WorldWideScience

Sample records for fatigue fracture surfaces

  1. Quantitative analysis by X-ray fractography of fatigue fractured surface under variable amplitude loading

    International Nuclear Information System (INIS)

    Akita, Koichi; Kodama, Shotaro; Misawa, Hiroshi

    1994-01-01

    X-ray fractography is a method of analysing the causes of accidental fracture of machine components or structures. Almost all of the previous research on this problem has been carried out using constant amplitude fatigue tests. However, the actual loads on components and structures are usually of variable amplitudes. In this study, X-ray fractography was applied to fatigue fractured surfaces produced by variable amplitude loading. Fatigue tests were carried out on Ni-Cr-Mo steel CT specimens under the conditions of repeated, two-step and multiple-step loading. Residual stresses were measured on the fatigue fractured surface by an X-ray diffraction method. The relationships between residual stress and stress intensity factor or crack propagation rate were studied. They were discussed in terms of the quantitative expressions under constant amplitude loading, proposed by the authors in previous papers. The main results obtained were as follows : (1) It was possible to estimate the crack propagation rate of the fatigue fractured surface under variable amplitude loading by using the relationship between residual stress and stress intensity factor under constant amplitude loading. (2) The compressive residual stress components on the fatigue fractured surface correspond with cyclic softening of the material rather than with compressive plastic deformation at the crack tip. (author)

  2. X-ray analysis on the fatigue fracture surface of stainless steels

    International Nuclear Information System (INIS)

    Yoshioka, Yasuo; Guimard, B.

    1986-01-01

    Several X-ray diffraction parameters were observed on the fatigue fracture surface and its vicinity of both of SUS420J1 martensitic and SUS304 austenitic stainless steels and we discussed the relation between the stress intensity factor and these parameters. Monotonic plastic zone depth determined by the measurement of residual stress distribution proportionals to the squre of the maximum stress intensity factor as well as the case of ferritic steel. However, it is very difficult to find the relation between the stress intensity factor and residual stress or half value breadth of X-ray diffraction profile in the fracture surface for both materials. On the other hand, the amount of martensite induced by the transformation during fatigue process in SUS304 is related to the maximum stress intensity factor in the fracture surface regardless the stress ratio R. (author)

  3. Fatigue Fracture Characteristics of Ti6Al4V Subjected to Ultrasonic Nanocrystal Surface Modification

    Directory of Open Access Journals (Sweden)

    Xiaojian Cao

    2018-01-01

    Full Text Available The influence of ultrasonic nanocrystal surface modification (UNSM on the fatigue fracture characteristics of Ti6Al4V was investigated. Two groups of specimens were separated due to different heat treatment conditions. Group one was stress-relief annealed at 650 °C, and group two was then treated with solid solution-aging. UNSM with the conditions of a static load of 25 N, vibration amplitude of 30 μm, and 36,000 strikes per unit produced about 40 μm surface severe plastic deformation (SPD layers on both groups of specimens. UNSM improved the microhardness and the compressive residual stress. UNSM also helped achieve a neat surface, almost without changing the surface roughness. The fatigue strengths of these two groups were improved by 7% and 11.7%, respectively. After UNSM, fatigue cracks mainly initiated from the surface of the specimen before the fatigue life of 106 cycles, while they appeared at the internal compress deformed α-phase at the zone between the SPD layer and the core after the fatigue life of 106 cycles. The cracks usually extended along the deformation overflow bands and the process traces on the surface. Through the change of micro-dimples in the fatigue final rupture region, nanocrystals were achieved in the SPD layer. The crystal slip and the surface remodeling together influenced the energy field of crack evolution.

  4. X-ray fractography of fatigue fracture surface under mode I and mode III loading

    International Nuclear Information System (INIS)

    Akiniwa, Yoshiaki; Tanaka, Keisuke; Tsumura, Tsuyoshi

    2001-01-01

    The propagation behavior of a circumferential fatigue crack in cylindrical bars of a carbon steel (JIS SGV410) and a stainless steel (JIS SUS316NG) was investigated under cyclic axial and torsional loadings. The J-integral range was used as a fracture mechanics parameter. When compared at the same J-integral range, the crack propagation rate under mode III was smaller than that under mode I. Parallel markings perpendicular to the crack propagation direction were observed on the fatigue fracture surface obtained under mode III loading. The residual stresses in the radial direction, σ r , and in the tangential direction, σ θ , were measured for both mode I and mode III fatigue fracture surfaces. For mode I fracture surface, σ r was tension, and was almost constant irrespective of the applied J-integral range. σ θ was close to zero for both materials. On the other hand, for mode III, σ r and σ θ were compression. For SUS316NG steel, the compressive stress of σ θ increased with the J-integral range. For SGV410 steel, the change of σ θ with the J-integral range was small. The breadth of diffraction profiles increased with J-integral range for both mode I and III. The breadth was found to be a good parameter to evaluate the applied J-integral range. (author)

  5. X-ray fractography on fatigue fracture surface of high manganese austenitic steel

    International Nuclear Information System (INIS)

    Akita, Koichi; Misawa, Hiroshi; Kodama, Shotaro; Saito, Tetsuro.

    1997-01-01

    Fatigue tests were carried out under constant stress amplitude, using a non-magnetic high manganese Mn-Cr steel. X-ray fractography was applied on the fatigue fractured surface to investigate the relationship between stress intensity factor and residual stress or half-value breadth of the X-ray diffraction profile. The fatigue crack propagation rate of this non-magnetic Mn-Cr steel had the same tendency as in the ordinary structural ferritic steels. The relationship between stress intensity factor and the residual stress or half-value breadth of the steel was almost the same as that of the ferritic cyclic work hardening steels. No stress induced transformation was observed on the fracture surface, but the residual stress on the fractured surface was compressive in the high stress intensity factors range, which is typical in the cyclic work hardening steels. The half-value breadth on the fractured surface increased with increasing effective stress intensity factor range. The relationship between the half-value breadth and stress intensity factor range was represented by a linear line regardless of the stress ratio. Therefore, the acting stress intensity factor range at the time of fracture can be estimated from the half-value breadth. The depth of monotonic plastic zone was estimated from the distribution of half-value breadth beneath the fractured surface. The relationship between the maximum stress intensity factor and half-value breadth was expressed by the equation ω m α(K max /σ y ) 2 , where the value of α was 0.025. This is about one sixth of the value for ferritic steels, and the fact shows the severe work hardening occuring in the plastic zone in this manganese steel. (author)

  6. Correlation between Fatigue Crack Growth Behavior and Fracture Surface Roughness on Cold-Rolled Austenitic Stainless Steels in Gaseous Hydrogen

    Directory of Open Access Journals (Sweden)

    Tai-Cheng Chen

    2018-03-01

    Full Text Available Austenitic stainless steels are often considered candidate materials for use in hydrogen-containing environments because of their low hydrogen embrittlement susceptibility. In this study, the fatigue crack growth behavior of the solution-annealed and cold-rolled 301, 304L, and 310S austenitic stainless steels was characterized in 0.2 MPa gaseous hydrogen to evaluate the hydrogen-assisted fatigue crack growth and correlate the fatigue crack growth rates with the fracture feature or fracture surface roughness. Regardless of the testing conditions, higher fracture surface roughness could be obtained in a higher stress intensity factor (∆K range and for the counterpart cold-rolled specimen in hydrogen. The accelerated fatigue crack growth of 301 and 304L in hydrogen was accompanied by high fracture surface roughness and was associated with strain-induced martensitic transformation in the plastic zone ahead of the fatigue crack tip.

  7. X-ray fractographic study on fatigue fracture surface of structural steels

    International Nuclear Information System (INIS)

    Ogura, Keiji; Miyoshi, Yoshio; Kawaguchi, Masahiro; Kayama, Masahiro.

    1985-01-01

    An X-ray fractographic study was made on the fatigue fracture surface of the structural steels with various strength levels. An emphasis was put on examining the effect of strength level on the residual stress and half-value breadth on and under the fracture surface. It was found that the residual stress on the fracture surface was controlled by Ksub(max) in a low Ksub(max) or ΔK region (Region I), while it was controlled by ΔK rather than Ksub(max) in a high Ksub(max) or ΔK region (Region III). It was also found that another transitional region (Region II) was observed between these two regions in SNCM 815 steel. An explanation for all these behavior was discussed by a proposed model. The distribution of the residual stress and half-value breadth under the fracture surface was found to be usefull for estimating the value of Ksub(max), although the distribution itself was strongly influenced by strength level, particularly the work-softening behavior, of the materials. (author)

  8. Fatigue crack growth and fracture behavior of bainitic rail steels.

    Science.gov (United States)

    2011-09-01

    "The microstructuremechanical properties relationships, fracture toughness, fatigue crack growth and fracture surface morphology of J6 bainitic, manganese, and pearlitic rail steels were studied. Microstructuremechanical properties correlation ...

  9. Fatigue and fracture: Overview

    Science.gov (United States)

    Halford, G. R.

    1984-01-01

    A brief overview of the status of the fatigue and fracture programs is given. The programs involve the development of appropriate analytic material behavior models for cyclic stress-strain-temperature-time/cyclic crack initiation, and cyclic crack propagation. The underlying thrust of these programs is the development and verification of workable engineering methods for the calculation, in advance of service, of the local cyclic stress-strain response at the critical life governing location in hot section compounds, and the resultant crack initiation and crack growth lifetimes.

  10. X-ray fractography by using synchrotron radiation source. Residual stress distribution just beneath fatigue fracture surface

    International Nuclear Information System (INIS)

    Akita, Koichi; Yoshioka, Yasuo; Suzuki, Hiroshi; Sasaki, Toshihiko

    2000-01-01

    The residual stress distributions just beneath the fatigue fracture surface were measured using synchrotron radiation with three different wavelengths, i.e., three different penetration depths. The residual stress distributions were estimated from three kinds of diffraction data by the following process. First, a temporary residual stress distribution in the depth direction is assumed. Theoretical 2θ-sin 2 ψ diagrams for each wavelength, where each has a different penetration depth, are calculated by the cosψ method developed by one of the authors. The sum total of the differences between the theoretical and experimental values of the diffraction angle in 2θ-sin 2 ψ diagrams is calculated. This total value is minimized by changing the assumed stress distribution by the quasi-Newton optimization method. Finally, optimized 2θ-sin 2 ψ diagrams for each penetration depth and detailed stress distribution are determined. The true surface residual stress is obtained from this stress distribution. No effect of load ratio R (= P min /P max ) on the residual stresses of the fatigue fracture surfaces in low-carbon steels was observed when the sin 2 ψ method was used for stress measurement. However, the residual stresses became higher with increasing R when these were measured by the proposed method. On the basis of this, the stress intensity factor range, ΔK, can be estimated from the residual stress on the fatigue fracture surface. (author)

  11. The Fracture of Plasma-Treated Polyurethane Surface under Fatigue Loading

    Directory of Open Access Journals (Sweden)

    Ilya A. Morozov

    2018-02-01

    Full Text Available Plasma treatment of soft polymers is a promising technique to improve biomedical properties of the materials. The response to the deformation of such materials is not yet clear. Soft elastic polyurethane treated with plasma immersion ion implantation is subjected to fatigue uniaxial loading. The influence of the strain amplitude and the plasma treatment regime on damage character is discussed. Surface defects are studied in unloaded and stretched states of the material. As a result of fatigue loading, transverse cracks (with closed overlapping edges as well as with open edges deeply propagating into the polymer and longitudinal folds which are break and bend inward, appear on the surface. Hard edges of cracks cut the soft polymer which is squeezed from the bulk to the surface. The observed damages are related to the high stiffness of the modified surface and its transition to the polymer substrate.

  12. A Study on the Fatigue-Fractured Surface of Normalized SS41 Steel and M.E.F. Dual Phase Steel by an X-ray Diffraction Technique

    International Nuclear Information System (INIS)

    Oh, Sae Wook; Park, Young Chul; Park, Soo Young; Kim, Deug Jin; Hue, Sun Chul

    1996-01-01

    This study verified the relationship between fracture mechanics parameters and X-ray parameters for normalized SS41 steel with homogeneous crystal structure and M.E.F. dual phase steel(martensite encapsulated islands of ferrite). The fatigue crack propagation test were carried out and X-ray diffraction technique was applied to fatigue fractured surface. The change in X-ray parameters(residual stress, half-value breadth) according to the depth of fatigue fractured surface were investigated. The depth of maximum plastic zone, W y , were determined on the basis of the distribution of the half-value breadth for normalized SS41 steel and that of the residual stress for M.E.F. dual phase steel. K max could be estimated by the measurement of W y

  13. Fatigue and insufficiency fractures

    International Nuclear Information System (INIS)

    Lodwick, G.S.; Rosenthal, D.I.; Kattapuram, S.V.; Hudson, T.M.

    1987-01-01

    The incidence of stress fracture is increasing. In our younger society this is due largely to a preocupation with physical conditioning, but in our elderly population it is due to improved recognition and better methods of detection and diagnosis. Stress fracture of the elderly is an insufficiency fracture which occurs in the spine, the pelvis, the sacrum and other bones afflicted with disorders which cause osteopenia. Stress fracture is frequently misdiagnosed as a malignant lesion of bone resulting in biopsy. Scintiscanning provides the greatest frequency of detection, while computed tomography often provides the definitive diagnosis. With increased interest and experience a better insight into the disease has been achieved, and what was once thought of as a simple manifestation of mechanical stress is now known to be an orderly, complex pattern of physiological changes in bone which conform to a model by Frost. The diffuse nature of these changes can be recognized by scintigraphy, radiography and magnetic resonance imaging. 27 refs.; 8 figs

  14. 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

  15. 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.

  16. 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

  17. Fatigue fracture modes of a stainless steel

    International Nuclear Information System (INIS)

    Pacheco, D.J.; Souza e Silva, A.S. de; Monteiro, S.N.

    1977-01-01

    The influence of strain hardening and martensite phase transformation on the fatigue fracture regions (pulsative tension) of a Stainless Steel type AISI 316 was investigated. This lead to the conclusion that the greater austenite strain hardening level only favours the occurrence of a brittle fracture. Also, in as much as the static induced martensite is concerned, a direct influence on the failure process was not observed, whereas, apparently, the one transformed under cyclic loading has no contribution to the rupture mechanisms. (author) [pt

  18. Computational predictive methods for fracture and fatigue

    Science.gov (United States)

    Cordes, J.; Chang, A. T.; Nelson, N.; Kim, Y.

    1994-09-01

    The damage-tolerant design philosophy as used by aircraft industries enables aircraft components and aircraft structures to operate safely with minor damage, small cracks, and flaws. Maintenance and inspection procedures insure that damages developed during service remain below design values. When damage is found, repairs or design modifications are implemented and flight is resumed. Design and redesign guidelines, such as military specifications MIL-A-83444, have successfully reduced the incidence of damage and cracks. However, fatigue cracks continue to appear in aircraft well before the design life has expired. The F16 airplane, for instance, developed small cracks in the engine mount, wing support, bulk heads, the fuselage upper skin, the fuel shelf joints, and along the upper wings. Some cracks were found after 600 hours of the 8000 hour design service life and design modifications were required. Tests on the F16 plane showed that the design loading conditions were close to the predicted loading conditions. Improvements to analytic methods for predicting fatigue crack growth adjacent to holes, when multiple damage sites are present, and in corrosive environments would result in more cost-effective designs, fewer repairs, and fewer redesigns. The overall objective of the research described in this paper is to develop, verify, and extend the computational efficiency of analysis procedures necessary for damage tolerant design. This paper describes an elastic/plastic fracture method and an associated fatigue analysis method for damage tolerant design. Both methods are unique in that material parameters such as fracture toughness, R-curve data, and fatigue constants are not required. The methods are implemented with a general-purpose finite element package. Several proof-of-concept examples are given. With further development, the methods could be extended for analysis of multi-site damage, creep-fatigue, and corrosion fatigue problems.

  19. Fracture probability properties of pure and cantilever bending fatigue of STS304 steel

    International Nuclear Information System (INIS)

    Roh, Sung Kuk; Park, Dae Hyun; Jeong, Soon Uk

    2001-01-01

    Big accidents of flyings, vessel, subways, gas equipments, buildings and bridge happens frequently. Therefore many people are suffering harm of property. The destruction cause of marcaine components is almost accused by fatigue. This study is test for STS304 specimen using pure and cantilever bending state. Rounded and notched specimen including fracture surface investigation was comparatively experimented, fatigue life according to degree of surface finishing was examined. Fatigue fracture probability of notched canilever specimens were predicted by P-S-N curve, median rank and Weibull distribution. And at the relation with the rotational speed and stress, the fatigue life of the test specimen was higher at high speed than low speed

  20. Fatigue fracture of steel after mechanical and ultrasonic strengthening

    International Nuclear Information System (INIS)

    Stotskij, I.M.

    1978-01-01

    Fatigue fracture surfaces of samples after mechanical and ultrasonic strengthening have been studied metallographically and by electron fractography. Studied was the 40Kh steel hardened from 850 deg and then tempered at 180 deg or at 550 deg C. The ultrasound power was 25 kWt, the frequency was 20 kHz, the sample rotation velocity was 39.5 m/min. Mechanical and ultrasonic treatment was found to cause structural changes (formation of a white layer) and deformation of the material under the layer. The fatigue cracks were extending beyond the white layer; their propagation involved generation and coalescence of microcracks on account of segregation of carbides. It is concluded that mechanical and ultrasonic treatment should be used for increasing the fatigue strength of low and average strength materials rather than hardened or low-tempered ones

  1. Fatigue and fracture of fibre metal laminates

    CERN Document Server

    Alderliesten, René

    2017-01-01

    This book contributes to the field of hybrid technology, describing the current state of knowledge concerning the hybrid material concept of laminated metallic and composite sheets for primary aeronautical structural applications. It is the only book to date on fatigue and fracture of fibre metal laminates (FMLs). The first section of the book provides a general background of the FML technology, highlighting the major FML types developed and studied over the past decades in conjunction with an overview of industrial developments based on filed patents. In turn, the second section discusses the mechanical response to quasi-static loading, together with the fracture phenomena during quasi-static and cyclic loading. To consider the durability aspects related to strength justification and certification of primary aircraft structures, the third section discusses thermal aspects related to FMLs and their mechanical response to various environmental and acoustic conditions.

  2. The fracture behavior of an Al-Mg-Si alloy during cyclic fatigue

    International Nuclear Information System (INIS)

    Azzam, Diya; Menzemer, Craig C.; Srivatsan, T.S.

    2010-01-01

    In this paper, is presented and discussed the cyclic fracture behavior of the Al-Mg-Si alloy 6063 that is a candidate used in luminaire light poles. The light poles were subject to fatigue deformation. Test sections were taken from the failed region of the light pole and carefully examined in a scanning electron microscope with the objective of rationalizing the macroscopic fracture mode and intrinsic micromechanisms governing fracture under cyclic loading. The fatigue fracture surface of the alloy revealed distinct regions of early microscopic crack growth, stable crack growth and unstable crack growth and overload. An array of fine striations was found covering the regions of early and stable crack growth. Both macroscopic and fine microscopic cracks were found in the region of unstable crack growth. Very few microscopic voids and shallow dimples were evident on the fatigue fracture surface indicative of the limited ductility of the alloy under cyclic loading conditions.

  3. Surface crack nucleation and propagation in electrodeposited nanocrystalline Ni-P alloy during high cycle fatigue

    Energy Technology Data Exchange (ETDEWEB)

    Kobayashi, Shigeaki; Kamata, Akiyuki [Department of Mechanical Engineering, Faculty of Engineering, Ashikaga Institute of Technology, 268-1 Omae, Ashikaga, Tochigi 326-8558 (Japan); Watanabe, Tadao, E-mail: skoba@ashitech.ac.j [Key Laboratory for Anisotropy and Texture of Materials, Northeastern University, Shenyang, 110004 (China)

    2010-07-01

    The morphology of specimen surface after fatigue fracture was evaluated in connection with grain orientation distribution and grain boundary microstructure to reveal a mechanism of fatigue fracture in nanocrystalline materials. The electrodeposited and sharply {l_brace}001{r_brace} textured Ni -2.0 mass% P alloy with the average grain size of ca. 45 nm and high fractions of low-angle and {Sigma}3 boundaries showed 2 times higher fatigue limit than electrodeposited microcrystalline Ni polycrystal. The surface features of fatigued specimen were classified into two different types of morphologies characterized as brittle fracture at the central area and as ductile fracture at the surrounding area.

  4. High-Cycle, Push–Pull Fatigue Fracture Behavior of High-C, Si–Al-Rich Nanostructured Bainite Steel

    Science.gov (United States)

    Zhao, Jing; Ji, Honghong

    2017-01-01

    The high-cycle, push–pull fatigue fracture behavior of high-C, Si–Al-rich nanostructured bainitic steel was studied through the measurement of fatigue limits, a morphology examination and phase composition analysis of the fatigue fracture surface, as well as fractography of the fatigue crack propagation. The results demonstrated that the push–pull fatigue limits at 107 cycles were estimated as 710–889 MPa, for the samples isothermally transformed at the temperature range of 220–260 °C through data extrapolation, measured under the maximum cycle number of 105. Both the interior inclusion and the sample surface constituted the fatigue crack origins. During the fatigue crack propagation, a high amount of secondary cracks were formed in almost parallel arrangements. The apparent plastic deformation occurred in the fracture surface layer, which induced approximately all retained austenite to transform into martensite. PMID:29286325

  5. High-Cycle, Push–Pull Fatigue Fracture Behavior of High-C, Si–Al-Rich Nanostructured Bainite Steel

    Directory of Open Access Journals (Sweden)

    Jing Zhao

    2017-12-01

    Full Text Available The high-cycle, push–pull fatigue fracture behavior of high-C, Si–Al-rich nanostructured bainitic steel was studied through the measurement of fatigue limits, a morphology examination and phase composition analysis of the fatigue fracture surface, as well as fractography of the fatigue crack propagation. The results demonstrated that the push–pull fatigue limits at 107 cycles were estimated as 710–889 MPa, for the samples isothermally transformed at the temperature range of 220–260 °C through data extrapolation, measured under the maximum cycle number of 105. Both the interior inclusion and the sample surface constituted the fatigue crack origins. During the fatigue crack propagation, a high amount of secondary cracks were formed in almost parallel arrangements. The apparent plastic deformation occurred in the fracture surface layer, which induced approximately all retained austenite to transform into martensite.

  6. Fatigue damage and fracture behavior of tungsten fiber reinforced Zr-based metallic glassy composite

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, H. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China); Zhang, Z.F. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China)]. E-mail: zhfzhang@imr.ac.cn; Wang, Z.G. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China); Qiu, K.Q. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China); Zhang, H.F. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China); Zang, Q.S. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China); Hu, Z.Q. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China)

    2006-02-25

    The fatigue life, damage and fracture behavior of tungsten fiber reinforced metallic glass Zr{sub 41.25}Ti{sub 13.75}Ni{sub 10}Cu{sub 12.5}Be{sub 22.5} composites are investigated under cyclic push-pull loading. It is found that the fatigue life of the composite increases with increasing the volume fraction of tungsten fibers. Similar to crystalline metals, the regions of crack initiation, propagation and overload fracture can be discerned on the fracture surface of the specimen. Fatigue crack normally initiates in the metallic glass matrix at the outer surface of the composite specimen and propagates predominantly in the matrix. Different crack front profile around the tungsten fibers and fiber pullout demonstrate that fatigue crack may propagate around the fiber, leading to bridging of the crack faces by the unbroken fiber and hence improved fatigue crack-growth resistance. Locally decreased effective stiffness in the region where fiber distribution is sparse may provide preferential crack path in the composite. A proposed model was exercised to elucidate different tungsten fiber fracture morphologies in the fatigue crack propagation and overload fracture regions in the light of Poisson's ratio effect during fatigue loading.

  7. Fatigue damage and fracture behavior of tungsten fiber reinforced Zr-based metallic glassy composite

    International Nuclear Information System (INIS)

    Zhang, H.; Zhang, Z.F.; Wang, Z.G.; Qiu, K.Q.; Zhang, H.F.; Zang, Q.S.; Hu, Z.Q.

    2006-01-01

    The fatigue life, damage and fracture behavior of tungsten fiber reinforced metallic glass Zr 41.25 Ti 13.75 Ni 10 Cu 12.5 Be 22.5 composites are investigated under cyclic push-pull loading. It is found that the fatigue life of the composite increases with increasing the volume fraction of tungsten fibers. Similar to crystalline metals, the regions of crack initiation, propagation and overload fracture can be discerned on the fracture surface of the specimen. Fatigue crack normally initiates in the metallic glass matrix at the outer surface of the composite specimen and propagates predominantly in the matrix. Different crack front profile around the tungsten fibers and fiber pullout demonstrate that fatigue crack may propagate around the fiber, leading to bridging of the crack faces by the unbroken fiber and hence improved fatigue crack-growth resistance. Locally decreased effective stiffness in the region where fiber distribution is sparse may provide preferential crack path in the composite. A proposed model was exercised to elucidate different tungsten fiber fracture morphologies in the fatigue crack propagation and overload fracture regions in the light of Poisson's ratio effect during fatigue loading

  8. 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....

  9. The concept of fatigue fracture toughness in fatigue delamination growth behavior

    NARCIS (Netherlands)

    Yao, L.; Alderliesten, R.C.; Benedictus, R.

    2015-01-01

    This paper provides a study on mode I fatigue delamination growth in composite laminates using energy principles. Experimental data has been obtained from fatigue tests conducted on Double Cantilever Beam (DCB) specimens at various stress ratios. A concept of fatigue fracture toughness is proposed

  10. Fatigue fracture of cutter blade made of high-speed steel

    Directory of Open Access Journals (Sweden)

    Beata Letkowska

    2015-04-01

    Full Text Available The quality of the surface of cyclically loaded components is very important. Many observations confirm that the root cause of the micro cracks (causing the fatigue fracture are primarily a surface's defects appearing during production process. These surface defects can be also caused by engraving processes used to perform identification marks. This paper presents the failure analysis of broken blade of the cutter Ku 500VX. The blade was subject of standard metallographic examination, hardness measurements, fractography analysis and metallographic studies using stereoscopic, light and scanning electron microscopes. The damage of the blade was caused by changes of the structure (formation of the brittle micro dendritic structure that occurred during manual electric engraving process when the material was heated till its melting point. As a result the stresses occurred in surface what provided to micro cracking and to propagate the fatigue fracture. The origin of this fatigue fracture was in the place where the inscription was made.

  11. Fatigue fracture of the sacrum in an adolescent

    International Nuclear Information System (INIS)

    Patterson, Scott P.; Daffner, Richard H.; Sciulli, Robert L.; Schneck-Jacob, Stephanie L.

    2004-01-01

    There are relatively few reports of sacral stress fractures in children. In adolescents, sacral stress fractures have been reported in patients involved in vigorous athletic activity. Recognition of these fractures is important to avoid unnecessary biopsy if the findings are confused with tumor or infection. We report a sacral fatigue fracture in a 15-year-old without a history of athletic participation or trauma. (orig.)

  12. Detection of fatigue fracture in pearlitic flake graphite cast iron with the help of scanning and transmission electron microscopy

    International Nuclear Information System (INIS)

    Dunger, B.; Hunger, J.

    1976-01-01

    To prove the existence of the characteristic features of fatigue fracture in a pearlitic flake graphite cast iron, its fracture surface topography revealed by scanning electron microscopy has been compared with that of a pearlitic steel, the fractures having been caused by static tensile and by cyclic bending tests. The characteristic features of fatigue fracture were visible in the pearlitic matrix of the steel and of the flake graphite cast iron as well. These features differ characteristically from the lamellar structure of the pearlite, particularly after etching the surface area of the fractures. The graphite structures as viewed on the electron scanning and the electron transmission microscope are described. (orig.) [de

  13. Fracture surfaces of granular pastes.

    Science.gov (United States)

    Mohamed Abdelhaye, Y O; Chaouche, M; Van Damme, H

    2013-11-01

    Granular pastes are dense dispersions of non-colloidal grains in a simple or a complex fluid. Typical examples are the coating, gluing or sealing mortars used in building applications. We study the cohesive rupture of thick mortar layers in a simple pulling test where the paste is initially confined between two flat surfaces. After hardening, the morphology of the fracture surfaces was investigated, using either the box counting method to analyze fracture profiles perpendicular to the mean fracture plane, or the slit-island method to analyze the islands obtained by cutting the fracture surfaces at different heights, parallel to the mean fracture plane. The fracture surfaces were shown to exhibit scaling properties over several decades. However, contrary to what has been observed in the brittle or ductile fracture of solid materials, the islands were shown to be mass fractals. This was related to the extensive plastic flow involved in the fracture process.

  14. 2014 New Trends in Fatigue and Fracture Conference

    CERN Document Server

    Milovic, Ljubica

    2017-01-01

    This book is a compilation of selected papers from the 2014 New Trends in Fatigue and Fracture (NT2F14) Conference, which was held in Belgrade, Serbia. This prestigious conference brought together delegates from around the globe to discuss how to characterize, predict and analyze the fatigue and fracture of engineering materials, components, and structures using theoretical, experimental, numerical and practical approaches. It highlights some important new trends in fracture mechanics presented at the conference, such as: • two-parameter fracture mechanics, arising from the coupling of fracture toughness and stress constraints • high-performance steel for gas and oil transportation and production (pressure vessels and boilers) • safety and reliability of welded joints This book includes 12 contributions from well-known international scientists and a special tribute dedicated to the scientific contributions of Stojan Sedmark, who passed away in 2014.

  15. Fatigue Fracture Behaviors of Transparent Polycarbonate Materials

    OpenAIRE

    ZHANG Xiao-wen; WU Nan; ZHANG Xuan; MA Li-ting; LI Lei

    2017-01-01

    The effect of the different stress ratios (R) and annealing treatment on the fatigue properties of the transparent polycarbonate (PC) sheet and the mechanism behind were studied, the fatigue crack propagation (FCP) process and mechanism were analyzed. The results show that after annealing, the residual stress of the PC samples decreases obviously and the fatigue properties are greatly improved. This is because the machining process results in tensile stress in the PC samples, eliminating the ...

  16. Fatigue and fracture behavior of low alloy ferritic forged steels

    International Nuclear Information System (INIS)

    Chaudhry, V.; Sharma, A.K.; Muktibodh, U.C.; Borwankar, Neeraj; Singh, D.K.; Srinivasan, K.N.; Kulkarni, R.G.

    2016-01-01

    Low alloy ferritic steels are widely used in nuclear industry for the construction of pressure vessels. Pressure vessel forged low alloy steels 20MnMoNi55 (modified) have been developed indigenously. Experiments have been carried out to study the Low Cycle Fatigue (LCF) and fracture behavior of these forged steels. Fully reversed strain controlled LCF testing at room temperature and at 350 °C has been carried out at a constant strain rate, and for different axial strain amplitude levels. LCF material behavior has been studied from cyclic stress-strain responses and the strain-life relationships. Fracture behavior of the steel has been studied based on tests carried out for crack growth rate and fracture toughness (J-R curve). Further, responses of fatigue crack growth rate tests have been compared with the rate evaluated from fatigue precracking carried out for fracture toughness (J-R) tests. Fractography of the samples have been carried out to reveal dominant damage mechanisms in crack propagation and fracture. The fatigue and fracture properties of indigenously developed low alloy steel 20MnMoNi55 (modified) steels are comparable with similar class of steels. (author)

  17. Evaluation of hot hardness, creep, fatigue and fracture properties of zirconia ceramics by an indentation technique

    International Nuclear Information System (INIS)

    Kutty, T.R.G.; Ganguly, C.; Upadhyaya, D.D.

    1996-01-01

    Zirconia ceramics have wide range engineering applications at room and elevated temperatures. For understanding the mechanical behaviour, the indentation technique was adapted for quick evaluation of hot hardness, creep, fatigue and fracture properties. A Vicker's diamond indentor with 10 N load was employed for hot hardness and creep measurement up to 1300 deg. The fatigue data were evaluated at room temperature by repeated indentation with a constant load (10-2500N) at the same location for a dwell time of 5s until it resulted in the formation of a lateral chip on the sample surface. Thus, the number of cycles for chip formation at a specific indentation load was obtained. The fracture toughness was evaluated at room temperature with a load of 300N using a Vicker's diamond indentor. The results of hot hardness, creep, fatigue, and fracture data ol 3Y-TZP and Mg-PSZ are discussed along with their microstructural features. (authors)

  18. Influence of Aging Conditions on Fatigue Fracture Behaviour of 6063 Aluminum Alloy

    Directory of Open Access Journals (Sweden)

    Rafiq Ahmed Siddiqui

    2001-12-01

    Full Text Available Aluminum - Magnesium - Silicon (Al-Mg-Si 6063 alloy was heat-treated using under aged, peak aged and overage temperatures. The numbers of cycles required to cause the fatigue fracture, at constant stress, was considered as criteria for the fatigue resistance. Moreover, the fractured surface of the alloy at different aging conditions was evaluated by optical microscopy and the Scanning Electron Microscopy (SEM. The SEM micrographs confirmed the cleavage surfaces with well-defined fatigue striations. It has been observed that the various aging time and temperature of the 6063 Al-alloy, produces different modes of fractures. The most suitable age hardening time and temperature was found to be between 4 to 5 hours and to occur at 460 K. The increase in fatigue fracture property of the alloy due to aging could be attributed to a vacancy assisted diffusion mechanism or due to pinning of dislocations movement by the precipitates produced during aging. However, the decrease in the fatigue resistance, for the over aged alloys, might be due to the coalescence of precipitates into larger grains.

  19. Quantitative x-ray fractographic analysis of fatigue fractures

    International Nuclear Information System (INIS)

    Saprykin, Yu.V.

    1983-01-01

    The study deals with quantitative X-ray fractographic investigation of fatigue fractures of samples with sharp notches tested at various stresses and temperatures with the purpose of establishing a connection between material crack resistance parameters and local plastic instability zones restraining and controlling the crack growth. At fatigue fractures of notched Kh18N9T steel samples tested at +20 and -196 deg C a zone of sharp ring notch effect being analogous to the zone in which crack growth rate is controlled by the microshifting mechanisms is singled out. The size of the notched effect zone in the investigate steel is unambiguosly bound to to the stress amplitude. This provides the possibility to determine the stress value by the results of quantitative fractographic analysis of notched sample fractures. A possibility of determining one of the threshold values of cyclic material fracture toughness by the results of fatigue testing and fractography of notched sample fractures is shown. Correlation between the size of the hsub(s) crack effect zone in the notched sample, delta material yield limit and characteristic of cyclic Ksub(s) fracture toughness has been found. Such correlation widens the possibilities of quantitative diagnostics of fractures by the methods of X-ray fractography

  20. Influence of cyclical fatigue on torsional fracture morphology in endodontic instruments.

    Science.gov (United States)

    Lopreite, Gustavo; Basilaki, Jorge; Hecht, Pedro

    2013-01-01

    Cyclical fatigue may influence the appearance and propagation of the type of fracture of an endodontic instrument. The aim of this study was to assess the influence of cyclic fatigue on morphological features of torsional fracture in Pathfile nickel-titanium rotary instruments for surgical preparation in endodontics. Thirty new Pathfile instruments (Dentsply- Maillefer. Ballaigues-Switzerland) diameter .13 and taper .02 were randomly divided into 5 groups (n = 6). Twenty-four of them were subject to cyclical fatigue by continuous rotation using a stainless steel cylinder with internal bore 0.5 mm, length 25 mm, with a curve of 45 degrees and radius 8 mm at 5 mm from the tip, at 300 rpm and 1 Ncm torque for different times: A: 15 sec, B: 75 sec, C: 150 sec and D: 300 sec, while the fifth group was kept as a control (group N). As a second step, the instruments were rotated at 2 rpm and 1 Ncm torque, with their apical 3 mm fixed in a resin block until they suffered torsional fracture. The fracture surfaces were analyzed using a conventional high-vacuum scanning electron microscope (Phillips mod. 515) at 400x. All instruments had ductile fracture areas of different sizes. The ductile fracture areas were measured as percentages of the total area of the instrument by means of Golden Ratio (Softonic) software for measuring images. The data obtained were analyzed statistically using one-way variance analysis followed by Tukey's multiple comparison test. There were significant differences among groups regarding cyclic fatigue time and fragile fracture area (P fatigue to which the rotating PathFile instrument is subject significantly increases the percentage of ductile fracture area produced by torsion.

  1. Fracture and Fatigue: Some New Insights

    Indian Academy of Sciences (India)

    It is over nine decades since fracture mechanics found its importance in the design of mechanical, aerospace and civil engineering structures. Its application started in naval structures during the early part of 20th century. The theory of fracture mechanics was initially found ideal to explain the failure of brittle materials like ...

  2. 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

  3. Creep fracture and creep-fatigue fracture in ceramics and ceramic composites

    International Nuclear Information System (INIS)

    Suresh, S.

    1993-01-01

    This paper summarizes recent advances in the areas of subcritical crack growth in ceramics subjected to static and cyclic loads at elevated temperatures. Attention is devoted to the specific role of pre-existing and in-situ-formed glass films in influencing creep fracture and creep-fatigue fracture. Experimental results on the effects of cyclic frequency and load ratio, along with detailed transmission electron microscopy of crack-tip and crack-wake damage are highlighted. Some general conclusions are drawn about the dependence of high-temperature damage tolerance on interfacial glass films and about the susceptibility of ceramic materials to cyclic fatigue fracture

  4. 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.

  5. Probabilistic finite elements for fatigue and fracture analysis

    Science.gov (United States)

    Belytschko, Ted; Liu, Wing Kam

    1993-04-01

    An overview of the probabilistic finite element method (PFEM) developed by the authors and their colleagues in recent years is presented. The primary focus is placed on the development of PFEM for both structural mechanics problems and fracture mechanics problems. The perturbation techniques are used as major tools for the analytical derivation. The following topics are covered: (1) representation and discretization of random fields; (2) development of PFEM for the general linear transient problem and nonlinear elasticity using Hu-Washizu variational principle; (3) computational aspects; (4) discussions of the application of PFEM to the reliability analysis of both brittle fracture and fatigue; and (5) a stochastic computational tool based on stochastic boundary element (SBEM). Results are obtained for the reliability index and corresponding probability of failure for: (1) fatigue crack growth; (2) defect geometry; (3) fatigue parameters; and (4) applied loads. These results show that initial defect is a critical parameter.

  6. Rotary bending fatigue properties of Inconel 718 alloys by ultrasonic nanocrystal surface modification technique

    Directory of Open Access Journals (Sweden)

    Jun-Hyong Kim

    2015-08-01

    Full Text Available This study investigates the influence of ultrasonic nanocrystal surface modification (UNSM technique on fatigue properties of SAE AMS 5662 (solution treatment of Inconel 718 alloys. The fatigue properties of the specimens were investigated using a rotary bending fatigue tester. Results revealed that the UNSM-treated specimens showed longer fatigue life in comparison with those of the untreated specimens. The improvement in fatigue life of the UNSM-treated specimens is attributed mainly to the induced compressive residual stress, increased hardness, reduced roughness and refined grains at the top surface. Fractured surfaces were analysed using a scanning electron microscopy (SEM in order to give insight into the effectiveness of UNSM technique on fracture mechanisms and fatigue life.

  7. Macro and Microscopic Investigation on Fracture Specimen of Alloy 617 Base Metal and Weldment in Low Cycle Fatigue Regime

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Seon Jin; Dewa, Rando Tungga [Pukyung National Univ., Busan (Korea, Republic of); Kim, Won Gon [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2016-06-15

    This paper investigates macro- and microscopic fractography performed on fracture specimens from low cycle fatigue (LCF) testings through an Alloy 617 base metal and weldments. The weldment specimens were taken from gas tungsten arc welding (GTAW) pad of Alloy 617. The aim of the present study is to investigate the macro- and microscopic aspects of the low cycle fatigue fracture mode and mechanism of Alloy 617 base metal and GTAWed weldment specimens. Fully axial total strain controlled fatigue tests were conducted at room temperature with total strain ranges of 0.6, 0.9, 1.2 and 1.5%. Macroscopic fracture surfaces of Alloy 617 base metal specimens showed a flat type normal to the fatigue loading direction, whereas the GTAWed weldment specimens were of a shear/star type. The fracture surfaces of both the base metal and weldment specimens revealed obvious fatigue striations at the crack propagation regime. In addition, the fatigue crack mechanism of the base metal showed a transgranular normal to fatigue loading direction; however, the GTAWed weldment specimens showed a transgranular at approximately 45° to the fatigue loading direction.

  8. Macro and Microscopic Investigation on Fracture Specimen of Alloy 617 Base Metal and Weldment in Low Cycle Fatigue Regime

    International Nuclear Information System (INIS)

    Kim, Seon Jin; Dewa, Rando Tungga; Kim, Won Gon

    2016-01-01

    This paper investigates macro- and microscopic fractography performed on fracture specimens from low cycle fatigue (LCF) testings through an Alloy 617 base metal and weldments. The weldment specimens were taken from gas tungsten arc welding (GTAW) pad of Alloy 617. The aim of the present study is to investigate the macro- and microscopic aspects of the low cycle fatigue fracture mode and mechanism of Alloy 617 base metal and GTAWed weldment specimens. Fully axial total strain controlled fatigue tests were conducted at room temperature with total strain ranges of 0.6, 0.9, 1.2 and 1.5%. Macroscopic fracture surfaces of Alloy 617 base metal specimens showed a flat type normal to the fatigue loading direction, whereas the GTAWed weldment specimens were of a shear/star type. The fracture surfaces of both the base metal and weldment specimens revealed obvious fatigue striations at the crack propagation regime. In addition, the fatigue crack mechanism of the base metal showed a transgranular normal to fatigue loading direction; however, the GTAWed weldment specimens showed a transgranular at approximately 45° to the fatigue loading direction

  9. Flexural fracture and fatigue behavior of steel-fiber-reinforced concrete structures

    International Nuclear Information System (INIS)

    Chang, D.I.

    1995-01-01

    Fracture and fatigue tests were performed in order to investigate the fracture and fatigue behavior of steel-fibre-reinforced concrete (SFRC) structures. 33 SFRC beams were used in the fracture and fatigue tests. The relationship between loading, strain and midspan deflection of the beams was observed under the three-point loading system.From the test results, the effects of the fiber content, fiber aspect ratio and notch-to-depth ratio on the concrete fracture and fatigue behavior were studied, and the fatigue strengths of SFRC beams were calculated. According to the regression technique, some empirical formulae for predicting the fatigue strength of SFRC beams were also suggested. (orig.)

  10. 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.

  11. Fatigue stress fractures of the sacrum: diagnosis with MR imaging

    International Nuclear Information System (INIS)

    Ahovuo, J.A.; Vusuri, T.

    2004-01-01

    The aim of this study was to describe the MRI findings and clinical observations in a fatigue stress fracture of the sacrum. In this retrospective study, 380 conscripts (53 women, 327 men; age range 18-29 years, mean age 20.7 years) who suffered from stress-related hip pain were studied with MRI of the pelvis. The findings of MRI were evaluated with regard to stress fracture of the sacrum. Thirty-one (8%) patients had MRI changes in signal intensity of the cranial part of the sacrum, extending to the first and second sacral foramina. The MRI changes in signal intensity were intermediate on T1-weighted images, and high on short tau inversion recovery or T2-weighted fat-suppressed images. A linear signal void fracture line was also seen. Multiple stress injuries to the pelvic bones were also seen in 7 of 31 (23%) patients. Five patients (16%) had bilateral sacral stress fracture. Fatigue sacral stress fractures appeared more commonly in women than in men (p<0.001). During recovery time 20 of the 31 patients underwent control MRI, and fatty marrow conversion was seen in 8 (40%) cases as high signal intensity on T1-weighted images, which disappeared 5-6 months after the onset of symptoms. Fatigue sacral stress fractures are associated with stress-related hip pain. These fractures were more common in women than in men. Other stress injuries of the pelvis may be seen simultaneously with sacral stress fractures. Signal intensity of the sacrum was normal after 5-6 months

  12. 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

  13. Fatigue and fracture behavior of coiled pipes; Comportamento a fratura e fadiga de tubos bobinados

    Energy Technology Data Exchange (ETDEWEB)

    Pope, Alexandre M.; Silva, Renato M.C. [PETROBRAS, Rio de Janeiro, RJ (Brazil); Frainer, Vitor J; Tarnowski, Gabriel A.; Strohaecker, Telmo R. [Rio Grande do Sul Univ., Porto Alegre, RS (Brazil)

    2005-07-01

    The possibility of applying coiled pipes in dynamic situations, such as risers, was investigated through full scale fatigue and fracture tests. A total of sixteen X-65 pipe specimens 41/2'' Od x 0.3'' x 13', containing a bias weld at the mid length, were fatigue tested in a resonance rig at 27 Hz. Six specimens were tested in the as fabricated condition while the ten others were previously subjected to five plastic deformation cycles, simulating reeling operations.. Tests were run until a crack propagated through thickness or 10{sup 7} cycles were achieved. Two cracked specimens were fracture tested in tension. All tests were carried out at room temperature. Test results showed that the fatigue lives were above the Bs-7608 mean class 'B' curves independently whether the specimen were plastically deformed or not. Post fatigue inspection and fractographic examination revealed that fatigue cracks propagate mostly from pits or surface scratches rather than from the bias weld. The two full size tensile specimens failed by ductile fracture at 80% of the material measured strength. (author)

  14. Committee III.2 Fatigue and Fracture

    DEFF Research Database (Denmark)

    Brennan, F. P.; Branner, Kim; den Besten, J.H.

    2015-01-01

    Concern for crack initiation and growth under cyclic loading as well as unstable crack propagation and tearing in ship and offshore structures. Due attention shall be paid to practical application and statistical description of fracture control methods in design, fabrication and service. Consider......Concern for crack initiation and growth under cyclic loading as well as unstable crack propagation and tearing in ship and offshore structures. Due attention shall be paid to practical application and statistical description of fracture control methods in design, fabrication and service...

  15. Probabilistic finite elements for fracture and fatigue analysis

    Science.gov (United States)

    Liu, W. K.; Belytschko, T.; Lawrence, M.; Besterfield, G. H.

    1989-01-01

    The fusion of the probabilistic finite element method (PFEM) and reliability analysis for probabilistic fracture mechanics (PFM) is presented. A comprehensive method for determining the probability of fatigue failure for curved crack growth was developed. The criterion for failure or performance function is stated as: the fatigue life of a component must exceed the service life of the component; otherwise failure will occur. An enriched element that has the near-crack-tip singular strain field embedded in the element is used to formulate the equilibrium equation and solve for the stress intensity factors at the crack-tip. Performance and accuracy of the method is demonstrated on a classical mode 1 fatigue problem.

  16. Observation of fracture behavior of 3-D printed specimens under rolling contact fatigue in water

    Directory of Open Access Journals (Sweden)

    Mizobe Koshiro

    2017-01-01

    Full Text Available Polymer bearing was widely used in the corrosive conditions because of its high corrosion durability. The polymer bearing had been formed using molding and machining until the new 3-D printing method was developed. In this study, we performed the rolling contact fatigue tests of the 3-D printed specimens in water and observed the fracture behaviour of the specimens. We found that the surface cracks are related to both the rolling direction and the lamination directions.

  17. Fracture Toughness and Fatigue Crack Growth Behavior of As-Cast High-Entropy Alloys

    Science.gov (United States)

    Seifi, Mohsen; Li, Dongyue; Yong, Zhang; Liaw, Peter K.; Lewandowski, John J.

    2015-08-01

    The fracture toughness and fatigue crack growth behavior of two as-vacuum arc cast high-entropy alloys (HEAs) (Al0.2CrFeNiTi0.2 and AlCrFeNi2Cu) were determined. A microstructure examination of both HEA alloys revealed a two-phase structure consisting of body-centered cubic (bcc) and face-centered cubic (fcc) phases. The notched and fatigue precracked toughness values were in the range of those reported in the literature for two-phase alloys but significantly less than recent reports on a single phase fcc-HEA that was deformation processed. Fatigue crack growth experiments revealed high fatigue thresholds that decreased significantly with an increase in load ratio, while Paris law slopes exhibited metallic-like behavior at low R with significant increases at high R. Fracture surface examinations revealed combinations of brittle and ductile/dimpled regions at overload, with some evidence of fatigue striations in the Paris law regime.

  18. Fatigue fracture analysis in medium carbon structural steel and austenitic stainless steel by X-ray fractography

    International Nuclear Information System (INIS)

    Rao, N.N.; Azmi bin Rahmat

    1994-01-01

    Apart from the reidual stresses present in the bulk material, a growing fatigue crack may develop its own stress field ahead of the crack tip which in turn could influence the crack propagation behaviour. A fracture surface analysis through measurement of the residual stress of a failed component may provide some additional useful information to that obtained through conventional metallurgical and fracture mechanics investigations. This method of fracture surface analysis using x-ray diffraction technique is known as X -ray Fractography . Residual stress (ρ sub γ) and the full width at half maximum (FWHM) of the x-ray diffraction profile of any reflection are determined at different crack lengths on the fracture surface. These are then corelated to the fracture toughness parameters such as fracture toughness K sub I sub C, the maximum stress intensity factor K sub max and the stress intensity factor range δK. The present investigation aims at detailed x-ray analysis of the fatigue fractured surfaces of the compact tension specimens prepared from ferritic and austenitic stainless steels. The ferritic steel has been subjected to various heat treatments to obtain different microstructures and mechanical properties. The overall observations are analyzed through fatigue (cumulative) damage and material science concepts

  19. Fatigue test results of straight pipe with flaws in inner surface

    International Nuclear Information System (INIS)

    Shibata, Katsuyuki; Oba, Toshihiro; Kawamura, Takaichi; Yokoyama, Norio; Miyazono, Shohachiro

    1981-01-01

    Fatigue and fracture tests of piping models with flaws in the inner surface were carried out to investigate the fatigue crack growth, coalescence of multiple cracks and fracture behavior. Two straight test pipes with and without weldment in the test section of SUS304L stainless steel were tested under almost the same test conditions. Three artificial defects were machined in the inner surface of the test section of the test pipes. The fatigue test were performed untill the cracks coalesced and grew through the thickness. Subsequently, a static load was imposed on test pipe which contained a large crack in the test section. The test results show that the fatigue crack growth is slower than that predicted by the method specified in the Section XI of ASME Boiler and Pressure Vessel Code, and that the test pipes can endure more than the static load of 3Sm without an unstable fracture. (author)

  20. Fatigue and fracture mechanics in pressure vessels and piping. PVP-Volume 304

    International Nuclear Information System (INIS)

    Mehta, H.S.; Wilkowski, G.; Takezono, S.; Bloom, J.; Yoon, K.; Aoki, S.; Rahman, S.; Nakamura, T.; Brust, F.; Yoshimura, S.

    1995-01-01

    Fracture mechanics and fatigue evaluations are an important part of the structural integrity analyses to assure safe operation of pressure vessels and piping components during their service life. The paper presented in this volume illustrate the application of fatigue and fracture mechanics techniques to assess the structural integrity of a wide variety of Pressure Vessels and Piping components. The papers are organized in six sections: (1) fatigue and fracture--vessels; (2) fatigue and fracture--piping; (3) fatigue and fracture--material property evaluations; (4) constraint effects in fracture mechanics; (5) probabilistic fracture mechanics analyses; and (6) user's experience with failure assessment diagrams. Separate abstracts were prepared for most of the papers in this book

  1. Surface contact fatigue failures in gears

    CSIR Research Space (South Africa)

    Fernandes, PJL

    1997-06-01

    Full Text Available Surface contact fatigue is the most common cause of gear failure. It results in damage to contacting surfaces which can significantly reduce the load-carrying capacity of components, and may ultimately lead to complete failure of a gear. Three types...

  2. A study of fatigue and fracture response of cantilevered luminaire structures made from aluminum alloy 6063

    Energy Technology Data Exchange (ETDEWEB)

    Menzemer, Craig C. [Department of Civil Engineering, University of Akron, Akron, OH 443265 (United States); Azzam, Diya [Department of Civil Engineering, University of Akron, Akron, OH 443265 (United States); California Department of Transportation (Caltrans), Bridge Structure Design (Branch, 10) Los Angeles Projects, 1801 30th Street, Sacramento, CA 95816 (United States); Srivatsan, T.S., E-mail: TSrivatsan@uakron.edu [Division of Materials Science and Engineering, Department of Mechanical Engineering, University of Akron, Akron, OH 44325-3903 (United States)

    2010-07-15

    In the experimental results elegantly and exhaustively elaborated upon in this paper the local stresses, obtained from finite element analysis, was used to develop estimates of the stress intensity factor (SIF). In combination with crack growth data, the fatigue lives of both the through-plate and an integrally stiffened socket connection were estimated using software developed by the U.S. Air Force (and referred to as AFGROW). The fatigue life estimates correlated well with the test results provided the crack growth rate data was obtained under conditions of minimal closure at higher stress ratios (of the order R = 0.7). In an attempt to establish the fatigue lives in the high cycle regime, the measured residual stresses had to be included in the analysis. For identical stress ranges, the 25 mm thick through-plate socket connection exhibited noticeably lower fatigue lives when compared to the integrally stiffened shoe-base structure. Scanning electron microscopy observations revealed pockets of well-defined striations consistent with stable growth of the crack through the microstructure prior to the onset of unstable crack growth culminating in catastrophic fracture. In the slow growth region, the fracture surface revealed pockets of shallow, well-defined striations that were uniformly spaced indicative of the occurrence of localized microplastic deformation.

  3. Fatigue and fracture toughness characteristics of laser rapid manufactured Inconel 625 structures

    International Nuclear Information System (INIS)

    Ganesh, P.; Kaul, R.; Paul, C.P.; Tiwari, Pragya; Rai, S.K.; Prasad, R.C.; Kukreja, L.M.

    2010-01-01

    Research highlights: → Mechanical test results of Laser rapid manufactured (LRM) Inconel 625 are reported. → 12 and 25 mm thick CT specimens of LRM Inconel 625 showed similar fatigue crack growth. → Stage II crack growth behavior is observed in the investigated ΔK range. → Fracture toughness testing by J-integral method yielded J 1c of about 200-250 kJ/m 2 . - Abstract: Fatigue crack growth and fracture toughness characteristics of laser rapid manufactured (LRMed) Inconel 625 compact tension specimens of thickness 12 and 25 mm were investigated. Fatigue crack propagation in all the specimens investigated in the stress intensity range (ΔK) of 14-38 MPa√m, exhibited stage II crack growth in Paris' regime with nearly same slopes of crack growth per cycle versus ΔK plot. Fatigue crack growth rates in the LRMed specimens of present study were found to be lower than the reported values for wrought Inconel 625 in the ΔK range of 14-24 MPa√m and above this range they tended to coincide. X-ray diffraction patterns of the fractured surfaces revealed that the crack propagated along the growth direction of the specimens which was predominantly along the (1 1 1) plane. The fracture toughness values (J 0.2 ) for LRMed Inconel 625 specimens were found to be in the range of about 200-255 kJ/m 2 . The LRMed specimens exhibited stable crack growth during the J-integral test.

  4. Fatigue and fracture toughness characteristics of laser rapid manufactured Inconel 625 structures

    Energy Technology Data Exchange (ETDEWEB)

    Ganesh, P., E-mail: ganesh@rrcat.gov.in [Laser Materials Processing Division, Raja Ramanna Centre for Advanced Technology, Indore (MP) 452013 (India); Kaul, R.; Paul, C.P. [Laser Materials Processing Division, Raja Ramanna Centre for Advanced Technology, Indore (MP) 452013 (India); Tiwari, Pragya; Rai, S.K. [Indus Synchrotrons Utilization Division, Raja Ramanna Centre for Advanced Technology, Indore (MP) 452013 (India); Prasad, R.C. [Metallurgy and Materials Science Department, IIT Bombay, Mumbai 400 076 (India); Kukreja, L.M. [Laser Materials Processing Division, Raja Ramanna Centre for Advanced Technology, Indore (MP) 452013 (India)

    2010-11-15

    Research highlights: {yields} Mechanical test results of Laser rapid manufactured (LRM) Inconel 625 are reported. {yields} 12 and 25 mm thick CT specimens of LRM Inconel 625 showed similar fatigue crack growth. {yields} Stage II crack growth behavior is observed in the investigated {Delta}K range. {yields} Fracture toughness testing by J-integral method yielded J{sub 1c} of about 200-250 kJ/m{sup 2}. - Abstract: Fatigue crack growth and fracture toughness characteristics of laser rapid manufactured (LRMed) Inconel 625 compact tension specimens of thickness 12 and 25 mm were investigated. Fatigue crack propagation in all the specimens investigated in the stress intensity range ({Delta}K) of 14-38 MPa{radical}m, exhibited stage II crack growth in Paris' regime with nearly same slopes of crack growth per cycle versus {Delta}K plot. Fatigue crack growth rates in the LRMed specimens of present study were found to be lower than the reported values for wrought Inconel 625 in the {Delta}K range of 14-24 MPa{radical}m and above this range they tended to coincide. X-ray diffraction patterns of the fractured surfaces revealed that the crack propagated along the growth direction of the specimens which was predominantly along the (1 1 1) plane. The fracture toughness values (J{sub 0.2}) for LRMed Inconel 625 specimens were found to be in the range of about 200-255 kJ/m{sup 2}. The LRMed specimens exhibited stable crack growth during the J-integral test.

  5. Fracture resistance of dental nickel–titanium rotary instruments with novel surface treatment: Thin film metallic glass coating

    Directory of Open Access Journals (Sweden)

    Chih-Wen Chi

    2017-05-01

    Conclusion: The novel surface treatment of Ti-Zr-B thin film metallic glass on dental NiTi rotary files can effectively improve the fatigue fracture resistance by offering a smooth coated surface with amorphous microstructure.

  6. Effects of electropolishing surface treatment on the cyclic fatigue resistance of BioRace nickel-titanium rotary instruments.

    Science.gov (United States)

    Lopes, Hélio P; Elias, Carlos N; Vieira, Victor T L; Moreira, Edson J L; Marques, Raquel V L; de Oliveira, Julio C Machado; Debelian, Gilberto; Siqueira, José F

    2010-10-01

    This study evaluated the influence of electropolishing surface treatment on the number of cycles to fracture of BioRace rotary nickel-titanium endodontic instruments. BioRace size BR5C instruments with or without electropolishing surface treatment were used in an artificial curved canal under rotational speed of 300 rpm until fracture. Fractured surfaces and the helical shafts of fractured instruments were analyzed by scanning electron microscopy (SEM). Polished instruments displayed a significantly higher number of cycles to fracture when compared with nonpolished instruments (P ductile morphologic characteristics. Evaluation of the separated fragments after cyclic fatigue testing showed the presence of microcracks near the fracture surface. Polished instruments exhibited fine cracks that assumed an irregular path (zigzag crack pattern), whereas nonpolished instruments showed cracks running along the machining grooves. Electropolishing surface treatment of BioRace endodontic instruments significantly increased the cyclic fatigue resistance. Copyright © 2010 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

  7. The interaction between non-metallic inclusions and surface roughness in fatigue failure and their influence on fatigue strength

    International Nuclear Information System (INIS)

    Saberifar, S.; Mashreghi, A.R.; Mosalaeepur, M.; Ghasemi, S.S.

    2012-01-01

    Highlights: ► The fatigue strength of a tested steel was affected by inclusions and surface notches. ► Inclusions were the main fatigue crack sources even in rough specimens. ► The stress intensity factor represented the behavior of inclusions properly. ► In rough steels the effect of inclusions was intensified by surface roughness. ► The critical inclusion size increased when surface roughness was removed. -- Abstract: In this study, the influence of non-metallic inclusions on the fatigue behavior of 30MnVS6 steel containing different inclusion sizes and surface roughness has been investigated. Scanning electron microscope (SEM) was used to examine fatigue fracture origins. It was concluded that the non-metallic inclusions were dominant fatigue crack initiation sites in both smooth and rough specimens. This was justified by the calculation of stress intensity factor generated by both surface roughness and non-metallic inclusions, based on Murakami’s model. In addition, it was found that for a given stress, the critical inclusion size could be increased by eliminating the surface roughness.

  8. Effects of fatigue induced damage on the longitudinal fracture resistance of cortical bone.

    Science.gov (United States)

    Fletcher, Lloyd; Codrington, John; Parkinson, Ian

    2014-07-01

    As a composite material, cortical bone accumulates fatigue microdamage through the repetitive loading of everyday activity (e.g. walking). The accumulation of fatigue microdamage is thought to contribute to the occurrence of fragility fractures in older people. Therefore it is beneficial to understand the relationship between microcrack accumulation and the fracture resistance of cortical bone. Twenty longitudinally orientated compact tension fracture specimens were machined from a single bovine femur, ten specimens were assigned to both the control and fatigue damaged groups. The damaged group underwent a fatigue loading protocol to induce microdamage which was assessed via fluorescent microscopy. Following fatigue loading, non-linear fracture resistance tests were undertaken on both the control and damaged groups using the J-integral method. The interaction of the crack path with the fatigue induced damage and inherent toughening mechanisms were then observed using fluorescent microscopy. The results of this study show that fatigue induced damage reduces the initiation toughness of cortical bone and the growth toughness within the damage zone by three distinct mechanisms of fatigue-fracture interaction. Further analysis of the J-integral fracture resistance showed both the elastic and plastic component were reduced in the damaged group. For the elastic component this was attributed to a decreased number of ligament bridges in the crack wake while for the plastic component this was attributed to the presence of pre-existing fatigue microcracks preventing energy absorption by the formation of new microcracks.

  9. The Effect of Creep Aging on the Fatigue Fracture Behavior of 2524 Aluminum Alloy

    OpenAIRE

    Wenke Li; Lihua Zhan; Lingfeng Liu; Yongqian Xu

    2016-01-01

    Normal temperature tensile and fatigue tests were adopted to test the mechanical performance and fatigue life of 2524 aluminum alloy under the three states of T3, artificial aging, and creep aging, and scanning electron microscope and transmission electron microscope were also used to observe the fatigue fracture morphology and aging precipitation features of the alloy under the above three states. Results showed that the alloy treated by creep aging can obtain higher fatigue life, but that t...

  10. The effect of surface corrosion damage on the fatigue life of 6061-T6 aluminum alloy extrusions

    Energy Technology Data Exchange (ETDEWEB)

    Weber, Matthew; Eason, Paul D.; Özdeş, Hüseyin; Tiryakioğlu, Murat, E-mail: m.tiryakioglu@unf.edu

    2017-04-06

    An investigation was performed where 6061-T6 extrusions were exposed to a 3.5% NaCl solution at pH 2 for 2 days and 24 days to create distinct surface flaws. The effect of these flaws on the rotating beam fatigue life was then investigated and analyzed by using Wöhler curves, Weibull statistics and scanning electron microscopy (SEM). It was determined that corrosion damage reduced the fatigue life significantly and specimens corroded for both 2-days and 24-days exhibited similar fatigue lives. Statistical analyses showed that fatigue life of all three datasets followed the 3-parameter Weibull distribution and the difference between the fatigue lives of two corroded datasets was statistically insignificant. Analysis of fracture surfaces showed that sizes of pits that led to fatigue crack initiation were very different in the two corroded datasets. Implications of the similarity in fatigue lives despite disparity in surface condition are discussed in detail in the paper.

  11. Stresses, fatigue and fracture analysis in the tube sheets

    International Nuclear Information System (INIS)

    Billon, F.

    1986-05-01

    The purpose of the present work is to study the behaviour of the nuclear PWR steam generator tube sheet. But the methods developed in this field can easily be generalized in order to study tube sheets from any other type of heat exchangers. The aim of the stress analysis of these sheets is to verify their correct design, to quantify the risk of fatigue damage in the areas submitted to a high stress concentration and through the fracture mechanic, to make sure there is no risk of fast fracture resulting from initiated or pre-existing defects. This analysis necessarily relates to the calculation of stresses in all parts of the multidrilled area, mainly around the holes where they are concentrated. However the tube sheets are so complexe structures that their direct modelization cannot be envisaged within the context of the finite element method. We then must refer to the concept of equivalent medium in order to calculate the nominal stresses. Then using the stresses multiple fonctions appropriate to the net geometry, we can calculate the actual stresses concentrated around the holes. The method depends on the behaviour of the elementary volume which represents the behaviour of the multidrilled medium. This approach must allow to correctly take account of the ''thermal skin effect'', which is a phenomenon particular to the tube sheets with thermal loads. It must as well be generalized in order to analyse the irregular ligaments which affect the periodical stresses distribution and locally overconcentrate them [fr

  12. NASGRO(registered trademark): Fracture Mechanics and Fatigue Crack Growth Analysis Software

    Science.gov (United States)

    Forman, Royce; Shivakumar, V.; Mettu, Sambi; Beek, Joachim; Williams, Leonard; Yeh, Feng; McClung, Craig; Cardinal, Joe

    2004-01-01

    This viewgraph presentation describes NASGRO, which is a fracture mechanics and fatigue crack growth analysis software package that is used to reduce risk of fracture in Space Shuttles. The contents include: 1) Consequences of Fracture; 2) NASA Fracture Control Requirements; 3) NASGRO Reduces Risk; 4) NASGRO Use Inside NASA; 5) NASGRO Components: Crack Growth Module; 6) NASGRO Components:Material Property Module; 7) Typical NASGRO analysis: Crack growth or component life calculation; and 8) NASGRO Sample Application: Orbiter feedline flowliner crack analysis.

  13. Fatigue and Fracture Characterization of Aircraft Aluminum Alloys Damaged by Prior Corrosion

    National Research Council Canada - National Science Library

    Baldwin, J

    2002-01-01

    At the time of the initiation of this project, there was no comprehensive data describing corrosion's effect on the fatigue and fracture behavior of aluminum alloys typically found in aging aircraft...

  14. Fracture resistance and fatigue crack growth characteristics of two Al-Cu-Mg-Zr alloys

    Science.gov (United States)

    Sarkar, Bhaskar; Lisagor, W. B.

    1992-01-01

    The dependence of strength, fracture resistance, and fatigue crack growth rate on the aging conditions of two alloy compositions based on Al-3.7Cu-1.85Mg-0.2Mn is investigated. Mechanical properties were evaluated in two heat treatment conditions and in two orientations (longitudinal and transverse). Compact tension specimens were used to determine fatigue crack growth characteristics and fracture resistance. The aging response was monitored on coupons using hardness measurements determined with a standard Rockwell hardness tester. Fracture resistance is found to increase with increasing yield strength during artificial aging of age-hardenable 2124-Zr alloys processed by powder metallurgy techniques. Fatigue crack growth rate increases with increasing strength. It is argued that these changes are related to deformation modes of the alloys; a homogeneous deformation mode tends to increase fracture resistance and to decrease the resistance to the fatigue crack propagation rate.

  15. Correction of fatigue parameters of concrete using approximation of mechanical-Fracture parameters in time

    Czech Academy of Sciences Publication Activity Database

    Šimonová, H.; Keršner, Z.; Seitl, Stanislav; Pryl, D.; Pukl, R.

    -, č. 1 (2012), s. 57-59 ISSN 1213-3116 R&D Projects: GA ČR(CZ) GAP104/11/0833 Institutional support: RVO:68081723 Keywords : fatigue * concrete * correction * fracture parameters Subject RIV: JL - Materials Fatigue, Friction Mechanics

  16. A study on the ductile fracture of a surface crack, 1

    International Nuclear Information System (INIS)

    Kikuchi, Masanori; Nishio, Tamaki; Yano, Kazunori; Machida, Kenji; Miyamoto, Hiroshi

    1988-01-01

    Ductile fracture of surface crack is studied experimentally and numerically. At first, fatigue pre-crack is introduced, and the aspect ratios of the growing fatigue crack are measured. Then the ductile fracture test is carried out and the distributions of SZW and Δa are measured. It is noted that Δa is largest where φ, the angle from surface, is nearly 30deg. J integral distribution is evaluated by the finite element method, and it is shown that the J value is also the largest where φ is nearly 30deg. (author)

  17. Effects of micro arc oxidation on fatigue limits and fracture morphologies of 7475 high strength aluminum alloy

    Energy Technology Data Exchange (ETDEWEB)

    Dejun, Kong, E-mail: kong-dejun@163.com [College of Mechanical Engineering, Changzhou University, Changzhou, 213164 (China); Jiangsu Key Laboratory of Materials Surface Science and Technology, Changzhou University, Changzhou, 213164 (China); Hao, Liu; Jinchun, Wang [College of Mechanical Engineering, Changzhou University, Changzhou, 213164 (China)

    2015-11-25

    The oxide coatings with thicknesses of 8 μm, 10 μm, and 15 μm were prepared on 7475 aluminum alloy with micro arc oxidation (MAO) by controlling MAO time, the fatigue limits of original and MAO samples were contrastively measured by the Roccati method. The surface-interface morphologies, fracture morphologies, surface phases, and residual stresses of MAO coating were analyzed with a scanning electron microscopy (SEM), X-ray diffractometer (XRD) and XRD stress tester, respectively. The results show that fatigue limits of the MAO samples decreases as the coating thickness increasing. The fatigue limit of MAO sample with thickness of 8 μm, 10 μm, and 15 μm decreases by 6.48%, 8.33%, and 11.11%, respectively, compared with the original sample. The residual stress and defects introduced by MAO were the main factors of decreasing fatigue limits. - Graphical abstract: The fatigue limit of original sample was 216 MPa (a), while that of MAO samples with thickness of 8 μm, 10 μm and 15 μm was 202 MPa, 198 MPa and 192 MPa (b). The fatigue limit of MAO samples with thickness of 8 μm, 10 μm and 15 μm decreased by 6.48%, 8.33% and 11.11% compared with that of the original sample, as a result, the fatigue limit decreased with the MAO film thickness increasing. - Highlights: • The fatigue limits of MAO samples decrease with the oxide thickness increasing. • The overgrowth regions cause the crack source expanding. • The overgrowth of MAO film and tensile residual stress decrease fatigue limit.

  18. 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...... 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...... 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....

  19. 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...

  20. Evaluation of fatigue crack growth and fracture resistance of SA350 LF2 material

    International Nuclear Information System (INIS)

    Singh, P.K.; Dubey, J.S.; Chakrabarty, J.K.; Vaze, K.K.; Kushwaha, H.S.

    2003-01-01

    The aim of the present paper is to evaluate the tensile and fracture mechanics properties of the SA350 LF2 carbon steel material used as the Header material in the primary heat transport (PHT) system piping of the Indian pressurized heavy water reactors (PHWR). Tensile, fatigue crack growth rate and fracture toughness tests have been carried out on specimens machined from the Header of the actual PHT pipes. The effect of temperature on tensile properties has been discussed. The effect of temperature and notch orientation on fracture resistance behavior of the material and fatigue crack growth rate dependence on the notch orientation and stress ratio has also been discussed. (author)

  1. Prediction of Ductile Fracture Surface Roughness Scaling

    DEFF Research Database (Denmark)

    Needleman, Alan; Tvergaard, Viggo; Bouchaud, Elisabeth

    2012-01-01

    . Ductile crack growth in a thin strip under mode I, overall plane strain, small scale yielding conditions is analyzed. Although overall plane strain loading conditions are prescribed, full 3D analyses are carried out to permit modeling of the three dimensional material microstructure and of the resulting......Experimental observations have shown that the roughness of fracture surfaces exhibit certain characteristic scaling properties. Here, calculations are carried out to explore the extent to which a ductile damage/fracture constitutive relation can be used to model fracture surface roughness scaling...... three dimensional stress and deformation states that develop in the fracture process region. An elastic-viscoplastic constitutive relation for a progressively cavitating plastic solid is used to model the material. Two populations of second phase particles are represented: large inclusions with low...

  2. Effect of aging time and aging temperature on fatigue and fracture behavior of 6063 aluminum alloy under seawater influence

    International Nuclear Information System (INIS)

    Siddiqui, R.A.; Abdul-Wahab, S.A.; Pervez, T.

    2008-01-01

    This paper describes experimentally the effect of seawater corrosion, aging time, and aging temperature on the fatigue resistance property of 6063 aluminum alloy. The 6063 aluminum alloy that was used for the study was heat treated and soaked in seawater for different intervals of time between 2 and 30 weeks. It was found that the maximum fatigue resistance property in the 6063 aluminum alloy was observed when aged between 7 and 9 h and heat treated at temperatures between 160 o C and 200 o C. Generally at constant load, the results indicated that the number of cycles to fail the 6063 aluminum alloy decreased with increasing the soaking time in seawater. Moreover, fracture surfaces were considered and studied under a scanning electron microscope (SEM). The results showed that the brittle fracture pattern tended to occur with the increase in aging time and temperature. The fatigue striations were observed very clearly at low and peak aging temperature. The increase in the fatigue resistance property with aging time was linked with the vacancies assisted diffusion mechanism and also by the hindering of dislocation movement by impure atoms

  3. Mode II Interlaminar Fracture Toughness and Fatigue Characterization of a Graphite Epoxy Composite Material

    Science.gov (United States)

    O'Brien, T. Kevin; Johnston, William M.; Toland, Gregory J.

    2010-01-01

    Mode II interlaminar fracture toughness and delamination onset and growth characterization data were generated for IM7/8552 graphite epoxy composite materials from two suppliers for use in fracture mechanics analyses. Both the fracture toughness testing and the fatigue testing were conducted using the End-notched Flexure (ENF) test. The ENF test for mode II fracture toughness is currently under review by ASTM as a potential standard test method. This current draft ASTM protocol was used as a guide to conduct the tests on the IM7/8552 material. This report summarizes the test approach, methods, procedures and results of this characterization effort.

  4. 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.

  5. Failure by fracture and fatigue in 'NANO' and 'BIO'materials

    Energy Technology Data Exchange (ETDEWEB)

    Ritchie, R.O.; Muhlstein, C.L.; Nalla, R.K.

    2003-12-19

    The behavior of nanostructured materials/small-volumestructures and biologi-cal/bio-implantable materials, so-called "nano"and "bio" materials, is currently much in vogue in materials science. Oneaspect of this field, which to date has received only limited attention,is their fracture and fatigue properties. In this paper, we examine twotopics in this area, namely the premature fatigue failure ofsilicon-based micron-scale structures for microelectromechanical systems(MEMS), and the fracture properties of mineralized tissue, specificallyhuman bone.

  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. MR imaging findings of fatigue fractures of lower extremity in young soldiers

    International Nuclear Information System (INIS)

    Mo, Jong Hyun; Moon, Sung Hee; Kim, Young Bok; Park, Yang Hee; Park, Jin Kyoon

    1999-01-01

    To evaluate the MR imaging findings of fatigue fractures of the lower extremity in young soldiers. In 22 cases of fatigue fractures of the lower extremity in young soldiers proven by clinical findings and radiological follow up, the MRI findings were retrospectively evalvated. All patients were male and aged between 19 and 21 years. As seen on MRI, the bone marrow edema, intramedullary low signal intensity band, cortical fracture line, periosteal reaction, surrounding soft tissue edema, and enhancement pattern were analyzed and the site of involvement was determined in the axial plane. The locations of fatigue fractures of the lower extremity were the tibia (n=12), fibula (n=8), femur (n=1) and second metatarsus (n=1). All occurred in diaphyses: the junction of the proximal and middle (n=10), middle (n=9), proximal (n=2), and distal shaft (n=1). The sites of involvement were the posteromedial (n=6) and medial side (n=6) of the tibia, and the entire portion of the fibula(n=5) in the axial plane. MRI findings were bone marrow edema in 20 cases, intramedullary low signal intensity band in 14 (which were continuous with the cortex or cortical fracture line), cortical fracture line in 13, and periosteal reaction and surrounding soft tissue edema in all. On gadolinium-enhanced images, enhancement was seen in the bone marrow in 19 cases, in the subperiosteal region in 18, and in the surrounding soft tissue in 22. In fatigue fractures of the lower extremity in young soldiers, the main locations were the tibia and fibula, and characteristic MR imaging findings were intramedullary low signal intensity bands, which were continuous with the cortex or cortical fracture line and often accompanied by bone marrow edema, periosteal reaction, and surrounding soft tissue edema

  8. Fatigue crack growth rates and fracture toughness of rapidly solidified Al-8.5 pct Fe-1.2 pct V-1.7 pct Si alloys

    International Nuclear Information System (INIS)

    Hariprasad, S.; Sastry, S.M.L.; Jerina, K.L.

    1994-01-01

    The room-temperature fatigue crack growth rates (FCGR) and fracture toughness were evaluated for different crack plane Orientations of an Al-8.5 pct Fe-1.2 pct V-1.7 pct Si alloy produced by planar flow casting (PFC) and atomized melt deposition (AMD) processes. For the alloy produced by the PFC process, properties were determined in six different orientations, including the short transverse directions S-T and S-L. Diffusion bonding and adhesive bonding methods were used to prepare specimens for determining FCGR and fracture toughness in the short transverse direction. Interparticle boundaries control fracture properties in the alloy produced by PFC. Fracture toughness of the PFC alloy varies from 13.4 MPa√ bar m to 30.8 MPa√ bar m, depending on the orientation of the crack plane relative to the interparticle boundaries. Fatigue crack growth resistance and fracture toughness are greater in the L-T, L-S, and T-S directions than in the T-L, S-T, and S-L orientations. The alloy produced by AMD does not exhibit anisotropy in fracture toughness and fatigue crack growth resistance in the as-deposited condition or in the extruded condition. The fracture toughness varies from 17.2 MPa√ bar m to 18.5 MPa√ bar m for the as-deposited condition and from 19.8 MPa√ bar m to 21.0 MPa√ bar m for the extruded condition. Fracture properties are controlled by intrinsic factors in the alloy produced by AMD. Fatigue crack growth rates of the AMD alloy are comparable to those of the PFC alloy in the L-T orientation. The crack propagation modes were studied by optical metallographic examination of crack-microstructure interactions and scanning electron microscopy of the fracture surfaces

  9. The stability of a hip fracture determines the fatigue of an intramedullary nail.

    Science.gov (United States)

    Eberle, S; Bauer, C; Gerber, C; von Oldenburg, G; Augat, P

    2010-01-01

    The purpose of this study was to address the question of how the stability of a proximal hip fracture determines the fatigue and failure mechanism of an intramedullary implant. To answer this question, mechanical experiments and finite element simulations with two different loading scenarios were conducted. The two load scenarios differed in the mechanical support of the fracture by an artificial bone sleeve, representing the femoral head and neck. The experiments confirmed that an intramedullary nail fails at a lower load in an unstable fracture situation in the proximal femur than in a stable fracture. The nails with an unstable support failed at a load 28 per cent lower than the nails with a stable support by the femoral neck. Hence, the mechanical support of a fracture is crucial to the fatigue failure of an implant. The simulation showed why the fatigue fracture of the nail starts at the aperture of the lag screw. It is the location of the highest von Mises stress, which is the failure criterion for ductile materials.

  10. Assessment of Ductile, Brittle, and Fatigue Fractures of Metals Using Optical Coherence Tomography

    Directory of Open Access Journals (Sweden)

    Gheorghe Hutiu

    2018-02-01

    Full Text Available Some forensic in situ investigations, such as those needed in transportation (for aviation, maritime, road, or rail accidents or for parts working under harsh conditions (e.g., pipes or turbines would benefit from a method/technique that distinguishes ductile from brittle fractures of metals—as material defects are one of the potential causes of incidents. Nowadays, the gold standard in material studies is represented by scanning electron microscopy (SEM. However, SEM instruments are large, expensive, time-consuming, and lab-based; hence, in situ measurements are impossible. To tackle these issues, we propose as an alternative, lower-cost, sufficiently high-resolution technique, Optical Coherence Tomography (OCT to perform fracture analysis by obtaining the topography of metallic surfaces. Several metals have been considered in this study: low soft carbon steels, lamellar graphite cast iron, an antifriction alloy, high-quality rolled steel, stainless steel, and ductile cast iron. An in-house developed Swept Source (SS OCT system, Master-Slave (MS enhanced is used, and height profiles of the samples’ surfaces were generated. Two configurations were used: one where the dimension of the voxel was 1000 μm3 and a second one of 160 μm3—with a 10 μm and a 4 μm transversal resolution, respectively. These height profiles allowed for concluding that the carbon steel samples were subject to ductile fracture, while the cast iron and antifriction alloy samples were subjected to brittle fracture. The validation of OCT images has been made with SEM images obtained with a 4 nm resolution. Although the OCT images are of a much lower resolution than the SEM ones, we demonstrate that they are sufficiently good to obtain clear images of the grains of the metallic materials and thus to distinguish between ductile and brittle fractures—especially with the higher resolution MS/SS-OCT system. The investigation is finally extended to the most useful case of

  11. Continuum damage mechanics method for fatigue growth of surface cracks

    International Nuclear Information System (INIS)

    Feng Xiqiao; He Shuyan

    1997-01-01

    With the background of leak-before-break (LBB) analysis of pressurized vessels and pipes in nuclear plants, the fatigue growth problem of either circumferential or longitudinal semi-elliptical surface cracks subjected to cyclic loading is studied by using a continuum damage mechanics method. The fatigue damage is described by a scalar damage variable. From the damage evolution equation at the crack tip, a crack growth equation similar to famous Paris' formula is derived, which shows the physical meaning of Paris' formula. Thereby, a continuum damage mechanics approach is developed to analyze the configuration evolution of surface cracks during fatigue growth

  12. Water infiltration into exposed fractured rock surfaces

    International Nuclear Information System (INIS)

    Rasmussen, T.C.; Evans, D.D.

    1993-01-01

    Fractured rock media are present at many existing and potential waste disposal sites, yet characterization data and physical relationships are not well developed for such media. This study focused on water infiltration characteristics of an exposed fractured rock as an approach for defining the upper boundary condition for unsaturated-zone water percolation and contaminant transport modeling. Two adjacent watersheds of 0.24 and 1.73 ha with slopes up to 45% were instrumented for measuring rainfall and runoff. Fracture density was measured from readily observable fracture traces on the surface. Three methods were employed to evaluate the rainfall-runoff relationship. The first method used the annual totals and indicated that only 22.5% of rainfall occurred as runoff for the 1990-1991 water year, which demonstrates a high water intake rate by the exposed fracture system. The second method employed total rainfall and runoff for individual storms in conjunction with the commonly used USDA Soil Conservation Service curve number method developed for wide ranges of soils and vegetation. Curve numbers between 75 and 85 were observed for summer and winter storms with dry antecedent runoff conditions, while values exceeded 90 for wet conditions. The third method used a mass-balance approach for four major storms, which indicated that water intake rates ranged from 2.0 to 7.3 mm h -1 , yielding fracture intake velocities ranging from 122 to 293 m h -1 . The three analyses show the complexity of the infiltration process for fractured rock. However, they contribute to a better understanding of the upper boundary condition for predicting contaminant transport through an unsaturated fractured rock medium. 17 refs., 4 figs., 1 tab

  13. 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.

  14. Fracture strength and fatigue resistance of dental resin-based composites

    NARCIS (Netherlands)

    Keulemans, F.; Palav, P.; Aboushelib, M.M.N.; van Dalen, A.; Kleverlaan, C.J.; Feilzer, A.J.

    2009-01-01

    Objectives: The aim of this study was to evaluate in vitro the influence of fiber-reinforcement on the fracture strength and fatigue resistance of resin-based composites. Methods: One hundred rectangular bar-shaped specimens (2 mm × 2 mm × 25 mm) made of resin-based composite were prepared in a

  15. Probabilistic model for fatigue crack growth and fracture of welded joints in civil engineering structures

    NARCIS (Netherlands)

    Maljaars, J.; Steenbergen, H.M.G.M.; Vrouwenvelder, A.C.W.M.

    2012-01-01

    This paper presents a probabilistic assessment model for linear elastic fracture mechanics (LEFM). The model allows the determination of the failure probability of a structure subjected to fatigue loading. The distributions of the random variables for civil engineering structures are provided, and

  16. Fracture and fatigue considerations in the development of ductile-phase reinforced intermetallic-matrix composites

    International Nuclear Information System (INIS)

    Venkateswara Rao, K.T.; Ritchie, R.O.

    1994-01-01

    The salient microstructural factors influencing fracture and fatigue-crack growth resistance of ductile-particle reinforced intermetallic-matrix composites at ambient temperature are reviewed through examples from the Nb/MoSi 2 , TiNb/TiAl, Nb/TiAl and Nb/Nb 3 Al systems; specific emphasis is placed on properties and morphology of the reinforcement and its interfacial properties with the matrix. It is shown that composites must be fabricated with a high aspect ratio ductile-reinforcement morphology in order to promote crack-particle interception and resultant crack bridging for improved fracture and fatigue properties. Concurrently, however, the ductile phases have contrasting effects on crack growth under monotonic vs. cyclic loading suggesting that composite microstructures tailored for optimal toughness may not necessarily yield optimal fatigue resistance. Perspectives for the future development of damage-tolerant intermetallic-composite microstructures are discussed

  17. Crack growth and fracture in fiber reinforced concrete beams under static and fatigue loading

    International Nuclear Information System (INIS)

    Jeanfreau, J.; Arockiasamy, M.; Reddy, D.V.

    1987-01-01

    The paper presents the results of a two-phase experimental investigation on the fatigue and fracture of six different types of concrete: plain, 0.5%, 1.0%, 1.5%, and 2.0% steel fibers and 0.5% kevlar fibers. In the first phase the J-integral was evaluated for different types of concrete from load-displacement curves. The value shows a marked increase in the energy required to fracture concrete when fibers are added. The values did not vary substantially for different notch depths. In the second phase concrete beams were subjected to fatigue by applying a pure bending on the notch. The effect of fiber addition was examined with emphasis on the crack propagation and the increase in the fatigue strength. The crack pattern was mainly influenced by the presence, amount, and the distribution of the fibers in the concrete. (orig./HP)

  18. Talar body fatigue stress fractures: three cases observed in elite female gymnasts

    International Nuclear Information System (INIS)

    Rossi, F.; Dragoni, S.

    2005-01-01

    To introduce and emphasize the clinical and radiological findings of three talar body fatigue stress fractures in competitive athletes. Clinical and radiographic skeletal records of 24,562 athletes taken between 1962 and 2002 were retrospectively reviewed. Among these, 6851 files related to acute foot and ankle injuries or chronic post-traumatic sequelae were found. There were 925 (3.76%) stress fatigue fractures selected from the whole collection. Among these there were three cases (0.32%) of talar body stress fractures diagnosed in elite female gymnasts 15 - 17 years old. The negative first radiograph become positive 4-6 weeks later. Scintigraphy was positive at an early stage and consistent for the diagnosis. CT and MRI gave positive results 1-2 weeks after the beginning of symptoms which were always greatly diagnostic. The sports medicine literature lacks reports of talar body fatigue stress fractures. The poor initial sensitivity of radiography makes it problematic to establish an early diagnosis. A wise combination of scintigraphy, CT and MRI has therefore to be relied upon. Familiarity with this rare location for a stress fracture may prevent delayed diagnosis and long-lasting damage, both of which are important factors in competitive athletes. (orig.)

  19. Talar body fatigue stress fractures: three cases observed in elite female gymnasts

    Energy Technology Data Exchange (ETDEWEB)

    Rossi, F. [National Institute of Sports Medicine of the Italian Olympic Committee, Rome (Italy); Dragoni, S. [National Institute of Sports Medicine of the Italian Olympic Committee, Rome (Italy); Istituto Nazionale di Medicina dello Sport, Rome (Italy)

    2005-07-01

    To introduce and emphasize the clinical and radiological findings of three talar body fatigue stress fractures in competitive athletes. Clinical and radiographic skeletal records of 24,562 athletes taken between 1962 and 2002 were retrospectively reviewed. Among these, 6851 files related to acute foot and ankle injuries or chronic post-traumatic sequelae were found. There were 925 (3.76%) stress fatigue fractures selected from the whole collection. Among these there were three cases (0.32%) of talar body stress fractures diagnosed in elite female gymnasts 15 - 17 years old. The negative first radiograph become positive 4-6 weeks later. Scintigraphy was positive at an early stage and consistent for the diagnosis. CT and MRI gave positive results 1-2 weeks after the beginning of symptoms which were always greatly diagnostic. The sports medicine literature lacks reports of talar body fatigue stress fractures. The poor initial sensitivity of radiography makes it problematic to establish an early diagnosis. A wise combination of scintigraphy, CT and MRI has therefore to be relied upon. Familiarity with this rare location for a stress fracture may prevent delayed diagnosis and long-lasting damage, both of which are important factors in competitive athletes. (orig.)

  20. Microstructural modeling of fatigue fracture of shape memory alloys at thermomechanical cyclic loading

    Science.gov (United States)

    Belyaev, Fedor S.; Evard, Margarita E.; Volkov, Aleksandr E.

    2018-05-01

    A microstructural model of shape memory alloys (SMA) describing their deformation and fatigue fracture is presented. A new criterion of fracture has been developed which takes into account the effect of hydrostatic pressure, deformation defects and material damage. It is shown that the model can describe the fatigue fracture of SMA under various thermomechanical cycling regimes. Results of calculating the number of cycles to failure at thermocycling under a constant stress, at symmetric two-sided cyclic deformation, at straining-unloading cycles, at cycling in the regime of the thermodynamic cycles of a SMA working body in the hard (strain controlled) and soft (stress controlled) working cycles, is studied. Results of calculating the number of cycles to failure are presented for different parameters of these cycles.

  1. Fatigue Stress Fracture of the Talar Body: An Uncommon Cause of Ankle Pain.

    Science.gov (United States)

    Kim, Young Sung; Lee, Ho Min; Kim, Jong Pil; Moon, Han Sol

    2016-01-01

    Fatigue stress fractures of the talus are rare and usually involve the head of the talus in military recruits. We report an uncommon cause of ankle pain due to a fatigue stress fracture of the body of the talus in a 32-year-old male social soccer player. Healing was achieved after weightbearing suppression for 6 weeks. Although rare, a stress fracture of the body of the talus should be considered in an athlete with a gradual onset of chronic ankle pain. Magnetic resonance imaging and bone scan are useful tools for early diagnosis. Copyright © 2016 American College of Foot and Ankle Surgeons. Published by Elsevier Inc. All rights reserved.

  2. Assessing Impact Direction in 3-point Bending of Human Femora: Incomplete Butterfly Fractures and Fracture Surfaces,.

    Science.gov (United States)

    Isa, Mariyam I; Fenton, Todd W; Deland, Trevor; Haut, Roger C

    2018-01-01

    Current literature associates bending failure with butterfly fracture, in which fracture initiates transversely at the tensile surface of a bent bone and branches as it propagates toward the impact surface. The orientation of the resulting wedge fragment is often considered diagnostic of impact direction. However, experimental studies indicate bending does not always produce complete butterfly fractures or produces wedge fragments variably in tension or compression, precluding their use in interpreting directionality. This study reports results of experimental 3-point bending tests on thirteen unembalmed human femora. Complete fracture patterns varied following bending failure, but incomplete fractures and fracture surface characteristics were observed in all impacted specimens. A flat, billowy fracture surface was observed in tension, while jagged, angular peaks were observed in compression. Impact direction was accurately reconstructed using incomplete tension wedge butterfly fractures and tension and compression fracture surface criteria in all thirteen specimens. © 2017 American Academy of Forensic Sciences.

  3. Length scale of secondary stresses in fracture and fatigue

    International Nuclear Information System (INIS)

    Dong, P.

    2008-01-01

    In an attempt to provide a consistent framework for the analysis and treatment of secondary stresses associated with welding and thermal loading in the context of fracture mechanics, this paper starts with an effective stress characterization procedure by introducing a length-scale concept. With it, a traction-based stress separation procedure is then presented to provide a consistent characterization of stresses from various sources based on their length scale. Their relative contributions to fracture driving force are then quantified in terms of their characteristic length scales. Special attention is given to the implications of the length-scale argument on both analysis and treatment of welding residual stresses in fracture assessment. A series of examples is provided to demonstrate how the present developments can be applied for treating not only secondary stresses but also externally applied stresses, as well as their combined effects on the structural integrity of engineering components

  4. Fatigue and Fracture Resistance of Heavy-Section Ferritic Ductile Cast Iron

    Directory of Open Access Journals (Sweden)

    Matteo Benedetti

    2017-03-01

    Full Text Available In this paper, we explore the effect of a long solidification time (12 h on the mechanical properties of an EN-GJS-400-type ferritic ductile cast iron (DCI. For this purpose, static tensile, rotating bending fatigue, fatigue crack growth and fracture toughness tests are carried out on specimens extracted from the same casting. The obtained results are compared with those of similar materials published in the technical literature. Moreover, the discussion is complemented with metallurgical and fractographic analyses. It has been found that the long solidification time, representative of conditions arising in heavy-section castings, leads to an overgrowth of the graphite nodules and a partial degeneration into chunky graphite. With respect to minimum values prescribed for thick-walled (t > 60 mm EN-GJS-400-15, the reduction in tensile strength and total elongation is equal to 20% and 75%, respectively. The rotating bending fatigue limit is reduced by 30% with respect to the standard EN-1563, reporting the results of fatigue tests employing laboratory samples extracted from thin-walled castings. Conversely, the resistance to fatigue crack growth is even superior and the fracture toughness comparable to that of conventional DCI.

  5. Reliability Analysis of Fatigue Fracture of Wind Turbine Drivetrain Components

    DEFF Research Database (Denmark)

    Berzonskis, Arvydas; Sørensen, John Dalsgaard

    2016-01-01

    in the volume of the casted ductile iron main shaft, on the reliability of the component. The probabilistic reliability analysis conducted is based on fracture mechanics models. Additionally, the utilization of the probabilistic reliability for operation and maintenance planning and quality control is discussed....

  6. Fracture resistance of dental nickel-titanium rotary instruments with novel surface treatment: Thin film metallic glass coating.

    Science.gov (United States)

    Chi, Chih-Wen; Deng, Yu-Lun; Lee, Jyh-Wei; Lin, Chun-Pin

    2017-05-01

    Dental nickel-titanium (NiTi) rotary instruments are widely used in endodontic therapy because they are efficient with a higher success rate. However, an unpredictable fracture of instruments may happen due to the surface characteristics of imperfection (or irregularity). This study assessed whether a novel surface treatment could increase fatigue fracture resistance of dental NiTi rotary instruments. A 200- or 500-nm thick Ti-zirconium-boron (Ti-Zr-B) thin film metallic glass was deposited on ProTaper Universal F2 files using a physical vapor deposition process. The characteristics of coating were analyzed by scanning electron microscopy, transmission electron microscopy, and X-ray diffractometry. In cyclic fatigue tests, the files were performed in a simulated root canal (radius=5 mm, angulation=60°) under a rotating speed of 300rpm. The fatigue fractured cross sections of the files were analyzed with their fractographic performances through scanning electron microscopy images. The amorphous structure of the Ti-Zr-B coating was confirmed by transmission electron microscopy and X-ray diffractometry. The surface of treated files presented smooth morphologies without grinding irregularity. For the 200- and 500-nm surface treatment groups, the coated files exhibited higher resistance of cyclic fatigue than untreated files. In fractographic analysis, treated files showed significantly larger crack-initiation zone; however, no significant differences in the areas of fatigue propagation and catastrophic fracture were found compared to untreated files. The novel surface treatment of Ti-Zr-B thin film metallic glass on dental NiTi rotary files can effectively improve the fatigue fracture resistance by offering a smooth coated surface with amorphous microstructure. Copyright © 2016. Published by Elsevier B.V.

  7. Third metacarpal condylar fatigue fractures in equine athletes occur within previously modelled subchondral bone.

    Science.gov (United States)

    Whitton, R Christopher; Trope, Gareth D; Ghasem-Zadeh, Ali; Anderson, Garry A; Parkin, Timothy D H; Mackie, Eleanor J; Seeman, Ego

    2010-10-01

    Bone modelling and remodelling reduce the risk of fatigue fractures; the former by adapting bone to its loading circumstances, the latter by replacing fatigued bone. Remodelling transiently increases porosity because of the normal delay in onset of the formation phase of the remodelling sequence. Protracted intense loading suppresses remodelling leaving modelling as the only means of maintaining bone strength. We therefore hypothesized that race horses with fatigue fractures of the distal third metacarpal bone (MC3) will have reduced porosity associated with suppressed remodelling while continued adaptive modelling will result in higher volume fraction (BV/TV) at this site. Using high resolution peripheral quantitative computed tomography (HR-pQCT), we measured the distal aspect of the MC3 obtained at postmortem from 13 thoroughbred race horses with condylar fractures of the MC3 (cases), 8 horses without fractures (training controls), 14 horses with a fracture at another site (fractured controls) and 9 horses resting from training (resting controls). Porosity of the subchondral bone of MC3 was lower in cases than resting controls (12±1.4% vs. 18±1.6%, P=0.017) although areas of focal porosity were observed adjacent to fractures in 6/13 horses. BV/TV of the distal metacarpal epiphysis tended to be higher in horses with condylar fractures (0.79±0.015) than training controls (0.74±0.019, P=0.070), but also higher in controls with a fracture elsewhere (0.79±0.014) than the training controls (0.74±0.019, P=0.040). BV/TV was higher in horses over three years of age than those aged two or three years (0.79±0.01 vs. 0.74±0.01, P=0.016). All metacarpal condylar fractures occurred within focal areas of high BV/TV. We infer that intense training in equine athletes suppresses remodelling of third metacarpal subchondral bone limiting damage repair while modelling increases regional bone volume in an attempt to minimise local stresses but may fail to offset bone

  8. Fatigue stress fractures of the pubic ramus in the army: imaging features with radiographic, scintigraphic and MR imaging findings

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Sang Woo; Lee, Chang Hyun [The Armed Forces Capital Hospital, Seongnam (Korea, Republic of)

    2005-03-15

    Although fatigue fractures are not unusual in athletes and military personnel those of the pubic ramus are rare. We report three cases of fatigue fractures of the inferior pubic rami in two male recruits and one female military cadet. On the initial radiograph, most of the lesions were subtle and easy to overlook. However, bone scintigraphy provided more distinct images that allowed easy and early detection of lesion, and MR imaging presented more diagnostic information, which allowed a precise diagnosis.

  9. An investigation into the change of shape of fatigue cracks initiated at surface flaws

    International Nuclear Information System (INIS)

    Portch, D.J.

    1979-09-01

    Surface fatigue cracks found in plant can often be closely approximated in shape by a semi-ellipse. The stress intensity factor range at the deepest part of the surface crack is dependent upon a number of variables, including the crack aspect ratio. In fatigue life analysis, the aspect ratio of a propagating crack is frequently assumed to remain constant, possibly due to the complexity of estimating aspect ratio change on the basis of linear elastic fracture mechanics. This report describes the results of an experimental programme to examine the change of shape of fatigue cracks subjected to uniaxial tensile or bending stresses. The data obtained has been used to modify equations proposed by the author in a previous report to predict the change of aspect ratio of a crack propagating from a known defect. These modified equations, although not including terms to account for the effects of varying mean stress levels or material properties, generally give a good agreement with published experimental results. Crack propagation rate data obtained from the tensile fatigue tests has been used to estimate crack tip stress intensity factors. These are compared with values calculated from published solutions using both the constant geometry assumption and also the shape change equations proposed in this report. Use of these equations gives improved agreement with experiment in most cases. (author)

  10. Micromechanisms of fracture and fatigue in Ti3Al based and TiAl based intermetallics

    International Nuclear Information System (INIS)

    James, A.W.; Chave, R.A.; Hippsley, C.A.; Bowen, P.

    1993-01-01

    Micromechanisms of fracture and fatigue crack growth resistance in specific Ti 3 Al based and TiAl based intermetallics are reviewed. Effects of test temperature, environment and microstructure on crack growth resistance are considered in detail for several Ti 3 Al and Ti'Al based intermetallic systems under development. The implications of these studies for the structural reliability of these materials is also addressed briefly. (orig.)

  11. Evaluation of upper limb muscle fatigue based on surface electromyography.

    Science.gov (United States)

    Zhou, Qianxiang; Chen, Yuhong; Ma, Chao; Zheng, Xiaohui

    2011-10-01

    Fatigue is believed to be a major contributory factor to occupational injuries in machine operators. The development of accurate and usable techniques to measure operator fatigue is therefore important. In this study, we used a novel method based on surface electromyography (sEMG) of the biceps brachii and the Borg scale to evaluate local muscle fatigue in the upper limb after isometric muscle action. Thirteen young males performed isometric actions with the upper limb at different force levels. sEMG activities of the biceps brachii were recorded during the actions. Borg scales were used to evaluate the subjective sensation of local fatigue of the biceps brachii after the actions. sEMG activities were analyzed using the one-third band octave method, and an equation to determine the degree of fatigue was derived based on the relationship between the variable and the Borg scale. The results showed that the relationship could be expressed by a conic curve, and could be used to evaluate muscle fatigue during machine operation.

  12. 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

  13. Influence of Surface Roughness on the Fatigue Life of Nickel-Titanium Rotary Endodontic Instruments.

    Science.gov (United States)

    Lopes, Hélio P; Elias, Carlos N; Vieira, Márcia V B; Vieira, Victor T L; de Souza, Letícia Chaves; Dos Santos, Alexander Lopes

    2016-06-01

    The goal of the present study was to evaluate the influence of surface grooves (peaks and valleys) resulting from machining during the manufacturing process of polished and unpolished nickel-titanium BR4C endodontic files on the fatigue life of the instruments. Ten electropolished and 10 unpolished endodontic files were provided by the manufacturer. Specimens were from the same batch, but the unpolished instruments were removed from the production line before surface treatment. The instruments were evaluated with a profilometer to quantify the surface roughness on the working part of the instruments. Then the files were subjected to rotating bending fatigue tests. Analysis with the profilometer showed that surface grooves were deeper on the unpolished instruments compared with their electropolished counterparts. In the rotating bending fatigue test, the mean and standard deviation for the number of cycles until fracture (NCF) were greater for instruments with less pronounced grooves. Student t test revealed significant differences in all tests (P instruments tested; the smaller the groove depth, the greater the NCF. Copyright © 2016 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

  14. The Effect of Creep Aging on the Fatigue Fracture Behavior of 2524 Aluminum Alloy

    Directory of Open Access Journals (Sweden)

    Wenke Li

    2016-09-01

    Full Text Available Normal temperature tensile and fatigue tests were adopted to test the mechanical performance and fatigue life of 2524 aluminum alloy under the three states of T3, artificial aging, and creep aging, and scanning electron microscope and transmission electron microscope were also used to observe the fatigue fracture morphology and aging precipitation features of the alloy under the above three states. Results showed that the alloy treated by creep aging can obtain higher fatigue life, but that treated by artificial aging is lower than T3; T3 alloy is mainly dominated by GPB region. Meanwhile, the crystal boundary displays continuously distributed fine precipitated phases; after artificial aging and creep aging treatment, a large amount of needle-shaped S′ phases precipitate inside the alloy, while there are wide precipitated phases at the crystal boundary. Wide precipitation free zones appear at the crystal boundary of artificial-aging samples, but precipitation free zones at the alloy crystal boundary of creep aging become narrower and even disappear. It can be seen that creep aging can change the precipitation features of the alloy and improve its fatigue life.

  15. Ti–6Al–4V welded joints via electron beam welding: Microstructure, fatigue properties, and fracture behavior

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Xiaoguang [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Co-Innovation Center for Advanced Aero-Engine, Beijing 100191 (China); Li, Shaolin [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Qi, Hongyu, E-mail: qhy@buaa.edu.cn [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Co-Innovation Center for Advanced Aero-Engine, Beijing 100191 (China)

    2014-03-01

    The effect of microstructural characteristics on the fatigue properties of electron beam-welded joints of forged Ti–6Al–4V and its fracture behavior were investigated. Tensile tests and fatigue tests were conducted at room temperature in air atmosphere. The test data were analyzed in relation to microstructure, high-cycle fatigue properties, low-cycle fatigue properties, and fatigue crack propagation properties. The high-cycle fatigue test results indicated that the fatigue strength of the joint welded via electron beam welding was higher than that of the base metal because the former had a high yield strength and all high-cycle fatigue specimens were fractured in the base metal. Although the joint specimens had a lower low-cycle fatigue life than the base metal, they mainly ruptured at the fusion zone of the joint specimen and their crack initiation mechanism is load-dependent. The fatigue crack propagation test results show that the joint had a slower crack propagation rate than the base metal, which can be attributed to the larger grain in the fusion zone.

  16. Fatigue and pain limit independent mobility and physiotherapy after hip fracture surgery

    DEFF Research Database (Denmark)

    Münter, Kristine H.; Clemmesen, Christopher G.; Foss, Nicolai B.

    2017-01-01

    Purpose: The patient’s ability to complete their planned physiotherapy session after hip fracture surgery has been proposed as an independent predictor for achieving basic mobility independency upon hospital discharge. However, knowledge of factors limiting mobility is sparse. We therefore examined...... patient reported factors limiting ability to complete planned physiotherapy sessions as well as limitations for not achieving independency in basic mobility early after hip fracture surgery. Methods: A total of 204 consecutive patients with a hip fracture (mean (SD) age of 80 (9.9) years, 47 patients were......; pain, motor blockade, dizziness, fatigue, nausea, acute cognitive dysfunction and “other limitations”, for not achieving a full Cumulated Ambulation Score or inability to complete planned physiotherapy sessions were noted by the physiotherapist on each of the three first postoperative days. This period...

  17. A discrete element model for damage and fracture of geomaterials under fatigue loading

    Science.gov (United States)

    Gao, Xiaofeng; Koval, Georg; Chazallon, Cyrille

    2017-06-01

    Failure processes in geomaterials (concrete, asphalt concrete, masonry, etc.) under fatigue loading (repeated moving loads, cycles of temperature, etc.) are responsible for most of the dysfunctions in pavements, brick structures, etc. In the beginning of the lifetime of a structure, the material presents only inner defects (micro cracks, voids, etc.). Due to the effect of the cyclic loading, these small defects tend to grow in size and quantity which damage the material, reducing its stiffness. With a relatively high number of cycles, these growing micro cracks become large cracks, which characterizes the fracture behavior. From a theoretical point of view, both mechanisms are treated differently. Fracture is usually described locally, with the propagation of cracks defined by the energy release rate at the crack tip; damage is usually associated to non-local approaches. In the present work, damage and fracture mechanics are combined in a local discrete element approach.

  18. Bilateral Femoral Neck Fatigue Fracture due to Osteomalacia Secondary to Celiac Disease: Report of Three Cases.

    Science.gov (United States)

    Selek, Ozgur; Memisoglu, Kaya; Selek, Alev

    2015-08-01

    Bilateral non traumatic femoral neck fatigue fracture is a rare condition usually occurring secondary to medical conditions such as pregnancy, pelvic irradiation, corticosteroid exposure, chronic renal failure and osteomalacia. In this report, we present three young female patients with bilateral femoral neck fracture secondary to osteomalacia. The underlying cause of osteomalacia was Celiac disease in all patients. The patients were treated with closed reduction and internal fixation with cannulated lag screws. They were free of pain and full weight bearing was achieved at three months. There were no complications, avascular necrosis and nonunion during the follow up period. In patients with bone pain, non traumatic fractures and muscle weakness, osteomalacia should be kept in mind and proper diagnostic work-up should be performed to identify the underlying cause of osteomalacia such as celiac disease.

  19. The fatigue life and fatigue crack through thickness behavior of a surface cracked plate, 2

    International Nuclear Information System (INIS)

    Nam, Ki-Woo; Fujibayashi, Shinpei; Ando, Kotoji; Ogura, Nobukazu.

    1987-01-01

    Most structures have a region where stresses concentrate, and the probability of fatigue crack initiation may be higher than in other parts. Therefore, to improve the reliability of an LBB design, it is necessary to evaluate the growth and through thickness behavior of fatigue cracks in the stress concentration part. In this paper, a fatigue crack growth test at a stress concentration region has been made on 3 % NiCrMo and HT 80 steel. Stress concentration is caused by a fillet on the plate. The main results obtained are as follows : (1) Before cracking through the plate thickness, stress concentration has a remarkable effect on the fatigue crack growth behavior and it flatens the shape of a surface crack. The crack growth behavior can be explained quantatively by using the Newman-Raju equation and the stress resolving method proposed by ASME B and P Code SecXI. (2) The da/dN-ΔK relation obtained in a stress concentration specimen shows good agreement with that obtained in a surface cracked smooth specimen. (3) It is shown that stress concentration caused by a fillet has little effect on the crack growth rate after cracking through the plate thickness. (4) By using the K value based on eq. (1), (2), particular crack growth behavior and the change in crack shape after cracking through thickness can be explained quantatively. (author)

  20. An Experimental Investigation of the Effects of Vacuum Environment on the Fatigue Life, Fatigue-Crack-Growth Behavior, and Fracture Toughness of 7075-T6 Aluminum Alloy. Ph.D. Thesis - North Carolina State Univ.

    Science.gov (United States)

    Hudson, C. M.

    1972-01-01

    Axial load fatigue life, fatigue-crack propagation, and fracture toughness tests were conducted on 0.090-inch thick specimens made of 7075-T6 aluminum alloy. The fatigue life and fatigue-crack propagation experiments were conducted at a stress ratio of 0.02. Maximum stresses ranged from 33 to 60 ksi in the fatigue life experiments, and from 10 to 40 ksi in the fatigue-crack propagation experiments, and fatigue life experiments were conducted at gas pressures of 760, 0.5, 0.05, and 0.00000005 torr. Fatigue-crack-growth and fracture toughness experiments were conducted at gas pressures of 760 and 5 x 10 to the minus 8th power torr. Residual stress measurements were made on selected fatigue life specimens to determine the effect of such stresses on fatigue life. Analysis of the results from the fatigue life experiments indicated that fatigue life progressively increased as the gas pressure decreased. Analysis of the results from the fatigue-crack-growth experiments indicates that at low values of stress-intensity range, the fatigue crack growth rates were approximately twice as high in air as in vacuum. Fracture toughness data showed there was essentially no difference in the fracture toughness of 7075-T6 in vacuum and in air.

  1. Failure of metals III: Fracture and fatigue of nanostructured metallic materials

    International Nuclear Information System (INIS)

    Pineau, André; Amine Benzerga, A.; Pardoen, Thomas

    2016-01-01

    Pushing the internal or external dimensions of metallic alloys down to the nanometer scale gives rise to strong materials, though most often at the expense of a low ductility and a low resistance to cracking, with negative impact on the transfer to engineering applications. These characteristics are observed, with some exceptions, in bulk ultra-fine grained and nanocrystalline metals, nano-twinned metals, thin metallic coatings on substrates and freestanding thin metallic films and nanowires. This overview encompasses all these systems to reveal commonalities in the origins of the lack of ductility and fracture resistance, in factors governing fatigue resistance, and in ways to improve properties. After surveying the various processing methods and key deformation mechanisms, we systematically address the current state of the art in terms of plastic localization, damage, static and fatigue cracking, for three classes of systems: (1) bulk ultra-fine grained and nanocrystalline metals, (2) thin metallic films on substrates, and (3) 1D and 2D freestanding micro and nanoscale systems. In doing so, we aim to favour cross-fertilization between progress made in the fields of mechanics of thin films, nanomechanics, fundamental researches in bulk nanocrystalline metals and metallurgy to impart enhanced resistance to fracture and fatigue in high-strength nanostructured systems. This involves exploiting intrinsic mechanisms, e.g. to enhance hardening and rate-sensitivity so as to delay necking, or improve grain-boundary cohesion to resist intergranular cracks or voids. Extrinsic methods can also be utilized such as by hybridizing the metal with another material to delocalize the deformation - as practiced in stretchable electronics. Fatigue crack initiation is in principle improved by a fine structure, but at the expense of larger fatigue crack growth rates. Extrinsic toughening through hybridization allows arresting or bridging cracks. The content and discussions are based on

  2. Fatigue Fracture Strength of Implant-Supported Full Contour Zirconia and Metal Ceramic Fixed Partial Dentures

    Directory of Open Access Journals (Sweden)

    Fariborz Vafaee

    2017-10-01

    Full Text Available Objectives: Zirconia restorations have been suggested as a more durable and more appealing alternative to metal restorations. However, their mechanical properties may be negatively affected by fatigue due to superficial stresses or low temperature degradation. This study aimed to assess the fatigue fracture strength of three-unit implant-supported full contour zirconia and pre-sintered cobalt-chromium (Co-Cr alloy posterior fixed partial dentures (FPDs.Materials and Methods: In this in-vitro experimental study, 28 posterior three-unit implant-supported FPDs were fabricated of full contour zirconia and pre-sintered Co-Cr alloy, and were cemented on implant abutments. To simulate the oral environment, FPDs were subjected to 10,000 thermal cycles between 5-55°C for 30 seconds, and were then transferred to a chewing simulator (100,000 cycles, 50 N, 0.5 Hz. Afterwards, fatigue fracture strength was measured using a universal testing machine. Data were analyzed by Mann-Whitney U test.Results: The mean and standard deviation of fracture strength were 2108.6±440.1 N in full contour zirconia, and 3499.9±1106.5 N in pre-sintered Co-Cr alloy. According to Mann- Whitney U test, the difference in this respect was statistically significant between the two groups (P=0.007.Conclusions: Since the fracture strength values obtained in the two groups were significantly higher than the maximum mean masticatory load in the oral environment, both materials can be used for fabrication of posterior three-unit FPDs, depending on the esthetic demands of patients.

  3. Anisotropic characterization of rock fracture surfaces subjected to profile analysis

    International Nuclear Information System (INIS)

    Zhou, H.W.; Xie, H.

    2004-01-01

    The mechanical parameters of a rock fracture are dependent on its surface roughness anisotropy. In this Letter, we show how quantitatively describe the anisotropy of a rock fracture surface. A parameter, referred to as the index for the accumulation power spectral density psd*, is proposed to characterize the anisotropy of a rock fracture surface. Variation of psd*, with orientation angle θ of sampling, is also discussed

  4. Fatigue

    Science.gov (United States)

    ... to help you find out what's causing your fatigue and recommend ways to relieve it. Fatigue itself is not a disease. Medical problems, treatments, and personal habits can add to fatigue. These include Taking certain medicines, such as antidepressants, ...

  5. Influence of the geometry of curved artificial canals on the fracture of rotary nickel-titanium instruments subjected to cyclic fatigue tests.

    Science.gov (United States)

    Lopes, Hélio P; Vieira, Márcia V B; Elias, Carlos N; Gonçalves, Lucio S; Siqueira, José F; Moreira, Edson J L; Vieira, Victor T L; Souza, Letícia C

    2013-05-01

    This study evaluated the influence of different features of canal curvature geometry on the number of cycles to fracture of a rotary nickel-titanium endodontic instrument subjected to a cyclic fatigue test. BioRaCe BR4C instruments (FKG Dentaire, La Chaux-de Fonds, Switzerland) were tested in 4 grooves simulating curved metallic artificial canals, each one measuring 1.5 mm in width, 20 mm in total length, and 3.5 mm in depth with a U-shaped bottom. The parameters of curvature including the radius and arc lengths and the position of the arc differed in the 4 canal designs. Fractured surfaces and helical shafts of the separated instruments were analyzed by scanning electron microscopy. The Student's t test showed that a significantly lower number of cycles to fracture values were observed for instruments tested in canals with the smallest radius, the longest arc, and the arc located in the middle portion of the canal. Scanning electron microscopic analysis of the fracture surfaces revealed morphologic characteristics of ductile fracture. Plastic deformation was not observed in the helical shaft of the fractured instruments. Curvature geometry including the radius and arc lengths and the position of the arc along the root canal influence the number of cycles to fracture of rotary nickel-titanium instruments subjected to flexural load. Copyright © 2013 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

  6. Anatomical Thin Titanium Mesh Plate Structural Optimization for Zygomatic-Maxillary Complex Fracture under Fatigue Testing

    Directory of Open Access Journals (Sweden)

    Yu-Tzu Wang

    2018-01-01

    Full Text Available This study performs a structural optimization of anatomical thin titanium mesh (ATTM plate and optimal designed ATTM plate fabricated using additive manufacturing (AM to verify its stabilization under fatigue testing. Finite element (FE analysis was used to simulate the structural bending resistance of a regular ATTM plate. The Taguchi method was employed to identify the significance of each design factor in controlling the deflection and determine an optimal combination of designed factors. The optimal designed ATTM plate with patient-matched facial contour was fabricated using AM and applied to a ZMC comminuted fracture to evaluate the resting maxillary micromotion/strain under fatigue testing. The Taguchi analysis found that the ATTM plate required a designed internal hole distance to be 0.9 mm, internal hole diameter to be 1 mm, plate thickness to be 0.8 mm, and plate height to be 10 mm. The designed plate thickness factor primarily dominated the bending resistance up to 78% importance. The averaged micromotion (displacement and strain of the maxillary bone showed that ZMC fracture fixation using the miniplate was significantly higher than those using the AM optimal designed ATTM plate. This study concluded that the optimal designed ATTM plate with enough strength to resist the bending effect can be obtained by combining FE and Taguchi analyses. The optimal designed ATTM plate with patient-matched facial contour fabricated using AM provides superior stabilization for ZMC comminuted fractured bone segments.

  7. The theory of critical distances applied to problems in fracture and fatigue of bone

    Directory of Open Access Journals (Sweden)

    Emma Brazel

    2009-10-01

    Full Text Available The theory of critical distances (TCD has been applied to predict notch-based fracture and fatigue in a wide range of materials and components. The present paper describes a series of projects in which we applied this approach to human bone. Using experimental data from the literature, combined with finite element analysis, we showed that the TCD was able to predict the effect of notches and holes on the strength of bone failing in brittle fracture due to monotonic loading, in different loading regimes. Bone also displays short crack effects, leading to R-curve data for both fracture toughness and fatigue crack propagation thresholds; we showed that the TCD could predict this data. This analysis raised a number of questions for discussion, such as the significance of the L value itself in this and other materials. Finally, we applied the TCD to a practical problem in orthopaedic surgery: the management of bone defects, showing that predictions could be made which would enable surgeons to decide on whether a bone graft material would be needed to repair a defect, and to specify what mechanical properties this material should have.

  8. Resistance to corrosion fatigue fracture in heat resistant steels and their welded joints

    International Nuclear Information System (INIS)

    Timofeev, B.T.; Fedorova, V.A.; Zvezdin, Yu.I.; Vajner, L.A.; Filatov, V.M.

    1987-01-01

    Experimental data on cyclic crack resistance of heat-resistant steels and their welded joints employed for production of the reactor bodies are for the first time generalized and systematized. The formula is suggested accounting for surface and inner defects to calculate the fatigue crack growth in the process of operation. This formula for surface defects regards also the effect of the corrosion factor. Mechanisms of the reactor water effect on the fatigue crack growth rate are considered as well as a combined effect of radiation and corrosive medium on this characteristic

  9. Statistics of ductile fracture surfaces: the effect of material parameters

    DEFF Research Database (Denmark)

    Ponson, Laurent; Cao, Yuanyuan; Bouchaud, Elisabeth

    2013-01-01

    distributed. The three dimensional analysis permits modeling of a three dimensional material microstructure and of the resulting three dimensional stress and deformation states that develop in the fracture process region. Material parameters characterizing void nucleation are varied and the statistics...... of the resulting fracture surfaces is investigated. All the fracture surfaces are found to be self-affine over a size range of about two orders of magnitude with a very similar roughness exponent of 0.56 ± 0.03. In contrast, the full statistics of the fracture surfaces is found to be more sensitive to the material...

  10. Enhanced fatigue endurance of metallic glasses through a staircase-like fracture mechanism.

    Science.gov (United States)

    Gludovatz, Bernd; Demetriou, Marios D; Floyd, Michael; Hohenwarter, Anton; Johnson, William L; Ritchie, Robert O

    2013-11-12

    Bulk-metallic glasses (BMGs) are now candidate materials for structural applications due to their exceptional strength and toughness. However, their fatigue resistance can be poor and inconsistent, severely limiting their potential as reliable structural materials. As fatigue limits are invariably governed by the local arrest of microscopically small cracks at microstructural features, the lack of microstructure in monolithic glasses, often coupled with other factors, such as the ease of crack formation in shear bands or a high susceptibility to corrosion, can lead to low fatigue limits (some ~1/20 of their tensile strengths) and highly variable fatigue lives. BMG-matrix composites can provide a solution here as their duplex microstructures can arrest shear bands at a second phase to prevent cracks from exceeding critical size; under these conditions, fatigue limits become comparable with those of crystalline alloys. Here, we report on a Pd-based glass that similarly has high fatigue resistance but without a second phase. This monolithic glass displays high intrinsic toughness from extensive shear-band proliferation with cavitation and cracking effectively obstructed. We find that this property can further promote fatigue resistance through extrinsic crack-tip shielding, a mechanism well known in crystalline metals but not previously reported in BMGs, whereby cyclically loaded cracks propagate in a highly "zig-zag" manner, creating a rough "staircase-like" profile. The resulting crack-surface contact (roughness-induced crack closure) elevates fatigue properties to those comparable to crystalline alloys, and the accompanying plasticity helps to reduce flaw sensitivity in the glass, thereby promoting structural reliability.

  11. Influence of Initial Inclined Surface Crack on Estimated Residual Fatigue Lifetime of Railway Axle

    Czech Academy of Sciences Publication Activity Database

    Náhlík, Luboš; Pokorný, Pavel; Ševčík, Martin; Hutař, Pavel

    2016-01-01

    Roč. 7, č. 4 (2016), č. článku 1640007. ISSN 1756-9737. [FDM 2016 - International Conference on Fracture and Damage Mechanics /15./. Alicante, 14.09.2016-16.09.2016] R&D Projects: GA MŠk LM2015069; GA MŠk(CZ) ED1.1.00/02.0068 Institutional support: RVO:68081723 Keywords : inclined crack * railway axle * residual fatigue lifetime * fatigue crack propagation Subject RIV: JL - Materials Fatigue, Friction Mechanics

  12. 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...

  13. Fracture mechanical evaluation of high temperature structure and creep-fatigue defect assessment

    Energy Technology Data Exchange (ETDEWEB)

    Park, Chang Gyu; Kim, Jong Bum; Lee, Jae Han

    2004-02-01

    This study proposed the evaluation procedure of high temperature structures from the viewpoint of fracture mechanics on the cylindrical structure applicable to the KALIMER, which is developed by KAERI. For the evaluation of structural integrity, linear and non-linear fracture mechanics parameters were analyzed. Parameters used in creep defect growth applicable to high temperature structure of liquid metal reactor and the evaluation codes with these parameters were analyzed. The evaluation methods of defect initiation and defect growth which were established in R5/R6 code(UK), JNC method (Japan) and RCC-MR A16(France) code were analyzed respectively. The evaluation procedure of leak before break applicable to KALIMER was preliminarily developed and proposed. As an application example of defect growth, the creep-fatigue defect growth on circumferential throughwall defect in high temperature cylindrical structure was evaluated by RCC-MR A16 and this application technology was established.

  14. Evaluation of Surface Fatigue Strength Based on Surface Temperature

    Science.gov (United States)

    Deng, Gang; Nakanishi, Tsutomu

    Surface temperature is considered to be an integrated index that is dependent on not only the load and the dimensions at the contact point but also the sliding velocity, rolling velocity, surface roughness, and lubrication conditions. Therefore, the surface durability of rollers and gears can be evaluated more exactly and simply by the use of surface temperature rather than Hertzian stress. In this research, surface temperatures of rollers under different rolling and sliding conditions are measured using a thermocouple. The effects of load P, mean velocity Vm and sliding velocity Vs on surface temperature are clarified. An experimental formula, which expresses the linear relationship between surface temperature and the P0.86Vs1.31Vm-0.83 value, is used to determine surface temperature. By comparing calculated and measured temperature on the tooth surface of a gear, this formula is confirmed to be applicable for gear tooth surface temperature calculation.

  15. Influence of Nickel Particle Reinforcement on Cyclic Fatigue and Final Fracture Behavior of a Magnesium Alloy Composite

    Directory of Open Access Journals (Sweden)

    Manoj Gupta

    2012-06-01

    Full Text Available The microstructure, tensile properties, cyclic stress amplitude fatigue response and final fracture behavior of a magnesium alloy, denoted as AZ31, discontinuously reinforced with nano-particulates of aluminum oxide and micron size nickel particles is presented and discussed. The tensile properties, high cycle fatigue and final fracture behavior of the discontinuously reinforced magnesium alloy are compared with the unreinforced counterpart (AZ31. The elastic modulus and yield strength of the dual particle reinforced magnesium alloy is marginally higher than of the unreinforced counterpart. However, the tensile strength of the composite is lower than the monolithic counterpart. The ductility quantified by elongation to failure over 0.5 inch (12.7 mm gage length of the test specimen showed minimal difference while the reduction in specimen cross-section area of the composite is higher than that of the monolithic counterpart. At the microscopic level, cyclic fatigue fractures of both the composite and the monolithic alloy clearly revealed features indicative of the occurrence of locally ductile and brittle mechanisms. Over the range of maximum stress and at two different load ratios the cyclic fatigue resistance of the magnesium alloy composite is superior to the monolithic counterpart. The mechanisms responsible for improved cyclic fatigue life and resultant fracture behavior of the composite microstructure are highlighted.

  16. High temperature fracture and fatigue of ceramics. Annual technical progress report No. 6, August 15, 1994--August 14, 1995

    Energy Technology Data Exchange (ETDEWEB)

    Cox, B.

    1996-04-01

    This report covers work done in the first year of our new contract {open_quotes}High Temperature Fracture and Fatigue of Ceramics,{close_quotes} which commenced in August, 1995 as a follow-on from our prior contract {open_quotes}Mechanisms of Mechanical Fatigue in Ceramics.{close_quotes} Our activities have consisted mainly of studies of the failure of fibrous ceramic matrix composites (CMCs) at high temperature; with a little fundamental work on the role of stress redistribution in the statistics of fracture and cracking in the presence of viscous fluids.

  17. Fracture mechanics and residual fatigue life analysis for complex stress fields. Technical report

    International Nuclear Information System (INIS)

    Besuner, P.M.

    1975-07-01

    This report reviews the development and application of an influence function method for calculating stress intensity factors and residual fatigue life for two- and three-dimensional structures with complex stress fields and geometries. Through elastic superposition, the method properly accounts for redistribution of stress as the crack grows through the structure. The analytical methods used and the computer programs necessary for computation and application of load independent influence functions are presented. A new exact solution is obtained for the buried elliptical crack, under an arbitrary Mode I stress field, for stress intensity factors at four positions around the crack front. The IF method is then applied to two fracture mechanics problems with complex stress fields and geometries. These problems are of current interest to the electric power generating industry and include (1) the fatigue analysis of a crack in a pipe weld under nominal and residual stresses and (2) fatigue analysis of a reactor pressure vessel nozzle corner crack under a complex bivariate stress field

  18. Fatigue crack growth monitoring: fracture mechanics and non-destructive testing requirements

    International Nuclear Information System (INIS)

    Williams, S.; Mudge, P.J.

    1982-01-01

    If a fatigue crack is found in a component in service, two options exist if plant integrity is to be maintained: first, the plant can be removed from service and repairs effected or replacements fitted; second, the growth of the crack can be monitored non-destructively until it is either considered to be too large to tolerate, in which case it must be repaired, or until a convenient down time when repair can be effected. The second option has obvious benefits for plant operators, but in such a situation it is essential that errors of the non-destructive estimate of defect size, which will undoubtedly exist, and uncertainties in the fatigue crack growth laws in operation must both be allowed for if a safe extension of service life is to be obtained; i.e. without failure by leakage or fast fracture arising from the fatigue crack. This paper analyses the accuracy required of non-destructive crack measurement techniques to permit the safe monitoring of crack growth by periodic inspection. It then demonstrates that it is possible to achieve adequate crack monitoring using conventional ultrasonic techniques. (author)

  19. Investigation of the effect of vacuum environment on the fatigue and fracture behavior of 7075-T6.

    Science.gov (United States)

    Hudson, C. M.

    1972-01-01

    Axial-load fatigue-life, fatigue-crack propagation, and fracture-toughness experiments were conducted on sheet specimens made of 7075-T6 aluminum alloy. These experiments were conducted at air pressures ranging from 101 kN/sq m to 7 micronewtons/sq m to determine the effect of air pressure on fatigue behavior. Analysis of the results from the fatigue-life experiments indicated that for a given stress level, the lower the air pressure was the longer the fatigue life. At a pressure of 7 micronewtons/sq m, fatigue lives were 15 to 30 times longer than at 101 kN/sq m. Analysis of the results from the fatigue-crack-growth experiments indicates that at low values of stress-intensity range, the fatigue-crack-growth rates were approximately twice as high at atmospheric pressure as in vacuum. However, at higher values of stress-intensity range, the fatigue-crack-growth rates were nominally the same in vacuum and at atmospheric pressure.

  20. Fatigue behavior of Ti–6Al–4V alloy in saline solution with the surface modified at a micro- and nanoscale by chemical treatment

    Energy Technology Data Exchange (ETDEWEB)

    Claros, Cesar Adolfo Escobar; Oliveira, Diego Pedreira; Campanelli, Leonardo Contri; Pereira da Silva, Paulo Sergio Carvalho; Bolfarini, Claudemiro

    2016-10-01

    This work evaluated the influence of the surface modification using acid etching combined with alkaline treatment on the fatigue strength of Ti–6Al–4V ELI alloy. The topography developed by chemical surface treatments (CST) was examined by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Increased roughness and effective surface area were investigated and compared with the Ti–6Al–4V samples without modification. Surface composition was analyzed by energy dispersive X-ray spectroscopy (EDS). Axial fatigue resistance of polished and modified surfaces was determined by stepwise load increase tests and staircase test method. Light microscopy and SEM were employed to examine the fracture surface of the tested specimens. According to the results, a similar fatigue behavior was found and a negligible difference in the fatigue crack nucleation was observed for the Ti–6Al–4V with CST in comparison to the samples without treatment. - Highlights: • Fatigue behavior of Ti–6Al–4V with the surface modified by chemical treatments • The topography developed did not induce differences in the fatigue resistance. • Untreated and chemically treated surfaces presented fractographic similarities.

  1. Fatigue behavior of Ti–6Al–4V alloy in saline solution with the surface modified at a micro- and nanoscale by chemical treatment

    International Nuclear Information System (INIS)

    Claros, Cesar Adolfo Escobar; Oliveira, Diego Pedreira; Campanelli, Leonardo Contri; Pereira da Silva, Paulo Sergio Carvalho; Bolfarini, Claudemiro

    2016-01-01

    This work evaluated the influence of the surface modification using acid etching combined with alkaline treatment on the fatigue strength of Ti–6Al–4V ELI alloy. The topography developed by chemical surface treatments (CST) was examined by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Increased roughness and effective surface area were investigated and compared with the Ti–6Al–4V samples without modification. Surface composition was analyzed by energy dispersive X-ray spectroscopy (EDS). Axial fatigue resistance of polished and modified surfaces was determined by stepwise load increase tests and staircase test method. Light microscopy and SEM were employed to examine the fracture surface of the tested specimens. According to the results, a similar fatigue behavior was found and a negligible difference in the fatigue crack nucleation was observed for the Ti–6Al–4V with CST in comparison to the samples without treatment. - Highlights: • Fatigue behavior of Ti–6Al–4V with the surface modified by chemical treatments • The topography developed did not induce differences in the fatigue resistance. • Untreated and chemically treated surfaces presented fractographic similarities.

  2. The effect of manufacturing conditions on discontinuity population and fatigue fracture behavior in carbon/epoxy composites

    Science.gov (United States)

    Hakim, Issa; Laquai, Rene; Walter, David; Mueller, Bernd; Graja, Paul; Meyendorf, Norbert; Donaldson, Steven

    2017-02-01

    Carbon fiber composites have been increasingly used in aerospace, military, sports, automotive and other fields due to their excellent properties, including high specific strength, high specific modulus, corrosion resistance, fatigue resistance, and low thermal expansion coefficient. Interlaminar fracture is a serious failure mode leading to a loss in composite stiffness and strength. Discontinuities formed during manufacturing process degrade the fatigue life and interlaminar fracture resistance of the composite. In his study, three approaches were implemented and their results were correlated to quantify discontinuities effecting static and fatigue interlaminar fracture behavior of carbon fiber composites. Samples were fabricated by hand layup vacuum bagging manufacturing process under three different vacuum levels, indicated High (-686 mmHg), Moderate (-330 mmHg) and Poor (0 mmHg). Discontinuity content was quantified through-thickness by destructive and nondestructive techniques. Eight different NDE methods were conducted including imaging NDE methods: X-Ray laminography, ultrasonic, high frequency eddy current, pulse thermography, pulse phase thermography and lock-in-thermography, and averaging NDE techniques: X-Ray refraction and thermal conductivity measurements. Samples were subsequently destructively serial sectioned through-thickness into several layers. Both static and fatigue interlaminar fracture behavior under Mode I were conducted. The results of several imaging NDE methods revealed the trend in percentages of discontinuity. However, the results of averaging NDE methods showed a clear correlation since they gave specific values of discontinuity through-thickness. Serial sectioning exposed the composite's internal structure and provided a very clear idea about the type, shape, size, distribution and location of most discontinuities included. The results of mechanical testing showed that discontinuities lead to a decrease in Mode I static interlaminar

  3. Fractures on curved surfaces: A classic problem solved

    Science.gov (United States)

    Balcerak, Ernie

    2011-11-01

    Sheeting joints—large fractures parallel to a curved rock surface—are common in many locations on Earth, such as the iconic Half Dome in Yosemite National Park in California. Explaining how these fractures form has been a classic unsolved problem in geology. Martel solved the problem by reformulating the static equilibrium equations in a curvilinear reference frame. His analysis shows that compression along a curved surface can induce tension perpendicular to the surface, which can cause subsurface cracks to open. He found that the curvature of a rock surface plays a key role in the formation of fractures.

  4. 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.

  5. Influence of Cyclic Straining on Fatigue, Deformation, and Fracture Behavior of High-Strength Alloy Steel

    Science.gov (United States)

    Manigandan, K.; Srivatsan, T. S.; Vasudevan, V. K.; Tammana, D.; Poorganji, B.

    2016-01-01

    In this paper, the results of a study on microstructural influences on mechanical behavior of the high-strength alloy steel Tenax™ 310 are presented and discussed. Under the influence of fully reversed strain cycling, the stress response of this alloy steel revealed softening from the onset of deformation. Cyclic strain resistance exhibited a linear trend for the variation of both elastic strain amplitude with reversals-to-failure, and plastic strain amplitude with reversals-to-failure. Fracture morphology was essentially the same at the macroscopic level over the entire range of cyclic strain amplitudes examined. However, at the fine microscopic level, this high-strength alloy steel revealed fracture to be mixed-mode with features reminiscent of "locally" ductile and brittle mechanisms. The macroscopic mechanisms governing stress response at the fine microscopic level, resultant fatigue life, and final fracture behavior are presented and discussed in light of the mutually interactive influences of intrinsic microstructural effects, deformation characteristics of the microstructural constituents during fully reversed strain cycling, cyclic strain amplitude, and resultant response stress.

  6. Microstructural effects on constitutive and fatigue fracture behavior of TinSilverCopper solder

    Science.gov (United States)

    Tucker, Jonathon P.

    As microelectronic package construction becomes more diverse and complex, the need for accurate, geometry-independent material constitutive and failure models increases. Evaluations of packages based on accelerated environmental tests (such as accelerated thermal cycling or power cycling) only provide package-dependent reliability information. In addition, extrapolations of such test data to life predictions under field conditions are often empirical. Besides geometry, accelerated environmental test data must account for microstructural factors such as alloy composition or isothermal aging condition, resulting in expensive experimental variation. In this work, displacement-controlled, creep, and fatigue lap shear tests are conducted on specially designed SnAgCu test specimens with microstructures representative to those found in commercial microelectronic packages. The data are used to develop constitutive and fatigue fracture material models capable of describing deformation and fracture behavior for the relevant temperature and strain rate ranges. Furthermore, insight is provided into the microstructural variation of solder joints and the subsequent effect on material behavior. These models are appropriate for application to packages of any geometrical construction. The first focus of the thesis is on Pb-mixed SnAgCu solder alloys. During the transition from Pb-containing solders to Pb-free solders, joints composed of a mixture of SnPb and SnAgCu often result from either mixed assemblies or rework. Three alloys of 1, 5 and 20 weight percent Pb were selected so as to represent reasonable ranges of Pb contamination expected from different 63Sn37Pb components mixed with Sn3.0Ag0.5Cu. Displacement-controlled (constant strain rate) and creep tests were performed at temperatures of 25°C, 75°C, and 125°C using a double lap shear test setup that ensures a nearly homogeneous state of plastic strain at the joint interface. Rate-dependent constitutive models for Pb

  7. Effect of Grinding and Resintering on the Fatigue Limit and Surface Characterization of a Y-TZP Ceramic.

    Science.gov (United States)

    Polli, Gabriela Scatimburgo; Hatanaka, Gabriel Rodrigues; Abi-Rached, Filipe de Oliveira; Pinelli, Lígia Antunes Pereira; Góes, Márcio de Sousa; Cesar, Paulo Francisco; Reis, José Maurício Dos Santos Nunes

    2016-01-01

    This study evaluated the effect of grinding protocols and resintering on flexural fatigue limit and surface characterization of LavaTM Y-TZP. Bar-shaped specimens (20×4.0×1.2 mm, n=40; 20×4.0×1.5 mm, n=80) were obtained. Half of the thinner specimens (1.2 mm) constituted the as-sintered group (AS), while the thicker ones (1.5 mm) were ground with diamond burs under irrigation (WG) or not (G). The other half of thinner and half of ground specimens were resintered (1000 ºC, 30 min), forming the groups ASR, WGR and GR. Fatigue limit (500,000 cycles, 10 Hz) was evaluated by staircase method in a 4-point flexural fixture. Data were analyzed by 2-way ANOVA and Tukey's test (α=0.05). Surface topography (n=3) and fracture area (n=3) were evaluated by SEM. X-ray diffraction data (n=1) was analyzed by Rietveld refinement. ANOVA revealed significant differences (pgrinding protocol, resintering and their interaction. Grinding increased the fatigue limit of non-resintered groups. There was no significant difference among the resintered groups. Resintering significantly increased the fatigue limit of the AS group only. Both protocols created evident grooves on zirconia surface. The failures initiated at the tensile side of all specimens. The percentages (wt%) of monoclinic phase were AS (8.6), ASR (1.2), G (1.8), GR (0.0), WG (8.2), WGR (0.0) before, and AS (7.4), ASR (6.5), G (3.2), GR (0.2), WG (4.6), WGR (1.1) after cyclic loading. Grinding increased the fatigue limit of non-resintered Y-TZP and formed evident grooves on its surface. Resintering provided significant increase in the fatigue limit of as-sintered specimens. In general, grinding and resintering decreased or zeroed the monoclinic phase.

  8. 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.

  9. Effect of Ultrasonic Surface Impact on the Fatigue Behavior of Ti-6Al-4V Subject to Simulated Body Fluid

    Directory of Open Access Journals (Sweden)

    Xiaojian Cao

    2017-10-01

    Full Text Available The effect of ultrasonic nanocrystal surface modification (UNSM on the fatigue behavior of Ti6Al4V (TC4 in simulated body fluid (SBF was investigated. UNSM with the condition of a static load of 25 N, vibration amplitude of 30 μm and 36,000 strikes per unit produced about 35 μm surface severe plastic deformation (SPD layers on the TC4 specimens. One group was treated with a hybrid surface treatment (UNSM + TiN film. UNSM technique improves the micro hardness and the compressive residual stress. The surface roughness is increased slightly, but it can be remarkably improved by the TiN film. The fatigue strength of TC4 is improved by about 7.9% after UNSM. Though the current density of corrosion is increased and the pitting corrosion is accelerated, UNSM still improved the fatigue strength of TC4 after pre-soaking in SBF by 10.8%. Interior cracks initiate at the deformed carbide and oxide inclusions due to the ultrasonic impacts of UNSM. Corrosion products are always observed at the edge of fracture surface to both interior cracks and surface cracks. Coating a TiN film on the UNSMed surface helps to improve the whole properties of TC4 further.

  10. The effect of aging treatment on the high temperature fatigue strength and fatigue fracture behaviour of friction welded domestic heat resisting steels (SUH3-SUS303)

    International Nuclear Information System (INIS)

    Lee, K.Y.; Oh, S.K.; Kim, H.J.

    1981-01-01

    In this study the experiment was carried out as the high temperature rotary bending fatigue testing under the condition of 700 0 C high temperature to the friction welded domestic heat resisting steels, SUH3-SUS303, which were 10 hr., 100 hr. aging heat treated at 700 0 C after solution treatment 1 hr. at 1060 0 C for the purpose of observing the effects of the high temperature fatigue strength and fatigue fracture behaviours as well as with various mechanical properties of welded joints. The results obtained are summarized as follows: 1) Through mechanical tests and microstructural examinations, the determined optimum welding conditions, rotating speed 2420 rpm, heating pressure 8 kg/mm 2 , upsetting pressure 22 kg/mm 2 , the amount of total upset 7 mm (heating time 3 sec and upsetting time 2 sec) were satisfied. 2) The solution treated material SUH3, SUS303 and SUH3-SUS303, have the highest inclination gradiant on S-N curve due to the high temperature fatigue testing for long time at 700 0 C. 3) The optimum aging time of friction welded SUH3-SUS303, has been recognized near the 10 hr. at 700 0 C after the solution treatment of 1 hr. at 1060 0 C. 4) The high temperature fatigue limits of aging treated materials were compared with those of raw material according to the extender of aging time, on 10 hr. aging, fatigue limits were increased by SUH3 75.4%, SUS303 28.5%, friction welded joints SUH3-SUS303 44.2% and 100 hr. aging the rate were 64.9%, 30.4% and 36.6% respectively. 5) The fatigue fractures occurred at the side of the base metal SUS303 of the friction welded joints SUH3-SUS303 and it is difficult to find out fractures at the friction welding interfaces. 6) The cracking mode of SUS303, SUH3-SUS303 is intergranular in any case, but SUH3 is fractured by transgranular cracking. (author)

  11. Cyclic fatigue and fracture in pyrolytic carbon-coated graphite mechanical heart-valve prostheses: role of small cracks in life prediction.

    Science.gov (United States)

    Dauskardt, R H; Ritchie, R O; Takemoto, J K; Brendzel, A M

    1994-07-01

    A fracture-mechanics based study has performed to characterize the fracture toughness and rates of cyclic fatigue-crack growth of incipient flaws in prosthetic heart-valve components made of pyrolytic carbon-coated graphite. Such data are required to predict the safe structural lifetime of mechanical heart-valve prostheses using damage-tolerant analysis. Unlike previous studies where fatigue-crack propagation data were obtained using through-thickness, long cracks (approximately 2-20 mm long), growing in conventional (e.g., compact-tension) samples, experiments were performed on physically small cracks (approximately 100-600 microns long), initiated on the surface of the pyrolytic-carbon coating to simulate reality. Small-crack toughness results were found to agree closely with those measured conventionally with long cracks. However, similar to well-known observations in metal fatigue, it was found that based on the usual computations of the applied (far-field) driving force in terms of the maximum stress intensity, Kmax, small fatigue cracks grew at rates that exceeded those of long cracks at the same applied stress intensity, and displayed a negative dependency on Kmax; moreover, they grew at applied stress intensities less than the fatigue threshold value, below which long cracks are presumed dormant. To resolve this apparent discrepancy, it is shown that long and small crack results can be normalized, provided growth rates are characterized in terms of the total (near-tip) stress intensity (incorporating, for example, the effect of residual stress); with this achieved, in principle, either form of data can be used for life prediction of implant devices. Inspection of the long and small crack results reveals extensive scatter inherent in both forms of growth-rate data for the pyrolytic-carbon material.

  12. A study of microstructure, quasi-static response, fatigue, deformation and fracture behavior of high strength alloy steels

    Science.gov (United States)

    Kannan, Manigandan

    The history of steel dates back to the 17th century and has been instrumental in the betterment of every aspect of our lives ever since, from the pin that holds the paper together to the Automobile that takes us to our destination steel touches everyone every day. Path breaking improvements in manufacturing techniques, access to advanced machinery and understanding of factors like heat treatment, corrosion resistance have aided in the advancement in the properties of steel in the last few years. In this dissertation document, the results of a study aimed at the influence of alloy chemistry, processing and influence of the quasi static and fatigue behavior of seven alloy steels is discussed. The microstructure of the as-received steel was examined and characterized for the nature and morphology of the grains and the presence of other intrinsic features in the microstructure. The tensile, cyclic fatigue and bending fatigue tests were done on a fully automated closed-loop servo-hydraulic test machine at room temperature. The failed samples of high strength steels were examined in a scanning electron microscope for understanding the fracture behavior, especially the nature of loading be it quasi static, cyclic fatigue or bending fatigue . The quasi static and cyclic fatigue fracture behavior of the steels examined coupled with various factors contributing to failure are briefly discussed in light of the conjoint and mutually interactive influences of intrinsic microstructural effects, nature of loading, and stress (load)-deformation-microstructural interactions.

  13. New specimen design for studying the growth of small fatigue cracks with surface acoustic waves

    Science.gov (United States)

    London, Blair

    1985-08-01

    The study of small surface fatigue cracks in AISI 4140 quenched and tempered steel by a nondestructive surface acoustic wave technique is summarized. A novel cantilevered bending, plate-type fatigue specimen is described that is compatible with the acoustic method. Small cracks are initiated from a 25-μm deep surface pit produced by an electrospark machine. The importance of studying these cracks which closely approximate naturally occurring fatigue cracks is briefly discussed.

  14. Cyclic Strain Resistance, Stress Response, Fatigue Life, and Fracture Behavior of High Strength Low Alloy Steel 300 M

    Science.gov (United States)

    Manigandan, K.; Srivatsan, T. S.; Tammana, Deepthi; Poorgangi, Behrang; Vasudevan, Vijay K.

    2014-05-01

    The focus of this technical manuscript is a record of the specific role of microstructure and test specimen orientation on cyclic stress response, cyclic strain resistance, and cyclic stress versus strain response, deformation and fracture behavior of alloy steel 300 M. The cyclic strain amplitude-controlled fatigue properties of this ultra-high strength alloy steel revealed a linear trend for the variation of log elastic strain amplitude with log reversals-to-failure, and log plastic strain amplitude with log reversals-to-failure for both longitudinal and transverse orientations. Test specimens of the longitudinal orientation showed only a marginal improvement over the transverse orientation at equivalent values of plastic strain amplitude. Cyclic stress response revealed a combination of initial hardening for the first few cycles followed by gradual softening for a large portion of fatigue life before culminating in rapid softening prior to catastrophic failure by fracture. Fracture characteristics of test specimens of this alloy steel were different at both the macroscopic and fine microscopic levels over the entire range of cyclic strain amplitudes examined. Both macroscopic and fine microscopic observations revealed fracture to be a combination of both brittle and ductile mechanisms. The underlying mechanisms governing stress response, deformation characteristics, fatigue life, and final fracture behavior are presented and discussed in light of the competing and mutually interactive influences of test specimen orientation, intrinsic microstructural effects, deformation characteristics of the microstructural constituents, cyclic strain amplitude, and response stress.

  15. Effect of Si content on fatigue fracture behavior of hot-rolled high-silicon steels

    Science.gov (United States)

    Umezawa, Osamu; Kanda, Jyunichi; Yamazaki, Takao

    2017-05-01

    As the Si content was increased from 1.5 to 5 mass%, both the yield stress and ultimate tensile strength were increased, respectively. The work hardening rate was also increased as the increase of Si content. On the contrary, the elongation was decreased as the increase of Si content, and the fracture manner was shifted from ductile to brittle. The 107 cycles fatigue strength was higher as the increase of Si content. The small misorientation distribution as ladder-like was detected in the grains of 1.5 mass%Si steel. Around the grain boundary, the strain incompatibility was detected in the steels containing over 3 mass%Si. The lattice rotation was locally detected in the vicinity of grain boundaries.

  16. Fatigue Life Estimation of Medium-Carbon Steel with Different Surface Roughness

    Directory of Open Access Journals (Sweden)

    Changyou Li

    2017-03-01

    Full Text Available Medium-carbon steel is commonly used for the rail, wire ropes, tire cord, cold heading, forging steels, cold finished steel bars, machinable steel and so on. Its fatigue behavior analysis and fatigue life estimation play an important role in the machinery industry. In this paper, the estimation of fatigue life of medium-carbon steel with different surface roughness using established S-N and P-S-N curves is presented. To estimate the fatigue life, the effect of the average surface roughness on the fatigue life of medium-carbon steel has been investigated using 75 fatigue tests in three groups with average surface roughness (Ra: 0.4 μm, 0.8 μm, and 1.6 μm, respectively. S-N curves and P-S-N curves have been established based on the fatigue tests. The fatigue life of medium-carbon steel is then estimated based on Tanaka-Mura crack initiation life model, the crack propagation life model using Paris law, and material constants of the S-N curves. Six more fatigue tests have been conducted to validate the presented fatigue life estimation formulation. The experimental results have shown that the presented model could estimate well the mean fatigue life of medium-carbon steel with different surface roughness.

  17. Fatigue characteristics of ODS surface treated Zircaloy-4

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Sun Han; Jung, Yan gIl; Park, Dong Jun; Park, Jung Hwan; Kim, Hyun Gil; Yang, Jae Ho; Koo, Yang Hyun [KAERI, Daejeon (Korea, Republic of)

    2016-05-15

    Various accident tolerant fuel (ATF) cladding concepts are considered and have being developed to increase the oxidation resistance and ballooning/ rupture resistance of current Zr-based cladding material under accident conditions. One concept is to form an oxidation-resistant layer on Zr cladding surface. The other is to increase high temperature mechanical strength of Zr tube. The oxide dispersion strengthened (ODS) zirconium was proposed to increase the strength of the Zr-based alloy up to high temperatures. ODS treatment is a way of improve the high temperature- oxidation resistant and mechanical stress by disperse the hardened particles inside of metal to interrupt the movement of the electric potential. In this study, the accident tolerance improved zirconium alloy by the ODS surface treatment was evaluated for the fatigue characteristics which is one of the significant items of the integrity assessment.

  18. Dynamic characterisation of the specific surface area for fracture networks

    Science.gov (United States)

    Cvetkovic, V.

    2017-12-01

    One important application of chemical transport is geological disposal of high-level nuclear waste for which crystalline rock is a prime candidate for instance in Scandinavia. Interconnected heterogeneous fractures of sparsely fractured rock such as granite, act as conduits for transport of dissolved tracers. Fluid flow is known to be highly channelized in such rocks. Channels imply narrow flow paths, adjacent to essentially stagnant water in the fracture and/or the rock matrix. Tracers are transported along channelised flow paths and retained by minerals and/or stagnant water, depending on their sorption properties; this mechanism is critical for rocks to act as a barrier and ultimately provide safety for a geological repository. The sorbing tracers are retained by diffusion and sorption on mineral surfaces, whereas non-sorbing tracers can be retained only by diffusion into stagnant water of fractures. The retention and transport properties of a sparsely fractured rock will primarily depend on the specific surface area (SSA) of the fracture network which is determined by the heterogeneous structure and flow. The main challenge when characterising SSA on the field-scale is its dependence on the flow dynamics. We first define SSA as a physical quantity and clarify its importance for chemical transport. A methodology for dynamic characterisation of SSA in fracture networks is proposed that relies on three sets of data: i) Flow rate data as obtained by a flow logging procedure; ii) transmissivity data as obtained by pumping tests; iii) fracture network data as obtained from outcrop and geophysical observations. The proposed methodology utilises these data directly as well as indirectly through flow and particle tracking simulations in three-dimensional discrete fracture networks. The methodology is exemplified using specific data from the Swedish site Laxemar. The potential impact of uncertainties is of particular significance and is illustrated for radionuclide

  19. Fracture surface energy of the Punchbowl fault, San Andreas system.

    Science.gov (United States)

    Chester, Judith S; Chester, Frederick M; Kronenberg, Andreas K

    2005-09-01

    Fracture energy is a form of latent heat required to create an earthquake rupture surface and is related to parameters governing rupture propagation and processes of slip weakening. Fracture energy has been estimated from seismological and experimental rock deformation data, yet its magnitude, mechanisms of rupture surface formation and processes leading to slip weakening are not well defined. Here we quantify structural observations of the Punchbowl fault, a large-displacement exhumed fault in the San Andreas fault system, and show that the energy required to create the fracture surface area in the fault is about 300 times greater than seismological estimates would predict for a single large earthquake. If fracture energy is attributed entirely to the production of fracture surfaces, then all of the fracture surface area in the Punchbowl fault could have been produced by earthquake displacements totalling <1 km. But this would only account for a small fraction of the total energy budget, and therefore additional processes probably contributed to slip weakening during earthquake rupture.

  20. [The influence of autoclave sterilization on surface characteristics and cyclic fatigue resistance of 3 nickel-titanium rotary instruments].

    Science.gov (United States)

    Li, Xiang-fen; Zheng, Ping; Xu, Li; Su, Qin

    2015-12-01

    To investigate the effects of autoclave sterilization on surface characteristics and cyclic fatigue resistance of 3 types of nickel-titanium rotary instruments (K3, Mtwo, ProTaper). Three brands of NiTi rotary endodontic instruments of the same size (tip diameter 0.25 mm and constant 0.06 taper) were selected: K3, Mtwo and Protaper (F2). 24 instruments for each brand were used to evaluate the effects of autoclave sterilization on inner character in the as-received condition and after subjection to 0, 1, 5, and 10 sterilization cycles (6 for each group). Time to fracture (TtF) from the start of the test to the moment of file breakage and the length of the fractured fragment were recorded. Means and standard deviations of TtF and fragment length were calculated. The data was analyzed with SPSS13.0 software package. Another 12 NiTi rotary instruments for each brand were used, 6 subjected to 10 autoclave sterilization cycles and the other as control. Scanning electron microscope was used to observe the changes in surface topography and inner character. For cyclic fatigue resistance, when sterilization was not performed, K3 showed the highest value of TtF means and ProTaper the lowest. The differences between each brand were statistically significant (Pinstruments were intensified greatly after 10 cycles of sterilization. Cycle fatigue resistance is different among instruments of different brands. Autoclave sterilization may increase fatigue resistance of the 3 brands. Autoclave sterilization may increase the surface roughness and inner defects in cross section.

  1. Effect of laser shock processing on fatigue crack growth and fracture toughness of 6061-T6 aluminum alloy

    International Nuclear Information System (INIS)

    Rubio-Gonzalez, C.; Ocana, J.L.; Gomez-Rosas, G.; Molpeceres, C.; Paredes, M.; Banderas, A.; Porro, J.; Morales, M.

    2004-01-01

    Laser shock processing (LSP) or laser shock peening is a new technique for strengthening metals. This process induces a compressive residual stress field which increases fatigue crack initiation life and reduces fatigue crack growth rate. Specimens of 6061-T6 aluminum alloy are used in this investigation. A convergent lens is used to deliver 1.2 J, 8 ns laser pulses by a Q-switch Nd:YAG laser, operating at 10 Hz. The pulses are focused to a diameter of 1.5 mm onto a water-immersed type aluminum samples. Effect of pulse density in the residual stress field is evaluated. Residual stress distribution as a function of depth is assessed by the hole drilling method. It is observed that the higher the pulse density the larger the zone size with compressive residual stress. Densities of 900, 1350 and 2500 pulses/cm 2 with infrared (1064 nm) radiation are used. Pre-cracked compact tension specimens were subjected to LSP process and then tested under cyclic loading with R = 0.1. Fatigue crack growth rate is determined and the effect of LSP process parameters is evaluated. Fatigue crack growth rate is compared in specimens with and without LSP process. In addition fracture toughness is determined in specimens with and without LSP treatment. It is observed that LSP reduces fatigue crack growth and increases fracture toughness in the 6061-T6 aluminum alloy

  2. Fracture Resistance, Surface Defects and Structural Strength of Glass

    OpenAIRE

    Rodichev, Y.M.; Veer, F.A.

    2010-01-01

    This paper poses the theory that the fracture resistance of basic float glass is dependent on it physicochemical properties and the surface defects fonned under the float glass production, glass processing and handling at the service conditions compose the aggregate basis for structural glass strength assessment. The effect of loading conditions, constructional and technological factors on the engineering strength of glass can be evaluated in certain cases using fracture mechanics with inform...

  3. Fatigue

    Science.gov (United States)

    ... sleep. Fatigue is a lack of energy and motivation. Drowsiness and apathy (a feeling of not caring ... Call your provider right away if you have any of the following: Confusion or dizziness Blurred vision Little or no urine, or recent ...

  4. Fatigue properties for the fracture strength of columnar accessory minerals embedded within metamorphic tectonites: implications for stress magnitude in continental crust at the depth of the brittle-plastic transition zone

    Science.gov (United States)

    Kimura, N.; Iwashita, N.; Masuda, T.

    2009-04-01

    .0005 to 0.2 mm/min, respectively. Pressure and relative humidity were set to room conditions. Tourmaline was chosen for testing (as representative of columnar accessory minerals embedded within metamorphic tectonites) because this is the only mineral for which crystals are available of sufficient size and quality. A total of 120 prism-shaped tourmaline test pieces (dimensions, 2×2×12 mm) were prepared from a single tourmaline block collected from Minas Gerais, Brazil. The flexural strength of tourmaline shows a clear decrease with decreasing crosshead speed at ambient temperature (with n ≈ 15 as the static fatigue parameter); however, this trend weakens with increasing temperature (n > 50); that is, the influence of static fatigue on the strength of tourmaline decreases with increasing temperature. A comparable result has been reported for glass materials because of difficulties in the absorption of moisture on sample surfaces under high-temperature conditions. The fabric pattern of fracture planes developed in tourmaline specimens in the present study, which show rectilinear scratches, arrests, or Wallner lines on smooth surfaces, is similar to that observed for glass materials. 3. Fractography of naturally deformed minerals A ‘striation-like' pattern resulting from cyclic fatigue fracture was observed by scanning electron microscope (SEM) analysis of a natural fracture plane developed within marble-hosted amphibole. The sample was collected from the eastern flank of the Red River shear zone (Luc Yen district), northern Vietnam. The brittle fracturing of amphibole (open fractures were filled by calcite, which deforms plastically) is considered to have occurred at 6 km depth at 25 Ma, based on geological criteria. 4. Order of stress magnitude in continental crust at the depth of the brittle-plastic transition zone Assuming that the fracture behaviour of columnar accessory minerals during the development of microboudinage is independent of the mineral species, the

  5. Estimation of muscle fatigue by ratio of mean frequency to average rectified value from surface electromyography.

    Science.gov (United States)

    Fernando, Jeffry Bonar; Yoshioka, Mototaka; Ozawa, Jun

    2016-08-01

    A new method to estimate muscle fatigue quantitatively from surface electromyography (EMG) is proposed. The ratio of mean frequency (MNF) to average rectified value (ARV) is used as the index of muscle fatigue, and muscle fatigue is detected when MNF/ARV falls below a pre-determined or pre-calculated baseline. MNF/ARV gives larger distinction between fatigued muscle and non-fatigued muscle. Experiment results show the effectiveness of our method in estimating muscle fatigue more correctly compared to conventional methods. An early evaluation based on the initial value of MNF/ARV and the subjective time when the subjects start feeling the fatigue also indicates the possibility of calculating baseline from the initial value of MNF/ARV.

  6. Effect of Process Parameters on Fatigue and Fracture Behavior of Al-Cu-Mg Alloy after Creep Aging

    Directory of Open Access Journals (Sweden)

    Lihua Zhan

    2018-04-01

    Full Text Available A set of creep aging tests at different aging temperatures and stress levels were carried out for Al-Cu-Mg alloy, and the effects of creep aging on strength and fatigue fracture behavior were studied through tensile tests and fatigue crack propagation tests. The microstructures were further analyzed by using scanning electron microscopy (SEM and transmission electron microscopy (TEM. The results show that temperature and stress can obviously affect the creep behavior, mechanical properties, and fatigue life of Al-Cu-Mg alloy. As the aging temperature increases, the fatigue life of alloy first increases, and then decreases. The microstructure also displays a transition from the Guinier-Preston-Bagaryatsky (GPB zones to the precipitation of S phase in the grain interior. However, the precipitation phases grow up and become coarse at excessive temperatures. Increasing stress can narrow the precipitation-free zone (PFZ at the grain boundary and improve the fatigue life, but overhigh stress can produce the opposite result. In summary, the fatigue life of Al-Cu-Mg alloy can be improved by fine-dispersive precipitation phases and a narrow PFZ in a suitable creep aging process.

  7. Effect of surface integrity of hard turned AISI 52100 steel on fatigue performance

    International Nuclear Information System (INIS)

    Smith, Stephen; Melkote, Shreyes N.; Lara-Curzio, Edgar; Watkins, Thomas R.; Allard, Larry; Riester, Laura

    2007-01-01

    This paper addresses the relationship between surface integrity and fatigue life of hard turned AISI 52100 steel (60-62 HRC), with grinding as a benchmark. The impact of superfinishing on the fatigue performance of hard turned and ground surfaces is also discussed. Specifically, the surface integrity and fatigue life of the following five distinct surface conditions are examined: hard turned with continuous white layer, hard turned with no white layer, ground, and superfinished hard turned and ground specimens. Surface integrity of the specimens is characterized via surface topography measurement, metallography, residual stress measurements, transmission electron microscopy (TEM), and nano-indentation tests. High cycle tension-tension fatigue tests show that the presence of white layer does not adversely affect fatigue life and that, on average, the hard turned surface performs as well or better than the ground surface. The effect of superfinishing is to exaggerate these differences in performance. The results obtained from this study suggest that the effect of residual stress on fatigue life is more significant than the effect of white layer. For the hard turned surfaces, the fatigue life is found to be directly proportional to both the surface compressive residual stress and the maximum compressive residual stress. Possible explanations for the observed effects are discussed

  8. Influence of surface finish on fatigue properties of metallic materials: a bibliographic study

    International Nuclear Information System (INIS)

    Akamatsu, M.

    1997-01-01

    The investigation of a fatigue failed component very often shows that cracks initiated at the surface. It is actually well known that the surface finish notably influences the fatigue strength of a component. We have carried out a bibliographic study in order to clarify the influence of the different surface parameters. The analysis of the literature has shown that most of the data concerns high cycle fatigue. Three aspects of the surface finish have been examined: geometry (roughness), residual stresses and microstructure. In a general way, the influence of geometrical surface finish is tackled either empirically, with a factor assessing the fatigue limit decrease when the roughness and the tensile strength increase, or theoretically, with approaches modelling geometrical irregularities as notches or cracks. In all cases, the effect of roughness on fatigue strength depends on the material, through mechanical properties or microstructural features. The theoretical approaches seem particularly interesting, but their use is not straightforward and requires further development. The creation of residual stresses at the surface of a component can just as well reduce as improve its fatigue strength. In a first approach, these stresses can be regarded as a mean service stress. In fact, mechanical and metallurgical gradients near the surface have to be taken into account, which affect the relaxation of residual stresses during fatigue cycling. Actually, the effect of residual stresses can hardly be isolated, because these stresses are associated with geometrical and microstructural modifications. Microstructural features (metallurgical structure, grain size, inclusions, strain hardening) have an undoubted influence on fatigue strength, but the quantification of the effects remains tricky. The influence of the microstructure of surface layers on fatigue strength generally depends on the mechanical properties of materials. In short, fatigue strength predictions through a

  9. 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_t_h) 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_t_h 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_t_h). Further, it was found that following parameters: fracture toughness (K_C), fatigue threshold ((∆K_t_h) and impact strength are correlated with the total matrix carbon content and ferritic cell size. (author)

  10. Thermal Exposure and Environment Effects on Tension, Fracture and Fatigue of 5XXX Alloys Tested in Different Orientations

    Science.gov (United States)

    2017-12-27

    Thermal Exposure and Environment Effects on Tension, Fracture and Fatigue of 5XXX Alloys Tested in Different Orientations Sb. GRANT NUMBER ONR-N000 14...e.g.Hl31, HI 16, HI 28), thermal exposure conditions (i .e. time, temperature), and environment (e.g. dry air, humid air, solutions) on the... environmental cracking susceptibility at different load ing rates in both the S-T and L-T orientations. Experiments were conducted using slow strain rate

  11. A computer-controlled automated test system for fatigue and fracture testing

    International Nuclear Information System (INIS)

    Nanstad, R.K.; Alexander, D.J.; Swain, R.L.; Hutton, J.T.; Thomas, D.L.

    1989-01-01

    A computer-controlled system consisting of a servohydraulic test machine, an in-house designed test controller, and a desktop computer has been developed for performing automated fracture toughness and fatigue crack growth testing both in the laboratory and in hot cells for remote testing of irradiated specimens. Both unloading compliance and dc-potential drop can be used to monitor crack growth. The test controller includes a dc-current supply programmer, a function generator for driving the servohydraulic test machine to required test outputs, five measurement channels (each consisting of low-pass filter, track/hold amplifier, and 16-bit analog-to-digital converter), and digital logic for various control and data multiplexing functions. The test controller connects to the computer via a 16-bit wide photo-isolated bidirectional bus. The computer, a Hewlett-Packard series 200/300, inputs specimen and test parameters from the operator, configures the test controller, stores test data from the test controller in memory, does preliminary analysis during the test, and records sensor calibrations, specimen and test parameters, and test data on flexible diskette for later recall and analysis with measured initial and final crack length information. During the test, the operator can change test parameters as necessary. 24 refs., 6 figs

  12. Effect of weld metal toughness on fracture behavior under ultra-low cycle fatigue loading (earthquake)

    Energy Technology Data Exchange (ETDEWEB)

    Kermajani, M. [School of Materials Engineering, College of Engineering, Tarbiat Modares University, Tehran (Iran, Islamic Republic of); Ghaini, F. Malek, E-mail: Fmalek@modares.ac.ir [School of Materials Engineering, College of Engineering, Tarbiat Modares University, Tehran (Iran, Islamic Republic of); Miresmaeili, R. [School of Materials Engineering, College of Engineering, Tarbiat Modares University, Tehran (Iran, Islamic Republic of); Aghakouchak, A.A. [School of Civil Engineering, College of Engineering, Tarbiat Modares University, Tehran (Iran, Islamic Republic of); Shadmand, M. [Department of Research and Development, MAPNA Electric and Control (MECO) Company, Karaj (Iran, Islamic Republic of)

    2016-06-21

    Results from 12 ultra-low cycle fatigue tests performed on the weld metals of both toughness and non-toughness rated grades are presented. Fracture resistance under these loadings seemed to be dependent on materials' toughness, displacement amplitude, and stress state triaxiality, while the toughness effect was more highlighted at high stress levels and concentrations. To study the effect of microstructures on these failures, supporting ancillary tests including all-weld tension coupons, Charpy V-notched impact tests, and optical and scanning electron microscope analyses were performed. The favored microstructures appeared to be those which absorbed energy by plastic deformation and, hence, hindered void formation and/or could avoid crack propagation by deflection. Considering the response of the tested materials to cyclic loadings and the requirements of the materials specified in AISC341 Provisions could question the adequacy of these requirements for weld metals. However, the role of microstructural features like inclusions would be the same in both the Charpy impact tests and ultra-low cycle loadings.

  13. Influence of low temperature on kinetics of magnesium alloy fatigue fracture

    International Nuclear Information System (INIS)

    Serdyuk, V.A.; Grinberg, N.M.; Malinkina, T.I.; Kamyshkov, A.S.

    1980-01-01

    Studied is the effect of low temperature on kinetics of fatigue fracture in a number of magnesium alloys (MA2-1, MA15, IMV6, MA21, MA12). Cylindrical samples have been tested in vacuum at 20 deg C and at -120 deg C using cyclic symmetric tension-compression. Presented is a dependence of residual durability of alloys at low temperature on the number of preliminary deformation reversals at room temperature. It is shown that for the MA15, MA 12 alloys the durability increases at low temperature due to increasing crack initiation duration, and the out-of-grain crack growth rate is higher at low temperature than at room temperature; whereas for the second group alloys (IMV6, MA21, MA2-1) an increase in the crack initiation stage and a decrease in the crack growth at temperature decreasing are characteristic. A conclusion is made that different behavior of Mg alloys at low temperature is conditioned by their different structural states

  14. Influence of surface conditions on fatigue strength through the numerical simulation of microstructure

    International Nuclear Information System (INIS)

    Le Pecheur, A.; Clavel, M.; Rey, C.; Bompard, P.; Le Pecheur, A.; Curtit, F.; Stephan, J.M.

    2010-01-01

    A thermal fatigue test (INTHERPOL) was developed by EDF in order to study the initiation of cracks. These tests are carried out on tubular specimens under various thermal loadings and surface finish qualities in order to give an account of these parameters on crack initiation. The main topic of this study is to test the sensitivity of different fatigue criteria to surface conditions using a micro/macro modelling approach. Therefore a 304L polycrystalline aggregate, used for cyclic plasticity based FE modelling, have been considered as a Representative Volume Element located at the surface and subsurface of the test tube. This aggregate has been cyclically strained according to the results issued from FE simulation of INTHERPOL thermal fatigue experiment. Different surface parameters have been numerically simulated: effects of local microstructure and of grains orientation, effects of machining: metallurgical prehardening, residual stress gradient, and surface roughness. Three different fatigue criteria (Manson Coffin, Fatemi Socie and dissipated energy types), previously fitted at a macro-scale for thermal fatigue of 304L, have been computed at a meso scale, in order to show the surface 'hot spots' features and test the sensitivity of these three criteria to different surface conditions. Results show that grain orientation and neighbouring play an important role on the location of hot spots, and also that the positive effect of pre-straining and the negative effect of roughness on fatigue life are not all similarly predicted by these different fatigue criteria. (authors)

  15. Scaling exponents for fracture surfaces in opal glass

    International Nuclear Information System (INIS)

    Chavez-Guerrero, L.; Garza, F.J.; Hinojosa, M.

    2010-01-01

    We have investigated the scaling properties of fracture surfaces in opal glass. Specimens with two different opacifying particle sizes (1 μm and 0.4 μm) were broken by three-point bending test and the resulting fracture surfaces were analyzed using Atomic Force Microscopy. The analysis of the self-affine behavior was performed using the Variable Bandwidth and Height-Height Correlation Methods, and both the roughness exponent, ζ, and the correlation length, ξ, were determined. It was found that the roughness exponent obtained in both samples is ζ ∼ 0.8; whereas the correlation length in both fractures is of the order of the particle size, demonstrating the dependence of this self-affine parameter on the microstructure of opal glass.

  16. Scaling exponents for fracture surfaces in opal glass

    Energy Technology Data Exchange (ETDEWEB)

    Chavez-Guerrero, L., E-mail: guerreroleo@hotmail.com [Facultad de Ingenieria Mecanica y Electrica. Cd. Universitaria s/n, C.P. 66450, Universidad Autonoma de Nuevo Leon, Nuevo Leon (Mexico); Center of Innovation, Research and Development on Engineering and Technology, Universidad Autonoma de Nuevo Leon Monterrey, C.P. 66600, Apodaca, Nuevo Leon (Mexico); Garza, F.J., E-mail: fjgarza@gama.fime.uanl.mx [Facultad de Ciencias Quimicas, Cd. Universitaria s/n, C.P. 66450, Universidad Autonoma de Nuevo Leon, Nuevo Leon (Mexico); Hinojosa, M., E-mail: hinojosa@gama.fime.uanl.mx [Facultad de Ingenieria Mecanica y Electrica. Cd. Universitaria s/n, C.P. 66450, Universidad Autonoma de Nuevo Leon, Nuevo Leon (Mexico); Center of Innovation, Research and Development on Engineering and Technology, Universidad Autonoma de Nuevo Leon Monterrey, C.P. 66600, Apodaca, Nuevo Leon (Mexico)

    2010-09-25

    We have investigated the scaling properties of fracture surfaces in opal glass. Specimens with two different opacifying particle sizes (1 {mu}m and 0.4 {mu}m) were broken by three-point bending test and the resulting fracture surfaces were analyzed using Atomic Force Microscopy. The analysis of the self-affine behavior was performed using the Variable Bandwidth and Height-Height Correlation Methods, and both the roughness exponent, {zeta}, and the correlation length, {xi}, were determined. It was found that the roughness exponent obtained in both samples is {zeta} {approx} 0.8; whereas the correlation length in both fractures is of the order of the particle size, demonstrating the dependence of this self-affine parameter on the microstructure of opal glass.

  17. Deep surface rolling for fatigue life enhancement of laser clad aircraft aluminium alloy

    Energy Technology Data Exchange (ETDEWEB)

    Zhuang, W., E-mail: wyman.zhuang@dsto.defence.gov.au [Aerospace Division, Defence Science and Technology Organisation, 506 Lorimer Street, Fishermans Bend, Victoria 3207 (Australia); Liu, Q.; Djugum, R.; Sharp, P.K. [Aerospace Division, Defence Science and Technology Organisation, 506 Lorimer Street, Fishermans Bend, Victoria 3207 (Australia); Paradowska, A. [Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2232 (Australia)

    2014-11-30

    Highlights: • Deep surface rolling as a post-repair enhancement technology was applied to the laser cladded 7075-T651 aluminium alloy specimens that simulated corrosion damage blend-out repair. • The residual stresses induced by the deep surface rolling process were measured. • The deep surface rolling process can introduce deep and high magnitude compressive residual stresses beyond the laser clad and substrate interface. • Spectrum fatigue test showed the fatigue life was significantly increased by deep surface rolling. - Abstract: Deep surface rolling can introduce deep compressive residual stresses into the surface of aircraft metallic structure to extend its fatigue life. To develop cost-effective aircraft structural repair technologies such as laser cladding, deep surface rolling was considered as an advanced post-repair surface enhancement technology. In this study, aluminium alloy 7075-T651 specimens with a blend-out region were first repaired using laser cladding technology. The surface of the laser cladding region was then treated by deep surface rolling. Fatigue testing was subsequently conducted for the laser clad, deep surface rolled and post-heat treated laser clad specimens. It was found that deep surface rolling can significantly improve the fatigue life in comparison with the laser clad baseline repair. In addition, three dimensional residual stresses were measured using neutron diffraction techniques. The results demonstrate that beneficial compressive residual stresses induced by deep surface rolling can reach considerable depths (more than 1.0 mm) below the laser clad surface.

  18. Deep surface rolling for fatigue life enhancement of laser clad aircraft aluminium alloy

    International Nuclear Information System (INIS)

    Zhuang, W.; Liu, Q.; Djugum, R.; Sharp, P.K.; Paradowska, A.

    2014-01-01

    Highlights: • Deep surface rolling as a post-repair enhancement technology was applied to the laser cladded 7075-T651 aluminium alloy specimens that simulated corrosion damage blend-out repair. • The residual stresses induced by the deep surface rolling process were measured. • The deep surface rolling process can introduce deep and high magnitude compressive residual stresses beyond the laser clad and substrate interface. • Spectrum fatigue test showed the fatigue life was significantly increased by deep surface rolling. - Abstract: Deep surface rolling can introduce deep compressive residual stresses into the surface of aircraft metallic structure to extend its fatigue life. To develop cost-effective aircraft structural repair technologies such as laser cladding, deep surface rolling was considered as an advanced post-repair surface enhancement technology. In this study, aluminium alloy 7075-T651 specimens with a blend-out region were first repaired using laser cladding technology. The surface of the laser cladding region was then treated by deep surface rolling. Fatigue testing was subsequently conducted for the laser clad, deep surface rolled and post-heat treated laser clad specimens. It was found that deep surface rolling can significantly improve the fatigue life in comparison with the laser clad baseline repair. In addition, three dimensional residual stresses were measured using neutron diffraction techniques. The results demonstrate that beneficial compressive residual stresses induced by deep surface rolling can reach considerable depths (more than 1.0 mm) below the laser clad surface

  19. Statistical analysis of surface lineaments and fractures for characterizing naturally fractured reservoirs

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Genliang; George, S.A.; Lindsey, R.P.

    1997-08-01

    Thirty-six sets of surface lineaments and fractures mapped from satellite images and/or aerial photos from parts of the Mid-continent and Colorado Plateau regions were collected, digitized, and statistically analyzed in order to obtain the probability distribution functions of natural fractures for characterizing naturally fractured reservoirs. The orientations and lengths of the surface linear features were calculated using the digitized coordinates of the two end points of each individual linear feature. The spacing data of the surface linear features within an individual set were, obtained using a new analytical sampling technique. Statistical analyses were then performed to find the best-fit probability distribution functions for the orientation, length, and spacing of each data set. Twenty-five hypothesized probability distribution functions were used to fit each data set. A chi-square goodness-of-fit test was used to rank the significance of each fit. A distribution which provides the lowest chi-square goodness-of-fit value was considered the best-fit distribution. The orientations of surface linear features were best-fitted by triangular, normal, or logistic distributions; the lengths were best-fitted by PearsonVI, PearsonV, lognormal2, or extreme-value distributions; and the spacing data were best-fitted by lognormal2, PearsonVI, or lognormal distributions. These probability functions can be used to stochastically characterize naturally fractured reservoirs.

  20. The effect of loading rate on ductile fracture toughness and fracture surface roughness

    DEFF Research Database (Denmark)

    Osovski, S.; Srivastava, Akhilesh Kumar; Ponson, L.

    2015-01-01

    The variation of ductile crack growth resistance and fracture surface roughness with loading rate is modeled under mode I plane strain, small scale yielding conditions. Three-dimensional calculations are carried out using an elastic-viscoplastic constitutive relation for a progressively cavitatin...

  1. [Analysis of the Muscle Fatigue Based on Band Spectrum Entropy of Multi-channel Surface Electromyography].

    Science.gov (United States)

    Liu, Jian; Zou, Renling; Zhang, Dongheng; Xu, Xiulin; Hu, Xiufang

    2016-06-01

    Exercise-induced muscle fatigue is a phenomenon that the maximum voluntary contraction force or power output of muscle is temporarily reduced due to muscular movement.If the fatigue is not treated properly,it will bring about a severe injury to the human body.With multi-channel collection of lower limb surface electromyography signals,this article analyzes the muscle fatigue by adoption of band spectrum entropy method which combined electromyographic signal spectral analysis and nonlinear dynamics.The experimental result indicated that with the increase of muscle fatigue,muscle signal spectrum began to move to low frequency,the energy concentrated,the system complexity came down,and the band spectrum entropy which reflected the complexity was also reduced.By monitoring the entropy,we can measure the degree of muscle fatigue,and provide an indicator to judge fatigue degree for the sports training and clinical rehabilitation training.

  2. Fracture toughness and fatigue crack propagation in cast irons with spheroidal vanadium carbides dispersed within martensitic matrix microstructure

    International Nuclear Information System (INIS)

    Uematsu, Y.; Tokaji, K.; Horie, T.; Nishigaki, K.

    2007-01-01

    Fracture toughness and fatigue crack propagation (FCP) have been studied using compact tension (CT) specimens of as-cast and subzero-treated materials in a cast iron with spheroidal vanadium carbides (VCs) dispersed in the martensitic matrix microstructure. X-ray diffraction (XRD) analysis revealed that retained austenite was transformed to martensite by subzero treatment. Vickers hardness was increased from 738 for the as-cast material to 782 for the subzero-treated material, which could be attributed to retained austenite to martensite transformation. The subzero-treated material exhibited lower fracture toughness than the as-cast material because soft and ductile retained austenite which possesses high fracture toughness was transformed to martensite in the subzero-treated material. Intrinsic FCP resistance after taking account of crack closure was decreased by the subzero treatment, which was attributed to the predominant crack propagation through the interface between VCs and the matrix and the straight crack path in the matrix microstructure

  3. Fractal dimension of the fractured surface of materials

    International Nuclear Information System (INIS)

    Lung, C.W.; Zhang, S.Z.

    1989-05-01

    Fractal dimension of the fractured surface of materials is discussed to show that the origin of the negative correlation between D F and toughness lies in the method of fractal dimension measurement with perimeter-area relation and also in the physical mechanism of crack propagation. (author). 8 refs, 4 figs, 1 tab

  4. Fracture Resistance, Surface Defects and Structural Strength of Glass

    NARCIS (Netherlands)

    Rodichev, Y.M.; Veer, F.A.

    2010-01-01

    This paper poses the theory that the fracture resistance of basic float glass is dependent on it physicochemical properties and the surface defects fonned under the float glass production, glass processing and handling at the service conditions compose the aggregate basis for structural glass

  5. Ductile fracture surface morphology of amorphous metallic alloys

    NARCIS (Netherlands)

    Miskuf, J; Csach, K; Ocelik, [No Value; Bengus, VZ; Tabachnikova, ED; Duhaj, P; Ocelik, Vaclav

    1999-01-01

    Fracture surfaces of ductile failure of two types bulk amorphous metallic alloys were studied using quantitative and qualitative fractographic analysis. The observed fractographic behaviour of ductile failure in comparison with the ductile failure of amorphous alloy ribbons shows signs of the same

  6. Evolution of surface topography in dependence on the grain orientation during surface thermal fatigue of polycrystalline copper

    CERN Document Server

    Aicheler, M; Taborelli, M; Calatroni, S; Neupert, H; Wuensch, W; Sgobba, S

    2011-01-01

    Surface degradation due to cyclic thermal loading plays a major role in the Accelerating Structures (AS) of the future Compact Linear Collider (CLIC) In this article results on surface degradation of thermally cycled polycrystalline copper as a function of the orientation of surface grains are presented Samples with different grain sizes were subjected to thermal fatigue using two different methods and were then characterized using roughness measurements and Orientation Imaging Scanning-Electron-Microscopy (OIM-SEM) Samples fatigued by a pulsed laser show the same trend in the orientation-fatigue damage accumulation as the sample fatigued by pulsed Radio-Frequency-heating (RF) it is clearly shown that 11 1 1] surface grains develop significantly more damage than the surface grains oriented in {[}100] and three reasons for this behaviour are pointed out Based on observations performed near grain boundaries their role in the crack initiation process is discussed The results are in good agreement with previous f...

  7. Evaluation of the Effect of Surface Finish on High-Cycle Fatigue of SLM-IN718

    Science.gov (United States)

    Lambert, D. M.

    2016-01-01

    The surface finish of parts produced by additive manufacturing processes is much rougher than the surface finish generated by machining processes, and a rougher surface can reduce the fatigue strength of a part. This paper discusses an effort to quantify that reduction of strength in high-cycle fatigue for selective laser melt (SLM) coupons. A high-cycle fatigue (HCF) knockdown factor was estimated for Inconel 718, manufactured with the SLM process. This factor is the percentage reduction from the maximum stress in fatigue for low-stress ground (LSG) specimens to the maximum stress of those left with the original surface condition at the same fatigue life. Specimens were provided by a number of vendors, free to use their "best practice"; only one heat treat condition was considered; and several test temperatures were characterized, including room temperature, 800F, 1000F, and 1200F. The 1000F data had a large variance, and was omitted from consideration in this document. A first method used linear approximations extracted from the graphs, and only where data was available for both. A recommended knockdown factor of the as-built surface condition (average roughness of approximately 245 micro-inches/inch) versus low-stress ground condition (roughness no more than 4 micro-inches/inch) was established at approximately 1/3 or 33%. This is to say that for the as-built surface condition, a maximum stress of 2/3 of the stress for LSG can be expected to produce a similar life in the as-built surface condition. In this first evaluation, the knockdown factor did not appear to be a function of temperature. A second approach, the "KP method", incorporated the surface finish measure into a new parameter termed the pseudo-stress intensity factor, Kp, which was formulated to be similar to the fracture mechanics stress intensity factor. Using Kp, the variance seemed to be reduced across all sources, and knockdown factors were estimated using Kp over the range where data occurred. A

  8. Relationship between enamel bond fatigue durability and surface free-energy characteristics with universal adhesives.

    Science.gov (United States)

    Nagura, Yuko; Tsujimoto, Akimasa; Barkmeier, Wayne W; Watanabe, Hidehiko; Johnson, William W; Takamizawa, Toshiki; Latta, Mark A; Miyazaki, Masashi

    2018-04-01

    The relationship between enamel bond fatigue durability and surface free-energy characteristics with universal adhesives was investigated. The initial shear bond strengths and shear fatigue strengths of five universal adhesives to enamel were determined with and without phosphoric acid pre-etching. The surface free-energy characteristics of adhesive-treated enamel with and without pre-etching were also determined. The initial shear bond strength and shear fatigue strength of universal adhesive to pre-etched enamel were higher than those to ground enamel. The initial shear bond strength and shear fatigue strength of universal adhesive to pre-etched enamel were material dependent, unlike those to ground enamel. The surface free-energy of the solid (γ S ) and the hydrogen-bonding force (γSh) of universal adhesive-treated enamel were different depending on the adhesive, regardless of the presence or absence of pre-etching. The bond fatigue durability of universal adhesives was higher to pre-etched enamel than to ground enamel. In addition, the bond fatigue durability to pre-etched enamel was material dependent, unlike that to ground enamel. The surface free-energy characteristics of universal adhesive-treated enamel were influenced by the adhesive type, regardless of the presence or absence of pre-etching. The surface free-energy characteristics of universal adhesive-treated enamel were related to the results of the bond fatigue durability. © 2018 Eur J Oral Sci.

  9. Incomplete longitudinal fractures and fatigue injury of the proximopalmar medial aspect of the third metacarpal bone in 55 horses.

    Science.gov (United States)

    Morgan, R; Dyson, S

    2012-01-01

    Previous descriptions of incomplete longitudinal fractures and fatigue injury of the proximopalmar aspect of the third metacarpal bone (McIII) have focused on diagnostic imaging findings, especially in racehorses. To document the case details, clinical features, response to diagnostic analgesia, diagnostic imaging findings and follow-up data in a large group of horses with an incomplete longitudinal fracture or fatigue injury of the proximopalmar medial aspect of the McIII. Horses were included in the study if pain was localised to the proximopalmar aspect of the metacarpal region, with radiological evidence of an incomplete longitudinal fracture or generalised increased radiopacity in the proximopalmar medial aspect of the McIII, or focal increased radiopharmaceutical uptake (IRU) in the proximopalmar aspect of the McIII. Age, breed, gender, height, bodyweight, work discipline, work history, duration of lameness, clinical signs and responses to diagnostic analgesia were recorded. Radiographic and scintigraphic images were assessed subjectively and objectively. There were 55 horses representing a broad spectrum of ages and work disciplines, 73% of which had radiological abnormalities. The majority had no localising clinical signs, although 73% of horses with radiological abnormalities showed a characteristic pattern of lameness. Lameness was generally worse in straight lines than in circles. Increased radiopharmaceutical uptake ranged from mild to intense in the lame limb; 14% of nonlame limbs had mild IRU. Of horses for which long-term follow-up was available, 98% returned to full athletic function. Incomplete longitudinal fractures and fatigue injury of the proximopalmar medial aspect of the McIII may occur in horses of many types and sports disciplines, and are not confined to immature performance horses. They should be considered an important differential diagnosis for proximal metacarpal region pain. © 2011 EVJ Ltd.

  10. Influence of steel-making process and heat-treatment temperature on the fatigue and fracture properties of pressure vessel steels

    International Nuclear Information System (INIS)

    Koh, S. K.; Na, E. G.; Baek, T. H.; Won, S. Y.; Park, S. J.; Lee, S. W.

    2001-01-01

    In this paper, high strength pressure vessel steels having the same chemical compositions were manufactured by the two different steel-making processes, such as Vacuum Degassing(VD) and Electro-Slag Remelting(ESR) methods. After the steel-making process, they were normalized at 955 deg. C, quenched at 843 .deg. C, and finally tempered at 550 .deg. C or 450 deg. C, resulting in tempered martensitic microstructures with different yielding strengths depending on the tempering conditions. Low-Cycle Fatigue(LCF) tests, Fatigue Crack Growth Rate(FCGR) tests, and fracture toughness tests were performed to investigate the fatigue and fracture behaviors of the pressure vessel steels. In contrast to very similar monotonic, LCF, and FCGR behaviors between VD and ESR steels, a quite difference was noticed in the fracture toughness. Fracture toughness of ESR steel was higher than that of VD steel, being attributed to the removal of impurities in steel-making process

  11. Fatigue and Corrosion in Metals

    CERN Document Server

    Milella, Pietro Paolo

    2013-01-01

    This textbook, suitable for students, researchers and engineers, gathers the experience of more than 20 years of teaching fracture mechanics, fatigue and corrosion to professional engineers and running experimental tests and verifications to solve practical problems in engineering applications. As such, it is a comprehensive blend of fundamental knowledge and technical tools to address the issues of fatigue and corrosion. The book initiates with a systematic description of fatigue from a phenomenological point of view, since the early signs of submicroscopic damage in few surface grains and continues describing, step by step, how these precursors develop to become mechanically small cracks and, eventually, macrocracks whose growth is governed by fracture mechanics. But fracture mechanics is also introduced to analyze stress corrosion and corrosion assisted fatigue in a rather advanced fashion. The author dedicates a particular attention to corrosion starting with an electrochemical treatment that mechanical e...

  12. Fracture toughness and fracture surface energy of sintered uranium dioxide fuel pellets

    International Nuclear Information System (INIS)

    Kutty, T.R.G.; Chandrasekharan, K.N.; Panakkal, J.P.; Ghosh, J.K.

    1987-01-01

    The paper concerns the variation of fracture toughness Ksub(ic) and fracture surface energy γsub(s) in sintered uranium dioxide pellets in the density range 9.86 to 10.41 g cm -3 , using Vickers indentation technique. A minimum of four indentations were made on each pellet sample and the average crack length of each indentation and the hardness values were determined. The overall average crack-length datra and the data on volume fraction porosity in the pellets fitted a straight line, from which Ksub(ic) and γsub(s) were calculated. The fracture parameters of nonporous polycrystalline UO 2 , calculated from the experimental data, are presented in tabular form. (U.K.)

  13. The effect of a free surface on fatigue crack behaviour

    Czech Academy of Sciences Publication Activity Database

    Hutař, Pavel; Náhlík, Luboš; Knésl, Zdeněk

    2010-01-01

    Roč. 32, č. 8 (2010), s. 1265-1269 ISSN 0142-1123 R&D Projects: GA ČR GA106/09/1954; GA ČR GA101/09/0867 Institutional research plan: CEZ:AV0Z20410507 Keywords : Vertex singularity * Generalized stress intenzity factor * Stress singularity * Fatigue crack * V- notch Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.799, year: 2010

  14. Effect of Surface Impulsive Thermal Loads on Fatigue Behavior of Constant Volume Propulsion Engine Combustor Materials

    National Research Council Canada - National Science Library

    Zhu, Dongming

    2004-01-01

    .... In this study, a simulated engine test rig has been established to evaluate thermal fatigue behavior of a candidate engine combustor material, Haynes 188, under superimposed CO2 laser surface impulsive thermal loads (30 to 100 Hz...

  15. The Effect of the Free Surface on the Singular Stress Field at the Fatigue Crack Front

    Directory of Open Access Journals (Sweden)

    Oplt Tomáš

    2017-11-01

    Full Text Available Description of stress singularity in the vicinity of a free surface is presented. Its presence causes the retardation of the fatigue crack growth in that region and fatigue crack is being curved. Numerical model is used to study dependence of the stress singularity exponent on Poisson’s ratio. Estimated values are compared to those already published. Experimentally measured angles of fatigue crack on SENB specimens confirm the relation between Poisson’s ratio and the angle between crack front and free surface.

  16. Evaluation of the conditions imposed by the fracture surface geometry on water seepage through fractured porous media

    International Nuclear Information System (INIS)

    Fuentes, Nestor O.; Faybishenko, B.

    2003-01-01

    In order to determine the geometric patterns of the fracture surfaces that imposes conditions on the fluid flow through fractured porous media, a series a fracture models have been analyzed using the RIMAPS technique and the variogram method. Results confirm that the main paths followed by the fluid channels are determined by the surface topography and remain constant during water seepage evolution. Characteristics scale lengths of both situations: fracture surface and the flow of water, are also found. There exists a relationship between the scale lengths corresponding to each situation. (author)

  17. A fracture mechanics approach for estimating fatigue crack initiation in carbon and low-alloy steels in LWR coolant environments

    International Nuclear Information System (INIS)

    Park, H. B.; Chopra, O. K.

    2000-01-01

    A fracture mechanics approach for elastic-plastic materials has been used to evaluate the effects of light water reactor (LWR) coolant environments on the fatigue lives of carbon and low-alloy steels. The fatigue life of such steel, defined as the number of cycles required to form an engineering-size crack, i.e., 3-mm deep, is considered to be composed of the growth of (a) microstructurally small cracks and (b) mechanically small cracks. The growth of the latter was characterized in terms of ΔJ and crack growth rate (da/dN) data in air and LWR environments; in water, the growth rates from long crack tests had to be decreased to match the rates from fatigue S-N data. The growth of microstructurally small cracks was expressed by a modified Hobson relationship in air and by a slip dissolution/oxidation model in water. The crack length for transition from a microstructurally small crack to a mechanically small crack was based on studies on small crack growth. The estimated fatigue S-N curves show good agreement with the experimental data for these steels in air and water environments. At low strain amplitudes, the predicted lives in water can be significantly lower than the experimental values

  18. Mixed-mode fatigue fracture of adhesive joints in harsh environments and nonlinear viscoelastic modeling of the adhesive

    Science.gov (United States)

    Arzoumanidis, Alexis Gerasimos

    A four point bend, mixed-mode, reinforced, cracked lap shear specimen experimentally simulated adhesive joints between load bearing composite parts in automotive components. The experiments accounted for fatigue, solvent and temperature effects on a swirled glass fiber composite adherend/urethane adhesive system. Crack length measurements based on compliance facilitated determination of da/dN curves. A digital image processing technique was also utilized to monitor crack growth from in situ images of the side of the specimen. Linear elastic fracture mechanics and finite elements were used to determine energy release rate and mode-mix as a function of crack length for this specimen. Experiments were conducted in air and in a salt water bath at 10, 26 and 90°C. Joints tested in the solvent were fully saturated. In air, both increasing and decreasing temperature relative to 26°C accelerated crack growth rates. In salt water, crack growth rates increased with increasing temperature. Threshold energy release rate is shown to be the most appropriate design criteria for joints of this system. In addition, path of the crack is discussed and fracture surfaces are examined on three length scales. Three linear viscoelastic properties were measured for the neat urethane adhesive. Dynamic tensile compliance (D*) was found using a novel extensometer and results were considerably more accurate and precise than standard DMTA testing. Dynamic shear compliance (J*) was determined using an Arcan specimen. Dynamic Poisson's ratio (nu*) was extracted from strain gage data analyzed to include gage reinforcement. Experiments spanned three frequency decades and isothermal data was shifted by time-temperature superposition to create master curves spanning thirty decades. Master curves were fit to time domain Prony series. Shear compliance inferred from D* and nu* compared well with measured J*, forming a basis for finding the complete time dependent material property matrix for this

  19. The fatigue life and fatigue-crack-through-thickness behavior of a surface-cracked plate, 3

    International Nuclear Information System (INIS)

    Nam, Ki-Woo; Matsui, Kentaro; Ando, Kotoji; Ogura, Nobukazu

    1989-01-01

    The LBB (leak-before-break) design is one of the most important subjects for the evaluation and the assurance of safety in pressure vessels, piping systems, LNG carriers and various other structures. In the LBB design, it is necessary to evaluate precisely the lifetime of steel plate. Furthermore, the change in crack shape that occurs during the propagation after through thickness is of paramount importance. For this reason, in a previous report, the authors proposed a simplified evaluation model for the stress intensity factor after cracking through thickness. Using this model, the crack propagation behavior, crack-opening displacement and crack shape change of surface-cracked smooth specimens and surface-cracked specimens with a stress concentration were evaluated quantitatively. The present study was also done to investigate the fatigue crack propagation behavior of surface cracks subjected to combined tensile and bending stress. Estimation of fatigue crack growth was done using the Newman-Raju formula before through thickness, and using formula (7) and (8) after through thickness. Crack length a r at just through thickness increases with increasing a bending stress. Calculated fatigue crack shape showed very good agreement with experimental one. It was also found that particular crack growth behavior and change in crack shape after cracking through thickness can be explained quantitatively using the K value based on Eqs. (7) and (8). (author)

  20. Cement based composites for thin building elements: Fracture and fatigue parameters

    Czech Academy of Sciences Publication Activity Database

    Seitl, Stanislav; Bílek, V.; Keršner, Z.; Veselý, J.

    2010-01-01

    Roč. 2, č. 1 (2010), s. 911-916 E-ISSN 1877-7058. [Fatigue 2010. Praha, 06.06.2010-11.06.2010] R&D Projects: GA ČR GA103/08/0963 Institutional research plan: CEZ:AV0Z20410507 Keywords : Cement-based composites * Fatigue concrete * Wöhler curve * Fibers Subject RIV: JL - Materials Fatigue, Friction Mechanics

  1. Fatigue behaviour of 304L steel welded structures: influence of residual stresses and surface mechanical finishing

    International Nuclear Information System (INIS)

    Magnier-Monin, L.

    2007-12-01

    This study focuses on the influence of residual stresses and surface mechanical finishing on lifetime of stainless steel 304L welded structures. Residual stresses are determined on specific specimens of three types: base-metal, as-welded and ground-welded specimens. Each type is submitted to fatigue tests in order to assess the influence of these parameters on the lifetime, and to determine their evolution. The experiments show that an important surface stress concentration is located in the weld root of as-welded structures, which has a negative effect on the fatigue life. The grinding operation generates high-level surface residual stresses but the lifetime is higher thanks to the reduction of the notch effect. The fatigue test results are compared to the nuclear industry best-fit S-N curves. This enables the determination of correction factors related to fatigue test results of polished specimens, and to assess the lifetime of structures. (author)

  2. Texture, microstructure, and fractal features of the low-cycle fatigue failure of the metal in pipeline welded joints

    Science.gov (United States)

    Usov, V. V.; Gopkalo, E. E.; Shkatulyak, N. M.; Gopkalo, A. P.; Cherneva, T. S.

    2015-09-01

    Crystallographic texture and fracture features are studied after low-cycle fatigue tests of laboratory specimens cut from the base metal and the characteristic zones of a welded joint in a pipeline after its longterm operation. The fractal dimensions of fracture surfaces are determined. The fractal dimension is shown to increase during the transition from ductile to quasi-brittle fracture, and a relation between the fractal dimension of a fracture surface and the fatigue life of the specimen is found.

  3. Influence of grain orientation on evolution of surface features in fatigued polycrystalline copper: A comparison of thermal and uniaxial mechanical fatigue results

    International Nuclear Information System (INIS)

    Aicheler, Markus

    2010-01-01

    Surface state plays a major role in the crack nucleation process of pure metals in the High-Cycle-Fatigue (HCF) as well as in the Ultra-High-Cycle-Fatigue (UHCF) regime. Therefore, in studies dealing with HCF or UHCF, special attention is paid to the evolution of surface degradation during fatigue life. The accelerating structures of the future Compact Linear Collider (CLIC) under study at CERN will be submitted to a high number of thermal-mechanical fatigue cycles, arising from Radio Frequency (RF) induced eddy currents, causing local superficial cyclic heating. The number of cycles during the foreseen lifetime of CLIC reaches 2x10 11 . Fatigue may limit the lifetime of CLIC structures. In order to assess the effects of superficial fatigue, specific tests are defined and performed on polycrystalline Oxygen Free Electronic (OFE) grade Copper, a candidate material for the structures. Surface degradation depends on the orientation of near-surface grains. Copper samples thermally fatigued in two different fatigue experiments, pulsed laser and pulsed RF-heating, underwent postmortem Electron Backscattered Diffraction measurements. Samples fatigued by pulsed laser show the same trend in the orientation-fatigue damage behavior as samples fatigued by pulsed RF-heating. It is clearly observed that surface grains, oriented [1 1 1] with respect to the surface, show significantly more damage than surface grains oriented [1 0 0]. Results arising from a third fatigue experiment, the ultrasound (US) swinger, are compared to the results of the mentioned experiments. The US swinger is an uniaxial mechanical fatigue test enabling to apply within several days a total number of cycles representative of the life of the CLIC structures, thanks to a high repetition rate of 24 kHz. For comparison, laser fatigue experiments have much lower repetition rates. The dependence of surface degradation on grain orientation of samples tested by the US swinger was monitored during the fatigue life

  4. Surface integrity and fatigue behaviour of electric discharged machined and milled austenitic stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Lundberg, Mattias, E-mail: mattias.lundberg@liu.se; Saarimäki, Jonas; Moverare, Johan J.; Calmunger, Mattias

    2017-02-15

    Machining of austenitic stainless steels can result in different surface integrities and different machining process parameters will have a great impact on the component fatigue life. Understanding how machining processes affect the cyclic behaviour and microstructure are of outmost importance in order to improve existing and new life estimation models. Milling and electrical discharge machining (EDM) have been used to manufacture rectangular four-point bend fatigue test samples; subjected to high cycle fatigue. Before fatigue testing, surface integrity characterisation of the two surface conditions was conducted using scanning electron microscopy, surface roughness, residual stress profiles, and hardness profiles. Differences in cyclic behaviour were observed between the two surface conditions by the fatigue testing. The milled samples exhibited a fatigue limit. EDM samples did not show the same behaviour due to ratcheting. Recrystallized nano sized grains were identified at the severely plastically deformed surface of the milled samples. Large amounts of bent mechanical twins were observed ~ 5 μm below the surface. Grain shearing and subsequent grain rotation from milling bent the mechanical twins. EDM samples showed much less plastic deformation at the surface. Surface tensile residual stresses of ~ 500 MPa and ~ 200 MPa for the milled and EDM samples respectively were measured. - Highlights: •Milled samples exhibit fatigue behaviour, but not EDM samples. •Four-point bending is not suitable for materials exhibiting pronounced ratcheting. •LAGB density can be used to quantitatively measure plastic deformation. •Grain shearing and rotation result in bent mechanical twins. •Nano sized grains evolve due to the heat of the operation.

  5. Analysis of Muscle Fatigue Progression using Cyclostationary Property of Surface Electromyography Signals.

    Science.gov (United States)

    Karthick, P A; Venugopal, G; Ramakrishnan, S

    2016-01-01

    Analysis of neuromuscular fatigue finds various applications ranging from clinical studies to biomechanics. Surface electromyography (sEMG) signals are widely used for these studies due to its non-invasiveness. During cyclic dynamic contractions, these signals are nonstationary and cyclostationary. In recent years, several nonstationary methods have been employed for the muscle fatigue analysis. However, cyclostationary based approach is not well established for the assessment of muscle fatigue. In this work, cyclostationarity associated with the biceps brachii muscle fatigue progression is analyzed using sEMG signals and Spectral Correlation Density (SCD) functions. Signals are recorded from fifty healthy adult volunteers during dynamic contractions under a prescribed protocol. These signals are preprocessed and are divided into three segments, namely, non-fatigue, first muscle discomfort and fatigue zones. Then SCD is estimated using fast Fourier transform accumulation method. Further, Cyclic Frequency Spectral Density (CFSD) is calculated from the SCD spectrum. Two features, namely, cyclic frequency spectral area (CFSA) and cyclic frequency spectral entropy (CFSE) are proposed to study the progression of muscle fatigue. Additionally, degree of cyclostationarity (DCS) is computed to quantify the amount of cyclostationarity present in the signals. Results show that there is a progressive increase in cyclostationary during the progression of muscle fatigue. CFSA shows an increasing trend in muscle fatiguing contraction. However, CFSE shows a decreasing trend. It is observed that when the muscle progresses from non-fatigue to fatigue condition, the mean DCS of fifty subjects increases from 0.016 to 0.99. All the extracted features found to be distinct and statistically significant in the three zones of muscle contraction (p < 0.05). It appears that these SCD features could be useful in the automated analysis of sEMG signals for different neuromuscular conditions.

  6. Ability of multiaxial fatigue criteria accounting for stress gradient effect for surface defective material

    Directory of Open Access Journals (Sweden)

    Niamchaona Wichian

    2018-01-01

    Full Text Available New high strength steels are widely used nowadays in many industrial areas as in automotive industry. These steels are more resistant and provide higher fatigue limits than latter ones but they are also more sensible to small defects. Natural defects that outcome from metallurgy (as shrinkage, inclusion, void are not considered in this study. We focus on small manufacturing defects such as cutting edge defects generated by punching or other surface defects due to stamping. These defects are harmful on the material fatigue behaviour due to high stress concentration at defects root. They also generate stress gradient that is beneficial from the fatigue strength point of view. This study focusses on the stress gradient (it does not account for the size effect from cylindrical defect on specimen edge. Practically a normal stress gradient is added in multiaxial fatigue criteria formulation. Both critical plane approach and integral approach are involved in the present study. This gradient is calculated from stress states at defects root by using FEM. Criteria fatigue function at N cycles is used to assess the material fatigue strength. Obviously multiaxial fatigue criteria accounting for stress gradient give more precise fatigue functions than criteria that do not consider the gradient influence.

  7. 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

  8. Are bi-axial proximal sesamoid bone fractures in the British Thoroughbred racehorse a bone fatigue related fracture? A histological study.

    Science.gov (United States)

    Kristoffersen, M; Hetzel, U; Parkin, T D H; Singer, E R

    2010-01-01

    To investigate whether microfractures and alterations in the trabecular bone area are associated with catastrophic bi-axial proximal sesamoid bone fractures (PSBF). Proximal sesamoid bones (PSB) from 10 racehorses with PSBF and from 10 control racehorses without musculoskeletal injury were examined using the bulk basic fuchsin method. Bone histomorphometric and microfracture analysis was performed, and cases and controls compared using two-sample t-test, paired t-test, and Mann-Whitney U test. There was no significant difference in the microfracture density and the trabecular bone area between bones from case and control horses, and between fractured and non-fractured bones in case horses. Microfracture density was low in the areas of the PSB examined. Microfracture density was not significantly different between groups, indicating that propagation of micro-cracks is an unlikely predisposing pathologic alteration in PSBF in British racehorses. There was no significant difference in the bone surface area between groups, which one would expect if modelling, adaptation and an increase in bone density were associated with PSBF fracture in the case horses. Therefore, PSBF in the British racehorse does not appear to be associated with microfractures of the trabecular bone of the PSB. The PSB fractures might represent an acute monotonic fracture; however, the aetiology of the fractures remains unknown with additional research required.

  9. Muscle fatigue and contraction intensity modulates the complexity of surface electromyography.

    Science.gov (United States)

    Cashaback, Joshua G A; Cluff, Tyler; Potvin, Jim R

    2013-02-01

    Nonlinear dynamical techniques offer a powerful approach for the investigation of physiological time series. Multiscale entropy analyses have shown that pathological and aging systems are less complex than healthy systems and this finding has been attributed to degraded physiological control processes. A similar phenomenon may arise during fatiguing muscle contractions where surface electromyography signals undergo temporal and spectral changes that arise from the impaired regulation of muscle force production. Here we examine the affect of fatigue and contraction intensity on the short and long-term complexity of biceps brachii surface electromyography. To investigate, we used an isometric muscle fatigue protocol (parsed into three windows) and three contraction intensities (% of maximal elbow joint moment: 40%, 70% and 100%). We found that fatigue reduced the short-term complexity of biceps brachii activity during the last third of the fatiguing contraction. We also found that the complexity of surface electromyography is dependent on contraction intensity. Our results show that multiscale entropy is sensitive to muscle fatigue and contraction intensity and we argue it is imperative that both factors be considered when evaluating the complexity of surface electromyography signals. Our data contribute to a converging body of evidence showing that multiscale entropy can quantify subtle information content in physiological time series. Copyright © 2012 Elsevier Ltd. All rights reserved.

  10. Generation of synthetic surface electromyography signals under fatigue conditions for varying force inputs using feedback control algorithm.

    Science.gov (United States)

    Venugopal, G; Deepak, P; Ghosh, Diptasree M; Ramakrishnan, S

    2017-11-01

    Surface electromyography is a non-invasive technique used for recording the electrical activity of neuromuscular systems. These signals are random, complex and multi-component. There are several techniques to extract information about the force exerted by muscles during any activity. This work attempts to generate surface electromyography signals for various magnitudes of force under isometric non-fatigue and fatigue conditions using a feedback model. The model is based on existing current distribution, volume conductor relations, the feedback control algorithm for rate coding and generation of firing pattern. The result shows that synthetic surface electromyography signals are highly complex in both non-fatigue and fatigue conditions. Furthermore, surface electromyography signals have higher amplitude and lower frequency under fatigue condition. This model can be used to study the influence of various signal parameters under fatigue and non-fatigue conditions.

  11. Examination of fracture surfaces using focused ion beam milling

    International Nuclear Information System (INIS)

    Cairney, J.M.; Munroe, P.R.; Schneibel, J.H.

    2000-01-01

    Composite materials consisting of an iron aluminide matrix with composition approximately Fe-40at%Al, reinforced with a volume fraction of 40--70% ceramic particles (TiC, WC, TiB 2 or ZrB 2 ), are currently being developed. Focused ion beam milling is a relatively new tool to materials science. It uses a high resolution (<5nm), energetic beam of gallium ions to selectively sputter regions of a material, whilst also functioning as a scanning ion microscope. The milling accuracy is of the order of the beam size allowing very precise sectioning to be carried out. The focused ion beam can be used to prepare highly localized cross sections which reveal the internal sub-structure of materials, avoiding detrimental processes such as deformation, or closing of existing cracks by mechanical abrasion. An area is milled from the sample such that, upon tilting, the internal structure can be imaged. The focused ion beam therefore offers a unique opportunity to examine cross-sections of the fracture surfaces in FeAl-based composites. In the present study, the focused ion beam was used to obtain cross-sections of fracture surfaces in two composite materials, in order to examine the extent of interfacial debonding and matrix deformation, thus providing more information about the mode of fracture. These cross-sections were prepared at regions where significant debonding was observed

  12. Fracture resistance of Zr–Nb alloys under low-cycle fatigue tests

    Energy Technology Data Exchange (ETDEWEB)

    Nikulin, S.A.; Rozhnov, A.B. [The National University of Science and Technology ‘‘MISIS’’, Leninsky pr. 4, 119049 Moscow (Russian Federation); Gusev, A.Yu. [A.A. Bochvar All-Russia Research Institute of Inorganic Materials (VNIINM), Rogova St. 5a, 123060 Moscow (Russian Federation); Nechaykina, T.A. [The National University of Science and Technology ‘‘MISIS’’, Leninsky pr. 4, 119049 Moscow (Russian Federation); Rogachev, S.O., E-mail: csaap@mail.ru [The National University of Science and Technology ‘‘MISIS’’, Leninsky pr. 4, 119049 Moscow (Russian Federation); Zadorozhnyy, M.Yu. [The National University of Science and Technology ‘‘MISIS’’, Leninsky pr. 4, 119049 Moscow (Russian Federation)

    2014-03-15

    Highlights: •Low-cycle fatigue tests of Zr–Nb alloys using DMA have been carried out. •The characteristics of low-cycle fatigue of the Zr–Nb alloy at 25/350 °C were determined. •Increasing test temperature up to 350 °C leads to a decrease of fatigue life. •The test temperature doesn’t have an effect on the character of fatigue curves. -- Abstract: Comparative low-cycle fatigue tests of small-scale specimens cut from the cladding tubes of E110, E125, E110opt zirconium alloys at temperatures of 25 and 350 °C using a dynamic mechanical analyzer have been carried out. It is shown that the limited cycles fatigue stress for all alloys is 50% less at temperature of 350 °C comparing to 25 °C. Besides it has been revealed that the limited cycles fatigue stress increases with increasing the strength of zirconium alloy.

  13. Os peroneum friction syndrome complicated by sesamoid fatigue fracture: a new radiological diagnosis? Case report and literature review

    Energy Technology Data Exchange (ETDEWEB)

    Bashir, Waseem A.; Connell, David A. [Royal National Orthopaedic Hospital NHS Trust, Department of Radiology, London, Middlesex (United Kingdom); Lewis, Steve [Craven Cottage, Fulham Football Club, London (United Kingdom); Cullen, Nicholas [The Royal National Orthopaedic Hospital NHS Trust, Department of Orthopaedics, London, Middlesex (United Kingdom)

    2009-02-15

    Injuries to the peroneal tendons are relatively common worldwide but tendon rupture without significant trauma is uncommon. Ankle mechanics can be seriously affected by disruption of one or both of the peroneal tendons although complete rupture can also remain asymptomatic. Accessory ossicles are sesamoid bones and are common findings in routine radiology of the foot and ankle. Although in the vast majority these ''os'' are normal variants of anatomy, they can lead to painful syndromes and suffer fractures and even undergo degenerative changes in response to overuse and trauma. Although similar syndromes have been discussed in the surgical literature, there is a lack of literature describing the use of modern imaging in the accurate diagnosis and its subsequent assistance towards appropriate management of os peroneum friction syndrome complicated by sesamoid fatigue syndrome. This article presents the plain film, sonographic and magnetic resonance imaging findings in a case of os peroneum friction syndrome complicated by a sesamoid fatigue fracture as well as reviewing the pertinent literature. (orig.)

  14. Os peroneum friction syndrome complicated by sesamoid fatigue fracture: a new radiological diagnosis? Case report and literature review.

    Science.gov (United States)

    Bashir, Waseem A; Lewis, Steve; Cullen, Nicholas; Connell, David A

    2009-02-01

    Injuries to the peroneal tendons are relatively common worldwide but tendon rupture without significant trauma is uncommon. Ankle mechanics can be seriously affected by disruption of one or both of the peroneal tendons although complete rupture can also remain asymptomatic. Accessory ossicles are sesamoid bones and are common findings in routine radiology of the foot and ankle. Although in the vast majority these "os" are normal variants of anatomy, they can lead to painful syndromes and suffer fractures and even undergo degenerative changes in response to overuse and trauma. Although similar syndromes have been discussed in the surgical literature, there is a lack of literature describing the use of modern imaging in the accurate diagnosis and its subsequent assistance towards appropriate management of os peroneum friction syndrome complicated by sesamoid fatigue syndrome. This article presents the plain film, sonographic and magnetic resonance imaging findings in a case of os peroneum friction syndrome complicated by a sesamoid fatigue fracture as well as reviewing the pertinent literature.

  15. Os peroneum friction syndrome complicated by sesamoid fatigue fracture: a new radiological diagnosis? Case report and literature review

    International Nuclear Information System (INIS)

    Bashir, Waseem A.; Connell, David A.; Lewis, Steve; Cullen, Nicholas

    2009-01-01

    Injuries to the peroneal tendons are relatively common worldwide but tendon rupture without significant trauma is uncommon. Ankle mechanics can be seriously affected by disruption of one or both of the peroneal tendons although complete rupture can also remain asymptomatic. Accessory ossicles are sesamoid bones and are common findings in routine radiology of the foot and ankle. Although in the vast majority these ''os'' are normal variants of anatomy, they can lead to painful syndromes and suffer fractures and even undergo degenerative changes in response to overuse and trauma. Although similar syndromes have been discussed in the surgical literature, there is a lack of literature describing the use of modern imaging in the accurate diagnosis and its subsequent assistance towards appropriate management of os peroneum friction syndrome complicated by sesamoid fatigue syndrome. This article presents the plain film, sonographic and magnetic resonance imaging findings in a case of os peroneum friction syndrome complicated by a sesamoid fatigue fracture as well as reviewing the pertinent literature. (orig.)

  16. Small Crack Growth and Fatigue Life Predictions for High-Strength Aluminium Alloys. Part 1; Experimental and Fracture Mechanics Analysis

    Science.gov (United States)

    Wu, X. R.; Newman, J. C.; Zhao, W.; Swain, M. H.; Ding, C. F.; Phillips, E. P.

    1998-01-01

    The small crack effect was investigated in two high-strength aluminium alloys: 7075-T6 bare and LC9cs clad alloy. Both experimental and analytical investigations were conducted to study crack initiation and growth of small cracks. In the experimental program, fatigue tests, small crack and large crack tests A,ere conducted under constant amplitude and Mini-TWIST spectrum loading conditions. A pronounced small crack effect was observed in both materials, especially for the negative stress ratios. For all loading conditions, most of the fatigue life of the SENT specimens was shown to be crack propagation from initial material defects or from the cladding layer. In the analysis program, three-dimensional finite element and A weight function methods were used to determine stress intensity factors and to develop SIF equations for surface and corner cracks at the notch in the SENT specimens. A plastisity-induced crack-closure model was used to correlate small and large crack data, and to make fatigue life predictions, Predicted crack-growth rates and fatigue lives agreed well with experiments. A total fatigue life prediction method for the aluminum alloys was developed and demonstrated using the crack-closure model.

  17. Experimental verification of the statistical theories of scaling factor effect in fatigue fracture of steel

    International Nuclear Information System (INIS)

    Svistun, R.P.; Babej, Yu.I.; Tkachenko, N.N.

    1976-01-01

    Statistical theories of the scale effect in the fatigue failure of 40KH18N9T, 10 and 20 steels have been verified. The theories are shown to be not invariably suitable for a satisfactory exlanation of the fatigue strength of the samples with respect to their dimensions. One of the main reasons for displaying the scale effect in the process of steel fatigue is the sample self-heating, i.e. a temperature factor which in many cases overlaps a statistical one

  18. Experimental verification of the statistical theories of scaling factor effect in fatigue fracture of steel

    Energy Technology Data Exchange (ETDEWEB)

    Svistun, R P; Babei, Yu I; Tkachenko, N N [AN Ukrainskoj SSR, Lvov. Fiziko-Mekhanicheskij Inst.; L' vovskij Lesotekhnicheskij Inst. (Ukrainian SSR))

    1976-01-01

    Statistical theories of the scale effect in the fatigue failure of 40KH18N9T, 10 and 20 steels have been verified. The theories are shown to be not invariably suitable for a satisfactory exlanation of the fatigue strength of the samples with respect to their dimensions. One of the main reasons for displaying the scale effect in the process of steel fatigue is the sample self-heating, i.e. a temperature factor which in many cases overlaps a statistical one.

  19. Discrete wavelet transform analysis of surface electromyography for the fatigue assessment of neck and shoulder muscles.

    Science.gov (United States)

    Chowdhury, Suman Kanti; Nimbarte, Ashish D; Jaridi, Majid; Creese, Robert C

    2013-10-01

    Assessment of neuromuscular fatigue is essential for early detection and prevention of risks associated with work-related musculoskeletal disorders. In recent years, discrete wavelet transform (DWT) of surface electromyography (SEMG) has been used to evaluate muscle fatigue, especially during dynamic contractions when the SEMG signal is non-stationary. However, its application to the assessment of work-related neck and shoulder muscle fatigue is not well established. Therefore, the purpose of this study was to establish DWT analysis as a suitable method to conduct quantitative assessment of neck and shoulder muscle fatigue under dynamic repetitive conditions. Ten human participants performed 40min of fatiguing repetitive arm and neck exertions while SEMG data from the upper trapezius and sternocleidomastoid muscles were recorded. The ten of the most commonly used wavelet functions were used to conduct the DWT analysis. Spectral changes estimated using power of wavelet coefficients in the 12-23Hz frequency band showed the highest sensitivity to fatigue induced by the dynamic repetitive exertions. Although most of the wavelet functions tested in this study reasonably demonstrated the expected power trend with fatigue development and recovery, the overall performance of the "Rbio3.1" wavelet in terms of power estimation and statistical significance was better than the remaining nine wavelets. Copyright © 2013 Elsevier Ltd. All rights reserved.

  20. Two Parameter Fracture Mechanics: Fatigue Crack Behavior under Mixed Mode Conditions

    Czech Academy of Sciences Publication Activity Database

    Seitl, Stanislav; Knésl, Zdeněk

    2008-01-01

    Roč. 75, č. 3-4 (2008), s. 857-865 ISSN 0013-7944. [Crack Paths 2006. Parma, 14.09.2006-16.09.2006] R&D Projects: GA ČR GP101/04/P001 Institutional research plan: CEZ:AV0Z20410507 Keywords : Constraint * Mixed-mode loading * Fatigue crack * Crack growth * Crack path Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.713, year: 2008

  1. The Influence of Surface Roughness on Biocompatibility and Fatigue Life of Titanium Based Alloys

    Science.gov (United States)

    Major, S.; Cyrus, P.; Hubálovská, M.

    2017-02-01

    This article deals with the effect of treatment on the mechanical properties ofbiocompatible alloys. In the case of implants, it is desirable to ensure good biocompatibility. Generally, the environment in the body is very aggressive and implants can quickly degrade due the corrosion. The process of corrosion leads to the release of harmful particles into the body. Other reasons for rejection of the implants, is their coverage bacterial plaque. Another reason for the rejection of the implant may be a smooth surface. In some cases, the tissue does not adhere to the smooth surface of the implant, in this regionsoccurs an accumulation of body fluids. This problem can be solved with a rough surface. From the viewpoint of fatigue resistance, the rough surface containing grooves and holes has a negative influence on the fatigue resistance against mechanical loading. The rough surface can be produced by machining or asymmetric deposition of particles of oxides, nitrides or other particles on surface. In this work the formation and propagation of fatigue cracks in the material with granular surface is analysed. The formation and growth of fatigue crack originated from granular surface is simulated. Also, experimental studies were carried out.

  2. Two different mechanisms of fatigue damage due to cyclic stress loading at 77 K for MOCVD-YBCO-coated conductors

    International Nuclear Information System (INIS)

    Sugano, M; Yoshida, Y; Hojo, M; Shikimachi, K; Hirano, N; Nagaya, S

    2008-01-01

    Tensile fatigue tests were carried out at 77 K for YBCO-coated conductors fabricated by metal-organic chemical vapor deposition (MOCVD). The S-N relationship, variation of critical current (I c ) during cyclic loading and microscopic fatigue damage were investigated. Fatigue strength at 10 6 cycles was evaluated to be σ max = 1300 MPa and 890 MPa under the stress ratios of 0.5 and 0.1. Two different mechanisms of fatigue damage, depending on the number of stress cycles to failure, were observed. In one of the fracture mechanisms, fatigue behavior is characterized by overall fracture which occurs at 10 4 -10 5 cycles. For these specimens, I c after unloading does not degrade before overall fracture. Although only shallow slip bands were found at the Ag surface, fatigue cracks were found on the Hastelloy C-276 surface of the fractured specimen. These results suggest that overall fracture due to cyclic stress was caused by fatigue of the Hastelloy substrate. In the other fracture mechanism, even though overall fracture did not occur at 10 6 cycles, a slight decrease of I c was detected after 10 5 cycles. No fatigue crack was found on the Hastelloy surface, while deep slip bands corresponding to the initial stage of fatigue crack were observed on the Ag surface. From these results, we concluded that I c degradation at a high cycle number is attributed to the fatigue of the Ag stabilizing layer

  3. Fatigue life extension techniques for weldments via mechanical surface post treatment

    International Nuclear Information System (INIS)

    Han, Seung Ho; Han, Jeong Woo; Cho, In Ho

    2008-01-01

    In many welded structures, fatigue failures are often occurred at welded joints in which stress concentrations due to the joint geometry are relatively high. Although employing good detail design practices by upgrading the welded detail class enables to improve the fatigue performance, in many cases, the modification of the detail may not be practicable. As an alternative, fatigue life extension techniques, that reduce the severity of the stress concentration at the weld toe region, remove imperfections, and introduce local compressive welding residual stress, can be applied. These techniques are also used as remedial measures to extend the fatigue life of critical welds that have failed prematurely and have been repaired. This paper introduces peening techniques via a pneumatic hammer peening and ultrasonic impact which make it possible to give the weld not only a favorable shape reducing the local stress concentration, but also a beneficial compressive residual stress into material surface

  4. Muscle fatigue in women with primary biliary cirrhosis: Spectral analysis of surface electromyography

    Science.gov (United States)

    Biagini, Maria Rosa; Tozzi, Alessandro; Grippo, Antonello; Galli, Andrea; Milani, Stefano; Amantini, Aldo

    2006-01-01

    AIM: To evaluate the myoelectric manifestations of peripheral fatigability in patients with primary biliary cirrhosis in comparison to healthy subjects. METHODS: Sixteen women with primary biliary cirrhosis without comorbidity and 13 healthy women matched for age and body mass index (BMI) completed the self-reported questionnaire fatigue impact scale. All subjects underwent surface electromyography assessment of peripheral fatigability. Anterior tibial muscle isometric voluntary contraction was executed for 20 s at 80% of maximal voluntary isometric contraction. During the exercise electromyographic signal series were recorded and root mean square (expression of central drive) as well as mean and median of electromyographic signal frequency spectrum (estimates of muscle fatigability) were computed. Each subject executed the trial two times. EMG parameters were normalized, then linear regression was applied and slopes were calculated. RESULTS: Seven patients were fatigued (median fatigue impact scale score: 38, range: 26-66) and 9 were not fatigued (median fatigue impact scale score: 7, range: 0-17). The maximal voluntary isometric contraction was similar in patients (82, 54-115 N) and controls (87, 74-101 N), and in patients with high (81, 54-115 N) and low fatigue impact scale scores (86, 65-106 N). Root mean square as well as mean and median of frequency spectrum slopes were compared with the Mann-Whitney U test, and no significant difference was found between fatigued and non-fatigued patients and controls. CONCLUSION: No instrumental evidence of peripheral fatigability can be found in women with primary biliary cirrhosis but no comorbidity, suggesting that fatigue in such patients may be of central origin. PMID:16937530

  5. Evaluation of tensile strength and fracture toughness of yttria-stabilized zirconia polycrystals with fracture surface analysis

    International Nuclear Information System (INIS)

    Oishi, Manabu; Matsuda, Yukihisa; Noguchi, Kenichi; Masaki, Takaki

    1995-01-01

    The tensile strength of yttria-stabilized tetragonal zirconia polycrystals (Y-TZPs) was measured and the fracture surfaces were analyzed with the scanning electron microscope and X-ray microanalyzer. The fracture origins of the pressureless-sintered samples were voids or inclusions such as Al 2 O 3 , Al 2 O 3 with SiO 2 , and cubic-ZrO 2 , while the fracture origins of the hot isostatically pressed samples were inclusions; no voids were detected at fracture origins. The higher strengths of the hot isostatically pressed samples versus those of the pressureless-sintered samples were consistent with the change in fracture origins. The fracture toughness of the samples calculate from the tensile strength and analysis of the fracture origins was 3.4 to 3.7 MPa ·√m. These values are lower than those measured with the SEPB method. These discrepancies might be caused by the difference in the state of the fracture origin and its neighborhood, such as the size of the fracture origin and interaction between two surfaces in the precrack

  6. Fracture behavior of short circumferentially surface-cracked pipe

    International Nuclear Information System (INIS)

    Krishnaswamy, P.; Scott, P.; Mohan, R.

    1995-11-01

    This topical report summarizes the work performed for the Nuclear Regulatory Comniission's (NRC) research program entitled ''Short Cracks in Piping and Piping Welds'' that specifically focuses on pipes with short, circumferential surface cracks. The following details are provided in this report: (i) material property deteminations, (ii) pipe fracture experiments, (iii) development, modification and validation of fracture analysis methods, and (iv) impact of this work on the ASME Section XI Flaw Evaluation Procedures. The material properties developed and used in the analysis of the experiments are included in this report and have been implemented into the NRC's PIFRAC database. Six full-scale pipe experiments were conducted during this program. The analyses methods reported here fall into three categories (i) limit-load approaches, (ii) design criteria, and (iii) elastic-plastic fracture methods. These methods were evaluated by comparing the analytical predictions with experimental data. The results, using 44 pipe experiments from this and other programs, showed that the SC.TNP1 and DPZP analyses were the most accurate in predicting maximum load. New Z-factors were developed using these methods. These are being considered for updating the ASME Section XI criteria

  7. Fatigue crack growth in an aluminum alloy-fractographic study

    Science.gov (United States)

    Salam, I.; Muhammad, W.; Ejaz, N.

    2016-08-01

    A two-fold approach was adopted to understand the fatigue crack growth process in an Aluminum alloy; fatigue crack growth test of samples and analysis of fractured surfaces. Fatigue crack growth tests were conducted on middle tension M(T) samples prepared from an Aluminum alloy cylinder. The tests were conducted under constant amplitude loading at R ratio 0.1. The stress applied was from 20,30 and 40 per cent of the yield stress of the material. The fatigue crack growth data was recorded. After fatigue testing, the samples were subjected to detailed scanning electron microscopic (SEM) analysis. The resulting fracture surfaces were subjected to qualitative and quantitative fractographic examinations. Quantitative fracture analysis included an estimation of crack growth rate (CGR) in different regions. The effect of the microstructural features on fatigue crack growth was examined. It was observed that in stage II (crack growth region), the failure mode changes from intergranular to transgranular as the stress level increases. In the region of intergranular failure the localized brittle failure was observed and fatigue striations are difficult to reveal. However, in the region of transgranular failure the crack path is independent of the microstructural features. In this region, localized ductile failure mode was observed and well defined fatigue striations were present in the wake of fatigue crack. The effect of interaction of growing fatigue crack with microstructural features was not substantial. The final fracture (stage III) was ductile in all the cases.

  8. Role of prism decussation on fatigue crack growth and fracture of human enamel.

    Science.gov (United States)

    Bajaj, Devendra; Arola, Dwayne

    2009-10-01

    The role of prism decussation on the crack growth resistance of human enamel is evaluated. Miniature inset compact tension (CT) specimens embodying a section of cuspal enamel were subjected to Mode I cyclic or monotonic loads. Cracks were grown in either the forward (from outer enamel inwards) or reverse (from inner enamel outwards) direction and the responses were compared quantitatively. Results showed that the outer enamel exhibits lower resistance to the inception and growth of cracks. Regardless of the growth direction, the near-threshold region of cyclic extension was typical of "short crack" behavior (i.e. deceleration of growth with an increase in crack length). Cyclic crack growth was more stable in the forward direction and occurred over twice the spatial distance achieved in the reverse direction. In response to the monotonic loads, a rising R-curve response was exhibited by growth in the forward direction only. The total energy absorbed in fracture for the forward direction was more than three times that in the reverse. The rise in crack growth resistance was largely attributed to a combination of mechanisms that included crack bridging, crack bifurcation and crack curving, which were induced by decussation in the inner enamel. An analysis of the responses distinguished that the microstructure of enamel appears optimized for resisting crack growth initiating from damage at the tooth's surface.

  9. A Survey of Serious Aircraft Accidents Involving Fatigue Fracture. Volume 2. Rotary-Wing Aircraft (Etude sur des Accidents Importants d’Avions du aux Effets des Fractures de Fatigue. Volume 2. Effets sur des Helicopteres).

    Science.gov (United States)

    1983-04-01

    Convention on International Civil Aviation, Second Edition , March 1966. 5. WORLD AIRLINE ACCIDENT SUMMARY. Civil Aviation Authority, (Great Britain...people who either provided information, or who suggested other sources of information for the current edition of this survey. E.M.R. Alexander Civil...Waverley, New Zealand. F-28C Tail rotor drive shaft. Fatigue strength reduc- ed by softened condition & surface decarbur- isation. AISA 4130 steel. Ref: NZ

  10. Effects of fatiguing isometric and isokinetic ankle exercises on postural control while standing on firm and compliant surfaces.

    Science.gov (United States)

    Bisson, Etienne J; Remaud, Anthony; Boyas, Sébastien; Lajoie, Yves; Bilodeau, Martin

    2012-06-14

    Fatiguing exercises used across studies to induce alterations in postural control are diverse and may explain the different findings reported. This study aimed to compare the effects of two types of fatiguing plantarflexion exercises on postural control on a firm and a compliant surface. Ten healthy young men (29 ± 4 years) were asked to stand as steadily as possible for 30 s, blindfolded with feet together, on a firm and a compliant surface before and immediately after an isometric and an isokinetic fatiguing exercise. Maximal force reduction due to fatigue was found significant but similar between exercises. No significant difference was found between the fatiguing exercises on all Center of Pressure (CoP) parameters. Both fatiguing exercises induced increases in CoP excursion area, CoP variability and CoP velocity in both planes (antero-posterior, mediolateral) on the compliant surface. On the firm surface, both fatiguing exercises only induced increases in CoP variability and CoP velocity in the fatigued plane (antero-posterior). Isometric and isokinetic fatiguing exercises, when producing a similar level of force reduction, induce similar decreases in postural control. The effects of fatigue on postural control in healthy young men are more pronounced when standing on a compliant surface, i.e. when proprioceptive information at the ankle is altered.

  11. Acoustic emission technique for characterisation of deformation, fatigue, fracture and phase transformation and for leak detection with high sensitivity- our experiences

    International Nuclear Information System (INIS)

    Jayakumar, T.; Mukhopadhyay, C.K.; Baldev Raj

    1996-01-01

    Acoustic emission technique has been used for studying tensile deformation, fracture behaviour, detection and assessment of fatigue crack growth and α-martensite phase transformation in austenitic alloys. A methodology for amplification of weak acoustic emission signals has been established. Acoustic emission technique with advanced spectral analysis has enabled detection with high sensitivity of minute leaks in noisy environments. (author)

  12. FRACTURE MECHANICS APPROACH TO ESTIMATE FATIGUE LIVES OF WELDED LAP-SHEAR SPECIMENS

    Energy Technology Data Exchange (ETDEWEB)

    Lam, P.; Michigan, J.

    2014-04-25

    A full range of stress intensity factor solutions for a kinked crack is developed as a function of weld width and the sheet thickness. When used with the associated main crack solutions (global stress intensity factors) in terms of the applied load and specimen geometry, the fatigue lives can be estimated for the laser-welded lap-shear specimens. The estimations are in good agreement with the experimental data. A classical solution for an infinitesimal kink is also employed in the approach. However, the life predictions tend to overestimate the actual fatigue lives. The traditional life estimations with the structural stress along with the experimental stress-fatigue life data (S-N curve) are also provided. In this case, the estimations only agree with the experimental data under higher load conditions.

  13. Fracture and fatigue of high strength filaments. Final report, September 25, 1974--August 30, 1975

    International Nuclear Information System (INIS)

    Holt, N.L.; Finnie, I.

    1975-01-01

    The history of high strength filamentary materials is traced and it is seen that their use has been widespread. It is shown that today's demands upon these materials require a better understanding of their behavior than is presently available. Current theories for both the static and fatigue strength of filamentary materials are reviewed. An analysis of static strength tests on short filaments is presented that explains seemingly anomalous test behavior which has been reported in the literature. The proposed approach is supported by experiments and computer analysis. A new machine for the fatigue testing of filaments or wires was designed and is described in detail. Results are presented for fatigue tests on tungsten wire, graphite filaments and glass filaments. Graphite filaments showed an unexpected deterioration in strength after very many cycles (10 8 ). An explanation of this effect is offered and supported by scanning electron microscope observations. The work concludes with some suggestions for further research

  14. Fatigue, fracture, and life prediction criteria for composite materials in magnets

    International Nuclear Information System (INIS)

    Wong, F.M.G.

    1990-06-01

    An explosively-bonded copper/Inconel 718/copper laminate conductor was proposed to withstand the severe face compression stresses in the central core of the Alcator C-MOD tokamak toroidal field (TF) magnet. Due to the severe duty of the TF magnet, it is critical that an accurate estimate of useful life be determined. As part of the effort to formulate an appropriate life prediction, fatigue crack growth experiments were performed on the laminate as well as its components. Metallographic evaluation of the laminate interface revealed many shear bands in the Inconel 718. Shear bands and shear band cracks were produced in the Inconel 718 as a result of the explosion bonding process. These shear bands were shown to have a detrimental effect on the crack growth behavior of the laminate, by significantly reducing the load carrying capability of the reinforcement layer and providing for easy crack propagation paths. Fatigue crack growth rate was found not only to be dependent on temperature but also on orientation. Fatigue cracks grew faster in directions which contained shear bands in the plane of the propagating crack. Fractography showed crack advancement by fatigue cracking in the Inconel 718 and ductile tearing of the copper at the interface. However, further away from the interfaces, the copper exhibited fatigue striations indicating that cracks were now propagating by fatigue. Laminate life prediction results showed a strong dependence on shear band orientation, and exhibited little variation between room temperature and 77 degree K. Predicted life of this laminate was lower when the crack propagation was along a shear band than when crack propagation was across the shear bands. Shear bands appear to have a dominating effect on crack growth behavior

  15. Effectiveness of the Wavelet Transform on the Surface EMG to Understand the Muscle Fatigue During Walk

    Science.gov (United States)

    Hussain, M. S.; Mamun, Md.

    2012-01-01

    Muscle fatigue is the decline in ability of a muscle to create force. Electromyography (EMG) is a medical technique for measuring muscle response to nervous stimulation. During a sustained muscle contraction, the power spectrum of the EMG shifts towards lower frequencies. These effects are due to muscle fatigue. Muscle fatigue is often a result of unhealthy work practice. In this research, the effectiveness of the wavelet transform applied to the surface EMG (SEMG) signal as a means of understanding muscle fatigue during walk is presented. Power spectrum and bispectrum analysis on the EMG signal getting from right rectus femoris muscle is executed utilizing various wavelet functions (WFs). It is possible to recognize muscle fatigue appreciably with the proper choice of the WF. The outcome proves that the most momentous changes in the EMG power spectrum are symbolized by WF Daubechies45. Moreover, this research has compared bispectrum properties to the other WFs. To determine muscle fatigue during gait, Daubechies45 is used in this research to analyze the SEMG signal.

  16. Fatigue damage behavior of a surface-mount electronic package under different cyclic applied loads

    Science.gov (United States)

    Ren, Huai-Hui; Wang, Xi-Shu

    2014-04-01

    This paper studies and compares the effects of pull-pull and 3-point bending cyclic loadings on the mechanical fatigue damage behaviors of a solder joint in a surface-mount electronic package. The comparisons are based on experimental investigations using scanning electron microscopy (SEM) in-situ technology and nonlinear finite element modeling, respectively. The compared results indicate that there are different threshold levels of plastic strain for the initial damage of solder joints under two cyclic applied loads; meanwhile, fatigue crack initiation occurs at different locations, and the accumulation of equivalent plastic strain determines the trend and direction of fatigue crack propagation. In addition, simulation results of the fatigue damage process of solder joints considering a constitutive model of damage initiation criteria for ductile materials and damage evolution based on accumulating inelastic hysteresis energy are identical to the experimental results. The actual fatigue life of the solder joint is almost the same and demonstrates that the FE modeling used in this study can provide an accurate prediction of solder joint fatigue failure.

  17. Surface-finish effects on the high-cycle fatigue of Alloy 718

    International Nuclear Information System (INIS)

    Korth, G.E.

    1981-06-01

    Alloy 718 us a precipitation-hardening nickel-base superalloy that is being specified for various components for liquid-meal fast breeder reactors (LMFBRs). This alloy maintains high strength at elevated temperatures making it a desirable structural material. But the property that justifies most LMFBR applications is the alloy's resistance to thermal striping damage due to its high fatigue endurance strength. Thermal striping is a high-cycle fatigue phenomenon caused by thermal stresses from the fluctuating mixing action of sodium streams of differing temperatures impinging on the metal surfaces. Most of the design data is generated from laboratory fatigue specimens with carefully controlled surface finishes prepared with a low-stress grind and buffed to a surface finish 8--12 in. Since Alloy 718 has been shown to be quite notch sensitive under cyclic loading, the detrimental effect on the high-cycle fatigue properties caused by shop surface finishes of actual components has been questioned. This report examines some of the surface finishes that could be produced in a commercial shop on an actual component

  18. Reliability of surface electromyography in the assessment of paraspinal muscle fatigue: an updated systematic review.

    Science.gov (United States)

    Mohseni Bandpei, Mohammad A; Rahmani, Nahid; Majdoleslam, Basir; Abdollahi, Iraj; Ali, Shabnam Shah; Ahmad, Ashfaq

    2014-09-01

    The purpose of this study was to review the literature to determine whether surface electromyography (EMG) is a reliable tool to assess paraspinal muscle fatigue in healthy subjects and in patients with low back pain (LBP). A literature search for the period of 2000 to 2012 was performed, using PubMed, ProQuest, Science Direct, EMBASE, OVID, CINAHL, and MEDLINE databases. Electromyography, reliability, median frequency, paraspinal muscle, endurance, low back pain, and muscle fatigue were used as keywords. The literature search yielded 178 studies using the above keywords. Twelve articles were selected according to the inclusion criteria of the study. In 7 of the 12 studies, the surface EMG was only applied in healthy subjects, and in 5 studies, the reliability of surface EMG was investigated in patients with LBP or a comparison with a control group. In all of these studies, median frequency was shown to be a reliable EMG parameter to assess paraspinal muscles fatigue. There was a wide variation among studies in terms of methodology, surface EMG parameters, electrode location, procedure, and homogeneity of the study population. The results suggest that there seems to be a convincing body of evidence to support the merit of surface EMG in the assessment of paraspinal muscle fatigue in healthy subject and in patients with LBP. Copyright © 2014 National University of Health Sciences. Published by Elsevier Inc. All rights reserved.

  19. Influence of the surface roughness on the fatigue properties in ausferritic ductile irons (ADI

    Directory of Open Access Journals (Sweden)

    Svenningsson Roger

    2014-06-01

    Full Text Available Heat treatment of cast ductile iron (DI to ausferritic ductile iron (ADI is known to increase fatigue properties. However, the surface roughness of the cast material is also of significant importance. In this investigation, test rods with seven different surface qualities were cast from the same melt i.e. with same chemical composition. The surfaces of the test rods were varied by a number of parameters; grain size of the moulding sand, coated or non-coated mould surfaces, as-cast or machined and polished, shot peened or not. In addition, a reference material in conventional DI was cast and tested. All eight series were subjected to high-cycle fatigue bending tests. The results show that surface defects, such as micro porosity and minor inclusions drastically decrease the fatigue properties. For some ADI materials the stress amplitude limit was actually lower compared to the non-heat treated DI. The machined, polished and shot-peened material demonstrated the best fatigue properties, which is as expected.

  20. Quantifying voids effecting delamination in carbon/epoxy composites: static and fatigue fracture behavior

    Science.gov (United States)

    Hakim, I.; May, D.; Abo Ras, M.; Meyendorf, N.; Donaldson, S.

    2016-04-01

    On the present work, samples of carbon fiber/epoxy composites with different void levels were fabricated using hand layup vacuum bagging process by varying the pressure. Thermal nondestructive methods: thermal conductivity measurement, pulse thermography, pulse phase thermography and lock-in-thermography, and mechanical testing: modes I and II interlaminar fracture toughness were conducted. Comparing the parameters resulted from the thermal nondestructive testing revealed that voids lead to reductions in thermal properties in all directions of composites. The results of mode I and mode II interlaminar fracture toughness showed that voids lead to reductions in interlaminar fracture toughness. The parameters resulted from thermal nondestructive testing were correlated to the results of mode I and mode II interlaminar fracture toughness and voids were quantified.

  1. Kinetics of Accumulation of Damage in Surface Layers of Lithium-Containing Aluminum Alloys in Fatigue Tests with Rigid Loading Cycle and Corrosive Effect of Environment

    Science.gov (United States)

    Morozova, L. V.; Zhegina, I. P.; Grigorenko, V. B.; Fomina, M. A.

    2017-07-01

    High-resolution methods of metal physics research including electron, laser and optical microscopy are used to study the kinetics of the accumulation of slip lines and bands and the corrosion damage in the plastic zone of specimens of aluminum-lithium alloys 1441 and B-1469 in rigid-cycle fatigue tests under the joint action of applied stresses and corrosive environment. The strain parameters (the density of slip bands, the sizes of plastic zones near fracture, the surface roughness in singled-out zones) and the damage parameters (the sizes of pits and the pitting area) are evaluated.

  2. An investigation of the fatigue and fracture behavior of a Nb-12Al-44Ti-1.5Mo intermetallic alloy

    International Nuclear Information System (INIS)

    Soboyejo, W.O.; Dipasquale, J.; Ye, F.; Mercer, C.

    1999-01-01

    This article presents the results of a study of the fatigue and fracture behavior of a damage-tolerant Nb-12Al-44Ti-1.5Mo alloy. This partially ordered B2 + orthorhombic intermetallic alloy is shown to have attractive combinations of room-temperature ductility (11 to 14 pct), fracture toughness (60 to 92 MPa√m), and comparable fatigue crack growth resistance to IN718, Ti-6Al-4V, and pure Nb at room temperature. The studies show that tensile deformation in the Nb-12Al-44Ti-1.5Mo alloy involves localized plastic deformation (microplasticity via slip-band formation) which initiates at stress levels that are significantly below the uniaxial yield stress (∼9.6 pct of the 0.2 pct offset yield strength (YS)). The onset of bulk yielding is shown to correspond to the spread of microplasticity completely across the gage sections of the tensile specimen. Fatigue crack initiation is also postulated to occur by the accumulation of microplasticity (coarsening of slip bands). Subsequent fatigue crack growth then occurs by the unzipping of cracks along slip bands that form ahead of the dominant crack tip. The proposed mechanism of fatigue crack growth is analogous to the unzipping crack growth mechanism that was suggested originally by Neumann for crack growth in single-crystal copper. Slower near-threshold fatigue crack growth rates at 750 C are attributed to the shielding effects of oxide-induced crack closure. The fatigue and fracture behavior are also compared to those of pure Nb and emerging high-temperature niobium-based intermetallics

  3. Effect of different machining processes on the tool surface integrity and fatigue life

    Energy Technology Data Exchange (ETDEWEB)

    Cao, Chuan Liang [College of Mechanical and Electrical Engineering, Nanchang University, Nanchang (China); Zhang, Xianglin [School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan (China)

    2016-08-15

    Ultra-precision grinding, wire-cut electro discharge machining and lapping are often used to machine the tools in fine blanking industry. And the surface integrity from these machining processes causes great concerns in the research field. To study the effect of processing surface integrity on the fine blanking tool life, the surface integrity of different tool materials under different processing conditions and its influence on fatigue life were thoroughly analyzed in the present study. The result shows that the surface integrity of different materials was quite different on the same processing condition. For the same tool material, the surface integrity on varying processing conditions was quite different too and deeply influenced the fatigue life.

  4. Interpretation and significance of reverse chevron-shaped markings on fracture surfaces of API X100 pipeline steels

    International Nuclear Information System (INIS)

    Sowards, Jeffrey W.; McCowan, Chris N.; Drexler, Elizabeth S.

    2012-01-01

    Highlights: ► We investigated fractures of X100 steel linepine produced during fracture mechanics testing. ► Fractures exhibited a unique chevron pattern that points in the direction of crack propagation. ► A qualitative model is proposed to explain the fracture pattern formation. ► Findings indicate that careful interpretation of ductile material fractures is necessary. - Abstract: Fracture surfaces of X100 pipeline steels were examined with optical and electron microscopy after crack tip opening angle fracture testing. Some fracture surfaces exhibited chevron-shaped fracture patterns that are markedly different from classic chevron fracture. The chevron-shaped markings on the X100 fracture surfaces point in the direction of crack growth, rather than towards the location of fracture initiation, as observed in classic cases of chevron fracture. Existing models, predicting formation of chevron fracture patterns, do not explain the fracture behavior observed for X100 steel. A mechanism is proposed where reverse chevron-shaped patterns are developed due to the shape of the crack front itself. The chevron shape forms as a result of crack tunneling, and the overall pattern is developed on the fracture surface due to intermittent crack growth, resulting in alternating regions (bands) of fast fracture and slower, more ductile fracture. The contrast between these bands of alternating fracture defines the chevron. Care should be taken during interpretation of intermittent chevron markings on fractures of ductile materials, as they may point away from rather than towards the origin of fracture.

  5. Effects of multiple root canal usage on the surface topography and fracture of two different Ni-Ti rotary file systems.

    Science.gov (United States)

    Kottoor, Jojo; Velmurugan, Natanasabapathy; Gopikrishna, Velayutham; Krithikadatta, Jogikalmat

    2013-01-01

    The purpose of this study was to evaluate the effect of multiple root canal usage on the surface topography and fracture of Twisted File (TF) and ProTaper (PT) rotary Ni-Ti file systems, using scanning electron microscope (SEM). Ten sets of PT and TF instruments were used to prepare the mesial canals of mandibular first molars. TF 25, 0.06 taper and PT F1 instruments were analyzed by SEM when new and thereafter every three root canal usages. This sequence was repeated for both the TF and PT groups until 12 uses. Two images of the instrument were recorded, one of the instrument tip and the other 5 mm from the tip, both at × 100 magnification. The sequential use was continued till the instrument fractured and the number of root canal usages for the file to fracture was noted. All fracture surfaces were examined under the SEM. Fresh TF instruments showed no surface wear when compared to PT instruments (P 0.05), while at the 9 th usage TF showed a steep increase in the spiral distortion score when compared to PT (P < 0.05). PT instruments fractured at a mean root canal usage of 17.4, while TF instruments showed a mean root canal usage of 11.8. Fractographically, all the TF instruments failed due to torsion, while all the PT instruments failed because of cyclic fatigue. PT instruments showed more resistance to fracture than TF instruments.

  6. Crack propagation in disordered materials: how to decipher fracture surfaces

    Science.gov (United States)

    Ponson, L.

    For a half-century, engineers know how to describe and predict the propagation of a crack in a model elastic homogeneous medium. The case of real materials is much more complex. Indeed, we do not know how to relate their lifetime or their resistance to their microstructure. To achieve such a prediction, understanding the role of the microstructural disorder on the behavior of a crack is determinant. Fracture surfaces represent a promising field of investigation to address this question. From the study of various disordered materials, we propose a statistical description of their roughness and determine to which extent their properties are dependent of the material. We show that fracture surfaces display an anisotropic scale invariant geometry characterized by two universal exponents. Glass ceramics is then studied because its microstructure can be tuned in a controlled manner. Their fracture surfaces display the same general anisotropic properties but with surprisingly low exponents independent of the detail of the ceramics microstructure. This suggests the existence of a second universality class in failure problems. Using finally theoretical tools from out-of-equilibrium statistical physics and fracture mechanics, we relate the statistical properties of fracture surfaces with the mechanisms occurring at the microscopic scale during the failure of a material. In particular, we show that the first class of fracture surfaces results from a failure involving damage processes while the second one results from a perfectly brittle failure. Propagation de fissures dans les matériaux désordonnés : comment déchiffrer les surfaces de rupture. Depuis près d'un demi-siècle, les ingénieurs savent décrire et prévoir la propagation d'une fissure dans un milieu élastique homogène modèle. Le cas des matériaux réels est beaucoup plus complexe. En effet, on ne sait pas relier leur durée de vie ou leur résistance à leur microstructure. Passage obligé avant de telles

  7. Surface Irregularity Factor as a Parameter to Evaluate the Fatigue Damage State of CFRP

    Science.gov (United States)

    Zuluaga-Ramírez, Pablo; Frövel, Malte; Belenguer, Tomás; Salazar, Félix

    2015-01-01

    This work presents an optical non-contact technique to evaluate the fatigue damage state of CFRP structures measuring the irregularity factor of the surface. This factor includes information about surface topology and can be measured easily on field, by techniques such as optical perfilometers. The surface irregularity factor has been correlated with stiffness degradation, which is a well-accepted parameter for the evaluation of the fatigue damage state of composite materials. Constant amplitude fatigue loads (CAL) and realistic variable amplitude loads (VAL), representative of real in- flight conditions, have been applied to “dog bone” shaped tensile specimens. It has been shown that the measurement of the surface irregularity parameters can be applied to evaluate the damage state of a structure, and that it is independent of the type of fatigue load that has caused the damage. As a result, this measurement technique is applicable for a wide range of inspections of composite material structures, from pressurized tanks with constant amplitude loads, to variable amplitude loaded aeronautical structures such as wings and empennages, up to automotive and other industrial applications. PMID:28793655

  8. A Study on Surface Modification of Al7075-T6 Alloy against Fretting Fatigue Phenomenon

    Directory of Open Access Journals (Sweden)

    E. Mohseni

    2014-01-01

    Full Text Available Aircraft engines, fuselage, automobile parts, and energy saving strategies in general have promoted the interest and research in the field of lightweight materials, typically on alloys based on aluminum. Aluminum alloy itself does not have suitable wear resistance; therefore, it is necessary to enhance surface properties for practical applications, particularly when aluminum is in contact with other parts. Fretting fatigue phenomenon occurs when two surfaces are in contact with each other and one or both parts are subjected to cyclic load. Fretting drastically decreases the fatigue life of materials. Therefore, investigating the fretting fatigue life of materials is an important subject. Applying surface modification methods is anticipated to be a supreme solution to gradually decreasing fretting damage. In this paper, the authors would like to review methods employed so far to diminish the effect of fretting on the fatigue life of Al7075-T6 alloy. The methods include deep rolling, shot peening, laser shock peening, and thin film hard coatings. The surface coatings techniques are comprising physical vapor deposition (PVD, hard anodizing, ion-beam-enhanced deposition (IBED, and nitriding.

  9. Surface Irregularity Factor as a Parameter to Evaluate the Fatigue Damage State of CFRP

    Directory of Open Access Journals (Sweden)

    Pablo Zuluaga-Ramírez

    2015-11-01

    Full Text Available This work presents an optical non-contact technique to evaluate the fatigue damage state of CFRP structures measuring the irregularity factor of the surface. This factor includes information about surface topology and can be measured easily on field, by techniques such as optical perfilometers. The surface irregularity factor has been correlated with stiffness degradation, which is a well-accepted parameter for the evaluation of the fatigue damage state of composite materials. Constant amplitude fatigue loads (CAL and realistic variable amplitude loads (VAL, representative of real in- flight conditions, have been applied to “dog bone” shaped tensile specimens. It has been shown that the measurement of the surface irregularity parameters can be applied to evaluate the damage state of a structure, and that it is independent of the type of fatigue load that has caused the damage. As a result, this measurement technique is applicable for a wide range of inspections of composite material structures, from pressurized tanks with constant amplitude loads, to variable amplitude loaded aeronautical structures such as wings and empennages, up to automotive and other industrial applications.

  10. Residual stress relaxation due to fretting fatigue in shot peened surfaces of Ti-6Al-4V

    International Nuclear Information System (INIS)

    Martinez, S.A.; Blodgett, M.P.; Mall, S.; Sathish, S.; Namjoshi, S.

    2003-01-01

    Fretting fatigue occurs at locations where the materials are sliding against each other under load. In order to enhance the fatigue life under fretting conditions the surface of the component is shot peened. In general, the shot peening process produces a compressive stress on the surface of the material, thereby increasing the resistance of the material to crack initiation. This paper presents the relaxation of residual stress caused during fretting fatigue. X-ray diffraction has been utilized as the method to measure residual stress in fretting fatigued samples of Ti-6Al-4V

  11. Effect of interaction of embedded crack and free surface on remaining fatigue life

    Directory of Open Access Journals (Sweden)

    Genshichiro Katsumata

    2016-12-01

    Full Text Available Embedded crack located near free surface of a component interacts with the free surface. When the distance between the free surface and the embedded crack is short, stress at the crack tip ligament is higher than that at the other area of the cracked section. It can be easily expected that fatigue crack growth is fast, when the embedded crack locates near the free surface. To avoid catastrophic failures caused by fast fatigue crack growth at the crack tip ligament, fitness-for-service (FFS codes provide crack-to-surface proximity rules. The proximity rules are used to determine whether the cracks should be treated as embedded cracks as-is, or transformed to surface cracks. Although the concepts of the proximity rules are the same, the specific criteria and the rules to transform embedded cracks into surface cracks differ amongst FFS codes. This paper focuses on the interaction between an embedded crack and a free surface of a component as well as on its effects on the remaining fatigue lives of embedded cracks using the proximity rules provided by the FFS codes. It is shown that the remaining fatigue lives for the embedded cracks strongly depend on the crack aspect ratio and location from the component free surface. In addition, it can be said that the proximity criteria defined by the API and RSE-M codes give overly conservative remaining lives. On the contrary, the WES and AME codes always give long remaining lives and non-conservative estimations. When the crack aspect ratio is small, ASME code gives non-conservative estimation.

  12. Study of Fatigue and Fracture Behavior of Cr-Based Alloys and Intermetallic Materials

    Energy Technology Data Exchange (ETDEWEB)

    He, YH

    2001-01-31

    The microhardness, and tensile and fracture-toughness properties of drop-cast and directionally-solidified Cr-9.25 at.% (atomic percent) Ta alloys have been investigated. Directional solidification was found to soften the alloy, which could be related to the development of equilibrium and aligned microstructures. It was observed that the tensile properties of the Cr-Ta alloys at room and elevated temperatures could be improved by obtaining aligned microstructures. The directionally-solidified alloy also showed increased fracture toughness at room temperature. This trend is mainly associated with crack deflection and the formation of shear ribs in the samples with aligned microstructures. The sample with better-aligned lamellar exhibits greater fracture toughness.

  13. The bridge crane mechanism shaft reliability calculating in case of the fatigue fracture parameters correlation

    Directory of Open Access Journals (Sweden)

    Krutitskiy M.N.

    2016-03-01

    Full Text Available The method of statistical tests examines the impact of the correlation of the parameters of fatigue-such as the durability of the shaft mechanism of an overhead traveling crane for General use is under consideration in this article. It is be-lieved that the normal and shear stresses together affect the overall durability of the shaft. There may be a correlation between endurance limits and coefficients of block similarity of loading. To calculate resource used corrected linear theory of fatigue damage accumulation. Parameters on the reliability are computed after building the function, the reli-ability function directly or through private functions the reliability function for each type of stress.

  14. Fatigue-type stress fractures of the lower limb associated with fibrous cortical defects/non-ossifying fibromas in the skeletally immature

    Energy Technology Data Exchange (ETDEWEB)

    Shimal, A.; Davies, A.M. [Department of Radiology, Royal Orthopaedic Hospital, Birmingham B31 2AP (United Kingdom); James, S.L.J., E-mail: steven.james@roh.nhs.u [Department of Radiology, Royal Orthopaedic Hospital, Birmingham B31 2AP (United Kingdom); Grimer, R.J. [Department of Orthopaedic Oncology, Royal Orthopaedic Hospital, Birmingham B31 2AP (United Kingdom)

    2010-05-15

    Aim: To investigate the association of a fatigue-type stress fracture and a fibrous cortical defect/non-ossifying fibroma (FCD/NOF) of the lower limb long bones in skeletally immature patients. Materials and methods: The patient database of a specialist orthopaedic oncology centre was searched to determine the number of skeletally immature patients (<=16 years of age) over an 18 year period with a lower limb long bone lesion ultimately shown to be a fatigue-type stress fracture. The diagnosis was established by a combination of typical imaging findings of a fatigue-type stress fracture, the absence of aggressive features suggestive of a sarcoma (e.g., interrupted periosteal reaction, cortical breach, and a soft-tissue mass) together with evidence of consolidation or healing on follow-up radiographs and resolution of symptoms over the subsequent weeks. The database was also used to determine the number of skeletally immature cases (<=16 years of age) referred in the same period in which the principal lesion was shown to be a fibrous cortical defect (FCD) or non-ossifying fibroma (NOF) of the lower limb long bones. The clinical and imaging features of those cases common to both groups (i.e., with both a fatigue-type stress fracture and a FCD or NOF) were reviewed. Results: Six percent of patients (five cases) referred to an orthopaedic oncology unit, who were subsequently shown to have a stress fracture of the lower limb long bones, were found to have a related FCD/NOF. All had been referred with a suggested diagnosis of a bone sarcoma and/or osteomyelitis. The possibility of a stress fracture had been raised in only one case. Four cases involved the proximal tibia and one the distal femur. Radiographs revealed that both lesions arose in the posteromedial cortex in all but one of the cases. The radiographs and magnetic resonance imaging (MRI) features were considered typical of the overlapping pathological features of the lesions. Conclusions: A sarcoma could be

  15. Fatigue-type stress fractures of the lower limb associated with fibrous cortical defects/non-ossifying fibromas in the skeletally immature.

    Science.gov (United States)

    Shimal, A; Davies, A M; James, S L J; Grimer, R J

    2010-05-01

    To investigate the association of a fatigue-type stress fracture and a fibrous cortical defect/non-ossifying fibroma (FCD/NOF) of the lower limb long bones in skeletally immature patients. The patient database of a specialist orthopaedic oncology centre was searched to determine the number of skeletally immature patients (lower limb long bone lesion ultimately shown to be a fatigue-type stress fracture. The diagnosis was established by a combination of typical imaging findings of a fatigue-type stress fracture, the absence of aggressive features suggestive of a sarcoma (e.g., interrupted periosteal reaction, cortical breach, and a soft-tissue mass) together with evidence of consolidation or healing on follow-up radiographs and resolution of symptoms over the subsequent weeks. The database was also used to determine the number of skeletally immature cases (lower limb long bones. The clinical and imaging features of those cases common to both groups (i.e., with both a fatigue-type stress fracture and a FCD or NOF) were reviewed. Six percent of patients (five cases) referred to an orthopaedic oncology unit, who were subsequently shown to have a stress fracture of the lower limb long bones, were found to have a related FCD/NOF. All had been referred with a suggested diagnosis of a bone sarcoma and/or osteomyelitis. The possibility of a stress fracture had been raised in only one case. Four cases involved the proximal tibia and one the distal femur. Radiographs revealed that both lesions arose in the posteromedial cortex in all but one of the cases. The radiographs and magnetic resonance imaging (MRI) features were considered typical of the overlapping pathological features of the lesions. A sarcoma could be effectively excluded in the absence of true cortical destruction and soft-tissue extension. Both fatigue-type stress fractures and FCD/NOFs occur at similar sites in the long bones. It is postulated that the existence of the latter may cause localized weakening of

  16. Fatigue-type stress fractures of the lower limb associated with fibrous cortical defects/non-ossifying fibromas in the skeletally immature

    International Nuclear Information System (INIS)

    Shimal, A.; Davies, A.M.; James, S.L.J.; Grimer, R.J.

    2010-01-01

    Aim: To investigate the association of a fatigue-type stress fracture and a fibrous cortical defect/non-ossifying fibroma (FCD/NOF) of the lower limb long bones in skeletally immature patients. Materials and methods: The patient database of a specialist orthopaedic oncology centre was searched to determine the number of skeletally immature patients (≤16 years of age) over an 18 year period with a lower limb long bone lesion ultimately shown to be a fatigue-type stress fracture. The diagnosis was established by a combination of typical imaging findings of a fatigue-type stress fracture, the absence of aggressive features suggestive of a sarcoma (e.g., interrupted periosteal reaction, cortical breach, and a soft-tissue mass) together with evidence of consolidation or healing on follow-up radiographs and resolution of symptoms over the subsequent weeks. The database was also used to determine the number of skeletally immature cases (≤16 years of age) referred in the same period in which the principal lesion was shown to be a fibrous cortical defect (FCD) or non-ossifying fibroma (NOF) of the lower limb long bones. The clinical and imaging features of those cases common to both groups (i.e., with both a fatigue-type stress fracture and a FCD or NOF) were reviewed. Results: Six percent of patients (five cases) referred to an orthopaedic oncology unit, who were subsequently shown to have a stress fracture of the lower limb long bones, were found to have a related FCD/NOF. All had been referred with a suggested diagnosis of a bone sarcoma and/or osteomyelitis. The possibility of a stress fracture had been raised in only one case. Four cases involved the proximal tibia and one the distal femur. Radiographs revealed that both lesions arose in the posteromedial cortex in all but one of the cases. The radiographs and magnetic resonance imaging (MRI) features were considered typical of the overlapping pathological features of the lesions. Conclusions: A sarcoma could be

  17. On fatigue crack growth mechanisms of MMC: Reflection on analysis of 'multi surface initiations'

    International Nuclear Information System (INIS)

    Mkaddem, A.; El Mansori, M.

    2009-01-01

    This work attempts to examine the mechanisms of fatigue when cracks synergetically initiate in more than one site at the specimen surface. The metal matrix composites (MMC) i.e. silicon carbide particles reinforced aluminium matrix composites (Al/SiC p -MMC), seem to be good candidates to accelerate fatigue failures following multi surface initiations (MSI). Closure effects of MSI mechanisms on the variation of fatigue behaviour are explored for various stress states. Experiments were carried out using non pre-treated and pre-treated specimens. Using an Equivalent Ellipse Method (EEM), it is shown that the aspect of surface finish of specimen plays an important role on crack growth. Scanning Electron Microscope (SEM) inspections have lead to distinguishing the initiation regions from propagation regions and final separation regions. It is also revealed that the total lifetime of specimens is sensitive to heat treatment. Moreover, it is found that the appearance of MSI in cycled materials is more probable at high level of fatigue loads.

  18. Normalised Mutual Information of High-Density Surface Electromyography during Muscle Fatigue

    Directory of Open Access Journals (Sweden)

    Adrian Bingham

    2017-12-01

    Full Text Available This study has developed a technique for identifying the presence of muscle fatigue based on the spatial changes of the normalised mutual information (NMI between multiple high density surface electromyography (HD-sEMG channels. Muscle fatigue in the tibialis anterior (TA during isometric contractions at 40% and 80% maximum voluntary contraction levels was investigated in ten healthy participants (Age range: 21 to 35 years; Mean age = 26 years; Male = 4, Female = 6. HD-sEMG was used to record 64 channels of sEMG using a 16 by 4 electrode array placed over the TA. The NMI of each electrode with every other electrode was calculated to form an NMI distribution for each electrode. The total NMI for each electrode (the summation of the electrode’s NMI distribution highlighted regions of high dependence in the electrode array and was observed to increase as the muscle fatigued. To summarise this increase, a function, M(k, was defined and was found to be significantly affected by fatigue and not by contraction force. The technique discussed in this study has overcome issues regarding electrode placement and was used to investigate how the dependences between sEMG signals within the same muscle change spatially during fatigue.

  19. High temperature mechanical properties and surface fatigue behavior improving of steel alloy via laser shock peening

    International Nuclear Information System (INIS)

    Ren, N.F.; Yang, H.M.; Yuan, S.Q.; Wang, Y.; Tang, S.X.; Zheng, L.M.; Ren, X.D.; Dai, F.Z.

    2014-01-01

    Highlights: • The properties of 00C r 12 were improved by laser shock processing. • A deep layer of residual compressive stresses was introduced. • Fatigue life was enhanced about 58% at elevated temperature up to 600 °C. • The pinning effect is the reason of prolonging fatigue life at high temperature. - Abstract: Laser shock peening was carried out to reveal the effects on ASTM: 410L 00C r 12 microstructures and fatigue resistance in the temperature range 25–600 °C. The new conception of pinning effect was proposed to explain the improvements at the high temperature. Residual stress was measured by X-ray diffraction with sin 2 ψ method, a high temperature extensometer was utilized to measure the strain and control the strain signal. The grain and precipitated phase evolutionary process were observed by scanning electron microscopy. These results show that a deep layer of compressive residual stress is developed by laser shock peening, and ultimately the isothermal stress-controlled fatigue behavior is enhanced significantly. The formation of high density dislocation structure and the pinning effect at the high temperature, which induces a stronger surface, lower residual stress relaxation and more stable dislocation arrangement. The results have profound guiding significance for fatigue strengthening mechanism of components at the elevated temperature

  20. High-temperature fracture and fatigue resistance of a ductile β-TiNb reinforced γ-TiAl intermetallic composite

    International Nuclear Information System (INIS)

    Rao, K.T.V.; Ritchie, R.O.

    1998-01-01

    The high-temperature fatigue-crack propagation and fracture resistance of a model γ-TiAl intermetallic composite reinforced with 20 vol. % ductile β-TiNb particles is examined at elevated temperatures of 650 and 800 C and compared with behavior at room temperature. TiNb reinforcements are found to enhance the fracture toughness of γ-TiAl, even at high temperatures, from about 123 to ∼40 MPa m 1/2 , although their effectiveness is lower compared to room temperature due to the reduction in strength of TiNb particles. Under monotonic loading, crack-growth response in the composite is characterized by resistance-curve behavior arising from crack trapping, renucleation and resultant crack bridging effects attributable to the presence of TiNb particles. In addition, crack-tip blunting associated with plasticity increases the crack-initiation (matrix) toughness of the composite, particularly at 800 C, above the ductile-to-brittle transition temperature (DBTT) for γ-TiAl. High-temperature fatigue-crack growth resistance, however, is marginally degraded by the addition of TiNb particles in the C-R (edge) orientation, similar to observations made at room temperature; premature fatigue failure of TiNb ligaments in the crack wake diminishes the role of bridging under cyclic loading. Both fatigue and fracture resistance of the composite are slightly lower at 650 C (just below the DBTT for TiAl) compared to the behavior at ambient and 800 C. Overall, the beneficial effect of adding ductile TiNb reinforcements to enhance the room-temperature fracture and fatigue resistance of γ-TiAl alloys is retained up to 800 C, in air environments. There is concern, however, regarding the long-term environmental stability of these composite microstructures in unprotected atmospheres

  1. Remodeled articular surface after surgical fixation of patella fracture in a child

    Directory of Open Access Journals (Sweden)

    Moruf Babatunde Yusuf

    2017-01-01

    Full Text Available Patella fracture is uncommon in pediatric age group and their patella is better preserved in any class of patella fracture. We reported a case of a 13-year-old male with right patella fracture nonunion. He had open reduction and internal fixation using tension band wire device. Fracture union was monitored with serial radiographs and he was followed up for 60 weeks. There was articular surface step after surgical fixation of the patella fracture. At 34 weeks postoperative, there was complete remodeling of the articular surface with good knee function after removal of the tension band wire. Children have good capacity of bone remodeling after fracture. Little retropatella step in a child after patella fracture surgical fixation will remodel with healing.

  2. Fatigue Crack Topography.

    Science.gov (United States)

    1984-01-01

    alloys (2). [--I Fig. 6. Fatigue fracture in Nitrile- butadien rubber ( NBR ). Fig. 7. The characteristic features of fatigue fracture in press moulded...in plastics and even in rubber . It follows therefore, that fatigue fractures must also occur in the mineral layers of our earth or in the rock on...effective until the weakest point yields and forms a crack. To get a feeling for this process, you can imagine that the stressed article is made of rubber

  3. Fatigue Strength of Titanium Risers - Defect Sensitivity

    Energy Technology Data Exchange (ETDEWEB)

    Babalola, Olusegun Tunde

    2001-07-01

    This study is centred on assessment of the fatigue strength of titanium fusion welds for deep-water riser's applications. Deep-water risers are subjected to significant fatigue loading. Relevant fatigue data for titanium fusion welds are very scarce. Hence there is a need for fatigue data and life prediction models for such weldments. The study has covered three topics: Fatigue testing, Fractography and defect assessment, and Fracture Mechanics modelling of fatigue crack growth. Two series of welded grade of titanium consisting of 14 specimens in each series were fatigue tested under constant amplitude loading. Prior to fatigue testing, strain gauge measurements of some specimens was conducted to enable the definition of stress range in the fatigue assessment procedure. The results were compared with finite solid element analysis and related to fatigue stresses in a riser pipe wall. Distribution and geometry of internal and surface defects both in the as-welded and in the post-weld machined conditions were assessed using fractography. This served as a tool to determine the fatigue initiation point in the welds. Fracture mechanics was applied to model fatigue strength of titanium welds with initiation from weld defects. Two different stress intensity factor formulations for embedded eccentrically placed cracks were used for analysis of elliptical cracks with the major axis parallel and close to one of the free surfaces. The methods were combined to give a satisfactory model for crack growth analysis. The model analyses crack growth of elliptical and semi-elliptical cracks in two directions, with updating of the crack geometry. Fatigue strength assessment was conducted using two crack growth models, the Paris-Erdogan relation with no threshold and the Donahue et al. relation with an implied threshold. The model was validated against experimental data, with a discussion on the choice of crack growth model. (author)

  4. Fracture Testing with Surface Crack Specimens. [especially the residual tensile strength test

    Science.gov (United States)

    Orange, T. W.

    1974-01-01

    Recommendations are given for the design, preparation, and static fracture testing of surface crack specimens. The recommendations are preceded by background information including discussions of stress intensity factors, crack opening displacements, and fracture toughness values associated with surface crack specimens. Cyclic load and sustained load tests are discussed briefly.

  5. Fatigue crack growth from handling surface anomalies in a nickel based superalloy at high temperature

    Directory of Open Access Journals (Sweden)

    Gourdin Stéphane

    2014-01-01

    Full Text Available Aircraft engine manufacturers have to demonstrate that handling surface anomalies in sensitive areas of discs are not critical for in-service life of a component. Currently, the models used consider anomalies as long cracks propagating from the first cycle, which introduces a certain degree of conservatism when calculating the fatigue life of surface flaws. Preliminary studies have shown that the first stages of crack propagation from surface anomalies are responsible for the conservative results. Thus, the aim of the study is to characterize the crack propagation from typical surface anomalies and to establish a new crack growth model, which can account for the micro-propagation stage. To separate the effects of the geometry of the anomalies and the residual stress state after introduction of the surface flaws, two V-type anomalies are studied: scratches and dents. Different studies have shown that the residual stresses beneath the anomalies seem to control the fatigue life of samples exhibiting scratches and dents. In order to monitor the crack micro-propagation, a direct current potential drop technique, coupled with heat tints is used during fatigue tests at elevated temperature. Thermal treatments releasing the residual stresses are also used to decouple the effect of crack morphology and residual stresses.

  6. Evaluation of Fatigue Behavior and Surface Characteristics of Aluminum Alloy 2024 T6 After Electric Discharge Machining

    Science.gov (United States)

    Mehmood, Shahid; Shah, Masood; Pasha, Riffat Asim; Sultan, Amir

    2017-10-01

    The effect of electric discharge machining (EDM) on surface quality and consequently on the fatigue performance of Al 2024 T6 is investigated. Five levels of discharge current are analyzed, while all other electrical and nonelectrical parameters are kept constant. At each discharge current level, dog-bone specimens are machined by generating a peripheral notch at the center. The fatigue tests are performed on four-point rotating bending machine at room temperature. For comparison purposes, fatigue tests are also performed on the conventionally machined specimens. Linearized SN curves for 95% failure probability and with four different confidence levels (75, 90, 95 and 99%) are plotted for each discharge current level as well as for conventionally machined specimens. These plots show that the electric discharge machined (EDMed) specimens give inferior fatigue behavior as compared to conventionally machined specimen. Moreover, discharge current inversely affects the fatigue life, and this influence is highly pronounced at lower stresses. The EDMed surfaces are characterized by surface properties that could be responsible for change in fatigue life such as surface morphology, surface roughness, white layer thickness, microhardness and residual stresses. It is found that all these surface properties are affected by changing discharge current level. However, change in fatigue life by discharge current could not be associated independently to any single surface property.

  7. Influence of surface defects on the fatigue crack initiation in pearlitic steel

    Directory of Open Access Journals (Sweden)

    Toribio Jesús

    2014-06-01

    Full Text Available Tensile fatigue tests were performed under load control, with constant stress range Δσ on pearlitic steel wires, from the hot rolled bar to the commercial prestressing steel wire (which has undergone seven cold drawing steps. Results show that fatigue cracks in pearlitic steels initiate at the wire surface starting from small defects, whose size decreases with the drawing process. Fatigue cracks created from defects (initiation phase exhibit a fractographic appearance consisting of ductile microtearing events which can be classified as tearing topography surface or TTS, and exhibit a remarkably lower spacing in the prestressing steel wire than in the hot rolled bar. In addition, some S-N tests were performed in both material forms under a stress range of about half the yield strength. In these tests, the main part of the fatigue life corresponds to the propagation stage in the hot rolled bar whereas such a main part of the life is associated with the initiation stage in the case of the prestressing steel wire.

  8. A NEW HIGH RESOLUTION OPTICAL METHOD FOR OBTAINING THE TOPOGRAPHY OF FRACTURE SURFACES IN ROCKS

    Directory of Open Access Journals (Sweden)

    Steven Ogilvie

    2011-05-01

    Full Text Available Surface roughness plays a major role in the movement of fluids through fracture systems. Fracture surface profiling is necessary to tune the properties of numerical fractures required in fluid flow modelling to those of real rock fractures. This is achieved using a variety of (i mechanical and (ii optical techniques. Stylus profilometry is a popularly used mechanical method and can measure surface heights with high precision, but only gives a good horizontal resolution in one direction on the fracture plane. This method is also expensive and simultaneous coverage of the surface is not possible. Here, we describe the development of an optical method which images cast copies of rough rock fractures using in-house developed hardware and image analysis software (OptiProf™ that incorporates image improvement and noise suppression features. This technique images at high resolutions, 15-200 μm for imaged areas of 10 × 7.5 mm and 100 × 133 mm, respectively and a similar vertical resolution (15 μm for a maximum topography of 4 mm. It uses in-house developed hardware and image analysis (OptiProf™ software and is cheap and non-destructive, providing continuous coverage of the fracture surface. The fracture models are covered with dye and fluid thicknesses above the rough surfaces converted into topographies using the Lambert-Beer Law. The dye is calibrated using 2 devices with accurately known thickness; (i a polycarbonate tile with wells of different depths and (ii a wedge-shaped vial made from silica glass. The data from each of the two surfaces can be combined to provide an aperture map of the fracture for the scenario where the surfaces touch at a single point or any greater mean aperture. The topography and aperture maps are used to provide data for the generation of synthetic fractures, tuned to the original fracture and used in numerical flow modelling.

  9. Review of the margins for ASME code fatigue design curve - effects of surface roughness and material variability

    International Nuclear Information System (INIS)

    Chopra, O. K.; Shack, W. J.

    2003-01-01

    The ASME Boiler and Pressure Vessel Code provides rules for the construction of nuclear power plant components. The Code specifies fatigue design curves for structural materials. However, the effects of light water reactor (LWR) coolant environments are not explicitly addressed by the Code design curves. Existing fatigue strain-vs.-life ((var e psilon)-N) data illustrate potentially significant effects of LWR coolant environments on the fatigue resistance of pressure vessel and piping steels. This report provides an overview of the existing fatigue (var e psilon)-N data for carbon and low-alloy steels and wrought and cast austenitic SSs to define the effects of key material, loading, and environmental parameters on the fatigue lives of the steels. Experimental data are presented on the effects of surface roughness on the fatigue life of these steels in air and LWR environments. Statistical models are presented for estimating the fatigue (var e psilon)-N curves as a function of the material, loading, and environmental parameters. Two methods for incorporating environmental effects into the ASME Code fatigue evaluations are discussed. Data available in the literature have been reviewed to evaluate the conservatism in the existing ASME Code fatigue evaluations. A critical review of the margins for ASME Code fatigue design curves is presented

  10. Review of the margins for ASME code fatigue design curve - effects of surface roughness and material variability.

    Energy Technology Data Exchange (ETDEWEB)

    Chopra, O. K.; Shack, W. J.; Energy Technology

    2003-10-03

    The ASME Boiler and Pressure Vessel Code provides rules for the construction of nuclear power plant components. The Code specifies fatigue design curves for structural materials. However, the effects of light water reactor (LWR) coolant environments are not explicitly addressed by the Code design curves. Existing fatigue strain-vs.-life ({var_epsilon}-N) data illustrate potentially significant effects of LWR coolant environments on the fatigue resistance of pressure vessel and piping steels. This report provides an overview of the existing fatigue {var_epsilon}-N data for carbon and low-alloy steels and wrought and cast austenitic SSs to define the effects of key material, loading, and environmental parameters on the fatigue lives of the steels. Experimental data are presented on the effects of surface roughness on the fatigue life of these steels in air and LWR environments. Statistical models are presented for estimating the fatigue {var_epsilon}-N curves as a function of the material, loading, and environmental parameters. Two methods for incorporating environmental effects into the ASME Code fatigue evaluations are discussed. Data available in the literature have been reviewed to evaluate the conservatism in the existing ASME Code fatigue evaluations. A critical review of the margins for ASME Code fatigue design curves is presented.

  11. Evaluation of surgeon's muscle fatigue during thoracoscopic pulmonary lobectomy using interoperative surface electromyography.

    Science.gov (United States)

    Yoon, Seung-Hyun; Jung, Myung-Chul; Park, Seong Yong

    2016-06-01

    The aim of this study was to document the physical stress experienced by a surgeon during thoracoscopic pulmonary lobectomy and mediastinal lymph node dissection for lung cancer by measuring the intraoperative electromyography (EMG). Surface EMG was recorded during 12 cases of thoracoscopic lobectomy. During the operation, 16 channels of a wireless EMG were used to measure muscle activity and fatigue from the bilateral muscles of the splenius capitis (SC), upper trapezius (UT), middle deltoid (MD), flexor carpi radialis (FCR), extensor carpi radialis (ECR), lumbar erector spinae (LES), rectus femoralis (RF), and tibialis anterior (TA). The EMG signals were processed to collect the values of the root mean square for muscle activity and median frequency (MF) for muscle fatigue. All operations were completed without adverse events. The mean operating time was 99.16±35.15 minutes. During the operation, the mean muscle activity of all muscles was 21.91±12.85 mV. High muscle activity was observed in the bilateral FCR and ECR, whereas low muscle activity was observed in the bilateral SC and LES. The final MFs in the bilateral SC and LES were found to be decreased from the initial status, which implied increased muscle fatigue. The muscles of the right and left LES were significantly fatigued by up to 29% and 37% compared to their initial status (P=0.021 and P=0.007, respectively). The MFs of the bilateral LES decreased with time (an average decreases of 0.008/5 minutes, P=0.002 in right LES and 0.004/5 minutes, P=0.018 in left LES). During thoracoscopic lobectomy, muscle fatigue was observed in muscles related to a static posture, such as the bilateral SC, UT, and ES. Further studies are required to investigate the ergonomic adjustments needed to reduce muscle fatigue in these static muscles.

  12. Effects of a laser surface processing induced heat-affected zone on the fatigue behavior of AISI 4340 steel

    International Nuclear Information System (INIS)

    McDaniels, R.L.; White, S.A.; Liaw, K.; Chen, L.; McCay, M.H.; Liaw, P.K.

    2008-01-01

    The effects of the heat-affected zone (HAZ) in AISI 4340 steel created by laser-surface alloying (LSA) on high-cycle fatigue behavior have been investigated. This research was performed by producing several lots of laser-processed AISI 4340 steel using different laser processing parameters, and then subjecting the samples to high-cycle fatigue and Knoop microindentation hardness studies. Samples of tested material from each lot were examined using scanning-electron microscopy (SEM) in order to establish the effects of laser processing on the microstructure of the fatigue-tested AISI 4340 steel. When these three techniques, microindentation hardness testing, high-cycle fatigue testing, and SEM, are combined, a mechanistic understanding of the effect of the HAZ on the fatigue behavior of this alloy might be gained. It was found that the HAZ did not appear to have an adverse effect on the high-cycle fatigue behavior of LSA-processed AISI 4340 steel

  13. The surface fatigue life of contour induction hardened AISI 1552 gears

    Science.gov (United States)

    Townsend, Dennis P.; Turza, Alan; Chaplin, Mike

    1995-07-01

    Two groups of spur gears manufactured from two different materials and heat treatments were endurance tested for surface fatigue life. One group was manufactured from AISI 1552 and was finished ground to a 0.4 micron (16 micro-in.) rms surface finish and then dual frequency contour induction hardened. The second group was manufactured from CEVM AISI 9310 and was carburized, hardened, and ground to a 0.4 micron (16 micro-in.) rms surface finish. The gear pitch diameter was 8.89 cm (3.5 in.). Test conditions were a maximum Hertz stress of 1.71 GPa (248 ksi), a bulk gear temperature of approximately 350 K (170 F) and a speed of 10,000 rpm. The lubricant used for the tests was a synthetic paraffinic oil with an additive package. The test results showed that the 10 percent surface fatigue (pitting) life of the contour hardened AISI 1552 test gears was 1.7 times that of the carburized and hardened AISI 9310 test gears. Also there were two early failures of the AISI 1552 gears by bending fatigue.

  14. Improved fatigue behavior of low-carbon steel 20GL by applying ultrasonic impact treatment combined with the electric discharge surface alloying

    Energy Technology Data Exchange (ETDEWEB)

    Mordyuk, B.N., E-mail: mordyuk@imp.kiev.ua [Kurdyumov Institute for Metal Physics, NAS of Ukraine, 36 Academician Vernadsky blvd., UA-03142, Kyiv (Ukraine); Prokopenko, G.I.; Volosevich, P.Yu. [Kurdyumov Institute for Metal Physics, NAS of Ukraine, 36 Academician Vernadsky blvd., UA-03142, Kyiv (Ukraine); Matokhnyuk, L.E.; Byalonovich, A.V. [Pisarenko Institute for Strength of Materials, NAS of Ukraine, 2 Timiryazevs’ka str., UA-01014, Kyiv (Ukraine); Popova, T.V. [Ukrainian Research Institute Rail carriage building, 33 Prikhodko str., UA-39621, Kremenchuk (Ukraine)

    2016-04-06

    The effects of severe plastic deformation induced by ultrasonic impact treatment (UIT) and the electric discharge surface alloying (EDSA) with chromium on the stress-controlled fatigue response of low-carbon steel 20GL are studied. The surface microrelief and integrity were analyzed using light microscopy and scanning electron microscopy (SEM). The structural formations in the sub-surface layers were characterized by means of X-ray diffraction analysis and transmission electron microscopy (TEM). The steel specimens underwent UIT, and complex UIT+EDSA and UIT+EDSA+UIT processes demonstrate the fatigue strength magnitudes increased respectively by ~15, ~5 and ~30% on the base of 10{sup 7} cycles in comparison with that for the pristine specimen. SEM analysis of fracture surfaces reveals the subsurface crack nucleation in the UIT-processed specimens instead of superficial crack initiation observed in the pristine and EDSA-processed ones. TEM studies demonstrate that a dislocation-cell structure forms in ferrite grains and partial dissolution of cementite occurs in pearlite grains both at the surface after UIT and in the layer at a depth of 15–25 µm after the UIT+EDSA+UIT process. The enhanced fatigue strength and prolonged lifetime of the low-carbon steel specimens after UIT and UIT+EDSA+UIT processes are concluded to be associated with the subsurface crack nucleation achieved by the following factors: (i) minimized surface roughness and improved integrity of the modified layer; (ii) compressive residual stresses; and (iii) surface hardening coupled with the alloying by chromium and with the formation of the dislocation-cell structure containing the cell walls impenetrable to moving dislocations at cyclic loading.

  15. Low-cycle fatigue of sheet elements with ''soft'' surface layer

    International Nuclear Information System (INIS)

    Luk'yanov, V.F.; Kharchenko, V.Ya.; Berezutskij, V.I.; Ovsyannikov, V.G.

    1978-01-01

    Investigated are regularities of low-cycle fatigue of bimetallic sheet constructions made of chrome-nickel-molybdenum steel, plated with a low-alloyed steel with a reduced yield limit. Static repeated bending tests have been carried out using two-layer samples. The surface layer has been shown to increase resistance to nucleation and propagation of cracks under pulsating load if stresses are not more than 2 times higher than the yield limit. Increase in stresses leads to elastoplastic deformation and reduces durability. The positive effect of the surface layer is advisable to be used when welding-up surface defects and strengthening welded joints of high-strength steels

  16. Stage I surface crack formation in thermal fatigue: A predictive multi-scale approach

    International Nuclear Information System (INIS)

    Osterstock, S.; Robertson, C.; Sauzay, M.; Aubin, V.; Degallaix, S.

    2010-01-01

    A multi-scale numerical model is developed, predicting the formation of stage I cracks, in thermal fatigue loading conditions. The proposed approach comprises 2 distinct calculation steps. Firstly, the number of cycles to micro-crack initiation is determined, in individual grains. The adopted initiation model depends on local stress-strain conditions, relative to sub-grain plasticity, grain orientation and grain deformation incompatibilities. Secondly, 2-4 grains long surface cracks (stage I) is predicted, by accounting for micro-crack coalescence, in 3 dimensions. The method described in this paper is applied to a 500 grains aggregate, loaded in representative thermal fatigue conditions. Preliminary results provide quantitative insight regarding position, density, spacing and orientations of stage I surface cracks and subsequent formation of crack networks. The proposed method is fully deterministic, provided all grain crystallographic orientations and micro-crack linking thresholds are specified. (authors)

  17. Investigating the road surface effect to the fatigue life of an automotive coil spring

    Science.gov (United States)

    Putra, T. E.; Husaini

    2018-05-01

    This work aims to estimate the life of a coil spring considering road surface profiles. Strain signals were measured by installing a strain gage at the highest stress location of the coil spring and then driving the vehicle on country and village roads. The village road gave high amplitudes containing spikes when the tire touched a curb, bump or pothole. These conditions contributed to a higher loading rate to the car component, contributing to shorter useful fatigue life, which was only 140 reversals of blocks. Driving on the village road resulted in a 6-times decrease in the useful fatigue life of the component in comparison to the country road. In conclusion, the village road caused stronger vibrations to the component because it has a rough surface; meanwhile, the country road provided lower vibrations because the road was smooth.

  18. Thermal fatigue of austenitic stainless steel: influence of surface conditions through a multi-scale approach

    International Nuclear Information System (INIS)

    Le-Pecheur, Anne

    2008-01-01

    Some cases of cracking of 304L austenitic stainless steel components due to thermal fatigue were encountered in particular on the Residual Heat Removal Circuits (RHR) of the Pressurized Water Reactor (PWR). EDF has initiated a R and D program to understand assess the risks of damage on nuclear plant mixing zones. The INTHERPOL test developed at EDF is designed in order to perform pure thermal fatigue test on tubular specimen under mono-frequency thermal load. These tests are carried out under various loadings, surface finish qualities and welding in order to give an account of these parameters on crack initiation. The main topic of this study is the research of a fatigue criterion using a micro:macro modelling approach. The first part of work deals with material characterization (stainless steel 304L) emphasising the specificities of the surface roughness link with a strong hardening gradient. The first results of the characterization on the surface show a strong work-hardening gradient on a 250 microns layer. This gradient does not evolved after thermal cycling. Micro hardness measurements and TEM observations were intensively used to characterize this gradient. The second part is the macroscopic modelling of INTHERPOL tests in order to determine the components of the stress and strain tensors due to thermal cycling. The third part of work is thus to evaluate the effect of surface roughness and hardening gradient using a calculation on a finer scale. This simulation is based on the variation of dislocation density. A goal for the future is the determination of the fatigue criterion mainly based on polycrystalline modelling. Stocked energy or critical plane being available that allows making a sound choice for the criteria. (author)

  19. Surface Relief and Internal Structure in Fatigued Stainless Sanicro 25 Steel

    Czech Academy of Sciences Publication Activity Database

    Polák, Jaroslav; Kuběna, Ivo; Mazánová, Veronika; Heczko, Milan; Man, Jiří

    47A, č. 5 (2016), s. 1907-1911 ISSN 1073-5623 R&D Projects: GA ČR GA13-32665S; GA ČR(CZ) GA13-23652S; GA MŠk(CZ) ED1.1.00/02.0068 Institutional support: RVO:68081723 Keywords : surface relief * dislocation structure * Sanicro 25 * extrusion * intrusion Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.874, year: 2016

  20. Exercise muscle fatigue detection system implementation via wireless surface electromyography and empirical mode decomposition.

    Science.gov (United States)

    Chang, Kang-Ming; Liu, Shing-Hong; Wang, Jia-Jung; Cheng, Da-Chuan

    2013-01-01

    Surface electromyography (sEMG) is an important measurement for monitoring exercise and fitness. A wireless Bluetooth transmission sEMG measurement system with a sampling frequency of 2 KHz is developed. Traditional muscle fatigue is detected from the median frequency of the sEMG power spectrum. The regression slope of the linear regression of median frequency is an important muscle fatigue index. As fatigue increases, the power spectrum of the sEMG shifts toward lower frequencies. The goal of this study is to evaluate the sensitivity of empirical mode decomposition (EMD) quantifying the electrical manifestations of the local muscle fatigue during exercising in health people. We also compared this method with the raw data and discrete wavelet transform (DWT). Five male and five female volunteers participated. Each subject was asked to run on a multifunctional pedaled elliptical trainer for about 30 minutes, twice a week, and there were a total of six recording times for each subject with a wireless EMG recording system. The results show that sensitivity of the highest frequency component of EMD is better than the highest frequency component of DWT, and raw data.

  1. Surface electromyography based muscle fatigue analysis for stroke patients at different Brunnstrom stages.

    Science.gov (United States)

    Yinjun Tu; Zhe Zhang; Xudong Gu; Qiang Fang

    2016-08-01

    Muscle fatigue analysis has been an important topic in sport and rehabilitation medicine due to its role in muscle performance evaluation and pathology investigation. This paper proposes a surface electromyography (sEMG) based muscle fatigue analysis approach which was specifically designed for stroke rehabilitation applications. 14 stroke patients from 5 different Brunnstrom recovery stage groups were involved in the experiment and features including median frequency and mean power frequency were extracted from the collected sEMG samples for investigation. After signal decomposition, the decline of motor unit firing rate of patients from different groups had also been studied. Statistically significant presence of fatigue had been observed in deltoideus medius and extensor digitorum communis of patients at early recovery stages (P0.01). It had also been discovered that the motor unit firing frequency declines with a range positively correlated to the recovery stage during repetitive movements. Based on the experiment result, it can be verified that as the recovery stage increases, the central nervous system's control ability strengthens and the patient motion becomes more stable and resistive to fatigue.

  2. Effects of striated laser tracks on thermal fatigue resistance of cast iron samples with biomimetic non-smooth surface

    International Nuclear Information System (INIS)

    Tong, Xin; Zhou, Hong; Liu, Min; Dai, Ming-jiang

    2011-01-01

    In order to enhance the thermal fatigue resistance of cast iron materials, the samples with biomimetic non-smooth surface were processed by Neodymium:Yttrium Aluminum Garnet (Nd:YAG) laser. With self-controlled thermal fatigue test method, the thermal fatigue resistance of smooth and non-smooth samples was investigated. The effects of striated laser tracks on thermal fatigue resistance were also studied. The results indicated that biomimetic non-smooth surface was benefit for improving thermal fatigue resistance of cast iron sample. The striated non-smooth units formed by laser tracks which were vertical with thermal cracks had the best propagation resistance. The mechanisms behind these influences were discussed, and some schematic drawings were introduced to describe them.

  3. On the Specific Role of Microstructure in Governing Cyclic Fatigue, Deformation, and Fracture Behavior of a High-Strength Alloy Steel

    Science.gov (United States)

    Manigandan, K.; Srivatsan, T. S.

    2015-06-01

    In this paper, the results of an experimental study that focused on evaluating the conjoint influence of microstructure and test specimen orientation on fully reversed strain-controlled fatigue behavior of the high alloy steel X2M are presented and discussed. The cyclic stress response of this high-strength alloy steel revealed initial hardening during the first few cycles followed by gradual softening for most of fatigue life. Cyclic strain resistance exhibited a linear trend for the variation of elastic strain amplitude with reversals to failure, and plastic strain amplitude with reversals to failure. Fracture morphology was the same at the macroscopic level over the entire range of cyclic strain amplitudes examined. However, at the fine microscopic level, the alloy steel revealed fracture to be essentially ductile with features reminiscent of predominantly "locally" ductile and isolated brittle mechanisms. The mechanisms governing stress response at the fine microscopic level, fatigue life, and final fracture behavior are presented and discussed in light of the mutually interactive influences of intrinsic microstructural effects, deformation characteristics of the microstructural constituents during fully reversed strain cycling, cyclic strain amplitude, and resultant response stress.

  4. Surface modification and fatigue behavior of nitinol for load bearing implants

    Science.gov (United States)

    Bernard, Sheldon A.

    Musculoskeletal disorders are recognized amongst the most significant human health problems that exist today. Even though considerable research and development has gone towards understanding musculoskeletal disorders, there is still lack of bone replacement materials that are appropriate for restoring lost structures and functions, particularly for load-bearing applications. Many materials on the market today, such as titanium and stainless steel, suffer from significantly higher modulus than natural bone and low bioactivity leading to stress shielding and implant loosening over longer time use. Nitinol (NiTi) is an equiatomic intermetallic compound of nickel and titanium whose unique biomechanical and biological properties contributed to its increasing use as a biomaterial. An innovative method for creating dense and porous net shape NiTi alloy parts has been developed to improve biological properties while maintaining comparable or better mechanical properties than commercial materials that are currently in use. Laser engineered net shaping (LENS(TM)) and surface electrochemistry modification was used to create dense/porous samples and micro textured surfaces on NiTi parts, respectively. Porous implants are known to promote cell adhesion and have a low elastic modulus, a combination that can significantly increase the life of an implant. However, porosity can significantly reduce the fatigue life of an implant, and very little work has been reported on the fatigue behavior of bulk porous metals, specifically on porous nitinol alloy. High-cycle rotating bending and compression-compression fatigue behavior of porous NiTi fabricated using LENS(TM) were studied. In cyclic compression loading, plastic strain increased with increasing porosity and it was evident that maximum strain was achieved during the first 50000 cycles and remained constant throughout the remaining loading. No failures were observed due to loading up to 150% of the yield strength. When subjected

  5. Qualitative assessment of bone density at the distal articulating surface of the third metacarpal in Thoroughbred racehorses with and without condylar fracture.

    Science.gov (United States)

    Loughridge, A B; Hess, A M; Parkin, T D; Kawcak, C E

    2017-03-01

    Changes in subchondral bone density, induced by the repetitive cyclical loading of exercise, may potentiate fatigue damage and the risk of fracture. To use computed tomography (CT) to characterise bone density patterns at the articular surface of the third metacarpal bone in racehorses with and without lateral condylar fractures. Case control METHODS: Computed tomographic images of the distal articulating surface of the third metacarpal bone were obtained from Thoroughbred racehorses subjected to euthanasia in the UK. Third metacarpal bones were divided into 3 groups based on lateral condyle status; fractured (FX, n = 42), nonfractured contralateral condyle (NFX, n = 42) and control condyles from horses subjected to euthanasia for reasons unrelated to the third metacarpal bone (control, n = 94). Colour CT images were generated whereby each colour represented a range of pixel values and thus a relative range of bone density. A density value was calculated qualitatively by estimating the percentage of each colour within a specific region. Subchondral bone density was assessed in 6 regions from dorsal to palmar and 1 mm medial and lateral to the centre of the lateral parasagittal groove in NFX and control condyles and 1 mm medial and lateral to the fracture in FX condyles. Bone density was significantly higher in the FX and NFX condyles compared with control condyles for all 6 regions. A significantly higher bone density was observed in FX condyles relative to NFX condyles in the lateral middle and lateral palmar regions. Fractured condyles had increased heterogeneity in density among the 6 regions of interest compared with control and NFX condyles. Adjacent to the fracture, a focal increase in bone density and increased heterogeneity of density were characteristic of limbs with lateral condylar fractures compared with control and NFX condyles. These differences may represent pathological changes in bone density that increase the risk for lateral condylar fractures in

  6. Influence of surface treatment of yttria-stabilized tetragonal zirconia polycrystal with hot isostatic pressing on cyclic fatigue strength.

    Science.gov (United States)

    Iijima, Toshihiko; Homma, Shinya; Sekine, Hideshi; Sasaki, Hodaka; Yajima, Yasutomo; Yoshinari, Masao

    2013-01-01

    Hot isostatic pressing processed yttria-stabilized tetragonal zirconia polycrystal (HIP Y-TZP) has the potential for application to implants due to its high mechanical performance. The aim of this study was to investigate the influence of surface treatment of HIP Y-TZP on cyclic fatigue strength. HIP Y-TZP specimens were subjected to different surface treatments. Biaxial flexural strength was determined by both static and cyclic fatigue testing. In the cyclic fatigue test, the load was applied at a frequency of 10 Hz for 10(6) cycles in distilled water at 37°C. The surface morphology, roughness, and crystal phase of the surfaces were also evaluated. The cyclic fatigue strength (888 MPa) of HIP Y-TZP with sandblasting and acid-etching was more than twice that of Y-TZP as specified in ISO 13356 for surgical implants (320 MPa), indicating the clinical potential of this material.

  7. Age-related mechanical strength evolution of trabecular bone under fatigue damage for both genders: Fracture risk evaluation.

    Science.gov (United States)

    Ben Kahla, Rabeb; Barkaoui, Abdelwahed; Merzouki, Tarek

    2018-05-04

    Bone tissue is a living composite material, providing mechanical and homeostatic functions, and able to constantly adapt its microstructure to changes in long term loading. This adaptation is conducted by a physiological process, known as "bone remodeling". This latter is manifested by interactions between osteoclasts and osteoblasts, and can be influenced by many local factors, via effects on bone cell differentiation and proliferation. In the current work, age and gender effects on damage rate evolution, throughout life, have been investigated using a mechanobiological finite element modeling. To achieve the aim, a mathematical model has been developed, coupling both cell activities and mechanical behavior of trabecular bone, under cyclic loadings. A series of computational simulations (ABAQUS/UMAT) has been performed on a 3D human proximal femur, allowing to investigate the effects of mechanical and biological parameters on mechanical strength of trabecular bone, in order to evaluate the fracture risk resulting from fatigue damage. The obtained results revealed that mechanical stimulus amplitude affects bone resorption and formation rates, and indicated that age and gender are major factors in bone response to the applied loadings. Copyright © 2018 Elsevier Ltd. All rights reserved.

  8. Surface Studies of Ultra Strength Drilling Steel after Corrosion Fatigue in Simulated Sour Environment

    Energy Technology Data Exchange (ETDEWEB)

    M. Ziomek-Moroz; J.A. Hawk; R. Thodla; F. Gui

    2012-05-06

    The Unites States predicted 60% growth in energy demand by 2030 makes oil and natural gas primary target fuels for energy generation. The fact that the peak of oil production from shallow wells (< 5000 m) is about to be reached, thereby pushing the oil and natural gas industry into deeper wells. However, drilling to depths greater than 5000 m requires increasing the strength-to weight ratio of the drill pipe materials. Grade UD-165 is one of the ultra- high yield strength carbon steels developed for ultra deep drilling (UDD) activities. Drilling UDD wells exposes the drill pipes to Cl{sup -}, HCO{sub 3}{sup -}/CO{sub 3}{sup 2-}, and H{sub 2}S-containig corrosive environments (i.e., sour environments) at higher pressures and temperatures compared to those found in conventional wells. Because of the lack of synergism within the service environment, operational stresses can result in catastrophic brittle failures characteristic for environmentally assisted cracking (EAC). Approximately 75% of all drill string failures are caused by fatigue or corrosion fatigue. Since there is no literature data on the corrosion fatigue performance of UD-165 in sour environments, research was initiated to better clarify the fatigue crack growth (FCGR) behavior of this alloy in UDD environments. The FCGR behavior of ultra-strength carbon steel, grade UD-165, was investigated by monitoring crack growth rate in deaerated 5%NaCl solution buffered with NaHCO{sub 3}/Na{sub 2}CO{sub 3} and in contact with H{sub 2}S. The partial pressure of H{sub 2}S (p{sub H2S}) was 0.83 kPa and pH of the solution was adjusted by NaOH to 12. The fatigue experiments were performed at 20 and 85 C in an autoclave with surface investigations augmented by scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) spectroscopy. In this study, research focused on surface analyses supported by the fatigue crack growth rate measurements. Fig. 1 shows an SEM micrograph of the crack that propagated from the

  9. Model of thermal fatigue of a copper surface under the action of high-power microwaves

    Science.gov (United States)

    Kuzikov, S. V.; Plotkin, M. E.

    2007-10-01

    The accelerating structures of modern supercolliders, as well as the components of high-power microwave electron devices operated in strong cyclic electromagnetic fields should have long lifetimes. Along with the electric breakdown, the surfaces of these microwave components deteriorate and their lifetimes decrease due to thermal strains and subsequent mechanical loads on the surface metal layer. The elementary theory of thermal fatigue was developed in the 1970s. In particular, a model of metal as a continuous medium was considered. Within the framework of this model, thermal fatigue is caused by the strains arising between the hot surface layer and the cold internal layer of the metal. However, this theory does not describe all the currently available experimental data. In particular, the notion of “safe temperature” of the heating, i.e., temperature at which the surface is not destroyed during an arbitrarily long series of pulses, which was proposed in the theoretical model, is in poor agreement with the experiment performed in the Stanford Linear Accelerator Center (SLAC, USA). In this work, the thermal-fatigue theory is developed on the basis of consideration of the copper polycrystalline structure. The necessity to take it into account was demonstrated by the results of the SLAC experiment, in which a change in the mutual orientation of copper grains and the formation of cracks at their boundaries was recorded for the first time. The developed theory makes it possible to use the experimental data to refine the coefficients in the obtained formulas for the lifetime of the metal surface and to predict the number of microwave pulses before its destruction as a function of the radiation power, the surface-temperature increase at the pulse peak, and the pulse duration.

  10. Effective Wettability of Heterogenous Fracture Surfaces Using the Lattice-Boltzmann Method

    Science.gov (United States)

    E Santos, J.; Prodanovic, M.; Landry, C. J.

    2017-12-01

    Fracture walls in the subsurface are often structured by minerals of different composition (potentially further altered in contact with fluids during hydrocarbon extraction or CO2 sequestration), this yields in a heterogeneous wettability of the surface in contact with the fluids. The focus of our work is to study how surfaces presenting different mineralogy and roughness affect multiphase flow in fractures. Using the Shan-Chen model of the lattice-Boltzmann method (LBM) we define fluid interaction and surface attraction parameters to simulate a system of a wetting and a non-wetting fluid. In this work, we use synthetically created fractures presenting different arrangements of wetting and non-wetting patches, and with or without roughness; representative of different mineralogy, similar workflow can be applied to fractures extracted from X-ray microtomography images of fractures porous media. The results from the LBM simulations provide an insight on how the distribution of mineralogy and surface roughness are related with the observed macroscopic contact angle. We present a comparison between the published analytical models, and our results based on surface areas, spatial distribution and local fracture aperture. The understanding of the variables that affect the contact angle is useful for the comprehension of multiphase processes in naturally fractured reservoirs like primary oil production, enhanced oil recovery and CO2 sequestration. The macroscopic contact angle analytical equations for heterogeneous surfaces with variable roughness are no longer valid in highly heterogeneous systems; we quantify the difference thus offering an alternative to analytical models.

  11. Estimation of muscle fatigue using surface electromyography and near-infrared spectroscopy.

    Science.gov (United States)

    Taelman, Joachim; Vanderhaegen, Joke; Robijns, Mieke; Naulaers, Gunnar; Spaepen, Arthur; Van Huffel, Sabine

    2011-01-01

    This study looks at various parameters, derived from surface electromyography (sEMG) and Near Infrared Spectroscopy (NIRS) and their relationship in muscle fatigue during a static elbow flexion until exhaustion as well as during a semidynamic exercise.We found a linear increasing trend for a corrected amplitude parameter and a linear decreasing slope for the frequency content of the sEMG signal. The tissue oxygenation index (TOI) extracted from NIRS recordings showed a four-phase response for all the subjects. A strong correlation between frequency content of the sEMG signal and TOI was established. We can conclude that both sEMG and NIRS give complementary information concerning muscle fatigue.

  12. QAPP for Hydraulic Fracturing (HF) Surface Spills Data Analysis

    Science.gov (United States)

    This QAPP provides information concerning the analysis of spills associated with hydraulic fracturing. This project is relevant to both the chemical mixing and flowback and produced water stages of the HF water cycle as found in the HF Study Plan.

  13. Surface crack behavior in socket weld of nuclear piping under fatigue loading condition

    International Nuclear Information System (INIS)

    Choi, Y.H.; Kim, J.S.; Choi, S.Y.

    2005-01-01

    The ASME B and PV Code Sec. III allows the socket weld for the nuclear piping in spite of the weakness on the weld integrity. Recently, the integrity of the socket weld is regarded as a safety concern in nuclear power plants because many failures and leaks have been reported in the socket weld. OPDE (OECD Piping Failure Data Exchange) database lists 108 socket weld failures among 2,399 nuclear piping failure cases during 1970 to 2001. Eleven failures in the socket weld were also reported in Korean NPPs. Many failure cases showed that the root cause of the failure is the fatigue and the gap requirement for the socket weld given in ASME Code was not satisfied. The purpose of this paper is to evaluate the fatigue crack behavior of a surface crack in the socket weld under fatigue loading condition considering the gap effect. Three-dimensional finite element analysis was performed to estimate the fatigue crack behavior of the surface crack. Three types of loading conditions such as the deflection due to vibration, the pressure transient ranging from P=0 to 15.51 MPa, and the thermal transient ranging from T=25 C to 288 C were considered. The results are as follows; 1) The socket weld is susceptible to the vibration where the vibration levels exceed the requirement in the ASME operation and maintenance (OM) Code. 2) The effect of pressure or temperature transient load on the socket weld integrity is not significant. 3) No-gap condition gives very high possibility of the crack initiation at the socket weld under vibration loading condition. 4) For the specific systems having the vibration condition to exceed the requirement in the ASME Code OM and/or the transient loading condition from P=0 and T=25 C to P=15.51 MPa and T=288 C, radiographic examination to examine the gap during the construction stage is recommended. (orig.)

  14. Cyclic fatigue-crack propagation, stress-corrosion, and fracture-toughness behavior in pyrolytic carbon-coated graphite for prosthetic heart valve applications.

    Science.gov (United States)

    Ritchie, R O; Dauskardt, R H; Yu, W K; Brendzel, A M

    1990-02-01

    Fracture-mechanics tests were performed to characterize the cyclic fatigue, stress-corrosion cracking, and fracture-toughness behavior of a pyrolytic carbon-coated graphite composite material used in the manufacture of cardiac valve prostheses. Testing was carried out using compact tension C(T) samples containing "atomically" sharp precracks, both in room-temperature air and principally in a simulated physiological environment of 37 degrees C Ringer's lactate solution. Under sustained (monotonic) loads, the composite exhibited resistance-curve behavior, with a fracture toughness (KIc) between 1.1 and 1.9 MPa square root of m, and subcritical stress-corrosion crack velocities (da/dt) which were a function of the stress intensity K raised to the 74th power (over the range approximately 10(-9) to over 10(-5) m/s). More importantly, contrary to common perception, under cyclic loading conditions the composite was found to display true (cyclic) fatigue failure in both environments; fatigue-crack growth rates (da/dN) were seen to be a function of the 19th power of the stress-intensity range delta K (over the range approximately 10(-11) to over 10(-8) m/cycle). As subcritical crack velocities under cyclic loading were found to be many orders of magnitude faster than those measured under equivalent monotonic loads and to occur at typically 45% lower stress-intensity levels, cyclic fatigue in pyrolytic carbon-coated graphite is reasoned to be a vital consideration in the design and life-prediction procedures of prosthetic devices manufactured from this material.

  15. Fractal Dimension of Fracture Surface in Rock Material after High Temperature

    Directory of Open Access Journals (Sweden)

    Z. Z. Zhang

    2015-01-01

    Full Text Available Experiments on granite specimens after different high temperature under uniaxial compression were conducted and the fracture surfaces were observed by scanning electron microscope (SEM. The fractal dimensions of the fracture surfaces with increasing temperature were calculated, respectively. The fractal dimension of fracture surface is between 1.44 and 1.63. Its value approximately goes up exponentially with the increase of temperature. There is a quadratic polynomial relationship between the rockburst tendency and fractal dimension of fracture surface; namely, a fractal dimension threshold can be obtained. Below the threshold value, a positive correlativity shows between rockburst tendency and fractal dimension; when the fractal dimension is greater than the threshold value, it shows an inverse correlativity.

  16. Fatigue failure analysis of V-4Ti-4Cr alloy

    International Nuclear Information System (INIS)

    Aglan, H.; Gan, Y.X.; Grossbeck, M.

    1999-01-01

    In the present work, the fatigue fracture and failure behavior of a V-4Ti-4Cr has been studied. Static tests were conducted to study the overloading behavior and to select the magnitude of the stress level for the fatigue studies. Fatigue tests were performed using single edge notched (SEN) specimens under tension-tension load control conditions. Fatigue crack propagation (FCP) data such as the crack length, number of cycles, and hysteresis loops were recorded to calculate the crack speed, the energy release rate, and the change in work expended on damage formation and dissipative processes within the material. Parameters characterizing the fatigue fracture resistance of V-4Ti-4Cr alloy, namely the specific energy of damage (γ'), and the dissipative coefficient (β'), were determined from the fatigue data using the modified crack layer (MCL) theory. Fracture surface examination using scanning electron microscopy (SEM) revealed ductile failure mechanisms under tensile overloading conditions. The fatigue fracture surface of the V-4Ti-4Cr consists of three distinct regions, corresponding to the threshold, stable and unstable crack propagation stages. (orig.)

  17. Three-point bending fatigue behavior of WC–Co cemented carbides

    International Nuclear Information System (INIS)

    Li, Anhai; Zhao, Jun; Wang, Dong; Gao, Xinliang; Tang, Hongwei

    2013-01-01

    Highlights: ► Mechanical fatigue tests were conducted on a specific designed jig. ► Three-point bending fatigue behavior of WC–Co cemented carbides was studied. ► Fatigue mechanisms of WC–Co cemented carbides with different WC grain sizes and Co binder contents were revealed. -- Abstract: WC–Co cemented carbides with different WC grain sizes and Co binder contents were sintered and fabricated. The three-point bending specimens with a single edge notch were prepared for tests. In the experiments, the mechanical properties of materials were investigated under static and cyclic loads (20 Hz) in air at room temperature. The fatigue behaviors of the materials under the same applied loading conditions are presented and discussed. Optical microscope and scanning electron microscopy were used to investigate the micro-mechanisms of damage during fatigue, and the results were used to correlate with the mechanical fatigue behavior of WC–Co cemented carbides. Experimental results indicated that the fatigue fracture surfaces exhibited more fracture origins and diversification of crack propagation paths than the static strength fracture surfaces. The fatigue fracture typically originates from inhomogeneities or defects such as micropores or aggregates of WC grains near the notch tip. Moreover, due to the diversity and complexity of the fatigue mechanisms, together with the evolution of the crack tip and the ductile deformation zone, the fatigue properties of WC–Co cemented carbides were largely relevant with the combination of transverse rupture strength and fracture toughness, rather than only one of them. Transverse rupture strength dominated the fatigue behavior of carbides with low Co content, whilst the fatigue behavior of carbides with high Co content was determined by fracture toughness.

  18. Improvement in surface fatigue life of hardened gears by high-intensity shot peening

    Science.gov (United States)

    Townsend, Dennis P.

    1992-04-01

    Two groups of carburized, hardened, and ground spur gears that were manufactured from the same heat vacuum induction melted vacuum arc melted (VIM VAR) AISI 9310 steel were endurance tested for surface fatigue. Both groups were manufactured with a standard ground 16 rms surface finish. One group was subjected to a shot peening (SP) intensity of 7 to 9A, and the second group was subjected to a SP intensity of 15 to 17A. All gears were honed after SP to a surface finish of 16 rms. The gear pitch diameter was 8.89 cm. Test conditions were a maximum Hertz stress of 1.71 GPa, a gear temperature of 350 K, and a speed of 10000 rpm. The lubricant used for the tests was a synthetic paraffinic oil with an additive package. The following results were obtained: The 10 pct. surface fatigue (pitting) life of the high intensity (15 to 17A) SPed gears was 2.15 times that of the medium intensity (7 to 9A) SPed gears, the same as that calculated from measured residual stress at a depth of 127 microns. The measured residual stress for the high intensity SPed gears was 57 pct. higher than that for the medium intensity SPed gears at a depth of 127 microns and 540 pct. higher at a depth of 51 microns.

  19. Monitoring of surface-fatigue crack propagation in a welded steel angle structure using guided waves and principal component analysis

    Science.gov (United States)

    Lu, Mingyu; Qu, Yongwei; Lu, Ye; Ye, Lin; Zhou, Limin; Su, Zhongqing

    2012-04-01

    An experimental study is reported in this paper demonstrating monitoring of surface-fatigue crack propagation in a welded steel angle structure using Lamb waves generated by an active piezoceramic transducer (PZT) network which was freely surface-mounted for each PZT transducer to serve as either actuator or sensor. The fatigue crack was initiated and propagated in welding zone of a steel angle structure by three-point bending fatigue tests. Instead of directly comparing changes between a series of specific signal segments such as S0 and A0 wave modes scattered from fatigue crack tips, a variety of signal statistical parameters representing five different structural status obtained from marginal spectrum in Hilbert-huang transform (HHT), indicating energy progressive distribution along time period in the frequency domain including all wave modes of one wave signal were employed to classify and distinguish different structural conditions due to fatigue crack initiation and propagation with the combination of using principal component analysis (PCA). Results show that PCA based on marginal spectrum is effective and sensitive for monitoring the growth of fatigue crack although the received signals are extremely complicated due to wave scattered from weld, multi-boundaries, notch and fatigue crack. More importantly, this method indicates good potential for identification of integrity status of complicated structures which cause uncertain wave patterns and ambiguous sensor network arrangement.

  20. Assessment of Diaphragm and External Intercostals Fatigue from Surface EMG using Cervical Magnetic Stimulation

    Directory of Open Access Journals (Sweden)

    Ya-Ju Chang

    2008-03-01

    Full Text Available This study was designed: (1 to test the reliability of surface electromyography (sEMG recording of the diaphragm and external intercostals contractions response to cervical magnetic stimulation (CMS, (2 to examine the amount and the types of inspiratory muscle fatigue that developed after maximum voluntary ventilation (MVV maneuvers.Ten male college students without physical disability (22.1±2.0 years old participated in the study and each completed a control (quiet breathing trial and a fatigue (MVV maneuvers trial sequentially. In the quiet breathing trial, the subjects maintained quiet breathing for five minutes. The subjects performed five maximal static inspiratory efforts and received five CMS before and after the quiet breathing. In the MVV trial, subjects performed five maximal inspiratory efforts and received five CMS before, immediately after, and ten minutes after two sets of MVV maneuvers performed five minutes apart. Maximal inspiratory pressure (PImax, sEMG of diaphragm and external intercostals during maximal static inspiratory efforts and during CMS were recorded. In the quiet breathing trial, high intraclass correlation coefficients (ICC=0.95-0.99 were observed in all the variables. In the MVV trial, the PImax, the EMG amplitude and the median power frequency during maximal static inspiratory efforts significantly decreased in both the diaphragm and the external intercostals immediately after the MVV maneuvers Sensors 2008, 8 2175 (P 0.05. It is concluded that the sEMG recordings of the diaphragm during maximal static inspiratory efforts and in response to CMS allow reproducible sequential assessment of diaphragm contractility. MVV maneuvers resulted in inspiratory muscles fatigue, possibly central fatigue.

  1. Experimental Investigation and Finite Element Analysis on Fatigue Behavior of Aluminum Alloy 7050 Single-Lap Joints

    Science.gov (United States)

    Zhou, Bing; Cui, Hao; Liu, Haibo; Li, Yang; Liu, Gaofeng; Li, Shujun; Zhang, Shangzhou

    2018-03-01

    The fatigue behavior of single-lap four-riveted aluminum alloy 7050 joints was investigated by using high-frequency fatigue test and scanning electron microscope (SEM). Stress distributions obtained by finite element (FE) analysis help explain the fatigue performance. The fatigue test results showed that the fatigue lives of the joints depend on cold expansion and applied cyclic loads. FE analysis and fractography indicated that the improved fatigue lives can be attributed to the reduction in maximum stress and evolution of fatigue damage at the critical location. The beneficial effects of strengthening techniques result in tearing ridges or lamellar structure on fracture surface, decrease in fatigue striations spacing, delay of fatigue crack initiation, crack deflection in fatigue crack propagation and plasticity-induced crack closure.

  2. Combining periodic hydraulic tests and surface tilt measurements to explore in situ fracture hydromechanics

    Science.gov (United States)

    Schuite, Jonathan; Longuevergne, Laurent; Bour, Olivier; Guihéneuf, Nicolas; Becker, Matthew W.; Cole, Matthew; Burbey, Thomas J.; Lavenant, Nicolas; Boudin, Frédéric

    2017-08-01

    Fractured bedrock reservoirs are of socio-economical importance, as they may be used for storage or retrieval of fluids and energy. In particular, the hydromechanical behavior of fractures needs to be understood as it has implications on flow and governs stability issues (e.g., microseismicity). Laboratory, numerical, or field experiments have brought considerable insights to this topic. Nevertheless, in situ hydromechanical experiments are relatively uncommon, mainly because of technical and instrumental limitations. Here we present the early stage development and validation of a novel approach aiming at capturing the integrated hydromechanical behavior of natural fractures. It combines the use of surface tiltmeters to monitor the deformation associated with the periodic pressurization of fractures at depth in crystalline rocks. Periodic injection and withdrawal advantageously avoids mobilizing or extracting significant amounts of fluid, and it hinders any risk of reservoir failure. The oscillatory perturbation is intended to (1) facilitate the recognition of its signature in tilt measurements and (2) vary the hydraulic penetration depth in order to sample different volumes of the fractured bedrock around the inlet and thereby assess scale effects typical of fractured systems. By stacking tilt signals, we managed to recover small tilt amplitudes associated with pressure-derived fracture deformation. Therewith, we distinguish differences in mechanical properties between the three tested fractures, but we show that tilt amplitudes are weakly dependent on pressure penetration depth. Using an elastic model, we obtain fracture stiffness estimates that are consistent with published data. Our results should encourage further improvement of the method.

  3. Effects of multiple root canal usage on the surface topography and fracture of two different Ni-Ti rotary file systems

    Directory of Open Access Journals (Sweden)

    Jojo Kottoor

    2013-01-01

    Full Text Available Aim: The purpose of this study was to evaluate the effect of multiple root canal usage on the surface topography and fracture of Twisted File (TF and ProTaper (PT rotary Ni-Ti file systems, using scanning electron microscope (SEM. Materials and Methods: Ten sets of PT and TF instruments were used to prepare the mesial canals of mandibular first molars. TF 25, 0.06 taper and PT F1 instruments were analyzed by SEM when new and thereafter every three root canal usages. This sequence was repeated for both the TF and PT groups until 12 uses. Two images of the instrument were recorded, one of the instrument tip and the other 5 mm from the tip, both at ×100 magnification. The sequential use was continued till the instrument fractured and the number of root canal usages for the file to fracture was noted. All fracture surfaces were examined under the SEM. Results: Fresh TF instruments showed no surface wear when compared to PT instruments (P 0.05, while at the 9 th usage TF showed a steep increase in the spiral distortion score when compared to PT (P < 0.05. PT instruments fractured at a mean root canal usage of 17.4, while TF instruments showed a mean root canal usage of 11.8. Fractographically, all the TF instruments failed due to torsion, while all the PT instruments failed because of cyclic fatigue. Conclusion: PT instruments showed more resistance to fracture than TF instruments.

  4. Surface self-potential patterns related to transmissive fracture trends during a water injection test

    Science.gov (United States)

    DesRoches, A. J.; Butler, K. E.; MacQuarrie, K. TB

    2018-03-01

    Variations in self-potential (SP) signals were recorded over an electrode array during a constant head injection test in a fractured bedrock aquifer. Water was injected into a 2.2 m interval isolated between two inflatable packers at 44 m depth in a vertical well. Negative SP responses were recorded on surface corresponding to the start of the injection period with strongest magnitudes recorded in electrodes nearest the well. SP response decreased in magnitude at electrodes further from the well. Deflation of the packer system resulted in a strong reversal in the SP signal. Anomalous SP patterns observed at surface at steady state were found to be aligned with dominant fracture strike orientations found within the test interval. Numerical modelling of fluid and current flow within a simplified fracture network showed that azimuthal patterns in SP are mainly controlled by transmissive fracture orientations. The strongest SP gradients occur parallel to hydraulic gradients associated with water flowing out of the transmissive fractures into the tighter matrix and other less permeable cross-cutting fractures. Sensitivity studies indicate that increasing fracture frequency near the well increases the SP magnitude and enhances the SP anomaly parallel to the transmissive set. Decreasing the length of the transmissive fractures leads to more fluid flow into the matrix and into cross-cutting fractures proximal to the well, resulting in a more circular and higher magnitude SP anomaly. Results from the field experiment and modelling provide evidence that surface-based SP monitoring during constant head injection tests has the ability to identify groundwater flow pathways within a fractured bedrock aquifer.

  5. A numerical procedure for transient free surface seepage through fracture networks

    Science.gov (United States)

    Jiang, Qinghui; Ye, Zuyang; Zhou, Chuangbing

    2014-11-01

    A parabolic variational inequality (PVI) formulation is presented for the transient free surface seepage problem defined for a whole fracture network. Because the seepage faces are specified as Signorini-type conditions, the PVI formulation can effectively eliminate the singularity of spillpoints that evolve with time. By introducing a continuous penalty function to replace the original Heaviside function, a finite element procedure based on the PVI formulation is developed to predict the transient free surface response in the fracture network. The effects of the penalty parameter on the solution precision are analyzed. A relative error formula for evaluating the flow losses at steady state caused by the penalty parameter is obtained. To validate the proposed method, three typical examples are solved. The solutions for the first example are compared with the experimental results. The results from the last two examples further demonstrate that the orientation, extent and density of fractures significantly affect the free surface seepage behavior in the fracture network.

  6. Correlation analysis between surface electromyography and continuous-wave near-infrared spectroscopy parameters during isometric exercise to volitional fatigue

    OpenAIRE

    ŞAYLİ, Ömer; AKIN, Ata; ÇOTUK, Hasan Birol

    2014-01-01

    In this study, the process of muscular fatigue was examined using surface electromyography (sEMG) and continuous-wave near-infrared spectroscopy (cw-NIRS) simultaneously during an isometric hand grip exercise at 50% and 75% of the maximal voluntary contraction (MVC), sustained until volitional fatigue. The mean frequency of the sEMG decreased during the whole exercise, whereas the root mean square had a tendency to increase. Oxyhemoglobin/deoxyhemoglobin concentration changes computed ...

  7. Sub-surface Fatigue Crack Growth at Alumina Inclusions in AISI 52100 Roller Bearings

    DEFF Research Database (Denmark)

    Cerullo, Michele

    2014-01-01

    Sub-surface fatigue crack growth at non metallic inclusions is studied in AISI 52100 bearing steel under typical rolling contact loads. A first 2D plane strain finite element analysis is carried out to compute the stress history in the innner race at a characteristic depth, where the Dang Van...... damage factor is highest. Subsequently the stress history is imposed as boundary conditions in a periodic unit cell model, where an alumina inclusion is embedded in a AISI 52100 matrix. Cracks are assumed to grow radially from the inclusion under cyclic loading. The growth is predicted by means...

  8. Fundamental principles of the cyclic behaviour and the fatigue damage for metallic materials

    International Nuclear Information System (INIS)

    Vogt, J.B.

    2001-01-01

    The aim of this paper is a pedagogic presentation of the basic concepts concerning the cyclic behaviour and the fatigue damage of metallic materials in order to offer a better understand of mechanisms. The following aspects are taking into account: the fatigue fracture, the cyclic accommodation, the dislocations structures, the surface and bulk cracks and the influence of the medium. (A.L.B.)

  9. Ductile-reinforcement toughening in γ-TiAl intermetallic-matrix composites: Effects on fracture toughness and fatigue-crack propagation resistance

    International Nuclear Information System (INIS)

    Venkateswara Rao, K.T.; Ritchie, R.O.; Odette, G.R.

    1994-01-01

    The influence of the type, volume fraction, thickness and orientation of ductile phase reinforcements on the room temperature fatigue and fracture resistance of γ-TiAl intermetallic alloys is investigated. Large improvements in toughness compared to monolithic γ-TiAl are observed in both the TiNb- and Nb-reinforced composites under monotonic loading. Toughness increases with increasing ductile phase content, reinforcement thickness and strength; orientation effect are minimal. Crack-growth behavior is characterized by steep resistance curves primarily due to crack trapping/renucleation and extensive crack bridging by the ductile-phase particles. In contrast, under cyclic loading the influence of ductile phases on fatigue resistance is strongly dependent upon reinforcement orientation. Compared to monolithic γ-TiAl, improvements in fatigue-crack growth resistance are observed in TiNb-reinforced composites only in the face (C-L) orientation; crack-growth rates for the edge (C-R) orientation are actually faster in the composite. In comparison, Nb-particle reinforcements offer less toughening under monotonic loading but enhance the fatigue properties compared to TiNb reinforcements under cyclic loading

  10. Effects of fracture surface roughness and shear displacement on geometrical and hydraulic properties of three-dimensional crossed rock fracture models

    Science.gov (United States)

    Huang, Na; Liu, Richeng; Jiang, Yujing; Li, Bo; Yu, Liyuan

    2018-03-01

    While shear-flow behavior through fractured media has been so far studied at single fracture scale, a numerical analysis of the shear effect on the hydraulic response of 3D crossed fracture model is presented. The analysis was based on a series of crossed fracture models, in which the effects of fracture surface roughness and shear displacement were considered. The rough fracture surfaces were generated using the modified successive random additions (SRA) algorithm. The shear displacement was applied on one fracture, and at the same time another fracture shifted along with the upper and lower surfaces of the sheared fracture. The simulation results reveal the development and variation of preferential flow paths through the model during the shear, accompanied by the change of the flow rate ratios between two flow planes at the outlet boundary. The average contact area accounts for approximately 5-27% of the fracture planes during shear, but the actual calculated flow area is about 38-55% of the fracture planes, which is much smaller than the noncontact area. The equivalent permeability will either increase or decrease as shear displacement increases from 0 to 4 mm, depending on the aperture distribution of intersection part between two fractures. When the shear displacement continuously increases by up to 20 mm, the equivalent permeability increases sharply first, and then keeps increasing with a lower gradient. The equivalent permeability of rough fractured model is about 26-80% of that calculated from the parallel plate model, and the equivalent permeability in the direction perpendicular to shear direction is approximately 1.31-3.67 times larger than that in the direction parallel to shear direction. These results can provide a fundamental understanding of fluid flow through crossed fracture model under shear.

  11. Imaging of acute injuries of the articular surfaces (chondral, osteochondral and subchondral fractures)

    Energy Technology Data Exchange (ETDEWEB)

    Bohndorf, K. [Department of Radiology, Zentralklinikum Augsburg (Germany)

    1999-10-01

    Fractures involving the articulating surfaces of bone are a common cause of chronic disability after joint injury. Acute fractures of the articular surface typically run parallel to the surface and are confined to the cartilage and/or the immediate subchondral cancellous bone. They should be distinguished from vertical or oblique bone fractures with intra-articular extension. This article reviews the mechanism of acute articular surface injuries, as well as their incidence, clinical presentation, radiologic appearance and treatment. A classification is presented based on direct inspection (arthroscopy) and imaging (especially MRI), emphasizing the distinction between lesions with intact (subchondral impaction and subchondral bone bruises) and disrupted (chondral, osteochondral lesions) cartilage. Hyaline cartilage, subchondral bone plate and subchondral cancellous bone are to be considered an anatomic unit. Subchondral articular surface lesions, osteochondral fractures and solely chondral fractures are different manifestations of impaction injuries that affect the articulating surface. Of the noninvasive imaging modalities, conventional radiography and MRI provide the most relevant information. The appropriate use of short tau inversion recovery, T1-weighted and T2-weighted (turbo) spin-echo as well as gradient-echo sequences, enables MRI to classify the various acute articular surface lesions with great accuracy and provides therapeutic guidance. (orig.)

  12. Imaging of acute injuries of the articular surfaces (chondral, osteochondral and subchondral fractures)

    International Nuclear Information System (INIS)

    Bohndorf, K.

    1999-01-01

    Fractures involving the articulating surfaces of bone are a common cause of chronic disability after joint injury. Acute fractures of the articular surface typically run parallel to the surface and are confined to the cartilage and/or the immediate subchondral cancellous bone. They should be distinguished from vertical or oblique bone fractures with intra-articular extension. This article reviews the mechanism of acute articular surface injuries, as well as their incidence, clinical presentation, radiologic appearance and treatment. A classification is presented based on direct inspection (arthroscopy) and imaging (especially MRI), emphasizing the distinction between lesions with intact (subchondral impaction and subchondral bone bruises) and disrupted (chondral, osteochondral lesions) cartilage. Hyaline cartilage, subchondral bone plate and subchondral cancellous bone are to be considered an anatomic unit. Subchondral articular surface lesions, osteochondral fractures and solely chondral fractures are different manifestations of impaction injuries that affect the articulating surface. Of the noninvasive imaging modalities, conventional radiography and MRI provide the most relevant information. The appropriate use of short tau inversion recovery, T1-weighted and T2-weighted (turbo) spin-echo as well as gradient-echo sequences, enables MRI to classify the various acute articular surface lesions with great accuracy and provides therapeutic guidance. (orig.)

  13. Experimental study on creep-fatigue interaction behavior of GH4133B superalloy

    International Nuclear Information System (INIS)

    Hu Dianyin; Wang Rongqiao

    2009-01-01

    The creep-fatigue tests have been conducted with nickel-based superalloy GH4133B at 600 deg. C in three cases of type loading to study the creep-fatigue behavior of the alloy and the loading history effect on the creep-fatigue damage. Since the conventional linear cumulative damage rule failed in evaluating the creep-fatigue life based on experimental data, a continuous non-linear model proposed by Mao et al. was employed to describe the creep-fatigue interaction. The creep-fatigue damage in the cases of continuous cyclic creep loading (CF) and prior fatigue followed by creep loading (F + C) was larger than unity and smaller than unity when the type loading was prior creep followed by fatigue loading (C + F). Scanning electron microscope (SEM) analyses of the fracture surface showed that the cracks initiated from the specimen surface and the fracture modes in different loading history were different. The crack mode at CF loading depended on the cyclic period. In the case of F + C loading, the primary fracture mode was transgranular, and in the condition where the type of waveform was C + F, the fracture mode was of mixed transgranular and intergranular type. In addition, the origin of the history effect on creep-fatigue interaction was explained by the SEM observations.

  14. Cyclic fatigue of a high-strength corrosion-resistant sheet TRIP steel

    Science.gov (United States)

    Terent'ev, V. F.; Alekseeva, L. E.; Korableva, S. A.; Prosvirnin, D. V.; Pankova, M. N.; Filippov, G. A.

    2014-04-01

    The mechanical properties of 0.3- and 0.8-mm-thick high-strength corrosion-resistant TRIP steel having various levels of strength properties are studied during static and cyclic loading in the high-cycle fatigue range. The fatigue fracture surface is analyzed by fractography, and the obtained results demonstrate ductile and quasi-brittle fracture mechanisms of this steel depending on the strength properties of the steel and the content of deformation martensite in it.

  15. Experimental investigation on low cycle fatigue and creep-fatigue interaction of DZ125 in different dwell time at elevated temperatures

    International Nuclear Information System (INIS)

    Shi Duoqi; Liu Jinlong; Yang Xiaoguang; Qi Hongyu; Wang Jingke

    2010-01-01

    Research highlights: → This paper has researched creep-fatigue interaction of directionally solidified superalloy DZ125 with different dwell time at high temperature combined with micro-mechanism by experiment. → The results indicated that the life of creep-fatigue decreases as dwell time increases, but the life of this alloy was almost unchanged when dwell time exceeds a critical value at 850 deg. C. - Abstract: The low cycle fatigue (LCF) and creep-fatigue tests have been conducted with directionally solidified nickel-based superalloy DZ125 at 850 and 980 deg. C to study the creep-fatigue interaction behavior of alloy with different dwell time. On the average, the life of creep-fatigue tests are about 70% less than the life of LCF tests under the same strain range at 850 deg. C. The life of creep-fatigue decreases as dwell time increases, but the life of this alloy was almost unchanged when dwell time exceeds a critical value at 850 deg. C. Scanning electron microscope (SEM) analyses of the fracture revealed that the fracture modes were influenced by different way of loading. In case of LCF, the primary fracture mode was transgranular, while in case of creep-fatigue, the primary fracture mode was mixed with transgranular and intergranular. There were also obvious different morphologies of surface crack between LCF and creep-fatigue.

  16. Structural changes of radial forging die surface during service under thermo-mechanical fatigue

    International Nuclear Information System (INIS)

    Nematzadeh, Fardin; Akbarpour, Mohammad Reza; Kokabi, Amir Hosein; Sadrnezhaad, Seyed Khatiboleslam

    2009-01-01

    Radial forging is one of the modern open die forging techniques and has a wide application in producing machine parts. During operation at high temperatures, severe temperature change associated with mechanical loads and the resultant wearing of the die surface lead to intense variation in strain on the die surface. Therefore, under this operating condition, thermo-mechanical fatigue (TMF) occurs on the surface of the radial forging die. TMF decreases the life of the die severely. In the present research, different layers were deposited on a 1.2714 steel die by SMAW and GTAW, with a weld wire of UDIMET 520. The microstructure of the radial forging die surface was investigated during welding and service using an optical microscope and scanning electron microscope. The results revealed that, after welding, the structure of the radial forging die surface includes the γ matrix with a homogeneous distribution of fine semi-spherical carbides. The weld structure consisted mostly of columnar dendrites with low grain boundaries. Also, microstructural investigation of the die surface during operation showed that the weld structure of the die surface has remained without any considerable change. Only dendrites were deformed and broken. Moreover, grain boundaries of the dendrites were revealed during service.

  17. Gear Fault Detection Effectiveness as Applied to Tooth Surface Pitting Fatigue Damage

    Science.gov (United States)

    Lewicki, David G.; Dempsey, Paula J.; Heath, Gregory F.; Shanthakumaran, Perumal

    2010-01-01

    A study was performed to evaluate fault detection effectiveness as applied to gear-tooth-pitting-fatigue damage. Vibration and oil-debris monitoring (ODM) data were gathered from 24 sets of spur pinion and face gears run during a previous endurance evaluation study. Three common condition indicators (RMS, FM4, and NA4 [Ed. 's note: See Appendix A-Definitions D were deduced from the time-averaged vibration data and used with the ODM to evaluate their performance for gear fault detection. The NA4 parameter showed to be a very good condition indicator for the detection of gear tooth surface pitting failures. The FM4 and RMS parameters perfomu:d average to below average in detection of gear tooth surface pitting failures. The ODM sensor was successful in detecting a significant 8lDOunt of debris from all the gear tooth pitting fatigue failures. Excluding outliers, the average cumulative mass at the end of a test was 40 mg.

  18. Analysis of fracture surface of CFRP material by three-dimensional reconstruction methods

    International Nuclear Information System (INIS)

    Lobo, Raquel M.; Andrade, Arnaldo H.P.

    2009-01-01

    Fracture surfaces of CFRP (carbon Fiber Reinforced Polymer) materials, used in the nuclear fuel cycle, presents an elevated roughness, mainly due to the fracture mode known as pulling out, that displays pieces of carbon fibers after debonding between fiber and matrix. The fractographic analysis, by bi-dimensional images is deficient for not considering the so important vertical resolution as much as the horizontal resolution. In this case, the knowledge of this heights distribution that occurs during the breaking, can lead to the calculation of the involved energies in the process that would allows a better agreement on the fracture mechanisms of the composite material. An important solution for the material characterization, whose surface presents a high roughness due to the variation in height, is to reconstruct three-dimensionally these fracture surfaces. In this work, the 3D reconstruction was done by two different methods: the variable focus reconstruction, through a stack of images obtained by optical microscopy (OM) and the parallax reconstruction, carried through with images acquired by scanning electron microscopy (SEM). The results of both methods present an elevation map of the reconstructed image that determine the height of the surface pixel by pixel,. The results obtained by the methods of reconstruction for the CFRP surfaces, have been compared with others materials such as aluminum and copper that present a ductile type fracture surface, with lower roughness. (author)

  19. Diagnostic value of 3 D CT surface reconstruction in spinal fractures

    Energy Technology Data Exchange (ETDEWEB)

    Koesling, S. [Department of Radiology, Univ. of Leipzig (Germany); Dietrich, K. [Department of Radiology, Univ. of Leipzig (Germany); Steinecke, R. [Department of Radiology, Univ. of Leipzig (Germany); Kloeppel, R. [Department of Radiology, Univ. of Leipzig (Germany); Schulz, H.G. [Department of Radiology, Univ. of Leipzig (Germany)

    1997-02-01

    Our purpose was to evaluate the diagnostic value of three-dimensional (3 D) CT surface reconstruction in spinal fractures in comparison with axial and reformatted images. A total of 50 patients with different CT-proven spinal fractures were analysed retrospectively. Based on axial scans and reformatted images, the spinal fractures were classified according to several classifications as Magerl for the thoraco-lumbar and lower cervical spine by one radiologist. Another radiologist performed 3 D CT surface reconstructions with the aim of characterizing the different types of spinal fractures. A third radiologist classified the 3 D CT surface reconstruction according to the Magerl classification. The results of the blinded reading process were compared. It was checked to see in which type and subgroup 3 D surface reconstructions were helpful. Readers one and two obtained the same results in the classification. The 3 D surface reconstruction did not yield any additional diagnostic information concerning type A and B injuries. Indeed, the full extent of the fracture could be easier recognized with axial and reformatted images in all cases. In 10 cases of C injuries, the dislocation of parts of vertebrae could be better recognized with the help of 3 D reconstructions. A 3 D CT surface reconstruction is only useful in rotational and shear vertebral injuries (Magerl type C injury). (orig.). With 4 figs., 1 tab.

  20. Cumulative fatigue and creep-fatigue damage at 3500C on recrystallized zircaloy 4

    International Nuclear Information System (INIS)

    Brun, G.; Pelchat, J.; Floze, J.C.; Galimberti, M.

    1985-06-01

    An experimental programme undertaken by C.E.A., E.D.F. and FRAGEMA with the aim of characterizing the fatigue and creep fatigue behaviour of zircaloy-4 following annealing treatments (recrystallized, stress-delived) is in progress. The results given below concern only recrystallized material. Cyclic properties, low-cycle fatigue curves and creep behaviour laws under stresses have been established. Sequential tests of pure fatigue and creep-fatigue were performed. The cumulative life fractions at fracture depend on the sequence of leading, stress history and number of cycles of prestressing. The MINER's rule appears to be conservative with regard to a low-high loading sequence whereas it is not for the reverse high-low loading sequences. Fatigue and creep damage are not interchangeable. Pre-creep improves the fatigue resistance. Pre-fatigue improves the creep strength as long as the beneficial effect of cyclic hardening overcomes the damaging effect of surface cracking. The introduction of a tension hold time into the fatigue cycle slightly increases cyclic hardening and reduces the number of cycles to failure. For hold times of less than one hour, the sum of fatigue and creep life fractions is closed to one

  1. Fracture behaviour of a magnesium–aluminium alloy treated by selective laser surface melting treatment

    International Nuclear Information System (INIS)

    Taltavull, C.; López, A.J.; Torres, B.; Rams, J.

    2014-01-01

    Highlights: • β-Mg 17 Al 12 presents fragile fracture behavior decreasing the ductility of AZ91D. • SLSM treatment only modifies the β-Mg 17 Al 12 phase whilst α-Mg remains unaltered. • In-situ SEM bending test allows to observe and data record of the crack propagation. • Eutectic microestructure of modified β-phase presents ductile fracture behaviour. • Fracture toughness of laser treated specimen is 40% greater than as-received alloy. - Abstract: Fracture behaviour of AZ91D magnesium alloy is dominated by the brittle fracture of the β-Mg 17 Al 12 phase so its modification is required to improve the toughness of this alloy. The novel laser treatment named as Selective Laser Surface Melting (SLSM) is characterized by the microstructural modification of the β-Mg 17 Al 12 phase without altering the α-Mg matrix. We have studied the effect of the selected microstructural modification induced by the laser treatment in the fracture behaviour of the alloy has been studied using in situ Scanning Electron Microscopy bending test. This test configuration allows the in situ observation of the crack progression and the record of the load–displacement curve. It has been observed that the microstructural modification introduced by SLSM causes an increase of 40% of the fracture toughness of the treated specimen. This phenomenon can be related with the transition from brittle to ductile fracture behaviour of the laser modified β-phase

  2. Analysis of the intergranular fracture surface by the Fourier spectrum method

    Energy Technology Data Exchange (ETDEWEB)

    Hao Yao; Tian Jifeng; Wang Zhongguang (National Lab. for Fatigue and Fracture of Materials, Inst. of Metal Research, Academia Sinica, Shen Yang (China))

    1991-11-30

    A quantitative analysis of the fracture surface of a 1045 steel was undertaken in order to relate important microstructural features to brittle intergranular fractures in the steel. It was found that the character of the profile was not random but periodic. There is a direct correspondence between the Fourier spectrum of the profile and the microstructure features. Utilization of secondary-electron line scanning facilitated the analysis of the fracture surface in this case. The results of the analysis from both the profile and the scanning line showed that the first autocorrelation length is related to the average grain size and that the total power corresponds to the impact energy of the fracture. (orig.).

  3. New model for surface fracture induced by dynamical stress

    OpenAIRE

    Andersen, J. V.; Lewis, L. J.

    1997-01-01

    We introduce a model where an isotropic, dynamically-imposed stress induces fracture in a thin film. Using molecular dynamics simulations, we study how the integrated fragment distribution function depends on the rate of change and magnitude of the imposed stress, as well as on temperature. A mean-field argument shows that the system becomes unstable for a critical value of the stress. We find a striking invariance of the distribution of fragments for fixed ratio of temperature and rate of ch...

  4. Analysis of progression of fatigue conditions in biceps brachii muscles using surface electromyography signals and complexity based features.

    Science.gov (United States)

    Karthick, P A; Makaram, Navaneethakrishna; Ramakrishnan, S

    2014-01-01

    Muscle fatigue is a neuromuscular condition where muscle performance decreases due to sustained or intense contraction. It is experienced by both normal and abnormal subjects. In this work, an attempt has been made to analyze the progression of muscle fatigue in biceps brachii muscles using surface electromyography (sEMG) signals. The sEMG signals are recorded from fifty healthy volunteers during dynamic contractions under well defined protocol. The acquired signals are preprocessed and segmented in to six equal parts for further analysis. The features, such as activity, mobility, complexity, sample entropy and spectral entropy are extracted from all six zones. The results are found showing that the extracted features except complexity feature have significant variations in differentiating non-fatigue and fatigue zone respectively. Thus, it appears that, these features are useful in automated analysis of various neuromuscular activities in normal and pathological conditions.

  5. Fracture mechanics assessment of surface and sub-surface cracks in the RPV under non-symmetric PTS loading

    Energy Technology Data Exchange (ETDEWEB)

    Keim, E; Shoepper, A; Fricke, S [Siemens AG Unternehmensbereich KWU, Erlangen (Germany)

    1997-09-01

    One of the most severe loading conditions of a reactor pressure vessel (rpv) under operation is the loss of coolant accident (LOCA) condition. Cold water is injected through nozzles in the downcomer of the rpv, while the internal pressure may remain at a high level. Complex thermal hydraulic situations occur and the fluid and downcomer temperatures as well as the fluid to wall heat transfer coefficient at the inner surface are highly non-linear. Due to this non-symmetric conditions, the problem is investigated by three-dimensional non-linear finite element analyses, which allow for an accurate assessment of the postulated flaws. Transient heat transfer analyses are carried out to analyze the effect of non-symmetrical cooling of the inner surface of the pressure vessel. In a following uncoupled stress analysis the thermal shock effects for different types of defects, surface flaws and sub-surface flaws are investigated for linear elastic and elastic-plastic material behaviour. The obtained fracture parameters are calculated along the crack fronts. By a fast fracture analysis the fracture parameters at different positions along the crack front are compared to the material resistance. Safety margins are pointed out in an assessment diagram of the fracture parameters and the fracture resistance versus the transient temperature at the crack tip position. (author). 4 refs, 10 figs.

  6. The morphologies of fractured surfaces and fracture toughness in some As-Se-Sb-S-I glasses

    International Nuclear Information System (INIS)

    Lukic, S.R.; Petrovic, D.M.; Skuban, F.; Sidanin, L.; Guth, I.O.

    2006-01-01

    As part of a general physical characterization of amorphous materials in the pseudobinary system (As 2 Se 3 ) 100-x (SbSI) x type, their indentation fracture toughness was determined. It is a system with the variable ratio of classical amorphous compound As 2 Se 3 and the molecule of antimony sulfoiodide, SbSI, which in the monocrystal form is characterized as ferroelectrics. Because of chalcogenides are generally very brittle and under load they crack very easily, these glasses have been studied with the aim of examining the possibility of obtaining some new structures on the basis of the materials with amorphous internal network, the structures that will have a higher quality in respect of mechanical properties. The morphologies of fractured surfaces were investigated by scanning electron microscope

  7. The morphologies of fractured surfaces and fracture toughness in some As-Se-Sb-S-I glasses

    Energy Technology Data Exchange (ETDEWEB)

    Lukic, S.R. [Department of Physics, Faculty of Sciences, University of Novi Sad, Trg D. Obradovica 4, 21000 Novi Sad (Serbia and Montenegro)]. E-mail: svetdrag@im.ns.ac.yu; Petrovic, D.M. [Department of Physics, Faculty of Sciences, University of Novi Sad, Trg D. Obradovica 4, 21000 Novi Sad (Serbia and Montenegro); Skuban, F. [Department of Physics, Faculty of Sciences, University of Novi Sad, Trg D. Obradovica 4, 21000 Novi Sad (Serbia and Montenegro); Sidanin, L. [Department for Production Engineering, Faculty of Technical Sciences, University of Novi Sad, Trg D. Obradovica 6, 21000 Novi Sad (Serbia and Montenegro); Guth, I.O. [Department of Physics, Faculty of Sciences, University of Novi Sad, Trg D. Obradovica 4, 21000 Novi Sad (Serbia and Montenegro)

    2006-09-15

    As part of a general physical characterization of amorphous materials in the pseudobinary system (As{sub 2}Se{sub 3}){sub 100-x}(SbSI) {sub x} type, their indentation fracture toughness was determined. It is a system with the variable ratio of classical amorphous compound As{sub 2}Se{sub 3} and the molecule of antimony sulfoiodide, SbSI, which in the monocrystal form is characterized as ferroelectrics. Because of chalcogenides are generally very brittle and under load they crack very easily, these glasses have been studied with the aim of examining the possibility of obtaining some new structures on the basis of the materials with amorphous internal network, the structures that will have a higher quality in respect of mechanical properties. The morphologies of fractured surfaces were investigated by scanning electron microscope.

  8. Fatigue of coated and laser hardened steels

    International Nuclear Information System (INIS)

    La Cruz, P. de.

    1990-01-01

    In the present work the effect of ion nitriding, laser hardening and hot dip galvanizing upon the fatigue limit and notch sensitivity of a B-Mn Swedish steel SS 2131 have been investigated. The fatigue tests were performed in plane reverse bending fatigue (R=1). The quenched and tempered condition was taken as the reference condition. The microstructure, microhardness, fracture surface and coating appearance of the fatigue surface treated specimens were studied. Residual stress and retained austenite measurements were also carried out. It was found that ion nitriding improves the fatigue limit by 53 % for smooth specimens and by 115 % for notched specimens. Laser hardening improves the fatigue limit by 18 % and 56 % for smooth and notched specimen respectively. Hot dip galvanizing gives a slight deterioration of the fatigue limit (9 % and 10 % for smooth and notched specimen respectively). Ion nitriding and laser hardening decrease the value of the notch sensitivity factor q by 78 % and 65 % respectively. Hot dip galvanizing does not modify it. A simple schematic model based on a residual stress distribution, has been used to explain the different effects. It seems that the presence of the higher compressive residual stresses and the higher uniformity of the microstructure may be the causes of the better fatigue performance of ion nitrided specimens. (119 refs.) (author)

  9. Ductile cast irons: microstructure influence on fatigue crack propagation resistance

    Directory of Open Access Journals (Sweden)

    Mauro Cavallini

    2010-07-01

    Full Text Available Microstructure influence on fatigue crack propagation resistance in five different ductile cast irons (DCI was investigated. Four ferrite/pearlite volume fractions were considered, performing fatigue crack propagation tests according to ASTM E647 standard (R equals to 0.1, 0.5 and 0.75, respectively. Results were compared with an austempered DCI. Damaging micromechanisms were investigated according to the following procedures: - “traditional” Scanning Electron Microscope (SEM fracture surfaces analysis; - SEM fracture surface analysis with 3D quantitative analysis; - SEM longitudinal crack profile analysis - Light Optical Microscope (LOM transversal crack profile analysis;

  10. Properties of fracture surfaces of glassy polymers: chain scission versus chain pullout

    NARCIS (Netherlands)

    Fischer, H.R.

    2010-01-01

    Fresh fracture surfaces formed by tensile failure of craze in molded polystyrene (PS) bars have been compared with the molded surfaces of the same bars, using an atomic force microscope with a thermal probe and operated in local thermal analysis. The results indicate that molecular weight is much

  11. A comparison of tensile, fracture and fatigue mechanical behaviour of structural reinforcing bars made with different steels

    Directory of Open Access Journals (Sweden)

    Rodríguez, C.

    2013-09-01

    Full Text Available The use of austenitic stainless steels as rebar is an option increasingly used in reinforced concrete structures exposed to aggressive environments and especially those that have to work in marine environments. The same is true for duplex stainless steel rebars, although nowadays they have a lower use, mainly due to the fact that their inclusion in the reinforced concrete standards was delayed 10 years compared to austenitic stainless steel ones, and consequently their in-service behavior is not as well known. A study of the mechanical properties, including fracture toughness, fatigue behaviour and corrosion resistance in saline alkaline environments of austenitic (AISI 304LN and 316LN and duplex (D2205 stainless steel reinforcing bars was performed in this work. Bars made on a high ductility carbon steel (B500SD that are normally used to reinforce concrete were also characterized and used as a comparison. Stainless steel reinforcing bars show mechanical properties at least similar but usually higher than one of the best carbon steel re-bars (B500SD, along with a significantly higher ductility and, of course, much better corrosion behaviour in saline alkaline environments.El uso de aceros inoxidables austeníticos como armaduras de refuerzo es una opción cada vez más utilizada en estructuras de hormigón armado expuestas a ambientes agresivos y especialmente en las que han de trabajar en ambientes marinos. Lo mismo cabe decir de las armaduras de acero inoxidable dúplex, si bien su uso es menor, debido sobre todo a que su inclusión en la normativa aplicable al armado de hormigón se retrasó 10 años con respecto a los inoxidables austeníticos y, consecuentemente, su comportamiento en servicio es menos conocido. En este trabajo se analiza el comportamiento mecánico, incluyendo fractura y fatiga, así como la resistencia a la corrosión en medios que simulan un hormigón contaminado de cloruros, de armaduras fabricadas tanto con

  12. Hydraulic-fracture growth in dipping anisotropic strata as viewed through the surface deformation field

    International Nuclear Information System (INIS)

    Holzhausen, G.R.; Haase, C.S.; Stow, S.H.; Gazonas, G.

    1985-01-01

    In 1983 and 1984 Oak Rdige National Laboratory conducted a series of precision ground deformation measurements before, during, and after the generation of several large hydraulic fractures in a dipping member of the Cambrian Conasauga Shale. Each fracture was produced by the injection of approximately 500,000 L of slurry on a single day. Injection depth was 300 m. Leveling surveys were run several days before and several days after the injections. An array of eight high-precision borehole tiltmeters monitored ground deformations continuously for a period of several weeks. Analysis of the leveling and the tilt measurements revealed surface uplifts as great as 25 mm and tilts of tens of microradians during each injection. Furthermore, partial recovery (subsidence) of the ground took place during the days following an injection, accompanied by shifts in the position of maximum resultant uplift. Interpretation of the tilt measurements is consistent with stable widening and extension of hydraulic fractures with subhorizontal orientations. Comparison of the measured tilt patterns with fracture orientations established from logging of observation wells suggests that shearing parallel to the fracture planes accompanied fracture dilation. This interpretation is supported by measured tilts and ground uplifts that were as much as 100 percent greater than those expected from fracture dilation alone. Models of elastically anisotropic overburden rock do not explain the measured tilt patterns in the absence of shear stresses in the fracture planes. This work represents the first large-scale hydraulic-fracturing experiment in which the possible effects of material anisotropy and fracture-parallel shears have been measured and interpreted

  13. Hydraulic-fracture growth in dipping anisotropic strata as viewed through the surface deformation field

    International Nuclear Information System (INIS)

    Holzhausen, G.R.; Haase, C.S.; Stow, S.H.; Gazonas, G.

    1985-01-01

    In 1983 and 1984 Oak Ridge National Laboratory conducted a series of precision ground deformation measurements before, during, and after the generation of several large hydraulic fractures in a dipping member of the Cambrian Conassauga Shale. Each fracture was produced by the injection of approximately 500,000 liters of slurry on a single day. Injection depth was 300 m. Leveling surveys were run several days before and several days after the injections. An array of eight high-precision borehole tiltmeters monitored ground deformations continuously for a period of several weeks. Analysis of the leveling and the tilt measurements revealed surface uplifts as great as 25 mm and tilts of tens of microradians during each injection. Furthermore, partial recovery (subsidence) of the ground took place during the days following an injection, accompanied by shifts in the position of maximum resultant uplift. Interpretation of the tilt measurements is consistent with stable widening and extension of hydraulic fractures with subhorizontal orientations. Comparison of the measured tilt patterns with fracture orientations established from logging of observation wells suggests that shearing parallel to the fracture planes accompanied fracture dilation. This interpretation is supported by measured tilts and ground uplifts that were as much as 100 percent greater than those expected from fracture dilation alone. Models of elastically anisotropic overburden rock do not explain the measured tilt patterns in the absence of shear stresses in the fracture planes. This work represents the first large-scale hydraulic-fracturing experiment in which the possible effects of material anisotropy and fracture-parallel shears have been measured and interpreted

  14. Structural integrity of additive materials: Microstructure, fatigue behavior, and surface processing

    Science.gov (United States)

    Book, Todd A.

    Although Additive Manufacturing (AM) offers numerous performance advantages over existing methods, AM structures are not being utilized for critical aerospace and mechanical applications due to uncertainties in their structural integrity as a result of the microstructural variations and defects arising from the AM process itself. Two of these uncertainties are the observed scatter in tensile strength and fatigue lives of direct metal laser sintering (DMLS) parts. With strain localization a precursor for material failure, this research seeks to explore the impact of microstructural variations in DMLS produced materials on strain localization. The first part of this research explores the role of the microstructure in strain localization of DMLS produced IN718 and Ti6Al4V specimens (as-built and post-processed) through the characterization of the linkage between microstructural variations, and the accumulation of plastic strain during monotonic and low cycle fatigue loading. The second part of this research explores the feasibility for the application of select surface processing techniques in-situ during the DMLS build process to alter the microstructure in AlSi10Mg to reduce strain localization and improve material cohesion. This study is based on utilizing experimental observations through the employment of advanced material characterization techniques such as digital image correlation to illustrate the impacts of DMLS microstructural variation.

  15. Radiation effects on low cycle fatigue properties of reduced activation ferritic/martensitic steels

    International Nuclear Information System (INIS)

    Hirose, T.; Tanigawa, H.; Ando, M.; Kohyama, A.; Katoh, Y.; Narui, M.

    2002-01-01

    The reduced activation ferritic/martensitic steel, RAFs F82H IEA heat has been fatigue-tested at ambient temperature under diametral strain controlled conditions. In order to evaluate the effects of radiation damage and transmutation damage on fatigue characteristics, post-neutron irradiation and post-helium ion implantation fatigue tests were carried out. Fracture surfaces and fatigue crack initiation on the specimen surface were observed by SEM. Low-temperature irradiation caused an increase in stress amplitude and a reduction in fatigue lifetime corresponding to radiation hardening and loss of ductility. Neutron irradiated samples showed brittle fracture surface, and it was significant for large strain tests. On the other hand, helium implantation caused delay of cyclic softening. However, brittle crack initiation and propagation did not depend on the helium concentration profiles

  16. Influence of surface finish on the high cycle fatigue behavior of a 304L austenitic stainless steel

    International Nuclear Information System (INIS)

    Petitjean, S.

    2003-06-01

    This work has dealt with the influence of surface finish on the high cycle fatigue behavior of a 304L. The role played by roughness, surface hardening and residual stresses has been particularly described. First part of this study has consisted of the production of several surface finishes. These latter were obtained by turning, grinding, mechanical polishing and sandblasting. The obtained surfaces were then characterised in terms of roughness, hardening, microstructure and residual stresses. Fatigue tests were finally conducted under various stress ratios or mean stresses at two temperatures (25 C and 300 C). Results clearly evidenced an effect of the surface integrity on the fatigue resistance of the 304L. This influence is nevertheless more pronounced at ambient temperature and for a positive mean stress. For all explored testing conditions, the lowest endurance limit was obtained for ground specimens whereas polished samples exhibited the best fatigue strength. Results also cleared out a detrimental influence of a positive mean stress in the case of specimens having surface defaults of a great acuity. The study of the relative effect of each of the surface parameter, under a positive stress ratio and at the ambient temperature, showed that roughness profile and surface hardening are the two more influential factors. The role of the residual stresses remains negligible due to their rapid relaxation during the application of the first cycles of fatigue. The estimation of the initiation and propagation periods showed that mechanisms differed as a function of the applied stress ratio. Crack propagation is governed by the parameter DK at a positive stress ratio and by Dep/2 in the case of tension-compression tests. (author)

  17. Monitoring massive fracture growth at 2-km depths using surface tiltmeter arrays

    Science.gov (United States)

    Wood, M.D.

    1979-01-01

    Tilt due to massive hydraulic fractures induced in sedimentary rocks at depths of up to 2.2 km have been recorded by surface tiltmeters. Injection of fluid volumes up to 4 ?? 105 liters and masses of propping agent up to 5 ?? 105 kg is designed to produce fractures approximately 1 km long, 50-100 m high and about 1 cm wide. The surface tilt data adequately fit a dislocation model of a tensional fault in a half-space. Theoretical and observational results indicate that maximum tilt occurs at a distance off the strike of the fracture equivalent to 0.4 of the depth to the fracture. Azimuth and extent of the fracture deduced from the geometry of the tilt field agree with other kinds of geophysical measurements. Detailed correlation of the tilt signatures with pumping parameters (pressure, rate, volume, mass) have provided details on asymmetry in geometry and growth rate. Whereas amplitude variations in tilt vary inversely with the square of the depth, changes in flow rate or pressure gradient can produce a cubic change in width. These studies offer a large-scale experimental approach to the study of problems involving fracturing, mass transport, and dilatancy processes. ?? 1979.

  18. School playground surfacing and arm fractures in children: a cluster randomized trial comparing sand to wood chip surfaces.

    Directory of Open Access Journals (Sweden)

    Andrew W Howard

    2009-12-01

    Full Text Available The risk of playground injuries, especially fractures, is prevalent in children, and can result in emergency room treatment and hospital admissions. Fall height and surface area are major determinants of playground fall injury risk. The primary objective was to determine if there was a difference in playground upper extremity fracture rates in school playgrounds with wood fibre surfacing versus granite sand surfacing. Secondary objectives were to determine if there were differences in overall playground injury rates or in head injury rates in school playgrounds with wood fibre surfacing compared to school playgrounds with granite sand surfacing.The cluster randomized trial comprised 37 elementary schools in the Toronto District School Board in Toronto, Canada with a total of 15,074 students. Each school received qualified funding for installation of new playground equipment and surfacing. The risk of arm fracture from playground falls onto granitic sand versus onto engineered wood fibre surfaces was compared, with an outcome measure of estimated arm fracture rate per 100,000 student-months. Schools were randomly assigned by computer generated list to receive either a granitic sand or an engineered wood fibre playground surface (Fibar, and were not blinded. Schools were visited to ascertain details of the playground and surface actually installed and to observe the exposure to play and to periodically monitor the depth of the surfacing material. Injury data, including details of circumstance and diagnosis, were collected at each school by a prospective surveillance system with confirmation of injury details through a validated telephone interview with parents and also through collection (with consent of medical reports regarding treated injuries. All schools were recruited together at the beginning of the trial, which is now closed after 2.5 years of injury data collection. Compliant schools included 12 schools randomized to Fibar that installed

  19. Fracture strength and probability of survival of narrow and extra-narrow dental implants after fatigue testing: In vitro and in silico analysis.

    Science.gov (United States)

    Bordin, Dimorvan; Bergamo, Edmara T P; Fardin, Vinicius P; Coelho, Paulo G; Bonfante, Estevam A

    2017-07-01

    To assess the probability of survival (reliability) and failure modes of narrow implants with different diameters. For fatigue testing, 42 implants with the same macrogeometry and internal conical connection were divided, according to diameter, as follows: narrow (Ø3.3×10mm) and extra-narrow (Ø2.9×10mm) (21 per group). Identical abutments were torqued to the implants and standardized maxillary incisor crowns were cemented and subjected to step-stress accelerated life testing (SSALT) in water. The use-level probability Weibull curves, and reliability for a mission of 50,000 and 100,000 cycles at 50N, 100, 150 and 180N were calculated. For the finite element analysis (FEA), two virtual models, simulating the samples tested in fatigue, were constructed. Loading at 50N and 100N were applied 30° off-axis at the crown. The von-Mises stress was calculated for implant and abutment. The beta (β) values were: 0.67 for narrow and 1.32 for extra-narrow implants, indicating that failure rates did not increase with fatigue in the former, but more likely were associated with damage accumulation and wear-out failures in the latter. Both groups showed high reliability (up to 97.5%) at 50 and 100N. A decreased reliability was observed for both groups at 150 and 180N (ranging from 0 to 82.3%), but no significant difference was observed between groups. Failure predominantly involved abutment fracture for both groups. FEA at 50N-load, Ø3.3mm showed higher von-Mises stress for abutment (7.75%) and implant (2%) when compared to the Ø2.9mm. There was no significant difference between narrow and extra-narrow implants regarding probability of survival. The failure mode was similar for both groups, restricted to abutment fracture. Copyright © 2017 Elsevier Ltd. All rights reserved.

  20. Probabilistic fracture mechanics of nuclear structural components. Consideration of transition from embedded crack to surface crack

    International Nuclear Information System (INIS)

    Yagawa, Genki; Yoshimura, Shinobu; Kanto, Yasuhiro

    1998-01-01

    This paper describes a probabilistic fracture mechanics (PFM) analysis of aged nuclear reactor pressure vessel (RPV) material. New interpolation formulas are first derived for both embedded elliptical surface cracks and semi-elliptical surface cracks. To investigate effects of transition from embedded crack to surface crack in PFM analyses, one of PFM round-robin problems set by JSME-RC111 committee, i.e. 'aged RPV under normal and upset operating conditions' is solved, employing the interpolation formulas. (author)

  1. Experimental study of microstructure changes due to low cycle fatigue of a steel nanocrystallised by Surface Mechanical Attrition Treatment (SMAT)

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Z. [ICD, P2MN, LASMIS, University of Technology of Troyes, UMR 6281, CNRS, Troyes (France); Retraint, D., E-mail: delphine.retraint@utt.fr [ICD, P2MN, LASMIS, University of Technology of Troyes, UMR 6281, CNRS, Troyes (France); Baudin, T.; Helbert, A.L.; Brisset, F. [ICMMO, Univ Paris-Sud, Université Paris-Saclay, UMR CNRS 8182, 91405 Orsay Cedex (France); Chemkhi, M.; Zhou, J. [ICD, P2MN, LASMIS, University of Technology of Troyes, UMR 6281, CNRS, Troyes (France); Kanouté, P. [ICD, P2MN, LASMIS, University of Technology of Troyes, UMR 6281, CNRS, Troyes (France); ONERA, The French Aerospace Lab, 29 avenue de la Division Leclerc, 92322 Chatillon Cedex (France)

    2017-02-15

    Electron Backscatter Diffraction technique is used to characterize the microstructure of 316L steel generated by Surface Mechanical Attrition Treatment (SMAT) before and after low cycle fatigue tests. A grain size gradient is generated from the top surface to the interior of the samples after SMAT so that three main regions can be distinguished below the treated surface: (i) the ultra-fine grain area within 5 μm under the top surface with preferably oriented grains, (ii) the intermediate area where the original grains are partially transformed, and (iii) the edge periphery area where the original grains are just mechanically deformed with the presence of plastic slips. Fatigue tests show that cyclic loading does not change the grain orientation spread and does not activate any plastic slip in the ultra-fine grain top surface area induced by SMAT. On the opposite, in the plastically SMAT affected region including the intermediate area and the edge periphery area, new slip systems are activated by low cycle fatigue while the grain orientation spread is increased. These results represent a first very interesting step towards the characterization and understanding of mechanical mechanisms involved during the fatigue of a grain size gradient material. - Highlights: •LCF tests are carried out on specimens processed by SMAT. •EBSD is used to investigate microstructural changes induced by LCF. •A grain size gradient is generated by SMAT from surface to the bulk of the fatigue samples. •New slip systems are activated by LCF and GOS is increased in plastically deformed region. •However, these phenomena are not observed in the top surface ultra-fine grain area.

  2. Experimental study of microstructure changes due to low cycle fatigue of a steel nanocrystallised by Surface Mechanical Attrition Treatment (SMAT)

    International Nuclear Information System (INIS)

    Sun, Z.; Retraint, D.; Baudin, T.; Helbert, A.L.; Brisset, F.; Chemkhi, M.; Zhou, J.; Kanouté, P.

    2017-01-01

    Electron Backscatter Diffraction technique is used to characterize the microstructure of 316L steel generated by Surface Mechanical Attrition Treatment (SMAT) before and after low cycle fatigue tests. A grain size gradient is generated from the top surface to the interior of the samples after SMAT so that three main regions can be distinguished below the treated surface: (i) the ultra-fine grain area within 5 μm under the top surface with preferably oriented grains, (ii) the intermediate area where the original grains are partially transformed, and (iii) the edge periphery area where the original grains are just mechanically deformed with the presence of plastic slips. Fatigue tests show that cyclic loading does not change the grain orientation spread and does not activate any plastic slip in the ultra-fine grain top surface area induced by SMAT. On the opposite, in the plastically SMAT affected region including the intermediate area and the edge periphery area, new slip systems are activated by low cycle fatigue while the grain orientation spread is increased. These results represent a first very interesting step towards the characterization and understanding of mechanical mechanisms involved during the fatigue of a grain size gradient material. - Highlights: •LCF tests are carried out on specimens processed by SMAT. •EBSD is used to investigate microstructural changes induced by LCF. •A grain size gradient is generated by SMAT from surface to the bulk of the fatigue samples. •New slip systems are activated by LCF and GOS is increased in plastically deformed region. •However, these phenomena are not observed in the top surface ultra-fine grain area.

  3. Fracture surface analysis on nano-SiO{sub 2}/epoxy composite

    Energy Technology Data Exchange (ETDEWEB)

    Zhao Rongguo [Institute of Fundamental Mechanics and Material Engineering, Xiangtan University, Hunan 411105 (China); Key Laboratory of Low Dimensional Materials and Application Technology, Xiangtan University, Ministry of Education, Hunan 411105 (China)], E-mail: zhaorongguo@xtu.edu.cn; Luo Wenbo [Institute of Fundamental Mechanics and Material Engineering, Xiangtan University, Hunan 411105 (China); Key Laboratory of Low Dimensional Materials and Application Technology, Xiangtan University, Ministry of Education, Hunan 411105 (China)

    2008-06-15

    Fracture surface morphologies of nano-SiO{sub 2}/epoxy composite with different weight percentage of SiO{sub 2} are investigated using scanning electron microscopy. Two types of curing agent, dimethylbenzanthracene (DMBA) and methyltetrahydrophthalic anhydride (MeTHPA), are individually used for preparing the composites. It is found that the fracture surface morphology of the composite cured by DMBA shows as radial striations, which suggests a rapid brittle fracture mode, while the fracture surface morphology of the composite cured by MeTHPA shows as regularly spaced 'rib' markings, which indicates a stick-slip motion during the fracture process. Furthermore, the uniaxial tensile behavior under constant loading rate and ambient temperature are investigated. It is shown that the elastic modulus of the composite cured by DMBA firstly increases, and then decreases with the mass fraction of nano-SiO{sub 2} particles, but the elongation of the composite cured by MeTHPA is reversed with increasing fraction of nano-SiO{sub 2} particles. For nano-SiO{sub 2}/epoxy composite cured with MeTHPA that possesses a suitable fraction of nano-SiO{sub 2}, an excellent synthetic mechanical property on elastic modulus and elongation is obtained.

  4. Investigation on effect of laser shock processing on fatigue crack initiation and its growth in aluminum alloy plate

    International Nuclear Information System (INIS)

    Zhang, X.Q.; Li, H.; Yu, X.L.; Zhou, Y.; Duan, S.W.; Li, S.Z.; Huang, Z.L.; Zuo, L.S.

    2015-01-01

    Highlights: • LSP can greatly delay crack formation. • The micro-crack growing processes and its fracture are showed clearly. • Surface topographies and crack initiation locations are displayed. - Abstract: A series of contrasting experiments were carried out to examine the effects of laser shock processing (LSP) on fatigue properties of slot in 7075-T6 aluminum alloy plate. Both side surfaces of slot were subjected to LSP. The surface topographies were observed and the residual stresses were tested. The treated and the un-treated specimens were pulled by the fatigue cyclic loading respectively. The fatigue crack propagating processes were recorded, and the fatigue fracture microscopic morphologies were analyzed by scanning electron microscope (SEM). Experimental results and analyses show that LSP induces micro-dent on surface and squeezes the compressive residual stresses into surface layer of specimen. It can remarkably delay the micro-crack formation, and transfer the location of fatigue crack initiation from top surface to sub-surface. The spacing of fatigue striations on the treated specimen fatigue fracture obviously decreases. Therefore, the fatigue life of specimen after LSP treatment significantly increases

  5. Low cycle fatigue behavior of die cast Mg-Al-Mn-Ce magnesium alloy

    Directory of Open Access Journals (Sweden)

    Wu Wei

    2013-11-01

    Full Text Available Fatigue failure is a main failure mode for magnesium and other alloys. It is beneficial for fatigue design and fatigue life improvement to investigate the low cycle fatigue behavior of magnesium alloys. In order to investigate the low cycle fatigue behavior of die cast Mg-Al-Mn-Ce magnesium alloy, the strain controlled fatigue experiments were performed at room temperature and fatigue fracture surfaces of specimens were observed with scanning election microscopy for the alloys under die-cast and aged states. Cyclic stress response curves, strain amplitude versus reversals to failure curve, total strain amplitude versus fatigue life curves and cyclic stress-strain curves of Mg-Al-Mn-Ce alloys were analyzed. The results show that the Mg-Al-Mn-Ce alloys under die-cast (F and aged (T5 states exhibit cyclic strain hardening under the applied total strain amplitudes, and aging treatment could greatly increase the cyclic stress amplitudes of die cast Mg-Al-Mn-Ce alloys. The relationships between the plastic strain amplitude, the elastic strain amplitude and reversals to failure of Mg-Al-Mn-Ce magnesium alloy under different treatment states could be described by Coffin-Manson and Basquin equations, respectively. Observations on the fatigue fracture surface of specimens reveal that the fatigue cracks initiate on the surface of specimens and propagate transgranularly.

  6. Statistical Distribution of Fatigue Life for Cast TiAl Alloy

    Directory of Open Access Journals (Sweden)

    WAN Wenjuan

    2016-08-01

    Full Text Available Statistic distribution of fatigue life data and its controls of cast Ti-47.5Al-2.5V-1.0Cr-0.2Zr (atom fraction/% alloy were investigated. Fatigue tests were operated by means of load-controlled rotating bending fatigue tests (R=-1 performed at a frequency of 100 Hz at 750 ℃ in air. The fracture mechanism was analyzed by observing the fracture surface morphologies through scanning electron microscope,and the achieved fatigue life data were analyzed by Weibull statistics. The results show that the fatigue life data present a remarkable scatter ranging from 103 to 106 cycles, and distribute mainly in short and long life regime. The reason for this phenomenon is that the fatigue crack initiators are different with different specimens. The crack initiators for short-life specimens are caused by shrinkage porosity, and for long-life ones are caused by bridged porosity interface and soft-oriented lamellar interface. Based on the observation results of fracture surface, two-parameter Weibull distribution model for fatigue life data can be used for the prediction of fatigue life at a certain failure probability. It has also shown that the shrinkage porosity causes the most detrimental effect to fatigue life.

  7. On the formation and nature of quasi-cleavage fracture surfaces in hydrogen embrittled steels

    Energy Technology Data Exchange (ETDEWEB)

    Martin, May L.; Fenske, Jamey A.; Liu, Grace S.; Sofronis, Petros [University of Illinois, Dept. of Materials Science and Engineering, 1304 W. Green St., Urbana, IL 61801 (United States); Robertson, Ian M., E-mail: ianr@illinois.edu [University of Illinois, Dept. of Materials Science and Engineering, 1304 W. Green St., Urbana, IL 61801 (United States)

    2011-02-15

    Quasi-cleavage, a common feature of hydrogen-induced fracture surfaces, is generally taken as being cleavage-like but not along a known cleavage plane. Despite the frequency with which this surface is observed, the relationship to the underlying microstructure remains unknown. Through a combination of topographical reconstruction of secondary electron microscope fractographs and a transmission electron microscopy study of the microstructure from site-specific locations, it will be shown that the features on quasi-cleavage surfaces are ridges that can be correlated with sub-surface intense and highly localized deformation bands. It will be demonstrated that the fracture surface arises from the growth and coalescence of voids that initiate at and extend along slip band intersections. This mechanism and process is fully consistent with hydrogen enhancing and localizing plastic processes.

  8. Systematic investigation of the fatigue performance of a friction stir welded low alloy steel

    International Nuclear Information System (INIS)

    Toumpis, Athanasios; Galloway, Alexander; Molter, Lars; Polezhayeva, Helena

    2015-01-01

    Highlights: • The fatigue behaviour of a friction stir welded low alloy steel has been assessed. • The welds’ fatigue lives outperform the International Institute of Welding’s recommendations for fusion welds. • The slow weld exhibits the best fatigue performance of the investigated welds. • Fracture surface analysis shows that minor embedded flaws do not offer crack initiation sites. • Process-related surface breaking flaws have a significant effect on the fatigue life. - Abstract: A comprehensive fatigue performance assessment of friction stir welded DH36 steel has been undertaken to address the relevant knowledge gap for this process on low alloy steel. A detailed set of experimental procedures specific to friction stir welding has been put forward, and the consequent study extensively examined the weld microstructure and hardness in support of the tensile and fatigue testing. The effect of varying welding parameters was also investigated. Microstructural observations have been correlated to the weldments’ fatigue behaviour. The typical fatigue performance of friction stir welded steel plates has been established, exhibiting fatigue lives well above the weld detail class of the International Institute of Welding even for tests at 90% of yield strength, irrespective of minor instances of surface breaking flaws which have been identified. An understanding of the manner in which these flaws impact on the fatigue performance has been established, concluding that surface breaking irregularities such as these produced by the tool shoulder’s features on the weld top surface can be the dominant factor for crack initiation under fatigue loading

  9. Influence of different surface treatments on the fracture toughness of a commercial ZTA dental ceramic

    Directory of Open Access Journals (Sweden)

    Flavio Teixeira da Silva

    2007-03-01

    Full Text Available The objective of this study was to investigate how mechanical surface treatments performed for removal of excess of molten glass, influence the fracture toughness of a dental zirconia toughened alumina (In-Ceram® Zirconia. Infiltrated ZTA disks were submitted to three different surface treatments (grinding, sandblasting and grinding + sandblasting + annealing. Fracture toughness was accessed through indentation strength test (IS. X ray diffraction was used to investigate the metastability of tetragonal zirconia particles under all treatments proposed. Kruskall-Wallis non-parametrical test and Weibull statistics were used to analyze the results. Grinding (group 1 introduced defects which decreased the fracture toughness and reliability, presenting the lowest K IC. On the other hand, grinding followed by sandblasting and annealing (group 3 presented the highest K IC. Sandblasting (group 2 presented the highest reliability but lower K IC compared to group 3.

  10. Effect of helium on fatigue crack growth and life of reduced activation ferritic/martensitic steel

    International Nuclear Information System (INIS)

    Nogami, Shuhei; Takahashi, Manabu; Hasegawa, Akira; Yamazaki, Masanori

    2013-01-01

    The effects of helium on the fatigue life, micro-crack growth behavior up to final fatigue failure, and fracture mode under fatigue in the reduced activation ferritic/martensitic steel, F82H IEA-heat, were investigated by low cycle fatigue tests at room temperature in air at a total strain range of 0.6–1.5%. Significant reduction of the fatigue life due to helium implantation was observed for a total strain range of 1.0–1.5%, which might be attributable to an increase in the micro-crack propagation rate. However, the reduction of fatigue life due to helium implantation was not significant for a total strain range of 0.6–0.8%. A brittle fracture surface (an original point of micro-crack initiation) and a cleavage fracture surface were observed in the helium-implanted region of fracture surface. A striation pattern was observed in the non-implanted region. These fracture modes of the helium-implanted specimen were independent of the strain range

  11. Fracture behavior of circumferentially surface-cracked elbows. Technical report, October 1993--March 1996

    International Nuclear Information System (INIS)

    Kilinski, T.; Mohan, R.; Rudland, D.; Fleming, M.

    1996-12-01

    This report presents the results from Task 2 of the Second International Piping Integrity Research Group (IPIRG-2) program. The focus of the Task 2 work was directed towards furthering the understanding of the fracture behavior of long-radius elbows. This was accomplished through a combined analytical and experimental program. J-estimation schemes were developed for both axial and circumferential surface cracks in elbows. Large-scale, quasi-static and dynamic, pipe-system, elbow fracture experiments under combined pressure and bending loads were performed on elbows containing an internal surface crack at the extrados. In conjunction with the elbow experiments, material property data were developed for the A106-90 carbon steel and WP304L stainless steel elbow materials investigated. A comparison of the experimental data with the maximum stress predictions using existing straight pipe fracture prediction analysis methods, and elbow fracture prediction methods developed in this program was performed. This analysis was directed at addressing the concerns regarding the validity of using analysis predictions developed for straight pipe to predict the fracture stresses of cracked elbows. Finally, a simplified fitting flaw acceptance criteria incorporating ASME B2 stress indices and straight pipe, circumferential-crack analysis was developed

  12. Fracture behavior of circumferentially surface-cracked elbows. Technical report, October 1993--March 1996

    Energy Technology Data Exchange (ETDEWEB)

    Kilinski, T.; Mohan, R.; Rudland, D.; Fleming, M. [and others

    1996-12-01

    This report presents the results from Task 2 of the Second International Piping Integrity Research Group (IPIRG-2) program. The focus of the Task 2 work was directed towards furthering the understanding of the fracture behavior of long-radius elbows. This was accomplished through a combined analytical and experimental program. J-estimation schemes were developed for both axial and circumferential surface cracks in elbows. Large-scale, quasi-static and dynamic, pipe-system, elbow fracture experiments under combined pressure and bending loads were performed on elbows containing an internal surface crack at the extrados. In conjunction with the elbow experiments, material property data were developed for the A106-90 carbon steel and WP304L stainless steel elbow materials investigated. A comparison of the experimental data with the maximum stress predictions using existing straight pipe fracture prediction analysis methods, and elbow fracture prediction methods developed in this program was performed. This analysis was directed at addressing the concerns regarding the validity of using analysis predictions developed for straight pipe to predict the fracture stresses of cracked elbows. Finally, a simplified fitting flaw acceptance criteria incorporating ASME B2 stress indices and straight pipe, circumferential-crack analysis was developed.

  13. Fatigue of Austempered Ductile Iron with Two Strength Grades in Very High Cycle Regime

    Science.gov (United States)

    Zhang, Jiwang; Li, Wei; Song, Qingpeng; Zhang, Ning; Lu, Liantao

    2016-03-01

    In this study, Austempered ductile irons (ADIs) with two different strength grades were produced and the fatigue properties were measured at 109 cycles. The results show that the S-N curves give a typical step-wise shape and there is no fatigue limit in the very high cycle fatigue regime. The two grades ADI have the similar fracture behaviors and fatigue failure can initiate from defects at specimen surface and subsurface zone. On the fracture surfaces of some specimens, the `granular-bright-facet' area with rich carbon distribution is observed in the vicinity of the defect. The microstructure affects the crack behaviors at the early propagation stage. The ADI with upper and lower bainite shows higher fatigue strength compared with the ADI with coarse upper bainite.

  14. Quantitative estimation of muscle fatigue using surface electromyography during static muscle contraction.

    Science.gov (United States)

    Soo, Yewguan; Sugi, Masao; Nishino, Masataka; Yokoi, Hiroshi; Arai, Tamio; Kato, Ryu; Nakamura, Tatsuhiro; Ota, Jun

    2009-01-01

    Muscle fatigue is commonly associated with the musculoskeletal disorder problem. Previously, various techniques were proposed to index the muscle fatigue from electromyography signal. However, quantitative measurement is still difficult to achieve. This study aimed at proposing a method to estimate the degree of muscle fatigue quantitatively. A fatigue model was first constructed using handgrip dynamometer by conducting a series of static contraction tasks. Then the degree muscle fatigue can be estimated from electromyography signal with reasonable accuracy. The error of the estimated muscle fatigue was less than 10% MVC and no significant difference was found between the estimated value and the one measured using force sensor. Although the results were promising, there were still some limitations that need to be overcome in future study.

  15. Effects of Ultrasonics-Assisted Face Milling on Surface Integrity and Fatigue Life of Ni-Alloy 718

    Science.gov (United States)

    Suárez, Alfredo; Veiga, Fernando; de Lacalle, Luis N. López; Polvorosa, Roberto; Lutze, Steffen; Wretland, Anders

    2016-11-01

    This work investigates the effects of ultrasonic vibration-assisted milling on important aspects such us material surface integrity, tool wear, cutting forces and fatigue resistance. As an alternative to natural application of ultrasonic milling in brittle materials, in this study, ultrasonics have been applied to a difficult-to-cut material, Alloy 718, very common in high-temperature applications. Results show alterations in the sub-superficial part of the material which could influence fatigue resistance of the material, as it has been observed in a fatigue test campaign of specimens obtained with the application of ultrasonic milling in comparison with another batch obtained applying conventional milling. Tool wear pattern was found to be very similar for both milling technologies, concluding the study with the analysis of cutting forces, exhibiting certain improvement in case of the application of ultrasonic milling with a more stable evolution.

  16. Computation and Evaluation of Features of Surface Electromyogram to Identify the Force of Muscle Contraction and Muscle Fatigue

    Directory of Open Access Journals (Sweden)

    Sridhar P. Arjunan

    2014-01-01

    Full Text Available The relationship between force of muscle contraction and muscle fatigue with six different features of surface electromyogram (sEMG was determined by conducting experiments on thirty-five volunteers. The participants performed isometric contractions at 50%, 75%, and 100% of their maximum voluntary contraction (MVC. Six features were considered in this study: normalised spectral index (NSM5, median frequency, root mean square, waveform length, normalised root mean square (NRMS, and increase in synchronization (IIS index. Analysis of variance (ANOVA and linear regression analysis were performed to determine the significance of the feature with respect to the three factors: muscle force, muscle fatigue, and subject. The results show that IIS index of sEMG had the highest correlation with muscle fatigue and the relationship was statistically significant (P0.05.

  17. Computation and evaluation of features of surface electromyogram to identify the force of muscle contraction and muscle fatigue.

    Science.gov (United States)

    Arjunan, Sridhar P; Kumar, Dinesh K; Naik, Ganesh

    2014-01-01

    The relationship between force of muscle contraction and muscle fatigue with six different features of surface electromyogram (sEMG) was determined by conducting experiments on thirty-five volunteers. The participants performed isometric contractions at 50%, 75%, and 100% of their maximum voluntary contraction (MVC). Six features were considered in this study: normalised spectral index (NSM5), median frequency, root mean square, waveform length, normalised root mean square (NRMS), and increase in synchronization (IIS) index. Analysis of variance (ANOVA) and linear regression analysis were performed to determine the significance of the feature with respect to the three factors: muscle force, muscle fatigue, and subject. The results show that IIS index of sEMG had the highest correlation with muscle fatigue and the relationship was statistically significant (P 0.05).

  18. Accelerated ultrasonic fatigue testing applications and research trends

    Energy Technology Data Exchange (ETDEWEB)

    Cho, In Sik; Shin, Choongshig; Kim, Jong Yup; Jeon, Yongho [Ajou Univ., Gyeonggi (Somalia)

    2012-06-15

    Very high cycle fatigue (VHCF) behavior of aerospace components has emerged much attention due to their long service life. In this study, a piezoelectric ultrasonic fatigue testing (UFT) system has been developed by Mbrosiatec Co., Ltd. to study the high cycle fatigue (HCF) strength of Ti 6Al 4V alloy. Hourglass shaped specimens have been investigated in the range from 10'6' to 10'9' cycles at room temperature under completely reversed R=-1 loading conditions, Scanning electron microscopy (SEM) analysis revealed that failures occurred in the entire range up to the gigacycle regime, and the fractures have been found to be initiated from the surface, unlike in steels. However, it was found from the SEM microgprahs that microcracks transformed into intergranular fractures. Thus, it can be concluded from according to the results that this test method can be applicable to commercialized automotive and railroad parts that require high cycle fatigue strength.

  19. Accelerated ultrasonic fatigue testing applications and research trends

    International Nuclear Information System (INIS)

    Cho, In Sik; Shin, Choongshig; Kim, Jong Yup; Jeon, Yongho

    2012-01-01

    Very high cycle fatigue (VHCF) behavior of aerospace components has emerged much attention due to their long service life. In this study, a piezoelectric ultrasonic fatigue testing (UFT) system has been developed by Mbrosiatec Co., Ltd. to study the high cycle fatigue (HCF) strength of Ti 6Al 4V alloy. Hourglass shaped specimens have been investigated in the range from 10'6' to 10'9' cycles at room temperature under completely reversed R=-1 loading conditions, Scanning electron microscopy (SEM) analysis revealed that failures occurred in the entire range up to the gigacycle regime, and the fractures have been found to be initiated from the surface, unlike in steels. However, it was found from the SEM microgprahs that microcracks transformed into intergranular fractures. Thus, it can be concluded from according to the results that this test method can be applicable to commercialized automotive and railroad parts that require high cycle fatigue strength

  20. The Statistic Test on Influence of Surface Treatment to Fatigue Lifetime with Limited Data

    OpenAIRE

    Suhartono, Agus

    2009-01-01

    Justifications on the influences of two or more parameters on fatigue strength are some times problematic due to the scatter nature of the fatigue data. Statistic test can facilitate the evaluation, whether the changes in material characteristics as a result of specific parameters of interest is significant. The statistic tests were applied to fatigue data of AISI 1045 steel specimens. The specimens are consisted of as received specimen, shot peened specimen with 15 and 16 Almen intensity as ...

  1. Improvement of the fatigue strength of AISI 4140 steel by an ion nitriding process

    Energy Technology Data Exchange (ETDEWEB)

    Celik, A. [Atatuerk Univ., Erzurum (Turkey). Dept. of Mech. Eng.; Karadeniz, S. [Dokuz Eyluel Univ., Izmir (Turkey). Dept. of Mech. Eng.

    1995-06-01

    The influence of plasma nitriding on the fatigue behaviour of AISI 4140 low-alloy steel was investigated under varying process conditions of temperature (500-600 C), time (1-12 h), heat treatment before ion nitriding (quenched and tempered, normalized) and gas mixture (50% H{sub 2}-50% N{sub 2}). A rotating bending fatigue machine was used to determine the fatigue strength. It was found that the plasma nitriding improves the fatigue strength and increases the fatigue limit depending on the surface hardness of the case depth. The microstructure of surface and diffusion layers was examined by optical microscopy. The fracture surface of specimens and the origin of fatigue cracks were observed by scanning electron microscopy.

  2. Fracture Surface Morphology Under Ductile Tearing of Metal Plates

    DEFF Research Database (Denmark)

    Kacar, Muhammet F.; Tekoglu, Cihan; Nielsen, Kim Lau

    2017-01-01

    The present work takes as offset the hypothesis that microstructural parameters, related to particle size and distribution, govern the transition between crack surface morphologies observed in experiments. The key question is; why does tearing of a given metal plate leave a specific morphology...

  3. 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.

  4. 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

  5. Fracture Surface Morphology and Impact Strength of Cellulose/PLA Composites.

    Science.gov (United States)

    Gao, Honghong; Qiang, Tao

    2017-06-07

    Polylactide (PLA)-based composite materials reinforced with ball-milled celluloses were manufactured by extrusion blending followed by injection molding. Their surface morphology from impact fracture were imaged with scanning electron microscopy (SEM) and investigated by calculating their fractal dimensions. Then, linear regression was used to explore the relationship between fractal dimension and impact strength of the resultant cellulose/PLA composite materials. The results show that filling the ball-milled celluloses into PLA can improve the impact toughness of PLA by a minimum of 38%. It was demonstrated that the fracture pattern of the cellulose/PLA composite materials is different from that of pristine PLA. For the resultant composite materials, the fractal dimension of the impact fractured surfaces increased with increasing filling content and decreasing particle size of the ball-milled cellulose particles. There were highly positive correlations between fractal dimension of the fractured surfaces and impact strength of the cellulose/PLA composites. However, the linearity between fractal dimension and impact strength were different for the different methods, due to their different R-squared values. The approach presented in this work will help to understand the structure-property relationships of composite materials from a new perspective.

  6. Creep, Fatigue and Fracture Behavior of Environmental Barrier Coating and SiC-SiC Ceramic Matrix Composite Systems: The Role of Environment Effects

    Science.gov (United States)

    Zhu, Dongming; Ghosn, Louis J.

    2015-01-01

    Advanced environmental barrier coating (EBC) systems for low emission SiCSiC CMC combustors and turbine airfoils have been developed to meet next generation engine emission and performance goals. This presentation will highlight the developments of NASAs current EBC system technologies for SiC-SiC ceramic matrix composite combustors and turbine airfoils, their performance evaluation and modeling progress towards improving the engine SiCSiC component temperature capability and long-term durability. Our emphasis has also been placed on the fundamental aspects of the EBC-CMC creep and fatigue behaviors, and their interactions with turbine engine oxidizing and moisture environments. The EBC-CMC environmental degradation and failure modes, under various simulated engine testing environments, in particular involving high heat flux, high pressure, high velocity combustion conditions, will be discussed aiming at quantifying the protective coating functions, performance and durability, and in conjunction with damage mechanics and fracture mechanics approaches.

  7. Tidal Disruption of Phobos as the Cause of Surface Fractures

    Science.gov (United States)

    Hurford, T. A.; Asphaug, E.; Spitale, J. N.; Hemingway, D.; Rhoden, A. R.; Henning, W. G.; Bills, B. G.; Kattenhorn, S. A.; Walker, M.

    2016-01-01

    Phobos, the innermost satellite of Mars, displays an extensive system of grooves that are mostly symmetric about its sub-Mars point. Phobos is steadily spiraling inward due to the tides it raises on Mars lagging behind Phobos' orbital position and will suffer tidal disruption before colliding with Mars in a few tens of millions of years. We calculate the surface stress field of the deorbiting satellite and show that the first signs of tidal disruption are already present on its surface. Most of Phobos' prominent grooves have an excellent correlation with computed stress orientations. The model requires a weak interior that has very low rigidity on the tidal evolution time scale, overlain by an approximately 10-100 m exterior shell that has elastic properties similar to lunar regolith as described by Horvath et al. (1980).

  8. Deformation behaviour and fracture of Ni-base single crystals at simultaneous action of high-cycle fatigue and creep

    Czech Academy of Sciences Publication Activity Database

    Kunz, Ludvík; Lukáš, Petr

    2007-01-01

    Roč. 14, č. 2 (2007), s. 15-20 ISSN 1335-0803 R&D Projects: GA ČR GA106/05/2112 Institutional research plan: CEZ:AV0Z20410507 Keywords : CMSX-4 * CM186LC * Fatigue life * Constant lifetime diagram Subject RIV: JG - Metallurgy

  9. An evaluation on fatigue crack growth in a fine-grained isotropic graphite

    Energy Technology Data Exchange (ETDEWEB)

    Wang Hongtao; Sun Libin [Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084 (China); Li Chenfeng [College of Engineering, Swansea University, Singleton Park, Swansea SA2 8PP (United Kingdom); Shi Li [Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084 (China); Wang Haitao, E-mail: wanght@tsinghua.edu.cn [Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084 (China)

    2012-09-15

    Highlights: Black-Right-Pointing-Pointer The propagation of micro- and macro-fatigue cracks in IG-11 graphite was studied. Black-Right-Pointing-Pointer The curves of the fatigue crack growth rate versus the SIF range show three stages. Black-Right-Pointing-Pointer The fatigue microcrack propagation is very sensitive to graphite's microstructures. Black-Right-Pointing-Pointer Graphite's microstructures have no significant impact on fatigue macrocrack growth. Black-Right-Pointing-Pointer The fatigue fracture surface indicates the fracture mechanism of the IG-11 graphite. - Abstract: The aim of this paper is to investigate the mechanism of fatigue crack propagation in IG-11 graphite, and determine the crack growth rate in relation to the stress level. Experimental studies were performed at both micro and macro scales. For fatigue microcrack propagation, single-edge-notch specimens were chosen for testing and the fatigue crack growth was measured in situ with a scanning electron microscope. For fatigue macrocrack propagation, CT specimens were used and the fatigue crack growth was measured with a high-accuracy optic microscope. Combining the two groups of experimental results, the following conclusions are derived: (1) The heterogeneous microstructures of the graphite material have significant impact on the fatigue microcrack growth, while their influence on fatigue macrocrack growth is very limited. (2) The relationship between the fatigue crack growth rate and the crack-tip stress intensity factor range can be expressed in the form of Paris formulae, which contains three stages: an initial rising part with a small slope, an abrupt rise with a very large acceleration, and a short final part with a small slope. (3) The fatigue fracture surface of the graphite material contains considerable sliding of leaf-shape graphite flakes combined with small cotton-shape plastic deformations. These sliding traces are approximately aligned at 45 Degree-Sign , showing the

  10. An evaluation on fatigue crack growth in a fine-grained isotropic graphite

    International Nuclear Information System (INIS)

    Wang Hongtao; Sun Libin; Li Chenfeng; Shi Li; Wang Haitao

    2012-01-01

    Highlights: ► The propagation of micro- and macro-fatigue cracks in IG-11 graphite was studied. ► The curves of the fatigue crack growth rate versus the SIF range show three stages. ► The fatigue microcrack propagation is very sensitive to graphite's microstructures. ► Graphite's microstructures have no significant impact on fatigue macrocrack growth. ► The fatigue fracture surface indicates the fracture mechanism of the IG-11 graphite. - Abstract: The aim of this paper is to investigate the mechanism of fatigue crack propagation in IG-11 graphite, and determine the crack growth rate in relation to the stress level. Experimental studies were performed at both micro and macro scales. For fatigue microcrack propagation, single-edge-notch specimens were chosen for testing and the fatigue crack growth was measured in situ with a scanning electron microscope. For fatigue macrocrack propagation, CT specimens were used and the fatigue crack growth was measured with a high-accuracy optic microscope. Combining the two groups of experimental results, the following conclusions are derived: (1) The heterogeneous microstructures of the graphite material have significant impact on the fatigue microcrack growth, while their influence on fatigue macrocrack growth is very limited. (2) The relationship between the fatigue crack growth rate and the crack-tip stress intensity factor range can be expressed in the form of Paris formulae, which contains three stages: an initial rising part with a small slope, an abrupt rise with a very large acceleration, and a short final part with a small slope. (3) The fatigue fracture surface of the graphite material contains considerable sliding of leaf-shape graphite flakes combined with small cotton-shape plastic deformations. These sliding traces are approximately aligned at 45°, showing the main cause of the fatigue fracture is the shear stress. There are also a large amount of secondary cracks inside unit cells and on cell walls

  11. Fatigue cracking on a steam generator tube

    International Nuclear Information System (INIS)

    Boccanfuso, M.; Lothios, J.; Thebault, Y.; Bruyere, B.; Duisabeau, L.; Herms, E.

    2015-01-01

    A circumferential fatigue crack was observed on a steam generator tube of the unit 2 of the Fessenheim plant. The results of destructive testing and the examination of the fracture surface show that the circumferential crack is linked to a large number of cycles with a very low stress intensity factor. Other aggravating factors like inter-granular corrosion have played a role in the initiating phase of fatigue cracking. The damage has been exacerbated by the lack of support of the tube at the level of the anti-vibration bars. (A.C.)

  12. Monitoring Induced Fractures with Electrical Measurements using Depth to Surface Resistivity: A Field Case Study

    Science.gov (United States)

    Wilt, M.; Nieuwenhuis, G.; Sun, S.; MacLennan, K.

    2016-12-01

    Electrical methods offer an attractive option to map induced fractures because the recovered anomaly is related to the electrical conductivity of the injected fluid in the open (propped) section of the fracture operation. This is complementary to existing micro-seismic technology, which maps the mechanical effects of the fracturing. In this paper we describe a 2014 field case where a combination of a borehole casing electrode and a surface receiver array was used to monitor hydrofracture fracture creation and growth in an unconventional oil field project. The fracture treatment well was 1 km long and drilled to a depth of 2.2 km. Twelve fracture events were induced in 30 m intervals (stages) in the 1 km well. Within each stage 5 events (clusters) were initiated at 30 m intervals. Several of the fracture stages used a high salinity brine, instead of fresh water, to enhance the electrical signal. The electrical experiment deployed a downhole source in a well parallel to the treatment well and 100 m away. The source consisted of an electrode attached to a wireline cable into which a 0.25 Hz square wave was injected. A 60-station electrical field receiver array was placed above the fracture and extending for several km. Receivers were oriented to measure electrical field parallel with the presumed fracture direction and those perpendicular to it. Active source electrical data were collected continuously during 7 frac stages, 3 of which used brine as the frac fluid over a period of several days. Although the site was quite noisy and the electrical anomaly small we managed to extract a clear frac anomaly using field separation, extensive signal averaging and background noise rejection techniques. Preliminary 3D modeling, where we account for current distribution of the casing electrode and explicitly model multiple thin conductive sheets to represent fracture stages, produces a model consistent with the field measurements and also highlights the sensitivity of the

  13. Surface Reconstruction from Parallel Curves with Application to Parietal Bone Fracture Reconstruction.

    Directory of Open Access Journals (Sweden)

    Abdul Majeed

    Full Text Available Maxillofacial trauma are common, secondary to road traffic accident, sports injury, falls and require sophisticated radiological imaging to precisely diagnose. A direct surgical reconstruction is complex and require clinical expertise. Bio-modelling helps in reconstructing surface model from 2D contours. In this manuscript we have constructed the 3D surface using 2D Computerized Tomography (CT scan contours. The fracture part of the cranial vault are reconstructed using GC1 rational cubic Ball curve with three free parameters, later the 2D contours are flipped into 3D with equidistant z component. The constructed surface is represented by contours blending interpolant. At the end of this manuscript a case report of parietal bone fracture is also illustrated by employing this method with a Graphical User Interface (GUI illustration.

  14. Titanium and steel fracture fixation plates with different surface topographies: Influence on infection rate in a rabbit fracture model.

    Science.gov (United States)

    Metsemakers, W J; Schmid, Tanja; Zeiter, Stephan; Ernst, Manuela; Keller, Iris; Cosmelli, Nicolo; Arens, Daniel; Moriarty, T Fintan; Richards, R Geoff

    2016-03-01

    Implant-related infection is a challenging complication in musculoskeletal trauma surgery. In the present study, we examined the role of implant material and surface topography as influencing factors on the development of infection in an experimental model of plating osteosynthesis in the rabbit. The implants included in this experimental study were composed of: standard Electropolished Stainless Steel (EPSS), standard titanium (Ti-S), roughened stainless steel (RSS) and surface polished titanium (Ti-P). Construct stability and load-to-failure of Ti-P implants was compared to that of Ti-S implants in a rabbit cadaveric model. In an in vivo study, a rabbit humeral fracture model was used. Each rabbit received one of three Staphylococcus aureus inocula, aimed at determining the infection rate at a low, medium and high dose of bacteria. Outcome measures were quantification of bacteria on the implant and in the surrounding tissues, and determination of the infectious dose 50 (ID50). No significant differences were observed between Ti-S and Ti-P regarding stiffness or failure load in the cadaver study. Of the 72 rabbits eventually included in the in vivo study, 50 developed an infection. The ID50 was found to be: EPSS 3.89×10(3) colony forming units (CFU); RSS 8.23×10(3) CFU; Ti-S 5.66×10(3) CFU; Ti-P 3.41×10(3) CFU. Significantly lower bacterial counts were found on the Ti-S implants samples compared with RSS implants (ptitanium and steel implants with conventional or modified topographies. Ti-P implants, which have previously been shown in preclinical studies to reduce complications associated with tissue adherence, do not affect infection rate in this preclinical fracture model. Therefore, Ti-P implants are not expected to affect the infection rate, or influence implant stability in the clinical situation. Copyright © 2016 Elsevier Ltd. All rights reserved.

  15. Fatigue behaviour of a 9Cr1MoNbV martensitic steel in a liquid metal

    Energy Technology Data Exchange (ETDEWEB)

    Vogt, Jean-Bernard; Serre, Ingrid [Ecole National Superieure de Chimie de Lille (France); Verleene, Arnaud [Ecole National Superieure de Chimie de Lille (France); Michelin, Clermond Ferrand (France)

    2009-07-01

    The low cycle fatigue behaviour of the T91 martensitic steel is studied in the range {delta}{epsilon}{sub t} from 0.4% to 2.4%, at 300 C, in air and in liquid Lead Bismuth Eutectic (LBE). It is shown that the cyclic stress response consists of a cyclic softening that is not modified by the environment. However, the fatigue life is reduced after fatigue in LBE as compared to air and the effect is especially marked at high strain range. Metallographic analysis of the external surfaces and of transverse cross sections of specimen show that the short crack density is very low in the specimen failed in liquid metal while it is high for tests in air. Fracture surface observations show that multiple crack initiations occurred in air. In liquid metal, the fracture surfaces were flat and contained widely spaced fatigue striations. Strain localization promoted by the liquid metal is responsible for the decrease in fatigue resistance. (orig.)

  16. Fracture and Fatigue Resistance of Cemented versus Fused CAD-on Veneers over Customized Zirconia Implant Abutments.

    Science.gov (United States)

    Nossair, Shereen Ahmed; Aboushelib, Moustafa N; Morsi, Tarek Salah

    2015-01-05

    To evaluate the fracture mechanics of cemented versus fused CAD-on veneers on customized zirconia implant abutments. Forty-five identical customized CAD/CAM zirconia implant abutments (0.5 mm thick) were prepared and seated on short titanium implant abutments (Ti base). A second scan was made to fabricate 45 CAD-on veneers (IPS Empress CAD, A2). Fifteen CAD-on veneers were cemented on the zirconia abutments (Panavia F2.0). Another 15 were fused to the zirconia abutments using low-fusing glass, while manually layered veneers served as control (n = 15). The restorations were subjected to artificial aging (3.2 million cycles between 5 and 10 kg in a water bath at 37°C) before being axially loaded to failure. Fractured specimens were examined using scanning electron microscopy to detect fracture origin, location, and size of critical crack. Stress at failure was calculated using fractography principles (alpha = 0.05). Cemented CAD-on restorations demonstrated significantly higher (F = 72, p CAD-on and manually layered restorations. Fractographic analysis of fractured specimens indicated that cemented CAD-on veneers failed due to radial cracks originating from the veneer/resin interface. Branching of the critical crack was observed in the bulk of the veneer. Fused CAD-on veneers demonstrated cohesive fracture originating at the thickest part of the veneer ceramic, while manually layered veneers failed due to interfacial fracture at the zirconia/veneer interface. Within the limitations of this study, cemented CAD-on veneers on customized zirconia implant abutments demonstrated higher fracture than fused and manually layered veneers. © 2014 by the American College of Prosthodontists.

  17. Changes in force, surface and motor unit EMG during post-exercise development of low frequency fatigue in vastus lateralis muscle

    NARCIS (Netherlands)

    de Ruiter, C.J.; Elzinga, M.J.; Verdijk, P.W.L.; van Mechelen, W.; de Haan, A.

    2005-01-01

    We investigated the effects of low frequency fatigue (LFF) on post-exercise changes in rectified surface EMG (rsEMG) and single motor unit EMG (smuEMG) in vastus lateralis muscle (n=9). On two experimental days the knee extensors were fatigued with a 60-s-isometric contraction (exercise) at 50%

  18. The effect of residual stresses induced by prestraining on fatigue life of notched specimens

    Science.gov (United States)

    Sadeler, R.; Ozel, A.; Kaymaz, I.; Totik, Y.

    2005-06-01

    The effect of tensile prestraining-induced residual stress on the fatigue life of notched steel parts was investigated. The study was performed on AISI 4140 steel. Rotating bending fatigue tests were carried out on semicircular notched specimens with different notch radii in the as-quenched and tempered conditions. Metallography of the specimens was performed by means of light optical microscopy. The finite-element method was used to evaluate the residual stress distribution near the notch region. Fatigue tests revealed fatigue life improvement for notched specimens, which changes depending on the notch radii and applied stress. Scanning electron microscopy was used to examine the fracture surfaces of the specimens.

  19. Surface electromyography based muscle fatigue detection using high-resolution time-frequency methods and machine learning algorithms.

    Science.gov (United States)

    Karthick, P A; Ghosh, Diptasree Maitra; Ramakrishnan, S

    2018-02-01

    Surface electromyography (sEMG) based muscle fatigue research is widely preferred in sports science and occupational/rehabilitation studies due to its noninvasiveness. However, these signals are complex, multicomponent and highly nonstationary with large inter-subject variations, particularly during dynamic contractions. Hence, time-frequency based machine learning methodologies can improve the design of automated system for these signals. In this work, the analysis based on high-resolution time-frequency methods, namely, Stockwell transform (S-transform), B-distribution (BD) and extended modified B-distribution (EMBD) are proposed to differentiate the dynamic muscle nonfatigue and fatigue conditions. The nonfatigue and fatigue segments of sEMG signals recorded from the biceps brachii of 52 healthy volunteers are preprocessed and subjected to S-transform, BD and EMBD. Twelve features are extracted from each method and prominent features are selected using genetic algorithm (GA) and binary particle swarm optimization (BPSO). Five machine learning algorithms, namely, naïve Bayes, support vector machine (SVM) of polynomial and radial basis kernel, random forest and rotation forests are used for the classification. The results show that all the proposed time-frequency distributions (TFDs) are able to show the nonstationary variations of sEMG signals. Most of the features exhibit statistically significant difference in the muscle fatigue and nonfatigue conditions. The maximum number of features (66%) is reduced by GA and BPSO for EMBD and BD-TFD respectively. The combination of EMBD- polynomial kernel based SVM is found to be most accurate (91% accuracy) in classifying the conditions with the features selected using GA. The proposed methods are found to be capable of handling the nonstationary and multicomponent variations of sEMG signals recorded in dynamic fatiguing contractions. Particularly, the combination of EMBD- polynomial kernel based SVM could be used to

  20. Probabilistic fracture mechanics of nuclear structural components: consideration of transition from embedded crack to surface crack

    International Nuclear Information System (INIS)

    Yagawa, G.; Yoshimura, S.

    1999-01-01

    This paper describes a probabilistic fracture mechanics (PFM) analysis of aged nuclear reactor pressure vessel (RPV) material. New interpolation formulas of three-dimensional stress intensity factors are presented for both embedded elliptical surface cracks and semi-elliptical surface cracks. To investigate effects of transition from embedded crack to surface crack in PFM analyses, one of the PFM round-robin problems set by JSME-RC111 committee (i.e. aged RPV under normal and upset operating conditions) is solved, employing the interpolation formulas. (orig.)

  1. The relationship of seismic velocity structure and surface fracture characteristics of basalt outcrops to rippability estimates

    International Nuclear Information System (INIS)

    Kay, S.E.; Dougherty, M.E.; Pelton, J.R.

    1994-01-01

    Seismic velocity has been shown in previous engineering studies to be related to the fracture characteristics and rippability of rock outcrops. However, common methods of measuring seismic velocity in outcrops do not take into account the many possible travel paths for wave propagation and the fact that velocity zones may exist within an outcrop. Presented here are the results of using raytracing inversion of first-arrival travel-time data to map P-velocity structure in basalt outcrops, and also the investigation of the relationship of the mapped velocities to observed surface fractures and hand-sample P-velocities. It is shown that basalt outcrops commonly consist of an irregular near-surface low-velocity zone underlain by higher velocity material; that velocity gradients can exist in outcrops; that hand-sample velocity measurements are typically higher than outcrop-scale measurements; and that the characteristics of surface fractures are empirically related to near-surface P-velocity. All of these findings are relevant to the estimated rippability of rock in geotechnical engineering. The data for this study are derived from eleven sites on basalt outcrops of the Troodos Ophiolite in Cyprus. The basalt types include pillow basalts, massive flows, and a pillow breccia. A commonly available raytracing inversion program (RAYINVR) was used to produce a velocity profile of each outcrop. Different velocity zones were detailed by inverting observed travel times to produce a model of outcrop velocity structure which produces rippability profiles for each outcrop. 16 refs., 9 figs

  2. Continuous Wavelet Transform Analysis of Surface Electromyography for Muscle Fatigue Assessment on the Elbow Joint Motion

    Directory of Open Access Journals (Sweden)

    Triwiyanto Triwiyanto

    2017-01-01

    Full Text Available Studying muscle fatigue plays an important role in preventing the risks associated with musculoskeletal disorders. The effect of elbow-joint angle on time-frequency parameters during a repetitive motion provides valuable information in finding the most accurate position of the angle causing muscle fatigue. Therefore, the purpose of this study is to analyze the effect of muscle fatigue on the spectral and time-frequency domain parameters derived from electromyography (EMG signals using the Continuous Wavelet Transform (CWT. Four male participants were recruited to perform a repetitive motion (flexion and extension movements from a non-fatigue to fatigue condition. EMG signals were recorded from the biceps muscle. The recorded EMG signals were then analyzed offline using the complex Morlet wavelet. The time-frequency domain data were analyzed using the time-averaged wavelet spectrum (TAWS and the Scale-Average Wavelet Power (SAWP parameters. The spectral domain data were analyzed using the Instantaneous Mean Frequency (IMNF and the Instantaneous Mean Power Spectrum (IMNP parameters. The index of muscle fatigue was observed by calculating the increase of the IMNP and the decrease of the IMNF parameters. After performing a repetitive motion from non-fatigue to fatigue condition, the average of the IMNF value decreased by 15.69% and the average of the IMNP values increased by 84%, respectively. This study suggests that the reliable frequency band to detect muscle fatigue is 31.10-36.19Hz with linear regression parameters of 0.979mV^2Hz^(-1 and 0.0095mV^2Hz^(-1 for R^2 and slope, respectively.

  3. Mechanism of fatigue crack initiation in austenitic stainless steels in light water reactor environments

    International Nuclear Information System (INIS)

    Chopra, O.K.; Shack, W.J.; Muscara, J.

    2003-01-01

    This paper examines the mechanism of fatigue crack initiation in austenitic stainless steels (SSs) in light water reactor (LWR) coolant environments. The effects of key material and loading variables on the fatigue lives of wrought and cast austenitic SSs in air and LWR environments have been evaluated. The influence of reactor coolant environments on the formation and growth of fatigue cracks in polished smooth SS specimens is discussed. The results indicate that the fatigue lives of these steels are decreased primarily by the effects of the environment on the growth of cracks <200 μm and, to a lesser extent, on enhanced growth rates of longer cracks. The fracture morphology in the specimens has been characterized. Exploratory fatigue tests were conducted to study the effects of surface micropits or minor differences in the surface oxide on fatigue crack initiation. (author)

  4. AFM study of surface relief evolution in 316L steel fatigued at low and high temperatures

    Czech Academy of Sciences Publication Activity Database

    Man, Jiří; Valtr, B.; Weidner, A.; Petrenec, Martin; Obrtlík, Karel; Polák, Jaroslav

    2010-01-01

    Roč. 2, č. 1 (2010), s. 1625-1633 E-ISSN 1877-7058. [Fatigue 2010. Praha, 06.06.2010-11.06.2010] R&D Projects: GA ČR GAP108/10/2371; GA AV ČR 1QS200410502; GA ČR GA106/06/1096 Institutional research plan: CEZ:AV0Z20410507 Keywords : Fatigue crack initiation * 316L steel * Persistent slip band (PSB) * Extrusion * Intrusion * Atomic force microscopy (AFM) Subject RIV: JL - Materials Fatigue, Friction Mechanics

  5. CYCLIC FATIGUE RESISTANCE OF AZ91 MAGNESIUM ALLOY

    Directory of Open Access Journals (Sweden)

    Aneta Němcová

    2009-11-01

    Full Text Available The paper deals with determination of principal mechanical properties and the investigation of fatigue behaviour of AZ91 magnesium alloy. The experimental material was made by squeeze casting technique and heat treated to obtain T4 state (solution annealing, when hard, brittle Mg17Al12 intermetallic phase is dissolved. The basic mechanical properties (Young’s modulus, ultimate tensile strength, yield strength, elongation to fracture and reduction of area were determined by static tensile test. Furthermore, fatigue parameters were investigated. The S-N curve on the basis of smooth test bars tested under symmetrical push-pull loading at room temperature was evaluated. The measured data were subsequently used for fitting with suitable regression functions (Kohout & Věchet and Stromeyer for determination of the fatigue parameters. Fatigue limit sigma-c of the studied alloy for 108 cycles is approaching 50 MPa. In addition, the fracture surfaces were observed by scanning electron microscopy. The failure analysis proved that the striations were observed in fatigue crack propagation area and in the area of static fracture was observed the transgranular ductile fracture. The structure of the studied alloy in the basic state and after heat treatment was observed by light and scanning electron microscopy.

  6. The effects of novel surface treatments on the wear and fatigue properties of steel and chilled cast iron

    Science.gov (United States)

    Carroll, Jason William

    Contact fatigue driven wear is a principal design concern for gear and camshaft engineering of power systems. To better understand how to engineer contact fatigue resistant surfaces, the effects of electroless nickel and hydrogenated diamond-like-carbon (DLC) coatings on the fatigue life at 108 cycles of SAE 52100 steel were studied using ultrasonic fatigue methods. The addition of DLC and electroless nickel coatings to SAE 52100 bearing steel had no effect on the fatigue life. Different inclusion types were found to affect the stress intensity value beyond just the inclusion size, as theorized by Murakami. The difference in stress intensity values necessary to propagate a crack for Ti (C,N) and alumina inclusions was due to the higher driving force for crack extension at the Ti (C,N) inclusions and was attributed to differences in the shape of the inclusion: rhombohedral for the Ti (C,N) versus spherical for the oxides. A correction factor was added to the Murakami equation to account for inclusion type. The wear properties of DLC coated SAE 52100 and chilled cast iron were studied using pin-on-disk tribometry and very high cycle ultrasonic tribometry. A wear model that includes sliding thermal effects as well as thermodynamics consistent with the wear mechanism for DLCs was developed based on empirical results from ultrasonic wear testing to 108 cycles. The model fit both ultrasonic and classic tribometer data for wear of DLCs. Finally, the wear properties of laser hardened steels - SAE 8620, 4140, and 52100 - were studied at high contact pressures and low numbers of cycles. A design of experiments was conducted to understand how the laser processing parameters of power, speed, and beam size, as well as carbon content of the steel, affected surface hardness. A hardness maximum was found at approximately 0.7 wt% carbon most likely resulting from increased amounts of retained austenite. The ratcheting contact fatigue model of Kapoor was found to be useful in

  7. Changes in surface electromyography signals and kinetics associated with progression of fatigue at two speeds during wheelchair propulsion.

    Science.gov (United States)

    Qi, Liping; Wakeling, James; Grange, Simon; Ferguson-Pell, Martin

    2012-01-01

    The purpose of this study was to determine whether muscle balance is influenced by fatigue in a recordable way, toward creating novel defensive activity strategies for manual wheelchair users (MWUs). Wheelchair propulsion to a point of mild fatigue, level 15 on the Rating of Perceived Exertion scale, was investigated at two different speeds. Surface electromyographic (EMG) activity of 7 muscles was recorded on 14 nondisabled participants. Kinetic variables were measured using a SmartWheel. No significant effect was found of percentage endurance time on kinetic variables for the two propulsion speeds. Fatigue-related changes in the EMG spectra were identified as an increase of EMG intensity and a decrease of mean power frequency as a function of percent endurance time for the tested muscles under both fast and slow speed conditions. The greater increases in activity for propulsive muscles compared with recovery muscles during fast speed wheelchair propulsion indicated muscle imbalance associated with fatiguing wheelchair propulsion. This study shows how kinetic and EMG information might be used as feedback to MWUs to ensure that they conduct activity in ways that do not precipitate injury.

  8. Microstructural Characterization Of Laser Heat Treated AISI 4140 Steel With Improved Fatigue Behavior

    Directory of Open Access Journals (Sweden)

    Oh M.C.

    2015-06-01

    Full Text Available The influence of surface heat treatment using laser radiation on the fatigue strength and corresponding microstructural evolution of AISI 4140 alloy steel was investigated in this research. The AISI 4140 alloy steel was radiated by a diode laser to give surface temperatures in the range between 600 and 800°C, and subsequently underwent vibration peening. The fatigue behavior of surface-treated specimens was examined using a giga-cycle ultrasonic fatigue test, and it was compared with that of non-treated and only-peened specimens. Fatigue fractured surfaces and microstructural evolution with respect to the laser treatment temperatures were investigated using an optical microscope. Hardness distribution was measured using Vickers micro-hardness. Higher laser temperature resulted in higher fatigue strength, attributed to the phase transformation.

  9. Fatigue properties of X80 pipeline steels with ferrite/bainite dual-phase microstructure

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Zuo-peng [Key Lab of Metastable Materials Science & Technology and College of Materials Science & Engineering, Yanshan University, Qinhuangdao 066004 (China); Qiao, Gui-ying [Key Lab of Metastable Materials Science & Technology and College of Materials Science & Engineering, Yanshan University, Qinhuangdao 066004 (China); Key Lab of Applied Chemistry of Hebei Province and School of Environment and Chemical Engineering, Yanshan University, Qinhuangdao 066004 (China); Tang, Lei [Key Lab of Applied Chemistry of Hebei Province and School of Environment and Chemical Engineering, Yanshan University, Qinhuangdao 066004 (China); Zhu, Hong-wei; Liao, Bo [Key Lab of Metastable Materials Science & Technology and College of Materials Science & Engineering, Yanshan University, Qinhuangdao 066004 (China); Xiao, Fu-ren, E-mail: frxiao@ysu.edu.cn [Key Lab of Metastable Materials Science & Technology and College of Materials Science & Engineering, Yanshan University, Qinhuangdao 066004 (China)

    2016-03-07

    Fatigue properties are important parameters for the safety design and security evaluation of gas transmission pipelines. In this work, the fatigue life at different stresses of full-thickness X80 pipeline steel plates with a ferrite/bainite dual-phase microstructure was investigated using a MTS servo-hydraulic universal testing machine; the fatigue crack propagation rate was examined with CT specimens by using an INSTRON 8874 testing machine. Results indicate that fatigue life increases as maximum stress decreases; as the maximum stress decreases to the maximum operating stress (440 MPa), the fatigue life is approximately 4.2×10{sup 5} cycles. The fatigue crack of the full-thickness fatigue life specimens is generated at the surface of rolled steel plates and then the crack propagates and grows inward until a fracture is formed. During fatigue crack growth, a transitional turning point appears in the curve of da/dN with ΔK in the Paris region. The transitional turning point that divides the Paris region to two stages is approximately ΔK≅30 MPa m{sup 1/2}. The change in the growth rate (da/dN) is related to the variation of the crack path and in the fracture mode because of the possible microstructural sensitivity of fatigue crack propagation behavior. This study also discussed the effect of duple phase ferrite/bainite microstructure on fatigue crack initiation and propagation.

  10. Fatigue properties of X80 pipeline steels with ferrite/bainite dual-phase microstructure

    International Nuclear Information System (INIS)

    Zhao, Zuo-peng; Qiao, Gui-ying; Tang, Lei; Zhu, Hong-wei; Liao, Bo; Xiao, Fu-ren

    2016-01-01

    Fatigue properties are important parameters for the safety design and security evaluation of gas transmission pipelines. In this work, the fatigue life at different stresses of full-thickness X80 pipeline steel plates with a ferrite/bainite dual-phase microstructure was investigated using a MTS servo-hydraulic universal testing machine; the fatigue crack propagation rate was examined with CT specimens by using an INSTRON 8874 testing machine. Results indicate that fatigue life increases as maximum stress decreases; as the maximum stress decreases to the maximum operating stress (440 MPa), the fatigue life is approximately 4.2×10"5 cycles. The fatigue crack of the full-thickness fatigue life specimens is generated at the surface of rolled steel plates and then the crack propagates and grows inward until a fracture is formed. During fatigue crack growth, a transitional turning point appears in the curve of da/dN with ΔK in the Paris region. The transitional turning point that divides the Paris region to two stages is approximately ΔK≅30 MPa m"1"/"2. The change in the growth rate (da/dN) is related to the variation of the crack path and in the fracture mode because of the possible microstructural sensitivity of fatigue crack propagation behavior. This study also discussed the effect of duple phase ferrite/bainite microstructure on fatigue crack initiation and propagation.

  11. Fatigue test results of flat plate specimens with surface cracks and evaluation of crack growth in structural components

    International Nuclear Information System (INIS)

    Shibata, Katsuyuki; Yokoyama, Norio; Ohba, Toshihiro; Kawamura, Takaichi; Miyazono, Shohachiro

    1982-12-01

    Part-through surface cracks are most frequently observed in the inspection of structural components, and it is one of the important subjects in the assessment of safety to evaluate appropriately the growth of such cracks during the service life of structural components. Due to the complexity of the stress at the front free surface, the crack growth at the surface shows a different behavior from the other part. Besides, an effect of interaction is caused in the growth of multiple surface cracks. These effects should be included in the growth analysis of surface part-through cracks. Authors have carried out a series of fatigue tests on some kinds of pipes with multiple cracks in the inner surface, and subsequently the fatigue test of flat plate specimens, made of Type 304L stainless steel, with a single or double surface cracks was carried out to study the basic characteristics in the growth of multiple surface cracks. Based on the results of the flat plate test. the correction factors for the front free surface (Cs) and interaction (Ci) of surface cracks were derived quantitatively by the following empirical expressions; Cs = 0.824. Ci = (0.227(a/b) 2 (sec(PI X/2) - 1) + 1)sup(1/m). Using these two correction factors, a procedure to predict the growth of surface cracks was developed by applying the crack growth formula to both the thickness and surface directions. Besides, the crack growth predictions based on the procedure of ASME Code Sex. XI, and the above procedure without the correction of the free surface and interactions on the crack growth behaviors were compared with the test results of flat plate specimens. The crack growth behavior predicted by the procedure described in this report showed the best agreement with the test results in respects of the crack growth life and the change in the crack shape. The criteria of the ASME Code did not agree with the test results. (author)

  12. Traitement de surface par explosif du cuivre polycristallin : caractérisation microstructurale et comportement en fatigue plastique

    Science.gov (United States)

    Gerland, M.; Dufour, J. P.; Presles, H. N.; Violan, P.; Mendez, J.

    1991-10-01

    A new surface treatment technique with a primary explosive deposited in thin layer was applied to a polycrystalline pure copper. After treatment, surface roughness remains of high quality especially when compared to shot peened surfaces. The treated zone extends over several hundreds microns in depth and the microhardness profile exhibits a significant increasing of hardness with a maximum reaching 100% at the surface. The transmission electron microscopy shows a microstructure which changes with depth : below the surface, there is a thin recrystallized layer with very small grains followed by a region with numerous mechanical twins the density of which decreases when depth increases. Tested in fatigue with a constant plastic strain amplitude, the treated copper specimens exhibit a strong hardening from the first cycles compared to the untreated specimen ; however this initial hardening erases after 2% of the fatigue life. The fatigue resistance is not modified by the treatment. Une nouvelle technique de traitement de surface à l'aide d'un explosif primaire déposé en couche mince a été utilisée sur du cuivre pur polycristallin. L'état de surface après traitement reste de très bonne qualité, surtout comparé aux surfaces grenaillées. La zone traitée s'étend sur une profondeur de quelques centaines de microns et le profil de microdureté montre une importante augmentation de dureté avec un maximum en surface pouvant atteindre 100%. La micrcrostructure, observée par microscopie électronique en transmission, est caractérisée par une fine recristallisation en surface, puis par un abondant maclage dont la densité décroît lorsque la profondeur augmente. Testé en fatigue à déformation plastique imposée, le cuivre traité présente un fort écrouissage initial dès les premiers cycles, mais qui s'efface progressivement au cours du cyclage après 2% de la durée de vie, cette dernière n'étant pas modifiée par le traitement.

  13. Identification of modes of fracture in a 2618-T6 aluminum alloy using stereophotogrammetry

    Energy Technology Data Exchange (ETDEWEB)

    Salas Zamarripa, A., E-mail: a.salaszamarripa@gmail.com [Facultad de Ingenieria Mecanica y Electrica, Universidad Autonoma de Nuevo Leon. Av. Universidad S/N, Ciudad Universitaria, C.P. 66451, Apartado Postal 076 Suc. ' F' San Nicolas de los Garza, N.L. (Mexico); Pinna, C.; Brown, M.W. [Department of Mechanical Engineering, University of Sheffield. Sir Frederick Mappin Building, Mappin Street, Sheffield, S1 3JD (United Kingdom); Mata, M.P. Guerrero; Morales, M. Castillo; Beber-Solano, T.P. [Facultad de Ingenieria Mecanica y Electrica, Universidad Autonoma de Nuevo Leon. Av. Universidad S/N, Ciudad Universitaria, C.P. 66451, Apartado Postal 076 Suc. ' F' San Nicolas de los Garza, N.L. (Mexico)

    2011-12-15

    The identification and the development of a quantification technique of the modes of fracture in fatigue fracture surfaces of a 2618-T6 aluminum alloy were developed during this research. Fatigue tests at room and high temperature (230 Degree-Sign C) were carried out to be able to compare the microscopic fractographic features developed by this material under these testing conditions. The overall observations by scanning electron microscopy (SEM) of the fracture surfaces showed a mixture of transgranular and ductile intergranular fracture. The ductile intergranular fracture contribution appears to be more significant at room temperature than at 230 Degree-Sign C. A quantitative methodology was developed to identify and to measure the contribution of these microscopic fractographic features. The technique consisted of a combination of stereophotogrammetry and image analysis. Stereo-pairs were randomly taken along the crack paths and were then analyzed using the profile module of MeX software. The analysis involved the 3-D surface reconstruction, the trace of primary profile lines in both vertical and horizontal directions within the stereo-pair area, the measurements of the contribution of the modes of fracture in each profile, and finally, the calculation of the average contribution in each stereo-pair. The technique results confirmed a higher contribution of ductile intergranular fracture at room temperature than at 230 Degree-Sign C. Moreover, there was no indication of a direct relationship between this contribution and the strain amplitudes range applied during the fatigue testing. - Highlights: Black-Right-Pointing-Pointer Stereophotogrammetry and image analysis as a measuring tool of modes of fracture in fatigue fracture surfaces. Black-Right-Pointing-Pointer A mixture of ductile intergranular and transgranular fracture was identified at room temperature and 230 Degree-Sign C testing. Black-Right-Pointing-Pointer Development of a quantitative methodology to

  14. Identification of modes of fracture in a 2618-T6 aluminum alloy using stereophotogrammetry

    International Nuclear Information System (INIS)

    Salas Zamarripa, A.; Pinna, C.; Brown, M.W.; Mata, M.P. Guerrero; Morales, M. Castillo; Beber-Solano, T.P.

    2011-01-01

    The identification and the development of a quantification technique of the modes of fracture in fatigue fracture surfaces of a 2618-T6 aluminum alloy were developed during this research. Fatigue tests at room and high temperature (230 °C) were carried out to be able to compare the microscopic fractographic features developed by this material under these testing conditions. The overall observations by scanning electron microscopy (SEM) of the fracture surfaces showed a mixture of transgranular and ductile intergranular fracture. The ductile intergranular fracture contribution appears to be more significant at room temperature than at 230 °C. A quantitative methodology was developed to identify and to measure the contribution of these microscopic fractographic features. The technique consisted of a combination of stereophotogrammetry and image analysis. Stereo-pairs were randomly taken along the crack paths and were then analyzed using the profile module of MeX software. The analysis involved the 3-D surface reconstruction, the trace of primary profile lines in both vertical and horizontal directions within the stereo-pair area, the measurements of the contribution of the modes of fracture in each profile, and finally, the calculation of the average contribution in each stereo-pair. The technique results confirmed a higher contribution of ductile intergranular fracture at room temperature than at 230 °C. Moreover, there was no indication of a direct relationship between this contribution and the strain amplitudes range applied during the fatigue testing. - Highlights: ► Stereophotogrammetry and image analysis as a measuring tool of modes of fracture in fatigue fracture surfaces. ► A mixture of ductile intergranular and transgranular fracture was identified at room temperature and 230 °C testing. ► Development of a quantitative methodology to obtain the percentage of modes of fracture within the fracture surface.

  15. Surface profile evolution and fatigue crack initiation in Sanicro 25 steel at room temperature

    Czech Academy of Sciences Publication Activity Database

    Polák, Jaroslav; Petráš, Roman; Chai, G.; Škorík, Viktor

    2016-01-01

    Roč. 658, MAR (2016), s. 221-228 ISSN 0921-5093 R&D Projects: GA MŠk(CZ) ED1.1.00/02.0068; GA MŠk(CZ) EE2.3.30.0063; GA ČR(CZ) GA13-23652S Institutional support: RVO:68081723 Keywords : Sanicro 25 steel * Fatigue crack initiation * Persistent slip markings * Extrusions * Intrusions Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 3.094, year: 2016

  16. Atomic force microscopy of surface relief in individual grains of fatigued 316L austenitic stainless steel

    Czech Academy of Sciences Publication Activity Database

    Man, Jiří; Obrtlík, Karel; Blochwitz, C.; Polák, Jaroslav

    2002-01-01

    Roč. 50, č. 15 (2002), s. 3767-3780 ISSN 1359-6454 R&D Projects: GA ČR GA106/00/D055; GA ČR GA106/01/0376 Institutional research plan: CEZ:AV0Z2041904 Keywords : fatigue * persistent slip band * atomic force microscopy Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 3.104, year: 2002

  17. Low-cycle fatigue behavior of oxygen-free high-conductivity copper at 3000C in high vacuum

    International Nuclear Information System (INIS)

    Liu, K.C.; Loring, C.M. Jr.

    1983-01-01

    In-vacuum fatigue tests were performed on commercially-pure OFHC copper and 35% Au-65% Cu brazing filler metal at 300 0 C. Excessive recrystallization due to exposure in the 1025 0 C brazing temperature cycle was detrimental to the fatigue life of the base metal; cold work was beneficial to the fatigue resistance. Triple-point cracking and grain boundary sliding were the prevailing modes of fatigue failure observed in the full-size specimens. However, a mixed morphology of ductile and cleavage-like fracture was observed on the fracture surface of the subsize specimen in which the grain structure appeared to have undergone a change because of the presence of surface cold work. The braze has superior fatigue resistance, but to exploit the maximum strength, the brazed joint must be devoid of defects such as cavities and cracks

  18. The Eligibility of Surface Electromyography in the Assessment of Paraspinal Muscles Fatigue Following Interventions in Patients with Chronic Low Back Pain: A Systematic Review

    OpenAIRE

    Nahid Rahmani; Mohammad Ali Mohseni-Bandpei; Iraj Abdollahi

    2013-01-01

    Objective: Evaluation of paraspinal muscles endurance in patients with chronic low back pain (LBP) seems to be of great importance. Many studies demonstrated that surface electromyography has merit to assess muscle fatigue using frequency spectrum. The purpose of this study was to systematically review the eligibility of the surface electromyography in the assessment of paraspinal muscles fatigue changes following different interventions in patients with chronic LBP. Materials & Methods: ...

  19. Analysis of BTEX groundwater concentrations from surface spills associated with hydraulic fracturing operations.

    Science.gov (United States)

    Gross, Sherilyn A; Avens, Heather J; Banducci, Amber M; Sahmel, Jennifer; Panko, Julie M; Tvermoes, Brooke E

    2013-04-01

    Concerns have arisen among the public regarding the potentialfor drinking-water contamination from the migration of methane gas and hazardous chemicals associated with hydraulic fracturing and horizontal drilling. However, little attention has been paid to the potentialfor groundwater contamination resulting from surface spills from storage and production facilities at active well sites. We performed a search for publically available data regarding groundwater contamination from spills at ULS. drilling sites. The Colorado Oil and Gas Conservation Commission (COGCC) database was selected for further analysis because it was the most detailed. The majority ofspills were in Weld County, Colorado, which has the highest density of wells that used hydraulic fracturing for completion, many producing both methane gas and crude oil. We analyzed publically available data reported by operators to the COGCC regarding surface spills that impacted groundwater From July 2010 to July 2011, we noted 77 reported surface spills impacting the groundwater in Weld County, which resulted in surface spills associated with less than 0.5% of the active wells. The reported data included groundwater samples that were analyzed for benzene, toluene, ethylbenzene, andxylene (BTEX) components of crude oil. For groundwater samples taken both within the spill excavation area and on the first reported date of sampling, the BTEX measurements exceeded National Drinking Water maximum contaminant levels (MCLs) in 90, 30, 12, and 8% of the samples, respectively. However, actions taken to remediate the spills were effective at reducing BJTEX levels, with at least 84% of the spills reportedly achieving remediation as of May 2012. Our analysis demonstrates that surface spills are an important route of potential groundwater contamination from hydraulic fracturing activities and should be a focus of programs to protect groundwater While benzene can occur naturally in groundwater sources, spills and migration

  20. Fracture surface analysis in composite and titanium bonding: Part 1: Titanium bonding

    Science.gov (United States)

    Sanderson, K. A.; Wightman, J. P.

    1985-01-01

    Fractured lap shear Ti 6-4 adherends bonded with polyphenyquinoxaline (PPQ) and polysulfone were analyzed. The effects of adherend pretreatment, stress level, thermal aging, anodizing voltage, and modified adhesive of Ti 6-4 adherend bonded with PPQ on lap shear strength were studied. The effect of adherend pretreatment on lap shear strength was investigated for PS samples. Results of scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) used to study the surface topography and surface composition are also discussed.

  1. Creep-Fatigue Failure Diagnosis

    Science.gov (United States)

    Holdsworth, Stuart

    2015-01-01

    Failure diagnosis invariably involves consideration of both associated material condition and the results of a mechanical analysis of prior operating history. This Review focuses on these aspects with particular reference to creep-fatigue failure diagnosis. Creep-fatigue cracking can be due to a spectrum of loading conditions ranging from pure cyclic to mainly steady loading with infrequent off-load transients. These require a range of mechanical analysis approaches, a number of which are reviewed. The microstructural information revealing material condition can vary with alloy class. In practice, the detail of the consequent cracking mechanism(s) can be camouflaged by oxidation at high temperatures, although the presence of oxide on fracture surfaces can be used to date events leading to failure. Routine laboratory specimen post-test examination is strongly recommended to characterise the detail of deformation and damage accumulation under known and well-controlled loading conditions to improve the effectiveness and efficiency of failure diagnosis. PMID:28793676

  2. The surface and interior evolution of Ceres revealed by fractures and secondary crater chains

    Science.gov (United States)

    Scully, Jennifer E. C.; Buczkowski, Debra; Schmedemann, Nico; King, Scott; O'Brien, David P.; Castillo-Rogez, Julie; Raymond, Carol; Marchi, Simone; Russell, Christopher T.; Mitri, Giuseppe; Bland, Michael T.

    2016-10-01

    Dawn became the first spacecraft to visit and orbit Ceres, a dwarf planet and the largest body in the asteroid belt (radius ~470 km) (Russell et al., 2016). Before Dawn's arrival, telescopic observations and thermal evolution modeling indicated Ceres was differentiated, with an average density of 2,100 kg/m3 (e.g. McCord & Sotin, 2005; Castillo-Rogez & McCord, 2010). Moreover, pervasive viscous relaxation in a water-ice-rich outer layer was predicted to erase most features on Ceres' surface (Bland, 2013). However, a full understanding of Ceres' surface and interior evolution remained elusive. On the basis of global geologic mapping, we identify prevalent ≥1 km wide linear features that formed: 1) as the surface expression of subsurface fractures, and 2) as material ejected during impact-crater formation impacted and scoured the surface, forming secondary crater chains. The formation and preservation of these linear features indicates Ceres' outer layer is relatively strong, and is not dominated by viscous relaxation as predicted. The fractures also give us insights into Ceres' interior: their spacing indicates the fractured layer is ~30 km thick, and we interpret the fractures formed because of uplift and extension induced by an upwelling region, which is consistent with geodynamic modeling (King et al., 2016). In addition, we find that some secondary crater chains do not form radial patterns around their source impact craters, and are located in a different hemisphere from their source impact craters, because of Ceres' fast rotation (period of ~9 hours) and relatively small radius. Our results show Ceres has a surface and outer layer with characteristics that are different than predicted, and underwent complex surface and interior evolution. Our fuller understanding of Ceres, based on Dawn data, gives us important insights into the evolution of bodies in the asteroid belt, and provides unique constraints that can be used to evaluate predictions of the surface

  3. Effects of a high mean stress on the high cycle fatigue life of PWA 1480 and correlation of data by linear elastic fracture mechanics

    Science.gov (United States)

    Majumdar, S.; Kwasny, R.

    1985-01-01

    High-cycle fatigue tests using 5-mm-diameter smooth specimens were performed on the single crystal alloy PWA 1480 (001 axis) at 70F (room temperature) in air and at 100F (538C) in vacuum (10 to the -6 power torr). Tests were conducted at zero mean stress as well as at high tensile mean stress. The results indicate that, although a tensile mean stress, in general, reduces life, the reduction in fatigue strength, for a given mean stress at a life of one million cycles, is much less than what is predicted by the usual linear Goodman plot. Further, the material appears to be significantly more resistant to mean stress effects at 1000F than at 70F. Metallographic examinations of failed specimens indicate that failures in all cases are initiated from micropores of sizes of the order of 30 to 40 microns. Since the macroscopic stress-strain response in all cases was observed to be linear elastic, linear elastic fracture mechanics (LEFM) analyses were carried out to determine the crack growth curves of the material assuming that crack initiation from a micropore (a sub o = 40 microns) occurs very early in life. The results indicate that the calculated crack growth rates at an R (defined as the ratio between minimum stress to maximum stress) value of zero are approximately the same at 70F as at 1000F. However, the calculated crack growth rates at other R ratios, both positive and negative, tend to be higher at 70F than at 1000F. Calculated threshold effects at large R values tend to be independent of temperature in the temperature regime studied. They are relatively constant with increasing R ratio up to a value of about 0.6, beyond which the calculated threshold stress intensity factor range decreases rapidly with increasing R ratios.

  4. 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

  5. High volume hydraulic fracturing operations: potential impacts on surface water and human health.

    Science.gov (United States)

    Mrdjen, Igor; Lee, Jiyoung

    2016-08-01

    High volume, hydraulic fracturing (HVHF) processes, used to extract natural gas and oil from underground shale deposits, pose many potential hazards to the environment and human health. HVHF can negatively affect the environment by contaminating soil, water, and air matrices with potential pollutants. Due to the relatively novel nature of the process, hazards to surface waters and human health are not well known. The purpose of this article is to link the impacts of HVHF operations on surface water integrity, with human health consequences. Surface water contamination risks include: increased structural failure rates of unconventional wells, issues with wastewater treatment, and accidental discharge of contaminated fluids. Human health risks associated with exposure to surface water contaminated with HVHF chemicals include increased cancer risk and turbidity of water, leading to increased pathogen survival time. Future research should focus on modeling contamination spread throughout the environment, and minimizing occupational exposure to harmful chemicals.

  6. Identification method of fracture mode based on measurement of microscopic plastic deformation in a Mg cast alloy

    Energy Technology Data Exchange (ETDEWEB)

    Ochi, Naoya [Department of Material Science and Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); Higuchi, Yu-ki [Department of Mechanical Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); Narita, Ichihito, E-mail: i-narita@live.jp [Department of Material Science and Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); Miyahara, Hirofumi, E-mail: miyahara@zaiko.kyushu-u.ac.jp [Department of Material Science and Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); Matsumoto, Toshiharu [Tobata Seisakusho Co., Ltd., 8-21 Shinsone, Kokuraminami-ku, Kitakyushu 800-0211 (Japan); Noguchi, Hiroshi, E-mail: noguchi.hiroshi.936@m.kyushu-u.ac.jp [Department of Mechanical Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan)

    2015-08-26

    Plastic deformation under fracture surface in non-combustible magnesium alloy was investigated using electron backscatter diffraction analysis after tensile tests of specimens having a fatigue pre-crack or shrinkage porosity, so that it revealed that the fracture mode of shrinkage porosity of the magnesium alloy can be treated as a crack.

  7. Evaluations of environmental effect on micro crack initiation and propagation by surface observations of fatigue specimens

    International Nuclear Information System (INIS)

    Fujikawa, Ryosuke; Abe, Shigeki; Nakamura, Takao; Kamaya, Masayuki

    2014-01-01

    Fatigue life of nuclear facilities tends to be decreased by the influence of reactor coolant, which is called environmental effect. The effect accelerates crack growth rate but the influence for crack initiation is not clarified. This study intends to discuss the environmental effect in crack initiation. The crack length and the number of cracks are measured from the investigation of fatigue test specimens in reactor coolant and air. The behavior of crack initiation is revealed from the measurement of number of cracks, crack sizes and fatigue life. From this study, environmental effect of reactor coolant is considered to influence crack initiation and increase the number of micro crack. It is also estimated that the coalescence of cracks influences the acceleration of crack growth. (author)

  8. Scanning Electron Microscope Mapping System Developed for Detecting Surface Defects in Fatigue Specimens

    Science.gov (United States)

    Bonacuse, Peter J.; Kantzos, Peter T.

    2002-01-01

    An automated two-degree-of-freedom specimen positioning stage has been developed at the NASA Glenn Research Center to map and monitor defects in fatigue specimens. This system expedites the examination of the entire gauge section of fatigue specimens so that defects can be found using scanning electron microscopy (SEM). Translation and rotation stages are driven by microprocessor-based controllers that are, in turn, interfaced to a computer running custom-designed software. This system is currently being used to find and record the location of ceramic inclusions in powder metallurgy materials. The mapped inclusions are periodically examined during interrupted fatigue experiments. The number of cycles to initiate cracks from these inclusions and the rate of growth of initiated cracks can then be quantified. This information is necessary to quantify the effect of this type of defect on the durability of powder metallurgy materials. This system was developed with support of the Ultra Safe program.

  9. Fracture-free surfaces of CAD/CAM lithium metasilicate glass-ceramic using micro-slurry jet erosion.

    Science.gov (United States)

    Yin, Ling; Baba, Takashi; Nakanishi, Yoshitaka

    2018-04-01

    This paper reports the use of micro-slurry jet erosion (MSJE) on CAD/CAM lithium mesilicate glass ceramic (LMGC) that is capable of achieving the fracture-free surface quality. A computer-controlled MSJE process using a low-pressure and low-concentration alumina slurry was applied to diamond-ground LMGC surfaces with surface and subsurface damage. The MSJE processed and diamond-ground LMGC surfaces were examined using scanning electron microscopy (SEM) to examine surface morphology, fractures, and residual defects. 3D confocal laser microscopy (CLM) was used to quantitatively characterize all machined surface textures as a function of processing conditions. Our results show that surface and subsurface damage induced in diamond-ground surfaces were significantly diminished after 50-cycle MSJE processing. Fracture-free surfaces were obtained after 100 MSJE cycles. Our measured parameters of the 3D surface topography included the average surface roughness, maximum peak-valley height, highest peak height, lowest valley height, and kurtosis and absolute skewness of height distributions. All these parameters were significantly reduced with the increase of MSJE cycles. This work implies that MSJE promises to be an effective manufacturing technique for the generation of fracture-free LMGC surfaces which are crucial for high-quality monolithic restorations made from the material. Copyright © 2018 Elsevier Ltd. All rights reserved.

  10. Detection and Alert of muscle fatigue considering a Surface Electromyography Chaotic Model

    International Nuclear Information System (INIS)

    Herrera, V; Romero, J F; Amestegui, M

    2011-01-01

    This work propose a detection and alert algorithm for muscle fatigue in paraplegic patients undergoing electro-therapy sessions. The procedure is based on a mathematical chaotic model emulating physiological signals and Continuous Wavelet Transform (CWT). The chaotic model developed is based on a logistic map that provides suitable data accomplishing some physiological signal class patterns. The CWT was applied to signals generated by the model and the resulting vector was obtained through Total Wavelet Entropy (TWE). In this sense, the presented work propose a viable and practical alert and detection algorithm for muscle fatigue.

  11. Detection and Alert of muscle fatigue considering a Surface Electromyography Chaotic Model

    Energy Technology Data Exchange (ETDEWEB)

    Herrera, V; Romero, J F [Engineering, Modeling and Applied Social Sciences Center, ABC Federal University, Santo Andr - SP (Brazil); Amestegui, M, E-mail: victoria.herrera@ufabc.edu.br [Engineering Faculty, Electronics Engineering, Universidad Mayor de San Andres, La Paz (Bolivia, Plurinational State of)

    2011-03-01

    This work propose a detection and alert algorithm for muscle fatigue in paraplegic patients undergoing electro-therapy sessions. The procedure is based on a mathematical chaotic model emulating physiological signals and Continuous Wavelet Transform (CWT). The chaotic model developed is based on a logistic map that provides suitable data accomplishing some physiological signal class patterns. The CWT was applied to signals generated by the model and the resulting vector was obtained through Total Wavelet Entropy (TWE). In this sense, the presented work propose a viable and practical alert and detection algorithm for muscle fatigue.

  12. Study of surface relief evolution in fatigued 316L austenitic stainless steel by AFM

    Czech Academy of Sciences Publication Activity Database

    Man, Jiří; Obrtlík, Karel; Polák, Jaroslav

    2003-01-01

    Roč. 351, 1-2 (2003), s. 123-132 ISSN 0921-5093 R&D Projects: GA AV ČR IBS2041001; GA AV ČR IAA2041201; GA ČR GA106/00/D055; GA ČR GA106/01/0376 Institutional research plan: CEZ:AV0Z2041904 Keywords : fatigue * atomic force microscopy * persistent slip band Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.365, year: 2003

  13. Influence of surface conditions on fatigue strength through the numerical simulation of microstructure; Etude par simulation numerique de la microstructure de l'influence de l'etat de surface sur la resistance a la fatigue d'un acier 304L

    Energy Technology Data Exchange (ETDEWEB)

    Le Pecheur, A.; Clavel, M.; Rey, C.; Bompard, P. [Laboratoire MSSMat, UMR 8579 CNRS, Ecole Centrale Paris (France); Le Pecheur, A.; Curtit, F.; Stephan, J.M. [Departement MMC, EDF RD, Site des Renardieres (France)

    2010-11-15

    A thermal fatigue test (INTHERPOL) was developed by EDF in order to study the initiation of cracks. These tests are carried out on tubular specimens under various thermal loadings and surface finish qualities in order to give an account of these parameters on crack initiation. The main topic of this study is to test the sensitivity of different fatigue criteria to surface conditions using a micro/macro modelling approach. Therefore a 304L polycrystalline aggregate, used for cyclic plasticity based FE modelling, have been considered as a Representative Volume Element located at the surface and subsurface of the test tube. This aggregate has been cyclically strained according to the results issued from FE simulation of INTHERPOL thermal fatigue experiment. Different surface parameters have been numerically simulated: effects of local microstructure and of grains orientation, effects of machining: metallurgical prehardening, residual stress gradient, and surface roughness. Three different fatigue criteria (Manson Coffin, Fatemi Socie and dissipated energy types), previously fitted at a macro-scale for thermal fatigue of 304L, have been computed at a meso scale, in order to show the surface 'hot spots' features and test the sensitivity of these three criteria to different surface conditions. Results show that grain orientation and neighbouring play an important role on the location of hot spots, and also that the positive effect of pre-straining and the negative effect of roughness on fatigue life are not all similarly predicted by these different fatigue criteria. (authors)

  14. Effect of Reduced Phosphoric Acid Pre-etching Times 
on Enamel Surface Characteristics and Shear Fatigue Strength Using Universal Adhesives.

    Science.gov (United States)

    Tsujimoto, Akimasa; Fischer, Nicholas; Barkmeier, Wayne; Baruth, Andrew; Takamizawa, Toshiki; Latta, Mark; Miyazaki, Masashi

    2017-01-01

    To examine the effect of reduced phosphoric acid pre-etching times on enamel fatigue bond strength of universal adhesives and surface characteristics by using atomic force microscopy (AFM). Three universal adhesives were used in this study (Clearfil Universal Bond [C], G-Premio Bond [GP], Scotchbond Universal Adhesive [SU]). Four pre-etching groups were employed: enamel pre-etched with phosphoric acid and immediately rinsed with an air-water spray, and enamel pre-etched with phosphoric acid for 5, 10, or 15 s. Ground enamel was used as the control group. For the initial bond strength test, 15 specimens per etching group for each adhesive were used. For the shear fatigue test, 20 specimens per etching group for each adhesive were loaded using a sine wave at a frequency of 20 Hz for 50,000 cycles or until failure occurred. Initial shear bond strengths and fatigue shear strengths of composite adhesively bonded to ground and pre-etched enamel were determined. AFM observations of ground and pre-etched enamel were also conducted, and surface roughness as well as surface area were evaluated. The initial shear bond strengths and fatigue shear strengths of the universal adhesives in the pre-etched groups were significantly higher than those of the control group, and were not influenced by the pre-etching time. Significantly higher surface roughness and surface area of enamel surfaces in pre-etched groups were observed compared with those in the control group. While the surface area was not significantly influenced by etching time, surface roughness of the enamel surfaces in the pre-etched groups significantly increased with pre-etching time. The results of this in vitro study suggest that reduced phosphoric acid pre-etching times do not impair the fatigue bond strength of universal adhesives. Although fatigue bond strength and surface area were not influenced by phosphoric-acid etching times, surface roughness increased with increasing etching time.

  15. Microstructural heterogeneities and fatigue anisotropy of forged steels

    Energy Technology Data Exchange (ETDEWEB)

    Pessard, Etienne, E-mail: etienne.pessard@angers.ensam.fr [LAMPA, Arts et Metiers ParisTech Angers, 2 Bd du Ronceray, 49035 Angers Cedex 01 (France); Morel, Franck [LAMPA, Arts et Metiers ParisTech Angers, 2 Bd du Ronceray, 49035 Angers Cedex 01 (France); Verdu, Catherine [MATEIS, INSA-Lyon, Universite de Lyon, 25 Av Jean Capelle, 69621 Villeurbanne Cedex (France); Flaceliere, Laurent; Baudry, Gilles [CREAS - ASCOMETAL, BP 70045, 57301 Hagondange (France)

    2011-11-25

    Highlights: {yields} Tomography result: fibering is composed of non-metallic inclusions bands. {yields} Elongated inclusions decreases the: ductility, fracture toughness and fatigue limit. {yields} Cracks initiate from both inclusion clusters and from the bainitic matrix. {yields} The classical self-heating method does not predict the effect of the inclusions. - Abstract: In this study, various experimental methods are employed to determine the anisotropic fatigue behavior of a 25MnCrSiVB6 forged steel (Metasco MC). This material has a bainitic microstructure and contains many elongated non-metallic inclusions in the rolled direction, which are grouped into clusters. Specimens with different orientations relative to the rolling direction have been extracted from a hot rolled bar and the ability of certain experimental techniques to capture the fatigue anisotropy has been tested. Results obtained from monotonic tensile tests and Charpy impact tests show that the material has isotropic fracture strength and anisotropic ductility. The influence of the 'inclusion clusters' is clearly demonstrated via observation of the fracture surfaces. Concerning the fatigue behavior, results from a classical staircase experimental procedure are compared to results from self-heating fatigue tests. For specimens orientated at 0{sup o} relative to the rolled direction, microcrack initiation is controlled by the material matrix and the prediction of the fatigue strength with the self-heating method has been observed to be correct. For specimens orientated at 45{sup o} and 90{sup o}, the elongated manganese sulfide inclusion clusters are the origin of crack initiation and the fatigue strength drops significantly. For this case, it appears that the self-heating method has difficulty predicting the fatigue behavior.

  16. Microstructural heterogeneities and fatigue anisotropy of forged steels

    International Nuclear Information System (INIS)

    Pessard, Etienne; Morel, Franck; Verdu, Catherine; Flaceliere, Laurent; Baudry, Gilles

    2011-01-01

    Highlights: → Tomography result: fibering is composed of non-metallic inclusions bands. → Elongated inclusions decreases the: ductility, fracture toughness and fatigue limit. → Cracks initiate from both inclusion clusters and from the bainitic matrix. → The classical self-heating method does not predict the effect of the inclusions. - Abstract: In this study, various experimental methods are employed to determine the anisotropic fatigue behavior of a 25MnCrSiVB6 forged steel (Metasco MC). This material has a bainitic microstructure and contains many elongated non-metallic inclusions in the rolled direction, which are grouped into clusters. Specimens with different orientations relative to the rolling direction have been extracted from a hot rolled bar and the ability of certain experimental techniques to capture the fatigue anisotropy has been tested. Results obtained from monotonic tensile tests and Charpy impact tests show that the material has isotropic fracture strength and anisotropic ductility. The influence of the 'inclusion clusters' is clearly demonstrated via observation of the fracture surfaces. Concerning the fatigue behavior, results from a classical staircase experimental procedure are compared to results from self-heating fatigue tests. For specimens orientated at 0 o relative to the rolled direction, microcrack initiation is controlled by the material matrix and the prediction of the fatigue strength with the self-heating method has been observed to be correct. For specimens orientated at 45 o and 90 o , the elongated manganese sulfide inclusion clusters are the origin of crack initiation and the fatigue strength drops significantly. For this case, it appears that the self-heating method has difficulty predicting the fatigue behavior.

  17. Effect of irrigation on surface roughness and fatigue resistance of controlled memory wire nickel-titanium instruments.

    Science.gov (United States)

    Cai, J-J; Tang, X-N; Ge, J-Y

    2017-07-01

    To investigate the effect of irrigation on the surface roughness and fatigue resistance of HyFlex and M3 controlled memory (CM) wire nickel-titanium instruments. Two new files of each brand were analysed by atomic force microscopy (AFM). Then, the instruments were dynamically immersed in either 5.25% sodium hypochlorite (NaOCl) or 17% ethylene diamine tetraacetic acid (EDTA) solution for 10 min, followed by AFM analysis. The roughness average (Ra) and root mean square (RMS) values were analysed statistically using an independent sample t-test. Then, 36 files of each brand were randomly assigned to three groups (n = 12). Group 1 (the control group) was composed of new instruments. Groups 2 and 3 were dynamically immersed in 5.25% NaOCl and 17% EDTA solutions for 10 min, respectively. The number of rotations to failure for various groups was analysed using the one-way analysis of variance software. For M3 files, the Ra and RMS values significantly increased (P  0.05) NaOCl. The resistance to cyclic fatigue of both HyFlex and M3 files did not significantly decrease (P > 0.05) by immersing in 5.25% NaOCl and 17% EDTA solutions. Except the HyFlex files immersed in NaOCl, the surface roughness of other files exposed to irrigants increased. However, a change in the surface tomography of CM wire instruments caused by contact with irrigants for 10 min did not trigger a decrease in cyclic fatigue resistance. © 2016 International Endodontic Journal. Published by John Wiley & Sons Ltd.

  18. Fatigue data compilation and evaluation of fatigue on design

    International Nuclear Information System (INIS)

    Nyilas, A.

    1985-05-01

    The aim of this report is a review of the available fatigue data of various materials necessary for the design of large superconducting magnets for fusion. One of the primary objectives of this work is to present a broad outline of the low temperature fatigue data of relevant materials within the scope of available data. Besides the classical fatigue data of materials the fatigue crack propagation measurements are outlined widely. The existing recommendations for the design of cryogenic structures are described. A brief introduction of fracture mechanics as well as a historical background of the development of our present day understanding of fatigue has been done. (orig.) [de

  19. Outcrop-scale fracture trace identification using surface roughness derived from a high-density point cloud

    Science.gov (United States)

    Okyay, U.; Glennie, C. L.; Khan, S.

    2017-12-01

    Owing to the advent of terrestrial laser scanners (TLS), high-density point cloud data has become increasingly available to the geoscience research community. Research groups have started producing their own point clouds for various applications, gradually shifting their emphasis from obtaining the data towards extracting more and meaningful information from the point clouds. Extracting fracture properties from three-dimensional data in a (semi-)automated manner has been an active area of research in geosciences. Several studies have developed various processing algorithms for extracting only planar surfaces. In comparison, (semi-)automated identification of fracture traces at the outcrop scale, which could be used for mapping fracture distribution have not been investigated frequently. Understanding the spatial distribution and configuration of natural fractures is of particular importance, as they directly influence fluid-flow through the host rock. Surface roughness, typically defined as the deviation of a natural surface from a reference datum, has become an important metric in geoscience research, especially with the increasing density and accuracy of point clouds. In the study presented herein, a surface roughness model was employed to identify fracture traces and their distribution on an ophiolite outcrop in Oman. Surface roughness calculations were performed using orthogonal distance regression over various grid intervals. The results demonstrated that surface roughness could identify outcrop-scale fracture traces from which fracture distribution and density maps can be generated. However, considering outcrop conditions and properties and the purpose of the application, the definition of an adequate grid interval for surface roughness model and selection of threshold values for distribution maps are not straightforward and require user intervention and interpretation.

  20. Correlation between residual stress and plastic strain amplitude during low cycle fatigue of mechanically surface treated austenitic stainless steel AISI 304 and ferritic-pearlitic steel SAE 1045

    Energy Technology Data Exchange (ETDEWEB)

    Nikitin, I. [Institute of Materials Engineering, University of Kassel, 34125 Kassel, Hessen (Germany)], E-mail: Ivan.Nikitin@infineon.com; Besel, M. [Institute of Materials Engineering, University of Kassel, 34125 Kassel, Hessen (Germany)

    2008-09-15

    Mechanical surface treatments such as deep rolling are known to affect the near-surface microstructure and induce, e.g. residual stresses and/or increase the surface hardness. It is well known that, e.g. compressive residual stress states usually increase the lifetime under fatigue loading. The stress relaxation behaviour and the stability of the residual stress during fatigue loading depend on the mechanical surface treatment method. In this paper three different surface treatments are used and their effects on the low cycle fatigue behaviour of austenitic stainless steel (AISI 304) and ferritic-pearlitic steel (SAE 1045) are investigated. X-ray diffraction is applied for the non-destructive evaluation of the stress state and the microstructure. It is found that consecutive deep rolling and annealing as well as high temperature deep rolling produce more stable near-surface stress states than conventional deep rolling at room temperature. The plastic strain amplitudes during fatigue loading are measured and it is shown that they correlate well with the induced residual stress and its relaxation, respectively. Furthermore, Coffin-Manson plots are presented which clearly show the correlation between the plastic strain amplitude and the fatigue lifetime.

  1. Fracture zones constrained by neutral surfaces in a fault-related fold: Insights from the Kelasu tectonic zone, Kuqa Depression

    Science.gov (United States)

    Sun, Shuai; Hou, Guiting; Zheng, Chunfang

    2017-11-01

    Stress variation associated with folding is one of the controlling factors in the development of tectonic fractures, however, little attention has been paid to the influence of neutral surfaces during folding on fracture distribution in a fault-related fold. In this study, we take the Cretaceous Bashijiqike Formation in the Kuqa Depression as an example and analyze the distribution of tectonic fractures in fault-related folds by core observation and logging data analysis. Three fracture zones are identified in a fault-related fold: a tensile zone, a transition zone and a compressive zone, which may be constrained by two neutral surfaces of fold. Well correlation reveals that the tensile zone and the transition zone reach the maximum thickness at the fold hinge and get thinner in the fold limbs. A 2D viscoelastic stress field model of a fault-related fold was constructed to further investigate the mechanism of fracturing. Statistical and numerical analysis reveal that the tensile zone and the transition zone become thicker with decreasing interlimb angle. Stress variation associated with folding is the first level of control over the general pattern of fracture distribution while faulting is a secondary control over the development of local fractures in a fault-related fold.

  2. Study on fatigue life evaluation of structural component based on crack growth criterion

    International Nuclear Information System (INIS)

    Shibata, Katsuyuki

    1984-07-01

    As one of the practical application of fracture mechanics, fatigue life evaluation method based on crack growth criterion has been diffusing in various field of technology in order to determine the rational and reliable life of structural components. The fatigue life by this method is evaluated based on the fatigue crack growth analysis from defects, while many problems, such as the influence of residual stress on the crack growth behavior, the effect of overloading, and evaluation method for multiple surface cracks, are not sufficiently solved yet. In this paper, the above problems are treated, and based on some exprimental data some simple mehtods for fatigue life evaluation are proposed regarding the above problems. Verification of the proposed methods are shown in the paper by comparing with some experimental results, and the applicability of the proposed method is also examined by the fatigue test of pipes with cracks in the inner surface. (author)

  3. Effects of stress concentrations on the fatigue life of a gamma based titanium aluminide

    International Nuclear Information System (INIS)

    Trail, S.J.; Bowen, P.

    1995-01-01

    S-N curves for a gamma based titanium aluminide alloy of composition Ti-47.2Al-2.1Mn-1.9Nb(at.%)+2TiB 2 (wt.%) have been used to define fatigue life. Effects of residual stress, stressed volume, loading ratio, loading mode, elevated temperature and surface roughness have been considered. Residual tensile stresses and micro-cracking are introduced by Electro Discharge Machining and the fatigue life is reduced slightly compared with polished samples. Notched fatigue tests show a significant notch strengthening effect which increases with increasing stress concentration factor. The fracture surfaces of specimens tested at room temperature reveal fully brittle failure mechanisms and no evidence of stable crack growth is observed. The fatigue life appears, therefore, to be determined predominantly by the number of cycles to crack initiation. At the elevated temperature of 830 C, evidence for some stable fatigue crack growth has been found. Probable sites for crack initiation are addressed

  4. Fatigue behavior of niobium--hydrogen alloys

    International Nuclear Information System (INIS)

    Chung, D.W.; Stoloff, N.S.

    1978-01-01

    The effects of hydrogen on room temperature fatigue behavior of niobium were investigated under both high frequency stress control and low frequency strain control conditions, in air. Hydrogen markedly improved the fatigue life in high frequency tests, while low frequency tests resulted in decreased fatigue life with increasing hydrogen content. Notches in hydrogen-charged alloys reduced high cycle life significantly but had little effect on low cycle tests. Fracture surfaces of annealed niobium mainly exhibited striations, with numerous cracks originating at troughs of striated bands in both stress and strain control tests. The fracture mode for alloys with hydrogen in solution was mixed, with striations interspersed with cleavage facets at high frequencies but generally cleavage steps at low frequencies. For the hydrided alloys, distinctive steps of mixed ductile-brittle appearance were revealed under high frequency conditions, but large cleavage facets only were observed for low frequency tests. The results are discussed in terms of the effects of hydrogen on the cyclic strain hardening rate, as well as on fatigue strength and ductility of niobium

  5. The effect of microstructure on fatigue performance of Ti-6Al-4V alloy after EDM surface treatment for application in orthopaedics.

    Science.gov (United States)

    Stráský, Josef; Janeček, Miloš; Harcuba, Petr; Bukovina, Michal; Wagner, Lothar

    2011-11-01

    Three different microstructures--equiaxed, bi-modal and coarse lamellar--are prepared from Ti-6Al-4V alloy. Electric discharge machining (EDM) with a high peak current (29 A) is performed in order to impose surface roughness and modify the chemical composition of the surface. Detailed scanning electron microscopy (SEM) investigation revealed a martensitic surface layer and subsurface heat affected zone (HAZ). EDX measurements showed carbon enriched remnants of the EDM process on the material surface. Rotating bending fatigue tests are undertaken for EDM processed samples for all three microstructures and also for electropolished-benchmark-samples. The fatigue performance is found to be rather poor and not particularly dependent on microstructure. The bi-modal microstructure shows a slightly superior high cycle fatigue performance. This performance can be further improved by a suitable heat treatment to an endurance limit of 200 MPa. Copyright © 2011 Elsevier Ltd. All rights reserved.

  6. A direct comparison in the fatigue resistance enhanced by surface severe plastic deformation and shot peening in a C-2000 superalloy

    Energy Technology Data Exchange (ETDEWEB)

    Shaw, Leon L., E-mail: leon.shaw@uconn.edu [Department of Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, CT (United States); Tian, Jia-Wan [Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN (United States); Ortiz, Angel L. [Departamento de Ingenieria Mecanica, Energetica y de los Materiales, Universidad de Extremadura, 06071 Badajoz (Spain); Dai Kun [Quality Engineering and Software Technology, East Hartford, CT 06108 (United States); Villegas, Juan C. [Intel Corporation, Chandler, AZ (United States); Liaw, Peter K. [Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN (United States); Ren Ruiming [School of Materials Science and Engineering, Dalian Jiaotong University, Dalian (China); Klarstrom, Dwaine L. [Haynes International, Inc., Kokomo, IN (United States)

    2010-02-15

    In this study, we present the first evidence and modeling efforts showing that surface severe plastic deformation (S{sup 2}PD) can be more effective in producing metallic components with superior fatigue properties than shot peening (SP). With the aid of a wide battery of characterization techniques (i.e., X-ray diffractometry, optical microscopy, scanning electron microscopy, transmission electron microscopy, and 3-dimensional non-contact optical profilometry), micro- and nano-hardness testing, and finite element modeling, we have identified the underlying mechanism for the fatigue improvement. It is shown that the enhancement in the fatigue limit is derived from a nanocrystalline surface layer, a work-hardened surface region, and residual compressive stresses at the surface, all of which are introduced by S{sup 2}PD and more substantial than that introduced by SP.

  7. Provision of wear resistance and fatigue strength of surfaces during electroerosive processing

    Science.gov (United States)

    Fedonin, O. N.; Syanov, S. Yu; Papikyan, A. M.

    2018-03-01

    This article is a generalization of the results of theoretical studies of the effect of erosion control regimes on the operational properties of mold-forming parts of molds. The main problem is the provision of wear resistance and fatigue strength in the electroerosion processing of these types of products. The analysis showed that the fatigue strength is affected by the processing regimes and the coefficient after the erosion treatment. The index of wear resistance is determined both by the treatment modes and by the physical-mechanical properties of the billet materials. To ensure the operational performance of products, it is necessary to establish the physical picture of the processing of complex profile parts by finding the optimum eroding regime.

  8. Corrosion fatigue behavior of high strength brass in aqueous solutions

    Energy Technology Data Exchange (ETDEWEB)

    Hamada, A.S.; Kassem, M.A.; Ramadan, R.M.; El-Zeky, M.A. [Suez Canal Univ., Dept. of Metallurgy and Materials Engineering (Egypt)

    2000-07-01

    Corrosion fatigue behavior of British Standard high strength brass, CZ 127 has been studied in various environments, 3.5%NaC1 solution and 3.5%NaC1 containing 1000ppm ammonia by applying the reverse bending technique, strain-controlled cyclic, at 67 cycles/min. Characteristics of the produced alloy were studied using differential thermal analysis with applying its results in heat treating of the alloy; metallographic examinations; hardness measurements; X-ray; and electrochemical behavior of the unstressed alloy. CZ 127 was fatigued at three different conditions, solution treated, peak aged, and over aged at a fixed strain amplitude, 0.03 5. Solution treated alloy gave the best fatigue properties in all environments tested among the other materials. Results of the alloy studied were compared with that obtained of 70/30 {alpha}-brass. Fracture surface of the fatigued alloy was examined using optical microscope and scanning electron microscope equipped with EDX. (author)

  9. Corrosion fatigue behavior of high strength brass in aqueous solutions

    International Nuclear Information System (INIS)

    Hamada, A.S.; Kassem, M.A.; Ramadan, R.M.; El-Zeky, M.A.

    2000-01-01

    Corrosion fatigue behavior of British Standard high strength brass, CZ 127 has been studied in various environments, 3.5%NaC1 solution and 3.5%NaC1 containing 1000ppm ammonia by applying the reverse bending technique, strain-controlled cyclic, at 67 cycles/min. Characteristics of the produced alloy were studied using differential thermal analysis with applying its results in heat treating of the alloy; metallographic examinations; hardness measurements; X-ray; and electrochemical behavior of the unstressed alloy. CZ 127 was fatigued at three different conditions, solution treated, peak aged, and over aged at a fixed strain amplitude, 0.03 5. Solution treated alloy gave the best fatigue properties in all environments tested among the other materials. Results of the alloy studied were compared with that obtained of 70/30 α-brass. Fracture surface of the fatigued alloy was examined using optical microscope and scanning electron microscope equipped with EDX. (author)

  10. Scaling properties of fracture surfaces on glass strengthened by ionic exchange

    International Nuclear Information System (INIS)

    Garza-Mendez, F.J.; Hinojosa-Rivera, M.; Gomez, I.; Sanchez, E.M.

    2007-01-01

    In this work the results of the statistical topometric analysis of fracture surfaces of soda-lime-silica glass with and without ionic exchange treatment are reported. In this case, the mechanism of substitution is K + -Na + . atomic force microscopy (AFM) was employed to record the topometric data from the fracture surface. The roughness exponent (ζ) and the correlation length (ξ) were calculated by the variable bandwidth method. The analysis for both glasses (subjected and non-subjected to ionic exchange) for ζ shows a value ∼0.8, this value agrees well with that reported in the literature for rapid crack propagation in a variety of materials. The correlation length shows different values for each condition. These results, along with those of microhardness indentations suggest that the self-affine correlation length is influenced by the complex interactions of the stress field of microcracks with that resulting from the collective behavior of the point defects introduced by the strengthening mechanism of ionic exchange

  11. Thermography detection on the fatigue damage

    Science.gov (United States)

    Yang, Bing

    It has always been a great temptation in finding new methods to in-situ "watch" the material fatigue-damage processes so that in-time reparations will be possible, and failures or losses can be minimized to the maximum extent. Realizing that temperature patterns may serve as fingerprints for stress-strain behaviors of materials, a state-of-art infrared (IR) thermography camera has been used to "watch" the temperature evolutions of both crystalline and amorphous materials "cycle by cycle" during fatigue experiments in the current research. The two-dimensional (2D) thermography technique records the surface-temperature evolutions of materials. Since all plastic deformations are related to heat dissipations, thermography provides an innovative method to in-situ monitor the heat-evolution processes, including plastic-deformation, mechanical-damage, and phase-transformation characteristics. With the understanding of the temperature evolutions during fatigue, thermography could provide the direct information and evidence of the stress-strain distribution, crack initiation and propagation, shear-band growth, and plastic-zone evolution, which will open up wide applications in studying the structural integrity of engineering components in service. In the current research, theoretical models combining thermodynamics and heat-conduction theory have been developed. Key issues in fatigue, such as in-situ stress-strain states, cyclic softening and hardening observations, and fatigue-life predictions, have been resolved by simply monitoring the specimen-temperature variation during fatigue. Furthermore, in-situ visulizations as well as qualitative and quantitative analyses of fatigue-damage processes, such as Luders-band evolutions, crack propagation, plastic zones, and final fracture, have been performed by thermography. As a method requiring no special sample preparation or surface contact by sensors, thermography provides an innovative and convenient method to in-situ monitor

  12. Low cycle fatigue and creep-fatigue interaction behavior of nickel-base superalloy GH4169 at elevated temperature of 650 °C

    Energy Technology Data Exchange (ETDEWEB)

    Chen, G., E-mail: agang@tju.edu.cn [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Zhang, Y. [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Xu, D.K. [Environmental Corrosion Center, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Lin, Y.C. [School of Mechanical and Electrical Engineering, Central South University, Changsha 410083 (China); Chen, X. [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China)

    2016-02-08

    Total strain-controlled low cycle fatigue (LCF) tests of a nickel based superalloy were performed at 650 °C. Various hold times were introduced at the peak tensile strain to investigate the high-temperature creep-fatigue interaction (CFI) effects under the same temperature. A substantial decrease in fatigue life occurred as the total strain amplitude increased. Moreover, tensile strain holding further reduced fatigue life. The saturation phenomenon of holding effect was found when the holding period reached 120 s. Cyclic softening occurred during the LCF and CFI process and it was related to the total strain amplitude and the holding period. The relationship between life-time and total strain amplitude was obtained by combining Basquin equation and Coffin-Manson equation. The surface and fracture section of the fatigued specimens were observed via scanning electronic microscope (SEM) to determine the failure mechanism.

  13. Viscosity and surface tension effects during multiphase flow in propped fractures

    Science.gov (United States)

    Dzikowski, Michał; Dąbrowski, Marcin

    2017-04-01

    Geological sequestration of CO2 was proposed as an important mechanism to reduce its emission into atmosphere. CO2 exhibits a higher affinity to organic matter than methane molecules and, potentially, it could be pumped and stored in shale reservoirs while enhancing late stage shale gas production. A successful analysis of CO2 sequestration in low matrix permeability rocks such as shales requires a thorough understanding of multiphase flow in stimulated rock fractures, which provide most significant pathways for fluids in such systems. Multiphase fracture flows are also of great relevance to brine, oil and gas migration in petroleum systems, water and stream circulation in geothermal reservoirs, and chemical transport of non-aqueous phase liquids in shallow hydrogeological systems, particularly in partially saturated zones. There are various physical models that describe phenomena taking place during multiphase flow through porous media. One of key aspects that need to be considered are pore-scale effects related to capillarity. Unfortunately, detailed models that describe motion and evolution of phase or component boundary require direct numerical simulations and spatial resolutions that are hard to reach when considering industrial relevant systems. Main aim of the presented work was the development of reduced 2.5D models based on Brinkman approximation of thin domain flow that would be able to capture local scale phenomena without expensive 3D simulations. Presented approach was designed specifically to tackle incompressible and immiscible systems and is based on Continuous Surface Force approach presented by Brackbill et al., implemented using Lattice Boltzmann Method. Presented approach where firstly validated against standard test cases with known classical solution and known experimental data. In the second part, we present and discuss two component, immiscible permeability data for rough and propped fracture obtained with our code for a rage of proppants

  14. Effect of implantoplasty on fracture resistance and surface roughness of standard diameter dental implants.

    Science.gov (United States)

    Costa-Berenguer, Xavier; García-García, Marta; Sánchez-Torres, Alba; Sanz-Alonso, Mariano; Figueiredo, Rui; Valmaseda-Castellón, Eduard

    2018-01-01

    To assess the effect of implantoplasty on the fracture resistance, surface roughness, and macroscopic morphology of standard diameter (4.1 mm) external connection dental implants. An in vitro study was conducted in 20 screw-shaped titanium dental implants with an external connection. In 10 implants, the threads and surface were removed and polished with high-speed burs (implantoplasty), while the remaining 10 implants were used as controls. The final implant dimensions were recorded. The newly polished surface quality was assessed by scanning electron microscopy (SEM) and by 3D surface roughness analysis using a confocal laser microscope. Finally, all the implants were subjected to a mechanical pressure resistance test. A descriptive analysis of the data was made. Also, Student's t tests were employed to detect differences regarding the compression tests. Implantoplasty was carried out for a mean time of 10 min and 48 s (standard deviation (SD) of 1 min 22 s). Macroscopically, the resulting surface had a smooth appearance, although small titanium shavings and silicon debris were present. The final surface roughness (S a values 0.1 ± 0.02 μm) was significantly lower than that of the original (0.75 ± 0.08 μm S a ) (p = .005). There was minimal reduction in the implant's inner body diameter (0.19 ± 0.03 mm), and no statistically significant differences were found between the test and control implants regarding the maximum resistance force (896 vs 880 N, respectively). Implantoplasty, although technically demanding and time-consuming, does not seem to significantly alter fracture resistance of standard diameter external connection implants. A smooth surface with S a values below 0.1 μm can be obtained through the use of silicon polishers. A larger sample is required to confirm that implantoplasty does not significantly affect the maximum resistance force of standard diameter external connection implants. © 2017 John Wiley & Sons A/S. Published

  15. Three-dimensional reconstruction of fracture surfaces of CFRP type composite materials

    International Nuclear Information System (INIS)

    Lobo, Raquel de Moraes

    2009-01-01

    The three-dimensional reconstruction of fracture surfaces of CFRP type composite materials is presented in this work as a possible method for the fractographic analysis of this material, whose rupture surface can present an accentuated roughness, with great variation in height. Two methods are presented for this purpose: the reconstruction for variable focus, carried through with images of optic microscopy and the reconstruction for parallax, carried through with pair of stereo images, obtained by means of scanning electronic microscopy. An evaluation is carried through for each one of the two methods, having argued its limits and the efficiency of each one of them, before the difficulties of analysis of unidirectional and multidirectional composite materials. The method of variable focus presented an excellent reconstruction result, but it has the need of a great number of images, spent time of the instrument and magnifying limit of the images as factors to be considered in the choice of better method. The tilting of the specimen, during the parallax method, discloses alterations in the histograms of the images acquired in the clockwise direction that limit the use of the method for materials with high roughness. The acquiring of images in only one direction and the construction of a region of interest, located in the center of the image are suggestions to turn the method most including. The linearity of the projections of features in the inclined image also suggests the possibility to carry through the reconstruction using, instead of only two, multiple images gotten in the counter-clockwise direction. The alterations proposals to modify the routine, are suggested so that the program can be applied in a more comprehensive form, independent of the quality of the observed fracture surface. (author)

  16. Influence of UFG structure formation on mechanical and fatigue properties in Ti-6Al-7Nb alloy

    Science.gov (United States)

    Polyakova, V. V.; Anumalasetty, V. N.; Semenova, I. P.; Valiev, R. Z.

    2014-08-01

    Ultrafine-grained (UFG) Ti alloys have potential applications in osteosynthesis and orthopedics due to high bio-compatibility and increased weight-to- strength ratio. In current study, Ti6Al7Nb ELI alloy is processed through equal channel angular pressing-conform (ECAP-Conform) and subsequent thermomechanical processing to generate a UFG microstructure. The fatigue properties of UFG alloys are compared to coarse grained (CG) alloys. Our study demonstrates that the UFG alloys with an average grain size of ~180 nm showed 35% enhancement of fatigue endurance limit as compared to coarse-grained alloys. On the fracture surfaces of the UFG and CG samples fatigue striations and dimpled relief were observed. However, the fracture surface of the UFG sample looks smoother; fewer amounts of secondary micro-cracks and more ductile rupture were also observed, which testifies to the good crack resistance in the UFG alloy after high-cyclic fatigue tests.

  17. Morphological Changes Of The Root Surface And Fracture Resistance After Treatment Of Root Fracture By CO2 Laser And Glass Ionomer Or Mineral Trioxide Aggregates

    Science.gov (United States)

    Badr, Y. A.; Abd El-Gawad, L. M.; Ghaith, M. E.

    2009-09-01

    This in vitro study evaluates the morphological changes of the root surface and fracture resistance after treatment of root cracks by CO2 laser and glass Ionomer or mineral trioxide aggregates (MTA). Fifty freshly extracted human maxillary central incisor teeth with similar dimension were selected. Crowns were sectioned at the cemento-enamel junction, and the lengths of the roots were adjusted to 13 mm. A longitudinal groove with a dimension of 1×5 mm2 and a depth of 1.5 mm was prepared by a high speed fissure bur on the labial surface of the root. The roots were divided into 5 groups: the 10 root grooves in group 1 were remained unfilled and were used as a control group. The 10 root grooves in group 2 were filled with glass Ionomer, 10 root grooves in group 3 were filled with MTA, the 10 root grooves in group 4 were filled with glass Ionomer and irradiated by CO2 laser and the 10 root grooves in group 5 were filled with MTA and irradiated with CO2 laser. Scanning electron microscopy was performed for two samples in each group. Tests for fracture strength were performed using a universal testing machine and a round tip of a diameter of 4 mm. The force was applied vertically with a constant speed of 1 mm min 1. For each root, the force at the time of fracture was recorded in Newtons. Results were evaluated statistically with ANOVA and Turkey's Honestly Significant Difference (HSD) tests. SEM micrographs revealed that the melted masses and the plate-like crystals formed a tight Chemical bond between the cementum and glass Ionomer and melted masses and globular like structure between cementum and MTA. The mean fracture resistance was the maximum fracture resistance in group 5 (810.8 N). Glass Ionomer and MTA with the help of CO2 laser can be an alternative to the treatment of tooth crack or fracture. CO2 laser increase the resistance of the teeth to fracture.

  18. Evaluation of muscle fatigue of wheelchair basketball players with spinal cord injury using recurrence quantification analysis of surface EMG.

    Science.gov (United States)

    Uzun, S; Pourmoghaddam, A; Hieronymus, M; Thrasher, T A

    2012-11-01

    Wheelchair basketball is the most popular exercise activity among individuals with spinal cord injury (SCI). The purpose of this study was to investigate muscular endurance and fatigue in wheelchair basketball athletes with SCI using surface electromyography (SEMG) and maximal torque values. SEMG characteristics of 10 wheelchair basketball players (WBP) were compared to 13 able-bodied basketball players and 12 sedentary able-bodied subjects. Participants performed sustained isometric elbow flexion at 50% maximal voluntary contraction until exhaustion. Elbow flexion torque and SEMG signals were recorded from three elbow flexor muscles: biceps brachii longus, biceps brachii brevis and brachioradialis. SEMG signals were clustered into 0.5-s epochs with 50% overlap. Root mean square (RMS) and median frequency (MDF) of SEMG signals were calculated for each muscle and epoch as traditional fatigue monitoring. Recurrence quantification analysis was used to extract the percentage of determinism (%DET) of SEMG signals. The slope of the %DET for basketball players and WBP showed slower increase with time than the sedentary able-bodied control group for three different elbow flexor muscles, while no difference was observed for the slope of the %DET between basketball and WBP. This result indicated that the athletes are less fatigable during the task effort than the nonathletes. Normalized MDF slope decay exhibited similar results between the groups as %DET, while the slope of the normalized RMS failed to show any significant differences among the groups (p > 0.05). MDF and %DET could be useful for the evaluation of muscle fatigue in wheelchair basketball training. No conclusions about special training for WBP could be determined.

  19. Influence of material ductility and crack surface roughness on fracture instability

    International Nuclear Information System (INIS)

    Khezrzadeh, Hamed; Wnuk, Michael P; Yavari, Arash

    2011-01-01

    This paper presents a stability analysis for fractal cracks. First, the Westergaard stress functions are proposed for semi-infinite and finite smooth cracks embedded in the stress fields associated with the corresponding self-affine fractal cracks. These new stress functions satisfy all the required boundary conditions and according to Wnuk and Yavari's (2003 Eng. Fract. Mech. 70 1659-74) embedded crack model they are used to derive the stress and displacement fields generated around a fractal crack. These results are then used in conjunction with the final stretch criterion to study the quasi-static stable crack extension, which in ductile materials precedes the global failure. The material resistance curves are determined by solving certain nonlinear differential equations and then employed in predicting the stress levels at the onset of stable crack growth and at the critical point, where a transition to the catastrophic failure occurs. It is shown that the incorporation of the fractal geometry into the crack model, i.e. accounting for the roughness of the crack surfaces, results in (1) higher threshold levels of the material resistance to crack propagation and (2) higher levels of the critical stresses associated with the onset of catastrophic fracture. While the process of quasi-static stable crack growth (SCG) is viewed as a sequence of local instability states, the terminal instability attained at the end of this process is identified with the global instability. The phenomenon of SCG can be used as an early warning sign in fracture detection and prevention.

  20. Development of autoradiographic method for measuring sorption of radionuclides on natural fracture surfaces

    International Nuclear Information System (INIS)

    Muuronen, S.

    1983-11-01

    On the basis of positive results about sorption of radionuclides in rock thin sections an autoradiographic method applicable for measurement sorption of radionuclides on rough rock surfaces was developed. There is no method available because 1) a plane film cannot be used because due to the roughness of rock surfaces 2) rock samples used in this investigation cannot be studied with microscopes and 3) autoradiogram cannot be studied fixed on the surface of a rock sample because the colours of the minerals in the sample will interfere with the interpretation. This report discusses experimental work done to find an useful proedure. In the development of the method main emphasis was put on investigation of the following steps: 1) preparation of the sample for equilibration and spiking; 2) properties of the covering paint for the rock surface and 3) testing of autoradiographic methods using different nuclear emulsions. As the result of these experiments promising autoradiograms with gel emulsion for sawed rock surfaces and with stripping film for rough rock surfaces were obtained. The mineralogic disribution of sorbed activity is easily seen in autoradiograms. Much work must still be done to get reliable quantitative information from autoradiograms. For developing of the autoradiographic method sawed plane rock samples of quartz feldspar intergrowth, pegmatite and limestone were used. In addition core samples of tonalite and mica gneiss from Olkiluoto were utilized. The distribution coefficients (Ksub(a)) obtained for cesium were 560 x 10 -4 and 620 x 10 -4 m 3 /m 2 for tonalite and mica gneiss, respectively. The results are little higher but of the same order of magnitude as obtained by the autoradiographic method using rock thin sections and by the batch method using crused samples. The natural fracture surface sorption study is a logical step in determining the scaling factor from laboratory to field studies. Field data will be needed to determine whether laboratory

  1. RIMAPS characterization of a surface in the variable aperture fracture model and determination of the main paths for water flow

    International Nuclear Information System (INIS)

    Fuentes, Nestor O.

    2003-01-01

    To understand the real incidence of fracture geometry in the unsteady behavior of flowing water channels, the RIMAPS (Rotated Image with Maximum Average Power Spectrum) technique is used to determine the main directions of these channels. This new characterization technique works on digitized images obtained from the surfaces under study. The present work presents the results of a comparison between the flow directions predicted by RIMAPS and the real channels directions observed in a laboratory experiment. A perfect accordance was verified between the directions obtained in both cases. It can be concluded from these results that geometrical characteristics of a fracture surface determine the main path directions for water flow. (author)

  2. 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...

  3. Effect of surface roughness on the fatigue life of laser additive manufactured Ti6Al4V alloy

    Czech Academy of Sciences Publication Activity Database

    Bača, A.; Konečná, R.; Nicoletto, G.; Kunz, Ludvík

    2015-01-01

    Roč. 15, č. 4 (2015), s. 498-502 ISSN 1213-2489 Institutional support: RVO:68081723 Keywords : Additive manufacturing * direct metal laser sintering * Fatigue life Subject RIV: JL - Materials Fatigue, Friction Mechanics

  4. Standard practice for fracture testing with surface-crack tension specimens

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2003-01-01

    1.1 This practice covers the design, preparation, and testing of surface-crack tension (SCT) specimens. It relates specifically to testing under continuously increasing force and excludes cyclic and sustained loadings. The quantity determined is the residual strength of a specimen having a semielliptical or circular-segment fatigue crack in one surface. This value depends on the crack dimensions and the specimen thickness as well as the characteristics of the material. 1.2 Metallic materials that can be tested are not limited by strength, thickness, or toughness. However, tests of thick specimens of tough materials may require a tension test machine of extremely high capacity. The applicability of this practice to nonmetallic materials has not been determined. 1.3 This practice is limited to specimens having a uniform rectangular cross section in the test section. The test section width and length must be large with respect to the crack length. Crack depth and length should be chosen to suit the ultimate pu...

  5. Small fatigue cracks; Proceedings of the Second International Conference/Workshop, Santa Barbara, CA, Jan. 5-10, 1986

    Energy Technology Data Exchange (ETDEWEB)

    Ritchie, R.O.; Lankford, J.

    1986-01-01

    Topics discussed in this volume include crack initiation and stage I growth, microstructure effects, crack closure, environment effects, the role of notches, analytical modeling, fracture mechanics characterization, experimental techniques, and engineering applications. Papers are presented on fatigue crack initiation along slip bands, the effect of microplastic surface deformation on the growth of small cracks, short fatigue crack behavior in relation to three-dimensional aspects and the crack closure effect, the influence of crack depth on crack electrochemistry and fatigue crack growth, and nondamaging notches in fatigue. Consideration is also given to models of small fatigue cracks, short crack theory, assessment of the growth of small flaws from residual strength data, the relevance of short crack behavior to the integrity of major rotating aero engine components, and the relevance of short fatigue crack growth data to the durability and damage tolerance analyses of aircraft.

  6. Detection of surface electromyography recording time interval without muscle fatigue effect for biceps brachii muscle during maximum voluntary contraction.

    Science.gov (United States)

    Soylu, Abdullah Ruhi; Arpinar-Avsar, Pinar

    2010-08-01

    The effects of fatigue on maximum voluntary contraction (MVC) parameters were examined by using force and surface electromyography (sEMG) signals of the biceps brachii muscles (BBM) of 12 subjects. The purpose of the study was to find the sEMG time interval of the MVC recordings which is not affected by the muscle fatigue. At least 10s of force and sEMG signals of BBM were recorded simultaneously during MVC. The subjects reached the maximum force level within 2s by slightly increasing the force, and then contracted the BBM maximally. The time index of each sEMG and force signal were labeled with respect to the time index of the maximum force (i.e. after the time normalization, each sEMG or force signal's 0s time index corresponds to maximum force point). Then, the first 8s of sEMG and force signals were divided into 0.5s intervals. Mean force, median frequency (MF) and integrated EMG (iEMG) values were calculated for each interval. Amplitude normalization was performed by dividing the force signals to their mean values of 0s time intervals (i.e. -0.25 to 0.25s). A similar amplitude normalization procedure was repeated for the iEMG and MF signals. Statistical analysis (Friedman test with Dunn's post hoc test) was performed on the time and amplitude normalized signals (MF, iEMG). Although the ANOVA results did not give statistically significant information about the onset of the muscle fatigue, linear regression (mean force vs. time) showed a decreasing slope (Pearson-r=0.9462, pfatigue starts after the 0s time interval as the muscles cannot attain their peak force levels. This implies that the most reliable interval for MVC calculation which is not affected by the muscle fatigue is from the onset of the EMG activity to the peak force time. Mean, SD, and range of this interval (excluding 2s gradual increase time) for 12 subjects were 2353, 1258ms and 536-4186ms, respectively. Exceeding this interval introduces estimation errors in the maximum amplitude calculations

  7. Separation of surface, subsurface and volume fatigue damage effects in AISI 348 steel for power plant applications

    Energy Technology Data Exchange (ETDEWEB)

    Klein, Martin; Nowak, David; Walther, Frank [Technical Univ. Dortmund (Germany). Dept. of Materials Test Engineering (WPT); Starke, Peter [Saarland Univ., Saarbruecken (Germany). Chair of Non-Destructive Testing and Quality Assurance; Boller, Christian [Saarland Univ., Saarbruecken (Germany). Chair of Non-Destructive Testing and Quality Assurance; Fraunhofer IZFP, Saarbruecken (Germany)

    2016-08-01

    A wide range of industries including energy, chemistry, pharmacy, textiles, food and drink, pulp and paper, etc. is using stainless steels. Metastable austenitic steels such as used in power plants and chemical industry are subjected to cyclic mechanical and thermal loading in air as well as under the influence of corrosive media. This paper provides an overview on different nondestructive and electrochemical measurement techniques, which allow differentiating fatigue damage effects in total strain controlled multiple and constant amplitude tests with respect to damage appearance on surface, in subsurface area as well as in volume of specimens or components microstructure. In addition to conventional mechanical stress-strain hysteresis curves, electrical resistance, magnetic and open circuit potential measurements have been applied to characterize the cyclic deformation behavior of the metastable austenitic steel AISI 348 (X10CrNiNb18-9) in laboratory air and in distilled water. Based on these results obtained, the paper provides an outlook on the possibility for an efficient (remaining) fatigue life evaluation approach, which is adapted to the needs of the application areas.

  8. Estimating the progression of muscle fatigue based on dependence between motor units using high density surface electromyogram.

    Science.gov (United States)

    Bingham, Adrian; Arjunan, Sridhar P; Kumar, Dinesh K

    2016-08-01

    In this study we have tested the hypothesis regarding the increase in synchronization with the onset of muscle fatigue. For this aim, we have investigated the difference in the synchronicity between high density surface electromyogram (sEMG) channels of the rested muscles and when at the limit of endurance. Synchronization was measured by computing and normalizing the mutual information between the sEMG signals recorded from the high-density array electrode locations. Ten volunteers (Age range: 21 and 35 years; Mean age = 26 years; Male = 6, Female = 4) participated in our experiment. The participants performed isometric dorsiflexion of their dominate foot at two levels of contraction; 40% and 80% of their maximum voluntary contraction (MVC) until task failure. During the experiment an array of 64 electrodes (16 by 4) placed over the TA parallel to the muscle fiber was used to record the HD-sEMG. Normalized Mutual Information (NMI) between electrodes was calculated using the HD-sEMG data and then analyzed. The results show that that the average NMI of the TA significantly increased during fatigue at both levels of contraction. There was a statistically significant difference between NMI of the rested muscle compared with it being at the point of task failure.

  9. Effect of tensile dwell on high-temperature low-cycle fatigue and fracture behaviour of cast superalloy MAR-M247

    Czech Academy of Sciences Publication Activity Database

    Šulák, Ivo; Obrtlík, Karel

    2017-01-01

    Roč. 185, NOV (2017), s. 92-100 ISSN 0013-7944. [ICMFM 2016 - International Colloquium on Mechanical Fatigue of Metals /18./. Gijón, 05.09.2016-07.09.2016] R&D Projects: GA ČR(CZ) GA15-20991S Institutional support: RVO:68081723 Keywords : Nickel-based superalloy * High-temperature low-cycle fatigue * Tensile dwell * Fatigue life * Damage mechanisms Subject RIV: JL - Materials Fatigue, Friction Mechanics OBOR OECD: Audio engineering , reliability analysis Impact factor: 2.151, year: 2016

  10. Assessing the Therapeutic Effect of 630 nm Light-Emitting Diodes Irradiation on the Recovery of Exercise-Induced Hand Muscle Fatigue with Surface Electromyogram

    Directory of Open Access Journals (Sweden)

    Dandan Yang

    2012-01-01

    Full Text Available This paper aims to investigate the effect of light emitting diode therapy (LEDT on exercise-induced hand muscle fatigue by measuring the surface electromyography (sEMG of flexor digitorum superficialis. Ten healthy volunteers were randomly placed in the equal sized LEDT group and control group. All subjects performed a sustained fatiguing isometric contraction with the combination of four fingertips except thumb at 30% of maximal voluntary contraction (MVC until exhaustion. The active LEDT or an identical passive rest therapy was then applied to flexor digitorum superficialis. Each subject was required to perform a re-fatigue task immediately after therapy which was the same as the pre-fatigue task. Average rectified value (ARV and fractal dimension (FD of sEMG were calculated. ARV and FD were significantly different between active LEDT and passive rest groups at 20%–50%, 70%–80%, and 100% of normalized contraction time (P<0.05. Compared to passive rest, active LEDT induced significantly smaller increase in ARV values and decrease in FD values, which shows that LEDT is effective on the recovery of muscle fatigue. Our preliminary results also suggest that ARV and FD are potential replacements of biochemical markers to assess the effects of LEDT on muscle fatigue.

  11. Fatigue assessment of a double submerged arc welded gas pipeline

    Energy Technology Data Exchange (ETDEWEB)

    Fazzini, Pablo; Otegui, Jose Luis [Universidad Nacional Mar del Plata, Mar del Plata (Argentina). Instituto de Ciencia y Tecnologia de Materiales (INTEMA); Teutonico, Mauricio; Manfredi, Carlos [GIE S.A., Mar del Plata (Argentina)

    2005-07-01

    An uncommon blowout in a 24'' diameter, 7 mm thick API 5L X52 gas pipeline was due to fracture at the longitudinal double submerged arc weld. Oddly enough for gas pipelines, it was found that fatigue cracks had propagated from a large embedded weld defect of lack of fusion resulting from severe geometrical mismatch between inner and outer weld passes. What makes this failure particularly interesting is that: previous in line inspections failed to detect any defect, no evidence of third party damage was found, and very few large pressure cycles had been recorded during the last 5 years of service, which were believed to be representative of the entire service life of the pipeline. Fatigue tests were carried out to characterize propagation of fatigue cracks in weld metal, it was found that a large Paris exponent made the few large amplitude cycles most contributing to crack propagation. Crack growth path and striation patterns were studied. Fatigue growth was modelled by integrating experimental results and by extrapolating striation spacing in the fracture surface of the failed pipe. Crack growth path and striation patterns were studied. It was found that microstructure discontinuities govern propagation at low {delta}K, but one striation per cycle was produced at large {delta}K, due to a mostly ductile propagation mode. Fatigue growth was modelled by integrating experimental results and by extrapolating striation spacing in the fracture surface of the failed pipe. It was found that in the early life of the line many more large pressure cycles than expected had occurred. Good correspondence between predicted and actual fatigue lives was in this way obtained (author)

  12. Fatigue assessment of a double submerged arc welded gas pipeline

    Energy Technology Data Exchange (ETDEWEB)

    Fazzini, Pablo; Otegui, Jose Luis [Universidad Nacional Mar del Plata, Mar del Plata (Argentina). Instituto de Ciencia y Tecnologia de Materiales (INTEMA); Teutonico, Mauricio; Manfredi, Carlos [GIE S.A., Mar del Plata (Argentina)

    2005-07-01

    An uncommon blowout in a 24'' diameter, 7 mm thick API 5L X52 gas pipeline was due to fracture at the longitudinal double submerged arc weld. Oddly enough for gas pipelines, it was found that fatigue cracks had propagated from a large embedded weld defect of lack of fusion resulting from severe geometrical mismatch between inner and outer weld passes. What makes this failure particularly interesting is that: previous in line inspections failed to detect any defect, no evidence of third party damage was found, and very few large pressure cycles had been recorded during the last 5 years of service, which were believed to be representative of the entire service life of the pipeline. Fatigue tests were carried out to characterize propagation of fatigue cracks in weld metal, it was found that a large Paris exponent made the few large amplitude cycles most contributing to crack propagation. Crack growth path and striation patterns were studied. Fatigue growth was modelled by integrating experimental results and by extrapolating striation spacing in the fracture surface of the failed pipe. Crack growth path and striation patterns were studied. It was found that microstructure discontinuities govern propagation at low {delta}K, but one striation per cycle was produced at large {delta}K, due to a mostly ductile propagation mode. Fatigue growth was modelled by integrating experimental results and by extrapolating striation spacing in the fracture surface of the failed pipe. It was found that in the early life of the line many more large pressure cycles than expected had occurred. Good correspondence between predicted and actual fatigue lives was in this way obtained (author)

  13. Investigations into the fatigue behaviour of nuclear grades of austenitic stainless steel

    International Nuclear Information System (INIS)

    Mann, J.

    2015-01-01

    Full text of publication follows. Fatigue is an important problem within the nuclear industry due to the complex combination of thermal and mechanical loading that components experience during the operation of a nuclear reactor. Austenitic stainless steels are widely used within nuclear reactors for a number of applications including piping systems and pressure vessels. A number of studies have shown that austenitic stainless steel components operating within a light water reactor (LWR) environment may experience a significant reduction in fatigue life under certain circumstances, however the precise mechanisms responsible for the reduction are still not fully understood. The effects of environment are included in some fatigue assessment methods, however these are generally considered to be over-conservative and predicted fatigue lifetimes are not reflected well by service experience. This project aims to enhance the understanding of fatigue in both air and LWR environments through the synergistic use of a wide range of different microscopy techniques. It is expected that a better understanding of each of the different stages of fatigue will lead to more accurate fatigue predictions that ultimately result in better and safer lifetime predictions. This paper focuses on introducing the background behind the project, highlighting the current methods for assessing fatigue lifetimes and the motivations for the current research. The results of various initial microscopic investigations are presented, with a focus on a number of novel applications using laser scanning confocal microscopy to perform large scale analyses of fatigue fracture surfaces and test specimen gauge length surfaces. The use of surface replicas in conjunction with laser scanning confocal microscopy is discussed along with its potential applications for the assessment of fatigue damage in in-service components. Initial finite element modelling of crack growth within fatigue test specimens is discussed

  14. Fatigue of dental ceramics.

    Science.gov (United States)

    Zhang, Yu; Sailer, Irena; Lawn, Brian R

    2013-12-01

    Clinical data on survival rates reveal that all-ceramic dental prostheses are susceptible to fracture from repetitive occlusal loading. The objective of this review is to examine the underlying mechanisms of fatigue in current and future dental ceramics. The nature of various fatigue modes is elucidated using fracture test data on ceramic layer specimens from the dental and biomechanics literature. Failure modes can change over a lifetime, depending on restoration geometry, loading conditions and material properties. Modes that operate in single-cycle loading may be dominated by alternative modes in multi-cycle loading. While post-mortem examination of failed prostheses can determine the sources of certain fractures, the evolution of these fractures en route to failure remains poorly understood. Whereas it is commonly held that loss of load-bearing capacity of dental ceramics in repetitive loading is attributable to chemically assisted 'slow crack growth' in the presence of water, we demonstrate the existence of more deleterious fatigue mechanisms, mechanical rather than chemical in nature. Neglecting to account for mechanical fatigue can lead to gross overestimates in predicted survival rates. Strategies for prolonging the clinical lifetimes of ceramic restorations are proposed based on a crack-containment philosophy. Copyright © 2013 Elsevier Ltd. All rights reserved.

  15. Detection of Natural Fractures from Observed Surface Seismic Data Based on a Linear-Slip Model

    Science.gov (United States)

    Chen, Huaizhen; Zhang, Guangzhi

    2018-03-01

    Natural fractures play an important role in migration of hydrocarbon fluids. Based on a rock physics effective model, the linear-slip model, which defines fracture parameters (fracture compliances) for quantitatively characterizing the effects of fractures on rock total compliance, we propose a method to detect natural fractures from observed seismic data via inversion for the fracture compliances. We first derive an approximate PP-wave reflection coefficient in terms of fracture compliances. Using the approximate reflection coefficient, we derive azimuthal elastic impedance as a function of fracture compliances. An inversion method to estimate fracture compliances from seismic data is presented based on a Bayesian framework and azimuthal elastic impedance, which is implemented in a two-step procedure: a least-squares inversion for azimuthal elastic impedance and an iterative inversion for fracture compliances. We apply the inversion method to synthetic and real data to verify its stability and reasonability. Synthetic tests confirm that the method can make a stable estimation of fracture compliances in the case of seismic data containing a moderate signal-to-noise ratio for Gaussian noise, and the test on real data reveals that reasonable fracture compliances are obtained using the proposed method.

  16. Fatigue life evaluation of 42CrMo4 nitrided steel by local approach: Equivalent strain-life-time

    International Nuclear Information System (INIS)

    Terres, Mohamed Ali; Sidhom, Habib

    2012-01-01

    Highlights: → Ion nitriding treatment of 42CrMo4 steel improves their fatigue strength by 32% as compared with the untreated state. → This improvement is the result of the beneficial effects of the superficial work- hardening and of the stabilized compressive residual stress. → The notch region is found to be the fatigue crack nucleation site resulting from a stress concentration (Kt = 1.6). → The local equivalent strain-fatigue life method was found to be an interesting predictive fatigue life method for nitrided parts. -- Abstract: In this paper, the fatigue resistance of 42CrMo4 steel in his untreated and nitrided state was evaluated, using both experimental and numerical approaches. The experimental assessment was conducted using three points fatigue flexion tests on notched specimens at R = 0.1. Microstructure analysis, micro-Vickers hardness test, and scanning electron microscope observation were carried out for evaluating experiments. In results, the fatigue cracks of nitrided specimens were initiated at the surface. The fatigue life of nitrided specimens was prolonged compared to that of the untreated. The numerical method used in this study to predict the nucleation fatigue life was developed on the basis of a local approach, which took into account the applied stresses and stabilized residual stresses during the cyclic loading and the low cyclic fatigue characteristics. The propagation fatigue life was calculated using fracture mechanics concepts. It was found that the numerical results were well correlated with the experimental ones.

  17. Environmental fatigue behaviors of wrought and cast stainless steels in 310degC deoxygenated water

    International Nuclear Information System (INIS)

    Cho, Pyung-Yeon; Jang, Hun; Jang, Changheui; Jeong, Ill-Seok; Lee, Jae-Gon

    2009-01-01

    Environmental fatigue behaviors of wrought type 316LN stainless steel and cast CF8M stainless steel were investigated. Low cycle fatigue tests were performed in a 310degC deoxygenated water environment at a strain rate of 0.04%/s with various strain amplitudes. It was shown that the low cycle fatigue life of CF8M was slightly longer than that of 316LN. To understand the causes of the difference, fracture surface was observed and material factors like microstructure, mechanical properties, and chemical compositions of both materials were analyzed. In a duplex microstructure of CF8M, the fatigue crack growth was affected by barrier role of ferrite phase and acceleration role of microvoids in ferrite phase. Test results indicate that the former is greater than the latter, resulting in slower fatigue crack growth rate, or longer LCF lives in CF8M than in 316LN. (author)

  18. The influences of mesh subdivision on nonlinear fracture analysis for surface cracked structures

    International Nuclear Information System (INIS)

    Shimakawa, T.

    1991-01-01

    The leak-before-break (LBB) concept can be expected to be applied not only to safety assessment, but also to the rationalization of nuclear power plants. The development of a method to evaluate fracture characteristics is required to establish this concept. The finite element method (FEM) is one of the most useful tools for this evaluation. However, the influence of various factors on the solution is not well understood and the reliability has not been fully verified. In this study, elastic-plastic 3D analyses are performed for two kinds of surface cracked structure, and the influence of mesh design is discussed. The first problem is surface crack growth in a carbon steel plate subjected to tension loading. A crack extension analysis is performed under a generation phase simulation using the crack release technique. Numerical instability of the J-integral solution is observed when the number of elements in the thickness direction of the ligament is reduced to three. The influence of mesh design in the ligament on the solution is discussed. The second problem is a circumferential part-through crack in a carbon steel pipe subjected to a bending moment. Two kinds of mesh design are employed, and a comparison between two sets of results shows that the number of elements on the crack surface also affects the solution as well as the number of elements in the ligament. (author)

  19. Fatigue life prediction of pedicle screw for spinal surgery

    Czech Academy of Sciences Publication Activity Database

    Major, Štěpán; Kocour, Vladimír; Cyrus, P.

    2016-01-01

    Roč. 10, č. 35 (2016), s. 379-388 ISSN 1971-8993. [European Conference on Fracture. ECF21. Catania, 20.06.2015-20.06.2015] Institutional support: RVO:68378297 Keywords : pedicle-screw * titan alloy * fatigue life * finite element analysis Subject RIV: JK - Corrosion ; Surface Treatment of Materials http://www.fracturae.com/index.php/fis/article/view/IGF-ESIS.35.43

  20. Fatigue life of layered metallic and ceramic plasma sprayed coatings

    Czech Academy of Sciences Publication Activity Database

    Kovářík, O.; Haušild, P.; Siegl, J.; Matějíček, Jiří; Davydov, V.

    2014-01-01

    Roč. 3, July (2014), s. 586-591 ISSN 2211-8128. [European Conference on Fracture (ECF20)/20./. Trondheim, 30.06.2014-04.07.2014] R&D Projects: GA ČR(CZ) GAP108/12/1872 Institutional support: RVO:61389021 Keywords : functionally graded materials * fatigue life * neutron diffraction * grit blasting Subject RIV: JK - Corrosion ; Surface Treatment of Materials http://www.sciencedirect.com/science/article/pii/S2211812814000984#

  1. Response Surface Approximation for Fatigue Life Prediction and Its Application to Multi-Criteria Optimization With a Priori Preference Information

    International Nuclear Information System (INIS)

    Baek, Seok Heum; Joo, Won Sik; Cho, Seok Swoo

    2009-01-01

    In this paper, a versatile multi-criteria optimization concept for fatigue life prediction is introduced. Multi-criteria decision making in engineering design refers to obtaining a preferred optimal solution in the context of conflicting design objectives. Compromise decision support problems are used to model engineering decisions involving multiple trade-offs. These methods typically rely on a summation of weighted attributes to accomplish trade-offs among competing objectives. This paper gives an interpretation of the decision parameters as governing both the relative importance of the attributes and the degree of compensation between them. The approach utilizes a response surface model, the compromise decision support problem, which is a multi-objective formulation based on goal programming. Examples illustrate the concepts and demonstrate their applicability

  2. Computer simulation of fatigue under diametrical compression

    OpenAIRE

    Carmona, H. A.; Kun, F.; Andrade Jr., J. S.; Herrmann, H. J.

    2006-01-01

    We study the fatigue fracture of disordered materials by means of computer simulations of a discrete element model. We extend a two-dimensional fracture model to capture the microscopic mechanisms relevant for fatigue, and we simulate the diametric compression of a disc shape specimen under a constant external force. The model allows to follow the development of the fracture process on the macro- and micro-level varying the relative influence of the mechanisms of damage accumulation over the ...

  3. Fatigue crack propagation in self-assembling nanocomposites

    Energy Technology Data Exchange (ETDEWEB)

    Klingler, Andreas; Wetzel, Bernd [Institute for Composite Materials (IVW GmbH) Technical University of Kaiserslautern, 67633 Kaiserslautern (Germany)

    2016-05-18

    Self-assembling block-copolymers allow the easy manufacturing of nanocomposites due to the thermodynamically driven in situ formation of nanosized phases in thermosetting resins during the curing process. Complex mechanical dispersion processes can be avoided. The current study investigates the effect of a block-copolymer on the fatigue crack propagation resistance of a cycloaliphatic amine cured epoxy resin. It was found that a small amount of MAM triblock-copolymer significantly increases the resistance to fatigue crack propagation of epoxy. Crack growth rate and the Paris law exponent for fatigue-crack growth were considerably reduced from m=15.5 of the neat epoxy to m=8.1 of the nanocomposite. To identify the related reinforcing and fracture mechanisms structural analyses of the fractured surfaces were performed by scanning electron microscope. Characteristic features were identified to be deformation, debonding and fracture of the nano-phases as well as crack pinning. However, the highest resistance against fatigue crack propagation was achieved in a bi-continuous microstructure that consisted of an epoxy-rich phase with embedded submicron sized MAM inclusions, and which was surrounded by a block-copolymer-rich phase that showed rupture and plastic deformation.

  4. Fatigue crack propagation in self-assembling nanocomposites

    Science.gov (United States)

    Klingler, Andreas; Wetzel, Bernd

    2016-05-01

    Self-assembling block-copolymers allow the easy manufacturing of nanocomposites due to the thermodynamically driven in situ formation of nanosized phases in thermosetting resins during the curing process. Complex mechanical dispersion processes can be avoided. The current study investigates the effect of a block-copolymer on the fatigue crack propagation resistance of a cycloaliphatic amine cured epoxy resin. It was found that a small amount of MAM triblock-copolymer significantly increases the resistance to fatigue crack propagation of epoxy. Crack growth rate and the Paris law exponent for fatigue-crack growth were considerably reduced from m=15.5 of the neat epoxy to m=8.1 of the nanocomposite. To identify the related reinforcing and fracture mechanisms structural analyses of the fractured surfaces were performed by scanning electron microscope. Characteristic features were identified to be deformation, debonding and fracture of the nano-phases as well as crack pinning. However, the highest resistance against fatigue crack propagation was achieved in a bi-continuous microstructure that consisted of an epoxy-rich phase with embedded submicron sized MAM inclusions, and which was surrounded by a block-copolymer-rich phase that showed rupture and plastic deformation.

  5. Fatigue crack propagation in self-assembling nanocomposites

    International Nuclear Information System (INIS)

    Klingler, Andreas; Wetzel, Bernd

    2016-01-01

    Self-assembling block-copolymers allow the easy manufacturing of nanocomposites due to the thermodynamically driven in situ formation of nanosized phases in thermosetting resins during the curing process. Complex mechanical dispersion processes can be avoided. The current study investigates the effect of a block-copolymer on the fatigue crack propagation resistance of a cycloaliphatic amine cured epoxy resin. It was found that a small amount of MAM triblock-copolymer significantly increases the resistance to fatigue crack propagation of epoxy. Crack growth rate and the Paris law exponent for fatigue-crack growth were considerably reduced from m=15.5 of the neat epoxy to m=8.1 of the nanocomposite. To identify the related reinforcing and fracture mechanisms structural analyses of the fractured surfaces were performed by scanning electron microscope. Characteristic features were identified to be deformation, debonding and fracture of the nano-phases as well as crack pinning. However, the highest resistance against fatigue crack propagation was achieved in a bi-continuous microstructure that consisted of an epoxy-rich phase with embedded submicron sized MAM inclusions, and which was surrounded by a block-copolymer-rich phase that showed rupture and plastic deformation.

  6. Muscle Fatigue in the Three Heads of the Triceps Brachii During a Controlled Forceful Hand Grip Task with Full Elbow Extension Using Surface Electromyography.

    Science.gov (United States)

    Ali, Asraf; Sundaraj, Kenneth; Badlishah Ahmad, R; Ahamed, Nizam Uddin; Islam, Anamul; Sundaraj, Sebastian

    2015-06-27

    The objective of the present study was to investigate the time to fatigue and compare the fatiguing condition among the three heads of the triceps brachii muscle using surface electromyography during an isometric contraction of a controlled forceful hand grip task with full elbow extension. Eighteen healthy subjects concurrently performed a single 90 s isometric contraction of a controlled forceful hand grip task and full elbow extension. Surface electromyographic signals from the lateral, long and medial heads of the triceps brachii muscle were recorded during the task for each subject. The changes in muscle activity among the three heads of triceps brachii were measured by the root mean square values for every 5 s period throughout the total contraction period. The root mean square values were then analysed to determine the fatiguing condition for the heads of triceps brachii muscle. Muscle fatigue in the long, lateral, and medial heads of the triceps brachii started at 40 s, 50 s, and 65 s during the prolonged contraction, respectively. The highest fatiguing rate was observed in the long head (slope = -2.863), followed by the medial head (slope = -2.412) and the lateral head (slope = -1.877) of the triceps brachii muscle. The results of the present study concurs with previous findings that the three heads of the triceps brachii muscle do not work as a single unit, and the fiber type/composition is different among the three heads.

  7. Monitoring of surface deformation and microseismicity applied to radioactive waste disposal through hydraulic fracturing at Oak Ridge National Laboratory

    International Nuclear Information System (INIS)

    Stow, S.H.; Haase, C.S.; Switek, J.; Holzhausen, G.R.; Majer, E.

    1985-01-01

    Low-level liquid nuclear wastes are disposed of at Oak Ridge National Laboratory by the hydrofracture process. Wastes are mixed with cement and other additives to form a slurry that is injected into shale of low permeability at 300 m depth. The slurry spreads radially along bedding plane fractures before setting as a grout. Different methods for monitoring the location and behavior of the fractures have been investigated. Radioactive grout sheets can be located by gamma-ray logging of cased observation wells. Two other methods are based on the fact that the ground surface is deformed by the injection. The first entails surface leveling of a series of benchmarks; uplift up to 2.5 cm occurs. The second method involves use of tiltmeters that are sensitive and measure ground deformation in real time during an injection. Both methods show subsidence during the weeks following an injection. Interpretive models for the tiltmeter data are based on the elastic response of isotropic and anisotropic media to the inflation of a fluid-filled fracture. A fourth monitoring method is based on microseismicity. Geophone arrays were used to characterize the fracture process and to provide initial assessment of the feasibility of using seismic measurements to map the fractures as they form. An evaluation of each method is presented. 8 refs., 6 figs

  8. Monitoring of surface deformation and microseismicity applied to radioactive waste disposal through hydraulic fracturing at Oak Ridge National Laboratory

    International Nuclear Information System (INIS)

    Stow, S.H.; Haase, C.S.; Switek, J.; Holzhausen, G.R.; Majer, E.; Applied Geomechanics, Inc., Santa Cruz, CA; Lawrence Berkeley Lab., CA)

    1985-01-01

    Low-level liquid nuclear wastes are disposed of at Oak Ridge National Laboratory by the hydrofracture process. Wastes are mixed with cement and other additives to form a slurry that is injected into shale of low permeability at 300 m depth. The slurry spreads radially along bedding plane fractures before setting as a grout. Different methods for monitoring the location and behavior of the fractures have been investigated. Radioactive grout sheets can be located by gamma-ray logging of cased observation wells. Two other methods are based on the fact that the ground surface is deformed by the injection. The first entails surface leveling of a series of benchmarks; uplift up to 2.5 cm occurs. The second method involves use of tiltmeters that are sensitive and measure ground deformation in real time during an injection. Both methods show subsidence during the weeks following an injection. Interpretive models for the tiltmeter data are based on the elastic response of isotropic and anisotropic media to the inflation of a fluid-filled fracture. A fourth monitoring method is based on microseismicity. Geophone arrays were used to characterize the fracture process and to provide initial assessment of the feasibility of using seismic measurements to map the fractures as they form. An evaluation of each method is presented

  9. Corrosion fatigue behaviors of steel wires used in coalmine

    International Nuclear Information System (INIS)

    Wang, Songquan; Zhang, Dekun; Chen, Kai; Xu, Linmin; Ge, Shirong

    2014-01-01

    Highlights: • The CF life of steel wire in acid solution is the shortest. • The fatigue source zone showed dimple morphology when coupled with anode potential. • The area of dimple increases with the increase of the applied anode potential. • The strong cathode potential cannot reduce the CF life of the smooth steel wire. • The hydrogen impacted mainly on the plastic deformation of the wire surface. - Abstract: The corrosion fatigue (CF) behaviors of the mining steel wire in different solutions at different applied polarization potentials were investigated in this paper. The surfaces and fracture morphologies of the steel wire at different applied potentials were observed by scanning electron microscope (SEM). The results showed that the CF life of steel wire in acid solution is the shortest. Moreover, the strong anodic polarization potential greatly reduced the CF life of steel wire, while the strong cathode potential did not reduce the CF life. For the smooth steel wire, the hydrogen impacted mainly on the plastic deformation of the wire surface. There was obvious dimple in the fatigue source zone of the wire when coupled with anode potential, and the area of the dimple increased with the increase of the applied anode potential. Conversely, the fatigue source zone of the fracture was relatively smooth at cathode polarization potential, which indicated that the crack propagation followed the mechanism of hydrogen induced cracking

  10. Cyclic deformation and fatigue behaviors of Hadfield manganese steel

    Energy Technology Data Exchange (ETDEWEB)

    Kang, J. [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Zhang, F.C., E-mail: zfc@ysu.edu.cn [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Long, X.Y. [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Lv, B. [School of Environmental and Chemical Engineering, Yanshan University, Qinhuangdao 066004 (China)

    2014-01-03

    The cyclic deformation characteristics and fatigue behaviors of Hadfield manganese steel have been investigated by means of its ability to memorize strain and stress history. Detailed studies were performed on the strain-controlled low cycle fatigue (LCF) and stress-controlled high cycle fatigue (HCF). Initial cyclic hardening to saturation or peak stress followed by softening to fracture occurred in LCF. Internal stress made the dominant contribution to the fatigue crack propagation until failure. Effective stress evolution revealed the existence of C–Mn clusters with short-range ordering in Hadfield manganese steel and demonstrated that the interaction between C atoms in the C–Mn cluster and dislocation was essential for its cyclic hardening. The developing/developed dislocation cells and stacking faults were the main cyclic deformation microstructures on the fractured sample surface in LCF and HCF, which manifested that fatigue failure behavior of Hadfield manganese steel was induced by plastic deformation during strain-controlled or stress-controlled testing.

  11. Effects of irradiation on low cycle fatigue properties for reduced activation ferritic/martensitic steel

    International Nuclear Information System (INIS)

    Kim, S.W.; Tanigawa, H.; Hirose, T.; Kohyama, A.

    2007-01-01

    Full text of publication follows: In materials life decision for a commercial blanket, thermal fatigue property of materials is a particularly important. The loading of structural materials in fusion reactor is, besides the plasma surface interactions, a combined effect of high heat fluxes and neutron irradiation. Depending on the pulse lengths, the operating conditions, and the thermal conductivity, these oscillating temperature gradients will cause elastic and elastic-plastic cyclic deformation giving rise to (creep-) fatigue in structural first wall and blanket components. Especially, investigation of the fatigue property in Reduced Activation Ferritic/Martensitic (RAF/M) steel and establishment of the evaluation technology are demanded in particular immediately for design/manufacturing of ITER-TBM. And also, fatigue testing after irradiation will be carried out in hot cells with remote control system. Considering limited ability of specimen manipulation in the cells, the specimen and the test method need to be simple for operation. The existing data bases of RAF/M steel provide baseline data set including post-irradiation fatigue data. However, to perform the accurate fatigue lifetime assessment for ITER-TBM and beyond utilizing the existing data base, the mechanical understanding of fatigue fracture is mandatory. It has been previously reported by co-authors that dislocation cell structure was developed on low cycle fatigued RAF/M steel, and led the fatigue crack to develop along prior austenitic grain boundary. In this work, the effects of nuclear irradiation on low cycle fatigue properties for RAF/M steels and its fracture mechanisms were examined based on the flow stress analysis and detailed microstructure analysis. Fracture surfaces and crack initiation site were investigated by scanning electron microscope (SEM). Transmission electron microscopy (TEM) was also applied to clarify the microstructural features of fatigue behavior. It is also important to

  12. Effects of irradiation on low cycle fatigue properties for reduced activation ferritic/martensitic steel

    Energy Technology Data Exchange (ETDEWEB)

    Kim, S.W. [Kyoto Univ., Graduate School of Energy Science (Japan); Tanigawa, H. [Japan Atomic Energy Agency, Tokai-mura, Naga-gun, Ibaraki-ken (Japan); Hirose, T. [Blanket Engineering Group, Japan Atomic Energy Agency, Naka, Ibaraki (Japan); Kohyama, A. [Kyoto Univ., lnstitute of Advanced Energy (Japan)

    2007-07-01

    Full text of publication follows: In materials life decision for a commercial blanket, thermal fatigue property of materials is a particularly important. The loading of structural materials in fusion reactor is, besides the plasma surface interactions, a combined effect of high heat fluxes and neutron irradiation. Depending on the pulse lengths, the operating conditions, and the thermal conductivity, these oscillating temperature gradients will cause elastic and elastic-plastic cyclic deformation giving rise to (creep-) fatigue in structural first wall and blanket components. Especially, investigation of the fatigue property in Reduced Activation Ferritic/Martensitic (RAF/M) steel and establishment of the evaluation technology are demanded in particular immediately for design/manufacturing of ITER-TBM. And also, fatigue testing after irradiation will be carried out in hot cells with remote control system. Considering limited ability of specimen manipulation in the cells, the specimen and the test method need to be simple for operation. The existing data bases of RAF/M steel provide baseline data set including post-irradiation fatigue data. However, to perform the accurate fatigue lifetime assessment for ITER-TBM and beyond utilizing the existing data base, the mechanical understanding of fatigue fracture is mandatory. It has been previously reported by co-authors that dislocation cell structure was developed on low cycle fatigued RAF/M steel, and led the fatigue crack to develop along prior austenitic grain boundary. In this work, the effects of nuclear irradiation on low cycle fatigue properties for RAF/M steels and its fracture mechanisms were examined based on the flow stress analysis and detailed microstructure analysis. Fracture surfaces and crack initiation site were investigated by scanning electron microscope (SEM). Transmission electron microscopy (TEM) was also applied to clarify the microstructural features of fatigue behavior. It is also important to

  13. Ductile fracture evaluation of ductile cast iron and forged steel by nonlinear-fracture-mechanics. Pt. 1. Tensile test by large scaled test pieces with surface crack

    International Nuclear Information System (INIS)

    Kosaki, Akio; Ajima, Tatsuro; Inohara, Yasuto

    1999-01-01

    The ductile fracture tests of Ductile Cast Iron and Forged Steel under a tensile stress condition were conducted using large-scaled flat test specimens with a surface crack and were evaluated by the J-integral values, in order to propose an evaluation method of initiation of ductile fracture of a cask body with crack by nonlinear-fracture-mechanics. Following results were obtained. 1) 1 -strain relations of Ductile Cast Iron and Forged Steel under the tensile stress condition were obtained, which is necessary for the development of J-integral design curves for evaluating the initiation of ductile fracture of the cask body. 2) In case of Ductile Cast Iron, the experimental J-integral values obtained from strain-gauges showed a good agreement with the linear-elastic-theory by Raju and Newman at room temperature, in both elastic and plastic regions. But, at 70degC in plastic region, the experimental i-integral values showed middle values between those predicted by the linear-elastic-theory and by the non- linear-elastic- theory (based on the fully plastic solution by Yagawa et al.). 3) In case of Forged Steel at both -25degC and room temperature, the experimental i-integral values obtained from strain-gauges showed a good agreement with those predicted by the linear-elastic-theory by Raju and Newman, in the elastic region. In the plastic region, however, the experimental i-integral values fell apart from the curve predicted by the linear-elastic-theory by Raju and Newman, and also approached to those by the non-linear-elastic-theory with increasing strain.(author)

  14. Effect of heat-treatment on elevated temperature fatigue-crack growth behavior of two heats of Alloy 718

    International Nuclear Information System (INIS)

    Mills, W.J.; James, L.A.

    1978-05-01

    The room temperature and elevated temperature fatigue-crack growth behavior of two heats of Alloy 718 was characterized within a linear-elastic fracture mechanics framework. Two different heat-treatments were used: the ''conventional'' (ASTM A637) treatment, and a ''modified'' heat-treatment designed to improve the toughness of Alloy 718 base metal and weldments. Heat-to-heat variations in the fatigue-crack propagation behavior were observed in the conventionally-treated material. On the other hand, no heat-to-heat variations were observed in the modified condition. Furthermore, both heats of Alloy 718 exhibited superior fatigue-crack growth resistance when given the modified heat-treatment. Electron fractographic examination of Alloy 718 fatigue fracture surfaces revealed that the operative crack growth mechanisms were dependent on heat-treatment, temperature, and ΔK level

  15. Fatigue Life of Titanium Alloys Fabricated by Additive Layer Manufacturing Techniques for Dental Implants

    Science.gov (United States)

    Chan, Kwai S.; Koike, Marie; Mason, Robert L.; Okabe, Toru

    2013-02-01

    Additive layer deposition techniques such as electron beam melting (EBM) and laser beam melting (LBM) have been utilized to fabricate rectangular plates of Ti-6Al-4V with extra low interstitial (ELI) contents. The layer-by-layer deposition techniques resulted in plates that have different surface finishes which can impact significantly on the fatigue life by providing potential sites for fatigue cracks to initiate. The fatigue life of Ti-6Al-4V ELI alloys fabricated by EBM and LBM deposition techniques was investigated by three-point testing of rectangular beams of as-fabricated and electro-discharge machined surfaces under stress-controlled conditions at 10 Hz until complete fracture. Fatigue life tests were also performed on rolled plates of Ti-6Al-4V ELI, regular Ti-6Al-4V, and CP Ti as controls. Fatigue surfaces were characterized by scanning electron microscopy to identify the crack initiation site in the various types of specimen surfaces. The fatigue life data were analyzed statistically using both analysis of variance techniques and the Kaplan-Meier survival analysis method with the Gehan-Breslow test. The results indicate that the LBM Ti-6Al-4V ELI material exhibits a longer fatigue life than the EBM counterpart and CP Ti, but a shorter fatigue life compared to rolled Ti-6Al-4V ELI. The difference in the fatigue life behavior may be largely attributed to the presence of rough surface features that act as fatigue crack initiation sites in the EBM material.

  16. Analysis of stress fractures associated with lameness in Thoroughbred flat racehorses training on different track surfaces undergoing nuclear scintigraphic examination.

    Science.gov (United States)

    MacKinnon, M C; Bonder, D; Boston, R C; Ross, M W

    2015-05-01

    There is limited information regarding the impact of training track surface on the occurrence of stress fractures. To evaluate the impact of training track surface on the proportion of long bone and pelvic stress fractures associated with lameness in Thoroughbred horses in flat race training undergoing nuclear scintigraphic examination. Retrospective study. Scintigraphic examinations of Thoroughbred flat racehorses were evaluated from 2 hospitals (hospital A [Toronto Equine Hospital], 2003-2009, and hospital B [George D. Widener Hospital for Large Animals, School of Veterinary Medicine, University of Pennsylvania], 1994-2006). Horses admitted to hospital A trained at a single track, at which the main training surface changed from dirt to synthetic on 27 August 2006. Two distinct populations existed at hospital B: horses that trained on dirt (numerous trainers) and those that trained on turf (single trainer). All scintigraphic images were evaluated by a blinded reviewer. Fisher's exact test and logistic regression were used when appropriate, and significance was set at Pfractures detected in scintigraphic examinations from horses training on a synthetic surface (31.7%) in comparison to scintigraphic examinations from horses training on a dirt surface (23.0%) at an earlier point in time (P = 0.03). There was a greater proportion of hindlimb/pelvic and tibial stress fractures diagnosed in horses from the synthetic surface-trained group than from the dirt-trained group at hospital A (Pfractures diagnosed, but other factors, such as training philosophy, appear to be important. Future prospective investigations to fully elucidate the relationship between training track surface and the proportion of stress fractures and other nonfatal musculoskeletal injuries are warranted. © 2014 EVJ Ltd.

  17. Parameters Studies on Surface Initiated Rolling Contact Fatigue of Turnout Rails by Three-Level Unreplicated Saturated Factorial Design

    Directory of Open Access Journals (Sweden)

    Xiaochuan Ma

    2018-03-01

    Full Text Available Surface initiated rolling contact fatigue (RCF, mainly characterized by cracks and material stripping, is a common type of damage to turnout rails, which can not only shorten service life of turnout but also lead to poor running safety of vehicle. The rail surface initiated RCF of turnouts is caused by a long-term accumulation, the size and distribution of which are related to the dynamic parameters of the complicated vehicle-turnout system. In order to simulate the accumulation of rail damage, some random samples of dynamic parameters significantly influencing it should be input. Based on the three-level unreplicated saturated factorial design, according to the evaluation methods of H, P and B statistic values, six dynamic parameters that influence the rail surface initiated RCF in turnouts, namely running speed of vehicle, axle load, wheel-rail profiles, integral vertical track stiffness and wheel-rail friction coefficient, are obtained by selecting 13 dynamic parameters significantly influencing the dynamic vehicle-turnout interaction as the analysis factors, considering four dynamic response results, i.e., the normal wheel-rail contact force, longitudinal creep force, lateral creep force and wheel-rail contact patch area as the observed parameters. In addition, the rail surface initiated RCF behavior in turnouts under different wheel-rail creep conditions is analyzed, considering the relative motion of stock/switch rails. The results show that the rail surface initiated RCF is mainly caused by the tangential stress being high under small creep conditions, the normal and tangential stresses being high under large creep conditions, and the normal stress being high under pure spin creep conditions.

  18. Filling Open Screw Holes in the Area of Metaphyseal Comminution Does Not Affect Fatigue Life of the Synthes Variable Angle Distal Femoral Locking Plate in the AO/OTA 33-A3 Fracture Model.

    Science.gov (United States)

    Grau, Luis; Collon, Kevin; Alhandi, Ali; Kaimrajh, David; Varon, Maria; Latta, Loren; Vilella, Fernando

    2018-06-01

    The aim of this study is to evaluate the biomechanical effect of filling locking variable angle (VA) screw holes at the area of metaphyseal fracture comminution in a Sawbones® (Sawbones USA, Vashon, Washington) model (AO/OTA 33A-3 fracture) using a Synthes VA locking compression plate (LCP) (Depuy Synthes, Warsaw, Indiana). Seven Sawbones® femur models had a Synthes VA-LCP placed as indicated by the manufacturers technique. A 4cm osteotomy was then created to simulate an AO/OTA 33-A3 femoral fracture pattern with metaphyseal comminution. The control group consisted of four constructs in which the open screw holes at the area of comminution were left unfilled; the experimental group consisted of three constructs in which the VA screw holes were filled with locking screws. One of the control constructs was statically loaded to failure at a rate of 5mm/min. A value equal to 75% of the ultimate load to failure was used as the loading force for fatigue testing of 250,000 cycles at 3Hz. Cycles to failure was recorded for each construct and averages were compared between groups. The average number of cycles to failure in the control and experimental groups were 37524±8187 and 43304±23835, respectively (p=0.72). No significant difference was observed with respect to cycles to failure or mechanism of failure between groups. In all constructs in both the control and experimental groups, plate failure reproducibly occurred with cracks through the variable angle holes in the area of bridged comminution. The Synthes VA-LCP in a simulated AO/OTA 33-A3 comminuted metaphyseal femoral fracture fails in a reproducible manner at the area of comminution through the "honeycomb" VA screw holes. Filling open VA screw holes at the site of comminution with locking screws does not increase