scale and strain rate-dependent defect nucleation, growth, and fracture in single-walled carbon nanotubes with diameters in the range of 0.47 to 2.03 nm and length which is about 6.17 to 26.45 nm are simulated. Nanotubes with long length and small diameter show brittle fracture, while those with short length and large diameter show transition from ductile to brittle fracture. In short nanotubes with small diameters, we observe several structural transitions like Stone-Wales defect initiation, its propagation to larger void nucleation, formation of multiple chains of atoms, conversion to monatomic chain of atoms, and finally complete fracture of the carbon nanotube. Hybridization state of carbon-carbon bonds near the end cap evolves, leading to the formation of monatomic chain in short nanotubes with small diameter. Transition from ductile to brittle fracture is also observed when strain rate exceeds a critical value. A generalized analytical model of failure is established, which correlates the defect energy during the formation of atomic chain with aspect ratio of the nanotube and strain rate. Variation in the mechanical properties such as elastic modulus, tensile strength, and fracture strain with the size and strain rate shows important implications in mitigating force fields and ways to enhance the life of electronic devices and nanomaterial conversion via fracture in manufacturing.

  8. Length-scale and strain rate-dependent mechanism of defect formation and fracture in carbon nanotubes under tensile loading

    Energy Technology Data Exchange (ETDEWEB)

    Javvaji, Brahmanandam [Indian Institute of Science, Department of Aerospace Engineering (India); Raha, S. [Indian Institute of Science, Department of Computational and Data Sciences (India); Mahapatra, D. Roy, E-mail: droymahapatra@aero.iisc.ernet.in [Indian Institute of Science, Department of Aerospace Engineering (India)

    2017-02-15

    Electromagnetic and thermo-mechanical forces play a major role in nanotube-based materials and devices. Under high-energy electron transport or high current densities, carbon nanotubes fail via sequential fracture. The failure sequence is governed by certain length scale and flow of current. We report a unified phenomenological model derived from molecular dynamic simulation data, which successfully captures the important physics of the complex failure process. Length-scale and strain rate-dependent defect nucleation, growth, and fracture in single-walled carbon nanotubes with diameters in the range of 0.47 to 2.03 nm and length which is about 6.17 to 26.45 nm are simulated. Nanotubes with long length and small diameter show brittle fracture, while those with short length and large diameter show transition from ductile to brittle fracture. In short nanotubes with small diameters, we observe several structural transitions like Stone-Wales defect initiation, its propagation to larger void nucleation, formation of multiple chains of atoms, conversion to monatomic chain of atoms, and finally complete fracture of the carbon nanotube. Hybridization state of carbon-carbon bonds near the end cap evolves, leading to the formation of monatomic chain in short nanotubes with small diameter. Transition from ductile to brittle fracture is also observed when strain rate exceeds a critical value. A generalized analytical model of failure is established, which correlates the defect energy during the formation of atomic chain with aspect ratio of the nanotube and strain rate. Variation in the mechanical properties such as elastic modulus, tensile strength, and fracture strain with the size and strain rate shows important implications in mitigating force fields and ways to enhance the life of electronic devices and nanomaterial conversion via fracture in manufacturing.

  9. Dependence of mechanical characteristics from composition and structure and optimization of mechanical fracture energy of polymer composite material based on high-molecular rubbers

    Directory of Open Access Journals (Sweden)

    E. Nurullaev

    2017-07-01

    Full Text Available By means of numerical experiment the authors investigate dependence of conventional rupturing stress and mechanical fracture energy at uniaxial tension from fractional composition of dispersed filler, plasticizer volume fraction in polymer binder, effective density of transverse bonds, applied to development of covering for different purposes and with advanced service life in temperature range from 223 to 323 K. They compare mechanical characteristics of polymer composite materials (PCMs based on high- and low-molecular rubbers. It was shown that rupturing stress of high-molecular rubber-based PCM is of a higher magnitude than the stress of low-molecular rubber-based one at almost invariable rupturing deformation. Numerical simulation by variation of composition parameters and molecular structure enables evaluation of its maximum fracture energy which is 1000 times higher than mechanical fracture energy of similar composites based on low-molecular rubbers.

  10. Mechanical Integrity of Copper Canister Lid and Cylinder. Sensitivity study

    International Nuclear Information System (INIS)

    Karlsson, Marianne

    2002-08-01

    This report is part of a study of the mechanical integrity of canisters used for disposal of nuclear fuel waste. The overall objective is to determine and ensure the static and long-term strength of the copper canister lid and cylinder casing. The canisters used for disposal nuclear fuel waste of type BWR consists of an inner part (insert) of ductile cast iron and an outer part of copper. The copper canister is to provide a sealed barrier between the contents of the canister and the surroundings. The study in this report complements the finite element analyses performed in an earlier study. The analyses aim to evaluate the sensitivity of the canister to tolerances regarding the gap between the copper cylinder and the cast iron insert. Since great uncertainties regarding the material's long term creep properties prevail, analyses are also performed to evaluate the effect of different creep data on the resulting strain and stress state. The report analyses the mechanical response of the lid and flange of the copper canister when subjected to loads caused by pressure from swelling bentonite and from groundwater at a depth of 500 meter. The loads acting on the canister are somewhat uncertain and the cases investigated in this report are possible cases. Load cases analysed are: Pressure 15 MPa uniformly distributed on lid and 5 MPa uniformly distributed on cylinder; Pressure 5 MPa uniformly distributed on lid and 15 MPa uniformly distributed on cylinder; Pressure 20 MPa uniformly distributed on lid and cylinder; and Side pressures 10 MPa and 20 MPa uniformly distributed on part of the cylinder. Creep analyses are performed for two of the load cases. For all considered designs high principal stresses appear on the outside of the copper cylinder in the region from the weld down to the level of the lid lower edge. Altering the gap between lid and cylinder and/or between cylinder and insert only marginally affects the resulting stress state. Fitting the lid in the cylinder

  11. Hsp90 Sensitivity to ADP Reveals Hidden Regulation Mechanisms.

    Science.gov (United States)

    Halpin, Jackson C; Street, Timothy O

    2017-09-15

    The ATPase cycle of the Hsp90 molecular chaperone is essential for maintaining the stability of numerous client proteins. Extensive analysis has focused on ATP-driven conformational changes of Hsp90; however, little is known about how Hsp90 operates under physiological nucleotide conditions in which both ATP and ADP are present. By quantifying Hsp90 activity under mixed nucleotide conditions, we find dramatic differences in ADP sensitivity among Hsp90 homologs. ADP acts as a strong ATPase inhibitor of cytosol-specific Hsp90 homologs, whereas organellular Hsp90 homologs (Grp94 and TRAP1) are relatively insensitive to the presence of ADP. These results imply that an ATP/ADP heterodimer of cytosolic Hsp90 is the predominant active state under physiological nucleotide conditions. ADP inhibition of human and yeast cytosolic Hsp90 can be relieved by the cochaperone aha1. ADP inhibition of bacterial Hsp90 can be relieved by bacterial Hsp70 and an activating client protein. These results suggest that altering ADP inhibition may be a mechanism of Hsp90 regulation. To determine the molecular origin of ADP inhibition, we identify residues that preferentially stabilize either ATP or ADP. Mutations at these sites can both increase and decrease ADP inhibition. An accounting of ADP is critically important for designing and interpreting experiments with Hsp90. For example, contaminating ADP is a confounding factor in fluorescence resonance energy transfer experiments measuring arm closure rates of Hsp90. Our observations suggest that ADP at physiological levels is important to Hsp90 structure, activity, and regulation. Copyright © 2017 Elsevier Ltd. All rights reserved.

  12. Neural mechanisms of rapid sensitivity to syntactic anomaly

    Directory of Open Access Journals (Sweden)

    Albert E. Kim

    2013-03-01

    Full Text Available Recent psycholinguistic models hypothesize that anticipatory processing can speed the response to linguistic input during language comprehension by pre-activating representations necessary for word recognition. We investigated the neurocognitive mechanisms of anticipatory processing by recording event-related brain responses (ERPs to syntactically anomalous (The thief was caught by for police and well-formed (e.g., The thief was caught by the police sentences. One group of participants saw anomalies elicited by the same word in every instance (e.g., for; low-variability stimuli, providing high affordances for predictions about the word-form appearing in the critical position. A second group saw anomalies elicited by seven different prepositions (at, of, on, for, from, over, with; high-variability stimuli across the study, creating a more difficult prediction task. Syntactic category anomalies enhanced the occipital-temporal N170 component of the ERP, indicating rapid sensitivity—within 200 ms of word onset—to syntactic anomaly. For low-variability but not the high-variability stimuli, syntactic anomaly also enhanced the earlier occipital-temporal P1 component, around 130 ms after word-onset, indicating that affordances for prediction engendered earlier sensitivity to syntactic anomaly. Independent components analysis revealed three sources within the ERP signal whose functional dynamics were consistent with predictive processing and early responses to syntactic anomaly. Distributed neural source modeling (sLORETA of these early-active sources produced a candidate network for early responses to words during reading in the right posterior-occipital, left occipital-temporal, and medial parietal cortex.

  13. FRACTURE MECHANICS UNCERTAINTY ANALYSIS IN THE RELIABILITY ASSESSMENT OF THE REACTOR PRESSURE VESSEL: (2D SUBJECTED TO INTERNAL PRESSURE

    Directory of Open Access Journals (Sweden)

    Entin Hartini

    2016-06-01

    Full Text Available ABSTRACT FRACTURE MECHANICS UNCERTAINTY ANALYSIS IN THE RELIABILITY ASSESSMENT OF THE REACTOR PRESSURE VESSEL: (2D SUBJECTED TO INTERNAL PRESSURE. The reactor pressure vessel (RPV is a pressure boundary in the PWR type reactor which serves to confine radioactive material during chain reaction process. The integrity of the RPV must be guaranteed either  in a normal operation or accident conditions. In analyzing the integrity of RPV, especially related to the crack behavior which can introduce break to the reactor pressure vessel, a fracture mechanic approach should be taken for this assessment. The uncertainty of input used in the assessment, such as mechanical properties and physical environment, becomes a reason that the assessment is not sufficient if it is perfomed only by deterministic approach. Therefore, the uncertainty approach should be applied. The aim of this study is to analize the uncertainty of fracture mechanics calculations in evaluating the reliability of PWR`s reactor pressure vessel. Random character of input quantity was generated using probabilistic principles and theories. Fracture mechanics analysis is solved by Finite Element Method (FEM with  MSC MARC software, while uncertainty input analysis is done based on probability density function with Latin Hypercube Sampling (LHS using python script. The output of MSC MARC is a J-integral value, which is converted into stress intensity factor for evaluating the reliability of RPV’s 2D. From the result of the calculation, it can be concluded that the SIF from  probabilistic method, reached the limit value of  fracture toughness earlier than SIF from  deterministic method.  The SIF generated by the probabilistic method is 105.240 MPa m0.5. Meanwhile, the SIF generated by deterministic method is 100.876 MPa m0.5. Keywords: Uncertainty analysis, fracture mechanics, LHS, FEM, reactor pressure vessels   ABSTRAK ANALISIS KETIDAKPASTIAN FRACTURE MECHANIC PADA EVALUASI KEANDALAN

  14. Hydraulic fracture propagation modeling and data-based fracture identification

    Science.gov (United States)

    Zhou, Jing

    Successful shale gas and tight oil production is enabled by the engineering innovation of horizontal drilling and hydraulic fracturing. Hydraulically induced fractures will most likely deviate from the bi-wing planar pattern and generate complex fracture networks due to mechanical interactions and reservoir heterogeneity, both of which render the conventional fracture simulators insufficient to characterize the fractured reservoir. Moreover, in reservoirs with ultra-low permeability, the natural fractures are widely distributed, which will result in hydraulic fractures branching and merging at the interface and consequently lead to the creation of more complex fracture networks. Thus, developing a reliable hydraulic fracturing simulator, including both mechanical interaction and fluid flow, is critical in maximizing hydrocarbon recovery and optimizing fracture/well design and completion strategy in multistage horizontal wells. A novel fully coupled reservoir flow and geomechanics model based on the dual-lattice system is developed to simulate multiple nonplanar fractures' propagation in both homogeneous and heterogeneous reservoirs with or without pre-existing natural fractures. Initiation, growth, and coalescence of the microcracks will lead to the generation of macroscopic fractures, which is explicitly mimicked by failure and removal of bonds between particles from the discrete element network. This physics-based modeling approach leads to realistic fracture patterns without using the empirical rock failure and fracture propagation criteria required in conventional continuum methods. Based on this model, a sensitivity study is performed to investigate the effects of perforation spacing, in-situ stress anisotropy, rock properties (Young's modulus, Poisson's ratio, and compressive strength), fluid properties, and natural fracture properties on hydraulic fracture propagation. In addition, since reservoirs are buried thousands of feet below the surface, the

  15. Microdamage detection and repair in bone: fracture mechanics, histology, cell biology.

    Science.gov (United States)

    Hazenberg, Jan G; Hentunen, Teuvo A; Heino, Terhi J; Kurata, Kosaku; Lee, Thomas C; Taylor, David

    2009-01-01

    Bone is an elementary component in the human skeleton. It protects vital organs, regulates calcium levels and allows mobility. As a result of daily activities, bones are cyclically strained causing microdamage. This damage, in the form of numerous microcracks, can cause bones to fracture and therefore poses a threat to mechanical integrity. Bone is able to repair the microcracks through a process called remodelling which is tightly regulated by bone forming and resorbing cells. However, the manner by which microcracks are detected, and repair initiated, has not been elucidated until now. Here we show that microcrack accumulation causes damage to the network of cellular processes, resulting in the release of RANKL which stimulates the differentiation of cells specialising in repair.

  16. Scaling of strength and lifetime probability distributions of quasibrittle structures based on atomistic fracture mechanics.

    Science.gov (United States)

    Bazant, Zdenek P; Le, Jia-Liang; Bazant, Martin Z

    2009-07-14

    The failure probability of engineering structures such as aircraft, bridges, dams, nuclear structures, and ships, as well as microelectronic components and medical implants, must be kept extremely low, typically theory for the strength cdf of quasibrittle structure is refined by deriving it from fracture mechanics of nanocracks propagating by small, activation-energy-controlled, random jumps through the atomic lattice. This refinement also provides a plausible physical justification of the power law for subcritical creep crack growth, hitherto considered empirical. The theory is further extended to predict the cdf of structural lifetime at constant load, which is shown to be size- and geometry-dependent. The size effects on structure strength and lifetime are shown to be related and the latter to be much stronger. The theory fits previously unexplained deviations of experimental strength and lifetime histograms from the Weibull distribution. Finally, a boundary layer method for numerical calculation of the cdf of structural strength and lifetime is outlined.

  17. Fracture mechanics analysis for a mooring system subjected to tension and out-of-plane bending

    Science.gov (United States)

    Xue, X.; Chen, N.-Z.

    2017-12-01

    A fracture mechanics analysis for the mooring system of a semi-submersible accounting for out-of-plane bending (OPB) is presented in this paper. Stress ranges acting on the mooring chain links are calculated based on tension and OPB of mooring chain links induced by motions of wave frequency (WF) and low frequency (LF). The narrow-banded method is used for predicting the combined mooring loading process. Initial cracks are assumed to propagate from surfaces of chain links and stress intensity factors are then calculated in terms of stress ranges determined by a finite element analysis. The influence of the OPB on the remaining service life of mooring chain links is investigated and the results show that the remaining service life of mooring chain links connecting to fairleads is significantly reduced due to the OPB effects.

  18. A probabilistic fracture mechanics approach for structural reliability assessment of space flight systems

    Science.gov (United States)

    Sutharshana, S.; Creager, M.; Ebbeler, D.; Moore, N.

    1992-01-01

    A probabilistic fracture mechanics approach for predicting the failure life distribution due to subcritical crack growth is presented. A state-of-the-art crack propagation method is used in a Monte Carlo simulation to generate a distribution of failure lives. The crack growth failure model expresses failure life as a function of stochastic parameters including environment, loads, material properties, geometry, and model specification errors. A stochastic crack growth rate model that considers the uncertainties due to scatter in the data and mode misspecification is proposed. The rationale for choosing a particular type of probability distribution for each stochastic input parameter and for specifying the distribution parameters is presented. The approach is demonstrated through a probabilistic crack growth failure analysis of a welded tube in the Space Shuttle Main Engine. A discussion of the results from this application of the methodology is given.

  19. Addendum to the User Manual for NASGRO Elastic-Plastic Fracture Mechanics Software Module

    Science.gov (United States)

    Gregg, M. Wayne (Technical Monitor); Chell, Graham; Gardner, Brian

    2003-01-01

    The elastic-plastic fracture mechanics modules in NASGRO have been enhanced by the addition of of the following: new J-integral solutions based on the reference stress method and finite element solutions; the extension of the critical crack and critical load modules for cracks with two degrees of freedom that tear and failure by ductile instability; the addition of a proof test analysis module that includes safe life analysis, calculates proof loads, and determines the flaw screening 1 capability for a given proof load; the addition of a tear-fatigue module for ductile materials that simultaneously tear and extend by fatigue; and a multiple cycle proof test module for estimating service reliability following a proof test.

  20. Path dependence of fracture mechanics integrals on the integration area of characteristic integrals

    International Nuclear Information System (INIS)

    Roche, Roland.

    1975-11-01

    The necessary and sufficient conditions for characteristic integrals of fracture mechanics to be independent of area (or integration path), without making any assumptions concerning the behavior of the material are defined. The principle of the method involves comparing the spatial variation in energy density received with that which would result from a spatial variation in strain alone. This introduces a defect vector at each point of the solid. The resultants of the total defect vectors situated within an area are the characteristic integrals of this area. The condition governing independence in a region requires that the defect vector be null at any point. This condition in set under different forms which actually state that the energy density per unit volume received must have the same form of variation in space as in time [fr

  1. The role of fracture mechanics in the design of fuel tanks in space vehicles

    Science.gov (United States)

    Denton, S. J.; Liu, C. K.

    1976-01-01

    With special reference to design of fuel tanks in space vehicles, the principles of fracture mechanics are reviewed. An approximate but extremely simple relationship is derived among the operating stress level, the length of crack, and the number of cycles of failure. Any one of the variables can be computed approximately from the knowledge of the other two, if the loading schedule (mission of the tank) is not greatly altered. Two sample examples illustrating the procedures of determining the allowable safe operating stress corresponding to a set of assumed loading schedule are included. The selection of sample examples is limited by the relatively meager available data on the candidate material for various stress ratios in the cycling.

  2. The mechanism of fracture for entangled polymer liquids in extensional flow

    DEFF Research Database (Denmark)

    Huang, Qian; Yu, Liyun; Skov, Anne Ladegaard

    In uniaxial extensional flow of entangled polymer liquids, different rupture modes may happen, including necking and fracture. Malkin andPetrie [1] proposed a ''master curve'' dividing the flow behavior into four zones based on the stretch rate: (I) Flow zone; (II) Transition zone; (III) Rubbery...... zone; and (IV) Glass-like zone. The master curve shows that steady extensional flow can only be reached in Zone I where thestretch rate is very slow, while rupture happens in Zones II-IV with faster stretch rate. Furthermore, Wang et al. [2-4] reported experimental datathat matches the master curve...... and suggested the mechanism of rupture in Zone III and IV is disentanglement and chain scission, respectively. In this work we measure two groups of entangled polystyrene solutions. In one group the samples have the same entanglement molecular weight (Me) but different number of entanglements (Z...

  3. An Analytical Model for Fatigue Life Prediction Based on Fracture Mechanics and Crack Closure

    DEFF Research Database (Denmark)

    Ibsø, Jan Behrend; Agerskov, Henning

    1996-01-01

    test specimens are compared with fatigue life predictions using a fracture mechanics approach. In the calculation of the fatigue life, the influence of the welding residual stresses and crack closure on the fatigue crack growth is considered. A description of the crack closure model for analytical...... of the analytical fatigue lives. Both the analytical and experimental results obtained show that the Miner rule may give quite unconservative predictions of the fatigue life for the types of stochastic loading studied....... determination of the fatigue life is included. Furthermore, the results obtained in studies of the various parameters that have an influence on the fatigue life, are given. A very good agreement between experimental and analytical results is obtained, when the crack closure model is used in determination...

  4. Deferoxamine restores callus size, mineralization, and mechanical strength in fracture healing after radiotherapy.

    Science.gov (United States)

    Donneys, Alexis; Ahsan, Salman; Perosky, Joseph E; Deshpande, Sagar S; Tchanque-Fossuo, Catherine N; Levi, Benjamin; Kozloff, Ken M; Buchman, Steven R

    2013-05-01

    Therapeutic augmentation of fracture-site angiogenesis with deferoxamine has proven to increase vascularity, callus size, and mineralization in long-bone fracture models. The authors posit that the addition of deferoxamine would enhance pathologic fracture healing in the setting of radiotherapy in a model where nonunions are the most common outcome. Thirty-five Sprague-Dawley rats were divided into three groups. Fracture, irradiated fracture, and irradiated fracture plus deferoxamine. The irradiated fracture and irradiated fracture plus deferoxamine groups received a human equivalent dose of radiotherapy [7 Gy/day for 5 days, (35 Gy)] 2 weeks before mandibular osteotomy and external fixation. The irradiated fracture plus deferoxamine group received injections of deferoxamine into the fracture callus after surgery. After a 40-day healing period, mandibles were dissected, clinically assessed for bony union, imaged with micro-computed tomography, and tension tested to failure. Compared with irradiated fractures, metrics of callus size, mineralization, and strength in deferoxamine-treated mandibles were significantly increased. These metrics were restored to a level demonstrating no statistical difference from control fractures. In addition, the authors observed an increased rate of achieving bony unions in the irradiated fracture plus deferoxamine-treated group when compared with irradiated fracture (67 percent and 20 percent, respectively). The authors' data demonstrate nearly total restoration of callus size, mineralization, and biomechanical strength, and a threefold increase in the rate of union with the use of deferoxamine. The authors' results suggest that the administration of deferoxamine may have the potential for clinical translation as a new treatment paradigm for radiation-induced pathologic fractures.

  5. Analysis of interlaminar fracture toughness and damage mechanisms in composite laminates reinforced with sprayed multi-walled carbon nanotubes

    KAUST Repository

    Almuhammadi, Khaled

    2014-01-01

    The present work is focused on the nanoreinforcement of prepreg based carbon fiber composite laminates to improve delamination resistance. Functionalized multi-walled carbon nanotubes (MWCNTs) were dispersed over the interface between prepreg layers through solvent spraying and the resulting mode I interlaminar fracture toughness was determined. For comparison, baseline samples with neat prepregs were also prepared. Results indicate that the introduction of functionalized MWCNTs can favorably affect the interlaminar fracture toughness, and the associated mechanisms of failure have been investigated. The manufacturing procedures and the interfacial reinforcing mechanism were explored by analyzing (i) the wettability between CNTs-solvent solution and prepreg surface, (ii) CNTs dispersion and (iii) the fractured surfaces through high resolution scanning electron microscopy and Raman mapping. © 2013 Elsevier Ltd.

  6. Some comments about the J1 integral criterion in post yield fracture mechanics

    International Nuclear Information System (INIS)

    Roche, R.L.

    1977-01-01

    Several criteria have been proposed for Post Yield Fracture Mechanics. One of the most interesting ones is the J 1 integral. When the behaviour of material is elastic (even non-linear) it can be shown that J 1 is not path dependent (for a straight crack without thermal stresses). For this reason, it may be considered that J 1 characterizes the crack tip singularity. Extension is easy to deformation-type elastic plastic material, but there is no proof of path independence for flow-type plastic material (incremental plasticity or creep). Experimental results are often given as a proof of J 1 criterion validity, but there is no experimental value of a contour integral and assumptions are made in the use of experimental results. The main assumption implies that the received mechanical work (strain energy) is not dependent on the loading history (is only dependent on mechanical state). A general method to assess J 1 path dependence can be founded on the 'defect vector' (or driving force) concept. It can be shown that the resultant of defects included in a volumne is the J integral on the surface surrounding the volume (and L for the moment). In order to have an empirical idea of the J 1 path independence, it is possible to make computations with finite elements method. Some results are given and it seems that no noticeable path dependence is seen with simple shapes and radial (proportional) loading. A few cases with complex way of loading are also studied. (Auth.)

  7. Correlating mode-I fracture toughness and mechanical properties of heat-treated crystalline rocks

    Directory of Open Access Journals (Sweden)

    Mayukh Talukdar

    2018-02-01

    Full Text Available For the effect of thermal treatment on the mode-I fracture toughness (FT, three crystalline rocks (two basalts and one tonalite were experimentally investigated. Semi-circular bend specimens of the rocks were prepared following the method suggested by the International Society for Rock Mechanics (ISRM and were treated at various temperatures ranging from room temperature (25 °C to 600 °C. Mode-I FT was correlated with tensile strength (TS, ultrasonic velocities, and Young's modulus (YM. Additionally, petrographic and X-ray diffraction analyses were carried out to find the chemical changes resulting from the heat treatment. Further, scanning electron microscopy (SEM was conducted to observe the micro structural changes when subjected to high temperatures. These experiments demonstrate that heat treatment has a strong negative impact on the FT and mechanical properties of the rocks. From room temperature to 600 °C, mode-I FT values of massive basalt, giant plagioclase basalt, and tonalite were reduced by nearly 52%, 68%, and 64%, respectively. Also, at all temperature levels, FT and mechanical properties are found to be exponentially correlated. However, the exact nature of the relationship mainly depends on rock type. Besides, TS was found to be a better indicator of degradation degree than the mode-I FT. SEM images show that micro crack density and structural disintegration of the mineral grains increase with temperature. These physical changes confirm the observed reduction in the stiffness of heat-treated crystalline rocks.

  8. Dense surface seismic data confirm non-double-couple source mechanisms induced by hydraulic fracturing

    Science.gov (United States)

    Pesicek, Jeremy; Cieślik, Konrad; Lambert, Marc-André; Carrillo, Pedro; Birkelo, Brad

    2016-01-01

    We have determined source mechanisms for nine high-quality microseismic events induced during hydraulic fracturing of the Montney Shale in Canada. Seismic data were recorded using a dense regularly spaced grid of sensors at the surface. The design and geometry of the survey are such that the recorded P-wave amplitudes essentially map the upper focal hemisphere, allowing the source mechanism to be interpreted directly from the data. Given the inherent difficulties of computing reliable moment tensors (MTs) from high-frequency microseismic data, the surface amplitude and polarity maps provide important additional confirmation of the source mechanisms. This is especially critical when interpreting non-shear source processes, which are notoriously susceptible to artifacts due to incomplete or inaccurate source modeling. We have found that most of the nine events contain significant non-double-couple (DC) components, as evident in the surface amplitude data and the resulting MT models. Furthermore, we found that source models that are constrained to be purely shear do not explain the data for most events. Thus, even though non-DC components of MTs can often be attributed to modeling artifacts, we argue that they are required by the data in some cases, and can be reliably computed and confidently interpreted under favorable conditions.

  9. On the mechanical interaction between a fluid-filled fracture and the earth's surface

    Science.gov (United States)

    Pollard, D.D.; Holzhausen, G.

    1979-01-01

    The mechanical interaction between a fluid-filled fracture (e.g., hydraulic fracture joint, or igneous dike) and the earth's surface is analyzed using a two-dimensional elastic solution for a slit of arbitrary inclination buried beneath a horizontal free surface and subjected to an arbitrary pressure distribution. The solution is obtained by iteratively superimposing two fundamental sets of analytical solutions. For uniform internal pressure the slit behaves essentially as if it were in an infinite region if the depth-to-center is three times greater than the half-length. For shallower slits interaction with the free surface is pronounced: stresses and displacements near the slit differ by more than 10% from values for the deeply buried slit. The following changes are noted as the depth-to-center decreases: 1. (1) the mode I stress intensity factor increases for both ends of the slit, but more rapidly at the upper end; 2. (2) the mode II stress-intensity factor is significantly different from zero (except for vertical slits) suggesting propagation out of the original plane of the slit; 3. (3) displacements of the slit wall are asymmetric such that the slit gaps open more widely near the upper end. Similar changes are noted if fluid density creates a linear pressure gradient that is smaller than the lithostatic gradient. Under such conditions natural fractures should propagate preferentially upward toward the earth's surface requiring less pressure as they grow in length. If deformation near the surface is of interest, the model should account explicitly for the free surface. Stresses and displacements at the free surface are not approximated very well by values calculated along a line in an infinite region, even when the slit is far from the line. As depth-to-center of a shallow pressurized slit decreases, the following changes are noted: 1. (1) displacements of the free surface increase to the same order of magnitude as the displacements of the slit walls, 2. (2

  10. Structure-Property-Fracture Mechanism Correlation in Heat-Affected Zone of X100 Ferrite-Bainite Pipeline Steel

    Science.gov (United States)

    Li, Xueda; Ma, Xiaoping; Subramanian, S. V.; Misra, R. D. K.; Shang, Chengjia

    2015-03-01

    Structural performance of a weld joint primarily depends on the microstructural characteristics of heat-affected zone (HAZ). In this regard, the HAZ in X100 ferrite-bainite pipeline steel was studied by separating the HAZ into intercritically reheated coarse-grained (ICCG) HAZ containing and non-containing regions. These two regions were individually evaluated for Charpy impact toughness and characterized by electron back-scattered diffraction (EBSD). Low toughness of ~50 J was obtained when the notch of impact specimen encountered ICCGHAZ and high toughness of ~180 J when the notch did not contain ICCGHAZ. Fracture surface was ~60 pct brittle in the absence of ICCGHAZ, and 95 pct brittle (excluding shear lip) in the presence of ICCGHAZ in the impact tested samples. The underlying reason is the microstructure of ICCGHAZ consisted of granular bainite and upper bainite with necklace-type martensite-austenite (M-A) constituent along grain boundaries. The presence of necklace-type M-A constituent notably increases the susceptibility of cleavage microcrack nucleation. ICCGHAZ was found to be both the initiation site of the whole fracture and cleavage facet initiation site during brittle fracture propagation stage. Furthermore, the study of secondary microcracks beneath CGHAZ and ICCGHAZ through EBSD suggested that the fracture mechanism changes from nucleation-controlled in CGHAZ to propagation-controlled in ICCGHAZ because of the presence of necklace-type M-A constituent in ICCGHAZ. Both fracture mechanisms contribute to the poor toughness of the sample contained ICCGHAZ.

  11. Study of the Fracture Mechanisms of Electroplated Metallization Systems Using In Situ Microtension Test

    Science.gov (United States)

    Msolli, Sabeur; Kim, Heung Soo

    2018-03-01

    This framework assesses the mechanical behavior of some potential thin/thick metallization systems in use as either ohmic contacts for diamond semi-conductors or for metallization on copper double bounded ceramic substrates present in the next-generation power electronics packaging. The interesting and unique characteristic of this packaging is the use of diamond as a semi-conductor material instead of silicon to increase the lifetime of embedded power converters for use in aeronautical applications. Theoretically, such packaging is able to withstand temperatures of up to 300 °C without breaking the semi-conductor, provided that the constitutive materials of the packaging are compatible. Metallization is very important to protect the chips and substrates. Therefore, we address this issue in the present work. The tested metallization systems are Ni/Au, Ni/Cr/Au and Ni/Cr. These specific systems were studied since they can be used in conjunction with existing bonding technologies, including AuGe soldering, Ag-In Transient liquid Phase Bonding and silver nanoparticle sintering. The metallization is achieved via electrodeposition, and a mechanical test, consisting of a microtension technique, is carried out at room temperature inside a scanning electron microscopy chamber. The technique permits observations the cracks initiation and growth in the metallization to locate the deformation zones and identify the fracture mechanisms. Different failure mechanisms were shown to occur depending on the metallic layers deposited on top of the copper substrate. The density of these cracks depends on the imposed load and the involved metallization. These observations will help choose the metallization that is compatible with the particular bonding material, and manage mechanical stress due to thermal cycling so that they can be used as a constitutive component for high-temperature power electronics packaging.

  12. A critical review on the application of elastic-plastic fracture mechanics to nuclear pressure vessel and piping systems

    International Nuclear Information System (INIS)

    Scarth, D.A.; Kim, Y.J.; Vanderglas, M.L.

    1985-10-01

    A comprehensive literature survey on the application of Elastic-Plastic Fracture Mechanics to the assessment of the structural integrity of nuclear pressure vessels and piping is presented. In particular, the J-integral/Tearing Modulus (J/T) approach and the Failure Assessment Diagram (FAD) are covered in detail because of their general suitability for use in Ontario Hydro. (25 refs.)

  13. First-order Description of the Mechanical Fracture Behavior of Fine-Grained Surficial Marine Sediments During Gas Bubble Growth

    Science.gov (United States)

    2010-01-01

    shape using an industrial CT scanner. 15. SUBJECT TERMS Linear Elastic Fracture Mechanics; (LEFM) 16. SECURITY CLASSIFICATION OF: a. REPORT...scales. These results do not preclude the visco- elasto-plastic behavior of sediment for all geomechanical problems, but in the case of growing gas

  14. Some aspects of fracture assessment diagrams, plastic zone size corrections and contour integrals in post-yield fracture mechanics

    International Nuclear Information System (INIS)

    Ainsworth, R.A.

    1981-03-01

    The CEGB failure assessment route is briefly described and is shown to be consistent with a plastic zone size correction method. Modifications to the assessment route which have recently been suggested for describing the effects of thermal and residual stresses are examined. It is shown that the plastic zone size correction method may be used to include local thermal and residual stresses in the assessment route in a simple manner. The assessment route is compared with finite-element solutions for a thermal stress problem and with strip-yield model solutions for a residual stress problem. In using finite-element solutions there are different contour integral methods available for calculating a post-yield fracture parameter. The J-integral of Rice and the J*-integral of Blackburn are examined and compared and the appropriate parameter is identified. (author)

  15. Comprehensive analysis of fractures, microstructure, and physical and mechanical properties for the evaluation of the crack resistance of medium-carbon Cr-Ni-Mo steel

    Science.gov (United States)

    Vorob'ev, R. A.; Dubinskii, V. N.; Evstifeeva, V. V.

    2017-10-01

    The crack resistance of the 38CrNi3MoV (34NiCrMoV14—5. 35NiCrMoV12—5) tempered steel (at various tempering temperatures) has been estimated based on a comprehensive study of the steel fractures, microstructure, physical, and mechanical properties. Stress-intensity factor K 1C at the apex of the crack is growing continuously with an increase in the tempering temperature from 200 to 620°C. This indicates that K 1C is a structural-sensitive parameter, which depends on the steel microstructure and submicrostructure, the fracture mechanism that occurs under these structural conditions, the internal stress level, and the existence of microdefects and microcracks. The linear correlation dependence is found between the coefficient K 1C and the transverse velocity V transv. The obtained results reveal that the acoustic method can be used to quickly and efficiently estimate the crack resistance of the thermostrengthened steel without the recourse to labor-consuming mechanical tests and computations of the K 1C value.

  16. TOUGH-RBSN simulator for hydraulic fracture propagation within fractured media: Model validations against laboratory experiments

    Science.gov (United States)

    Kim, Kunhwi; Rutqvist, Jonny; Nakagawa, Seiji; Birkholzer, Jens

    2017-11-01

    This paper presents coupled hydro-mechanical modeling of hydraulic fracturing processes in complex fractured media using a discrete fracture network (DFN) approach. The individual physical processes in the fracture propagation are represented by separate program modules: the TOUGH2 code for multiphase flow and mass transport based on the finite volume approach; and the rigid-body-spring network (RBSN) model for mechanical and fracture-damage behavior, which are coupled with each other. Fractures are modeled as discrete features, of which the hydrological properties are evaluated from the fracture deformation and aperture change. The verification of the TOUGH-RBSN code is performed against a 2D analytical model for single hydraulic fracture propagation. Subsequently, modeling capabilities for hydraulic fracturing are demonstrated through simulations of laboratory experiments conducted on rock-analogue (soda-lime glass) samples containing a designed network of pre-existing fractures. Sensitivity analyses are also conducted by changing the modeling parameters, such as viscosity of injected fluid, strength of pre-existing fractures, and confining stress conditions. The hydraulic fracturing characteristics attributed to the modeling parameters are investigated through comparisons of the simulation results.

  17. Fracture mechanics by three-dimensional crack-tip synchrotron X-ray microscopy.

    Science.gov (United States)

    Withers, P J

    2015-03-06

    To better understand the relationship between the nucleation and growth of defects and the local stresses and phase changes that cause them, we need both imaging and stress mapping. Here, we explore how this can be achieved by bringing together synchrotron X-ray diffraction and tomographic imaging. Conventionally, these are undertaken on separate synchrotron beamlines; however, instruments capable of both imaging and diffraction are beginning to emerge, such as ID15 at the European Synchrotron Radiation Facility and JEEP at the Diamond Light Source. This review explores the concept of three-dimensional crack-tip X-ray microscopy, bringing them together to probe the crack-tip behaviour under realistic environmental and loading conditions and to extract quantitative fracture mechanics information about the local crack-tip environment. X-ray diffraction provides information about the crack-tip stress field, phase transformations, plastic zone and crack-face tractions and forces. Time-lapse CT, besides providing information about the three-dimensional nature of the crack and its local growth rate, can also provide information as to the activation of extrinsic toughening mechanisms such as crack deflection, crack-tip zone shielding, crack bridging and crack closure. It is shown how crack-tip microscopy allows a quantitative measure of the crack-tip driving force via the stress intensity factor or the crack-tip opening displacement. Finally, further opportunities for synchrotron X-ray microscopy are explored.

  18. Thermomechanical Modeling of Sintered Silver - A Fracture Mechanics-based Approach: Extended Abstract: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Paret, Paul P [National Renewable Energy Laboratory (NREL), Golden, CO (United States); DeVoto, Douglas J [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Narumanchi, Sreekant V [National Renewable Energy Laboratory (NREL), Golden, CO (United States)

    2017-09-01

    Sintered silver has proven to be a promising candidate for use as a die-attach and substrate-attach material in automotive power electronics components. It holds promise of greater reliability than lead-based and lead-free solders, especially at higher temperatures (less than 200 degrees Celcius). Accurate predictive lifetime models of sintered silver need to be developed and its failure mechanisms thoroughly characterized before it can be deployed as a die-attach or substrate-attach material in wide-bandgap device-based packages. We present a finite element method (FEM) modeling methodology that can offer greater accuracy in predicting the failure of sintered silver under accelerated thermal cycling. A fracture mechanics-based approach is adopted in the FEM model, and J-integral/thermal cycle values are computed. In this paper, we outline the procedures for obtaining the J-integral/thermal cycle values in a computational model and report on the possible advantage of using these values as modeling parameters in a predictive lifetime model.

  19. Hygrothermal effects on dynamic mechanical snalysis and fracture behavior of polymeric composites

    Directory of Open Access Journals (Sweden)

    Michelle Leali Costa

    2005-09-01

    Full Text Available Polymer composites used above their glass transition temperatures Tg present a substantial degradation of physical properties; therefore a material's glass transition temperature and its change with moisture absorption are of practical importance. Little attention has been paid to the role of the adhesive bonding between the reinforcing fiber and matrix, particularly for BMI matrix. In this work the effect of moisture on the dynamic mechanical behavior and the fiber/matrix interface was investigated. Two systems were evaluated: carbon fabric/epoxy and carbon fabric/bismaleimide laminates. The results demonstrated that the moisture absorbed by the laminates causes either reversible or irreversible plasticization of the matrix. The humidity combined with the temperature effects may cause significant changes in the Tg matrix and toughness affecting the laminate strength. Moisture absorption was correlated to the fracture mode of the laminate demonstrating the deleterious effect of moisture on the interface. This leads to debonding between fiber and matrix. This behavior was investigated by scanning electron microscopy and dynamic mechanical analysis.

  20. Fracture Mechanics Method for Word Embedding Generation of Neural Probabilistic Linguistic Model

    Directory of Open Access Journals (Sweden)

    Size Bi

    2016-01-01

    Full Text Available Word embedding, a lexical vector representation generated via the neural linguistic model (NLM, is empirically demonstrated to be appropriate for improvement of the performance of traditional language model. However, the supreme dimensionality that is inherent in NLM contributes to the problems of hyperparameters and long-time training in modeling. Here, we propose a force-directed method to improve such problems for simplifying the generation of word embedding. In this framework, each word is assumed as a point in the real world; thus it can approximately simulate the physical movement following certain mechanics. To simulate the variation of meaning in phrases, we use the fracture mechanics to do the formation and breakdown of meaning combined by a 2-gram word group. With the experiments on the natural linguistic tasks of part-of-speech tagging, named entity recognition and semantic role labeling, the result demonstrated that the 2-dimensional word embedding can rival the word embeddings generated by classic NLMs, in terms of accuracy, recall, and text visualization.

  1. Nonlinear fracture mechanics investigation on the ductility of reinforced concrete beams

    Directory of Open Access Journals (Sweden)

    A. Carpinteri

    Full Text Available In the present paper, a numerical algorithm based on the finite element method is proposed for the prediction of the mechanical response of reinforced concrete (RC beams under bending loading. The main novelty of such an approach is the introduction of the Overlapping Crack Model, based on nonlinear fracture mechanics concepts, to describe concrete crushing. According to this model, the concrete dam- age in compression is represented by means of a fictitious interpenetration. The larger is the interpenetration, the lower are the transferred forces across the damaged zone. The well-known Cohesive Crack Model in tension and an elastic-perfectly plastic stress versus crack opening displacement relationship describing the steel reinforcement behavior are also integrated into the numerical algorithm. The application of the proposed Cohesive-Overlapping Crack Model to the assessment of the minimum reinforcement amount neces- sary to prevent unstable tensile crack propagation and to the evaluation of the rotational capacity of plastic hinges, permits to predict the size-scale effects evidenced by several experimental programs available in the literature. According to the obtained numerical results, new practical design formulae and diagrams are proposed for the improvement of the current code provisions which usually disregard the size effects.

  2. A fracture mechanics assessment of surface cracks existing in protective layers of multi-layer composite pipes

    Czech Academy of Sciences Publication Activity Database

    Hutař, Pavel; Náhlík, Luboš; Šestáková, Lucie; Ševčík, Martin; Knésl, Zdeněk; Nezbedová, E.

    2010-01-01

    Roč. 92, č. 5 (2010), s. 1120-1125 ISSN 0263-8223 R&D Projects: GA ČR GA106/09/0279 Institutional research plan: CEZ:AV0Z20410507 Keywords : Protective layers * Multi-layer pipes damage * Fracture mechanics * Bi-material interface * Generalized stress intensity factor Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 2.028, year: 2010

  3. Relationship between mechanical sensitivity and postamputation pain: A prospective study

    DEFF Research Database (Denmark)

    Nikolajsen, Lone; IlKjær, Susanne; Jensen, Troels Staehelin

    2000-01-01

    Limb amputation is followed by stump and phantom pain in a large proportion of amputees and postamputation pain may be associated with signs of hyperexcitability such as hyperalgesia to mechanical stimulation. The present study examined the possible relationship between mechanical pain threshold...

  4. Modeling of the fracture behavior of spot welds using advanced micro-mechanical damage models

    International Nuclear Information System (INIS)

    Sommer, Silke

    2010-01-01

    This paper presents the modeling of deformation and fracture behavior of resistance spot welded joints in DP600 steel sheets. Spot welding is still the most commonly used joining technique in automotive engineering. In overloading situations like crash joints are often the weakest link in a structure. For those reasons, crash simulations need reliable and applicable tools to predict the load bearing capacity of spot welded components. Two series of component tests with different spot weld diameters have shown that the diameter of the weld nugget is the main influencing factor affecting fracture mode (interfacial or pull-out fracture), load bearing capacity and energy absorption. In order to find a correlation between nugget diameter, load bearing capacity and fracture mode, the spot welds are simulated with detailed finite element models containing base metal, heat affected zone and weld metal in lap-shear loading conditions. The change in fracture mode from interfacial to pull-out or peel-out fracture with growing nugget diameter under lap-shear loading was successfully modeled using the Gologanu-Leblond model in combination with the fracture criteria of Thomason and Embury. A small nugget diameter is identified to be the main cause for interfacial fracture. In good agreement with experimental observations, the calculated pull-out fracture initiates in the base metal at the boundary to the heat affected zone.

  5. Modeling of the fracture behavior of spot welds using advanced micro-mechanical damage models

    Science.gov (United States)

    Sommer, Silke

    2010-06-01

    This paper presents the modeling of deformation and fracture behavior of resistance spot welded joints in DP600 steel sheets. Spot welding is still the most commonly used joining technique in automotive engineering. In overloading situations like crash joints are often the weakest link in a structure. For those reasons, crash simulations need reliable and applicable tools to predict the load bearing capacity of spot welded components. Two series of component tests with different spot weld diameters have shown that the diameter of the weld nugget is the main influencing factor affecting fracture mode (interfacial or pull-out fracture), load bearing capacity and energy absorption. In order to find a correlation between nugget diameter, load bearing capacity and fracture mode, the spot welds are simulated with detailed finite element models containing base metal, heat affected zone and weld metal in lap-shear loading conditions. The change in fracture mode from interfacial to pull-out or peel-out fracture with growing nugget diameter under lap-shear loading was successfully modeled using the Gologanu-Leblond model in combination with the fracture criteria of Thomason and Embury. A small nugget diameter is identified to be the main cause for interfacial fracture. In good agreement with experimental observations, the calculated pull-out fracture initiates in the base metal at the boundary to the heat affected zone.

  6. Formation of conical fractures in sedimentary basins: Experiments involving pore fluids and implications for sandstone intrusion mechanisms

    Science.gov (United States)

    Mourgues, R.; Bureau, D.; Bodet, L.; Gay, A.; Gressier, J. B.

    2012-01-01

    a flat cone. We make use of a P.I.V. (Particle Imaging Velocimetry) technique to analyse plastic deformation, showing that these inclined fractures are opened in mixed modes. Close to the surface, they change into steep shear bands where fluids can infiltrate. The final morphology of the fracture network is very similar to the common tripartite architecture of various injection complexes, indicating that different mechanisms may be involved in the formation of dykes. Feeder dykes under the sill zones may open as tensile fractures, while overlying dykes may be guided by the deformation induced by the growth of sills. These deformation conditions may also favour the formation of fluid escape structures and pockmarks.

  7. Studies on the influence of metallurgical variables on the stress corrosion behavior of aisi 304 stainless steel in sodium chloride solution using the fracture mechanics approach

    Science.gov (United States)

    Khatak, H. S.; Gnanamoorthy, J. B.; Rodriguez, P.

    1996-05-01

    Stress corrosion data on a nuclear grade AISI type 304 stainless steel in a boiling solution of 5M NaCl+ 0.15M Na2SO4+ 3 mL/L HC1 (bp 381 K) for various metallurgical conditions of the steel are presented in this article. The metallurgical conditions used are solution annealing, sensitization, 10 pct cold work, 20 pct cold work, solution annealing + sensitization, 10 pct cold work + sensi-tization, and 20 pct cold work + sensitization. The fracture mechanics approach has been used to obtain quantitative data on the stress corrosion crack growth rates. The stress intensity factor, K 1, and J integral, J 1, have been used as evaluation parameters. The crack growth rates have been measured using compact tension type samples under both increasing and decreasing stress intensity factors. A crack growth rate of 5 X 10-11 m/s was chosen for the determination of threshold para-meters. Results of the optical microscopic and fractographic examinations are presented. Acoustic signals were recorded during crack growth. Data generated from acoustic emissions, activation energy measurements, and fractographic features indicate hydrogen embrittlement as the possible mechanism of cracking.

  8. A frequency domain analysis to characterize heterogeneity and recharge mechanisms in a fractured crystalline-rock aquifer

    Science.gov (United States)

    Jimenez-Martinez, J.; Longuevergne, L.; Le Borgne, T.; Davy, P.; Bour, O.; Goderniaux, P.; Russian, A.; Thomas, Z.

    2011-12-01

    We investigate aquifer behavior and recharge mechanisms in fracture media using a frequency domain approach. Main interest was the quantification of aquifer characteristic time response, storativity and estimation of heterogeneity and connectivity impact on well behavior on a wide range of temporal scales from 1 day to 8 years. Transfer Functions were calculated for a fractured crystalline-rock aquifer system located in Ploemeur (S of Brittany, France). Recharge, first calculated as effective rainfall, and groundwater level fluctuations (tide effects removed) were used as input and output functions, respectively. The Transfer Function quantifies the ratio of amplitudes of the input and output in the frequency domain. The obtained transfer functions are typically constant at low frequency and decay with frequency for mid and high frequencies. Classical behavior models for interpreting transfer functions are the linear and Dupuit models, plus combination with fast flow component. For linear and Dupuit models, the transfer function |H(ω)|2 scales respectively as |H(ω)|2 ~ ω-2, and |H(ω)|2 ~ ω-1 for high frequencies. The transfer functions obtained for the fractured rock aquifer of Ploemeur do not follow these scaling. Instead, they scale as |H(ω)|2 ~ ω-β, with β=0.7. This suggests that the heterogeneity at different scales in this fractured system involves a variety of transfer processes that cannot be represented by classical models. We discuss the relevance of alternative dual-permeability and multi-permeability models for modeling the rainfall-hydraulic head response in this fractured media. We analyze the variability of the response (characteristic time, amplitude and asymptotic log-log slope) for wells intersecting the main fracture zone, intersecting secondary fracture zones or located in weathered rock.

  9. The feasibility of prefatigued sub size specimens to fracture mechanical studies in inert and in reactor environments

    International Nuclear Information System (INIS)

    Toivonen, A.; Moilanen, P.; Taehtinen, S.; Aaltonen, P.; Wallin, K.

    1998-01-01

    The feasibility of sub size specimens to fracture mechanical tests in inert and in reactor environment is studied in this paper. The need for using sub size specimens has arised from the need to study highly irradiated materials as well as to study localised stress corrosion cracking, i.e. stress corrosion cracking in very narrow heat affected zones for example in welded thin walled pipes. This paper focuses on the effects of high J-integral values on ductile tearing and on environmentally assisted crack growth rate. The main focus is on the stress corrosion tests. The subject is approached first by theoretical discussion. The experimental study consists of J-R tests in air and of slow J-R tests in simulated boiling water reactor (BWR) environment. In most cases the tests were continued until the J-integral level was significantly above the maximum allowable J values for ductile fracture toughness characterisation prescribed in test standards. The results indicate that the measurement capacity of the specimens depends on the specimen dimensions in J-R tests in air, as could be expected. The measurement capacity limitations are not necessarily important in stress corrosion testing as the environmentally assisted crack growth rate can be measured even without exceeding the J-integral limits given in J-R standards. The theoretical and experimental studies indicate that stress corrosion studies are not limited to linear elastic fracture mechanics approach, but elastic plastic fracture mechanics is applicable as well. (author)

  10. Mechanical fracture study of nuclear fuel high burn-up structure (HBS or RIM) during annealing test

    International Nuclear Information System (INIS)

    Marcet, M.

    2010-01-01

    The ceramics used in Power Water Reactors ar made of uranium dioxide. Irradiated at high Burn-up, they present a characteristic zone in periphery called High Burn-Up Structure or RIM zone with micrometer pores containing over-pressurized gas bubbles. Annealing texts simulating incidental or accidental reactor situations, a strong release of the RIM zone is observed. We have considered that the fission gas release mechanism is the mechanical fracture of the RIM grain boundaries. The we have compared the different types of mechanical stress applied to a grain boundary with the fracture stress of the oxide. The first stress is due to RIM over-pressurized gas bubbles, these bubbles apply a stress field determined at a microscopic level i.e. at the gas bubbles scale and its local environment. The second stress is generated by the Pellet-Cladding Mechanical Interaction (PCMI). This stress applies a stress field on a microscopic scale i.e. at the RIM zone and its overall environment. The last stress is occurred by a strain due to the RIM structural evolution during annealing test. The experimental results show that microscopic and macroscopic stress fields to do not explain the RIM grain boundary fracture during annealing test. The stresses induced by the RIM structural evolution as a function of the temperature is a possible mechanism to explain the overall mechanical behavior of the RIM zone during annealing test. (author)

  11. Liquid metal embrittlement of T91 and 316L steels by heavy liquid metals: A fracture mechanics assessment

    Science.gov (United States)

    Auger, T.; Hamouche, Z.; Medina-Almazàn, L.; Gorse, D.

    2008-06-01

    LME of the martensitic T91 and the austenitic 316L steels have been investigated in the CCT geometry in the plane-stress condition. Using such a geometry, premature cracking induced by a liquid metal (PbBi and Hg) can be studied using a fracture mechanics approach based on CTOD, J-Δ a and fracture assessment diagram. One is able to measure a reduction of the crack tip blunting and a reduction of the energy required for crack propagation induced by the liquid metal. In spite of some limitations, this qualitative evaluation shows that liquid metals do not induce strong embrittlement on steels in plane-stress condition. Rather, the effect of the liquid metal seems to promote a fracture mode by plastic collapse linked with strain localization. It indicates that the materials, in spite of a potential embrittlement, should still be acceptable in terms of safety criteria.

  12. Probabilistic fracture mechanics applied for DHC assessment in the cool-down transients for CANDU pressure tubes

    International Nuclear Information System (INIS)

    Radu, Vasile; Roth, Maria

    2012-01-01

    For CANDU pressure tubes made from Zr–2.5%Nb alloy, the mechanism called delayed hydride cracking (DHC) is widely recognized as main mechanism responsible for crack initiation and propagation in the pipe wall. Generation of some blunt flaws at the inner pressure tube surface during refueling by fuel bundle bearing pad or by debris fretting, combined with hydrogen/deuterium up-take (20–40 ppm) from normal corrosion process with coolant, may lead to crack initiation and growth. The process is governed by hydrogen hysteresis of terminal solid solubility limits in Zirconium and the diffusion of hydrogen atoms in the stress gradient near to a stress spot (flaw). Creep and irradiation growth under normal operating conditions promote the specific mechanisms for Zirconium alloys, which result in circumferential expansion, accompanied by wall thinning and length increasing. These complicate damage mechanisms in the case of CANDU pressure tubes that are also are affected by irradiation environment in the reactor core. The structural integrity assessment of CANDU fuel channels is based on the technical requirements and methodology stated in the Canadian Standard N285.8. Usually it works with fracture mechanics principles in a deterministic manner. However, there are inherent uncertainties from the in-service inspection, which are associated with those from material properties determination; therefore a necessary conservatism in deterministic evaluation should be used. Probabilistic approach, based on fracture mechanics principle and appropriate limit state functions defined as fracture criteria, appears as a promising complementary way to evaluate structural integrity of CANDU pressure tubes. To perform this, one has to account for the uncertainties that are associated with the main parameters for pressure tube assessment, such as: flaws distribution and sizing, initial hydrogen concentration, fracture toughness, DHC rate and dimensional changes induced by long term

  13. Fracture mechanics behavior of a Ni-Fe superalloy sheath for superconducting fusion magnets. Pt. 2. Magnet life analysis model

    International Nuclear Information System (INIS)

    Kim, J.H.

    1997-01-01

    For pt.1 see ibid., p.251-67,(1997). From previous results of fatigue crack growth and fracture toughness measurements for a Ni-Fe base superalloy, a primary candidate for the International Thermonuclear Experimental Reactor (ITER) central solenoid (CS) conduit, we derive an improved magnet life analysis model from the framework of Newman and Raju. For the superalloy conduit with an initial semielliptical surface crack in its thickness direction, the model predicts the evolution of crack aspect ratio for a wide range of initial crack geometries under pure tension and bending fatigue. The prediction of final fracture due to fatigue crack growth using the linear elastic fracture mechanics approach is shown to be underconservative. An alternative model based on Newman's elastic-plastic fracture toughness parameter is derived for the base metal with nearly semicircular cracks. The improved life analysis model taking into account the fatigue and fracture behavior is applied to the ITER CS magnet and the results are compared with those from earlier models. Accounting for the crack shape evolution leads to significantly longer life compared to assuming a constant aspect ratio. For the superalloy base metal we find that the expected fatigue life of engineering design activity design of the CS magnet is about eight times the design requirement. Even the conceptual design activity design with a free-standing CS meets the life requirement when analyzed by the improved model. (orig.)

  14. Fracture Profile and Crack Propagation of Ultra-High Strength Hot-Stamped Boron Steel During Mechanical Trimming Process

    Science.gov (United States)

    Han, Xianhong; Yang, Kun; Chen, Sisi; Chen, Jun

    2015-10-01

    Mechanical trimming process for ultra-high strength boron steel after hot stamping was carried out in this study. Shear and tensile tests were designed to analyze the influences of stress state on the fracture mode; trimmed fracture surface and profile were observed and compared to other commonly used steels such as DP980 and Q235 etc.; the crack propagation during trimming process was studied through step-by-step tests. The observation and analysis reveal that the fracture mode of hot-stamped boron steel is highly related to the stress state, it belongs to cleavage fracture on low stress triaxiality but dimple fracture on high stress triaxiality. Such phenomenon is reflected in the trimming process, during which the stress state changes from shear-dominated state to tensile-dominated state. In addition, the burnish zone of trimmed boron steel is much smaller than other high strength steels, and the profile of cutting surface shows an `S'-like shape which is destructive to the trimming tool. Moreover, during the trimming process, most martensite laths near the cutting edge are stretched and rotated markedly to the direction of the shear band, and the main crack expands along those grain boundaries, which may penetrate through a few martensite laths and form small crack branches.

  15. Sensitivity of mechanically transmitted pathogens to different disinfectants

    Science.gov (United States)

    The intensive hands-on activities of greenhouse tomato propagation and production favor the spread of mechanically transmitted pathogens, particularly Clavibacter michiganensis subsp. michiganensis (Cmm), viruses, viroids, and Botrytis cinerea. These pathogens can spread during crop handling, graft...

  16. Nanoindentation and micro-mechanical fracture toughness of electrodeposited nanocrystalline Ni–W alloy films

    International Nuclear Information System (INIS)

    Armstrong, D.E.J.; Haseeb, A.S.M.A.; Roberts, S.G.; Wilkinson, A.J.; Bade, K.

    2012-01-01

    Nanocrystalline nickel–tungsten alloys have great potential in the fabrication of components for microelectromechanical systems. Here the fracture toughness of Ni–12.7 at.%W alloy micro-cantilever beams was investigated. Micro-cantilevers were fabricated by UV lithography and electrodeposition and notched by focused ion beam machining. Load was applied using a nanoindenter and fracture toughness was calculated from the fracture load. Fracture toughness of the Ni–12.7 at.%W was in the range of 1.49–5.14 MPa √m. This is higher than the fracture toughness of Si (another important microelectromechanical systems material), but considerably lower than that of electrodeposited nickel and other nickel based alloys. - Highlights: ► Micro-scale cantilevers manufactured by electro-deposition and focused ion beam machining. ► Nanoindenter used to perform micro-scale fracture test on Ni-13at%W micro-cantilevers. ► Calculation of fracture toughness of electrodeposited Ni-13at%W thin films. ► Fracture toughness values lower than that of nanocrystalline nickel.

  17. Nanoindentation and micro-mechanical fracture toughness of electrodeposited nanocrystalline Ni-W alloy films

    Energy Technology Data Exchange (ETDEWEB)

    Armstrong, D.E.J., E-mail: david.armstrong@materials.ox.ac.uk [Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH (United Kingdom); Haseeb, A.S.M.A. [Department of Mechanical Engineering, University of Malaya, 50603 Kuala Lumpur (Malaysia); Roberts, S.G.; Wilkinson, A.J. [Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH (United Kingdom); Bade, K. [Institut fuer Mikrostrukturtechnik (IMT), Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany)

    2012-04-30

    Nanocrystalline nickel-tungsten alloys have great potential in the fabrication of components for microelectromechanical systems. Here the fracture toughness of Ni-12.7 at.%W alloy micro-cantilever beams was investigated. Micro-cantilevers were fabricated by UV lithography and electrodeposition and notched by focused ion beam machining. Load was applied using a nanoindenter and fracture toughness was calculated from the fracture load. Fracture toughness of the Ni-12.7 at.%W was in the range of 1.49-5.14 MPa {radical}m. This is higher than the fracture toughness of Si (another important microelectromechanical systems material), but considerably lower than that of electrodeposited nickel and other nickel based alloys. - Highlights: Black-Right-Pointing-Pointer Micro-scale cantilevers manufactured by electro-deposition and focused ion beam machining. Black-Right-Pointing-Pointer Nanoindenter used to perform micro-scale fracture test on Ni-13at%W micro-cantilevers. Black-Right-Pointing-Pointer Calculation of fracture toughness of electrodeposited Ni-13at%W thin films. Black-Right-Pointing-Pointer Fracture toughness values lower than that of nanocrystalline nickel.

  18. A ductile fracture mechanics methodology for predicting pressure vessel and piping failure

    International Nuclear Information System (INIS)

    Landes, J.D.; Zhou, Z.

    1991-01-01

    This paper reports on a ductile fracture methodology based on one used more generally for the prediction of fracture behavior that was applied to the prediction of fracture behavior in pressure vessel and piping components. The model uses the load versus displacement record from a fracture toughness test to develop inputs for predicting the behavior of the structural component. The principle of load separation is used to convert the test record into two pieces of information, calibration functions which describe the structural deformation behavior and fracture toughness which describes the response of a crack-like flaw to the loading. These calibration functions and fracture toughness values which relate to the test specimen are then transformed to those appropriate to the structure. Often in this step computation procedures could be used but are not always necessary. The calibration functions and fracture for the structure are recombined to predict a load versus displacement behavior for the structure. The input for the model was generated from tests of compact specimen geometries; this geometry is often used for fracture toughness testing. The predictions were done for five model structures

  19. Proceedings of the 1985 pressure vessels and piping conference. Volume PVP-98-8. Fracture, fatigue and advanced mechanics

    International Nuclear Information System (INIS)

    Short, W.E.; Zamrik, S.Y.

    1985-01-01

    State-of-the-art engineering practices in pressure vessel and piping technology are the result of continual efforts in the evaluation of problems which have been experienced and the development of appropriate design and analysis methods for those applications. The resulting advances in technology benefit industry with properly engineered, safe, cost-effective pressure vessels and piping systems. To this end, advanced study continues in specialized areas of mechanical engineering such as fracture mechanics, experimental stress analysis, high pressure applications and related material considerations, as well as advanced techniques for evaluation of commonly encountered design problems. This volume is comprised of current technical papers on various aspects of fracture, fatigue and advanced mechanics as related to the design and analysis of pressure vessels and piping

  20. Charge dividing mechanism in position-sensitive detectors

    International Nuclear Information System (INIS)

    Radeka, V.; Rehak, P.

    1978-01-01

    A complete charge-division mechanism, including both the diffusion and the electromagnetic wave propagation on resistive electrodes, is presented. The charge injected into such a transmission line divides between the two ends according to the ratio of resistances and independently of the value of the line resistance, of the propagation mechanism and of the distribution of inductance and capacitance along the line. The shortest charge division time is achieved for Rl = 2π (L/C)/sup 1/2), where R, L, C are resistance, inductance and capacitance per unit length and l is the length of the line

  1. Model of mechanical representation of the formation of natural fractures inside a petroleum reservoir; Modele de representation mecanique de la formation des fractures naturelles d'un reservoir petrolier

    Energy Technology Data Exchange (ETDEWEB)

    Picard, D.

    2005-09-15

    The optimisation of the oil production requires a better characterisation of naturally fractured reservoirs. We consider and analyse two spatial distributions. One with systematic joints is arranged in an homogeneous way; joint spacing is linked to individual bedding thickness with propagation frequently interrupted by stratigraphic interfaces (single layer jointing). The second, so-called fracture swarms, consists in fractures clustering, where stratigraphic interfaces seem to play a minor role. The analysis is based on the singularity theory and matched asymptotic expansions method with a fine scale for local perturbations and a global one for general trends. We examine the conditions of fracture propagation that are determined herein using simultaneously two fracture criteria an energy and a stress condition. We consider two modes of loading. Usually, the joint (crack opening mode) and fracture swarm growths are explained by a first order phenomenon involving effective traction orthogonal to fracture plane. Although commonly used, this hypothesis seems unrealistic in many circumstances and may conflict with geological observations. Then, we try to describe fracture growth as a second order phenomena resulting from crack parallel compression. As far as propagation across layer interfaces is concerned, the effect of loading and geometry has been summarised in maps of fracture mechanisms, describing areas of 'step-over', 'straight through propagation' and 'crack arrest'. Fracture criteria, relative size of heterogeneities, contrast of mechanical properties between bed and layer are parameters of the problem. For fracture swarms, we present a discussion bringing out what is reasonable as a loading to justify their morphology. In particular, horizontal effective tension is unable to explain neighbouring joints. Simultaneous propagation of parallel near cracks is explained by finite width cracks growing under the influence of vertical

  2. Non-linear finite element analyses of wide plate fracture mechanics experiments

    International Nuclear Information System (INIS)

    Harrop, L.P.; Gibson, S.

    1988-06-01

    A series of centre-cracked, wide plate fracture mechanics tests is being conducted with plates made from 0.36% carbon steel. This report gives an account of post-test finite element analyses performed to compare with the results of one of these tests (designated CSTP4) and a pre-test analysis of the next test which has a slightly different geometry (CSTP5). The plates are relatively thick (75mm) and have a width of 1.62m. The finite element analyses use a two-dimensional plane stress mesh. The work shows good agreement between the post-test analysis results and the overall experimental results for CSTP4. It is not expected that the analysis results will be accurate within the dimensions of the process zone ahead of the crack tip; the mesh is not sufficient for this. A vital ingredient in attaining the good overall agreement is the representation of the actual stress-strain curve of the material. The predicted response of test CSTP5 is markedly different from that of CSTP4 even though the only change is the increase in the height of the plate. In particular the shape and size of the plastic zone ahead of the crack tip is quite different in the two tests at the same nominal remote applied load. (author)

  3. Low Magnitude Mechanical Signals Reduce Risk-Factors for Fracture during 90-Day Bed Rest

    Science.gov (United States)

    Muir, J. W.; Xia, Y.; Holquin, N.; Judex, S.; Qin, Y.; Evans, H.; Lang, T.; Rubin, C.

    2007-01-01

    Long duration spaceflight leads to multiple deleterious changes to the musculoskeletal system, where loss of bone density, an order of magnitude more severe than that which follows the menopause, combined with increased instability, conspire to elevate the risk of bone fracture due to falls on return to gravitational fields. Here, a ground-based analog for spaceflight is used to evaluate the efficacy of a low-magnitude mechanical intervention, VIBE (Vibrational Inhibition of Bone Erosion), as a potential countermeasure to preserve musculoskeletal integrity in the face of disuse. Twenty-six subjects consented to ninety days of six-degree head-down tilt bed-rest. 18 completed the 90d protocol, 8 of which received daily 10-minute exposure to 30 Hz, 0.3g VIBE, applied in the supine position using a vest elastically coupled to the vibrating platform. The shoulder harness induced a load of 60% of the subjects body weight. At baseline and 90d, Qualitative Ultrasound Scans (QUS) of the calcaneus and CT-scans of the hip and spine were performed to measure changes in bone density. Postural control (PC) was assessed through center of pressure (COP) recordings while subjects stood on a force platform for 4 minutes of quiet stance with eyes closed, and again with eyes opened. As compared to control bedrest subjects,

  4. Pressure vessels design methods using the codes, fracture mechanics and multiaxial fatigue

    Directory of Open Access Journals (Sweden)

    Fatima Majid

    2016-10-01

    Full Text Available This paper gives a highlight about pressure vessel (PV methods of design to initiate new engineers and new researchers to understand the basics and to have a summary about the knowhow of PV design. This understanding will contribute to enhance their knowledge in the selection of the appropriate method. There are several types of tanks distinguished by the operating pressure, temperature and the safety system to predict. The selection of one or the other of these tanks depends on environmental regulations, the geographic location and the used materials. The design theory of PVs is very detailed in various codes and standards API, such as ASME, CODAP ... as well as the standards of material selection such as EN 10025 or EN 10028. While designing a PV, we must design the fatigue of its material through the different methods and theories, we can find in the literature, and specific codes. In this work, a focus on the fatigue lifetime calculation through fracture mechanics theory and the different methods found in the ASME VIII DIV 2, the API 579-1 and EN 13445-3, Annex B, will be detailed by giving a comparison between these methods. In many articles in the literature the uniaxial fatigue has been very detailed. Meanwhile, the multiaxial effect has not been considered as it must be. In this paper we will lead a discussion about the biaxial fatigue due to cyclic pressure in thick-walled PV. Besides, an overview of multiaxial fatigue in PVs is detailed

  5. Fracture mechanics and microstructure in NiTi shape memory alloys

    Energy Technology Data Exchange (ETDEWEB)

    Gollerthan, S. [Institut fuer Werkstoffe, Ruhr-Universitaet Bochum, Universitaetsstrasse 150, D-44801 Bochum (Germany); Young, M.L. [Institut fuer Werkstoffe, Ruhr-Universitaet Bochum, Universitaetsstrasse 150, D-44801 Bochum (Germany)], E-mail: marcus.young@rub.de; Baruj, A.; Frenzel, J. [Institut fuer Werkstoffe, Ruhr-Universitaet Bochum, Universitaetsstrasse 150, D-44801 Bochum (Germany); Schmahl, W.W. [Institut fuer Geologie, Mineralogie und Geophysik, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany); Department of Earth and Environmental Sciences, Materials Research, LMU Munich (Germany); Eggeler, G. [Institut fuer Werkstoffe, Ruhr-Universitaet Bochum, Universitaetsstrasse 150, D-44801 Bochum (Germany)

    2009-02-15

    Crack extension under static loading in pseudoplastic and pseudoelastic binary NiTi shape memory alloy (SMA) compact tension (CT) specimens was examined. Two material compositions of 50.3 at.% Ni (martensitic/pseudoplastic) and 50.7 at.% Ni (austenitic/pseudoelastic) were investigated. The SMAs were characterized using differential scanning calorimetry to identify the phase transformation temperatures and tensile testing to characterize the stress-strain behavior. A miniature CT specimen was developed, which yields reliable critical fracture mechanics parameters. At 295 K, cracks propagate at similar stress intensities of 30{+-}5MPa{radical}(m) into martensite and pseudoelastic austenite. Integrating the miniature CT specimen into a small test device which can be fitted into a scanning electron microscope shows that this is due to cracks propagating into regions of detwinned martensite in both materials. Investigating a pseudoelastic miniature CT specimen in a synchrotron beam proves that martensite forms in front of the crack in the center of the CT specimen, i.e. under plane strain conditions.

  6. Research on Crack Formation in Gypsum Partitions with Doorway by Means of FEM and Fracture Mechanics

    Science.gov (United States)

    Kania, Tomasz; Stawiski, Bohdan

    2017-10-01

    Cracking damage in non-loadbearing internal partition walls is a serious problem that frequently occurs in new buildings within the short term after putting them into service or even before completion of construction. Damage in partition walls is sometimes so great that they cannot be accepted by their occupiers. This problem was illustrated by the example of damage in a gypsum partition wall with doorway attributed to deflection of the slabs beneath and above it. In searching for the deflection which causes damage in masonry walls, fracture mechanics applied to the Finite Element Method (FEM) have been used. For a description of gypsum behaviour, the smeared cracking material model has been selected, where stresses are transferred across the narrowly opened crack until its width reaches the ultimate value. Cracks in the Finite Element models overlapped the real damage observed in the buildings. In order to avoid cracks under the deflection of large floor slabs, the model of a wall with reinforcement in the doorstep zone and a 40 mm thick elastic junction between the partition and ceiling has been analysed.

  7. Development of fracture mechanics data for two hydrazine APU turbine wheel materials

    Science.gov (United States)

    Curbishley, G.

    1975-01-01

    The effects of high temperature, high pressure ammonia were measured on the fracture mechanics and fatigue properties of Astroloy and Rene' 41 turbine wheel materials. Also, the influence of protective coatings on these properties was investigated. Specimens of forged bar stock were subjected to LCF and HCF tests at 950 K (1250 F) and 3.4 MN/sq m (500 psig) pressure, in ammonia containing about 1.5 percent H2O. Aluminized samples (Chromizing Company's Al-870) and gold plated test bars were compared with uncoated specimens. Comparison tests were also run in air at 950 K (1250 F), but at ambient pressures. K sub IE and K sub TH were determined on surface flawed specimens in both the air and ammonia in both uncoated and gold plated conditions. Gold plated specimens exhibited better properties than uncoated samples, and aluminized test bars generally had lower properties. The fatigue properties of specimens tested in ammonia were higher than those tested in air, yet the K sub TH values of ammonia tested samples were lower than those tested in air. However, insufficient specimens were tested to develop significant design data.

  8. Fracture Mechanics Analyses of the Slip-Side Joggle Regions of Wing-Leading Edge Panels

    Science.gov (United States)

    Raju, Ivatury S.; Knight, Norman F., Jr.; Song, Kyongchan; Phillips, Dawn R.

    2010-01-01

    The Space Shuttle Orbiter wing comprises of 22 leading edge panels on each side of the wing. These panels are part of the thermal protection system that protects the Orbiter wings from extreme heating that take place on the reentry in to the earth atmosphere. On some panels that experience extreme heating, liberation of silicon carbon (SiC) coating was observed on the slip side regions of the panels. Global structural and local fracture mechanics analyses were performed on these panels as a part of the root cause investigation of this coating liberation anomaly. The wing-leading-edge reinforced carbon-carbon (RCC) panels, Panel 9, T-seal 10, and Panel 10, are shown in Figure 1 and the progression of the stress analysis models is presented in Figure 2. The global structural analyses showed minimal interaction between adjacent panels and the T-seal that bridges the gap between the panels. A bounding uniform temperature is applied to a representative panel and the resulting stress distribution is examined. For this loading condition, the interlaminar normal stresses showed negligible variation in the chord direction and increased values in the vicinity of the slip-side joggle shoulder. As such, a representative span wise slice on the panel can be taken and the cross section can be analyzed using plane strain analysis.

  9. Mechanical Fracturing of Core-Shell Undercooled Metal Particles for Heat-Free Soldering

    Science.gov (United States)

    Çınar, Simge; Tevis, Ian D.; Chen, Jiahao; Thuo, Martin

    2016-02-01

    Phase-change materials, such as meta-stable undercooled (supercooled) liquids, have been widely recognized as a suitable route for complex fabrication and engineering. Despite comprehensive studies on the undercooling phenomenon, little progress has been made in the use of undercooled metals, primarily due to low yields and poor stability. This paper reports the use of an extension of droplet emulsion technique (SLICE) to produce undercooled core-shell particles of structure; metal/oxide shell-acetate (‘/’ = physisorbed, ‘-’ = chemisorbed), from molten Field’s metal (Bi-In-Sn) and Bi-Sn alloys. These particles exhibit stability against solidification at ambient conditions. Besides synthesis, we report the use of these undercooled metal, liquid core-shell, particles for heat free joining and manufacturing at ambient conditions. Our approach incorporates gentle etching and/or fracturing of outer oxide-acetate layers through mechanical stressing or shearing, thus initiating a cascade entailing fluid flow with concomitant deformation, combination/alloying, shaping, and solidification. This simple and low cost technique for soldering and fabrication enables formation of complex shapes and joining at the meso- and micro-scale at ambient conditions without heat or electricity.

  10. Mechanical Fracturing of Core-Shell Undercooled Metal Particles for Heat-Free Soldering.

    Science.gov (United States)

    Çınar, Simge; Tevis, Ian D; Chen, Jiahao; Thuo, Martin

    2016-02-23

    Phase-change materials, such as meta-stable undercooled (supercooled) liquids, have been widely recognized as a suitable route for complex fabrication and engineering. Despite comprehensive studies on the undercooling phenomenon, little progress has been made in the use of undercooled metals, primarily due to low yields and poor stability. This paper reports the use of an extension of droplet emulsion technique (SLICE) to produce undercooled core-shell particles of structure; metal/oxide shell-acetate ('/' = physisorbed, '-' = chemisorbed), from molten Field's metal (Bi-In-Sn) and Bi-Sn alloys. These particles exhibit stability against solidification at ambient conditions. Besides synthesis, we report the use of these undercooled metal, liquid core-shell, particles for heat free joining and manufacturing at ambient conditions. Our approach incorporates gentle etching and/or fracturing of outer oxide-acetate layers through mechanical stressing or shearing, thus initiating a cascade entailing fluid flow with concomitant deformation, combination/alloying, shaping, and solidification. This simple and low cost technique for soldering and fabrication enables formation of complex shapes and joining at the meso- and micro-scale at ambient conditions without heat or electricity.

  11. A New Approach to the Modeling and Analysis of Fracture through Extension of Continuum Mechanics to the Nanoscale

    KAUST Repository

    Sendova, T.

    2010-02-15

    In this paper we focus on the analysis of the partial differential equations arising from a new approach to modeling brittle fracture based on an extension of continuum mechanics to the nanoscale. It is shown that ascribing constant surface tension to the fracture surfaces and using the appropriate crack surface boundary condition given by the jump momentum balance leads to a sharp crack opening profile at the crack tip but predicts logarithmically singular crack tip stress. However, a modified model, where the surface excess property is responsive to the curvature of the fracture surfaces, yields bounded stresses and a cusp-like opening profile at the crack tip. Further, two possible fracture criteria in the context of the new theory are discussed. The first is an energy-based crack growth condition, while the second employs the finite crack tip stress the model predicts. The classical notion of energy release rate is based upon the singular solution, whereas for the modeling approach adopted here, a notion analogous to the energy release rate arises through a different mechanism associated with the rate of working of the surface excess properties at the crack tip. © The Author(s), 2010.

  12. Pressure-sensitive release mechanism for radiosonde applications

    International Nuclear Information System (INIS)

    Kulhanek, F.C.

    1975-01-01

    As part of the 1975 planetary boundary layer field experimental program, miniature radiosondes attached to pilot balloons were released into the atmosphere for routine sampling of the vertical temperature distribution. A new releasing mechanism used to continue sampling during descent by parachute is described

  13. Some comment on the use of J criterion in elastic plastic fracture mechanics

    International Nuclear Information System (INIS)

    Roche, R.L.

    1978-01-01

    In Post Yield Fracture Mechanics, several criteria have been proposed for the onset of crack propagation, one of the most popular being the J 1 integral criterion. This is only well established for elastic materials, where it can be shown that J 1 is not path dependent, and that J 1 is equal to the variation of potential energy with crack length. Extension is easy for material exhibiting deformation type plasticity, but there is no proof of path independence for flow-type plastic material. Experimental results are often given as a proof of J 1 criterion validity, but a critical analysis shows that important assumptions are made in the use of the test results. The main assumption is that the received work, known as strain energy, is not dependent on the loading history and is only dependent on the mechanical state. The study of the J 1 path dependence is the main point of the J 1 criteria validation. A general method to assess path dependence can be founded on the 'defect vector' (or driving force) concept. The space-density of defect is given by j = grad W - σ grad (W = strain-energy, σ stress tensor, epsilon strain tensor). It is shown that the virtual translation delta a of the defect vectors inside a volume, lead to a virtual work variation given by J 1 delta a and that J 1 is the resultant of all the defect vectors included in the volume surrounded by the integration surface. Using these results the path independence conditions are examined. Some numerical results are given for incremental processes such as plasticity or creep, and where the loading path is radial (proportional) and monotonic, no appreciable path variations found. Finally the results of direct applications of J 1 criterion to real structures are examined. (author)

  14. Modelling of hydro-thermo-mechanical effects in a fracture intersecting a nuclear waste deposition hole

    International Nuclear Information System (INIS)

    Rutqvist, J.; Stephansson, O.; Noorishad, J.; Tsang, C.F.

    1991-01-01

    The groundwater flow in a vertical fracture intersecting a hypothetical nuclear waste deposition hole was examined. After excavation and emplacement of the nuclear waste canister, the aperture of the radial fracture decreased close to the deposition hole. After swelling of the compacted bentonite buffer and when the rock mass has cooled to virgin temperature, the fracture aperture increased adjacent to the deposition hole wall. This causes a fluid flow velocity increase up to more than one order of magnitude adjacent to the deposition hole wall. The far field flow rate through the repository is slightly affected by the swelling of the bentonite buffer

  15. Mechanisms underlying KCNQ1channel cell volume sensitivity

    DEFF Research Database (Denmark)

    Hammami, Sofia

    in which ATP released from the cells in response to volume changes activates signaling pathways that subsequently lead to ion channel stimulation. Whether volume sensitivity of KCNQ1 is modulated by ATP release was investigated in Manuscript II. ATP release from KCNQ1 injected oocytes was monitored...... by a Luciferin/Luciferase assay during cell volume changes and the effect of exogenously added ATP and apyrase on the cell volume induced KCNQ1 current was studied. Based on our data to date, we postulate that KCNQ1 does not seem to be responsive to ATP during cell volume changes, which indicates another...... the level of KCNQ1 surface expression by using an enzyme-linked immunoassay (Manuscript III). To do this, a HA-tagged version of the KCNQ1 channel was expressed with and without KCNE1 in Xenopus oocytes. The results show that the KCNQ1 surface expression was significantly lower when KCNE1 is coexpressed...

  16. Acetabular Fracture

    Directory of Open Access Journals (Sweden)

    Chad Correa

    2017-09-01

    Full Text Available History of present illness: A 77-year-old female presented to her primary care physician (PCP with right hip pain after a mechanical fall. She did not lose consciousness or have any other traumatic injuries. She was unable to ambulate post-fall, so X-rays were ordered by her PCP. Her X-rays were concerning for a right acetabular fracture (see purple arrows, so the patient was referred to the emergency department where a computed tomography (CT scan was ordered. Significant findings: The non-contrast CT images show a minimally displaced comminuted fracture of the right acetabulum involving the acetabular roof, medial and anterior walls (red arrows, with associated obturator muscle hematoma (blue oval. Discussion: Acetabular fractures are quite rare. There are 37 pelvic fractures per 100,000 people in the United States annually, and only 10% of these involve the acetabulum. They occur more frequently in the elderly totaling an estimated 4,000 per year. High-energy trauma is the primary cause of acetabular fractures in younger individuals and these fractures are commonly associated with other fractures and pelvic ring disruptions. Fractures secondary to moderate or minimal trauma are increasingly of concern in patients of advanced age.1 Classification of acetabular fractures can be challenging. However, the approach can be simplified by remembering the three basic types of acetabular fractures (column, transverse, and wall and their corresponding radiologic views. First, column fractures should be evaluated with coronally oriented CT images. This type of fracture demonstrates a coronal fracture line running caudad to craniad, essentially breaking the acetabulum into two halves: a front half and a back half. Secondly, transverse fractures should be evaluated by sagittally oriented CT images. By definition, a transverse fracture separates the acetabulum into superior and inferior halves with the fracture line extending from anterior to posterior

  17. Fracture Mechanics Models for Brittle Failure of Bottom Rails due to Uplift in Timber Frame Shear Walls

    Directory of Open Access Journals (Sweden)

    Joergen L. Jensen

    2016-01-01

    Full Text Available In partially anchored timber frame shear walls, hold-down devices are not provided; hence the uplift forces are transferred by the fasteners of the sheathing-to-framing joints into the bottom rail and via anchor bolts from the bottom rail into the foundation. Since the force in the anchor bolts and the sheathing-to-framing joints do not act in the same vertical plane, the bottom rail is subjected to tensile stresses perpendicular to the grain and splitting of the bottom rail may occur. This paper presents simple analytical models based on fracture mechanics for the analysis of such bottom rails. An existing model is reviewed and several alternative models are derived and compared qualitatively and with experimental data. It is concluded that several of the fracture mechanics models lead to failure load predictions which seem in sufficiently good agreement with the experimental results to justify their application in practical design.

  18. Development of ductile cast iron for spent fuel cask applications using fracture mechanics principles

    International Nuclear Information System (INIS)

    Ray, K.K.; Tiwari, S.; Hemlata Kumari; Mamta Kumari; Kumar, Hemant; Albert, S.K.; Bhaduri, A.K.

    2016-01-01

    The structure-property relations of ductile cast irons (DCIs) with varying Cu content and ~1 wt.% Ni has been investigated with an emphasis on examining their fracture toughness property towards the development of suitable materials for large volume containers for transport of spent fuel. The detailed microstructural characteristics, hardness, tensile and fracture toughness properties of three DCIs were assessed in as-cast and annealed conditions. Fracture toughness values were determined using both ball indentation (K BI ) and J-integral (KJ Ic ) test. The obtained results assist to infer that: (i) the amount of pearlite and nodule count increases with increased amount of Cu, (ii) the hardness and strength values increases whereas fracture toughness values marginally decreases with increased Cu content, and (iii) the magnitudes of K BI estimated using a proposed analysis are in good agreement with KJ Ic values for the as-cast materials. (author)

  19. Aspects of fracture mechanics in cryogenic model design. Part 2: NTF materials

    Science.gov (United States)

    Newman, J. C., Jr.; Lisagor, W. B.

    1983-01-01

    Results of fatigue crack growth and fracture toughness tests conducted on three candidate materials are presented. Fatigue crack growth and fracture toughness tests were conducted on NITRONIC 40 at room temperature and -275 F. Fracture toughness tests were also conducted on Vascomax 200 and 250 maraging steel from room temperature to -320 F. NITRONIC 40 was used to make the Pathfinder 1 model. The fatigue crack growth rate tests were conducted at room temperature and -275 F on three-point notch bend specimens. The fracture toughness tests on the as received and stress relieved materials at -275 F were conducted on the center crack tension specimens. Toughness tests were also conducted on Vascomax CVM-200 and CVM-250 maraging steel from room temperature to -320 F using round and rectangular compact specimens.

  20. Effect of interfragmentary gap on the mechanical behavior of mandibular angle fracture with three fixation designs: A finite element analysis.

    Science.gov (United States)

    Wang, Russell; Liu, Yunfeng; Wang, Joanne Helen; Baur, Dale Allen

    2017-03-01

    The aim of this study was to simulate stress and strain distribution numerically on a normal mandible under physiological occlusal loadings. The results were compared with those of mandibles that had an angle fracture stabilized with different fixation designs under the same loadings. The amount of displacement at two interfragmentary gaps was also studied. A three-dimensional (3D) virtual mandible was reconstructed with an angle fracture that had a fracture gap of either 0.1 or 1 mm. Three types of plate fixation designs were used: Type I, a miniplate was placed across the fracture line following the Champy technique; Type II, two miniplates were used; and Type III, a reconstruction plate was used on the inferior border of the mandible. Loads of 100 and 500 N were applied to the models. The maximum von Mises stress, strain, and displacement were computed using finite element analysis. The results from the control and experimental groups were analyzed and compared. The results demonstrated that high stresses and strains were distributed to the condylar and angular areas regardless of the loading position. The ratio of the plate/bone average stress ranged from 215% (Type II design) to 848% (Type I design) irrespective of the interfragmentary gap size. With a 1-mm fracture gap, the ratio of the plate/bone stress ranged from 204% (Type II design) to 1130% (Type I design). All strains were well below critical bone strain thresholds. Displacement on the cross-sectional mapping at fracture interface indicated that uneven movement occurred in x, y, and z directions. Interfragmentary gaps between 0.1 and 1 mm did not have a substantial effect on the average stress distribution to the fractured bony segments; however, they had a greater effect on the stress distribution to the plates and screws. Type II fixation was the best mechanical design under bite loads. Type I design was the least stable system and had the highest stress distribution and the largest displacement

  1. Experimental study on the mechanism of hydraulic fracture growth in a glutenite reservoir

    Science.gov (United States)

    Ma, Xinfang; Zou, Yushi; Li, Ning; Chen, Ming; Zhang, Yinuo; Liu, Zizhong

    2017-04-01

    Glutenite reservoirs are frequently significantly heterogeneous because of their unique depositional environment. The presence of gravel in this type of formation complicates the growth path of hydraulic fracture (HF). In this study, laboratory fracturing experiments were conducted on six large natural glutenite specimens (300 mm × 300 mm × 300 mm) using a true triaxial hydraulic fracturing system to investigate the growth law of HF in glutenite reservoirs. Before the experiments were performed, the rock properties of the gravel particles and matrix in the glutenite specimens were determined using various apparatuses. The effects of gravel size, horizontal differential stress, fracturing fluid type (or viscosity), and flow rate on the HF growth pattern, fracture width, and injection pressure were examined in detail. Similar to previous studies, four types of HF intersections with gravel particles, namely, termination, penetration, deflection, and attraction, were observed. The HF growth path in the glutenite specimens with large gravel (40 mm-100 mm) is likely branched and tortuous even under high horizontal differential stress. The HF growth path in the glutenite specimens with small gravel (less than 20 mm) is simple, but a process zone with multiple thin fractures may be created. Breakdown pressure may increase significantly when HF initiates from high-strength gravel particles, which are mainly composed of quartz. HF propagation is likely limited within high-strength gravel particles, thereby resulting in narrow fractures and even termination. The use of low-viscosity fluids, such as slickwater, and the low injection rate can further limit HF growth, particularly its width. As a response, high extension pressure builds up during fracturing.

  2. Pressure and pressure derivative analysis for vertical gas and oil wells in stress sensitive homogeneous and naturally fractured formations without type-curve matching

    International Nuclear Information System (INIS)

    Escobar, Freddy Humberto; Cantillo, Jose Humberto; Montealegre M, Matilde

    2007-01-01

    Currently, rock mechanics plays an important role in the oil industry. Effects of reservoir subsidence, compaction and dilation are being taken into account in modern reservoir management of complex systems. On the other hand, pressure well tests run in stress sensitive formations ought to be interpreted with non conventional techniques. During the last three decades, several studies relating transient pressure analysis for characterization of stress sensitive reservoirs have been introduced in the literature. Some of them deal with type curves and/or automated history matching. However, due to the nature of the problem, it does not exist a definitive study focused on the adequate characterization of reservoirs which permeability changes as fluid withdrawal advances; in this paper, the permeability modulus concept introduced by Pedroso (1986) is token as the starting basis. A great number of type curves were generated to study the behavior of the above mentioned formations under stress influence. It was found that permeability modulus, therefore permeability changes, can be correlated with the slope of the pressure derivative trend during the radial flow regime when the reservoir suffers compaction. It is also worth to mention that the time of which the minimum characteristic point of a naturally fractured formation (or the inflection point of o semi-log plot) found on the pressure derivative plot is practically the same for formations without stress influence. This contributes to the extension of the TDS technique, Tiab (1993), so a new methodology to characterize this kind of reservoirs is proposed here. This was verified by the solution of synthetic problems

  3. NATO Advanced Study Institute on Disorder and Fracture

    CERN Document Server

    Roux, S; Guyon, E

    1990-01-01

    Fracture, and particularly brittle fracture, is a good example of an instability. For a homogeneous solid, subjected to a uniform stress field, a crack may appear anywhere in the structure once the threshold stress is reached. However, once a crack has been nucleated in some place, further damage in the solid will in most cases propagate from the initial crack, and not somewhere else in the solid. In this sense fracture is an unstable process. This property makes the process extremely sensitive to any heterogeneity present in the medium, which selects the location of the first crack nucleated. In particular, fracture appears to be very sensitive to disorder, which can favor or impede local cracks. Therefore, in most realistic cases, a good description of fracture mechanics should include the effect of disorder. Recently this need has motivated work in this direction starting from the usual description of fracture mechanics. Parallel with this first trend, statistical physics underwent a very important develop...

  4. Reliability-based sensitivity of mechanical components with arbitrary distribution parameters

    International Nuclear Information System (INIS)

    Zhang, Yi Min; Yang, Zhou; Wen, Bang Chun; He, Xiang Dong; Liu, Qiaoling

    2010-01-01

    This paper presents a reliability-based sensitivity method for mechanical components with arbitrary distribution parameters. Techniques from the perturbation method, the Edgeworth series, the reliability-based design theory, and the sensitivity analysis approach were employed directly to calculate the reliability-based sensitivity of mechanical components on the condition that the first four moments of the original random variables are known. The reliability-based sensitivity information of the mechanical components can be accurately and quickly obtained using a practical computer program. The effects of the design parameters on the reliability of mechanical components were studied. The method presented in this paper provides the theoretic basis for the reliability-based design of mechanical components

  5. The ribs unfolded - a CT visualization algorithm for fast detection of rib fractures: effect on sensitivity and specificity in trauma patients

    International Nuclear Information System (INIS)

    Ringl, Helmut; Lazar, Mathias; Toepker, Michael; Woitek, Ramona; Prosch, Helmut; Asenbaum, Ulrika; Balassy, Csilla; Toth, Daniel; Weber, Michael; Mang, Thomas; Hajdu, Stefan; Soza, Grzegorz; Wimmer, Andreas

    2015-01-01

    To assess a radiologist's detection rate of rib fractures in trauma CT when reading curved planar reformats (CPRs) of the ribs compared to reading standard MPRs. Two hundred and twenty trauma CTs (146 males, 74 females) were retrospectively subjected to a software algorithm to generate CPRs of the ribs. Patients were split into two equal groups. Sixteen patients were excluded due to insufficient segmentation, leaving 107 patients in group A and 97 patients in group B. Two radiologists independently evaluated group A using CPRs and group B using standard MPRs. Two different radiologists reviewed both groups with the inverse methods setting. Results were compared to a standard of reference created by two senior radiologists. The reference standard identified 361 rib fractures in 61 patients. Reading CPRs showed a significantly higher overall sensitivity (P < 0.001) for fracture detection than reading standard MPRs, with 80.9 % (584/722) and 71.5 % (516/722), respectively. Mean reading time was significantly shorter for CPRs (31.3 s) compared to standard MPRs (60.7 s; P < 0.001). Using CPRs for the detection of rib fractures accelerates the reading of trauma patient chest CTs, while offering an increased overall sensitivity compared to conventional standard MPRs. (orig.)

  6. Mechanical analysis of transversal iliac fracture stabilization using dynamic compression plate or screws and PMM in polyurethane bone model

    Directory of Open Access Journals (Sweden)

    T.C. Prada

    Full Text Available ABSTRACT Pelvic fractures correspond to 20 to 30 % of the fractures observed in dogs. Complete fractures, especially with bone axis deviation should be surgically treated. The mechanical study of surgical techniques is of utmost importance to assess the best way of treating these injuries. This study compared, biomechanically, the use of a dynamic compression plate (DCP and screws (group 1 or screws and polymethylmethacrylate (PMMA (group 2 to stabilize an iliac fracture using a static test. Sixteen canine synthetic hemi-pelvises (test specimens with a transverse iliac osteotomy were used. After fixation with implants, a load was applied to the acetabulum until failure. Group 1 maximal compressive load was 133.9±18.60 N, displacement at yield 21.10±3.59mm and stiffness 125.22±12.25N/mm. Group 2 maximal compressive load was 183.50±27.38N, displacement at yield 16.66±5.42mm and stiffness 215.68±33.34N/mm. The stabilization with polymethylmethacrylate was stronger than dynamic compression plate since it resisted a greater load in all test specimens.

  7. Application of probabilistic fracture mechanics to the reliability analysis of pressure-bearing reactor components

    International Nuclear Information System (INIS)

    Schmitt, W.; Roehrich, E.; Wellein, R.

    1977-01-01

    Since no failures in the primary reactor components have been reported so far, it is impossible to estimate the failure probability of those components just by means of statistics. Therefore the way of probabilistic fracture mechanics has been proposed. Here the material properties, the loads and the crack distributions are treated as statistical variables with certain distributions. From the distributions of these data probability density functions can be established for the loading of a component as well as for the resistance of this component. From these functions the failure probability for a given failure mode is easily obtained either by the application of direct integration procedures which are shortly reviewed here, or by the use of Monte Carlo techniques. The most important part of the concept is the collection of a sufficiently large amount of raw data from different sources. These data need to be processed so that they can be transformed into probability density functions. The method of data collection and processing in terms of histograms, plots of probability density functions etc. is described. The choice of the various types of distribution functions is discussed. As an example, the derivation of the probability density function for cracks of a given size in a component is presented. Here the raw data, i.e. the ultrasonic results, are transformed into real crack sizes by means of a conservative conversion rule. The true distribution of the indications is obtained by taking into account a detection probability function. The final probability density function is influenced by the fact that indications exceeding certain values need to be re

  8. Incidence of Dentinal Defects and Vertical Root Fractures after Endodontic Retreatment and Mechanical Cycling.

    Science.gov (United States)

    De Carlo Bello, Mariana; Pillar, Rafael; Mastella Lang, Pauline; Michelon, Carina; Abreu da Rosa, Ricardo; Souza Bier, Carlos Alexandre

    2017-01-01

    The aim of this study was to evaluate the incidence of dentinal defects and vertical root fractures (VRFs) after endodontic retreatment and mechanical cycling (MC). Two hundred mandibular premolars were selected. Forty teeth were left unprepared (control group). The remaining 160 root canals were prepared with ProTaper instruments and filled by using two different techniques [eighty with lateral compaction (LC) and eighty with single-cone (SC)]. Forty canals from each group (LC and SC) received no further treatment. The remaining eighty teeth were divided into two groups (LCR and SCR) ( n =40) in order to undergo the removal of the root filling, re-preparation and refilling with lateral compaction and single-cone, respectively. All of the teeth were subjected to MC (1000000 cycles, 130 N, 2.2 Hz and 37 ° C). The roots were sectioned at 3, 6 and 9 mm from the apex and observed under 20× magnification. The defects were classified as: no defect, VRF and other defects . Statistical analysis was performed using the Fisher's Exact test and the Chi -Squared tests ( α =0.05). MC alone did not promote any other defects or VRFs. Experimental groups presented higher dentinal defects than the control group ( P =0.021). Retreatment groups did not present a higher amount of dentinal defects than the groups that were subjected to the first treatment ( P >0.05). Endodontic treatment and retreatment, regardless of the filling technique and MC, did not influence the occurrence of dentinal defects or VRFs in the human premolars.

  9. The Relationships between Weight Functions, Geometric Functions,and Compliance Functions in Linear Elastic Fracture Mechanics

    Energy Technology Data Exchange (ETDEWEB)

    Yuan, Rong [Univ. of California, Berkeley, CA (United States)

    2007-01-01

    Linear elastic fracture mechanics is widely used in industry because it established simple and explicit relationships between the permissible loading conditions and the critical crack size that is allowed in a structure. Stress intensity factors are the above-mentioned functional expressions that relate load with crack size through geometric functions or weight functions. Compliance functions are to determine the crack/flaw size in a structure when optical inspection is inconvenient. As a result, geometric functions, weight functions and compliance functions have been intensively studied to determine the stress intensity factor expressions for different geometries. However, the relations between these functions have received less attention. This work is therefore to investigate the intrinsic relationships between these functions. Theoretical derivation was carried out and the results were verified on single-edge cracked plate under tension and bending. It is found out that the geometric function is essentially the non-dimensional weight function at the loading point. The compliance function is composed of two parts: a varying part due to crack extension and a constant part from the intact structure if no crack exists. The derivative of the compliance function at any location is the product of the geometric function and the weight function at the evaluation point. Inversely, the compliance function can be acquired by the integration of the product of the geometric function and the weight function with respect to the crack size. The integral constant is just the unchanging compliance from the intact structure. Consequently, a special application of the relations is to obtain the compliance functions along a crack once the geometric function and weight functions are known. Any of the three special functions can be derived once the other two functions are known. These relations may greatly simplify the numerical process in obtaining either geometric functions, weight

  10. Mesh construction for the 2-dimensional computational fracture mechanics using the I-DEAS

    International Nuclear Information System (INIS)

    Kim, Jong Wook; Kim, Tae Wan; Park, Keun Bae

    2000-09-01

    Recently research activities have been reported regarding the generation of the input data for the crack problems at a minimum of effort utilizing the general characteristics of the finite element modeling technique. Several automatic FE mesh generation methods for the cracked structure of particular geometries and boundary conditions have been proposed by using commercial codes or developing in-house programs. In general, development of software to deal with special crack problem can maximize the efficiency and accuracy for a specific environment. However, applicable range of such scheme is usually very restricted and new program should be formed in each case. On the other hand, commercial codes can be used for the automatic mesh generation of variety of geometries, but with an additional effort to accomodate the singular element for the cracked-body analysis. In the present study, a procedure for the generation of input data for the optimized computational fracture mechanics is developed as a series of effort to establish the structural integrity evaluation procedure of SMART reactor vessel assembly. Input data for the finite element analysis are prepared using the commercial code I-DEAS. The midpoint nodes near the crack front are shifted at the quarter-points. The complete finite element model generated is given to another commercial finite element code ABAQUS for the stress analysis. The stress intensity factors are calculated using the J-integral method. To demonstrate the validation of the present procedure, double-edge crack in a plate subjected to uniform tension is solved, and the effects of mesh construction are discussed in detail. The structural integrity evaluation procedure through the 2-D crack modeling is then established

  11. Nose fracture

    Science.gov (United States)

    Fracture of the nose; Broken nose; Nasal fracture; Nasal bone fracture; Nasal septal fracture ... A fractured nose is the most common fracture of the face. It most ... occurs with other fractures of the face. Nose injuries and neck ...

  12. Flaw preparations for HSST program vessel fracture mechanics testing: mechanical-cyclic pumping and electron-beam weld-hydrogen-charge cracking schemes

    International Nuclear Information System (INIS)

    Holz, P.P.

    1980-06-01

    The purpose of the document is to present schemes for flaw preparations in heavy section steel. The ability of investigators to grow representative sharp cracks of known size, location, and orientation is basic to representative field testing to determine data for potential flaw propagation, fracture behavior, and margin against fracture for high-pressure-, high-temperature-service steel vessels subjected to increasing pressurization and/or thermal shock. Gaging for analytical stress and strain procedures and ultrasonic and acoustic emission instrumentation can then be applied to monitor the vessel during testing and to study crack growth. This report presents flaw preparations for HSST fracture mechanics testing. Cracks were grown by two techniques: (1) a mechanical method wherein a premachined notch was sharpened by pressurization and (2) a method combining electron-beam welds and hydrogen charging to crack the chill zone of a rapidly placed autogenous weld. The mechanical method produces a naturally occurring growth shape controlled primarily by the shape of the machined notch; the welding-electrochemical method produces flaws of uniform depth from the surface of a wall or machined notch. Theories, details, discussions, and procedures are covered for both of the flaw-growing schemes

  13. Application of small specimens to fracture mechanics characterization of irradiated pressure vessel steels

    International Nuclear Information System (INIS)

    Sokolov, M.A.; Wallin, K.; McCabe, D.E.

    1996-01-01

    In this study, precracked Charpy V-notch (PCVN) specimens were used to characterize the fracture toughness of unirradiated and irradiated reactor pressure vessel steels in the transition region by means of three-point static bending. Fracture toughness at cleavage instability was calculated in terms of elastic-plastic K Jc values. A statistical size correction based upon weakest-link theory was performed. The concept of a master curve was applied to analyze fracture toughness properties. Initially, size-corrected PCVN data from A 533 grade B steel, designated HSST Plate O2, were used to position the master curve and a 5% tolerance bound for K Jc data. By converting PCVN data to IT compact specimen equivalent K Jc data, the same master curve and 5% tolerance bound curve were plotted against the Electric Power Research Institute valid linear-elastic K Jc database and the ASME lower bound K Ic curve. Comparison shows that the master curve positioned by testing several PCVN specimens describes very well the massive fracture toughness database of large specimens. These results give strong support to the validity of K Jc with respect to K Ic in general and to the applicability of PCVN specimens to measure fracture toughness of reactor vessel steels in particular. Finally, irradiated PCVN specimens of other materials were tested, and the results are compared to compact specimen data. The current results show that PCVNs demonstrate very good capacity for fracture toughness characterization of reactor pressure vessel steels. It provides an opportunity for direct measurement of fracture toughness of irradiated materials by means of precracking and testing Charpy specimens from surveillance capsules. However, size limits based on constraint theory restrict the operational test temperature range for K Jc data from PCVN specimens. 13 refs., 8 figs., 1 tab

  14. Tc1-mediated contact sensitivity reaction, its mechanism and regulation

    Directory of Open Access Journals (Sweden)

    Magdalena Zemelka-Wiącek

    2014-07-01

    Full Text Available The contact hypersensitivity reaction (CHS to haptens is a classic example of cell-mediated immune response. In the effector phase, two stages can be distinguished: an early component, that appears only 2 hours after subsequent contact with the hapten, and the late component that develops approximately 24 hours later which is mediated by TCRαβ+ cells. The effector lymphocytes may be CD4+ T helper 1 (Th1 cells or CD8+ T cytotoxic 1 (Tc1 cells, which depends on the employed hapten and/or mice strain. NKT lymphocytes play the crucial role in the CHS initiation, by supporting B1 cells in the antigen-specific IgM antibodies production. The development of an early component is essential for the recruitment of T effector (Teff cells to the side of hapten deposition and for the complete expansion of inflammatory reaction. The CHS reaction is under T regulatory (Treg cells control, both in the induction phase as well as in the effector phase. A new view of a negative regulation of the Tc1 mediated CHS response is based on the suppression induced by epicutaneous (EC application of protein antigen. The DNP-BSA skin application, on a gauze patch, leads to a state of immunosuppression. This maneuver results in rising the population of Treg cells with TCRαβ+CD4+CD25+Foxp3+ phenotype. The mechanism of suppression requires direct contact between Treg cells and Teff cells and the participation of CTLA-4 molecule is also necessary. The described method of evoking immune tolerance via EC immunization may contribute to elaborate a new method of allergic contact dermatitis therapy. This is because of its effectiveness, ease of induction and non-invasive protein antigen application.

  15. Use of fracture mechanical methods for the investigation of ambient impacts on crack propagation under constantly increased strain

    International Nuclear Information System (INIS)

    Dietzel, W.

    1991-01-01

    The stress corrosion cracking (SCC) of three metallic materials was investigated using both, linear elastic and elastic-plastic fracture mechanics methodologies. By comparison of the experimental results with existing models for the relationship between deformation rate and crack growth velocity additional information pertaining to the mechanisms of environmentally assisted cracking in the corrosion systems investigated was obtained. A proposal for a test procedure is presented, which allows the evaluation of the characteristic SCC parameters K lscc and da/dt in testing times significantly shorter than those required in conventional SCC tests. (orig.) With 61 figs., 8 tabs [de

  16. Effect of nicotine and tobacco administration method on the mechanical properties of healing bone following closed fracture.

    Science.gov (United States)

    Hastrup, Sidsel Gaarn; Chen, Xinqian; Bechtold, Joan E; Kyle, Richard F; Rahbek, Ole; Keyler, Daniel E; Skoett, Martin; Soeballe, Kjeld

    2010-09-01

    We previously showed different effects of tobacco and nicotine on fracture healing, but due to pump reservoir limits, maximum exposure period was 4 weeks. To allow flexibility in pre- and post-fracture exposure periods, the objective of this study was to compare a new oral administration route for nicotine to the established pump method. Four groups were studied: (1) pump saline, (2) pump saline + oral tobacco, (3) pump saline/nicotine + oral tobacco, and (4) pump saline + oral nicotine/tobacco. Sprague-Dawley rats (n = 84) received a transverse femoral fracture stabilized with an intramedullary pin 1 week after initiating dosing. After 3 weeks, no difference was found in torsional strength or stiffness between oral nicotine/tobacco or pump nicotine + tobacco, while energy absorption with oral nicotine/tobacco was greater than pump nicotine + tobacco (p < 0.05). Compared to saline control, strength for oral nicotine/tobacco was higher than control (p < 0.05), and stiffnesses for pump nicotine + tobacco and oral nicotine/tobacco were higher than control (p < 0.05). No differences in energy were found for either nicotine-tobacco group compared to saline control. Mean serum cotinine (stable nicotine metabolite) was different between pump and oral nicotine at 1 and 4 weeks, but all groups were in the range of 1-2 pack/day smokers. In summary, relevant serum cotinine levels can be reached in rats with oral nicotine, and, in the presence of tobacco, nicotine can influence mechanical aspects of fracture healing, dependent on administration method. Caution should be exercised when comparing results of fracture healing studies using different methods of nicotine administration. (c) 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.

  17. Fracture mechanics characterisation of the WWER-440 reactor pressure vessel beltline welding seam of Greifswald unit 8

    Energy Technology Data Exchange (ETDEWEB)

    Viehrig, Hans-Werner; Schuhknecht, Jan [Forschungszentrum Dresden-Rossendorf (Germany)

    2008-07-01

    WWER-440 second generation (V-213) reactor pressure vessels (RPV) were produced by IZHORA in Russia and by SKODA in the former Czechoslovakia. The surveillance Charpy-V and fracture mechanics SE(B) specimens of both producers have different orientations. The main difference is the crack extension direction which is through the RPV thickness and circumferential for ISHORA and SKODA RPV, respectively. In particular for the investigation of weld metal from multilayer submerged welding seams the crack extension direction is of importance. Depending on the crack extension direction in the specimen there are different welding beads or a uniform structure along the crack front. The specimen orientation becomes more important when the fracture toughness of the weld metal is directly determined on surveillance specimens according to the Master Curve (MC) approach as standardised in the ASTM Standard Test Method E1921. This approach was applied on weld metal of the RPV beltline welding seam of Greifswald Unit 8 RPV. Charpy size SE(B) specimens from 13 locations equally spaced over the thickness of the welding seam were tested. The specimens are in TL and TS orientation. The fracture toughness values measured on the SE(B) specimens with both orientations follow the course of the MC. Nearly all values lie within the fracture toughness curves for 5% and 95% fracture probability. There is a strong variation of the reference temperature T{sub 0} though the thickness of the welding seam, which can be explained with structural differences. The scatter is more pronounced for the TS SE(B) specimens. It can be shown that specimens with TS and TL orientation in the welding seam have a differentiating and integrating behaviour, respectively. The statistical assumptions behind the MC approach are valid for both specimen orientations even if the structure is not uniform along the crack front. By comparison crack extension, JR, curves measured on SE(B) specimens with TL and TS orientation

  18. Mechanical and hydraulic performance of sludge-mixed cement grout in rock fractures

    Directory of Open Access Journals (Sweden)

    Khomkrit Wetchasat

    2014-08-01

    Full Text Available The objective is to assess the performance of sludge mixed with commercial grade Portland cement type I for use in minimizing the permeability of fractured rock mass. The fractures were artificially made by applying a line load to sandstone block specimens. The sludge comprises over 80% of quartz with grain sizes less than 75 μm. The results indicate that the mixing ratios of sludge:cement (S:C of 1:10, 3:10, 5:10 with water:cement ratio of 1:1 by weight are suitable for fracture grouting. For S:C = 3:10, the compressive strength and elastic modulus are 1.22 MPa and 224 MPa which are comparable to those of bentonite mixed with cement. The shear strengths between the grouts and fractures surfaces are from 0.22 to 0.90 MPa. The S:C ratio of 5:10 gives the lowest permeability. The permeability of grouted fractures with apertures of 2, 10, and 20 mm range from 10-16 to 10-14 m2 and decrease with curing time.

  19. Mechanisms of Plastic and Fracture Instabilities for Alloy Development of Fusion Materials. Final Project Report for period July 15, 1998 - July 14, 2003

    International Nuclear Information System (INIS)

    Ghoniem, N.M.

    2003-01-01

    The main objective of this research was to develop new computational tools for the simulation and analysis of plasticity and fracture mechanisms of fusion materials, and to assist in planning and assessment of corresponding radiation experiments

  20. Mechanisms of Plastic and Fracture Instabilities for Alloy Development of Fusion Materials. Final Project Report for period July 15, 1998 - July 14, 2003

    Energy Technology Data Exchange (ETDEWEB)

    Ghoniem, N. M.

    2003-07-14

    The main objective of this research was to develop new computational tools for the simulation and analysis of plasticity and fracture mechanisms of fusion materials, and to assist in planning and assessment of corresponding radiation experiments.

  1. Laboratory mechanical parameters of composite resins and their relation to fractures and wear in clinical trials-A systematic review.

    Science.gov (United States)

    Heintze, Siegward D; Ilie, Nicoleta; Hickel, Reinhard; Reis, Alessandra; Loguercio, Alessandro; Rousson, Valentin

    2017-03-01

    To evaluate a range of mechanical parameters of composite resins and compare the data to the frequency of fractures and wear in clinical studies. Based on a search of PubMed and SCOPUS, clinical studies on posterior composite restorations were investigated with regard to bias by two independent reviewers using Cochrane Collaboration's tool for assessing risk of bias in randomized trials. The target variables were chipping and/or fracture, loss of anatomical form (wear) and a combination of both (summary clinical index). These outcomes were modelled by time and material in a linear mixed effect model including random study and experiment effects. The laboratory data from one test institute were used: flexural strength, flexural modulus, compressive strength, and fracture toughness (all after 24-h storage in distilled water). For some materials flexural strength data after aging in water/saliva/ethanol were available. Besides calculating correlations between clinical and laboratory outcomes, we explored whether a model including a laboratory predictor dichotomized at a cut-off value better predicted a clinical outcome than a linear model. A total of 74 clinical experiments from 45 studies were included involving 31 materials for which laboratory data were also available. A weak positive correlation between fracture toughness and clinical fractures was found (Spearman rho=0.34, p=0.11) in addition to a moderate and statistically significant correlation between flexural strength and clinical wear (Spearman rho=0.46, p=0.01). When excluding those studies with "high" risk of bias (n=18), the correlations were generally weaker with no statistically significant correlation. For aging in ethanol, a very strong correlation was found between flexural strength decrease and clinical index, but this finding was based on only 7 materials (Spearman rho=0.96, p=0.0001). Prediction was not consistently improved with cutoff values. Correlations between clinical and laboratory

  2. Temperature sensitivity of the penicillin-induced autolysis mechanism in nongrowing cultures of Escherichia coli.

    OpenAIRE

    Kusser, W; Ishiguro, E E

    1987-01-01

    The effect of incubation temperature on the ampicillin-induced autolysis of nongrowing Escherichia coli was determined. The autolysis mechanisms in amino acid-deprived relA mutant cells treated with chloramphenicol were temperature sensitive. This temperature-sensitive autolysis was demonstrated in three independent ways: turbidimetric determinations, viable cell counts, and solubilization of radiolabeled peptidoglycan.

  3. Numerical and Statistical Analysis of Fractures in Mechanically Dissimilar Rocks of Limestone Interbedded with Shale from Nash Point in Bristol Channel, South Wales, UK.

    Science.gov (United States)

    Adeoye-Akinde, K.; Gudmundsson, A.

    2017-12-01

    Heterogeneity and anisotropy, especially with layered strata within the same reservoir, makes the geometry and permeability of an in-situ fracture network challenging to forecast. This study looks at outcrops analogous to reservoir rocks for a better understanding of in-situ fracture networks and permeability, especially fracture formation, propagation, and arrest/deflection. Here, fracture geometry (e.g. length and aperture) from interbedded limestone and shale is combined with statistical and numerical modelling (using the Finite Element Method) to better forecast fracture network properties and permeability. The main aim is to bridge the gap between fracture data obtained at the core level (cm-scale) and at the seismic level (km-scale). Analysis has been made of geometric properties of over 250 fractures from the blue Lias in Nash Point, UK. As fractures propagate, energy is required to keep them going, and according to the laws of thermodynamics, this energy can be linked to entropy. As fractures grow, entropy increases, therefore, the result shows a strong linear correlation between entropy and the scaling exponent of fracture length and aperture-size distributions. Modelling is used to numerically simulate the stress/fracture behaviour in mechanically dissimilar rocks. Results show that the maximum principal compressive stress orientation changes in the host rock as the fracture-induced stress tip moves towards a more compliant (shale) layer. This behaviour can be related to the three mechanisms of fracture arrest/deflection at an interface, namely: elastic mismatch, stress barrier and Cook-Gordon debonding. Tensile stress concentrates at the contact between the stratigraphic layers, ahead of and around the propagating fracture. However, as shale stiffens with time, the stresses concentrated at the contact start to dissipate into it. This can happen in nature through diagenesis, and with greater depth of burial. This study also investigates how induced

  4. Mechanisms affecting the transport and retention of bacteria, bacteriophage and microspheres in laboratory-scale saturated fractures

    Science.gov (United States)

    Seggewiss, G.; Dickson, S. E.

    2013-12-01

    Groundwater is becoming an increasingly important water source due to the ever-increasing demands from agricultural, residential and industrial consumers. In search of more secure sources, wells are routinely finished over large vertical depths in bedrock aquifers, creating new hydraulic pathways and thus increasing the risk of cross contamination. Moreover, hydraulic pathways are also being altered and created by increasing water withdrawal rates from these wells. Currently, it is not well understood how biological contaminants are transported through, and retained in, fractured media thereby making risk assessment and land use decisions difficult. Colloid transport within fractured rock is a complex process with several mechanisms affecting transport and retention, including: advection, hydrodynamic dispersion, diffusion, size exclusion, adsorption, and decay. Several researchers have investigated the transport of bacteria, bacteriophage, and microspheres (both carboxylated and plain) to evaluate the effects of surface properties and size on transport and retention. These studies have suggested that transport is highly dependent on the physico-chemical properties of the particle, the fracture, and the carrying fluid. However, these studies contain little detail regarding the specific mechanisms responsible for transport beyond speculating about their existence. Further, little work has been done to compare the transport of these particulate materials through the same fracture, allowing for direct observations based on particulate size and surface properties. This research examines the similarities and differences in transport and retention between four different particles through two different laboratory-scale, saturated fractures. This work is designed to explore the effects of particle size, surface properties, ionic strength of the carrying solution, and aperture field characteristics on transport and retention in single, saturated fractures. The particulates

  5. Optimized Thermo-Mechanical Treatment Condition for Enhancing Fracture Toughness of 9Cr-Nanostructured Ferritic Alloy

    Energy Technology Data Exchange (ETDEWEB)

    Yoon, Ji Hyun; Kang, Suk Hoon [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Byun, Thak S.; Hoelzer, David T. [Oak Ridge National Laboratory, Oak Ridge (United States)

    2013-10-15

    The known limitations are the high swelling and low strength in austenitic stainless steels, radiation-induced embrittlement in refractory metals, and phase instability, swelling and radioactivity buildup in irradiation in nickel-based superalloy Recently, the nanostructured ferritic alloys (NFAs), advanced oxide dispersion strengthened (ODS) alloys, with an enhanced high-temperature strength and a high swelling resistance were developed. However, the fracture behaviors describing the material resistance to crack initiation and growth in this temperature region have been rarely investigated, although the NFAs were designed to operate at high temperatures, typically above 550 .deg. C. A few recent researches have reported that the fracture toughness of high strength NFAs is very low at above 300 .deg. C. To overcome this drawback of NFAs, the optimized condition for thermo-mechanical treatments (TMTs) that can modify the microstructure of the 9Cr base NFA were developed.

  6. Fracture mechanics parameters estimation of CCT specimens made of X 5 CrNi 18 10 steel

    Directory of Open Access Journals (Sweden)

    D. Kozak

    2009-04-01

    Full Text Available This study investigates fracture behaviour of specimens made of high ductile stainless steel. Investigated material was X 5 CrNi 18 10 steel and the specimens used in this investigation were prepared as centre crack tension (CCT specimens. Pre-cracking of specimens was done by controlled cycling loading. For determination of J-integral, as one of important fracture mechanics parameters, a single specimen method with loading-unloading procedure was used. The same experiment was numerically modelled by using commercial software for finite element analysis – ANSYS. The standard node releasing technique was implemented in finite element method simulation to simulate crack propagation. Numerically obtained results were compared to the results obtained by experiment.

  7. Effects of matrix structures on fracture mechanisms of austempered ductile cast iron

    Energy Technology Data Exchange (ETDEWEB)

    Doi, Shigeru; Matsufuji, Kenichi [Oita Univ. (Japan); Mitsunaga, Koichi [Kagoshima Junior Womens College (Japan); Takahara, Masao [Isuzu Motors, Kawasaki, Kanagawa (Japan)

    1995-12-31

    On the fatigue behavior of Austempered Ductile Iron (so called ADI), rotating fatigue tests in very high cycle region were performed. The S-N curve represented the double bending. This behavior is caused by the high cycle (>10{sup 7} cycles) fracture, and called the complex three region fractures. The main reason is the work hardening in the surface layer. Therefore, it was removed by electropolishing the surface layer with work hardening. The S-N curve did not show the double bending mentioned above. The fatigue strength with bainitic structure of electropolished ADI was higher than those of mother pearlitic structure.

  8. Double torsion fracture mechanics testing of shales under chemically reactive conditions

    Science.gov (United States)

    Chen, X.; Callahan, O. A.; Holder, J. T.; Olson, J. E.; Eichhubl, P.

    2015-12-01

    Fracture properties of shales is vital for applications such as shale and tight gas development, and seal performance of carbon storage reservoirs. We analyze the fracture behavior from samples of Marcellus, Woodford, and Mancos shales using double-torsion (DT) load relaxation fracture tests. The DT test allows the determination of mode-I fracture toughness (KIC), subcritical crack growth index (SCI), and the stress-intensity factor vs crack velocity (K-V) curves. Samples are tested at ambient air and aqueous conditions with variable ionic concentrations of NaCl and CaCl2, and temperatures up to 70 to determine the effects of chemical/environmental conditions on fracture. Under ambient air condition, KIC determined from DT tests is 1.51±0.32, 0.85±0.25, 1.08±0.17 MPam1/2 for Marcellus, Woodford, and Mancos shales, respectively. Tests under water showed considerable change of KIC compared to ambient condition, with 10.6% increase for Marcellus, 36.5% decrease for Woodford, and 6.7% decrease for Mancos shales. SCI under ambient air condition is between 56 and 80 for the shales tested. The presence of water results in a significant reduction of the SCI from 70% to 85% compared to air condition. Tests under chemically reactive solutions are currently being performed with temperature control. K-V curves under ambient air conditions are linear with stable SCI throughout the load-relaxation period. However, tests conducted under water result in an initial cracking period with SCI values comparable to ambient air tests, which then gradually transition into stable but significantly lower SCI values of 10-20. The non-linear K-V curves reveal that crack propagation in shales is initially limited by the transport of chemical agents due to their low permeability. Only after the initial cracking do interactions at the crack tip lead to cracking controlled by faster stress corrosion reactions. The decrease of SCI in water indicates higher crack propagation velocity due to

  9. A partitioned model order reduction approach to rationalise computational expenses in nonlinear fracture mechanics

    Science.gov (United States)

    Kerfriden, P.; Goury, O.; Rabczuk, T.; Bordas, S.P.A.

    2013-01-01

    We propose in this paper a reduced order modelling technique based on domain partitioning for parametric problems of fracture. We show that coupling domain decomposition and projection-based model order reduction permits to focus the numerical effort where it is most needed: around the zones where damage propagates. No a priori knowledge of the damage pattern is required, the extraction of the corresponding spatial regions being based solely on algebra. The efficiency of the proposed approach is demonstrated numerically with an example relevant to engineering fracture. PMID:23750055

  10. Correlation of nodular austempered ductile iron (ADI) microstructural parameters and fatigue properties using an approach based on fracture mechanics

    International Nuclear Information System (INIS)

    Dias, Jose Felipe; Fonseca, Vinicius Rizzuti; Godefroid, Leonardo Barbosa; Ribeiro, Gabriel de Oliveira

    2010-01-01

    An investigation has been accomplished to check the effect of temperature and austempering time on austempered ductile iron (ADI) properties by means of fracture toughness (K C ) and fatigue threshold (∆K th ) tests. The correlation of ADI microstructural parameters and ADI two mechanical parameters: KC and Kth, is evaluated. Three sets of samples have ben extracted from ADI casting Y blocks produced in industrial conditions.and austenitized at 900°C for 1.5 hour. The austempering process has been performed in the following ways: the first set was austenitized at 300 deg C for 4 hours, the second set at 360°C for 1.5 hour and the third at 360°C for 0.6 hour. These distinct austempering processes have been adopted in order to obtain distinct microstructures containing austenite with two different carbon rates and two ferritic cell sizes. The materials have been characterized by means of optical and electronic microscopy, X-ray diffraction and mechanical tests. All materials have presented equivalent fatigue crack propagation rates, fracture toughness in the range between 94 and 128 MPa·m 1/2 and ∆K th in the range between 5,7 and 6,4 MPa·m 1/2 . The experimental results have confirmed the effect of microstructural properties (austenitic volumetric rate, austenitic carbon rate, ferritic cell size, total matrix carbon content) on fracture toughness (K C ) and fatigue threshold (∆K th ). Further, it was found that following parameters: fracture toughness (K C ), fatigue threshold ((∆K th ) and impact strength are correlated with the total matrix carbon content and ferritic cell size. (author)

  11. Development of a new code to solve hydro-mechanical coupling, shear failure and tensile failure due to hydraulic fracturing operations.

    Science.gov (United States)

    María Gómez Castro, Berta; De Simone, Silvia; Carrera, Jesús

    2016-04-01

    Nowadays, there are still some unsolved relevant questions which must be faced if we want to proceed to the hydraulic fracturing in a safe way. How much will the fracture propagate? This is one of the most important questions that have to be solved in order to avoid the formation of pathways leading to aquifer targets and atmospheric release. Will the fracture failure provoke a microseismic event? Probably this is the biggest fear that people have in fracking. The aim of this work (developed as a part of the EU - FracRisk project) is to understand the hydro-mechanical coupling that controls the shear of existing fractures and their propagation during a hydraulic fracturing operation, in order to identify the key parameters that dominate these processes and answer the mentioned questions. This investigation focuses on the development of a new C++ code which simulates hydro-mechanical coupling, shear movement and propagation of a fracture. The framework employed, called Kratos, uses the Finite Element Method and the fractures are represented with an interface element which is zero thickness. This means that both sides of the element lie together in the initial configuration (it seems a 1D element in a 2D domain, and a 2D element in a 3D domain) and separate as the adjacent matrix elements deform. Since we are working in hard, fragile rocks, we can assume an elastic matrix and impose irreversible displacements in fractures when rock failure occurs. The formulation used to simulate shear and tensile failures is based on the analytical solution proposed by Okada, 1992 and it is part of an iterative process. In conclusion, the objective of this work is to employ the new code developed to analyze the main uncertainties related with the hydro-mechanical behavior of fractures derived from the hydraulic fracturing operations.

  12. Natural hydraulic fractures and the mechanical stratigraphy of shale-dominated strata

    NARCIS (Netherlands)

    Imber, J.; Armstrong, Howard; Atar, E.; Clancy, Sarah; Daniels, S.; Grattage, J.; Herringshaw, Liam; Trabucho-Alexandre, João; Warren, C.; Wille, J.; Yahaya, L.

    2016-01-01

    The aim of this study is to investigate stratigraphic variations in the spatial distribution and density of natural hydraulic and other fractures within oil mature, shale-dominated strata from the Cleveland Basin, northeast England. The studied interval includes the Pliensbachian Cleveland Ironstone

  13. Effect of orientation on the in vitro fracture toughness ofdentin: The role of toughening mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    Nalla, R.K.; Kinney, J.H.; Ritchie, R.O.

    2003-01-28

    A micro-mechanistic understanding of bone fracture thatencompasses how cracks interact with the underlying microstructure anddefines their local failure mode is lacking, despite extensive research nthe response of bone to a variety of factors like aging, loading, and/ordisease.

  14. Mechanical Comparison of Headless Screw Fixation and Locking Plate Fixation for Talar Neck Fractures.

    Science.gov (United States)

    Karakasli, Ahmet; Hapa, Onur; Erduran, Mehmet; Dincer, Cemal; Cecen, Berivan; Havitcioglu, Hasan

    2015-01-01

    For talar neck fractures, open reduction and internal fixation have been thought to facilitate revascularization and prevent osteonecrosis. Newer screw systems allow for placement of cannulated headless screws, which provide compression by virtue of a variable pitch thread. The present study compared the biomechanical fixation strength of cannulated headless variable-pitch screw fixation and locking plate fixation. A reproducible talar neck fracture was created in 14 fresh cadaver talar necks. Talar head fixation was then performed using 2 cannulated headless variable-pitch 4-mm/5-mm diameter (4/5) screws (Acutrak; Acumed, Hillsboro, OR) and locking plate fixation. Headless variable-pitch screw fixation had lower failure displacement than did locking plate fixation. No statistically significant differences were found in failure stiffness, yield stiffness (p = .655), yield load (p = .142), or ultimate load between the 2 fixation techniques. Cannulated headless variable-pitch screw fixation resulted in better failure displacement than locking plate fixation in a cadaveric talus model and could be considered a viable option for talus fracture fixation. Headless, fully threaded, variable-pitch screw fixation has inherent advantages compared with locking plate fixation, because it might cause less damage to the articular surface and can compress the fracture for improved reduction. Additionally, plate fixation can increase the risk of avascular necrosis owing to the wider incision and dissection of soft tissues. Copyright © 2015 American College of Foot and Ankle Surgeons. Published by Elsevier Inc. All rights reserved.

  15. Joint location and source mechanism inversion of microseismic events: benchmarking on seismicity induced by hydraulic fracturing

    Czech Academy of Sciences Publication Activity Database

    Anikiev, D.; Valenta, Jan; Staněk, František; Eisner, Leo

    2014-01-01

    Roč. 198, č. 1 (2014), s. 249-258 ISSN 0956-540X R&D Projects: GA ČR GAP210/12/2451 Institutional support: RVO:67985891 Keywords : inverse theory * probability distributions * wave scattering and diffraction * fractures and faults Subject RIV: DB - Geology ; Mineralogy Impact factor: 2.724, year: 2013

  16. Sensitivity of upconversion mechanisms to excitation laser wavelength in Er{sup 3+}-doped YAG

    Energy Technology Data Exchange (ETDEWEB)

    Du Shan; Xu Jiaxin; Dong Xiaorui; Zhang Jing; Fu Zuoling [College of Physics, Jilin University, and Key Lab of Coherent Light, Atomic and Molecular Spectroscopy, Ministry of Education, Changchun 130021 (China); Dai Zhenwen, E-mail: dai@jlu.edu.c [College of Physics, Jilin University, and Key Lab of Coherent Light, Atomic and Molecular Spectroscopy, Ministry of Education, Changchun 130021 (China)

    2010-05-15

    A sensitive dependence of upconversion (UC) mechanisms on excitation wavelength in a rather small region of 0.5 nm near to the resonant absorption of {sup 4}F{sub 7/2} in Er{sup 3+}(8.4 at%):YAG crystal has been observed and discussed. This kind of mechanism-sensitive UC luminescence comes from {sup 2}P{sub 3/2} which can be upconvertedly populated by both excited-stated absorption (ESA) and energy-transfer upconversion (ETU) processes. From a qualitative analysis, similar to the dependence of UC mechanisms on dopant concentration, the essence of this sensitivity reflects the influence of the interacting ion number on ETU. In order to give a quantitative description, we also performed a simulation for UC processes by rate equations, and the theoretical results attested the sensitivity as revealed in the experiment.

  17. Dynamical mechanisms for sensitive response of aperiodic firing cells to external stimulation

    Energy Technology Data Exchange (ETDEWEB)

    Xie Yong E-mail: xie813@263.net; Xu Jianxue; Hu Sanjue; Kang Yanmei; Yang Hongjun; Duan Yubin

    2004-10-01

    An interesting phenomenon that aperiodic firing neurons have a higher sensitivity to drugs than periodic firing neurons have been reported for the chronically compressed dorsal root ganglion neurons in rats. In this study, the dynamical mechanisms for such a phenomenon are uncovered from the viewpoint of dynamical systems theory. We use the Rose-Hindmarsh neuron model to illustrate our opinions. Periodic orbit theory is introduced to characterize the dynamical behavior of aperiodic firing neurons. It is considered that bifurcations, crises and sensitive dependence of chaotic motions on control parameters can be the underlying mechanisms. And then, a similar analysis is applied to the modified Chay model describing the firing behavior of pancreatic beta cells. The same dynamical mechanisms can be obtained underlying that aperiodic firing cells are more sensitive to external stimulation than periodic firing ones. As a result, we conjecture that sensitive response of aperiodic firing cells to external stimulation is a universal property of excitable cells.

  18. Fracture mechanisms of aluminium alloy AA7075-T651 under various loading conditions

    International Nuclear Information System (INIS)

    Pedersen, Ketill O.; Borvik, Tore; Hopperstad, Odd Sture

    2011-01-01

    The fracture behaviour of the aluminium alloy AA7075-T651 is investigated for quasi-static and dynamic loading conditions and different stress states. The fracture surfaces obtained in tensile tests on smooth and notched axisymmetric specimens and compression tests on cylindrical specimens are compared to the fracture surfaces that occur when a projectile, having either a blunt or an ogival nose shape, strikes a 20 mm thick plate of the aluminium alloy. The stress state in the impact tests is much more complex and the strain rate significantly higher than in the tensile and compression tests. Optical and scanning electron microscopes are used in the investigation. The fracture surface obtained in tests with smooth axisymmetric specimens indicates that the crack growth is partly intergranular along the grain boundaries or precipitation free zones and partly transgranular by void formation around fine and coarse intermetallic particles. When the stress triaxiality is increased through the introduction of a notch in the tensile specimen, delamination along the grain boundaries in the rolling plane is observed perpendicular to the primary crack. In through-thickness compression tests, the crack propagates within an intense shear band that has orientation about 45 o with respect to the load axis. The primary failure modes of the target plate during impact were adiabatic shear banding when struck by a blunt projectile and ductile hole-enlargement when struck by an ogival projectile. Delamination and fragmentation of the plates occurred for both loading cases, but was stronger for the ogival projectile. The delamination in the rolling plane was attributed to intergranular fracture caused by tensile stresses occurring during the penetration event.

  19. The combat burst fracture study--results of a cohort analysis of the most prevalent combat specific mechanism of major thoracolumbar spinal injury.

    Science.gov (United States)

    Freedman, Brett A; Serrano, Jose A; Belmont, Philip J; Jackson, Keith L; Cameron, Brian; Neal, Chris J; Wells, Rosemary; Yeoman, Chevas; Schoenfeld, Andrew J

    2014-10-01

    In 2009-2010, military physicians hypothesized that a new pattern of spinal injury had emerged, resulting from improvised explosive device assault on up-armored vehicles, associated with a high rate of point of first contact fracture and neurological injury-the combat burst fracture. We sought to determine the incidence of all thoracolumbar (TL) burst fractures and combat burst fractures in 2009-2010 as compared to two antecedent years. A screening process identified all individuals who sustained TL burst fractures in the time-period studied. Demographics, injury-specific characteristics, mechanism of injury, surgical interventions and early complications were recorded. Incidence rates were calculated for the three time periods using total deployed troop-strength and number of LRMC combat admissions as denominators. The incidences of TL burst fractures within each year group and by mechanism were compared, and clinical characteristics and process of care were described. Between 2007-2010, 65 individuals sustained a TL burst fracture. The incidence of these injuries in 2009-2010 was 2.1 per 10,000 soldier-years and accounted for 3.0 % of LRMC combat-casualty admissions, a significant increase from 0.6 % and 1.1 % in 2007-2008 and 2008-2009, respectively (p ≤ 0.001). In 2009-2010, US soldiers were 3.4-4.6 times more likely to sustain a TL burst fracture compared to 2008-2009 and 2007-2008 (p vehicle (65 %)-the combat burst fracture mechanism. Neurological deficits were present in 43 % of TL burst fractures and 1/3 were complete injuries. Spinal fixation was performed in 68 % overall and 74 % of combat burst fractures. There was a 3.4- to 4.6-fold increase in TL burst fractures in 2009-2010 compared to antecedent years. The primary driver of this phenomenon was the marked increased in combat burst fractures. Mitigating/preventing the mechanism behind this major spinal injury is a key research initiative for the US military. Level of Evidence III (Case-control).

  20. Dynamic Mechanical Properties and Fracture Surface Morphologies of Core-Shell Rubber (CSR) Toughened Epoxy at Liquid Nitrogen (Ln2) Temperatures

    Science.gov (United States)

    Wang, J.; Magee, D.; Schneider, J. A.

    2009-01-01

    The dynamic mechanical properties and fracture surface morphologies were evaluated for a commercial epoxy resin toughened with two types of core-shell rubber (CSR) toughening agents (Kane Ace(Registered TradeMark) MX130 and MX960). The impact resistance (R) was evaluated by the resulting breaking energy measured in Charpy impact tests conducted on an instrumented drop tower. The resulting fracture surface morphologies were examined using Scanning Electron Microscopy (SEM). Fractographic observations of the CSR toughened epoxy tested at ambient temperature, showed a fracture as characterized by slender dendrite textures with large voids. The increasing number of dendrites and decreasing size of scale-like texture with more CSR particles corresponded with increased R. As the temperature decreased to Liquid Nitrogen (LN 2), the fracture surfaces showed a fracture characterized by a rough, torn texture containing many river markings and deep furrows.

  1. Effect of framework design on fracture load after thermal cycling and mechanical loading of implant-supported zirconia-based prostheses.

    Science.gov (United States)

    Komine, Futoshi; Kamio, Shingo; Takata, Hiroki; Yagawa, Shogo; Taguchi, Serina; Taguchi, Kohei; Hashiguchi, Akiko; Matsumura, Hideo

    2018-01-30

    This study evaluated the effect of zirconia framework design on fracture load of implant-supported zirconia-based prostheses after thermal cycling and mechanical loading. Three different zirconia framework designs were investigated: uniform-thickness (UNI), anatomic (ANA), and supported anatomic (SUP) designs. Each framework was layered with feldspathic porcelain (ZAC group) or indirect composite material (ZIC group). The specimens then underwent fracture load testing after thermal cycling and cyclic loading. In the ZAC group, mean fracture load was significantly lower for UNI design specimens than for the other framework designs. In the ZIC group, there was no significant difference in mean fracture load between ANA design specimens and either UNI or SUP design specimens. To improve fracture resistance of implant-supported zirconia-based prostheses after artificial aging, uniformly thick layering material and appropriate lingual support with zirconia frameworks should be provided.

  2. Experimental Investigation of Damage and Fracture Mechanisms Controlling the Performance of Full Aperture Easy Open Ends for Food Containers

    Science.gov (United States)

    Taylor, D. L. P.; Nagy, G. T.; Owen, D. R. J.

    2011-05-01

    Can manufacturers produce hundreds of millions of cans annually, increasingly, food cans are being opened by lifting a tab on the can end that initiates a fracture, which then propagates around a circumferential score. The damage and fracture mechanisms that lead to crack initiation and propagation in the opening process, however, are not fully understood, therefore optimisation of easy open end scores is largely based on trial and error. This paper presents an experimental analysis that concentrates on the combined shear and bending forces as applied to the particular industrial method concerning full aperture easy open ends. The influence of a gradually increasing gap measured between the score and shear force location on traditional groove geometries and depths are examined for two different packaging steels. Earlier studies have shown that the complete opening cycle depends on fracture modes I, II & III as well as their combination. Experimental results for Modes I, II & III will be presented, however attention will focus on the behaviour of the initial fracture point, whereby prior investigations have shown it to be influenced primarily by mode II shearing. After initial specimen manufacture, where the score is formed by pressing a punch into a thin steel sheet the predeformed scored specimens are loaded in shear to simulate the local stress field found during the initial opening phase. Experiments have been completed using a novel Mode II experimental technique that has been designed for use in the majority of commercially available tensile test machines. Experimental results indicate that opening forces can change radically with different gap sizes and that there is considerable potential for the industrialised process of can end manufacture to be optimised through the efficient management and control of the can ends dimensional parameters.

  3. Salt-sensitive hypertension: mechanisms and effects of dietary and other lifestyle factors.

    Science.gov (United States)

    Pilic, Leta; Pedlar, Charles R; Mavrommatis, Yiannis

    2016-10-01

    Salt sensitivity, which is an increase in blood pressure in response to high dietary salt intake, is an independent risk factor for cardiovascular disease and mortality. It is associated with physiological, environmental, demographic, and genetic factors. This review focuses on the physiological mechanisms of salt sensitivity in populations at particular risk, along with the associated dietary factors. The interplay of mechanisms such as the renin-angiotensin aldosterone system, endothelial dysfunction, ion transport, and estrogen decrease in women contributes to development of salt sensitivity. Because of their effects on these mechanisms, higher dietary intakes of potassium, calcium, vitamin D, antioxidant vitamins, and proteins rich in L-arginine, as well as adherence to dietary patterns similar to the DASH (Dietary Approaches to Stop Hypertension) diet, can be beneficial to salt-sensitive populations. In contrast, diets similar to the typical Western diet, which is rich in saturated fats, sucrose, and fructose, together with excessive alcohol consumption, may exacerbate salt-sensitive changes in blood pressure. Identifying potential mechanisms of salt sensitivity in susceptible populations and linking them to protective or harmful dietary and lifestyle factors can lead to more specific guidelines for the prevention of hypertension and cardiovascular disease. © The Author(s) 2016. Published by Oxford University Press on behalf of the International Life Sciences Institute. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

  4. A Thermo-Hydro-Mechanical modeling of fracture opening and closing due heat extraction from geothermal reservoir

    Science.gov (United States)

    Nand Pandey, Sachchida; Chaudhuri, Abhijit; Kelkar, Sharad

    2015-04-01

    Increasing the carbon dioxide concentration in atmosphere become challenging task for the scientific community. To achieve the sustainable growth with minimum pollution in atmosphere requires the development of low carbon technology or switch towards renewable energy. Geothermal energy is one of the promising source of clean energy. Geothermal energy is also considered a sustainable, reliable and least-expensive. This study presents a numerical modeling of subsurface heat extraction from the reservoir. The combine flow, heat transfer and geo-mechanical problem are modeled using FEHM code, which was validated against existing field data, numerical code and commercial software. In FEHM the flow and heat transfer in reservoir are solved by control volume method while for mechanical deformation finite element technique is used. The 3-D computational domain (230m × 200m × 1000m) has single horizontal fault/fracture, which is located at 800 m depth from the ground surface. The fracture connects the injection and production wells. The distance between the wells is 100 m. A geothermal gradient 0.08 °C/m is considered. The temperatures at top and bottom boundaries are held fixed as 20 and 100 °C respectively. The zero heat and mass flux boundary conditions are imposed to all vertical side boundaries of the domain. The simulation results for 100 days suggests that the computational domain is sufficiently large as the temperature along the vertical boundaries are not affected by cold-water injection. To model the thermo-poro-elastic deformation, zero all three components of displacement are specified as zero at the bottom. The zero stress condition along all other boundaries allows the boundaries to move freely. The temperature and pressure dependent fluid properties such as density and viscosity with single phase flow in saturated medium is considered. We performed a series of thermo-hydro-mechanical (THM) simulations to show aperture alteration due to cold

  5. Fracture-mechanical investigations on the propagation of heat-tension-cracks, in boittle multi-component media

    International Nuclear Information System (INIS)

    Grebner, H.

    1983-01-01

    The quasistatic dissipation of thermically induced cracks in brittle multi-components material with plane boundary areas is studied. The distribution of Eigentension, which is causing the dissipation of cracks, is produced by cooling the composite material from the production temperature to room temperature. Tension distributions, respectively of the fracture-mechanical coefficients were determined by solving of the boundary value problems of the theory of plane thermoelasticity, a based on existence of a plane distortion state, respectively of a plane state of tension. Because of the complicated shape of the free surface one adopted a numerical solution, the finite-element method, to solve the corresponding mixed boundary value problems. (orig.) [de

  6. Microstructure, mechanical and fracture properties of groundnut shell ash and silicon carbide dispersion strengthened aluminium matrix composites

    Directory of Open Access Journals (Sweden)

    Kenneth Kanayo Alaneme

    2018-01-01

    Full Text Available The mechanical properties of aluminium hybrid composites reinforced with groundnut shell ash (GSA and silicon carbide was investigated. GSA and silicon carbide with different mix ratios (10:0, 7.5:2.5, 5.0:5.0, 2.5:7.5 and 0:10 constituted 6 and 10 wt.% of the reinforcing phase, while the matrix material was Al–Mg–Si alloy. The hybrid composites were produced via a two-step stir casting technique. Microstructural examination, hardness, tensile and fracture toughness testing were carried out to appraise the mechanical properties of the composites. The results show that with increasing GSA in the reinforcing phase, the hardness, ultimate tensile strength (UTS and specific strength of the composites decreased slightly for both 6 and 10 wt.% reinforced Al–Mg–Si based composites owing to the amount of the oxides of Al, Si, Ca, K2 and Mg present in the composition of GSA. However, the percentage elongation improved marginally and was generally invariant to increasing GSA content while the fracture toughness increased with increasing GSA content. GSA offered a favourable influence on the mechanical properties of Al–Mg–Si hybrid composites comparable to that of rice husk ash and bamboo leaf ash.

  7. Analysis of the competition between brittle and ductile fracture: application for the mechanical behaviour of C-Mn and theirs welds

    International Nuclear Information System (INIS)

    Le Corre, V.

    2006-09-01

    This study deals with the fracture behaviour of welded thin structures in the ductile to brittle transition range. It aims to propose a criterion to define the conditions for which the risk of fracture by cleavage does not exist on a cracked structure. The literature review shows that the difficulties of prediction of the fracture behaviour of a structure are related to the dependence of the fracture probability to the mechanical fields at the crack tip. The ductile to brittle transition range thus depends on the studied geometry of the structure. A threshold stress, below which cleavage cannot take place, is defined using fracture tests on notched specimens broken at very low temperature. The finite element numerical simulation of fracture tests on CT specimens in the transition range shows a linear relationship between the fracture probability and the volume exceeding the threshold stress, thus showing the relevance of the proposed criterion. Moreover, several relations are established allowing to simplify the identification of the criterion parameters. The criterion is applied to a nuclear structural C-Mn steel, by focusing more particularly on the higher boundary of the transition range. A fracture test on a full-scale pipe is designed, developed, carried out and analysed using its numerical simulation. The results show firstly that, on the structure, the transition range is shifted in temperature, compared to laboratory specimens, due to the low plasticity constraint achieved in thin structures, and secondly that the threshold stress criterion allows to estimate simply this shift. (author)

  8. Design sensitivity analysis of dynamic responses for a BLDC motor with mechanical and electromagnetic interactions

    Science.gov (United States)

    Im, Hyungbin; Bae, Dae Sung; Chung, Jintai

    2012-04-01

    This paper presents a design sensitivity analysis of dynamic responses of a BLDC motor with mechanical and electromagnetic interactions. Based on the equations of motion which consider mechanical and electromagnetic interactions of the motor, the sensitivity equations for the dynamic responses were derived by applying the direct differential method. From the sensitivity equation along with the equations of motion, the time responses for the sensitivity analysis were obtained by using the Newmark time integration method. The sensitivities of the motor performances such as the electromagnetic torque, rotating speed, and vibration level were analyzed for the six design parameters of rotor mass, shaft/bearing stiffness, rotor eccentricity, winding resistance, coil turn number, and residual magnetic flux density. Furthermore, to achieve a higher torque, higher speed, and lower vibration level, a new BLDC motor was designed by applying the multi-objective function method. It was found that all three performances are sensitive to the design parameters in the order of the coil turn number, magnetic flux density, rotor mass, winding resistance, rotor eccentricity, and stiffness. It was also found that the torque and vibration level are more sensitive to the parameters than the rotating speed. Finally, by applying the sensitivity analysis results, a new optimized design of the motor resulted in better performances. The newly designed motor showed an improved torque, rotating speed, and vibration level.

  9. Antipsychotic-induced sensitization and tolerance: Behavioral characteristics, developmental impacts, and neurobiological mechanisms.

    Science.gov (United States)

    Li, Ming

    2016-08-01

    Antipsychotic sensitization and tolerance refer to the increased and decreased drug effects due to past drug use, respectively. Both effects reflect the long-term impacts of antipsychotic treatment on the brain and result from the brain's adaptive response to the foreign property of the drug. In this review, clinical evidence of the behavioral aspect of antipsychotic sensitization and tolerance is selectively reviewed, followed by an overview of preclinical literature that examines these behavioral characteristics and the related pharmacological and nonpharmacological factors. Next, recent work on the developmental impacts of adolescent antipsychotic sensitization and tolerance is presented and recent research that delineates the neurobiological mechanisms of antipsychotic sensitization and tolerance is summarized. A theoretical framework based on "drug learning and memory" principles is proposed to account for the phenomena of antipsychotic sensitization and tolerance. It is maintained that antipsychotic sensitization and tolerance follow basic principles of learning or acquisition ("induction") and memory ("expression"). The induction and expression of both effects reflect the consequences of associative and nonassociative processing and are strongly influenced by various pharmacological, environmental, and behavioral factors. Drug-induced neuroplasticity, such as functional changes of striatal dopamine D2 and prefrontal serotonin (5-HT)2A receptors and their mediated signaling pathways, in principle, is responsible for antipsychotic sensitization and tolerance. Understanding the behavioral characteristics and neurobiological underpinnings of antipsychotic sensitization and tolerance has greatly enhanced our understanding of mechanisms of antipsychotic action, and may have important implications for future drug discovery and clinical practice. © The Author(s) 2016.

  10. Pathologic C-spine fracture with low risk mechanism and normal physical exam.

    Science.gov (United States)

    Hunter, Andrew; McGreevy, Jolion; Linden, Judith

    2017-09-01

    Cervical spinal fracture is a rare, but potentially disabling complication of trauma to the neck. Clinicians often rely on clinical decision rules and guidelines to decide whether or not imaging is necessary when a patient presents with neck pain. Validated clinical guidelines include the Canadian C-Spine Rule and the Nexus criteria. Studies suggest that the risks of a pathologic fracture from a simple rear end collision are negligible. We present a case of an individual who presented to an emergency department (ED) after a low speed motor vehicle collision complaining of lateral neck pain and had multiple subsequent visits for the same complaint with negative exam findings. Ultimately, he was found to have a severely pathologic cervical spine fracture with notable cord compression. Our objective is to discuss the necessity to incorporate clinical decision rules with physician gestalt and the need to take into account co-morbidities of a patient presenting after a minor MVC. Copyright © 2017 Elsevier Inc. All rights reserved.

  11. Exploring the molecular mechanisms of glucocorticoid receptor action from sensitivity to resistance.

    Science.gov (United States)

    Ramamoorthy, Sivapriya; Cidlowski, John A

    2013-01-01

    Glucocorticoids regulate a variety of physiological processes, and are commonly used to treat disorders of inflammation, autoimmune diseases, and cancer. Glucocorticoid action is predominantly mediated through the classic glucocorticoid receptor (GR), but sensitivity to glucocorticoids varies among individuals, and even within different tissues from the same individual. The molecular basis of this phenomenon can be partially explained through understanding the process of generating bioavailable ligand and the molecular heterogeneity of the GR. The molecular mechanisms that regulate glucocorticoid action highlight the dynamic nature of hormone signaling and provide novel insights into genomic glucocorticoid actions and glucocorticoid sensitivity. Although glucocorticoids are highly effective for therapeutic purposes, long-term and/or high-dose glucocorticoid administration often leads to reduced glucocorticoid sensitivity or resistance. Here, we summarize our current understanding of the mechanisms that modulate glucocorticoid sensitivity and resistance with a focus on GR-mediated signaling. Copyright © 2013 S. Karger AG, Basel.

  12. On chaos in quantum mechanics: The two meanings of sensitive dependence

    International Nuclear Information System (INIS)

    Ingraham, R.L.; Luna Acosta, G.A.

    1993-08-01

    Sensitive dependence on initial conditions, the most important signature of chaos, can mean failure of Lyapunov stability, the primary meaning adopted in dynamical systems theory, or the presence of positive Lyapunov exponents, the meaning favored in physics. These are not equivalent in general. We show that there is sensitive dependence in quantum mechanics in the sense of violation of Lyapunov stability for maps of the state vector like involving unbounded operators A. This is true even for bounded quantum systems, where the corresponding Lyapunov exponents are all zero. Experiments to reveal this sensitive dependence, a definite though unfamiliar prediction of quantum mechanics, should be devised. It may also invalidate the usual assumption of linear response theory in quantum statistical mechanics in some cases. (author) 13 refs

  13. Fracture healing in osteoporotic bone.

    Science.gov (United States)

    Cheung, Wing Hoi; Miclau, Theodore; Chow, Simon Kwoon-Ho; Yang, Frank F; Alt, Volker

    2016-06-01

    As the world population rises, osteoporotic fracture is an emerging global threat to the well-being of elderly patients. The process of fracture healing by intramembranous ossification or/and endochondral ossification involve many well-orchestrated events including the signaling, recruitment and differentiation of mesenchymal stem cells (MSCs) during the early phase; formation of a hard callus and extracellular matrix, angiogenesis and revascularization during the mid-phase; and finally callus remodeling at the late phase of fracture healing. Through clinical and animal research, many of these factors are shown to be impaired in osteoporotic bone. Animal studies related to post-menopausal estrogen deficient osteoporosis (type I) have shown healing to be prolonged with decreased levels of MSCs and decreased levels of angiogenesis. Moreover, the expression of estrogen receptor (ER) was shown to be delayed in ovariectomy-induced osteoporotic fracture. This might be related to the observed difference in mechanical sensitivity between normal and osteoporotic bones, which requires further experiments to elucidate. In mice fracture models related to senile osteoporosis (type II), it was observed that chondrocyte and osteoblast differentiation were impaired; and that transplantation of juvenile bone marrow would result in enhanced callus formation. Other factors related to angiogenesis and vasculogenesis have also been noted to be impaired in aged models, affecting the degradation of cartilaginous matrixes and vascular invasion; the result is changes in matrix composition and growth factors concentrations that ultimately impairs healing during age-related osteoporosis. Most osteoporotic related fractures occur at metaphyseal sites clinically, and reports have indicated that differences exist between diaphyseal and metaphyseal fractures. An animal model that satisfies three main criteria (metaphyseal region, plate fixation, osteoporosis) is suggested for future research for

  14. Imaging of insufficiency fractures

    Energy Technology Data Exchange (ETDEWEB)

    Krestan, Christian [Department of Radiology, Medical University of Vienna, Vienna General Hospital, Waehringerstr. 18-20, 1090 Vienna (Austria)], E-mail: christian.krestan@meduniwien.ac.at; Hojreh, Azadeh [Department of Radiology, Medical University of Vienna, Vienna General Hospital, Waehringerstr. 18-20, 1090 Vienna (Austria)

    2009-09-15

    This review focuses on the occurrence, imaging and differential diagnosis of insufficiency fractures. Prevalence, the most common sites of insufficiency fractures and their clinical implications are discussed. Insufficiency fractures occur with normal stress exerted on weakened bone. Postmenopausal osteoporosis is the most common cause of insufficiency fractures. Other conditions which affect bone turnover include osteomalacia, hyperparathyroidism, chronic renal failure and high-dose glucocorticoid therapy. It is a challenge for the radiologist to detect and diagnose insufficiency fractures, and to differentiate them from other bone lesions. Radiographs are still the most widely used imaging method for identification of insufficiency fractures, but sensitivity is limited, depending on the location of the fractures. Magnetic resonance imaging (MRI) is a very sensitive tool to visualize bone marrow abnormalities associated with insufficiency fractures. Thin section, multi-detector computed tomography (MDCT) depicts subtle fracture lines allowing direct visualization of cortical and trabecular bone. Bone scintigraphy still plays a role in detecting fractures, with good sensitivity but limited specificity. The most important differential diagnosis is underlying malignant disease leading to pathologic fractures. Bone densitometry and clinical history may also be helpful in confirming the diagnosis of insufficiency fractures.

  15. Hydraulic Fracture Containment in Sand

    NARCIS (Netherlands)

    Dong, Y.

    2010-01-01

    The mechanism of hydraulic fracturing in soft, high permeability material is considered fundamentally different from that in hard, low permeability rock, where a tensile fracture is created and conventional linear elastic fracture mechanics (LEFM) applies. The fracturing and associated modeling work

  16. Evaluation of mechanical hardness and fracture toughness of Co and Al co-doped ZnO

    International Nuclear Information System (INIS)

    Siddheswaran, R.; Mangalaraja, R.V.; Avila, Ricardo E.; Manikandan, D.; Esther Jeyanthi, C.; Ananthakumar, S.

    2012-01-01

    Combustion synthesized nanocrystalline Co and Al co-doped ZnO powders [(Zn 1−x−y Co x Al y O; x=0.04, 0.03, 0.02; y=0.01, 0.02, 0.03)] were fabricated into cylindrical discs by uni-axial pressing and sintered intentionally at 1000 °C for 2 h to assess the mechanical performance. The crystallinity of the pure and doped ZnO was confirmed by X-ray diffraction analysis. The microstructures of the sintered samples were investigated by scanning electron microscopy (SEM) to examine the density, porosity, grain size and its distribution. Grains of 0.5–3 μm were observed for the samples sintered at 1000 °C. The mechanical properties such as micro-hardness, fracture toughness and strain hardening co-efficient were investigated by the Vickers indentation method. It was found that the crack mode observed during the indentation on the samples belongs to median cracks under a load of 19.6 N. Also, the hardness was enhanced with increasing mol% of Co, while the trend was reversed with the increase of Al content. In addition, the strain hardening coefficient and fracture toughness were calculated using the indentation data.

  17. Intrinsic mechanical behavior of femoral cortical bone in young, osteoporotic and bisphosphonate-treated individuals in low- and high energy fracture conditions

    Science.gov (United States)

    Zimmermann, Elizabeth A.; Schaible, Eric; Gludovatz, Bernd; Schmidt, Felix N.; Riedel, Christoph; Krause, Matthias; Vettorazzi, Eik; Acevedo, Claire; Hahn, Michael; Püschel, Klaus; Tang, Simon; Amling, Michael; Ritchie, Robert O.; Busse, Björn

    2016-02-01

    Bisphosphonates are a common treatment to reduce osteoporotic fractures. This treatment induces osseous structural and compositional changes accompanied by positive effects on osteoblasts and osteocytes. Here, we test the hypothesis that restored osseous cell behavior, which resembles characteristics of younger, healthy cortical bone, leads to improved bone quality. Microarchitecture and mechanical properties of young, treatment-naïve osteoporosis, and bisphosphonate-treated cases were investigated in femoral cortices. Tissue strength was measured using three-point bending. Collagen fibril-level deformation was assessed in non-traumatic and traumatic fracture states using synchrotron small-angle x-ray scattering (SAXS) at low and high strain rates. The lower modulus, strength and fibril deformation measured at low strain rates reflects susceptibility for osteoporotic low-energy fragility fractures. Independent of age, disease and treatment status, SAXS revealed reduced fibril plasticity at high strain rates, characteristic of traumatic fracture. The significantly reduced mechanical integrity in osteoporosis may originate from porosity and alterations to the intra/extrafibrillar structure, while the fibril deformation under treatment indicates improved nano-scale characteristics. In conclusion, losses in strength and fibril deformation at low strain rates correlate with the occurrence of fragility fractures in osteoporosis, while improvements in structural and mechanical properties following bisphosphonate treatment may foster resistance to fracture during physiological strain rates.

  18. Fracture mechanical investigations about crack resistance behaviour in non-transforming ceramics in particular aluminum oxide

    International Nuclear Information System (INIS)

    Baer, K.K.O.; Kleist, G.; Nickel, H.

    1991-03-01

    The aim of this work is the clearification of R-curve behaviour of non-transforming ceramics, in particular aluminum oxide exhibiting incrystalline fracture. Investigations of crack growth in controlled bending experiments were performed using 3-Pt- and 4-Pt-bending samples of differing sizes under inert conditions. The fracture experiments were realized using several loading techniques, for example constant and varying displacement rates, load rupture (P = 0) and relaxation tests (v = 0). In addition unloading and reloading experiments were performed to investigate hysteresis curves and residual displacements in accordance with R-curve behaviour. During the crack-growth experiments, the crack extension was measured in situ using a high resolution immersion microscope. With this technique, the fracture processes near the crack tip (crack activity zone) was observed as well. The crack resistance as a function of crack extension (R-curve) was determined using differing calculation methods. All of the methods used resulted in approximately identical R-curves, within the statistical error band. The crack resistance at initiation R 0 was 20 N/m. The crack resistance increased during approximately 3 mm of growth to a maximum of 90 N/m. A decrease in the crack resistance was determined for large a/W (crack length normalized with sample height) values, independant of the calculation methods. The R-curve behaviour was interpreted as due to a functional resistance behind the observed crack tip, which arises from a volume dilatation in the crack activity zone while the crack proceeds. (orig.) [de

  19. Behaviour of generators retaining rings. Evaluation of material properties for fracture mechanics analyses

    International Nuclear Information System (INIS)

    Bethmont, M.; Masson, S.H.; Vaillant, F.

    1985-01-01

    Retaining rings of the first alternators of the French PWR program have been damaged by corrosion in humid medium. This led to the change of steel quality, 18 Mn 18 Cr instead of 18Mn 5Cr. This paper presents the results of tests concerning the fracture and tensile properties of these two steels. The temperature influence (between the ambient temperature and 300 0 C) and the hardening process influence have been studied. Crack propagation induced by stress corrosion has been measured at 80 0 C in aerated and desaerated water, and in an aerated solution of acidified sodium at pH3 [fr

  20. Fracture Mechanics Analysis of Reinforced DCB Sandwich Debond Specimen Loaded by Moments

    DEFF Research Database (Denmark)

    Saseendran, Vishnu; Berggreen, Christian; Carlsson, Leif A.

    2018-01-01

    Analytical expressions for the energy release rate and mode-mixity phase angle are derived for a sandwich composite double-cantilever beam fracture specimen with the face sheets reinforced by stiff plates. The sandwich beam is considered symmetric, with identical top and bottom facesheets. Only...... a pure moment loading is considered. The J-integral coupled with laminate beam theory is employed to derive closed-form expression for the energy releaserate in terms of the applied moments, geometry, and material properties .A scalar quantityωis obtained to express the mode-mixity phase angle...

  1. Fracture Toughness, Mechanical Property, And Chemical Characterization Of A Critical Modification To The NASA SLS Solid Booster Internal Material System

    Science.gov (United States)

    Pancoast, Justin; Garrett, William; Moe, Gulia

    2015-01-01

    A modified propellant-liner-insulation (PLI) bondline in the Space Launch System (SLS) solid rocket booster required characterization for flight certification. The chemical changes to the PLI bondline and the required additional processing have been correlated to mechanical responses of the materials across the bondline. Mechanical properties testing and analyses included fracture toughness, tensile, and shear tests. Chemical properties testing and analyses included Fourier transform infrared (FTIR) spectroscopy, cross-link density, high-performance liquid chromatography (HPLC), gas chromatography (GC), gel permeation chromatography (GPC), and wave dispersion X-ray fluorescence (WDXRF). The testing identified the presence of the expected new materials and found the functional bondline performance of the new PLI system was not significantly changed from the old system.

  2. Deep mechanisms of social affect - Plastic parental brain mechanisms for sensitivity versus contempt.

    Science.gov (United States)

    Swain, James E; Ho, S Shaun

    2017-01-01

    Insensitive parental thoughts and affect, similar to contempt, may be mapped onto a network of basic emotions moderated by attitudinal representations of social-relational value. Brain mechanisms that reflect emotional valence of baby signals among parents vary according to individual differences and show plasticity over time. Furthermore, mental health problems and treatments for parents may affect these brain systems toward or away from contempt, respectively.

  3. Ductile fracture mechanism of low-temperature In-48Sn alloy joint under high strain rate loading.

    Science.gov (United States)

    Kim, Jong-Woong; Jung, Seung-Boo

    2012-04-01

    The failure behaviors of In-48Sn solder ball joints under various strain rate loadings were investigated with both experimental and finite element modeling study. The bonding force of In-48Sn solder on an Ni plated Cu pad increased with increasing shear speed, mainly due to the high strain-rate sensitivity of the solder alloy. In contrast to the cases of Sn-based Pb-free solder joints, the transition of the fracture mode from a ductile mode to a brittle mode was not observed in this solder joint system due to the soft nature of the In-48Sn alloy. This result is discussed in terms of the relationship between the strain-rate of the solder alloy, the work-hardening effect and the resulting stress concentration at the interfacial regions.

  4. Incidence and mechanism of neurological deficit after thoracolumbar fractures sustained in motor vehicle collisions.

    Science.gov (United States)

    Mukherjee, Sourabh; Beck, Chad; Yoganandan, Narayan; Rao, Raj D

    2015-10-09

    OBJECT To determine the incidence of and assess the risk factors associated with neurological injury in motor vehicle occupants who sustain fractures of the thoracolumbar spine. METHODS In this study, the authors queried medical, vehicle, and crash data elements from the Crash Injury Research and Engineering Network (CIREN), a prospectively gathered multicenter database compiled from Level I trauma centers. Subjects had fractures involving the T1-L5 vertebral segments, an Abbreviated Injury Scale (AIS) score of ≥ 3, or injury to 2 body regions with an AIS score of ≥ 2 in each region. Demographic parameters obtained for all subjects included age, sex, height, body weight, and body mass index. Clinical parameters obtained included the level of the injured vertebra and the level and type of spinal cord injury. Vehicular crash data included vehicle make, seatbelt type, and usage and appropriate use of the seatbelt. Crash data parameters included the principal direction of force, change in velocity on impact (ΔV), airbag deployment, and vehicle rollover. The authors performed a univariate analysis of the incidence and the odds of sustaining spinal neurological injury associated with major thoracolumbar fractures with respect to the demographic, clinical, and crash parameters. RESULTS Neurological deficit associated with thoracolumbar fracture was most frequent at extremes of age; the highest rates were in the 0- to 10-year (26.7% [4 of 15]) and 70- to 80-year (18.4% [7 of 38]) age groups. Underweight occupants (OR 3.52 [CI 1.055-11.7]) and obese occupants (OR 3.27 [CI 1.28-8.31]) both had higher odds of sustaining spinal cord injury than occupants with a normal body mass index. The highest risk of neurological injury existed in crashes in which airbags deployed and the occupant was not restrained by a seatbelt (OR 2.35 [CI 0.087-1.62]). Reduction in the risk of neurological injuries occurred when 3-point seatbelts were used correctly in conjunction with the

  5. Evaluation of an injectable hydrogel and polymethyl methacrylate in restoring mechanics to compressively fractured spine motion segments.

    Science.gov (United States)

    Balkovec, Christian; Vernengo, Andrea J; Stevenson, Peter; McGill, Stuart M

    2016-11-01

    Compressive fracture can produce profound changes to the mechanical profile of a spine segment. Minimally invasive repair has the potential to restore both function and structural integrity to an injured spine. Use of both hydrogels to address changes to the disc, combined with polymethyl methacrylate (PMMA) to address changes to the vertebral body, has the potential to facilitate repair. The purpose of this investigation was to determine if the combined use of hydrogel injection and PMMA could restore the mechanical profile of an axially injured spinal motion segment. This is a basic science study evaluating a combination of hydrogel injection and vertebroplasty on restoring mechanics to compressively injured porcine spine motion segments. Fourteen porcine spine motion segments were subject to axial compression until fracture using a dynamic servohydraulic testing apparatus. Rotational and compressive stiffness was measured for each specimen under the following conditions: initial undamaged, fractured, fatigue loading under compression, hydrogel injection, PMMA injection, and fatigue loading under compression. Group 1 received hydrogel injection followed by PMMA injection, whereas Group 2 received PMMA injection followed by hydrogel injection. This study was funded under a Natural Sciences and Engineering Research Council of Canada discovery grant. PMMA injection was found to alter the compressive stiffness properties of axially injured spine motion segments, restoring values from Groups 1 and 2 to 89.3%±29.3% and 81%±27.9% of initial values respectively. Hydrogel injection was found to alter the rotational stiffness properties, restoring specimens in Groups 1 and 2 to 151.5%±81% and 177.2%±54.9% of initial values respectively. Prolonged restoration of function was not possible, however, after further fatigue loading. Using this repair technique, replication of the mechanism of injury appears to cause a rapid deterioration in function of the motion segments

  6. Perceiving Group Behavior: Sensitive Ensemble Coding Mechanisms for Biological Motion of Human Crowds

    Science.gov (United States)

    Sweeny, Timothy D.; Haroz, Steve; Whitney, David

    2013-01-01

    Many species, including humans, display group behavior. Thus, perceiving crowds may be important for social interaction and survival. Here, we provide the first evidence that humans use ensemble-coding mechanisms to perceive the behavior of a crowd of people with surprisingly high sensitivity. Observers estimated the headings of briefly presented…

  7. Design characteristics, primary stability and risk of fracture of orthodontic mini-implants: pilot scan electron microscope and mechanical studies.

    Science.gov (United States)

    Walter, André; Winsauer, Heinz; Marcé-Nogué, Jordi; Mojal, Sergi; Puigdollers, Andreu

    2013-09-01

    Orthodontic mini-implants (OMIs) are increasingly used in orthodontics but can fail for various reasons. This study investigates the effects of OMI design characteristics on the mechanical properties in artificial bone. Twelve self-drilling OMIs (2 small, 6 medium, 4 large) from 8 manufacturers were tested for their primary stability in simulated medium-high cancellous bone and the risk to fracture in high-density methacrylate blocks. For the assessments of the maximum insertion torque (IT) and torsional fracture (TF) 5 of each OMI were used and for the pull-out strength (POS) 10. The OMIs were inserted with a torque screwdriver (12 sec/360°) until the bottom at 8 mm depth was reached. OMI designs were analyzed with a scan electron microscope (SEM). SEM images revealed a great variation in product refinement. In the whole sample, a cylindrical OMI shape was associated with higher POS (pdesign characteristics well correlated with POS, IT and TF values (ranging from 0.601 to 0.961). Greater thread depth was related to greater POS values (r= 0.628), although OMIs with similar POS values may have different IT values. Thread depth and pitch had some impact on POS. TF depended mainly on the OMI inner (r= 0.961) and outer diameters (r=0.892). A thread depth to outer diameter ratio close to 40% increased TF risk. Although at the same insertion depth the OMI outer and inner diameters are the most important factors for primary stability, other OMI design characteristics (cylindrical vs. conical, thread design) may significantly affect primary stability and torsional fracture. This needs to be considered when selecting the appropriate OMI for the desired orthodontic procedures.

  8. [Pathophysiology of neuropathic pain: molecular mechanisms underlying central sensitization in the dorsal horn in neuropathic pain].

    Science.gov (United States)

    Yamanaka, Hiroki; Noguchi, Koichi

    2012-11-01

    Neuropathic pain syndromes are clinically characterized by spontaneous pain and evoked pain (hyperalgesia and allodynia). The optimal treatment approach for neuropathic pain is still under development because of the complex pathological mechanisms underlying this type of pain. The spinal cord is an important gateway thorough which peripheral pain signals are transmitted to the brain, and sensitization of the spinal neurons is one of the important mechanisms underlying neuropathic pain. Central sensitization represents enhancement of the function of neuronal circuits in nociceptive pathways and is a manifestation of the remarkable plasticity of the somatosensory nervous system after nerve injury. This review highlights the pathological features of central sensitization, which develops because of (1) injury-induced abnormal inputs from primary afferents, (2) increase in the excitability of dorsal horn neurons, and (3) activated glial cell-derived signals.

  9. Crack growth and fracture toughness of amorphous Li-Si anodes: Mechanisms and role of charging/discharging studied by atomistic simulations

    Science.gov (United States)

    Khosrownejad, S. M.; Curtin, W. A.

    2017-10-01

    Fracture is the main cause of degradation and capacity fading in lithiated silicon during cycling. Experiments on the fracture of lithiated silicon show conflicting results, and so mechanistic models can help interpret experiments and guide component design. Here, large-scale K-controlled atomistic simulations of crack propagation (R-curve KI vs. Δa) are performed at LixSi compositions x = 0.5 , 1.0 , 1.5 for as-quenched/relaxed samples and at x = 0.5 , 1.0 for samples created by discharging from higher Li compositions. In all cases, the fracture mechanism is void nucleation, growth, and coalescence. In as-quenched materials, with increasing Li content the plastic flow stress and elastic moduli decrease but void nucleation and growth happen at smaller stress, so that the initial fracture toughness KIc ≈ 1.0 MPa√{ m} decreases slightly but the initial fracture energy JIc ≈ 10.5J/m2 is similar. After 10 nm of crack growth, the fracture toughnesses increase and become similar at KIc ≈ 1.9 MPa√{ m} across all compositions. Plane-strain equi-biaxial expansion simulations of uncracked samples provide complementary information on void nucleation and growth. The simulations are interpreted within the framework of Gurson model for ductile fracture, which predicts JIc = ασy D where α ≃ 1 and D is the void spacing, and good agreement is found. In spite of flowing plastically, the fracture toughness of LixSi is low because voids nucleate within nano-sized distances ahead of the crack (D ≈ 1nm). Scaling simulation results to experimental conditions, reasonable agreement with experimentally-estimated fracture toughnesses is obtained. The discharging process facilitates void nucleation but decreases the flow stress (as shown previously), leading to enhanced fracture toughness at all levels of crack growth. Therefore, the fracture behavior of lithiated silicon at a given composition is not a material property but instead depends on the history of charging

  10. Hip fractures in young adults: a retrospective cross-sectional study of characteristics, injury mechanism, risk factors, complications and follow-up.

    Science.gov (United States)

    Wang, Michael T; Yao, Sarah H; Wong, Phillip; Trinh, Anne; Ebeling, Peter R; Tran, Ton; Milat, Frances; Mutalima, Nora

    2017-12-01

    This study characterises risk factors, complications and follow-up of minimal trauma hip fractures in young adults, adding to limited information examining the management framework. This group have severe systemic disease and significant risk of post-operative complications and subsequent fractures. Improved medical referral pathways enable management of osteoporosis and comorbid diseases. There is a paucity of literature examining minimal trauma hip fractures in young adults, despite extensive management guidelines for older patients. This study aims to characterise risk factors, complications and follow-up of hip fractures to guide management pathways. This is a retrospective study of patients presenting with hip fracture to a single institution from 2009 to 2015. Hip fractures were identified using ICD-10 codes and clinical information documented from medical records. Patients were categorised into minimal trauma (MTF) and high-energy fracture (HEF) groups based on mechanism of injury. Of 2512 patients admitted with hip fracture, 2.5% (n = 62) were aged 15-49 years. Two patients were excluded with pathological fractures, and seven were excluded with no recorded mechanism of injury. MTF occurred in 43 patients and 10 sustained HEF. These groups had similar demographics, fracture locations and treatments. The MTF group had higher American Society of Anaesthesiologists scores (MTF 2.44 ± 0.9; HEF 1.43 ± 0.5; p = 0.025) and higher rates of chronic endocrine disease (MTF 34.9%; HEF 0%; p = 0.046). Rates of post-operative surgical (MTF 24.0%; HEF 12.5%) and medical complications (MTF 27.8%; HEF 12.5%) were high in MTF patients. Subsequent fractures occurred in five (13.9%) MTF patients during the study period compared with none in the HEF group. Only 16 (44.4%) of the MTF patients were referred to endocrine care. Young adults with MTF of the hip have more severe systemic disease and are at risk of post-operative complications and subsequent fractures

  11. [Advanced findings on the molecular mechanisms for behavioral sensitization to psychostimulants].

    Science.gov (United States)

    Ujike, H

    2001-01-01

    Repeated administration of psychostimulants like methamphetamine and cocaine induce behavioral sensitization, which is recognized as an animal model for dependence and psychoses. Many previous studies have proved two major cascades play a crucial roles for molecular mechanisms underling sensitization. The first one is activation of D1 dopamine receptors by robust increase of dopamine release, followed by activation of adenylyl cyclase, increase of cyclic AMP, activation of protein kinase A (PKA) and phosphorylation of proteins by PKA. The second one is activation of NMDA receptor by enhanced release of glutamine, followed by increased intracellular Ca2+ concentration, formation of Ca2+/calmodulin complex, and phosphorylation of several proteins such as calcineurin, CaM-K II and nitric oxide synthase. Recent advanced findings on sensitization mechanisms were reviewed from three different aspects: 1) Studies using knockout mice offered quite amazing findings that D1DA-receptor-lacking mice or dopamine-transporter-lacking mice can develop sensitization and dependence, which were not consistent with the previously established hypotheses based on behavioral pharmacology. In addition, those data showed the important roles of vesicular monoamine transporter 2, 5HT1B receptors and delta FosB. 2) Research on neural-plasticity-related sensitization revealed the involvement of several molecules such as tissue plasminogen activator, arc (activity-regulated, cytoskeleton-associated), synaptophysin and stathmin. Increased expression of these genes may participate in the rearrangement of neural networks with synaptogenesis and expansion of dendrites 3) Trials to discover novel-genes-involved sensitization phenomenon using differential display or subtraction cloning found some candidate genes, mrt-1, NAC-1 and CART. Although in these areas are still in progress, accumulating findings will elucidate the details of the molecular mechanism of behavioral sensitization and dependence.

  12. Geometrical and mechanical properties of the fractures and brittle deformation zones based on the ONKALO tunnel mapping, 2400 - 4390 m tunnel chainage

    Energy Technology Data Exchange (ETDEWEB)

    Moenkkoenen, H.; Rantanen, T.; Kuula, H. [WSP Finland Oy, Helsinki (Finland)

    2012-05-15

    In this report, the rock mechanics parameters of fractures and brittle deformation zones have been estimated in the vicinity of the ONKALO area at the Olkiluoto site, western Finland. This report is an extension of the previously published report: Geometrical and Mechanical properties if the fractures and brittle deformation zones based on ONKALO tunnel mapping, 0-2400 m tunnel chainage (Kuula 2010). In this updated report, mapping data are from 2400-4390 m tunnel chainage. Defined rock mechanics parameters of the fractures are associated with the rock engineering classification quality index, Q', which incorporates the RQD, Jn, Jr and Ja values. The friction angle of the fracture surfaces is estimated from the Jr and Ja numbers. There are no new data from laboratory joint shear and normal tests. The fracture wall compressive strength (JCS) data are available from the chainage range 1280-2400 m. Estimation of the mechanics properties of the 24 brittle deformation zones (BDZ) is based on the mapped Q' value, which is transformed to the GSI value in order to estimate strength and deformability properties. A component of the mapped Q' values is from the ONKALO and another component is from the drill cores. In this study, 24 BDZs have been parameterized. The location and size of the brittle deformation are based on the latest interpretation. New data for intact rock strength of the brittle deformation zones are not available. (orig.)

  13. Incorporating Scale-Dependent Fracture Stiffness for Improved Reservoir Performance Prediction

    Science.gov (United States)

    Crawford, B. R.; Tsenn, M. C.; Homburg, J. M.; Stehle, R. C.; Freysteinson, J. A.; Reese, W. C.

    2017-12-01

    We present a novel technique for predicting dynamic fracture network response to production-driven changes in effective stress, with the potential for optimizing depletion planning and improving recovery prediction in stress-sensitive naturally fractured reservoirs. A key component of the method involves laboratory geomechanics testing of single fractures in order to develop a unique scaling relationship between fracture normal stiffness and initial mechanical aperture. Details of the workflow are as follows: tensile, opening mode fractures are created in a variety of low matrix permeability rocks with initial, unstressed apertures in the micrometer to millimeter range, as determined from image analyses of X-ray CT scans; subsequent hydrostatic compression of these fractured samples with synchronous radial strain and flow measurement indicates that both mechanical and hydraulic aperture reduction varies linearly with the natural logarithm of effective normal stress; these stress-sensitive single-fracture laboratory observations are then upscaled to networks with fracture populations displaying frequency-length and length-aperture scaling laws commonly exhibited by natural fracture arrays; functional relationships between reservoir pressure reduction and fracture network porosity, compressibility and directional permeabilities as generated by such discrete fracture network modeling are then exported to the reservoir simulator for improved naturally fractured reservoir performance prediction.

  14. Extent and mechanism of halothane sensitization of the carotid sinus baroreceptors.

    Science.gov (United States)

    Seagard, J L; Hopp, F A; Bosnjak, Z J; Elegbe, E O; Kampine, J P

    1983-05-01

    The present study was performed to determine the extent and mechanism of carotid sinus baroreceptor sensitization due to halothane in an isolated, denervated carotid sinus in anesthetized dogs (thiopental 25 mg/kg; 5 mg X kg-1 X h-1, maintenance dose). Efferent sympathetic nerves to the sinus were sectioned to eliminate the contribution of these fibers to any sensitization observed. Halothane (H) administration was localized to the carotid sinus by an isolated perfusion system. The perfusion system was used to make standardized sine wave changes in carotid sinus pressure. Carotid sinus afferent nerve activity from single or few-fiber nerve preparations was recorded during carotid sinus pressure changes and the slopes of nerve activity versus carotid sinus pressure were used to determine the gain, or sensitivity, of the baroreceptors. The addition of 0.75% H and 1.5% H to the sinus perfusion produced a dose-dependent sensitization of the baroreceptors. A greater increase in carotid sinus afferent nerve activity for a given increase in sinus pressure was used as an indication of an increase in receptor sensitivity, or sensitization. In the presence of sodium nitroprusside, given in doses to maximally dilate the sinus prior to H administration, only 1.5% H produced baroreceptor sensitization. This suggests the changes in sinus wall tension due to halothane may have contributed to the sensitization seen during H administration. The remaining sensitization at 1.5% H was eliminated in the presence of nitroprusside and 7.5 mM Ca++. This remaining sensitization therefore appears to be Ca++-related and may be due to direct effects of H on the baroreceptors.

  15. Proceedings of the Joint IAEA/CSNI Specialists` Meeting on Fracture Mechanics Verification by Large-Scale Testing held at Pollard Auditorium, Oak Ridge, Tennessee

    Energy Technology Data Exchange (ETDEWEB)

    Pugh, C.E.; Bass, B.R.; Keeney, J.A. [comps.] [Oak Ridge National Lab., TN (United States)

    1993-10-01

    This report contains 40 papers that were presented at the Joint IAEA/CSNI Specialists` Meeting Fracture Mechanics Verification by Large-Scale Testing held at the Pollard Auditorium, Oak Ridge, Tennessee, during the week of October 26--29, 1992. The papers are printed in the order of their presentation in each session and describe recent large-scale fracture (brittle and/or ductile) experiments, analyses of these experiments, and comparisons between predictions and experimental results. The goal of the meeting was to allow international experts to examine the fracture behavior of various materials and structures under conditions relevant to nuclear reactor components and operating environments. The emphasis was on the ability of various fracture models and analysis methods to predict the wide range of experimental data now available. The individual papers have been cataloged separately.

  16. Surface sensitization mechanism on negative electron affinity p-GaN nanowires

    Science.gov (United States)

    Diao, Yu; Liu, Lei; Xia, Sihao; Feng, Shu; Lu, Feifei

    2018-03-01

    The surface sensitization is the key to prepare negative electron affinity photocathode. The thesis emphasizes on the study of surface sensitization mechanism of p-type doping GaN nanowires utilizing first principles based on density function theory. The adsorption energy, work function, dipole moment, geometry structure, electronic structure and optical properties of Mg-doped GaN nanowires surfaces with various coverages of Cs atoms are investigated. The GaN nanowire with Mg doped in core position is taken as the sensitization base. At the initial stage of sensitization, the best adsorption site for Cs atom on GaN nanowire surface is BN, the bridge site of two adjacent N atoms. Surface sensitization generates a p-type internal surface with an n-type surface state, introducing a band bending region which can help reduce surface barrier and work function. With increasing Cs coverage, work functions decrease monotonously and the "Cs-kill" phenomenon disappears. For Cs coverage of 0.75 ML and 1 ML, the corresponding sensitization systems reach negative electron affinity state. Through surface sensitization, the absorption curves are red shifted and the absorption coefficient is cut down. All theoretical calculations can guide the design of negative electron affinity Mg doped GaN nanowires photocathode.

  17. Fracture Toughness Evaluation of a Ni2MnGa Alloy Through Micro Indentation Under Magneto-Mechanical Loading

    Science.gov (United States)

    Goanţă, Viorel; Ciocanel, Constantin

    2017-12-01

    Ni2MnGa is a ferromagnetic alloy that exhibits the shape memory effect either induced by an externally applied magnetic field or mechanical stress. Due to the former, the alloy is commonly called magnetic shape memory alloy or MSMA. The microstructure of the MSMA consists of tetragonal martensite variants (three in the most general case) that are characterized by a magnetization vector which is aligned with the short side of the tetragonal unit cell. Exposing the MSMA to a magnetic field causes the magnetization vector to rotate and align with the external field, eventually leading to variant reorientation. The variant reorientation is observed macroscopically in the form of recoverable strain of up to 6% [1, 2]. As the magnetic field induced reorientation happens instantaneously [1, 3], MSMAs are suitable for fast actuation, sensing, or power harvesting applications. However, actuation applications are limited by the maximum actuation stress of the material that is about 3.5MPa at approximately 2 to 3% reorientation strain. During MSMA fatigue magneto-mechanical characterization studies [4, 5] it was observed that cracks nucleate and grow on the surface of material samples, after a relatively small number of cycles, leading to loss in material performance. This triggered the need for understanding the mechanisms that govern crack nucleation and growth in MSMAs, as well as the nature of the material, i.e. ductile or brittle. The experimental study reported in this paper was carried out to determine material's fracture toughness, the predominant crack growth directions, and the orientation of the cracks relative to the mechanical loading direction and to the material's microstructure. A fixture has been developed to allow Vickers micro indentation of 3mm by 3mm by 20mm Ni2MnGa samples exposed to different levels of magnetic field and/or mechanical stress. Using the measured characteristics of the impression generated during micro indentation, the lengths of

  18. Fracture mechanics aspects in the safe design of ductile iron shipping and storage containers

    International Nuclear Information System (INIS)

    Sappok, M.; Bounin, D.

    1996-01-01

    Containers made of ductile cast iron provide a safe method for transport of radioactive material. Contrary to widespread opinion ductile cast iron is a very tough material and can be manufactured in heavy sections. The containers are designed to withstand the very high impact loads of accidents like free drops onto unyielding targets. The design is based on postulated undetected crack-like flaws at the highest stressed location. Design must show that applied stress intensities are smaller than fracture toughness and no crack initiation and therefore also no crack propagation can occur. The design procedure followed in this paper is given in a new guideline still being drafted by the International Atomic Energy Agency

  19. Mechanisms of boron removal from hydraulic fracturing wastewater by aluminum electrocoagulation.

    Science.gov (United States)

    Sari, Mutiara Ayu; Chellam, Shankararaman

    2015-11-15

    Boron uptake from highly saline hydraulic fracturing wastewater by freshly precipitated amorphous Al(OH)3 precipitates is due to ligand exchange and complexation with surface hydroxyl groups. Consequently, aluminum electrocoagulation can be a feasible approach to remove boron from flowback/produced water. Actual hydraulic fracturing wastewater containing ∼120mg/L boron from the Eagle Ford shale play was employed. Electrocoagulation was performed over a range of aluminum dosages (0-1350mg/L), pH 6.4 and 8, and high current densities (20-80mA/cm(2)) using a cylindrical aluminum anode encompassed by a porous cylindrical 316-stainless steel cathode. Direct measurements of boron uptake along with its chemical state and coordination were made using Attenuated Total Reflection-Fourier Transform Infrared spectroscopy (ATR-FTIR) and X-Ray