A general one-dimension nonlinear magneto-elastic coupled constitutive model for magnetostrictive materials

International Nuclear Information System (INIS)

Zhang, Da-Guang; Li, Meng-Han; Zhou, Hao-Miao

2015-01-01

For magnetostrictive rods under combined axial pre-stress and magnetic field, a general one-dimension nonlinear magneto-elastic coupled constitutive model was built in this paper. First, the elastic Gibbs free energy was expanded into polynomial, and the relationship between stress and strain and the relationship between magnetization and magnetic field with the polynomial form were obtained with the help of thermodynamic relations. Then according to microscopic magneto-elastic coupling mechanism and some physical facts of magnetostrictive materials, a nonlinear magneto-elastic constitutive with concise form was obtained when the relations of nonlinear strain and magnetization in the polynomial constitutive were instead with transcendental functions. The comparisons between the prediction and the experimental data of different magnetostrictive materials, such as Terfenol-D, Metglas and Ni showed that the predicted magnetostrictive strain and magnetization curves were consistent with experimental results under different pre-stresses whether in the region of low and moderate field or high field. Moreover, the model can fully reflect the nonlinear magneto-mechanical coupling characteristics between magnetic, magnetostriction and elasticity, and it can effectively predict the changes of material parameters with pre-stress and bias field, which is useful in practical applications

First-principles studies on the pressure dependences of the stress-strain relationship and elastic stability of semiconductors

International Nuclear Information System (INIS)

Wang, S Q; Ye, H Q; Yip, S

2006-01-01

We investigate the stress-strain relationship and elastic stability of zinc-blende GaP, GaN, InP and BN lattices under hydrostatic pressure by first-principles calculation. A simple and direct ab initio implementation for studying the mechanical properties of cubic crystals is developed. The four phases' full-set stress-strain coefficients in wide pressure ranges are theoretically calculated. The fundamental mechanism of elastic stability and the origin of phase transformation under hydrostatic pressure are explored. We found that the abilities for most of these lattices are enhanced to sustain axial strain but weaken to shear strain under higher pressure. The conditions of lattice stability are analysed using both the thermodynamic work-energy criterion and the elastic-stiffness criteria. We show that the lattice collapse of the perfect crystals is caused by the disappearance of their bulk moduli under volume dilation. Lattice defects are considered to be the main reason causing phase transformation under pressure. The correlation between the phonon softening and the variation of elastic coefficients is studied. The pressure dependence of the Kleinman internal strain parameter and its relationship to elastic stability is also explored

Propagation of the nonlinear plastic stress waves in semi-infinite bar

Directory of Open Access Journals (Sweden)

Edward Włodarczyk

2017-03-01

Full Text Available This paper presents the propagation longitudinal nonlinear plastic stress in thin semi-infinite rod or in wire. The rod is characterized by a nonlinear strain hardening model within the scope a plastic strain. The modulus of strain hardening is a decreasing function of the strain. The frontal bar end is suddenly launching to the velocity V, and subsequently moves with this one. General solution of this boundary value problem of the Lagrangian coordinate (material description and of the Eulerian one (spatial description has been presented. There has been carried out the physical interpretation of the obtained results by means of Lagrangian and Eulerian methods. The results of this paper may be utilized in scientific researches and in engineering practice.

Multiaxial Stress-Strain Modeling and Effect of Additional Hardening due to Nonproportional Loading

International Nuclear Information System (INIS)

Rashed, G.; Ghajar, R.; Farrahi, G.

2007-01-01

Most engineering components are subjected to multiaxial rather than uniaxial cyclic loading, which causes multiaxial fatigue. The pre-requisite to predict the fatigue life of such components is to determine the multiaxial stress strain relationship. In this paper the multiaxial cyclic stress-strain model under proportional loading is derived using the modified power law stress-strain relationship. The equivalent strain amplitude consisted of the normal strain excursion and maximum shear strain amplitude is used in the proportional model to include the additional hardening effect due to nonproportional loading. Therefore a new multiaxial cyclic stress-strain relationship is devised for out of phase nonproportional loading. The model is applied to the nonproportional loading case and the results are compared with the other researchers' experimental data published in the literature, which are in a reasonable agreement with the experimental data. The relationship presented here is convenient for the engineering applications

Representative Stress-Strain Curve by Spherical Indentation on Elastic-Plastic Materials

Directory of Open Access Journals (Sweden)

Chao Chang

2018-01-01

Full Text Available Tensile stress-strain curve of metallic materials can be determined by the representative stress-strain curve from the spherical indentation. Tabor empirically determined the stress constraint factor (stress CF, ψ, and strain constraint factor (strain CF, β, but the choice of value for ψ and β is still under discussion. In this study, a new insight into the relationship between constraint factors of stress and strain is analytically described based on the formation of Tabor’s equation. Experiment tests were performed to evaluate these constraint factors. From the results, representative stress-strain curves using a proposed strain constraint factor can fit better with nominal stress-strain curve than those using Tabor’s constraint factors.

Apparent stress-strain relationships in experimental equipment where magnetorheological fluids operate under compression mode

International Nuclear Information System (INIS)

Mazlan, S A; Ekreem, N B; Olabi, A G

2008-01-01

This paper presents an experimental investigation of two different magnetorheological (MR) fluids, namely, water-based and hydrocarbon-based MR fluids in compression mode under various applied currents. Finite element method magnetics was used to predict the magnetic field distribution inside the MR fluids generated by a coil. A test rig was constructed where the MR fluid was sandwiched between two flat surfaces. During the compression, the upper surface was moved towards the lower surface in a vertical direction. Stress-strain relationships were obtained for arrangements of equipment where each type of fluid was involved, using compression test equipment. The apparent compressive stress was found to be increased with the increase in magnetic field strength. In addition, the apparent compressive stress of the water-based MR fluid showed a response to the compressive strain of greater magnitude. However, during the compression process, the hydrocarbon-based MR fluid appeared to show a unique behaviour where an abrupt pressure drop was discovered in a region where the apparent compressive stress would be expected to increase steadily. The conclusion is drawn that the apparent compressive stress of MR fluids is influenced strongly by the nature of the carrier fluid and by the magnitude of the applied current

Nonlinear analysis of reinforced concrete beam with/without tension stiffening effect

International Nuclear Information System (INIS)

Dede, T.; Ayvaz, Y.

2009-01-01

The aim of this paper is to do materially nonlinear failure analysis of RC beam by using finite element method. In the finite element modeling, two different approaches and different tension stress-strain models with/without tension stiffening effect are used by considering two different mesh sizes. In the first approach, the material matrices of concrete and reinforcement are constructed separately, and then superimposed to obtain the element stiffness matrix. In the second approach, the reinforcement is assumed to be uniformly distributed throughout the beam. So, the beam is modeled as a single composite element with increasing the modulus of elasticity of concrete by considering the reinforcement ratio. For these two approaches, elastic-perfectly plastic stress-strain relationship is used for concrete in compression. For the concrete in tension, a stress-strain relationship with/without tension stiffening is used. It is concluded that the approaches and the models considered in this study can be effectively used in the materially nonlinear analysis of RC beams.

Compatible-strain mixed finite element methods for incompressible nonlinear elasticity

Science.gov (United States)

Faghih Shojaei, Mostafa; Yavari, Arash

2018-05-01

We introduce a new family of mixed finite elements for incompressible nonlinear elasticity - compatible-strain mixed finite element methods (CSFEMs). Based on a Hu-Washizu-type functional, we write a four-field mixed formulation with the displacement, the displacement gradient, the first Piola-Kirchhoff stress, and a pressure-like field as the four independent unknowns. Using the Hilbert complexes of nonlinear elasticity, which describe the kinematics and the kinetics of motion, we identify the solution spaces of the independent unknown fields. In particular, we define the displacement in H1, the displacement gradient in H (curl), the stress in H (div), and the pressure field in L2. The test spaces of the mixed formulations are chosen to be the same as the corresponding solution spaces. Next, in a conforming setting, we approximate the solution and the test spaces with some piecewise polynomial subspaces of them. Among these approximation spaces are the tensorial analogues of the Nédélec and Raviart-Thomas finite element spaces of vector fields. This approach results in compatible-strain mixed finite element methods that satisfy both the Hadamard compatibility condition and the continuity of traction at the discrete level independently of the refinement level of the mesh. By considering several numerical examples, we demonstrate that CSFEMs have a good performance for bending problems and for bodies with complex geometries. CSFEMs are capable of capturing very large strains and accurately approximating stress and pressure fields. Using CSFEMs, we do not observe any numerical artifacts, e.g., checkerboarding of pressure, hourglass instability, or locking in our numerical examples. Moreover, CSFEMs provide an efficient framework for modeling heterogeneous solids.

BILAM: a composite laminate failure-analysis code using bilinear stress-strain approximations

Energy Technology Data Exchange (ETDEWEB)

McLaughlin, P.V. Jr.; Dasgupta, A.; Chun, Y.W.

1980-10-01

The BILAM code which uses constant strain laminate analysis to generate in-plane load/deformation or stress/strain history of composite laminates to the point of laminate failure is described. The program uses bilinear stress-strain curves to model layer stress-strain behavior. Composite laminates are used for flywheels. The use of this computer code will help to develop data on the behavior of fiber composite materials which can be used by flywheel designers. In this program the stress-strain curves are modelled by assuming linear response in axial tension while using bilinear approximations (2 linear segments) for stress-strain response to axial compressive, transverse tensile, transverse compressive and axial shear loadings. It should be noted that the program attempts to empirically simulate the effects of the phenomena which cause nonlinear stress-strain behavior, instead of mathematically modelling the micromechanics involved. This code, therefore, performs a bilinear laminate analysis, and, in conjunction with several user-defined failure interaction criteria, is designed to provide sequential information on all layer failures up to and including the first fiber failure. The modus operandi is described. Code BILAM can be used to: predict the load-deformation/stress-strain behavior of a composite laminate subjected to a given combination of in-plane loads, and make analytical predictions of laminate strength.

Relationship between fatigue life in the creep-fatigue region and stress-strain response

Science.gov (United States)

Berkovits, A.; Nadiv, S.

1988-01-01

On the basis of mechanical tests and metallographic studies, strainrange partitioned lives were predicted by introducing stress-strain materials parameters into the Universal Slopes Equation. This was the result of correlating fatigue damage mechanisms and deformation mechanisms operating at elevated temperatures on the basis of observed mechanical and microstructural behavior. Correlation between high temperature fatigue and stress strain properties for nickel base superalloys and stainless steel substantiated the method. Parameters which must be evaluated for PP- and CC- life are the maximum stress achievable under entirely plastic and creep conditions respectively and corresponding inelastic strains, and the two more pairs of stress strain parameters must be ascertained.

Hydrostatic Stress Effects Incorporated Into the Analysis of the High-Strain-Rate Deformation of Polymer Matrix Composites

Science.gov (United States)

Goldberg, Robert K.; Roberts, Gary D.

2003-01-01

Procedures for modeling the effect of high strain rate on composite materials are needed for designing reliable composite engine cases that are lighter than the metal cases in current use. The types of polymer matrix composites that are likely to be used in such an application have a deformation response that is nonlinear and that varies with strain rate. The nonlinearity and strain rate dependence of the composite response is primarily due to the matrix constituent. Therefore, in developing material models to be used in the design of impact-resistant composite engine cases, the deformation of the polymer matrix must be correctly analyzed. However, unlike in metals, the nonlinear response of polymers depends on the hydrostatic stresses, which must be accounted for within an analytical model. An experimental program has been carried out through a university grant with the Ohio State University to obtain tensile and shear deformation data for a representative polymer for strain rates ranging from quasi-static to high rates of several hundred per second. This information has been used at the NASA Glenn Research Center to develop, characterize, and correlate a material model in which the strain rate dependence and nonlinearity (including hydrostatic stress effects) of the polymer are correctly analyzed. To obtain the material data, Glenn s researchers designed and fabricated test specimens of a representative toughened epoxy resin. Quasi-static tests at low strain rates and split Hopkinson bar tests at high strain rates were then conducted at the Ohio State University. The experimental data confirmed the strong effects of strain rate on both the tensile and shear deformation of the polymer. For the analytical model, Glenn researchers modified state variable constitutive equations previously used for the viscoplastic analysis of metals to allow for the analysis of the nonlinear, strain-rate-dependent polymer deformation. Specifically, we accounted for the effects of

A Study of Nonlinear Elasticity Effects on Permeability of Stress Sensitive Shale Rocks Using an Improved Coupled Flow and Geomechanics Model: A Case Study of the Longmaxi Shale in China

Directory of Open Access Journals (Sweden)

Chenji Wei

2018-02-01

Full Text Available Gas transport in shale gas reservoirs is largely affected by rock properties such as permeability. These properties are often sensitive to the in-situ stress state changes. Accurate modeling of shale gas transport in shale reservoir rocks considering the stress sensitive effects on rock petrophysical properties is important for successful shale gas extraction. Nonlinear elasticity in stress sensitive reservoir rocks depicts the nonlinear stress-strain relationship, yet it is not thoroughly studied in previous reservoir modeling works. In this study, an improved coupled flow and geomechanics model that considers nonlinear elasticity is proposed. The model is based on finite element methods, and the nonlinear elasticity in the model is validated with experimental data on shale samples selected from the Longmaxi Formation in Sichuan Basin China. Numerical results indicate that, in stress sensitive shale rocks, nonlinear elasticity affects shale permeability, shale porosity, and distributions of effective stress and pore pressure. Elastic modulus change is dependent on not only in-situ stress state but also stress history path. Without considering nonlinear elasticity, the modeling of shale rock permeability in Longmaxi Formation can overestimate permeability values by 1.6 to 53 times.

Measurement of stress-strain behaviour of human hair fibres using optical techniques.

Science.gov (United States)

Lee, J; Kwon, H J

2013-06-01

Many studies have presented stress-strain relationship of human hair, but most of them have been based on an engineering stress-strain curve, which is not a true representation of stress-strain behaviour. In this study, a more accurate 'true' stress-strain curve of human hair was determined by applying optical techniques to the images of the hair deformed under tension. This was achieved by applying digital image cross-correlation (DIC) to 10× magnified images of hair fibres taken under increasing tension to estimate the strain increments. True strain was calculated by summation of the strain increments according to the theoretical definition of 'true' strain. The variation in diameter with the increase in longitudinal elongation was also measured from the 40× magnified images to estimate the Poisson's ratio and true stress. By combining the true strain and the true stress, a true stress-strain curve could be determined, which demonstrated much higher stress values than the conventional engineering stress-strain curve at the same degree of deformation. Four regions were identified in the true stress-strain relationship and empirical constitutive equations were proposed for each region. Theoretical analysis on the necking condition using the constitutive equations provided the insight into the failure mechanism of human hair. This analysis indicated that local thinning caused by necking does not occur in the hair fibres, but, rather, relatively uniform deformation takes place until final failure (fracture) eventually occurs. © 2012 Society of Cosmetic Scientists and the Société Française de Cosmétologie.

Investigation of isochronous stress-strain formulations for elevated temperature structural design

International Nuclear Information System (INIS)

Koo, Gyeong Hoi; Kim, Jong Bum

2012-01-01

For elevated temperature design evaluations by the ASME-NH rules, the most important material data is the isochronous stress-strain curves, which can provide design creep information. The main purpose of this paper is to investigate appropriate formulations to be able to generate the isochronous stress-strain curves and implement it to the computer program which is coded the ASME-NH design evaluation procedures. To do this, formulations by the strain-time relationship are investigated in detail and the sensitivity studies for rapid initial transient creep contributions, slower and longer transient creep contribution, and secondary creep contributions are carried out for type 316 austenitic stainless steel. From the results of this study, it is found that the strain-time relationship formulations can well describe the isochronous stress-strain curves with the transient creep contributions

Investigation of Stress-Strain-Time Relationships of Concrete Filled Steel Tube Columns

Directory of Open Access Journals (Sweden)

Mutlu Seçer

2010-01-01

Full Text Available In this study, time dependent creep and shrinkage behaviors of concrete filled steel box section columns are investigated by using various methods. Time dependent behavior is examined by using effective modulus method, age-adjusted effective modulus method, creep rate method and Dischinger method. Shrinkage and creep strains are modeled using ACI 209 specification. In the study, in order to investigate time dependent behavior numerically, a concrete filled steel box section column is selected in a twenty story building and the time dependent stress decrease in concrete and stress increase in steel box section and the changes in strain components are calculated. Stress – time, strain – time and strain components – time graphics are shown and the advantages and the disadvantages of the numerical methods in modeling the time dependent behavior are revealed respectively.

A model for the stress-strain behavior of toughened polystyrene. Part 2

NARCIS (Netherlands)

Sjoerdsma, S.D.; Heikens, D.

1982-01-01

The general stress-strain relationship derived in an earlier paper is applied to analyse experimental stress-strain curves of polystyrene-polyethylene blends. It is concluded from the stress and temperature dependence of the rates of craze initiation and craze growth that these rates can be

Studies on Stress-Strain Relationships of Polymeric Materials Used in Space Applications

Science.gov (United States)

Jana, Sadhan C.; Freed, Alan

2002-01-01

A two-year research plan was undertaken in association with Polymers Branch, NASA Glenn Research Center, to carry out experimental and modeling work relating stress and strain behavior of polymeric materials, especially elastomers and vulcanized rubber. An experimental system based on MTS (Mechanical Testing and Simulation) A/T-4 test facility environment has been developed for a broader range of polymeric materials in addition to a design of laser compatible temperature control chamber for online measurements of various strains. Necessary material processing has been accomplished including rubber compounding and thermoplastic elastomer processing via injection molding. A broad suite of testing methodologies has been identified to reveal the complex non-linear mechanical behaviors of rubbery materials when subjected to complex modes of deformation. This suite of tests required the conceptualization, design and development of new specimen geometries, test fixtures, and test systems including development of a new laser based technique to measure large multi-axial deformations. Test data has been generated for some of these new fixtures and has revealed some complex coupling effects generated during multi-axial deformations. In addition, fundamental research has been conducted concerning the foundation principles of rubber thermodynamics and resulting theories of rubber elasticity. Studies have been completed on morphological properties of several thermoplastic elastomers. Finally, a series of steps have been identified to further advance the goals of NASA's ongoing effort.

Determination of Burst Pressure of API Steel Pipes using Stress Modified Critical Strain Model

International Nuclear Information System (INIS)

Alang, N A; Razak, N A; Sulaiman, A S

2012-01-01

This paper presents a technique which can be used to determine the burst pressure of defective steel pipes using non-linear finite element (FE) analysis. The technique uses stress modified critical strain (SMCS) failure criterion to study the effect of gouge defects on maximum working pressure of API X65 steel pipes. The procedures in determining the model parameters using 3-D, homogeneous isotropic elastic-plastic material model with large deformation finite element analyses from notched tensile bars were systematically discussed. The relationship between burst pressure and gouge depth was proposed. The burst pressure estimated then was compared to experimental data from the literature for validation showing overall good agreements.

Financial strain is associated with increased oxidative stress levels: the Women's Health and Aging Studies.

Science.gov (United States)

Palta, Priya; Szanton, Sarah L; Semba, Richard D; Thorpe, Roland J; Varadhan, Ravi; Fried, Linda P

2015-01-01

Elevated oxidative stress levels may be one mechanism contributing to poor health outcomes. Financial strain and oxidative stress are each predictors of morbidity and mortality, but little research has investigated their relationship. Community-dwelling older adults (n = 728) from the Women's Health and Aging Studies I and II were included in this cross-sectional analysis. Financial strain was ascertained as an ordinal response to: "At the end of the month, do you have more than enough money left over, just enough, or not enough?" Oxidative stress was measured using serum protein carbonyl concentrations. Linear regression was used to quantify the relationship between financial strain and oxidative stress. Participants who reported high financial strain exhibited 13.4% higher protein carbonyl concentrations compared to individuals who reported low financial strain (p = 0.002). High financial strain may be associated with increased oxidative stress, suggesting that oxidative stress could mediate associations between financial strain and poor health. Copyright © 2015 Elsevier Inc. All rights reserved.

The Effect of Grain Size and Strain on the Tensile Flow Stress of Aluminium at Room Temperature

DEFF Research Database (Denmark)

Hansen, Niels

1977-01-01

stress-grain size relationship was analyzed in terms of matrix strengthening and grain boundary strengthening according to the dislocation concept of Ashby. At intermediate strains this approach gives a good description of the effect of strain, grain size and purity on the flow stress.......Tensile-stress-strain data over a strain range from 0.2 to 30% were obtained at room temperature for 99.999 and 99.5% aluminium as a function of grain size. The yield stress-grain size relationship can be expressed by a Petch-Hall relation with approximately the same slope for the two materials....... The flow stress-grain size relationship can adequately be expressed by a modified Petch-Hall relation; for 99.999% aluminium material the slope increases with strain through a maximum around 15–20%, whereas for 99.5% aluminium the slope decreases with the strain to zero at strains about 10%. The flow...

Stress evaluation of metallic material under steady state based on nonlinear critically refracted longitudinal wave

Science.gov (United States)

Mao, Hanling; Zhang, Yuhua; Mao, Hanying; Li, Xinxin; Huang, Zhenfeng

2018-06-01

This paper presents the study of applying the nonlinear ultrasonic wave to evaluate the stress state of metallic materials under steady state. The pre-stress loading method is applied to guarantee components with steady stress. Three kinds of nonlinear ultrasonic experiments based on critically refracted longitudinal wave are conducted on components which the critically refracted longitudinal wave propagates along x, x1 and x2 direction. Experimental results indicate the second and third order relative nonlinear coefficients monotonically increase with stress, and the normalized relationship is consistent with simplified dislocation models, which indicates the experimental result is logical. The combined ultrasonic nonlinear parameter is proposed, and three stress evaluation models at x direction are established based on three ultrasonic nonlinear parameters, which the estimation error is below 5%. Then two stress detection models at x1 and x2 direction are built based on combined ultrasonic nonlinear parameter, the stress synthesis method is applied to calculate the magnitude and direction of principal stress. The results show the prediction error is within 5% and the angle deviation is within 1.5°. Therefore the nonlinear ultrasonic technique based on LCR wave could be applied to nondestructively evaluate the stress of metallic materials under steady state which the magnitude and direction are included.

Studies of biaxial mechanical properties and nonlinear finite element modeling of skin.

Science.gov (United States)

Shang, Xituan; Yen, Michael R T; Gaber, M Waleed

2010-06-01

The objective of this research is to conduct mechanical property studies of skin from two individual but potentially connected aspects. One is to determine the mechanical properties of the skin experimentally by biaxial tests, and the other is to use the finite element method to model the skin properties. Dynamic biaxial tests were performed on 16 pieces of abdominal skin specimen from rats. Typical biaxial stress-strain responses show that skin possesses anisotropy, nonlinearity and hysteresis. To describe the stress-strain relationship in forms of strain energy function, the material constants of each specimen were obtained and the results show a high correlation between theory and experiments. Based on the experimental results, a finite element model of skin was built to model the skin's special properties including anisotropy and nonlinearity. This model was based on Arruda and Boyce's eight-chain model and Bischoff et al.'s finite element model of skin. The simulation results show that the isotropic, nonlinear eight-chain model could predict the skin's anisotropic and nonlinear responses to biaxial loading by the presence of an anisotropic prestress state.

A comparative study on the uniaxial mechanical properties of the umbilical vein and umbilical artery using different stress-strain definitions.

Science.gov (United States)

Karimi, Alireza; Navidbakhsh, Mahdi

2014-12-01

The umbilical cord is part of the fetus and generally includes one umbilical vein (UV) and two umbilical arteries (UAs). As the saphenous vein and UV are the most commonly used veins for the coronary artery disease treatment as a coronary artery bypass graft (CABG), understating the mechanical properties of UV has a key asset in its performance for CABG. However, there is not only a lack of knowledge on the mechanical properties of UV and UA but there is no agreement as to which stress-strain definition should be implemented to measure their mechanical properties. In this study, the UV and UA samples were removed after caesarean from eight individuals and subjected to a series of tensile testing. Three stress definitions (second Piola-Kichhoff stress, engineering stress, and true stress) and four strain definitions (Almansi-Hamel strain, Green-St. Venant strain, engineering strain, and true strain) were employed to determine the linear mechanical properties of UVs and UAs. The nonlinear mechanical behavior of UV/UA was computationally investigated using hyperelastic material models, such as Ogden and Mooney-Rivlin. The results showed that the effect of varying the stress definition on the maximum stress measurements of the UV/UA is significant but not when calculating the elastic modulus. In the true stress-strain diagram, the maximum strain of UV was 92 % higher, while the elastic modulus and maximum stress were 162 and 42 % lower than that of UA. The Mooney-Rivlin material model was designated to represent the nonlinear mechanical behavior of the UV and UA under uniaxial loading.

Application of nonlinear ultrasonic method for monitoring of stress state in concrete

International Nuclear Information System (INIS)

Kim, Gyu Jin; Kwak, Hyo Gyoung; Park, Sun Jong

2016-01-01

As the lifespan of concrete structures increases, their load carrying capacity decreases owing to cyclic loads and long-term effects such as creep and shrinkage. For these reasons, there is a necessity for stress state monitoring of concrete members. Particularly, it is necessary to evaluate the concrete structures for behavioral changes by using a technique that can overcome the measuring limitations of usual ultrasonic nondestructive evaluation methods. This paper proposes the use of a nonlinear ultrasonic method, namely, nonlinear resonant ultrasonic spectroscopy (NRUS) for the measurement of nonlinearity parameters for stress monitoring. An experiment compared the use of NRUS method and a linear ultrasonic method, namely, ultrasonic pulse velocity (UPV) to study the effects of continuously increasing loads and cyclic loads on the nonlinearity parameter. Both NRUS and UPV methods found a similar direct relationship between load level and that parameter. The NRUS method showed a higher sensitivity to micro-structural changes of concrete than UPV method. Thus, the experiment confirms the possibility of using the nonlinear ultrasonic method for stress state monitoring of concrete members

Application of nonlinear ultrasonic method for monitoring of stress state in concrete

Energy Technology Data Exchange (ETDEWEB)

Kim, Gyu Jin; Kwak, Hyo Gyoung [Dept. of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of); Park, Sun Jong [Dept. of Structural System and Site Safety Evaluation, Korea Institute of Nuclear Safety, Daejeon (Korea, Republic of)

2016-04-15

As the lifespan of concrete structures increases, their load carrying capacity decreases owing to cyclic loads and long-term effects such as creep and shrinkage. For these reasons, there is a necessity for stress state monitoring of concrete members. Particularly, it is necessary to evaluate the concrete structures for behavioral changes by using a technique that can overcome the measuring limitations of usual ultrasonic nondestructive evaluation methods. This paper proposes the use of a nonlinear ultrasonic method, namely, nonlinear resonant ultrasonic spectroscopy (NRUS) for the measurement of nonlinearity parameters for stress monitoring. An experiment compared the use of NRUS method and a linear ultrasonic method, namely, ultrasonic pulse velocity (UPV) to study the effects of continuously increasing loads and cyclic loads on the nonlinearity parameter. Both NRUS and UPV methods found a similar direct relationship between load level and that parameter. The NRUS method showed a higher sensitivity to micro-structural changes of concrete than UPV method. Thus, the experiment confirms the possibility of using the nonlinear ultrasonic method for stress state monitoring of concrete members.

Nonlinear effects of high temperature on buckling of structural elements

International Nuclear Information System (INIS)

Iyengar, N.G.R.

1975-01-01

Structural elements used in nuclear reactors are subjected to high temperatures. Since with increase in temperature there is a gradual fall in the elastic modulus and the stress-strain relationship is nonlinear at these operating load levels, a realistic estimate of the buckling load should include this nonlinearity. In this paper the buckling loads for uniform columns with circular and rectangular cross-sections and different boundary conditions under high temperature environment are estimated. The stress-strain relationship for the material has been assumed to follow inverse Ramberg-Osgood law. In view of the fact that no closed form solutions are possible, approximate methods like perturbation and Galerkin techniques are used. Further, the solution for general value for 'm' is quite involved. Results have been obtained with values for 'm' as 3 and 5. Studies reveal that the influence of material nonlinearity on the buckling load is of the softening type, and it increases with increase in the value of 'm'. The nonlinear effects are more for clamped boundaries than for simply supported boundaries. For the first mode analysis both the methods are powerful. It is, however, felt that for higher modes the Galerkin method might be better in view of its simplicity. This investigation may be considered as a step towards a more general solution

Life Stress, Strain, and Deviance Across Schools: Testing the Contextual Version of General Strain Theory in China.

Science.gov (United States)

Zhang, Jinwu; Liu, Jianhong; Wang, Xin; Zou, Anquan

2017-08-01

General Strain Theory delineates different types of strain and intervening processes from strain to deviance and crime. In addition to explaining individual strain-crime relationship, a contextualized version of general strain theory, which is called the Macro General Strain Theory, has been used to analyze how aggregate variables influence aggregate and individual deviance and crime. Using a sample of 1,852 students (Level 1) nested in 52 schools (Level 2), the current study tests the Macro General Strain Theory using Chinese data. The results revealed that aggregate life stress and strain have influences on aggregate and individual deviance, and reinforce the individual stress-deviance association. The current study contributes by providing the first Macro General Strain Theory test based on Chinese data and offering empirical evidence for the multilevel intervening processes from strain to deviance. Limitations and future research directions are discussed.

Developing the multiple stress-strain creep recovery (MS-SCR) test

Science.gov (United States)

Elnasri, Mahmoud; Airey, Gordon; Thom, Nick

2018-04-01

While most published work from Europe has been concerned with evaluating binders' resistance to rutting based on their stiffness (deformation resistance), work originating in the US has mainly been concerned with ranking binders based on their recoverability in a multiple stress form. This paper details the design of a new modified multiple stress-strain creep recovery (MS-SCR) test. The test is designed to evaluate binders' rutting resistance based on two rutting resistance mechanisms: stiffness and recoverability. A preliminary investigation is presented in this paper followed by details of the design of the new modified test. A 40/60 penetration grade bitumen and bitumen-filler mastics prepared with three filler concentrations (35%, 50%, and 65% filler content by mass of mastic) were tested. In addition, two polymer modified bitumens (PMBs) using the same base bitumen type were examined for validation. Two parameters are introduced to characterise the short and long recovery in the new test. In terms of stiffness, the test allows the behaviour of binders at different stress levels and loading cycles to be studied and produces a new parameter that can quantify the degree of modification. Finally, a relationship between nonlinearity and normal force in the test was investigated.

Analysis of stress-strain behavior in Bi2223 composite tapes

International Nuclear Information System (INIS)

Sugano, M.; Osamura, K.; Nyilas, A.

2004-01-01

Tensile test was carried out for Bi2223/Ag/Ag alloy composite tapes at RT, 77 and 7 K. Two yielding points are observed in the stress-strain curves. From the stress-strain behavior of the components and critical current (I c ) as a function of tensile strain, it was found that the microscopic reason for these yieldings is attributed to yielding of Ag alloy and fracture of Bi2223, respectively. The strain at the second yielding has temperature dependence and it becomes larger with decreasing measured temperature. From the thermo-mechanical analysis, it can be explained by temperature dependence of compressive residual strain of Bi2223. Reversible recovery of I c was found during loading-unloading test. The relationship between the reversible strain limit and the intrinsic strain of Bi2223 was discussed

Model and prediction of stress relaxation of polyurethane fiber

Science.gov (United States)

You, Gexin; Wang, Chunyan; Mei, Shuqin; Yang, Bo; Zhou, Xiuwen

2018-03-01

In this study, the effect of small strain (less than 10%) on hydrogen bond (H-bond) and crystallinity of dry-spun polyurethane fiber was investigated with fourier transform infrared spectroscopy and x-ray diffractometer, respectively. The results showed that the H-bond of hard segments hardly broke and its degree of crystallinity scarcely varied below strain of 10%. The fiber stress relaxation behavior at 25 °C under small strain was researched using dynamic mechanical analyzer. The stress relaxation modulus constitutive equation was obtained by transforming the non-linear relationship between stress and time into the linear relationship between stress and strain. The stress relaxation modulus master curve at 25 °C was established in terms of short-term stress relaxation tests at elevated temperatures (35 °C, 45 °C, 65 °C and 75 °C) according to time-temperature superposition principle (TTS) to predict long-term behavior within 353 year.

Numerical analysis oriented biaxial stress-strain relation and failure criterion of plain concrete

International Nuclear Information System (INIS)

Link, J.

1975-01-01

A biaxial stress-strain relation and failure criterion is proposed, which is applicable to structural analysis methods. The formulation of material behavior of plain concrete in biaxial stress-state was developed. A nonlinear elastic, anisotropic stress-strain relation was derived with two moduli of elasticity, E 1 , E 2 and Poisson's ratios, ν 1 , ν 2 , which depend on the prevailing biaxial stress state. The stress-strain relation is valid in the whole biaxial stress field, that means with a smooth transition between the domains of tension/tension, tension/compression and compression/compression. The stress-dependent moduli E 1 , E 2 and the Poisson's ratios ν 1 , ν 2 are approximated by polynomials, trigonometrical and exponential functions. A failure criterion was defined by approximating the test results of the biaxial ultimate concrete strength with a 7th degree polynomial, which is also valid in the whole biaxial stress domain. The definition of the state of failure is given as a function of stresses as well as strains. Initial parameters of the formulation of the biaxial material behavior are the uniaxial cylindrical strength of concrete and the initial values of Young's modulus and Poisson's ratio. A simple expansion of this formulation makes it applicable not only to normal but also to light-weight concrete. Comparison of numerically calculated stress-strain curves up to the ultimate biaxial stresses which indicate the failure criteria with those obtained from tests show a very good agreement. It is shown, that the biaxial stress-strain relation can be extended for use in cases of triaxial tension/tension/compression stress state. Numerical examples of analysis of concrete slabs show the importance of incorporation of a realistic material behavior for better safety estimations

Nonlinear Finite Strain Consolidation Analysis with Secondary Consolidation Behavior

Directory of Open Access Journals (Sweden)

Jieqing Huang

2014-01-01

Full Text Available This paper aims to analyze nonlinear finite strain consolidation with secondary consolidation behavior. On the basis of some assumptions about the secondary consolidation behavior, the continuity equation of pore water in Gibson’s consolidation theory is modified. Taking the nonlinear compressibility and nonlinear permeability of soils into consideration, the governing equation for finite strain consolidation analysis is derived. Based on the experimental data of Hangzhou soft clay samples, the new governing equation is solved with the finite element method. Afterwards, the calculation results of this new method and other two methods are compared. It can be found that Gibson’s method may underestimate the excess pore water pressure during primary consolidation. The new method which takes the secondary consolidation behavior, the nonlinear compressibility, and nonlinear permeability of soils into consideration can precisely estimate the settlement rate and the final settlement of Hangzhou soft clay sample.

Adaptive regression for modeling nonlinear relationships

CERN Document Server

Knafl, George J

2016-01-01

This book presents methods for investigating whether relationships are linear or nonlinear and for adaptively fitting appropriate models when they are nonlinear. Data analysts will learn how to incorporate nonlinearity in one or more predictor variables into regression models for different types of outcome variables. Such nonlinear dependence is often not considered in applied research, yet nonlinear relationships are common and so need to be addressed. A standard linear analysis can produce misleading conclusions, while a nonlinear analysis can provide novel insights into data, not otherwise possible. A variety of examples of the benefits of modeling nonlinear relationships are presented throughout the book. Methods are covered using what are called fractional polynomials based on real-valued power transformations of primary predictor variables combined with model selection based on likelihood cross-validation. The book covers how to formulate and conduct such adaptive fractional polynomial modeling in the s...

Effect of initial strain and material nonlinearity on the nonlinear static and dynamic response of graphene sheets

Science.gov (United States)

Singh, Sandeep; Patel, B. P.

2018-06-01

Computationally efficient multiscale modelling based on Cauchy-Born rule in conjunction with finite element method is employed to study static and dynamic characteristics of graphene sheets, with/without considering initial strain, involving Green-Lagrange geometric and material nonlinearities. The strain energy density function at continuum level is established by coupling the deformation at continuum level to that at atomic level through Cauchy-Born rule. The atomic interactions between carbon atoms are modelled through Tersoff-Brenner potential. The governing equation of motion obtained using Hamilton's principle is solved through standard Newton-Raphson method for nonlinear static response and Newmark's time integration technique to obtain nonlinear transient response characteristics. Effect of initial strain on the linear free vibration frequencies, nonlinear static and dynamic response characteristics is investigated in detail. The present multiscale modelling based results are found to be in good agreement with those obtained through molecular mechanics simulation. Two different types of boundary constraints generally used in MM simulation are explored in detail and few interesting findings are brought out. The effect of initial strain is found to be greater in linear response when compared to that in nonlinear response.

The demonstration of nonlinear analytic model for the strain field induced by thermal copper filled TSVs (through silicon via

Directory of Open Access Journals (Sweden)

M. H. Liao

2013-08-01

Full Text Available The thermo-elastic strain is induced by through silicon vias (TSV due to the difference of thermal expansion coefficients between the copper (∼18 ppm/ °C and silicon (∼2.8 ppm/ °C when the structure is exposed to a thermal ramp budget in the three dimensional integrated circuit (3DIC process. These thermal expansion stresses are high enough to introduce the delamination on the interfaces between the copper, silicon, and isolated dielectric. A compact analytic model for the strain field induced by different layouts of thermal copper filled TSVs with the linear superposition principle is found to have large errors due to the strong stress interaction between TSVs. In this work, a nonlinear stress analytic model with different TSV layouts is demonstrated by the finite element method and the analysis of the Mohr's circle. The characteristics of stress are also measured by the atomic force microscope-raman technique with nanometer level space resolution. The change of the electron mobility with the consideration of this nonlinear stress model for the strong interactions between TSVs is ∼2–6% smaller in comparison with those from the consideration of the linear stress superposition principle only.

Bulk nonlinear elastic strain waves in a bar with nanosize inclusions

DEFF Research Database (Denmark)

Gula, Igor A.; Samsonov (†), Alexander M.

2018-01-01

We propose a mathematical model for propagation of the long nonlinearly elastic longitudinal strain waves in a bar, which contains nanoscale structural inclusions. The model is governed by a nonlinear doubly dispersive equation (DDE) with respect to the one unknown longitudinal strain function. We...

Hysteresis, Discrete Memory, and Nonlinear Wave Propagation in Rock: A New Paradigm

International Nuclear Information System (INIS)

Guyer, R.A.; McCall, K.R.; Boitnott, G.N.

1995-01-01

The structural elements in a rock are characterized by their density in Preisach-Mayergoyz space (PM space). This density is found for a Berea sandstone from stress-strain data and used to study the response of the sandstone to elaborate pressure protocols. Hysteresis with discrete memory, in agreement with experiment, is found. The relationship between strain, quasistatic modulus, and dynamic modulus is established. Nonlinear wave propagation, the production of copious harmonics, and nonlinear attenuation are demonstrated. PM space is shown to be the central construct in a new paradigm for the description of the elastic behavior of consolidated materials

Stress generation in a developmental context: the role of youth depressive symptoms, maternal depression, the parent-child relationship, and family stress.

Science.gov (United States)

Chan, Priscilla T; Doan, Stacey N; Tompson, Martha C

2014-02-01

The present study examined stress generation in a developmental and family context among 171 mothers and their preadolescent children, ages 8-12 years, at baseline (Time 1) and 1-year follow-up (Time 2). In the current study, we examined the bidirectional relationship between children's depressive symptoms and dependent family stress. Results suggest that children's baseline level of depressive symptoms predicted the generation of dependent family stress 1 year later. However, baseline dependent family stress did not predict an increase in children's depressive symptoms 1 year later. In addition, we examined whether a larger context of both child chronic strain (indicated by academic, behavioral, and peer stress) and family factors, including socioeconomic status and parent-child relationship quality, would influence the stress generation process. Although both chronic strain and socioeconomic status were not associated with dependent family stress at Time 2, poorer parent-child relationship quality significantly predicted greater dependent family stress at Time 2. Child chronic strain, but neither socioeconomic status nor parent-child relationship quality, predicted children's depression symptoms at Time 2. Finally, gender, maternal depression history, and current maternal depressive symptoms did not moderate the relationship between level of dependent family stress and depressive symptoms. Overall, findings provide partial support for a developmental stress generation model operating in the preadolescent period.

Stress strain tensors with their application to x-ray stress measurement

International Nuclear Information System (INIS)

Kurita, Masanori

2015-01-01

This paper describes in detail the method of obtaining the formulas of stress-strain tensor that express the directional dependence of stress-strain, that is, how these values change in response to coordinate transformation, and clarifies the preconditions for supporting both formulas. The two conversion formulas are both the second order of tensor, and the formula of strain tensor not only does not use the relational expression of stress and strain at all, but also is obtained completely independently of the formula of stress tensor. Except for the condition that the strain is very small (elastic deformation) in the conversion formula of strain, both formulas unconditionally come into effect. In other words, both formulas hold true even in the isotropic elastic body or anisotropic elastic body. It was shown that the conversion formula of strain can be derived from the conversion formula of stress using the formula of Hooke for isotropic elastic body. From these three-dimensional expressions, the two-dimensional stress-strain coordinate conversion formula that is used for Mohr's stress-strain circle was derived. It was shown that these formulas hold true for three-dimensional stress condition with stress-strain components in the three-axial direction that are not plane stress nor plane strain condition. In addition, as an application case of this theory, two-dimensional and three-dimensional X-ray stress measurements that are effective for residual stress measurement were shown. (A.O.)

Stress strain modelling of casting processes in the framework of the control volume method

DEFF Research Database (Denmark)

Hattel, Jesper; Andersen, Søren; Thorborg, Jesper

1998-01-01

Realistic computer simulations of casting processes call for the solution of both thermal, fluid-flow and stress/strain related problems. The multitude of the influencing parameters, and their non-linear, transient and temperature dependent nature, make the calculations complex. Therefore the nee......, the present model is based on the mainly decoupled representation of the thermal, mechanical and microstructural processes. Examples of industrial applications, such as predicting residual deformations in castings and stress levels in die casting dies, are presented...... for fast, flexible, multidimensional numerical methods is obvious. The basis of the deformation and stress/strain calculation is a transient heat transfer analysis including solidification. This paper presents an approach where the stress/strain and the heat transfer analysis uses the same computational...... domain, which is highly convenient. The basis of the method is the control volume finite difference approach on structured meshes. The basic assumptions of the method are shortly reviewed and discussed. As for other methods which aim at application oriented analysis of casting deformations and stresses...

Elevated temperature stress strain behavior of beryllium powder product

International Nuclear Information System (INIS)

Abeln, S.P.; Field, R.; Mataya, M.C.

1995-01-01

Several grades of beryllium powder product were tested under isothermal conditions in compression over a temperature range of room temperature to 1000 C and a strain rate range from 0.001 s -1 to 1 s -1 . Samples were compressed to a total strain of 1 (64% reduction in height). It is shown that all the grades are strain rate sensitive and that strain rate sensitivity increases with temperature. Yield points were exhibited by some grades up to a temperature of 500 C, and appeared to be primarily dependent on prior thermal history which determined the availability of mobile dislocations. Serrated flow in the form of stress drops was seen in all the materials tested and was most pronounced at 500 C. The appearance and magnitude of the stress drops were dependent on accumulated strain, strain rate, sample orientation, and composition. The flow stress and shape of the flow curves differed significantly from grade to grade due to variations in alloy content, the size and distribution of BeO particles, aging precipitates, and grain size. The ductile-brittle transition temperature (DBTT) was determined for each grade of material and shown to be dependent on composition and thermal treatment. Structure/property relationships are discussed using processing history, microscopy (light and transmission), and property data

Temperature-stress phase diagram of strain glass Ti48.5Ni51.5

International Nuclear Information System (INIS)

Wang, Y.; Ren, X.; Otsuka, K.; Saxena, A.

2008-01-01

The temperature and stress dependence of the properties of a recently discovered strain glass Ti 48.5 Ni 51.5 , which is a glass of frozen local lattice strains, was investigated systematically. It was found that the ideal freezing temperature (T 0 ) of the strain glass decreases with increasing stress. When the stress exceeds a critical value σ c (T), the pseudo-B2 strain glass transforms into B19' martensite. However, the stress-strain behavior associated with such a stress-induced transition showed a crossover at a crossover temperature T CR , which is ∼20 K below T 0 . Above T CR , the sample showed superelastic behavior; however, below T CR , the sample demonstrated plastic behavior. More interestingly, the σ c vs. temperature relation for unfrozen strain glass obeys the Clausius-Clapyeron relationship, whereas that for frozen strain glass disobeys this universal thermodynamic law. A phenomenological explanation is provided for all the phenomena observed, and it is shown that all the anomalous effects come from the broken ergodicity of the glass system and a temperature-dependent relative stability of the martensitic phase. Based on experimental observations, a temperature-stress phase diagram is constructed for this strain glass, which may serve as a guide map for understanding and predicting the properties of strain glass

Atlas of stress-strain curves

CERN Document Server

2002-01-01

The Atlas of Stress-Strain Curves, Second Edition is substantially bigger in page dimensions, number of pages, and total number of curves than the previous edition. It contains over 1,400 curves, almost three times as many as in the 1987 edition. The curves are normalized in appearance to aid making comparisons among materials. All diagrams include metric (SI) units, and many also include U.S. customary units. All curves are captioned in a consistent format with valuable information including (as available) standard designation, the primary source of the curve, mechanical properties (including hardening exponent and strength coefficient), condition of sample, strain rate, test temperature, and alloy composition. Curve types include monotonic and cyclic stress-strain, isochronous stress-strain, and tangent modulus. Curves are logically arranged and indexed for fast retrieval of information. The book also includes an introduction that provides background information on methods of stress-strain determination, on...

Coupled stress-strain and electrical resistivity measurements on copper based shape memory single crystals

Directory of Open Access Journals (Sweden)

Gonzalez Cezar Henrique

2004-01-01

Full Text Available Recently, electrical resistivity (ER measurements have been done during some thermomechanical tests in copper based shape memory alloys (SMA's. In this work, single crystals of Cu-based SMA's have been studied at different temperatures to analyse the relationship between stress (s and ER changes as a function of the strain (e. A good consistency between ER change values is observed in different experiments: thermal martensitic transformation, stress induced martensitic transformation and stress induced reorientation of martensite variants. During stress induced martensitic transformation (superelastic behaviour and stress induced reorientation of martensite variants, a linear relationship is obtained between ER and strain as well as the absence of hys teresis. In conclusion, the present results show a direct evidence of martensite electrical resistivity anisotropy.

Effect of Annealing on Strain-Temperature Response under Constant Tensile Stress in Cold-Worked NiTi Thin Wire

OpenAIRE

Yan, Xiaojun; Van Humbeeck, Jan

2011-01-01

The present paper aims to understand the influence of annealing on the strain-temperature response of a cold-worked NiTi wire under constant tensile stress. It was found that transformation behavior, stress-strain relationship, and strain-temperature response of the cold-worked NiTi wire are strongly affected by the annealing temperature. Large martensitic strains can be reached even though the applied stress is below the plateau stress of the martensite phase. At all stress levels transforma...

Leuconostoc strains isolated from dairy products: Response against food stress conditions.

Science.gov (United States)

D'Angelo, Luisa; Cicotello, Joaquín; Zago, Miriam; Guglielmotti, Daniela; Quiberoni, Andrea; Suárez, Viviana

2017-09-01

A systematic study about the intrinsic resistance of 29 strains (26 autochthonous and 3 commercial ones), belonging to Leuconostoc genus, against diverse stress factors (thermal, acidic, alkaline, osmotic and oxidative) commonly present at industrial or conservation processes were evaluated. Exhaustive result processing was made by applying one-way ANOVA, Student's test (t), multivariate analysis by Principal Component Analysis (PCA) and Matrix Hierarchical Cluster Analysis. In addition, heat adaptation on 4 strains carefully selected based on previous data analysis was assayed. The strains revealed wide diversity of resistance to stress factors and, in general, a clear relationship between resistance and Leuconostoc species was established. In this sense, the highest resistance was shown by Leuconostoc lactis followed by Leuconostoc mesenteroides strains, while Leuconostoc pseudomesenteroides and Leuconostoc citreum strains revealed the lowest resistance to the stress factors applied. Heat adaptation improved thermal cell survival and resulted in a cross-resistance against the acidic factor. However, all adapted cells showed diminished their oxidative resistance. According to our knowledge, this is the first study regarding response of Leuconostoc strains against technological stress factors and could establish the basis for the selection of "more robust" strains and propose the possibility of improving their performance during industrial processes. Copyright © 2017 Elsevier Ltd. All rights reserved.

Elucidating and tuning the strain-induced non-linear behavior of polymer nanocomposites: a detailed molecular dynamics simulation study.

Science.gov (United States)

Shen, Jianxiang; Liu, Jun; Gao, Yangyang; Li, Xiaolin; Zhang, Liqun

2014-07-28

By setting up a coarse-grained model of polymer nanocomposites, we monitored the change in the elastic modulus as a function of the strain, derived from the stress-strain behavior by determining uniaxial tension and simple shear of two typical spatial distribution states (aggregation and dispersion) of nanoparticles (NPs). In both these cases, we observed that the elastic modulus decreases non-linearly with the increase of strain and reaches a low plateau at larger strains. This phenomenon is similar to the so-called "Payne effect" for elastomer nanocomposites. Particularly, the modulus of the aggregation case is more sensitive to the imposed strain. By examining the structural parameters, such as the number of neighboring NPs, coordination number of NPs, root-mean-squared average force exerted on the NPs, local strain, chain conformations (bridge, dangle, loop, interface bead and connection bead), and the total interaction energy of NP-polymer and NP-NP, we inferred that the underlying mechanism of the aggregation case is the disintegration of the NP network or clusters formed through direct contact; however, for the dispersion case, the non-linear behavior is attributed to the destruction of the NP network or clusters formed through the bridging of adsorbed polymer segments among the NPs. The former physical network is influenced by NP-NP interaction and NP volume fraction, while the latter is influenced by NP-polymer interaction and NP volume fraction. Lastly, we found that for the dispersion case, further increasing the inter-particle distance or grafting NPs with polymer chains can effectively reduce the non-linear behavior due to the decrease of the physical network density. In general, this simulation work, for the first time, establishes the correlation between the micro-structural evolution and the strain-induced non-linear behavior of polymer nanocomposites, and sheds some light on how to reduce the "Payne effect".

Experimental Characterization of Stress- and Strain-Dependent Stiffness in Grouted Rock Masses.

Science.gov (United States)

Kim, Ji-Won; Chong, Song-Hun; Cho, Gye-Chun

2018-03-29

Grouting of fractured rock mass prior to excavation results in grout-filled discontinuities that govern the deformation characteristics of a site. The influence of joint characteristics on the properties of grouted rocks is important in assessing the effects of grouting on jointed rock mass. However, grouting remains a predominantly empirical practice and the effects of grouting on rock joint behavior and material properties have yet to be accurately assessed. Granular materials, including jointed rocks, typically display nonlinear strain-dependent responses that can be characterized by the shear modulus degradation curve. In this study, the effects of grouting on the strain-dependent shear stiffness of jointed rock mass were investigated at the small-strain (below 10 -5 ) and mid-strain (10 -5 to 10 -3 ) ranges using the quasi-static resonant column test and rock mass dynamic test devices. The effects of curing time, axial stress, initial joint roughness, and grouted joint thickness were examined. The results show that (1) grouting of rock joints leads to decreased stress sensitivity and increased small-strain shear stiffness for all tested samples; (2) the grouted rock samples display similar modulus degradation characteristics as the applied grout material; (3) the initial joint roughness determines the stress-dependent behaviors and general stiffness range of the jointed and grouted rocks, but the strain-dependent behaviors are dependent on the properties of the grout material; (4) increased grouted joint thickness results in larger contribution of the grout properties in the overall grouted rock mass.

Nonlinear response and avalanche behavior in metallic glasses

Science.gov (United States)

Riechers, B.; Samwer, K.

2017-08-01

The response to different stress amplitudes at temperatures below the glass transition temperature is analyzed by mechanical oscillatory excitation of Pd40Ni40P20 metallic glass samples in single cantilever bending geometry. While low amplitude oscillatory excitations are commonly used in mechanical spectroscopy to probe the relaxation spectrum, in this work the response to comparably high amplitudes is investigated. The strain response of the material is well below the critical yield stress even for highest stress amplitudes, implying the expectation of a linear relation between stress and strain according to Hooke's Law. However, a deviation from the linear behavior is evident, which is analyzed in terms of temperature dependence and influence of the applied stress amplitude by two different approaches of evaluation. The nonlinear approach is based on a nonlinear expansion of the stress-strain-relation, assuming an intrinsic nonlinear character of the shear or elastic modulus. The degree of nonlinearity is extracted by a period-by-period Fourier-analysis and connected to nonlinear coefficients, describing the intensity of nonlinearity at the fundamental and higher harmonic frequencies. The characteristic timescale to adapt to a significant change in stress amplitude in terms of a recovery timescale to a steady state value is connected to the structural relaxation time of the material, suggesting a connection between the observed nonlinearity and primary relaxation processes. The second approach of evaluation is termed the incremental analysis and relates the observed response behavior to avalanches, which occur due to the activation and correlation of local microstructural rearrangements. These rearrangements are connected with shear transformation zones and correspond to localized plastic events, which are superimposed on the linear response behavior of the material.

FEAST: a two-dimensional non-linear finite element code for calculating stresses

International Nuclear Information System (INIS)

Tayal, M.

1986-06-01

The computer code FEAST calculates stresses, strains, and displacements. The code is two-dimensional. That is, either plane or axisymmetric calculations can be done. The code models elastic, plastic, creep, and thermal strains and stresses. Cracking can also be simulated. The finite element method is used to solve equations describing the following fundamental laws of mechanics: equilibrium; compatibility; constitutive relations; yield criterion; and flow rule. FEAST combines several unique features that permit large time-steps in even severely non-linear situations. The features include a special formulation for permitting many finite elements to simultaneously cross the boundary from elastic to plastic behaviour; accomodation of large drops in yield-strength due to changes in local temperature and a three-step predictor-corrector method for plastic analyses. These features reduce computing costs. Comparisons against twenty analytical solutions and against experimental measurements show that predictions of FEAST are generally accurate to ± 5%

Stress-strain time-dependent behavior of A356.0 aluminum alloy subjected to cyclic thermal and mechanical loadings

Science.gov (United States)

Farrahi, G. H.; Ghodrati, M.; Azadi, M.; Rezvani Rad, M.

2014-08-01

This article presents the cyclic behavior of the A356.0 aluminum alloy under low-cycle fatigue (or isothermal) and thermo-mechanical fatigue loadings. Since the thermo-mechanical fatigue (TMF) test is time consuming and has high costs in comparison to low-cycle fatigue (LCF) tests, the purpose of this research is to use LCF test results to predict the TMF behavior of the material. A time-independent model, considering the combined nonlinear isotropic/kinematic hardening law, was used to predict the TMF behavior of the material. Material constants of this model were calibrated based on room-temperature and high-temperature low-cycle fatigue tests. The nonlinear isotropic/kinematic hardening law could accurately estimate the stress-strain hysteresis loop for the LCF condition; however, for the out-of-phase TMF, the condition could not predict properly the stress value due to the strain rate effect. Therefore, a two-layer visco-plastic model and also the Johnson-Cook law were applied to improve the estimation of the stress-strain hysteresis loop. Related finite element results based on the two-layer visco-plastic model demonstrated a good agreement with experimental TMF data of the A356.0 alloy.

Correction of the post -- necking true stress -- strain data using instrumented nanoindentation

Science.gov (United States)

Romero Fonseca, Ivan Dario

The study of large plastic deformations has been the focus of numerous studies particularly in the metal forming processes and fracture mechanics fields. A good understanding of the plastic flow properties of metallic alloys and the true stresses and true strains induced during plastic deformation is crucial to optimize the aforementioned processes, and to predict ductile failure in fracture mechanics analyzes. Knowledge of stresses and strains is extracted from the true stress-strain curve of the material from the uniaxial tensile test. In addition, stress triaxiality is manifested by the neck developed during the last stage of a tensile test performed on a ductile material. This necking phenomenon is the factor responsible for deviating from uniaxial state into a triaxial one, then, providing an inaccurate description of the material's behavior after the onset of necking. The research of this dissertation is aimed at the development of a correction method for the nonuniform plastic deformation (post-necking) portion of the true stress-strain curve. The correction proposed is based on the well-known relationship between hardness and flow (yield) stress, except that instrumented nanoindentation hardness is utilized rather than conventional macro or micro hardness. Three metals with different combinations of strain hardening behavior and crystal structure were subjected to quasi-static tensile tests: power-law strain hardening low carbon G10180 steel (BCC) and electrolytic tough pitch copper C11000 (FCC), and linear strain hardening austenitic stainless steel S30400 (FCC). Nanoindentation hardness values, measured on the broken tensile specimen, were converted into flow stress values by means of the constraint factor C from Tabor's, the representative plastic strainepsilonr and the post-test true plastic strains measured. Micro Vickers hardness testing was carried out on the sample as well. The constraint factors were 5.5, 4.5 and 4.5 and the representative plastic

Elasto-plastic stress/strain at notches, comparison of test and approximative computations

International Nuclear Information System (INIS)

Beste, A.; Seeger, T.

1979-01-01

The lifetime of cyclically loaded components is decisively determined by the value of the local load in the notch root. The determination of the elasto-plastic notch-stress and-strain is therefore an important element of recent methods of lifetime determination. These local loads are normally calculated with the help of approximation formulas. Yet there are no details about their accuracy. The basic construction of the approximation formulas is presented, along with some particulars. The use of approximations within the fully plastic range and for material laws which show a non-linear stress-strain (sigma-epsilon-)-behaviour from the beginning is explained. The use of approximation for cyclic loads is particularly discussed. Finally, the approximations are evaluated in terms of their exactness. The test results are compared with the results of the approximation calculations. (orig.) 891 RW/orig. 892 RKD [de

Stress and Support in Family Relationships after Hurricane Katrina

Science.gov (United States)

Reid, Megan; Reczek, Corinne

2011-01-01

In this article, the authors merge the study of support, strain, and ambivalence in family relationships with the study of stress to explore the ways family members provide support or contribute to strain in the disaster recovery process. The authors analyze interviews with 71 displaced Hurricane Katrina survivors, and identify three family…

Pace bowlers in cricket with history of lumbar stress fracture have increased risk of lower limb muscle strains, particularly calf strains.

Science.gov (United States)

Orchard, John; Farhart, Patrick; Kountouris, Alex; James, Trefor; Portus, Marc

2010-01-01

To assess whether a history of lumbar stress fracture in pace bowlers in cricket is a risk factor for lower limb muscle strains. This was a prospective cohort risk factor study, conducted using injury data from contracted first class pace bowlers in Australia during seasons 1998-1999 to 2008-2009 inclusive. There were 205 pace bowlers, 33 of whom suffered a lumbar stress fracture when playing first class cricket. Risk ratios ([RR] with 95% confidence intervals[CI]) were calculated to compare the seasonal incidence of various injuries between bowlers with a prior history of lumbar stress fracture and those with no history of lumbar stress fracture. Risk of calf strain was strongly associated with prior lumbar stress fracture injury history (RR = 4.1; 95% CI: 2.4-7.1). Risks of both hamstring strain (RR = 1.5; 95% CI: 1.03-2.1) and quadriceps strain (RR = 2.0; 95% CI: 1.1-3.5) were somewhat associated with history of lumbar stress fracture. Risk of groin strain was not associated with history of lumbar stress fracture (RR = 0.7; 95% CI: 0.4-1.1). Other injuries showed little association with prior lumbar stress fracture, although knee cartilage injuries were more likely in the non-stress fracture group. Bony hypertrophy associated with lumbar stress fracture healing may lead to subsequent lumbar nerve root impingement, making lower limb muscle strains more likely to occur. Confounders may be responsible for some of the findings. In particular, bowling speed is likely to be independently correlated with risk of lumbar stress fracture and risk of muscle strain. However, as the relationship between lumbar stress fracture history and calf strain was very strong, and that there is a strong theoretical basis for the connection, it is likely that this is a true association.

A general 3-D nonlinear magnetostrictive constitutive model for soft ferromagnetic materials

International Nuclear Information System (INIS)

Zhou Haomiao; Zhou Youhe; Zheng Xiaojing; Ye Qiang; Wei Jing

2009-01-01

In this paper, a new general nonlinear magnetostrictive constitutive model is proposed for soft ferromagnetic materials, and it can predict magnetostrictive strain and magnetization curves under various pre-stresses. From the viewpoint of magnetic domain, it is based on the important physical fact that a nonlinear part of the elastic strain produced by magnetic domain wall motion under a pre-stress is responsible for the change of the maximum magnetostrictive strain in accordance with the pre-stress. Then the reduction of magnetostrictive strain from the maximum is caused by the domain rotation. Meanwhile, the magnetization under various pre-stresses in this model is introduced by magnetostrictive effect under the same pre-stress. A simplified 3-D model is put forward by means of linearizing the nonlinear function, i.e. the nonlinear part of the elastic strain produced by domain wall motion, and by using the quartic of magnetization to describe domain rotation. Besides, for the convenience of engineering applications, two-dimensional (plate or film) and one-dimensional (rod) models are also given for isotropic materials and their application ranges are discussed too. In comparison with the experimental data of Kuruzar and Jiles, it is found that this model can predict magnetostrictive strain and magnetization curves under various pre-stresses. The numerical simulation further illustrates that the new model can effectively describe the effects of the pre-stress or residual stress on the magnetization and magnetostrictive strain curves. Additionally, this model can be degenerated to the existing magnetostrictive constitutive model for giant magnetostrictive materials (GMM), i.e. a special soft ferromagnetic material

[Job stress of nursing aides in Swiss nursing homes : Nonlinear canonical analysis].

Science.gov (United States)

Ziegler, A; Bernet, M; Metzenthin, P; Conca, A; Hahn, S

2016-08-01

Due to demographic changes, the demand for care in nursing homes for the elderly and infirmed is growing. At the same time nursing staff shortages are also increasing. Nursing aides are the primary care providers and comprise the largest staff group in Swiss nursing homes. They are exposed to various forms of job stress, which threaten job retention. The aim of this study was to discover which features of the work situation and which personal characteristics of the nursing aides were related to the workload. Data from nursing aides in Swiss nursing homes were investigated through a secondary analysis of a national quantitative cross-sectional study, using descriptive statistics and a nonlinear canonical correlation analysis. A total of 1054 nursing aides were included in the secondary analysis, 94.6 % of whom were women between the ages of 42 and 61 years. The job stress most frequently mentioned in the descriptive analysis, almost 60 % of the participants referred to it, was staff shortage. The nonlinear canonical correlation analysis revealed that many job strains are caused by social and organizational issues. In particular, a lack of support from supervisors was associated with staff not feeling appreciated. These job strains correlated with a high level of responsibility, the feeling of being unable to work independently and a feeling of being exploited. These strains were predominant in the nursing aides between 32 and 51 years old who had part time jobs but workloads of 80-90 %. Middle-aged nursing aides who worked to 80-90 % are particularly at risk to resign from the position prematurely. Measures need to be mainly implemented in the social and organizational areas. It can be assumed that a targeted individual support, recognition and promotion of nursing aides may decrease the level of job strain.

A New Theory of Non-Linear Thermo-Elastic Constitutive Equation of Isotropic Hyperelastic Materials

Science.gov (United States)

Li, Chen; Liao, Yufei

2018-03-01

Considering the influence of temperature and strain variables on materials. According to the relationship of conjugate stress-strain, a complete and irreducible non-linear constitutive equation of isotropic hyperelastic materials is derived and the constitutive equations of 16 types of isotropic hyperelastic materials are given we study the transformation methods and routes of 16 kinds of constitutive equations and the study proves that transformation of two forms of constitutive equation. As an example of application, the non-linear thermo-elastic constitutive equation of isotropic hyperelastic materials is combined with the natural vulcanized rubber experimental data in the existing literature base on MATLAB, The results show that the fitting accuracy is satisfactory.

Experimental Characterization of Stress- and Strain-Dependent Stiffness in Grouted Rock Masses

Directory of Open Access Journals (Sweden)

Ji-Won Kim

2018-03-01

Full Text Available Grouting of fractured rock mass prior to excavation results in grout-filled discontinuities that govern the deformation characteristics of a site. The influence of joint characteristics on the properties of grouted rocks is important in assessing the effects of grouting on jointed rock mass. However, grouting remains a predominantly empirical practice and the effects of grouting on rock joint behavior and material properties have yet to be accurately assessed. Granular materials, including jointed rocks, typically display nonlinear strain-dependent responses that can be characterized by the shear modulus degradation curve. In this study, the effects of grouting on the strain-dependent shear stiffness of jointed rock mass were investigated at the small-strain (below 10−5 and mid-strain (10−5 to 10−3 ranges using the quasi-static resonant column test and rock mass dynamic test devices. The effects of curing time, axial stress, initial joint roughness, and grouted joint thickness were examined. The results show that (1 grouting of rock joints leads to decreased stress sensitivity and increased small-strain shear stiffness for all tested samples; (2 the grouted rock samples display similar modulus degradation characteristics as the applied grout material; (3 the initial joint roughness determines the stress-dependent behaviors and general stiffness range of the jointed and grouted rocks, but the strain-dependent behaviors are dependent on the properties of the grout material; (4 increased grouted joint thickness results in larger contribution of the grout properties in the overall grouted rock mass.

The mechanical behaviour of NBR/FEF under compressive cyclic stress strain

Science.gov (United States)

Mahmoud, W. E.; El-Eraki, M. H. I.; El-Lawindy, A. M. Y.; Hassan, H. H.

2006-06-01

Acrylonitrile butadiene rubber compounds filled with different concentrations of fast extrusion furnace (FEF) carbon black were experimentally investigated. The stress-strain curves of the composites were studied, which suggest good filler-matrix adhesion. The large reinforcement effect of the filler followed the Guth model for non-spherical particles. The effect of FEF carbon black on the cyclic fatigue and hysteresis was also examined. The loading and unloading stress-strain relationships for any cycle were described by applying Ogden's model for rubber samples. The dissipation energy that indicates the vibration damping capacity for all samples was determined. A simple model was proposed, to investigate the relation between maximum stress and the number of cyclic fatigue.

The mechanical behaviour of NBR/FEF under compressive cyclic stress-strain

Energy Technology Data Exchange (ETDEWEB)

Mahmoud, W E [Faculty of Science, Physics Department, Suez Canal University, Ismailia (Egypt); El-Eraki, M H I [Faculty of Science, Physics Department, Suez Canal University, Ismailia (Egypt); El-Lawindy, A M Y [Faculty of Science, Physics Department, Suez Canal University, Ismailia (Egypt); Hassan, H H [Faculty of Science, Physics Department, Cairo University, Giza (Egypt)

2006-06-07

Acrylonitrile butadiene rubber compounds filled with different concentrations of fast extrusion furnace (FEF) carbon black were experimentally investigated. The stress-strain curves of the composites were studied, which suggest good filler-matrix adhesion. The large reinforcement effect of the filler followed the Guth model for non-spherical particles. The effect of FEF carbon black on the cyclic fatigue and hysteresis was also examined. The loading and unloading stress-strain relationships for any cycle were described by applying Ogden's model for rubber samples. The dissipation energy that indicates the vibration damping capacity for all samples was determined. A simple model was proposed, to investigate the relation between maximum stress and the number of cyclic fatigue.

The mechanical behaviour of NBR/FEF under compressive cyclic stress-strain

International Nuclear Information System (INIS)

Mahmoud, W E; El-Eraki, M H I; El-Lawindy, A M Y; Hassan, H H

2006-01-01

Acrylonitrile butadiene rubber compounds filled with different concentrations of fast extrusion furnace (FEF) carbon black were experimentally investigated. The stress-strain curves of the composites were studied, which suggest good filler-matrix adhesion. The large reinforcement effect of the filler followed the Guth model for non-spherical particles. The effect of FEF carbon black on the cyclic fatigue and hysteresis was also examined. The loading and unloading stress-strain relationships for any cycle were described by applying Ogden's model for rubber samples. The dissipation energy that indicates the vibration damping capacity for all samples was determined. A simple model was proposed, to investigate the relation between maximum stress and the number of cyclic fatigue

A new nonlinear parameter in the developed strain-to-applied strain of the soft tissues and its application in ultrasound elasticity imaging.

Science.gov (United States)

Xu, Jingping; Tripathy, Sakya; Rubin, Jonathan M; Stidham, Ryan W; Johnson, Laura A; Higgins, Peter D R; Kim, Kang

2012-03-01

Strain developed under quasi-static deformation has been mostly used in ultrasound elasticity imaging (UEI) to determine the stiffness change of tissues. However, the strain measure in UEI is often less sensitive to a subtle change of stiffness. This is particularly true for Crohn's disease where we have applied strain imaging to the differentiation of acutely inflamed bowel from chronically fibrotic bowel. In this study, a new nonlinear elastic parameter of the soft tissues is proposed to overcome this limit. The purpose of this study is to evaluate the newly proposed method and demonstrate its feasibility in the UEI. A nonlinear characteristic of soft tissues over a relatively large dynamic range of strain was investigated. A simplified tissue model based on a finite element (FE) analysis was integrated with a laboratory developed ultrasound radio-frequency (RF) signal synthesis program. Two-dimensional speckle tracking was applied to this model to simulate the nonlinear behavior of the strain developed in a target inclusion over the applied average strain to the surrounding tissues. A nonlinear empirical equation was formulated and optimized to best match the developed strain-to-applied strain relation obtained from the FE simulation. The proposed nonlinear equation was applied to in vivo measurements and nonlinear parameters were further empirically optimized. For an animal model, acute and chronic inflammatory bowel disease was induced in Lewis rats with trinitrobenzene sulfonic acid (TNBS)-ethanol treatments. After UEI, histopathology and direct mechanical measurements were performed on the excised tissues. The extracted nonlinear parameter from the developed strain-to-applied strain relation differentiated the three different tissue types with 1.96 ± 0.12 for normal, 1.50 ± 0.09 for the acutely inflamed and 1.03 ± 0.08 for the chronically fibrotic tissue. T-tests determined that the nonlinear parameters between normal, acutely inflamed and fibrotic tissue

Nonlinear FE analysis of reinforced concrete panels subjected to in-plane force

International Nuclear Information System (INIS)

Lee, H. P.; Lee, S. J.; Jun, Y. S.; Su, J. M.

2003-01-01

Reinforced concrete structures subjected to in-plane force exhibit strong nonlinear behaviour due to complex material properties, cracks, interactions between concrete and steel and shear transfer exists in crack surface. Especially if there is crack formations, nonlinear behaviour increases. Thus the prediction of nonlinear behaviour of reinforced concrete includes failure or crushing is very difficult task. Various constitutive equations for concrete stress-strain relationship to predict nonlinear behaviour of reinforced concrete have been proposed. But the study for reinforced concrete analysis model using plastic material model is still demanded. So the purpose of this research is to formulate standard 8-node shell element using plasticity material model for concrete and to analyze nonlinear behaviour of RC panel subjected to in-plane force

Model-based methodology to develop the isochronous stress-strain curves for modified 9Cr steels

International Nuclear Information System (INIS)

Kim, Woo Gon; Yin, Song Nan; Kim, Sung Ho; Lee, Chan Bock; Jung, Ik Hee

2008-01-01

Since high temperature materials are designed with a target life based on a specified amount of allowable strain and stress, their Isochronous Stress-Strain Curves (ISSC) are needed to avoid an excessive deformation during an intended service life. In this paper, a model-based methodology to develop the isochronous curves for a G91 steel is described. Creep strain-time curves were reviewed for typical high-temperature materials, and Garofalo's model which conforms well to the primary and secondary creep stages was proper for the G91 steel. Procedures to obtain an instantaneous elastic-plastic strain, ε i were given in detail. Also, to accurately determine the P 1 , P 2 and P 3 parameters in the Garofalo's model, a Nonlinear Least Square Fitting (NLSF) method was adopted and useful. The long-term creep curves for the G91 steel can be modeled by the Garofalo's model, and the long-term ISSCs can be developed using the modeled creep curves

Dynamic strain aging of zircaloy-4 PWR fuel cladding in biaxial stress state

International Nuclear Information System (INIS)

Park, Ki Seong; Lee, Byong Whi

1989-01-01

The expanding copper mandrel test performed at three strain rates (3.2x10E-5/s,2.0x10E-6/s and 1.2x10E-7/s) over 553-873 K temperature range by varying the heating rates (8-10deg C/s,1-2deg C/s and 0.5deg C/s) in air and in vacuum (5x10E-5 torr). The yield stress peak, the strain rate sensitivity minimum and the activation volume peaks could be explained in terms of the dynamic strain aging. The activation energy for dynamic strain aging obtained from the yield stress peak temperature and strain rate was 196 KJ/mol and this value was in good agreement with the activation energy for oxygen diffusion in α-zirconium and Zircaloy-2 (207-220KJ/mol). Therefore, oxygen atoms are responsible for the dynamic strain aging which appeared between 573K and 673K. The yield stress increase due to the oxidation was obtained by comparing the yield stress in air with that in vacuum and represented by the percentage increase of yield stress (σ y a -σ y v /σ y v ). The slower the strain rate, the greater the percentage increase occurs. In order to estimate the yield stress of PWR fuel cladding material under the service environment, the yield stress in water was obtained by comparing the oxidation rate in air that in water assuming the relationship between the oxygen pick-up amount and the yield stress increase. (Author)

Stress and strain measurements in solids

International Nuclear Information System (INIS)

Askegaard, V.

1978-01-01

A design basis is given for stress- and strain cells to be used in a solid either externally loaded or with a stressfree strain field (for example shrinkage). A stress- and a strain cell has been designed for use in granular materials. Calibration tests show either good or reasonably good correspondance with calculated values. (orig.) [de

Pace bowlers in cricket with history of lumbar stress fracture have increased risk of lower limb muscle strains, particularly calf strains

Directory of Open Access Journals (Sweden)

John Orchard

2010-09-01

Full Text Available John Orchard1, Patrick Farhart2, Alex Kountouris3, Trefor James3, Marc Portus31School of Public Health, University of Sydney, Australia; 2Punjab Kings XI team, Indian Premier League, India; 3Cricket Australia, Melbourne, AustraliaObjective: To assess whether a history of lumbar stress fracture in pace bowlers in cricket is a risk factor for lower limb muscle strains.Methods: This was a prospective cohort risk factor study, conducted using injury data from contracted first class pace bowlers in Australia during seasons 1998–1999 to 2008–2009 inclusive. There were 205 pace bowlers, 33 of whom suffered a lumbar stress fracture when playing first class cricket. Risk ratios ([RR] with 95% confidence intervals[CI] were calculated to compare the seasonal incidence of various injuries between bowlers with a prior history of lumbar stress fracture and those with no history of lumbar stress fracture.Results: Risk of calf strain was strongly associated with prior lumbar stress fracture injury history (RR = 4.1; 95% CI: 2.4–7.1. Risks of both hamstring strain (RR = 1.5; 95% CI: 1.03–2.1 and quadriceps strain (RR = 2.0; 95% CI: 1.1–3.5 were somewhat associated with history of lumbar stress fracture. Risk of groin strain was not associated with history of lumbar stress fracture (RR = 0.7; 95% CI: 0.4–1.1. Other injuries showed little association with prior lumbar stress fracture, although knee cartilage injuries were more likely in the non-stress fracture group.Conclusion: Bony hypertrophy associated with lumbar stress fracture healing may lead to subsequent lumbar nerve root impingement, making lower limb muscle strains more likely to occur. Confounders may be responsible for some of the findings. In particular, bowling speed is likely to be independently correlated with risk of lumbar stress fracture and risk of muscle strain. However, as the relationship between lumbar stress fracture history and calf strain was very strong, and that there is a

Methods for predicting isochronous stress-strain curves

International Nuclear Information System (INIS)

Kiyoshige, Masanori; Shimizu, Shigeki; Satoh, Keisuke.

1976-01-01

Isochronous stress-strain curves show the relation between stress and total strain at a certain temperature with time as a parameter, and they are drawn up from the creep test results at various stress levels at a definite temperature. The concept regarding the isochronous stress-strain curves was proposed by McVetty in 1930s, and has been used for the design of aero-engines. Recently the high temperature characteristics of materials are shown as the isochronous stress-strain curves in the design guide for the nuclear energy equipments and structures used in high temperature creep region. It is prescribed that these curves are used as the criteria for determining design stress intensity or the data for analyzing the superposed effects of creep and fatigue. In case of the isochronous stress-strain curves used for the design of nuclear energy equipments with very long service life, it is impractical to determine the curves directly from the results of long time creep test, accordingly the method of predicting long time stress-strain curves from short time creep test results must be established. The method proposed by the authors, for which the creep constitution equations taking the first and second creep stages into account are used, and the method using Larson-Miller parameter were studied, and it was found that both methods were reliable for the prediction. (Kako, I.)

The nonlinear unloading behavior of a typical Ni-based superalloy during hot deformation. A new elasto-viscoplastic constitutive model

Energy Technology Data Exchange (ETDEWEB)

Chen, Ming-Song; Li, Kuo-Kuo [Central South University, School of Mechanical and Electrical Engineering, Changsha (China); State Key Laboratory of High Performance Complex Manufacturing, Changsha (China); Lin, Y.C. [Central South University, School of Mechanical and Electrical Engineering, Changsha (China); State Key Laboratory of High Performance Complex Manufacturing, Changsha (China); Central South University, Light Alloy Research Institute, Changsha (China); Chen, Jian [Changsha University of Science and Technology, School of Energy and Power Engineering, Key Laboratory of Efficient and Clean Energy Utilization, Changsha (China)

2016-09-15

The nonlinear unloading behavior of a typical Ni-based superalloy is investigated by hot compressive experiments with intermediate unloading-reloading cycles. The experimental results show that there are at least four types of unloading curves. However, it is found that there is no essential difference among four types of unloading curves. The variation curves of instantaneous Young's modulus with stress for all types of unloading curves include four segments, i.e., three linear elastic segments (segments I, II, and III) and one subsequent nonlinear elastic segment (segment IV). The instantaneous Young's modulus of segments I and III is approximately equal to that of reloading process, while smaller than that of segment II. In the nonlinear elastic segment, the instantaneous Young's modulus linearly decreases with the decrease in stress. In addition, the relationship between stress and strain rate can be accurately expressed by the hyperbolic sine function. This study includes two parts. In the present part, the characters of unloading curves are discussed in detail, and a new elasto-viscoplastic constitutive model is proposed to describe the nonlinear unloading behavior based on the experimental findings. While in the latter part (Chen et al. in Appl Phys A. doi:10.1007/s00339-016-0385-0, 2016), the effects of deformation temperature, strain rate, and pre-strain on the parameters of this new constitutive model are analyzed, and a unified elasto-viscoplastic constitutive model is proposed to predict the unloading behavior at arbitrary deformation temperature, strain rate, and pre-strain. (orig.)

The nonlinear unloading behavior of a typical Ni-based superalloy during hot deformation. A new elasto-viscoplastic constitutive model

International Nuclear Information System (INIS)

Chen, Ming-Song; Li, Kuo-Kuo; Lin, Y.C.; Chen, Jian

2016-01-01

The nonlinear unloading behavior of a typical Ni-based superalloy is investigated by hot compressive experiments with intermediate unloading-reloading cycles. The experimental results show that there are at least four types of unloading curves. However, it is found that there is no essential difference among four types of unloading curves. The variation curves of instantaneous Young's modulus with stress for all types of unloading curves include four segments, i.e., three linear elastic segments (segments I, II, and III) and one subsequent nonlinear elastic segment (segment IV). The instantaneous Young's modulus of segments I and III is approximately equal to that of reloading process, while smaller than that of segment II. In the nonlinear elastic segment, the instantaneous Young's modulus linearly decreases with the decrease in stress. In addition, the relationship between stress and strain rate can be accurately expressed by the hyperbolic sine function. This study includes two parts. In the present part, the characters of unloading curves are discussed in detail, and a new elasto-viscoplastic constitutive model is proposed to describe the nonlinear unloading behavior based on the experimental findings. While in the latter part (Chen et al. in Appl Phys A. doi:10.1007/s00339-016-0385-0, 2016), the effects of deformation temperature, strain rate, and pre-strain on the parameters of this new constitutive model are analyzed, and a unified elasto-viscoplastic constitutive model is proposed to predict the unloading behavior at arbitrary deformation temperature, strain rate, and pre-strain. (orig.)

Stress analysis of liners for prestressed concrete reactor pressure vessels with regard to non-linear behaviour of liner material and of anchor-characteristics

International Nuclear Information System (INIS)

Oberpichler, R.; Schnellenbach, G.

1975-01-01

The thin liner attached by anchors like a membrane to the interior wall of a prestressed concrete reactor pressure vessel (PCRV) has to provide the leak-tightness of the vessel. Furthermore the liner may serve as internal shuttering for placing of concrete as well as a support for the cooling system. The two-dimensional behaviour of the liner is investigated with regard to non-linear anchor-characteristics and non-linear material behaviour of the liner. The analysis is based on a plane stress model under the assumption of a membrane state of the liner. Calculations are performed by the dynamic relaxation method. With the aid of available non-linear stress-strain diagrams, describing the post-buckling behaviour, individual panels are considered as buckled ones. The adjacent unbuckled panels are calculated on other non-linear diagrams. Strains and stresses in the liner and additional shear loads in the anchors can be calculated with arbitrary sizing and spacing of the anchors. With respect to the parameters they are easily controlled. Since actual loads on the liner are defined by the PCRV-behaviour, an economical and safe design is possible. Finally an extreme case is calculated to assess the maximum value of the shear-forces assuming zero post-buckling capacity for the buckled panel. (Auth.)

The Cyclic Stress-Strain Curve of Polycrystals

DEFF Research Database (Denmark)

Pedersen, Ole Bøcker; Rasmussen, K. V.; Winter, A. T.

1982-01-01

The internal stresses implied by the Sachs model are estimated for individual PSBs at low plastic strain amplitudes and for homogeneously sheared grains at higher plastic strain amplitudes. The analysis shows that the Sachs model can account semi-quantitatively for experimentally measured cyclic...... stress-strain curves for copper. A similar approximative analysis of the Taylor model cannot account for the data. An interesting feature of the Sachs model is that, although it is assumed that the flow condition is entirely controlled by the PSBs. the predicted cyclic stress-strain curve displays...

The development and validation of a numerical integration method for non-linear viscoelastic modeling

Science.gov (United States)

Ramo, Nicole L.; Puttlitz, Christian M.

2018-01-01

Compelling evidence that many biological soft tissues display both strain- and time-dependent behavior has led to the development of fully non-linear viscoelastic modeling techniques to represent the tissue’s mechanical response under dynamic conditions. Since the current stress state of a viscoelastic material is dependent on all previous loading events, numerical analyses are complicated by the requirement of computing and storing the stress at each step throughout the load history. This requirement quickly becomes computationally expensive, and in some cases intractable, for finite element models. Therefore, we have developed a strain-dependent numerical integration approach for capturing non-linear viscoelasticity that enables calculation of the current stress from a strain-dependent history state variable stored from the preceding time step only, which improves both fitting efficiency and computational tractability. This methodology was validated based on its ability to recover non-linear viscoelastic coefficients from simulated stress-relaxation (six strain levels) and dynamic cyclic (three frequencies) experimental stress-strain data. The model successfully fit each data set with average errors in recovered coefficients of 0.3% for stress-relaxation fits and 0.1% for cyclic. The results support the use of the presented methodology to develop linear or non-linear viscoelastic models from stress-relaxation or cyclic experimental data of biological soft tissues. PMID:29293558

Nonlinear fiber-optic strain sensor based on four-wave mixing in microstructured optical fiber

DEFF Research Database (Denmark)

Gu, Bobo; Yuan, Scott Wu; Frosz, Michael H.

2012-01-01

We demonstrate a nonlinear fiber-optic strain sensor, which uses the shifts of four-wave mixing Stokes and anti-Stokes peaks caused by the strain-induced changes in the structure and refractive index of a microstructured optical fiber. The sensor thus uses the inherent nonlinearity of the fiber a...

Stress strain flow curves for Cu-OFP

International Nuclear Information System (INIS)

Sandstroem, Rolf; Hallgren, Josefin

2009-04-01

Stress strain curves of oxygen free copper alloyed with phosphorus Cu-OFP have been determined in compression and tension. The compression tests were performed at room temperature for strain rates between 10 -5 and 10 -3 1/s. The tests in tension covered the temperature range 20 to 175 deg C for strain rates between 10 -7 and 5x10 -3 1/s. The results in compression and tension were close for similar strain rates. A model for stress strain curves has been formulated using basic dislocation mechanisms. The model has been set up in such a way that fitting of parameters to the curves is avoided. By using a fundamental creep model as a basis a direct relation to creep data has been established. The maximum engineering flow stress in tension is related to the creep stress giving the same strain rate. The model reproduces the measured flow curves as function of temperature and strain rate in the investigated interval. The model is suitable to use in finite-element computations of structures in Cu-OFP

Thermal conductance of suspended nanoribbons: interplay between strain and interatomic potential nonlinearity

Science.gov (United States)

Barreto, Roberto; Florencia Carusela, M.; Monastra, Alejandro G.

2017-10-01

We investigate the role that nonlinearity in the interatomic potential has on the thermal conductance of a suspended nanoribbon when it is subjected to a longitudinal strain. To focus on the first cubic and quartic nonlinear terms of a general potential, we propose an atomic system based on an α-β Fermi-Pasta-Ulam nearest neighbor interaction. We perform classical molecular dynamics simulations to investigate the contribution of longitudinal, transversal and flexural modes to the thermal conductance as a function of the α-β parameters and the applied strain. We compare the cases where atoms are allowed to vibrate only in plane (2D) with the case of vibrations in and out of plane (3D). We find that the dependence of conductance on α and β relies on a crossover phenomenon between linear/nonlinear delocalized/localized flexural and transversal modes, driven by an on/off switch of the strain.

Evaluation of the clamping force in high tension bolt by using the ultrasonic nonlinearity

International Nuclear Information System (INIS)

Jang, Kyung Young; Cheon, Hae Wha; Ha, Hob; Park, Man Sick; Kim, No You

2005-01-01

High tension bolts have been used widely for the clamping of many kinds of large structure. Therefore, its estimation has been regarded as main issue in the maintenance of high tension bolts. This paper proposes a novel method using the ultrasonic nonlinearity, which is based on the dependency of sound speed on the stress. For this we introduce nonlinear elastic constants in the stress-strain relationship, and derive the sound speed as a linear function of stress. In order to verify the usefulness of the proposed method, two kinds of experiments are carried out: The first one is to measure the sound speed when the bolt is stressed by the tension tester. The result showed good agreement with the expected linear relationship between the sound speed and the axial stress. The second one is to measure the sound speed when the bolt is stressed by the torque wrench. The results showed that the sound speed was decreased when the torque was increased. From these results we can say that the proposed method is enough useful to evaluate the clamping force in the high tension bolt.

Strain rate effects in stress corrosion cracking

Energy Technology Data Exchange (ETDEWEB)

Parkins, R.N. (Newcastle upon Tyne Univ. (UK). Dept. of Metallurgy and Engineering Materials)

1990-03-01

Slow strain rate testing (SSRT) was initially developed as a rapid, ad hoc laboratory method for assessing the propensity for metals an environments to promote stress corrosion cracking. It is now clear, however, that there are good theoretical reasons why strain rate, as opposed to stress per se, will often be the controlling parameter in determining whether or not cracks are nucleated and, if so, are propagated. The synergistic effects of the time dependence of corrosion-related reactions and microplastic strain provide the basis for mechanistic understanding of stress corrosion cracking in high-pressure pipelines and other structures. However, while this may be readily comprehended in the context of laboratory slow strain tests, its extension to service situations may be less apparent. Laboratory work involving realistic stressing conditions, including low-frequency cyclic loading, shows that strain or creep rates give good correlation with thresholds for cracking and with crack growth kinetics.

Micromechanical modeling of stress-induced strain in polycrystalline Ni–Mn–Ga by directional solidification

International Nuclear Information System (INIS)

Zhu, Yuping; Shi, Tao; Teng, Yao

2015-01-01

Highlights: • A micromechanical model of directional solidification Ni–Mn–Ga is developed. • The stress–strain curves in different directions are tested. • The martensite Young’s moduli in different directions are predicted. • The macro reorientation strains in different directions are investigated. - Abstract: Polycrystalline ferromagnetic shape memory alloy Ni–Mn–Ga produced by directional solidification possess unique properties. Its compressive stress–strain behaviors in loading–unloading cycle show nonlinear and anisotropic. Based on the self-consistent theory and thermodynamics principle, a micromechanical constitutive model of polycrystalline Ni–Mn–Ga by directional solidification is developed considering the generating mechanism of the macroscopic strain and anisotropy. Then, the stress induced strains at different angles to solidification direction are calculated, and the results agree well with the experimental data. The predictive curves of martensite Young’s modulus and macro reorientation strain in different directions are investigated. It may provide theoretical guidance for the design and use of ferromagnetic shape memory alloy

Nonlinear crack mechanics

International Nuclear Information System (INIS)

Khoroshun, L.P.

1995-01-01

The characteristic features of the deformation and failure of actual materials in the vicinity of a crack tip are due to their physical nonlinearity in the stress-concentration zone, which is a result of plasticity, microfailure, or a nonlinear dependence of the interatomic forces on the distance. Therefore, adequate models of the failure mechanics must be nonlinear, in principle, although linear failure mechanics is applicable if the zone of nonlinear deformation is small in comparison with the crack length. Models of crack mechanics are based on analytical solutions of the problem of the stress-strain state in the vicinity of the crack. On account of the complexity of the problem, nonlinear models are bason on approximate schematic solutions. In the Leonov-Panasyuk-Dugdale nonlinear model, one of the best known, the actual two-dimensional plastic zone (the nonlinearity zone) is replaced by a narrow one-dimensional zone, which is then modeled by extending the crack with a specified normal load equal to the yield point. The condition of finite stress is applied here, and hence the length of the plastic zone is determined. As a result of this approximation, the displacement in the plastic zone at the abscissa is nonzero

Probabilistic analysis of structures involving random stress-strain behavior

Science.gov (United States)

Millwater, H. R.; Thacker, B. H.; Harren, S. V.

1991-01-01

The present methodology for analysis of structures with random stress strain behavior characterizes the uniaxial stress-strain curve in terms of (1) elastic modulus, (2) engineering stress at initial yield, (3) initial plastic-hardening slope, (4) engineering stress at point of ultimate load, and (5) engineering strain at point of ultimate load. The methodology is incorporated into the Numerical Evaluation of Stochastic Structures Under Stress code for probabilistic structural analysis. The illustrative problem of a thick cylinder under internal pressure, where both the internal pressure and the stress-strain curve are random, is addressed by means of the code. The response value is the cumulative distribution function of the equivalent plastic strain at the inner radius.

Cyclic stress at mHz frequencies aligns fibroblasts in direction of zero strain.

Directory of Open Access Journals (Sweden)

Uta Faust

Full Text Available Recognition of external mechanical signals is vital for mammalian cells. Cyclic stretch, e.g. around blood vessels, is one such signal that induces cell reorientation from parallel to almost perpendicular to the direction of stretch. Here, we present quantitative analyses of both, cell and cytoskeletal reorientation of umbilical cord fibroblasts. Cyclic strain of preset amplitudes was applied at mHz frequencies. Elastomeric chambers were specifically designed and characterized to distinguish between zero strain and minimal stress directions and to allow accurate theoretical modeling. Reorientation was only induced when the applied stretch exceeded a specific amplitude, suggesting a non-linear response. However, on very soft substrates no mechanoresponse occurs even for high strain. For all stretch amplitudes, the angular distributions of reoriented cells are in very good agreement with a theory modeling stretched cells as active force dipoles. Cyclic stretch increases the number of stress fibers and the coupling to adhesions. We show that changes in cell shape follow cytoskeletal reorientation with a significant temporal delay. Our data identify the importance of environmental stiffness for cell reorientation, here in direction of zero strain. These in vitro experiments on cultured cells argue for the necessity of rather stiff environmental conditions to induce cellular reorientation in mammalian tissues.

Novel Approach for Prediction of Localized Necking in Case of Nonlinear Strain Paths

Science.gov (United States)

Drotleff, K.; Liewald, M.

2017-09-01

Rising customer expectations regarding design complexity and weight reduction of sheet metal components alongside with further reduced time to market implicate increased demand for process validation using numerical forming simulation. Formability prediction though often is still based on the forming limit diagram first presented in the 1960s. Despite many drawbacks in case of nonlinear strain paths and major advances in research in the recent years, the forming limit curve (FLC) is still one of the most commonly used criteria for assessing formability of sheet metal materials. Especially when forming complex part geometries nonlinear strain paths may occur, which cannot be predicted using the conventional FLC-Concept. In this paper a novel approach for calculation of FLCs for nonlinear strain paths is presented. Combining an interesting approach for prediction of FLC using tensile test data and IFU-FLC-Criterion a model for prediction of localized necking for nonlinear strain paths can be derived. Presented model is purely based on experimental tensile test data making it easy to calibrate for any given material. Resulting prediction of localized necking is validated using an experimental deep drawing specimen made of AA6014 material having a sheet thickness of 1.04 mm. The results are compared to IFU-FLC-Criterion based on data of pre-stretched Nakajima specimen.

Context and strain-dependent behavioral response to stress

Directory of Open Access Journals (Sweden)

Baum Amber E

2008-06-01

Full Text Available Abstract Background This study posed the question whether strain differences in stress-reactivity lead to differential behavioral responses in two different tests of anxiety. Strain differences in anxiety-measures are known, but strain differences in the behavioral responses to acute prior stress are not well characterized. Methods We studied male Fisher 344 (F344 and Wistar Kyoto (WKY rats basally and immediately after one hour restraint stress. To distinguish between the effects of novelty and prior stress, we also investigated behavior after repeated exposure to the test chamber. Two behavioral tests were explored; the elevated plus maze (EPM and the open field (OFT, both of which are thought to measure activity, exploration and anxiety-like behaviors. Additionally, rearing, a voluntary behavior, and grooming, a relatively automatic, stress-responsive stereotyped behavior were measured in both tests. Results Prior exposure to the test environment increased anxiety-related measures regardless of prior stress, reflecting context-dependent learning process in both tests and strains. Activity decreased in response to repeated testing in both tests and both strains, but prior stress decreased activity only in the OFT which was reversed by repeated testing. Prior stress decreased anxiety-related measures in the EPM, only in F344s, while in the OFT, stress led to increased freezing mainly in WKYs. Conclusion Data suggest that differences in stressfulness of these tests predict the behavior of the two strains of animals according to their stress-reactivity and coping style, but that repeated testing can overcome some of these differences.

Strain modulations as a mechanism to reduce stress relaxation in laryngeal tissues.

Science.gov (United States)

Hunter, Eric J; Siegmund, Thomas; Chan, Roger W

2014-01-01

Vocal fold tissues in animal and human species undergo deformation processes at several types of loading rates: a slow strain involved in vocal fold posturing (on the order of 1 Hz or so), cyclic and faster posturing often found in speech tasks or vocal embellishment (1-10 Hz), and shear strain associated with vocal fold vibration during phonation (100 Hz and higher). Relevant to these deformation patterns are the viscous properties of laryngeal tissues, which exhibit non-linear stress relaxation and recovery. In the current study, a large strain time-dependent constitutive model of human vocal fold tissue is used to investigate effects of phonatory posturing cyclic strain in the range of 1 Hz to 10 Hz. Tissue data for two subjects are considered and used to contrast the potential effects of age. Results suggest that modulation frequency and extent (amplitude), as well as the amount of vocal fold overall strain, all affect the change in stress relaxation with modulation added. Generally, the vocal fold cover reduces the rate of relaxation while the opposite is true for the vocal ligament. Further, higher modulation frequencies appear to reduce the rate of relaxation, primarily affecting the ligament. The potential benefits of cyclic strain, often found in vibrato (around 5 Hz modulation) and intonational inflection, are discussed in terms of vocal effort and vocal pitch maintenance. Additionally, elderly tissue appears to not exhibit these benefits to modulation. The exacerbating effect such modulations may have on certain voice disorders, such as muscle tension dysphonia, are explored.

Strain modulations as a mechanism to reduce stress relaxation in laryngeal tissues.

Directory of Open Access Journals (Sweden)

Eric J Hunter

Full Text Available Vocal fold tissues in animal and human species undergo deformation processes at several types of loading rates: a slow strain involved in vocal fold posturing (on the order of 1 Hz or so, cyclic and faster posturing often found in speech tasks or vocal embellishment (1-10 Hz, and shear strain associated with vocal fold vibration during phonation (100 Hz and higher. Relevant to these deformation patterns are the viscous properties of laryngeal tissues, which exhibit non-linear stress relaxation and recovery. In the current study, a large strain time-dependent constitutive model of human vocal fold tissue is used to investigate effects of phonatory posturing cyclic strain in the range of 1 Hz to 10 Hz. Tissue data for two subjects are considered and used to contrast the potential effects of age. Results suggest that modulation frequency and extent (amplitude, as well as the amount of vocal fold overall strain, all affect the change in stress relaxation with modulation added. Generally, the vocal fold cover reduces the rate of relaxation while the opposite is true for the vocal ligament. Further, higher modulation frequencies appear to reduce the rate of relaxation, primarily affecting the ligament. The potential benefits of cyclic strain, often found in vibrato (around 5 Hz modulation and intonational inflection, are discussed in terms of vocal effort and vocal pitch maintenance. Additionally, elderly tissue appears to not exhibit these benefits to modulation. The exacerbating effect such modulations may have on certain voice disorders, such as muscle tension dysphonia, are explored.

An ocean of stress? The relationship between psychosocial workload and mental strain among engine officers in the Swedish merchant fleet.

Science.gov (United States)

Rydstedt, Leif W; Lundh, Monica

2010-01-01

The first purpose of this study was to compare the psychosocial working conditions and mental health of our sample of maritime engine officers with a sample of British shore-based professional engineers. The second purpose was to analyse the relationship between the psychosocial working conditions onboard and mental strain for the Swedish maritime engine officers. There were a total of 731 engine officers in the Swedish merchant fleet, almost all males with higher education. The British comparison sample consisted of 312 professional shore-based engineers. A questionnaire was distributed to the Swedish engine officers with a modified version of the JCQ for the DC-S model, the Role conflict and Ambiguity scale, and two items on family-work inter-role conflicts (WFI/FWI), as workload indicators. The General Health Questionnaire (GHQ12) and Perceived Stress Scale (PSS10) were used as strain indicators. There were no significant differences in perceived job stain or in WFI/FWI between the Swedish engine officers and the British professional engineers in perceived job strain. While the British shore-based engineers reported significantly higher role ambiguity the Swedish engine officers perceived a significantly higher degree of role conflict and higher perceived stress. Hierarchic linear regression analysis showed that the Role Stress was strongly related to perceived stress (R(2) = 0.319) as well as to mental health (R(2) = 0.222). When introduced in the second step the DC-S model was significantly related to the outcome measures, as was WFI/FWI when finally introduced. The main source of the high degree of perceived stress among the engine officers does not seem to be the job content but may rather be understood from an interactional perspective, where conflicting requirements are directed towards the individual officer. It can be assumed that the fast technological and organizational changes and the increased pressure for economic profitability that characterize the

The relationship between the applied torque and stresses in post-tension structures

International Nuclear Information System (INIS)

Liew, F.K.; Hamdan, S.; Osman, M.S.

2008-01-01

This paper presents the nondestructive testing (NDT) method to determine the resultant stresses in mild steel bar usually employed in structures. The technique utilized ultrasonic pulse-echo that determined the wave velocity change due to torque applied between bolt and nut. Mild steel bar with nominal diameter of 19 and 25mm were used. The specimen was loaded by means of a torque wrench that gave the required amount of moment (∼300Nm). This was carefully achieved manually. In order to measure the strain, strain gauges were employed. The direct strain gauge method gives the strain values. This strain is used to calculate the stress due to the applied load. The experiment had been carried out in a control environment with constant temperature. The relationship between torque-velocity, torque-strain and stress-strain is obtained and compared. The test results indicate that ultrasonic wave velocity decrease with the applied torque. This is due to degradation or loss of strength of the material. The potential of this NDT method to obtain structure quality and strength determination is discussed. (author)

The relationship between the applied torque and stresses in post-tension structures

Energy Technology Data Exchange (ETDEWEB)

Liew, F.K.; Hamdan, S.; Osman, M.S. [Univ. Malaysia Sarawak, Faculty of Engineering, Kota Samarahan, Sarawak (Malaysia)

2008-09-15

This paper presents the nondestructive testing (NDT) method to determine the resultant stresses in mild steel bar usually employed in structures. The technique utilized ultrasonic pulse-echo that determined the wave velocity change due to torque applied between bolt and nut. Mild steel bar with nominal diameter of 19 and 25mm were used. The specimen was loaded by means of a torque wrench that gave the required amount of moment (∼300Nm). This was carefully achieved manually. In order to measure the strain, strain gauges were employed. The direct strain gauge method gives the strain values. This strain is used to calculate the stress due to the applied load. The experiment had been carried out in a control environment with constant temperature. The relationship between torque-velocity, torque-strain and stress-strain is obtained and compared. The test results indicate that ultrasonic wave velocity decrease with the applied torque. This is due to degradation or loss of strength of the material. The potential of this NDT method to obtain structure quality and strength determination is discussed. (author)

Geometrical nonlinear deformation model and its experimental study on bimorph giant magnetostrictive thin film

Institute of Scientific and Technical Information of China (English)

Wei LIU; Zhenyuan JIA; Fuji WANG; Yongshun ZHANG; Dongming GUO

2008-01-01

The geometrical nonlinearity of a giant magne-tostrictive thin film (GMF) can be clearly detected under the magnetostriction effect. Thus, using geometrical linear elastic theory to describe the strain, stress, and constitutive relationship of GMF is inaccurate. According to nonlinear elastic theory, a nonlinear deformation model of the bimorph GMF is established based on assumptions that the magnetostriction effect is equivalent to the effect of body force loaded on the GMF. With Taylor series method, the numerical solution is deduced. Experiments on TbDyFe/Polyimide (PI)/SmFe and TbDyFe/Cu/SmFe are then conducted to verify the proposed model, respectively. Results indicate that the nonlinear deflection curve model is in good conformity with the experimental data.

Stress-strain properties of railway steel at strain rates of upto 105 per second

International Nuclear Information System (INIS)

Hashmi, M.S.J.; Islam, M.N.

1985-01-01

This paper presents the stress-strain characteristics of railway steel at strain rates of up to 10 5 /s at room temperature determined by a new technique. In determining the results, account has been taken of the strain-rate variation, the total strain and the strain rate history. The effect of friction, material inertia and temperature rise is also assessed and an empirical constitutive equation describing the strain-rate and strain sensitive flow stress for this type of steel is proposed. (orig.)

Feasibility of Residual Stress Nondestructive Estimation Using the Nonlinear Property of Critical Refraction Longitudinal Wave

Directory of Open Access Journals (Sweden)

Yu-Hua Zhang

2017-01-01

Full Text Available Residual stress has significant influence on the performance of mechanical components, and the nondestructive estimation of residual stress is always a difficult problem. This study applies the relative nonlinear coefficient of critical refraction longitudinal (LCR wave to nondestructively characterize the stress state of materials; the feasibility of residual stress estimation using the nonlinear property of LCR wave is verified. The nonlinear ultrasonic measurements based on LCR wave are conducted on components with known stress state to calculate the relative nonlinear coefficient. Experimental results indicate that the relative nonlinear coefficient monotonically increases with prestress and the increment of relative nonlinear coefficient is about 80%, while the wave velocity only decreases about 0.2%. The sensitivity of the relative nonlinear coefficient for stress is much higher than wave velocity. Furthermore, the dependence between the relative nonlinear coefficient and deformation state of components is found. The stress detection resolution based on the nonlinear property of LCR wave is 10 MPa, which has higher resolution than wave velocity. These results demonstrate that the nonlinear property of LCR wave is more suitable for stress characterization than wave velocity, and this quantitative information could be used for residual stress estimation.

The Changing Nonlinear Relationship between Income and Terrorism

Science.gov (United States)

Enders, Walter; Hoover, Gary A.

2014-01-01

This article reinvestigates the relationship between real per capita gross domestic product (GDP) and terrorism. We devise a terrorism Lorenz curve to show that domestic and transnational terrorist attacks are each more concentrated in middle-income countries, thereby suggesting a nonlinear income–terrorism relationship. Moreover, this point of concentration shifted to lower income countries after the rising influence of the religious fundamentalist and nationalist/separatist terrorists in the early 1990s. For transnational terrorist attacks, this shift characterized not only the attack venue but also the perpetrators’ nationality. The article then uses nonlinear smooth transition regressions to establish the relationship between real per capita GDP and terrorism for eight alternative terrorism samples, accounting for venue, perpetrators’ nationality, terrorism type, and the period. Our nonlinear estimates are shown to be favored over estimates using linear or quadratic income determinants of terrorism. These nonlinear estimates are robust to additional controls. PMID:28579636

A strain-hardening bi-power law for the nonlinear behaviour of biological soft tissues.

Science.gov (United States)

Nicolle, S; Vezin, P; Palierne, J-F

2010-03-22

Biological soft tissues exhibit a strongly nonlinear viscoelastic behaviour. Among parenchymous tissues, kidney and liver remain less studied than brain, and a first goal of this study is to report additional material properties of kidney and liver tissues in oscillatory shear and constant shear rate tests. Results show that the liver tissue is more compliant but more strain hardening than kidney. A wealth of multi-parameter mathematical models has been proposed for describing the mechanical behaviour of soft tissues. A second purpose of this work is to develop a new constitutive law capable of predicting our experimental data in the both linear and nonlinear viscoelastic regime with as few parameters as possible. We propose a nonlinear strain-hardening fractional derivative model in which six parameters allow fitting the viscoelastic behaviour of kidney and liver tissues for strains ranging from 0.01 to 1 and strain rates from 0.0151 s(-1) to 0.7s(-1). Copyright (c) 2009 Elsevier Ltd. All rights reserved.

In situ stress determination by the overcoring of large surface strain gauge rosettes on the walls of a raise-bored shaft at the Underground Research Laboratory

International Nuclear Information System (INIS)

Chandler, N.A.

1991-08-01

AECL Research is conducting a series of experiments to examine the influence of scale on measured in situ stresses in granite rock. The ventilation raise rosette overcoring experiment is one such test. This experiment, modelled on a previous test conducted in Australia, consisted of overcoring four 120-mm strain gauge rosettes glued to the surface of a 1.8-m-diameter bored raise. The in situ stresses were calculated from the measured strains using the equations for stresses around a cylindrical excavation in an elastic material. The possibility of excavation disturbance around the ventilation raise was investigated using overcore stress measurements, elastic modulus tests on retrieved core, and visual inspection of thin sections obtained from removed core. The effect of a stress-dependent elastic modulus (referred to as non-linear elastic behaviour) is also addressed. Results from the ventilation raise rosette overcoring experiment suggest that rosette overcoring in a bored raise is an acceptable stress-measurement method. The effects of scale and excavation damage on the stress measurements were not considered to be significant; however, if the elastic modulus of the rock is strongly stress-dependent, non-linear elastic behaviour may have a small effect on the measured stresses

A model of nonlinear strain and damage accumulation in polymer composites

Directory of Open Access Journals (Sweden)

A. N. Ruslantsev

2014-01-01

Full Text Available This paper presents a model to predict a nonlinear strain of the carbon laminate; the model is based on the relations between the theory of laminated plates and the non-linear approximation of deformation curve of unidirectional layer at the shear in the layer plane. The explicit expressions of stiffness and compliance matrices were obtained via multiplying the matrices that correspond to the elastic characteristics by the matrices, considering the non-linear properties of the laminate. The paper suggests an approximation option for the non-linear properties of the layer at the shear using an exponential function. Some considerations on damage accumulation in carbon laminates were made.

Resiliency to social defeat stress relates to the inter-strain social interaction and is influenced by season variation.

Science.gov (United States)

Han, Qiuqin; Yang, Liu; Liu, Yan; Lv, Ning; Yu, Jin; Wu, Gencheng; Zhang, Yuqiu

2014-02-21

Exposure to social defeat (SD) stress exerts social avoidance and depressive disorders. Little is known about the relationship between resiliency to stressors and the inter-strain social interaction (SI) level. We hypothesized that SD resiliency is correlated with a high SI between the same strain. C57BL/6J mice experienced a 10-day period of SD stress by repeated CD-1 mice offensive. The susceptible mice exhibited significant social-avoidance behaviors with less time in interaction-zone (IZ) and lower social interaction ratio (SIR) toward the Target (CD-1 mice), while resilient ones exhibited similar social interaction to control mice. When the Target was C57BL/6J mouse, either susceptible or resilient mice spent more time in IZ and the inter-strain SI in the resilient group was significantly higher than the susceptible. Correlation analysis revealed a significantly non-zero slope of the linear relationship between SIRs toward two strains. But different groups had a similar baseline of the inter-strain SI before stress, indicating a SD-induced defect in both types of SI. In addition, in four different seasons, animals exhibited a significant resiliency to the stress in summer. These data suggest that SD resiliency is related to a higher SI toward the same-strain, and may be regulated by seasonal variations. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

Nonlinear Stress-Strain Behavior of Plasma Sprayed Ceramic Coatings

Czech Academy of Sciences Publication Activity Database

Nohava, Jiří; Kroupa, František

2005-01-01

Roč. 50, č. 3 (2005), s. 251-262 ISSN 0001-7043 R&D Projects: GA AV ČR KSK1010104 Institutional research plan: CEZ:AV0Z20430508 Keywords : plasma spraying * ceramic coatings * Young’s modulus * nonlinear behavior * microcracks Subject RIV: JH - Ceramics, Fire-Resistant Materials and Glass

Limitations of Hollomon and Ludwigson stress-strain relations in assessing the strain hardening parameters

International Nuclear Information System (INIS)

Samuel, K G

2006-01-01

It is shown that the deviation from the ideal Hollomon relation in describing the stress-strain behaviour is characteristic of all materials at low strains. The Ludwigson relation describing the deviation from the Hollomon relation at low strains is critically analysed and it is shown that the deviation at low strains is a consequence of some unknown 'plastic strain equivalent' present in the material. Stress strain curves obeying an ideal Hollomon relation as well as that of a structurally modified (prior cold worked) material were simulated and compared. The results show that the yield strength and the flow strength of a material at constant strain rate and temperature are dictated by the magnitude of the 'plastic strain equivalent' term. It is shown that this component need not necessarily mean a prior plastic strain present in the material due to prior cold work alone and that prior cold work strain will add to this. If this component is identified, the stress-strain behaviour can be adequately described by the Swift relation. It is shown that in both formalisms, the strain hardening index is a function of the yield strength of the material

In situ subsoil stress-strain behaviour in relation to soil precompression stress

DEFF Research Database (Denmark)

Keller, T; Arvidsson, J; Schjønning, Per

2012-01-01

is assumed to be elastic and reversible as long as [sigma] work examined soil stress-strain behavior as measured in situ during wheeling experiments and related it to the stress-strain behavior and [sigma]pc measured on soil cores in uniaxial compression tests in the laboratory. The data......Soil compaction negatively influences many important soil functions, including crop growth. Compaction occurs when the applied stress, [sigma], overcomes the soil strength. Soil strength in relation to compaction is typically expressed by the soil precompression stress, [sigma]pc. Deformation...... analyzed were from a large number of wheeling experiments carried out in Sweden and Denmark on soils with a wide range of texture. Contradicting the concept of precompression stress, we observed residual strain, [Latin Small Letter Open E]res, at [sigma

Relationship between ethanol and oxidative stress in laboratory and brewing yeast strains.

Science.gov (United States)

Bleoanca, Iulia; Silva, Ana Rita Courelas; Pimentel, Catarina; Rodrigues-Pousada, Claudina; Menezes, Regina de Andrade

2013-12-01

Ethanol is a chemical stress factor that inhibits cellular growth and determines metabolic changes leading to reduction of cell viability during fermentation and yeast storage. To determine the effect of time, temperature and ethanol during storage of brewing yeasts we have monitored viability of cells stored for 72 h, at 6 °C or 12 °C, in the presence of various ethanol concentrations. Under the conditions tested, 6 °C is the most favourable temperature to store brewing yeast creams emphasizing the importance of a tight temperature control in the storage vessels. Because W210 is less resistant to storage in the presence of ethanol than W34/70, the optimal storage parameters obtained under our laboratory conditions vary significantly. The ale strain is sensitive to storage under ethanol concentrations higher than 5% (v/v) for more than 48 h at 6 °C whereas at the same temperature the lager strain tolerates ethanol up to 7.5% (v/v) for 72 h. Also, the viability assays indicate that the antioxidant protein Yap1 is an important factor to storage resistance of BY4741 laboratory strain. To investigate the molecular mechanisms underlying tolerance of brewing yeast strains to ethanol, we have performed phenotypic analysis, localization studies and have monitored the activation of antioxidant and protection genes as well as the intracellular contents of glycogen and trehalose. Overall, our data suggest that the ale strain W210 has a defective antioxidant defence system and that ethanol may induce the antioxidant defences as well as glycogen and trehalose protection mechanisms in laboratory and brewing yeast strains. Copyright © 2013 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.

Three nonlinear performance relationships in the start-up state of IPMC strips based on finite element analysis

International Nuclear Information System (INIS)

Peng, Han Min; Ding, Qing Jun; Hui, Yao; Li, Hua Feng; Zhao, Chun Sheng

2010-01-01

Ionic polymer–metal composites (IPMC) are a class of electroactive polymers (EAP), and they currently attract numerous researchers to study their performance characteristics and applications. However, research on its start-up characteristics still requires more attention. In the IPMC start-up state (the moment of applying an actuation voltage at the very beginning), its mechanical performance is different in the stable working state (working for at least 10 min). Therefore, this paper focuses on three performance relationships of an IPMC strip between its maximal tip deformation and voltage, its maximal stress and voltage, as well as its maximal strain and voltage, both in the two states. Different from other reports, we found that they present nonlinear tendencies in the start-up state rather than linear ones. Therefore, based on the equivalent bimorph beam model, a finite element electromechanical coupling calculation module in the ANSYS software was utilized to simulate these characteristics. Furthermore, a test system is introduced to validate the phenomena. As a whole, these three relationships and the FEA method may be beneficial for providing control strategies effectively to IPMC actuators, especially in their start-up states

Apolipoprotein A-IV constrains HPA and behavioral stress responsivity in a strain-dependent manner.

Science.gov (United States)

Packard, Amy E B; Zhang, Jintao; Myers, Brent; Ko, Chih-Wei; Wang, Fei; Tso, Patrick; Ulrich-Lai, Yvonne M

2017-12-01

There is a critical gap in our knowledge of the mechanisms that govern interactions between daily life experiences (e.g., stress) and metabolic diseases, despite evidence that stress can have profound effects on cardiometabolic health. Apolipoprotein A-IV (apoA-IV) is a protein found in chylomicrons (lipoprotein particles that transport lipids throughout the body) where it participates in lipid handling and the regulation of peripheral metabolism. Moreover, apoA-IV is expressed in brain regions that regulate energy balance including the arcuate nucleus. Given that both peripheral and central metabolic processes are important modulators of hypothalamic-pituitary-adrenocortical (HPA) axis activity, the present work tests the hypothesis that apoA-IV activity affects stress responses. As emerging data suggests that apoA-IV actions can vary with background strain, we also explore the strain-dependence of apoA-IV stress regulation. These studies assess HPA axis, metabolic (hyperglycemia), and anxiety-related behavioral responses to psychogenic stress in control (wildtype) and apoA-IV-deficient (KO) mice on either the C57Bl/6J (C57) or 129×1/SvJ (129) background strain. The results indicate that apoA-IV KO increases post-stress corticosterone and anxiety-related behavior specifically in the 129 strain, and increases stress-induced hyperglycemia exclusively in the C57 strain. These data support the hypothesis that apoA-IV is a novel factor that limits stress reactivity in a manner that depends on genetic background. An improved understanding of the complex relationship among lipid homeostasis, stress sensitivity, and genetics is needed to optimize the development of personalized treatments for stress- and metabolism-related diseases. Copyright © 2017 Elsevier Ltd. All rights reserved.

A nonlinear magnetoelectric model for magnetoelectric layered composite with coupling stress

International Nuclear Information System (INIS)

Shi, Yang; Gao, Yuanwen

2014-01-01

Based on a linear piezoelectric relation and a nonlinear magnetostrictive constitutive relation, A nonlinear magnetoelectric (ME) effect model for flexural layered ME composites is established in in-plane magnetic field. In the proposed model, the true coupling stress and the equivalent piezomagnetic coefficient are taken into account and obtained through an iterative approach. Some calculations on nonlinear ME coefficient are conducted and discussed. Our results show that for both the flexural bilayer and trilayer composites, the true coupling stress in the composites first increase and then approach to a constant value with the increase of applied magnetic fields, affecting the nonlinear ME effect significantly. With consideration of the true coupling stress, the ME effect is smaller than that without consideration of the true coupling stress. Moreover, the proposed theoretical model predicts that the ME coefficient of the trilayer composite (does not generate the bending deflection) is much larger than that of bilayer composite (generates the bending deflection), which is in well agreement with the previous works. The influences of the applied magnetic field on the true coupling stress and fraction ratio corresponding to the extreme ME coefficients of layered structures are also investigated. - Highlights: • This paper develops a nonlinear model for layered ME composite. • The true coupling stress is obtained through an iterative approach. • The influences of coupling stress and flexural deformation are discussed. • The dependence of ME coefficient on magnetic field is studied

Fatigue life evaluation based on welding residual stress relaxation and notch strain approach for cruciform welded joint

International Nuclear Information System (INIS)

Han, Jeong Woo; Han, Seung Ho; Shin, Byung Chun; Kim, Jae Hoon

2003-01-01

The fatigue strength of welded joint is influenced by the welding residual stress which is relaxed depending on local stress distributed in vicinity of stress raisers, eg. under cut, overlap and blow hole. To evaluate its fatigue life the geometry of the stress raisers and the welding residual stress should be taken into account. The several methods based on notch strain approach have been proposed in order to consider the two factors above mentioned. These methods, however, have shown considerable differences between analytical and experimental results. It is due to the fact that the amount of the relaxed welding residual stress evaluated by the cyclic stress-strain relationship do not correspond with that occurred in reality. In this paper the residual stress relaxation model based on experimental results was used in order to reduce the discrepancy of the estimated amount of the relaxed welding residual stress. Under an assumption of the superimposition of the relaxed welding residual stress and the local stress, a modified notch strain approach was proposed and verified to the cruciform welded joint

Unified Hall-Petch description of nano-grain nickel hardness, flow stress and strain rate sensitivity measurements

Science.gov (United States)

Armstrong, R. W.; Balasubramanian, N.

2017-08-01

It is shown that: (i) nano-grain nickel flow stress and hardness data at ambient temperature follow a Hall-Petch (H-P) relation over a wide range of grain size; and (ii) accompanying flow stress and strain rate sensitivity measurements follow an analogous H-P relationship for the reciprocal "activation volume", (1/v*) = (1/A*b) where A* is activation area. Higher temperature flow stress measurements show a greater than expected reduction both in the H-P kɛ and in v*. The results are connected with smaller nano-grain size (tested at very low imposed strain rates.

Development of piping strain sensor for stress evaluation

International Nuclear Information System (INIS)

Takahama, Tsunemichi; Nishimura, Kazuma; Ninomiya, Seiichiro; Matsumoto, Yoshihiro; Harada, Yutaka

2014-01-01

In a small diameter piping, stresses are generated due to internal fluid or pump vibrations especially around the welding parts. Authors have successfully developed a pipe strain sensor which is able to measure such stresses. Unlike conventional methods using strain gages and adhesive bond, the sensor can measure the strain without putting adhesive bond on the piping surface. However, the strain sensor can provide measurements with a level of accuracy equivalent to that of conventional method using strain gages and adhesive bond. Accordingly, the strain sensor can significantly reduce the working time without any loss of the measurement accuracy. (author)

Undirected learning styles and academic risk: Analysis of the impact of stress, strain and coping.

Science.gov (United States)

Kimatian, Stephen; Lloyd, Sara; Berger, Jeffrey; Steiner, Lorraine; McKay, Robert; Schwengal, Deborah

2017-01-01

Learning style inventories used in conjunction with a measure of academic achievement consistently show an association of meaning directed learning patterns with academic success, but have failed to show a clear association of undirected learning styles with academic failure. Using survey methods with anesthesia residents, this study questioned whether additional assessment of factors related to stress, strain, and coping help to better define the association between undirected learning styles and academic risk. Pearson chi squared tests. 296 subjects were enrolled from eight institutions with 142 (48%) completing the study. American Board of Anesthesiologists In Training Examinations (ITE) percentiles (ITE%) were used as a measure of academic achievement. The Vermunt Inventory of Learning Styles (ILS) was used to identify four learning patterns and 20 strategies, and the Osipow Stress Inventory-Revised (OSI-R) was used as a measure of six scales of occupational stress, four of personal strain, and four coping resources. Two learning patterns had significant relationship with ITE scores. As seen in previous studies, Meaning Directed Learning was beneficial for academic achievement while Undirected Learning was the least beneficial. Higher scores on Meaning Directed Learning correlated positively with higher ITE scores while higher Undirected and lower Meaning Directed patterns related negatively to ITE%. OSI-R measures of stress, strain and coping indicated that residents with Undirected learning patterns had higher scores on three scales related to stress, and 4 related to strain, while displaying lower scores on two scales related to coping. Residents with higher Meaning Directed patterns scored lower on two scales of stress and two scales of strain, with higher scores on two scales for coping resources. Low Meaning Directed and high Undirected learning patterns correlated with lower ITE percentiles, higher scores for stress and strain, and lower coping resources

A Constitutive Model for Strain-Controlled Strength Degradation of Rockmasses (SDR)

Science.gov (United States)

Kalos, A.; Kavvadas, M.

2017-11-01

The paper describes a continuum, rate-independent, incremental plasticity constitutive model applicable in weak rocks and heavily fractured rockmasses, where mechanical behaviour is controlled by rockmass strength rather than structural features (discontinuities). The model describes rockmass structure by a generalised Hoek-Brown Structure Envelope (SE) in the stress space. Stress paths inside the SE are nonlinear and irreversible to better simulate behaviour at strains up to peak strength and under stress reversals. Stress paths on the SE have user-controlled volume dilatancy (gradually reducing to zero at large shear strains) and can model post-peak strain softening of brittle rockmasses via a structure degradation (damage) mechanism triggered by accumulated plastic shear strains. As the SE may strain harden with plastic strains, ductile behaviour can also be modelled. The model was implemented in the Finite Element Code Simulia ABAQUS and was applied in plane strain (2D) excavation of a cylindrical cavity (tunnel) to predict convergence-confinement curves. It is shown that small-strain nonlinearity, variable volume dilatancy and post-peak hardening/softening strongly affect the predicted curves, resulting in corresponding differences of lining pressures in real tunnel excavations.

The effect of non-local higher order stress to predict the nonlinear vibration behavior of carbon nanotube conveying viscous nanoflow

Energy Technology Data Exchange (ETDEWEB)

Mohammadimehr, M., E-mail: mmohammadimehr@kashanu.ac.ir [Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, P.O. Box: 87317-53153, Kashan (Iran, Islamic Republic of); Mohammadi-Dehabadi, A.A. [Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, P.O. Box: 87317-53153, Kashan (Iran, Islamic Republic of); Department of Mechanical Engineering, Iran University of Science and Technology, Narmak, Tehran (Iran, Islamic Republic of); Maraghi, Z. Khoddami [Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, P.O. Box: 87317-53153, Kashan (Iran, Islamic Republic of)

2017-04-01

In this research, the effect of non-local higher order stress on the nonlinear vibration behavior of carbon nanotube conveying viscous nanoflow resting on elastic foundation is investigated. Physical intuition reveals that increasing nanoscale stress leads to decrease the stiffness of nanostructure which firstly established by Eringen's non-local elasticity theory (previous nonlocal method) while many of papers have concluded otherwise at microscale based on modified couple stress, modified strain gradient theories and surface stress effect. The non-local higher order stress model (new nonlocal method) is used in this article that has been studied by few researchers in other fields and the results from the present study show that the trend of the new nonlocal method and size dependent effect including modified couple stress theory is the same. In this regard, the nonlinear motion equations are derived using a variational principal approach considering essential higher-order non-local terms. The surrounded elastic medium is modeled by Pasternak foundation to increase the stability of system where the fluid flow may cause system instability. Effects of various parameters such as non-local parameter, elastic foundation coefficient, and fluid flow velocity on the stability and dimensionless natural frequency of nanotube are investigated. The results of this research show that the small scale parameter based on higher order stress help to increase the natural frequency which has been approved by other small scale theories such as strain gradient theory, modified couple stress theory and experiments, and vice versa for previous nonlocal method. This study may be useful to measure accurately the vibration characteristics of nanotubes conveying viscous nanoflow and to design nanofluidic devices for detecting blood Glucose.

The effect of non-local higher order stress to predict the nonlinear vibration behavior of carbon nanotube conveying viscous nanoflow

International Nuclear Information System (INIS)

Mohammadimehr, M.; Mohammadi-Dehabadi, A.A.; Maraghi, Z. Khoddami

2017-01-01

In this research, the effect of non-local higher order stress on the nonlinear vibration behavior of carbon nanotube conveying viscous nanoflow resting on elastic foundation is investigated. Physical intuition reveals that increasing nanoscale stress leads to decrease the stiffness of nanostructure which firstly established by Eringen's non-local elasticity theory (previous nonlocal method) while many of papers have concluded otherwise at microscale based on modified couple stress, modified strain gradient theories and surface stress effect. The non-local higher order stress model (new nonlocal method) is used in this article that has been studied by few researchers in other fields and the results from the present study show that the trend of the new nonlocal method and size dependent effect including modified couple stress theory is the same. In this regard, the nonlinear motion equations are derived using a variational principal approach considering essential higher-order non-local terms. The surrounded elastic medium is modeled by Pasternak foundation to increase the stability of system where the fluid flow may cause system instability. Effects of various parameters such as non-local parameter, elastic foundation coefficient, and fluid flow velocity on the stability and dimensionless natural frequency of nanotube are investigated. The results of this research show that the small scale parameter based on higher order stress help to increase the natural frequency which has been approved by other small scale theories such as strain gradient theory, modified couple stress theory and experiments, and vice versa for previous nonlocal method. This study may be useful to measure accurately the vibration characteristics of nanotubes conveying viscous nanoflow and to design nanofluidic devices for detecting blood Glucose.

STRESS AND STRAIN STATE OF REPAIRING SECTION OF PIPELINE

Directory of Open Access Journals (Sweden)

V. V. Nikolaev

2015-01-01

Full Text Available Reliability of continuous operation of pipelines is an actual problem. For this reason should be developed an effective warning system of the main pipelines‘  failures and accidents not only in design and operation but also in selected repair. Changing of linear, unloaded by bending position leads to the change of stress and strain state of pipelines. And besides this, the stress and strain state should be determined and controlled in the process of carrying out the repair works. The article presents mathematical model of pipeline’s section straining in viscoelastic setting taking into account soils creep and high-speed stress state of pipeline with the purpose of stresses evaluation and load-supporting capacity of repairing section of pipeline, depending on time.  Stress and strain state analysis of pipeline includes longitudinal and circular stresses calculation  with  account of axis-asymmetrical straining and  was  fulfilled  on  the base of momentless theory of shells. To prove the consistency of data there were compared the calcu- lation results and the solution results by analytical methods for different cases (long pipeline’s section strain only under influence of cross-axis action; long pipeline’s section strain under in- fluence of longitudinal stress; long pipeline’s section strain; which is on the elastic foundation, under influence of cross-axis action. Comparison results shows that the calculation error is not more than 3 %.Analysis of stress-strain state change of pipeline’s section was carried out with development  of  this  model,  which  indicates  the  enlargement  of  span  deflection  in  comparison with problem’s solution in elastic approach. It is also proved, that for consistent assessment of pipeline maintenance conditions, it is necessary to consider the areolas of rheological processes of soils. On the base of complex analysis of pipelines there were determined stresses and time

A sheet metal necking formability diagram for nonlinear strain paths

DEFF Research Database (Denmark)

Christiansen, Peter; Jensen, Mikkel Ravn Boye; Winther, Grethe

2017-01-01

A new procedure for drawing forming limit curves is suggested. The theoretical basis for computing the forming limit curve due to diffuse necking, for nonlinear strain paths, is derived. The theoretically determined forming limit curve is compared with experimentally determined forming limits...

Non-linear elastic thermal stress analysis with phase changes

International Nuclear Information System (INIS)

Amada, S.; Yang, W.H.

1978-01-01

The non-linear elastic, thermal stress analysis with temperature induced phase changes in the materials is presented. An infinite plate (or body) with a circular hole (or tunnel) is subjected to a thermal loading on its inner surface. The peak temperature around the hole reaches beyond the melting point of the material. The non-linear diffusion equation is solved numerically using the finite difference method. The material properties change rapidly at temperatures where the change of crystal structures and solid-liquid transition occur. The elastic stresses induced by the transient non-homogeneous temperature distribution are calculated. The stresses change remarkably when the phase changes occur and there are residual stresses remaining in the plate after one cycle of thermal loading. (Auth.)

Analysis of stress-strain relationship in materials containing voids by means of plastic finite element method

International Nuclear Information System (INIS)

Shiraishi, Haruki; Tabuchi, Masaaki

2000-01-01

Applying the finite element method in two dimensions, an analysis is performed to derive the stress-strain relationship of material containing voids in matrix, and which is subjected to large deformation. The conditions assumed for the analysis are applicability of continuum body mechanics, Mises yield criterion, J2 flow theory, power work-hardening, plane stress in two-dimensional system and uniform cyclically recurring void distribution. Taking as example a case of material presenting 0.3 work-hardening, it is indicated from the analysis that: With voids arrayed in square lattice, total elongation would be little affected by change in void size; With a void spacing in lattice of 10 μ m, a uniform elongation 12-14% should be obtained in a wide range of void sizes from 0.01 to 8.0 μm; Tensile strength should start to lower at a void areal fraction of around 1%; A sharply lowered uniform elongation of a level far below 1% should be presented by material of low work-hardening exponent. The severe decline of ductility seen with 316 stainless steel upon neutron irradiation at temperatures around 600 K is interpreted as resulting from a combination of low work-hardening and the presence of voids in matrix. (author)

Probabilistic molecular dynamics evaluation of the stress-strain behavior of polyethylene

International Nuclear Information System (INIS)

Stowe, J.Q.; Predecki, P.K.; Laz, P.J.; Burks, B.M.; Kumosa, M.

2009-01-01

The primary goal of this study was to utilize molecular dynamics to predict the mechanical behavior of polyethylene. In particular, stress-strain relationships, the Young's modulus and Poisson ratio were predicted for low-density polyethylene at several molecular weights and polymer configurations with the number of united CH 2 atoms ranging between 500 and 5000. Probabilistic Monte Carlo methods were also used to identify the extent of uncertainty in mechanical property predictions. In general, asymptotic behavior was observed for stress and the Young's modulus as the molecular weight of the models increased. At the same time, significant variability, of the order of 1000% of the mean, in the stress-strain relationships and the Young's modulus predictions was observed, especially for low molecular weight models. The variability in the Young's modulus predictions ranged from 17.9 to 3.2 GPa for the models ranging from 100 to 5000 CH 2 atom models. However, it was also found that the mean value of the Young's modulus approached a physically possible value of 194 MPa for the 5000 atom model. Poisson ratio predictions also resulted in significant variability, from 200% to 425% of the mean, and ranged from 0.75 to 1.30. The mean value of the Poisson ratios calculated in this study ranged from 0.32 to 0.44 for the 100 to 5000 atom models, respectively.

Elastic-plastic potential functionals for rates and increments of stress and strain

International Nuclear Information System (INIS)

Feijoo, R.A.; Zouain, N.

1990-03-01

In this work attention is focused in the derivation of variational formulations of the constutive relationship in the form of conjugate potential functionals from which stress and strain rates are derived as elements of the corresponding sub-differential sets. The main result obtained is a pair of potential functionals. (A.C.A.S.) [pt

The Relationship of Occupational Stress, Psychological Strain, and Coping Resources to the Turnover Intentions of Rehabilitation Counselors

Science.gov (United States)

Layne, Christina Mann; Hohenshil, Thomas H.; Singh, Kusum

2004-01-01

The Occupational Stress Inventory?Revised (Osipow, 1998) and an individual data form were used to determine the turnover intentions of rehabilitation counselors, based on an interactive model of stress, strain, and coping as well as various demographic variables. The sample consisted of counselors who considered themselves to be employed full-time…

Nonlinear attenuation of S-waves and Love waves within ambient rock

Science.gov (United States)

Sleep, Norman H.; Erickson, Brittany A.

2014-04-01

obtain scaling relationships for nonlinear attenuation of S-waves and Love waves within sedimentary basins to assist numerical modeling. These relationships constrain the past peak ground velocity (PGV) of strong 3-4 s Love waves from San Andreas events within Greater Los Angeles, as well as the maximum PGV of future waves that can propagate without strong nonlinear attenuation. During each event, the shaking episode cracks the stiff, shallow rock. Over multiple events, this repeated damage in the upper few hundred meters leads to self-organization of the shear modulus. Dynamic strain is PGV divided by phase velocity, and dynamic stress is strain times the shear modulus. The frictional yield stress is proportional to depth times the effective coefficient of friction. At the eventual quasi-steady self-organized state, the shear modulus increases linearly with depth allowing inference of past typical PGV where rock over the damaged depth range barely reaches frictional failure. Still greater future PGV would cause frictional failure throughout the damaged zone, nonlinearly attenuating the wave. Assuming self-organization has taken place, estimated maximum past PGV within Greater Los Angeles Basins is 0.4-2.6 m s-1. The upper part of this range includes regions of accumulating sediments with low S-wave velocity that may have not yet compacted, rather than having been damaged by strong shaking. Published numerical models indicate that strong Love waves from the San Andreas Fault pass through Whittier Narrows. Within this corridor, deep drawdown of the water table from its currently shallow and preindustrial levels would nearly double PGV of Love waves reaching Downtown Los Angeles.

A NURBS approximation of experimental stress-strain curves

International Nuclear Information System (INIS)

Fedorov, Timofey V.; Morrev, Pavel G.

2016-01-01

A compact universal representation of monotonic experimental stress-strain curves of metals and alloys is proposed. It is based on the nonuniform rational Bezier splines (NURBS) of second order and may be used in a computer library of materials. Only six parameters per curve are needed; this is equivalent to a specification of only three points in a stress-strain plane. NURBS-functions of higher order prove to be surplus. Explicit expressions for both yield stress and hardening modulus are given. Two types of curves are considered: at a finite interval of strain and at infinite one. A broad class of metals and alloys of various chemical compositions subjected to various types of preliminary thermo-mechanical working is selected from a comprehensive data base in order to test the methodology proposed. The results demonstrate excellent correspondence to the experimental data. Keywords: work hardening, stress-strain curve, spline approximation, nonuniform rational B-spline, NURBS.

Resimulation of noise: a precision estimator for least square error curve-fitting tested for axial strain time constant imaging

Science.gov (United States)

Nair, S. P.; Righetti, R.

2015-05-01

Recent elastography techniques focus on imaging information on properties of materials which can be modeled as viscoelastic or poroelastic. These techniques often require the fitting of temporal strain data, acquired from either a creep or stress-relaxation experiment to a mathematical model using least square error (LSE) parameter estimation. It is known that the strain versus time relationships for tissues undergoing creep compression have a non-linear relationship. In non-linear cases, devising a measure of estimate reliability can be challenging. In this article, we have developed and tested a method to provide non linear LSE parameter estimate reliability: which we called Resimulation of Noise (RoN). RoN provides a measure of reliability by estimating the spread of parameter estimates from a single experiment realization. We have tested RoN specifically for the case of axial strain time constant parameter estimation in poroelastic media. Our tests show that the RoN estimated precision has a linear relationship to the actual precision of the LSE estimator. We have also compared results from the RoN derived measure of reliability against a commonly used reliability measure: the correlation coefficient (CorrCoeff). Our results show that CorrCoeff is a poor measure of estimate reliability for non-linear LSE parameter estimation. While the RoN is specifically tested only for axial strain time constant imaging, a general algorithm is provided for use in all LSE parameter estimation.

A nonlinear magneto-thermo-elastic coupled hysteretic constitutive model for magnetostrictive alloys

International Nuclear Information System (INIS)

Jin Ke; Kou Yong; Zheng Xiaojing

2012-01-01

This paper presents a general hysteretic constitutive law of nonlinear magneto-thermo-elastic coupling for magnetostrictive alloys. The model considered here is thermodynamically motivated and based on the Gibbs free energy function. A nonlinear part of the elastic strain arising from magnetic domain rotation induced by the pre-stress is taken into account. Furthermore, the movement of the domain walls is incorporated to describe hysteresis based on Jiles–Atherton's model. Then a set of closed and analytical expressions of the constitutive law for the magnetostrictive rods and films are obtained, and the parameters appearing in the model can be determined by those measurable experiments in mechanics and physics. Comparing this model with other existing models in this field, the quantitative results show that the relationships obtained here are more effective to describe the effects of the pre-stress or in-plane residual stress and ambient temperature on the magnetization or the magnetostriction hysteresis loops. - Highlights: ► A general hysteretic constitutive law of nonlinear magneto-thermo-elastic coupling for magnetostrictive materials is proposed. ► Model is thermodynamically motivated and the reversible magnetic domain rotation and irreversible domain wall motion are taken. ► The predictions are in good accordance with the experimental data including both rods and films. ► Magnetostrictive alloys are sensitive to environment temperature and pre-stress or residual stress.

Stress overshoot in stress-strain curves of Zr65Al10Ni10Cu15 metallic glass

International Nuclear Information System (INIS)

Kawamura, Y.; Shibata, T.; Inoue, A.; Masumoto, T.

1997-01-01

The essential features of the stress overshoot in the stress-strain curves of Zr 65 Al 10 Ni 10 Cu 15 (at.%) metallic glass that has a wide supercooled liquid region were revealed. The stress overshoot was dependent on temperature, strain rate, and stress relaxation. During the stretch, a change in strain rate gave rise to stress overshoot or undershoot which was sensitive to the variable quantities in the strain rate. copyright 1997 American Institute of Physics

Effective X-ray elastic constant measurement for in situ stress measurement of biaxially strained AA5754-O

International Nuclear Information System (INIS)

Iadicola, Mark A.; Gnäupel-Herold, Thomas H.

2012-01-01

Accurate measurement of stresses by X-ray diffraction requires accurate X-ray elastic constants. Calibration experiments are one method to determine these for a specific material in a specific condition. In this paper, uniaxial tension experiments are used to investigate the variation of these constants after uniaxial and equal-biaxial plastic deformation for an aluminum alloy (AA5754-O) of interest to the automotive industry. These data are critical for accurate measurement of the biaxial mechanical properties of the material using a recent experimental method combining specialized sheet metal forming equipment with portable X-ray diffraction equipment. The measured effective X-ray elastic constants show some minor variation with increased plastic deformation, and this behavior was found to be consistent for both uniaxially and equal-biaxially strained samples. The use of two average values for effective X-ray elastic constants, one in the rolling direction and one transverse to the rolling direction of the sheet material, is shown to be of sufficient accuracy for the combined tests of interest. Comparison of uniaxial data measured using X-ray diffraction and standard methods show good agreement, and biaxial stress–strain results show good repeatability. Additionally, the calibration data show some non-linear behavior, which is analyzed in regards to crystallographic texture and intergranular stress effects. The non-linear behavior is found to be the result of intergranular stresses based on comparison with additional measurements using other X-ray diffraction equipment and neutron diffraction.

Nonlinear Analysis of Cavities in Rock Salt

DEFF Research Database (Denmark)

Ottosen, N. S.; Krenk, Steen

1979-01-01

The paper covers some material and computational aspects of the rock mechanics of leached cavities in salt. A material model is presented in which the instantaneous stiffness of the salt is obtained by interpolation between the unloaded state and a relevant failure state. The model enables predic...... prediction of short term triaxial behaviour from uniaxial stress-strain curves. Key results from a nonlinear finite element calculation of a gas-filled cavity are given, and the general features are related to a simple nonlinear method of stress evaluation....

A fully coupled finite element model for stress distribution in buried gas pipeline

International Nuclear Information System (INIS)

Yahya Sukirman; Zainal Zakaria; Woong Soon Yue

2001-01-01

The study of stress-strain relationship is very important in many designs of buried structures over the years. The behavior and mechanism between the interaction of soil and buried structures such as a natural pipeline will mostly contributes to the integrity of the pipeline. This paper presents a fully coupled finite element of consolidation analysis model to study the stress-strain distribution along a buried pipeline before it excess its maximum deformation limit. The behavior of the soil-pipeline system can be modelled by a non-linear elasto-plastic based on Mohr-Coulomb and critical state yield surfaces. The deformation and deflection of the pipeline due to drained and external loading condition will be considered here. Finally the stress-strain distribution of the buried pipeline will be utilised to obtain the maximum deformation limit and the deflection of the buried pipeline. (Author)

Gender/Sex Differences in the Relationship between Psychosocial Work Exposures and Work and Life Stress.

Science.gov (United States)

Padkapayeva, Kathy; Gilbert-Ouimet, Mahée; Bielecky, Amber; Ibrahim, Selahadin; Mustard, Cameron; Brisson, Chantal; Smith, Peter

2018-04-18

Stress is an important factor affecting the health of working population. While work exposures are determinants of levels of work and life stress, we do not know whether similar or different exposures are related to stress levels for men and women. This study aimed to formally examine male/female differences in the relationships between psychosocial work exposures and work and life stress in a representative sample of Canadian labour market participants. We used data from 2012 cycle of the Canadian Community Health Survey (CCHS), a representative population-based survey conducted by Statistics Canada. The sample was restricted to employed labour force participants working 15+ hours per week (N = 8328, 48% female). To examine the relationship between work exposures and work and life stress, we conducted path analyses. Psychosocial work exposures included social support, job insecurity, job control, and job strain. Differences between estimates for men and women were explored using multigroup analyses, constraining paths between male and female models to be equivalent and examining the impact on change in model fit. Male/female differences were observed in the relationships between supervisor support and work stress levels as well as between job control, job insecurity, job strain, and life stress levels. Higher levels of supervisor support at work were associated with lower work stress among women, but not among men. Low job control had a direct protective effect on life stress for men but not for women, while high job strain had a direct adverse effect on life stress among women but not among men. Higher job insecurity was more strongly associated with higher life stress among men compared with women. The relationship between work stress and life stress was similar among men and women. The findings of this study suggest that the relationships between psychosocial exposures and work and life stress differ for men and women. Our study also raised important questions

Nonlinear Model of Pseudoelastic Shape Memory Alloy Damper Considering Residual Martensite Strain Effect

Directory of Open Access Journals (Sweden)

Y. M. Parulekar

2012-01-01

Full Text Available Recently, there has been increasing interest in using superelastic shape memory alloys for applications in seismic resistant-design. Shape memory alloys (SMAs have a unique property by which they can recover their original shape after experiencing large strains up to 8% either by heating (shape memory effect or removing stress (pseudoelastic effect. Many simplified shape memory alloy models are suggested in the past literature for capturing the pseudoelastic response of SMAs in passive vibration control of structures. Most of these models do not consider the cyclic effects of SMA's and resulting residual martensite deformation. Therefore, a suitable constitutive model of shape memory alloy damper which represents the nonlinear hysterical dynamic system appropriately is essential. In this paper a multilinear hysteretic model incorporating residual martensite strain effect of pseudoelastic shape memory alloy damper is developed and experimentally validated using SMA wire, based damper device. A sensitivity analysis is done using the proposed model along with three other simplified SMA models. The models are implemented on a steel frame representing an SDOF system and the comparison of seismic response of structure with all the models is made in the numerical study.

Nonlinear finite element analyses: advances and challenges in dental applications.

Science.gov (United States)

Wakabayashi, N; Ona, M; Suzuki, T; Igarashi, Y

2008-07-01

To discuss the development and current status of application of nonlinear finite element method (FEM) in dentistry. The literature was searched for original research articles with keywords such as nonlinear, finite element analysis, and tooth/dental/implant. References were selected manually or searched from the PUBMED and MEDLINE databases through November 2007. The nonlinear problems analyzed in FEM studies were reviewed and categorized into: (A) nonlinear simulations of the periodontal ligament (PDL), (B) plastic and viscoelastic behaviors of dental materials, (C) contact phenomena in tooth-to-tooth contact, (D) contact phenomena within prosthodontic structures, and (E) interfacial mechanics between the tooth and the restoration. The FEM in dentistry recently focused on simulation of realistic intra-oral conditions such as the nonlinear stress-strain relationship in the periodontal tissues and the contact phenomena in teeth, which could hardly be solved by the linear static model. The definition of contact area critically affects the reliability of the contact analyses, especially for implant-abutment complexes. To predict the failure risk of a bonded tooth-restoration interface, it is essential to assess the normal and shear stresses relative to the interface. The inclusion of viscoelasticity and plastic deformation to the program to account for the time-dependent, thermal sensitive, and largely deformable nature of dental materials would enhance its application. Further improvement of the nonlinear FEM solutions should be encouraged to widen the range of applications in dental and oral health science.

A mathematical formulation for large strain analysis of geologic continua

International Nuclear Information System (INIS)

Chaudhary, A.B.; Vakili, J.E.; Hume, H.R.

1987-12-01

A solution method is presented for finite-deformation analysis of geologic materials. The principle of virtual work is used to state the equations of equilibrium in a weak form. These equations are linearized about the last-established equilibrium configuration. A material constitutive relationship between the Green-Naghdi stress rate and the rate-of-deformation tensor is used to obtain the current stresses. The finite-element governing equations are expressed in a form suitable for an iterative solution strategy. The obtained gradient matrix contains the effects of both material and geometric nonlinearities. The primary application area of this formulation is the analysis of long-term deformation response of the region adjoining the mining shafts and the waste emplacement rooms within a nuclear waste repository. In this region, the strains are expected to be large, and the infinitesimal strain analysis would introduce inaccuracies in the solution. 19 refs., 6 figs

Geometrically Nonlinear Shell Analysis of Wrinkled Thin-Film Membranes with Stress Concentrations

Science.gov (United States)

Tessler, Alexander; Sleight, David W.

2006-01-01

Geometrically nonlinear shell finite element analysis has recently been applied to solar-sail membrane problems in order to model the out-of-plane deformations due to structural wrinkling. Whereas certain problems lend themselves to achieving converged nonlinear solutions that compare favorably with experimental observations, solutions to tensioned membranes exhibiting high stress concentrations have been difficult to obtain even with the best nonlinear finite element codes and advanced shell element technology. In this paper, two numerical studies are presented that pave the way to improving the modeling of this class of nonlinear problems. The studies address the issues of mesh refinement and stress-concentration alleviation, and the effects of these modeling strategies on the ability to attain converged nonlinear deformations due to wrinkling. The numerical studies demonstrate that excessive mesh refinement in the regions of stress concentration may be disadvantageous to achieving wrinkled equilibrium states, causing the nonlinear solution to lock in the membrane response mode, while totally discarding the very low-energy bending response that is necessary to cause wrinkling deformation patterns.

The stress and strain analysis research of class 1 eqnipments

International Nuclear Information System (INIS)

Ye Yuanwu; Tang Long; Wang Yueying; Qi Min; Yu Huajin

2008-01-01

The class 1 equipment is very important in the nuclear device, in the design and testing process required to carry out their stress and strain analysis, so as to ensure their safety. There are two ways to get stress and strain analysis of the class 1 equipment, the theoretical and experimental methods. Through theoretical method can get the stress and strain of the class 1 equipment, so as to provide a basis for the design of the equipment; through the experimental method to verify the accuracy of the theoretical methods and provide a basis for the safety assessment of the equipment. The main ressel of CEFR (China Experimental Fast Reactor) is the class 1 equipment. In this paper, according to the stress and strain analysis research of CEFR main vessel, the theories and expperimental methods of nuclear class 1 equipments stress and strain analysis has been described. (authors)

Shear Stress-Relative Slip Relationship at Concrete Interfaces

Directory of Open Access Journals (Sweden)

Keun-Hyeok Yang

2016-01-01

Full Text Available This study develops a simple and rational shear stress-relative slip model of concrete interfaces with monolithic castings or smooth construction joints. In developing the model, the initial shear cracking stress and relative slip amount at peak stress were formulated from a nonlinear regression analysis using test data for push-off specimens. The shear friction strength was determined from the generalized equations on the basis of the upper-bound theorem of concrete plasticity. Then, a parametric fitting analysis was performed to derive equations for the key parameters determining the shapes of the ascending and descending branches of the shear stress-relative slip curve. The comparisons of predictions and measurements obtained from push-off tests confirmed that the proposed model provides superior accuracy in predicting the shear stress-relative slip relationship of interfacial shear planes. This was evidenced by the lower normalized root mean square error than those in Xu et al.’s model and the CEB-FIB model, which have many limitations in terms of the roughness of the substrate surface along an interface and the magnitude of equivalent normal stress.

FEATURES APPLICATION CIRCUIT MOMENT FINITE ELEMENT (MSSE) NONLINEAR CALCULATIONS OF PLATES AND SHELLS

OpenAIRE

Bazhenov V.A.; Sacharov A.S.; Guliar A. I.; Pyskunov S.O.; Maksymiuk Y.V.

2014-01-01

Based MSSE created shell CE general type, which allows you to analyze the stress-strain state of axisymmetrical shells and plates in problems of physical and geometric nonlinearity. The principal nonlinear elasticity theory, algorithms for solving systems of nonlinear equations for determining the temperature and plastic deformation.

Maximum stress estimation model for multi-span waler beams with deflections at the supports using average strains.

Science.gov (United States)

Park, Sung Woo; Oh, Byung Kwan; Park, Hyo Seon

2015-03-30

The safety of a multi-span waler beam subjected simultaneously to a distributed load and deflections at its supports can be secured by limiting the maximum stress of the beam to a specific value to prevent the beam from reaching a limit state for failure or collapse. Despite the fact that the vast majority of accidents on construction sites occur at waler beams in retaining wall systems, no safety monitoring model that can consider deflections at the supports of the beam is available. In this paper, a maximum stress estimation model for a waler beam based on average strains measured from vibrating wire strain gauges (VWSGs), the most frequently used sensors in construction field, is presented. The model is derived by defining the relationship between the maximum stress and the average strains measured from VWSGs. In addition to the maximum stress, support reactions, deflections at supports, and the magnitudes of distributed loads for the beam structure can be identified by the estimation model using the average strains. Using simulation tests on two multi-span beams, the performance of the model is evaluated by estimating maximum stress, deflections at supports, support reactions, and the magnitudes of distributed loads.

Electrospun microcrimped fibers with nonlinear mechanical properties enhance ligament fibroblast phenotype.

Science.gov (United States)

Grace Chao, Pen-hsiu; Hsu, Hsiang-Yi; Tseng, Hsiao-Yun

2014-09-01

Fiber structure and order greatly impact the mechanical behavior of fibrous materials. In biological tissues, the nonlinear mechanics of fibrous scaffolds contribute to the functionality of the material. The nonlinear mechanical properties of the wavy structure (crimp) in collagen allow tissue flexibility while preventing over-extension. A number of approaches have tried to recreate this complex mechanical functionality. We generated microcrimped fibers by briefly heating electrospun parallel fibers over the glass transition temperature or by ethanol treatment. The crimp structure is similar to those of collagen fibers found in native aorta, intestines, or ligaments. Using poly-L-lactic acid fibers, we demonstrated that the bulk materials exhibit changed stress-strain behaviors with a significant increase in the toe region in correlation to the degree of crimp, similar to those observed in collagenous tissues. In addition to mimicking the stress-strain behavior of biological tissues, the microcrimped fibers are instructive in cell morphology and promote ligament phenotypic gene expression. This effect can be further enhanced by dynamic tensile loading, a physiological perturbation in vivo. This rapid and economical approach for microcrimped fiber production provides an accessible platform to study structure-function relationships and a novel functional scaffold for tissue engineering and cell mechanobiology studies.

Frequency Response of Synthetic Vocal Fold Models with Linear and Nonlinear Material Properties

Science.gov (United States)

Shaw, Stephanie M.; Thomson, Scott L.; Dromey, Christopher; Smith, Simeon

2012-01-01

Purpose: The purpose of this study was to create synthetic vocal fold models with nonlinear stress-strain properties and to investigate the effect of linear versus nonlinear material properties on fundamental frequency (F[subscript 0]) during anterior-posterior stretching. Method: Three materially linear and 3 materially nonlinear models were…

Development of a stress-mode sensitive viscoelastic constitutive relationship for asphalt concrete: experimental and numerical modeling

Science.gov (United States)

Karimi, Mohammad M.; Tabatabaee, Nader; Jahanbakhsh, H.; Jahangiri, Behnam

2017-08-01

Asphalt binder is responsible for the thermo-viscoelastic mechanical behavior of asphalt concrete. Upon application of pure compressive stress to an asphalt concrete specimen, the stress is transferred by mechanisms such as aggregate interlock and the adhesion/cohesion properties of asphalt mastic. In the pure tensile stress mode, aggregate interlock plays a limited role in stress transfer, and the mastic phase plays the dominant role through its adhesive/cohesive and viscoelastic properties. Under actual combined loading patterns, any coordinate direction may experience different stress modes; therefore, the mechanical behavior is not the same in the different directions and the asphalt specimen behaves as an anisotropic material. The present study developed an anisotropic nonlinear viscoelastic constitutive relationship that is sensitive to the tension/compression stress mode by extending Schapery's nonlinear viscoelastic model. The proposed constitutive relationship was implemented in Abaqus using a user material (UMAT) subroutine in an implicit scheme. Uniaxial compression and indirect tension (IDT) testing were used to characterize the viscoelastic properties of the bituminous materials and to calibrate and validate the proposed constitutive relationship. Compressive and tensile creep compliances were calculated using uniaxial compression, as well as IDT test results, for different creep-recovery loading patterns at intermediate temperature. The results showed that both tensile creep compliance and its rate were greater than those of compression. The calculated deflections based on these IDT test simulations were compared with experimental measurements and were deemed acceptable. This suggests that the proposed viscoelastic constitutive relationship correctly demonstrates the viscoelastic response and is more accurate for analysis of asphalt concrete in the laboratory or in situ.

Standard practice for statistical analysis of linear or linearized stress-life (S-N) and strain-life (ε-N) fatigue data

CERN Document Server

American Society for Testing and Materials. Philadelphia

2010-01-01

1.1 This practice covers only S-N and ε-N relationships that may be reasonably approximated by a straight line (on appropriate coordinates) for a specific interval of stress or strain. It presents elementary procedures that presently reflect good practice in modeling and analysis. However, because the actual S-N or ε-N relationship is approximated by a straight line only within a specific interval of stress or strain, and because the actual fatigue life distribution is unknown, it is not recommended that (a) the S-N or ε-N curve be extrapolated outside the interval of testing, or (b) the fatigue life at a specific stress or strain amplitude be estimated below approximately the fifth percentile (P ≃ 0.05). As alternative fatigue models and statistical analyses are continually being developed, later revisions of this practice may subsequently present analyses that permit more complete interpretation of S-N and ε-N data.

Effective stress coefficient for uniaxial strain condition

DEFF Research Database (Denmark)

Alam, M.M.; Fabricius, I.L.

2012-01-01

one dimensional rock mechanical deformation. We further investigated the effect of boundary condition on the stress dependency of effective stress coefficient and discussed its application in reservoir study. As stress field in the reservoirs are most unlikely to be hydrostatic, effective stress...... determined under uniaxial strain condition will be more relevant in reservoir studies. Copyright 2012 ARMA, American Rock Mechanics Association....

FEATURES APPLICATION CIRCUIT MOMENT FINITE ELEMENT (MSSE NONLINEAR CALCULATIONS OF PLATES AND SHELLS

Directory of Open Access Journals (Sweden)

Bazhenov V.A.

2014-06-01

Full Text Available Based MSSE created shell CE general type, which allows you to analyze the stress-strain state of axisymmetrical shells and plates in problems of physical and geometric nonlinearity. The principal nonlinear elasticity theory, algorithms for solving systems of nonlinear equations for determining the temperature and plastic deformation.

Development of a relationship between external measurements and reinforcement stress

Science.gov (United States)

Brault, Andre; Hoult, Neil A.; Lees, Janet M.

2015-03-01

As many countries around the world face an aging infrastructure crisis, there is an increasing need to develop more accurate monitoring and assessment techniques for reinforced concrete structures. One of the challenges associated with assessing existing infrastructure is correlating externally measured parameters such as crack widths and surface strains with reinforcement stresses as this is dependent on a number of variables. The current research investigates how the use of distributed fiber optic sensors to measure reinforcement strain can be correlated with digital image correlation measurements of crack widths to relate external crack width measurements to reinforcement stresses. An initial set of experiments was undertaken involving a series of small-scale beam specimens tested in three-point bending with variable reinforcement properties. Relationships between crack widths and internal reinforcement strains were observed including that both the diameter and number of bars affected the measured maximum strain and crack width. A model that uses measured crack width to estimate reinforcement strain was presented and compared to the experimental results. The model was found to provide accurate estimates of load carrying capacity for a given crack width, however, the model was potentially less accurate when crack widths were used to estimate the experimental reinforcement strains. The need for more experimental data to validate the conclusions of this research was also highlighted.

Tensile stress-strain and work hardening behaviour of P9 steel for wrapper application in sodium cooled fast reactors

Science.gov (United States)

Christopher, J.; Choudhary, B. K.; Isaac Samuel, E.; Mathew, M. D.; Jayakumar, T.

2012-01-01

Tensile flow behaviour of P9 steel with different silicon content has been examined in the framework of Hollomon, Ludwik, Swift, Ludwigson and Voce relationships for a wide temperature range (300-873 K) at a strain rate of 1.3 × 10 -3 s -1. Ludwigson equation described true stress ( σ)-true plastic strain ( ɛ) data most accurately in the range 300-723 K. At high temperatures (773-873 K), Ludwigson equation reduces to Hollomon equation. The variations of instantaneous work hardening rate ( θ = dσ/ dɛ) and θσ with stress indicated two-stage work hardening behaviour. True stress-true plastic strain, flow parameters, θ vs. σ and θσ vs. σ with respect to temperature exhibited three distinct temperature regimes and displayed anomalous behaviour due to dynamic strain ageing at intermediate temperatures. Rapid decrease in flow stress and flow parameters, and rapid shift in θ- σ and θσ- σ towards lower stresses with increase in temperature indicated dominance of dynamic recovery at high temperatures.

Measurement of the uniaxial mechanical properties of rat skin using different stress-strain definitions.

Science.gov (United States)

Karimi, A; Navidbakhsh, M

2015-05-01

The mechanical properties of skin tissue may vary according to the anatomical locations of a body. There are different stress-strain definitions to measure the mechanical properties of skin tissue. However, there is no agreement as to which stress-strain definition should be implemented to measure the mechanical properties of skin at different anatomical locations. Three stress definitions (second Piola-Kichhoff stress, engineering stress, and true stress) and four strain definitions (Almansi-Hamel strain, Green-St. Venant strain, engineering strain, and true strain) are employed to determine the mechanical properties of skin tissue at back and abdomen locations of a rat body. The back and abdomen skins of eight rats are excised and subjected to a series of tensile tests. The elastic modulus, maximum stress, and strain of skin tissues are measured using three stress definitions and four strain definitions. The results show that the effect of varying the stress definition on the maximum stress measurements of the back skin is significant but not when calculating the elastic modulus and maximum strain. No significant effects are observed on the elastic modulus, maximum stress, and strain measurements of abdomen skin by varying the stress definition. In the true stress-strain diagram, the maximum stress (20%), and elastic modulus (35%) of back skin are significantly higher than that of abdomen skin. The true stress-strain definition is favored to measure the mechanical properties of skin tissue since it gives more accurate measurements of the skin's response using the instantaneous values. © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Stress and Strain Gradients in a Low Carbon Steel Deformed under Heavy Sliding

DEFF Research Database (Denmark)

Zhang, Xiaodan; Hansen, Niels; Huang, Xiaoxu

A recent study [1] has shown that a microstructure can be refined to a record low of 5 nm and that dislocation glide is still a controlling mechanism at this length scale. In this study, by heavy rotatory sliding of a low carbon steel a gradient structure has been produced extending to about 2.5 mm...... on the deformation microstructure using the classic stress-structure relationship. Computational and materials modelling has been advanced from bulk to gradient structures leading to dissemination of constitutive stress-strain equations in gradient structures....

Predicted strains in austenitic stainless steels at stresses above yield

International Nuclear Information System (INIS)

Hammond, J.P.; Sikka, V.K.

1977-01-01

Tensile results on austenitic stainless steels were analyzed to develop means for predicting strains at stresses above yield for reactor regulatory applications. Eight heats each of types 316 and 304 were tested at 24, 93, 204, and 316 0 C as mill-annealed and at 24 0 C after reannealing. The effects of heat-to-heat variations on total strain (to 5%) at discrete stress levels were portrayed by a rational polynomial incorporating three constants that relate to the basic features of the true-stress-true-strain diagram. Because these constants usually are interrelated, a single parameter, yield strength (YS), proved adequate to predict results. For predictions analytical expressions of yield strength, an average value (YSa), and a lower bound value [YSa - 1.65SEE (standard error of estimate)] were used. Using the rational polynomial with these parameters we determined (1) limits of total maximum strain and (2) ratios of strain of material of lower bound YS to that of average YS. These are recorded at regular increments of stress [34 MPa (5 ksi)] and at ASME Code-related stresses (S/sub y), S/sub m/, 1.2S/sub m/ and 1.5S/sub m/). At intermediate stresses, strain penalties for using material of lower bound strength were large, generally larger for type 316 than type 304. For mill-annealed type 316 at 24, 93, 204, and 316 0 C, the maximum ratios of strain were 8.8, 13.0, 14.1, and 14.9, respectively, whereas for type 304 they were 3.5, 3.4, 5.6, and 4.6. At 1.5S/sub m/ and 316 0 C, a maximum strain of 2.08% was predicted for type 316 and 1.66% for type 304, as contrasted to values of 0.14 and 0.39% for average strain

Maximum Stress Estimation Model for Multi-Span Waler Beams with Deflections at the Supports Using Average Strains

Directory of Open Access Journals (Sweden)

Sung Woo Park

2015-03-01

Full Text Available The safety of a multi-span waler beam subjected simultaneously to a distributed load and deflections at its supports can be secured by limiting the maximum stress of the beam to a specific value to prevent the beam from reaching a limit state for failure or collapse. Despite the fact that the vast majority of accidents on construction sites occur at waler beams in retaining wall systems, no safety monitoring model that can consider deflections at the supports of the beam is available. In this paper, a maximum stress estimation model for a waler beam based on average strains measured from vibrating wire strain gauges (VWSGs, the most frequently used sensors in construction field, is presented. The model is derived by defining the relationship between the maximum stress and the average strains measured from VWSGs. In addition to the maximum stress, support reactions, deflections at supports, and the magnitudes of distributed loads for the beam structure can be identified by the estimation model using the average strains. Using simulation tests on two multi-span beams, the performance of the model is evaluated by estimating maximum stress, deflections at supports, support reactions, and the magnitudes of distributed loads.

Nonlinear elastic longitudinal strain-wave propagation in a plate with nonequilibrium laser-generated point defects

International Nuclear Information System (INIS)

Mirzade, Fikret Kh.

2005-01-01

The propagation of longitudinal strain wave in a plate with quadratic nonlinearity of elastic continuum was studied in the context of a model that takes into account the joint dynamics of elastic displacements in the medium and the concentration of the nonequilibrium laser-induced point defects. The input equations of the problem are reformulated in terms of only the total displacements of the medium points. In this case, the presence of structural defects manifests itself in the emergence of a delayed response of the system to the propagation of the strain-related perturbations, which is characteristic of media with relaxation or memory. The model equations describing the nonlinear displacement wave were derived with allowance made for the values of the relaxation parameter. The influence of the generation and relaxation of lattice defects on the propagation of this wave was analyzed. It is shown that, for short relaxation times of defects, the strain can propagate in the form of shock fronts. In the case of longer relaxation times, shock waves do not form and the strain wave propagates only in the form of solitary waves or a train of solitons. The contributions of the finiteness of the defect-recombination rate to linear and nonlinear elastic modulus, and spatial dispersion are determined

Study on elastic-plastic deformation analysis using a cyclic stress-strain curve

International Nuclear Information System (INIS)

Igari, Toshihide; Setoguchi, Katsuya; Yamauchi, Masafumi

1983-01-01

This paper presents the results of the elastic-plastic deformation analysis using a cyclic stress-strain curve with an intention to apply this method for predicting the low-cycle fatigue life. Uniaxial plastic cycling tests were performed on 2 1/4Cr-1Mo steel to investigate the correspondence between the cyclic stress-strain curve and the hysteresis loop, and also to determine what mathematical model should be used for analysis of deformation at stress reversal. Furthermore, a cyclic in-plane bending test was performed on a flat plate to clarify the validity of the cyclic stress-strain curve-based theoretical analysis. The results obtained are as follows: (1) The cyclic stress-strain curve corresponds nearly to the ascending curve of hysteresis loop scaled by a factor of 1/2 for both stress and strain. Therefore, the cyclic stress-strain curve can be determined from the shape of hysteresis loop, for simplicity. (2) To perform the elastic-plastic deformation analysis using the cyclic stress-strain curve is both practical and effective for predicting the cyclic elastic-plastic deformation of structures at the stage of advanced cycles. And Masing model can serve as a suitable mathematical model for such a deformation analysis. (author)

A non-linear elastic constitutive framework for replicating plastic deformation in solids.

Energy Technology Data Exchange (ETDEWEB)

Roberts, Scott Alan; Schunk, Peter Randall

2014-02-01

Ductile metals and other materials typically deform plastically under large applied loads; a behavior most often modeled using plastic deformation constitutive models. However, it is possible to capture some of the key behaviors of plastic deformation using only the framework for nonlinear elastic mechanics. In this paper, we develop a phenomenological, hysteretic, nonlinear elastic constitutive model that captures many of the features expected of a plastic deformation model. This model is based on calculating a secant modulus directly from a materials stress-strain curve. Scalar stress and strain values are obtained in three dimensions by using the von Mises invariants. Hysteresis is incorporated by tracking an additional history variable and assuming an elastic unloading response. This model is demonstrated in both single- and multi-element simulations under varying strain conditions.

Interpretation of large-strain geophysical crosshole tests

International Nuclear Information System (INIS)

Drnevich, V.P.; Salgado, R.; Ashmawy, A.; Grant, W.P.; Vallenas, P.

1995-10-01

At sites in earthquake-prone areas, the nonlinear dynamic stress-strain behavior of soil with depth is essential for earthquake response analyses. A seismic crosshole test has been developed where large dynamic forces are applied in a borehole. These forces generate shear strains in the surrounding soil that are well into the nonlinear range. The shear strain amplitudes decrease with distance from the source. Velocity sensors located in three additional holes at various distances from the source hole measure the particle velocity and the travel time of the shear wave from the source. This paper provides an improved, systematic interpretation scheme for the data from these large-strain geophysical crosshole tests. Use is made of both the measured velocities at each sensor and the travel times. The measured velocity at each sensor location is shown to be a good measure of the soil particle velocity at that location. Travel times to specific features on the velocity time history, such as first crossover, are used to generate travel time curves for the waves which are nonlinear. At some distance the amplitudes reduce to where the stress-strain behavior is essentially linear and independent of strain amplitude. This fact is used together with the measurements at the three sensor locations in a rational approach for fitting curves of shear wave velocity versus distance from the source hole that allow the determination of the shear wave velocity and the shear strain amplitude at each of the sensor locations as well as the shear wave velocity associated with small-strain (linear) behavior. The method is automated using off-the-shelf PC-based software. The method is applied to large-strain crosshole tests performed as part of the studies for the design and construction of the proposed Multi-Function Waste Tank Facility planned for Hanford Site

Psychosocial resources and the relationship between transformational leadership and employees' psychological strain.

Science.gov (United States)

Schmidt, Burkhard; Loerbroks, Adrian; Herr, Raphael; Litaker, David; Wilson, Mark; Kastner, Michael; Fischer, Joachim

2014-01-01

Leadership behavior may both serve as a supportive resource or as a source of psychological distress in the workplace. Transformational leadership (TL), a behavior of superiors that fosters motivation, empowerment and a sense of teamness, has been associated with employee well-being, but the mechanisms that underlie these effects are unclear. We therefore explored the relationship between TL and stress by examining potential mediating roles for established organizational and personal resources. We used cross-sectional data on TL, psychosocial resources and employee strain from a company wide survey. Linear regression and structural equation modeling assessed potential mediation following the method outlined by Baron and Kenny. In a convenience sample consisting of mostly white-collar employees (n=320, 42.6% male), we observed a relationship between TL and employees' perceived work-related stress that was fully mediated by protective psychosocial resources (ß =-0.33, pTransformational leadership seems to be associated with lower stress among employees and a perception of more available psychosocial resources. These findings indicate that TL might serve as a valuable focus for tailored interventions to improve employee health.

Stress-strain state analysis and optimization of rod system under periodic pulse load

Directory of Open Access Journals (Sweden)

Grebenyuk Grigory

2018-01-01

Full Text Available The paper considers the problem of analysis and optimization of rod systems subjected to combined static and periodic pulse load. As a result of the study the analysis method was developed based on traditional approach to solving homogeneous matrix equations of state and a special algorithm for developing a particular solution. The influence of pulse parameters variations on stress-strain state of a rod system was analyzed. Algorithms for rod systems optimization were developed basing on strength recalculation and statement and solution of optimization problem as a problem of nonlinear mathematical programming. Recommendations are developed for efficient organization of process for optimization of rod systems under static and periodic pulse load.

Family Roles as Moderators of the Relationship between Schedule Flexibility and Stress

Science.gov (United States)

Jang, Soo Jung; Zippay, Allison; Park, Rhokeun

2012-01-01

Employer initiatives that address the spillover of work strain onto family life include flexible work schedules. This study explored the mediating role of negative work-family spillover in the relationship between schedule flexibility and employee stress and the moderating roles of gender, family workload, and single-parent status. Data were drawn…

Regional variability among nonlinear chlorophyll-phosphorus relationships in lakes

Science.gov (United States)

Filstrup, Christopher T.; Wagner, Tyler; Soranno, Patricia A.; Stanley, Emily H.; Stow, Craig A.; Webster, Katherine E.; Downing, John A.

2014-01-01

The relationship between chlorophyll a (Chl a) and total phosphorus (TP) is a fundamental relationship in lakes that reflects multiple aspects of ecosystem function and is also used in the regulation and management of inland waters. The exact form of this relationship has substantial implications on its meaning and its use. We assembled a spatially extensive data set to examine whether nonlinear models are a better fit for Chl a—TP relationships than traditional log-linear models, whether there were regional differences in the form of the relationships, and, if so, which regional factors were related to these differences. We analyzed a data set from 2105 temperate lakes across 35 ecoregions by fitting and comparing two different nonlinear models and one log-linear model. The two nonlinear models fit the data better than the log-linear model. In addition, the parameters for the best-fitting model varied among regions: the maximum and lower Chl aasymptotes were positively and negatively related to percent regional pasture land use, respectively, and the rate at which chlorophyll increased with TP was negatively related to percent regional wetland cover. Lakes in regions with more pasture fields had higher maximum chlorophyll concentrations at high TP concentrations but lower minimum chlorophyll concentrations at low TP concentrations. Lakes in regions with less wetland cover showed a steeper Chl a—TP relationship than wetland-rich regions. Interpretation of Chl a—TP relationships depends on regional differences, and theory and management based on a monolithic relationship may be inaccurate.

Time-dependent strains and stresses in a pumpkin balloon

Science.gov (United States)

Gerngross, T.; Xu, Y.; Pellegrino, S.

This paper presents a study of pumpkin-shaped superpressure balloons consisting of gores made from a thin polymeric film attached to high stiffness meridional tendons This type of design is being used for the NASA ULDB balloons The gore film shows considerable time-dependent stress relaxation whereas the behaviour of the tendons is essentially time-independent Upon inflation and pressurization the instantaneous i e linear-elastic strain and stress distributions in the film show significantly higher values in the meridional direction However over time and due to the biaxial visco-elastic stress relaxation of the the gore material the em hoop strains increase and the em meridional stresses decrease whereas the em remaining strain and stress components remain substantially unchanged These results are important for a correct assessment of the structural integrity of a pumpkin balloon in a long-duration mission both in terms of the material performance and the overall stability of the shape of the balloon An experimental investigation of the time dependence of the biaxial strain distribution in the film of a 4 m diameter 48 gore pumpkin balloon is presented The inflated shape of selected gores has been measured using photogrammetry and the time variation in strain components at some particular points of these gores has been measured under constant pressure and temperature The results show good correlation with a numerical study using the ABAQUS finite-element package that includes a widely used model of

Nonlinear analysis of pre-stressed concrete containment vessel (PCCV) using the damage plasticity model

Energy Technology Data Exchange (ETDEWEB)

Shokoohfar, Ahmad; Rahai, Alireza, E-mail: rahai@aut.ac.ir

2016-03-15

Highlights: • This paper describes nonlinear analyses of a 1:4 scale model of a (PCCV). • Coupled temp-disp. analysis and concrete damage plasticity are considered. • Temperature has limited effects on correct failure mode estimation. • Higher pre-stressing forces have limited effects on ultimate radial displacements. • Anchorage details of liner plates leads to prediction of correct failure mode. - Abstract: This paper describes the nonlinear analyses of a 1:4 scale model of a pre-stressed concrete containment vessel (PCCV). The analyses are performed under pressure and high temperature effects with considering anchorage details of liner plate. The temperature-time history of the model test is considered as an input boundary condition in the coupled temp-displacement analysis. The constitutive model developed by Chang and Mander (1994) is adopted in the model as the basis for the concrete stress–strain relation. To trace the crack pattern of the PCCV concrete faces, the concrete damage plasticity model is applied. This study includes the results of the thermal and mechanical behaviors of the PCCV subject to temperature loading and internal pressure at the same time. The test results are compared with the analysis results. The analysis results show that the temperature has little impact on the ultimate pressure capacity of the PCCV. To simulate the exact failure mode of the PCCV, the anchorage details of the liner plates around openings should be maintained in the analytical models. Also the failure mode of the PCCV structure hasn’t influenced by hoop tendons pre-stressing force variations.

Stress-Strain state of structural elements of LWR fuel rods modeling in the MSC.MARC and ANSYS software

International Nuclear Information System (INIS)

Kuznetsov, A.; Kuznetsov, V.; Krupkin, A.; Kashirin, B.; Medvedev, A.; Novikov, V.

2009-01-01

The results of stress-strain state in the fuel rod spring fixing lock coils modeling are presented in this paper. The solution of this problem was realized in finite-element software MSC.MARC and ANSIS. The solution was obtained in the three-dimensional setting, taking into account multicontact interaction and all physical and geometric nonlinearities. The finite-element models were verified on analytical parities and experimental data. Results of verification have proved a correctness of the accepted finite-element models

A deep learning approach to estimate chemically-treated collagenous tissue nonlinear anisotropic stress-strain responses from microscopy images.

Science.gov (United States)

Liang, Liang; Liu, Minliang; Sun, Wei

2017-11-01

Biological collagenous tissues comprised of networks of collagen fibers are suitable for a broad spectrum of medical applications owing to their attractive mechanical properties. In this study, we developed a noninvasive approach to estimate collagenous tissue elastic properties directly from microscopy images using Machine Learning (ML) techniques. Glutaraldehyde-treated bovine pericardium (GLBP) tissue, widely used in the fabrication of bioprosthetic heart valves and vascular patches, was chosen to develop a representative application. A Deep Learning model was designed and trained to process second harmonic generation (SHG) images of collagen networks in GLBP tissue samples, and directly predict the tissue elastic mechanical properties. The trained model is capable of identifying the overall tissue stiffness with a classification accuracy of 84%, and predicting the nonlinear anisotropic stress-strain curves with average regression errors of 0.021 and 0.031. Thus, this study demonstrates the feasibility and great potential of using the Deep Learning approach for fast and noninvasive assessment of collagenous tissue elastic properties from microstructural images. In this study, we developed, to our best knowledge, the first Deep Learning-based approach to estimate the elastic properties of collagenous tissues directly from noninvasive second harmonic generation images. The success of this study holds promise for the use of Machine Learning techniques to noninvasively and efficiently estimate the mechanical properties of many structure-based biological materials, and it also enables many potential applications such as serving as a quality control tool to select tissue for the manufacturing of medical devices (e.g. bioprosthetic heart valves). Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Burial stress and elastic strain of carbonate rocks

DEFF Research Database (Denmark)

Fabricius, Ida Lykke

2014-01-01

Burial stress on a sediment or sedimentary rock is relevant for predicting compaction or failure caused by changes in, e.g., pore pressure in the subsurface. For this purpose, the stress is conventionally expressed in terms of its effect: “the effective stress” defined as the consequent elastic...... strain multiplied by the rock frame modulus. We cannot measure the strain directly in the subsurface, but from the data on bulk density and P‐wave velocity, we can estimate the rock frame modulus and Biot's coefficient and then calculate the “effective vertical stress” as the total vertical stress minus...... the product of pore pressure and Biot's coefficient. We can now calculate the elastic strain by dividing “effective stress” with the rock frame modulus. By this procedure, the degree of elastic deformation at a given time and depth can be directly expressed. This facilitates the discussion of the deformation...

Stress and strain patterns, kinematics and deformation mechanisms in a basement-cored anticline: Sheep Mountain Anticline, Wyoming

Science.gov (United States)

Amrouch, Khalid; Lacombe, Olivier; Bellahsen, Nicolas; Daniel, Jean-Marc; Callot, Jean-Paul

2010-02-01

In order to characterize and compare the stress-strain record prior to, during, and just after folding at the macroscopic and the microscopic scales and to provide insights into stress levels sustained by folded rocks, we investigate the relationship between the stress-strain distribution in folded strata derived from fractures, striated microfaults, and calcite twins and the development of the Laramide, basement-cored Sheep Mountain Anticline, Wyoming. Tectonic data were mainly collected in Lower Carboniferous to Permian carbonates and sandstones. In both rock matrix and veins, calcite twins recorded three different tectonic stages: the first stage is a pre-Laramide (Sevier) layer-parallel shortening (LPS) parallel to fold axis, the second one is a Laramide LPS perpendicular to the fold axis, and the third stage corresponds to Laramide late fold tightening with compression also perpendicular to the fold axis. Stress and strain orientations and regimes at the microscale agree with the polyphase stress evolution revealed by populations of fractures and striated microfaults, testifying for the homogeneity of stress record at different scales through time. Calcite twin analysis additionally reveals significant variations of differential stress magnitudes between fold limbs. Our results especially point to an increase of differential stress magnitudes related to Laramide LPS from the backlimb to the forelimb of the fold possibly in relation with motion of an underlying basement thrust fault that likely induced stress concentrations at its upper tip. This result is confirmed by a simple numerical model. Beyond regional implications, this study highlights the potential of calcite twin analyses to yield a representative quantitative picture of stress and strain patterns related to folding.

Normal and Fibrotic Rat Livers Demonstrate Shear Strain Softening and Compression Stiffening: A Model for Soft Tissue Mechanics.

Directory of Open Access Journals (Sweden)

Maryna Perepelyuk

Full Text Available Tissues including liver stiffen and acquire more extracellular matrix with fibrosis. The relationship between matrix content and stiffness, however, is non-linear, and stiffness is only one component of tissue mechanics. The mechanical response of tissues such as liver to physiological stresses is not well described, and models of tissue mechanics are limited. To better understand the mechanics of the normal and fibrotic rat liver, we carried out a series of studies using parallel plate rheometry, measuring the response to compressive, extensional, and shear strains. We found that the shear storage and loss moduli G' and G" and the apparent Young's moduli measured by uniaxial strain orthogonal to the shear direction increased markedly with both progressive fibrosis and increasing compression, that livers shear strain softened, and that significant increases in shear modulus with compressional stress occurred within a range consistent with increased sinusoidal pressures in liver disease. Proteoglycan content and integrin-matrix interactions were significant determinants of liver mechanics, particularly in compression. We propose a new non-linear constitutive model of the liver. A key feature of this model is that, while it assumes overall liver incompressibility, it takes into account water flow and solid phase compressibility. In sum, we report a detailed study of non-linear liver mechanics under physiological strains in the normal state, early fibrosis, and late fibrosis. We propose a constitutive model that captures compression stiffening, tension softening, and shear softening, and can be understood in terms of the cellular and matrix components of the liver.

The relationships among work stress, strain and self-reported errors in UK community pharmacy.

Science.gov (United States)

Johnson, S J; O'Connor, E M; Jacobs, S; Hassell, K; Ashcroft, D M

2014-01-01

Changes in the UK community pharmacy profession including new contractual frameworks, expansion of services, and increasing levels of workload have prompted concerns about rising levels of workplace stress and overload. This has implications for pharmacist health and well-being and the occurrence of errors that pose a risk to patient safety. Despite these concerns being voiced in the profession, few studies have explored work stress in the community pharmacy context. To investigate work-related stress among UK community pharmacists and to explore its relationships with pharmacists' psychological and physical well-being, and the occurrence of self-reported dispensing errors and detection of prescribing errors. A cross-sectional postal survey of a random sample of practicing community pharmacists (n = 903) used ASSET (A Shortened Stress Evaluation Tool) and questions relating to self-reported involvement in errors. Stress data were compared to general working population norms, and regressed on well-being and self-reported errors. Analysis of the data revealed that pharmacists reported significantly higher levels of workplace stressors than the general working population, with concerns about work-life balance, the nature of the job, and work relationships being the most influential on health and well-being. Despite this, pharmacists were not found to report worse health than the general working population. Self-reported error involvement was linked to both high dispensing volume and being troubled by perceived overload (dispensing errors), and resources and communication (detection of prescribing errors). This study contributes to the literature by benchmarking community pharmacists' health and well-being, and investigating sources of stress using a quantitative approach. A further important contribution to the literature is the identification of a quantitative link between high workload and self-reported dispensing errors. Copyright © 2014 Elsevier Inc. All rights

Mechanism of Strain Rate Effect Based on Dislocation Theory

International Nuclear Information System (INIS)

Kun, Qin; Shi-Sheng, Hu; Li-Ming, Yang

2009-01-01

Based on dislocation theory, we investigate the mechanism of strain rate effect. Strain rate effect and dislocation motion are bridged by Orowan's relationship, and the stress dependence of dislocation velocity is considered as the dynamics relationship of dislocation motion. The mechanism of strain rate effect is then investigated qualitatively by using these two relationships although the kinematics relationship of dislocation motion is absent due to complicated styles of dislocation motion. The process of strain rate effect is interpreted and some details of strain rate effect are adequately discussed. The present analyses agree with the existing experimental results. Based on the analyses, we propose that strain rate criteria rather than stress criteria should be satisfied when a metal is fully yielded at a given strain rate. (condensed matter: structure, mechanical and thermal properties)

Effect of Pre-strain and High Stresses on the Bainitic Transformation of Manganese-boron Steel 22MnB5

Science.gov (United States)

Said Schicchi, Diego; Hunkel, Martin

2018-06-01

During the last decade, the use of press-hardened components in the automotive industry has grown considerably. The so-called tailored tempering, also known as partial press hardening, employs locally heated tools seeking to obtain bainitic transformations. This leads to (seamless) zones within the formed parts with higher ductility. Due to the intrinsic nature of this process, phase transformations happen under the influence of high loads and in pre-deformed austenite. The austenite pre-strain state and applied stresses affect the kinetics of the bainitic transformation. Moreover, stresses have an additional relevant effect in this process, the so-called transformation plasticity. Linear transformation plasticity models have been successfully used to predict the behavior in the presence of low stresses. Nonetheless, because of the process's severe conditions, these tend to fail. A strong nonlinearity of the transformation plasticity strain is observed for applied stresses above the austenite yield strength. Using thermomechanical tests on sheet specimens of a manganese-boron steel (22MnB5), widely utilized in the industry, the effect on the bainitic transformation of various degrees of deformation in the range of 0 to 18 pct, applied stresses in the range of 0 to 250 MPa and the transformation plasticity effect are investigated in this work.

Effects of nonlinear rheology, temperature and anisotropy on the relationship between age and depth at ice divides

Directory of Open Access Journals (Sweden)

C. Martín

2012-10-01

Full Text Available Ice flow in divide areas is strongly anisotropic. The evolution of ice fabric, from the onset of divide flow towards steady state with a fully developed fabric, has been shown to profoundly affect both the stratigraphy and surface topography of ice divides. Here, we investigate the effects of ice flow on the age-versus-depth relationship at ice divides by using a full Stokes thermomechanical model with a non-linear anisotropic constitutive relation between stress and strain rates. We compare our results with analytical approximations commonly employed in age–depth predictions, such as the Dansgaard and Lliboutry approximations. We show that these approximations systematically underestimate the age of ice at fully developed divides by as much as one order of magnitude. We also show that divides with fully developed fabric are ideal locations for ice-core extraction because ice under them can be up to one order of magnitude older than ice at the same depth at the flanks. In addition, these divides have a distinctive morphological structure that allows them to be clearly identified from satellite imagery or ground-penetrating radar data.

Material Properties Test to Determine Ultimate Strain and True Stress-True Strain Curves for High Yield Steels

Energy Technology Data Exchange (ETDEWEB)

K.R. Arpin; T.F. Trimble

2003-04-01

This testing was undertaken to develop material true stress-true strain curves for elastic-plastic material behavior for use in performing transient analysis. Based on the conclusions of this test, the true stress-true strain curves derived herein are valid for use in elastic-plastic finite element analysis for structures fabricated from these materials. In addition, for the materials tested herein, the ultimate strain values are greater than those values cited as the limits for the elastic-plastic strain acceptance criteria for transient analysis.

Instantaneous strain measurements during high-temperature stress cycling of a dispersion-strengthened niobium alloy

International Nuclear Information System (INIS)

Farkas, D.M.; Mishra, R.S.; Mukherjee, A.K.

1995-01-01

Experimental results obtained from stress cycling tests performed during high-temperature creep of a dispersion strengthened niobium alloy indicate that the instantaneous strain following the stress change decreases with accumulated strain. The true work-hardening rate was shown to be a small fraction of the elastic modulus which remained fairly constant throughout the strain history. The instantaneous strain change from a stress addition was typically greater than the strain from the corresponding stress reduction. This effect is quite pronounced for small stress changes and diminishes as the magnitude of the stress change increases. This implies that the mobility of dislocations is impeded in the reverse direction unless the magnitude of stress reduction exceeds the value of the internal stress

Stress-Softening and Residual Strain Effects in Suture Materials

Directory of Open Access Journals (Sweden)

Alex Elías-Zúñiga

2013-01-01

Full Text Available This work focuses on the experimental characterization of suture material samples of MonoPlus, Monosyn, polyglycolic acid, polydioxanone 2–0, polydioxanone 4–0, poly(glycolide-co-epsilon-caprolactone, nylon, and polypropylene when subjected to cyclic loading and unloading conditions. It is found that all tested suture materials exhibit stress-softening and residual strain effects related to the microstructural material damage upon deformation from the natural, undistorted state of the virgin suture material. To predict experimental observations, a new constitutive material model that takes into account stress-softening and residual strain effects is developed. The basis of this model is the inclusion of a phenomenological nonmonotonous softening function that depends on the strain intensity between loading and unloading cycles. The theory is illustrated by modifying the non-Gaussian average-stretch, full-network model to capture stress-softening and residual strains by using pseudoelasticity concepts. It is shown that results obtained from theoretical simulations compare well with suture material experimental data.

[Appraisal of occupational stress and strain in primary and secondary school teachers].

Science.gov (United States)

Wang, Z; Lan, Y; Li, J; Wang, M

2001-09-01

This study was conducted to assess occupational stress and strain in primary and secondary school teachers. A test of occupational stress and strain was carried out by using Occupational Stress Inventory Revised Edition (OSI-R) in 1460 primary and secondary school teachers (teacher group) and 319 mental workers in non-educational area (non-teacher group as control). The results showed the level of occupational stress in role overload and physical environment in the teacher group was significantly higher than that in the non-teacher group (P < 0.05). In teacher group the level of occupational stress and strain increased with age; the occupational stress and strain in male teachers were significantly higher than those in female teachers (P < 0.01); the occupational stress and strain in secondary school teachers were significantly higher than those in primary school teachers. These results indicate: to protect and promote primary and secondary school teacher's health, particularly male teachers' health, to mitigate their work pressure and to raise the quality of education are important tasks in the area of occupational health.

Study of Post-Peak Strain Softening Mechanical Behaviour of Rock Material Based on Hoek–Brown Criterion

OpenAIRE

Qibin Lin; Ping Cao; Peixin Wang

2018-01-01

In order to build the post-peak strain softening model of rock, the evolution laws of rock parameters m,s were obtained by using the evolutionary mode of piecewise linear function regarding the maximum principle stress. Based on the nonlinear Hoek–Brown criterion, the analytical relationship of the rock strength parameters m,s, cohesion c, and friction angle φ has been developed by theoretical derivation. According to the analysis on the four different types of rock, it is found that, within ...

EXPERIMENTAL AND THEORETICAL STUDIES OF THE STRESS-STRAIN STATE OF WOOD-CONCRETE AND WOOD-GYPSUM MASONRY

Directory of Open Access Journals (Sweden)

Likhacheva Svetlana Yur'evna

2012-12-01

The findings of the prototype testing include identification of the two areas of deformations: areas of elastic deformations and areas of intensive development of deformations. The first area of partial elastic deformations is characterized by the linear stress function, while the second area demonstrates that this relationship is nonlinear. Permanent deformations appear as of the startup of the loading process and disproportionate stress is demonstrated throughout the deformation process. However, in the first area (partial elastic deformations residual deformations are so small that this area is considered as the area of "the area of incomplete elasticity".

Local stress modification during in situ transmission electron microscopy straining experiments

Czech Academy of Sciences Publication Activity Database

Zárubová, Niva; Gemperle, Antonín; Gemperlová, Juliana

2007-01-01

Roč. 462, - (2007), s. 407-411 ISSN 0921-5093 R&D Projects: GA ČR GA202/04/2016 Institutional research plan: CEZ:AV0Z10100520 Keywords : in situ TEM straining, Local stress in a strained foil * local stress in a strained foil Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.457, year: 2007

Triaxial Wetting Test on Rockfill Materials under Stress Combination Conditions of Spherical Stress p and Deviatoric Stress q

Directory of Open Access Journals (Sweden)

Yan-yi Zhang

2018-01-01

Full Text Available A GCTS medium-sized triaxial apparatus is used to conduct a single-line method wetting test on three kinds of rockfill materials of different mother rocks such as mixture of sandstone and slate, and dolomite and granite, and the test stress conditions is the combination of spherical stress p and deviatoric stress q. The test results show that (1 for wetting shear strain, the effects of spherical stress p and deviatoric stress q are equivalent, and wetting shear strain and deviatoric stress q show the power function relationship preferably. (2 For wetting volumetric strain, the effect of deviatoric stress q can be neglected because it is extremely insignificant, and spherical stress p is the main influencing factor and shows the power function relationship preferably. (3 The wetting strains decrease significantly with the increase in initial water content and sample density generally, but the excessively high dry density will increase the wetting deformation. Also, the wetting strains will decrease with the increase in the saturated uniaxial compressive strength and average softening coefficient of the mother rock. Based on the test results, a wetting strain model is proposed for rockfill materials. The verification results indicate that the model satisfactorily reflects the development law of wetting deformation.

Construction of long-term isochronous stress-strain curves by a modeling of short-term creep curves for a Grade 9Cr-1Mo steel

International Nuclear Information System (INIS)

Kim, Woo-Gon; Yin, Song-Nan; Koo, Gyeong-Hoi

2009-01-01

This study dealt with the construction of long-term isochronous stress-strain curves (ISSC) by a modeling of short-term creep curves for a Grade 9Cr-1Mo steel (G91) which is a candidate material for structural applications in the next generation nuclear reactors as well as in fusion reactors. To do this, tensile material data used in the inelastic constitutive equations was obtained by tensile tests at 550degC. Creep curves were obtained by a series of creep tests with different stress levels of 300MPa to 220MPa at an identical controlled temperature of 550degC. On the basis of these experimental data, the creep curves were characterized by Garofalo's creep model. Three parameters of P 1 , P 2 and P 3 in Garofalo's model were properly optimized by a nonlinear least square fitting (NLSF) analysis. The stress dependency of the three parameters was found to be a linear relationship. But, the P 3 parameter representing the steady state creep rate exhibited a two slope behavior with different stress exponents at a transient stress of about 250 MPa. The long-term creep curves of the G91 steel was modeled by Garofalo's model with only a few short-term creep data. Using the modeled creep curves, the long-term isochronous curves up to 10 5 hours were successfully constructed. (author)

The role of creep in stress strain curves for copper

International Nuclear Information System (INIS)

Sandström, Rolf; Hallgren, Josefin

2012-01-01

Highlights: ► A dislocation based model takes into account both dynamic and static recovery. ► Tests at constant load and at constant strain rate modelled without fitting parameters. ► The model can describe primary and secondary creep of Cu-OFP from 75 to 250 °C. ► The temperature and strain rate dependence of stress strain curves can be modelled. ► Intended for the slow strain rates in canisters for storage of nuclear waste. - Abstract: A model for plastic deformation in pure copper taking work hardening, dynamic recovery and static recovery into account, has been formulated using basic dislocation mechanisms. The model is intended to be used in finite-element computations of the long term behaviour of structures in Cu-OFP for storage of nuclear waste. The relation between the strain rate and the maximum flow stress in the model has been demonstrated to correspond to strain rate versus stress in creep tests for oxygen free copper alloyed with phosphorus Cu-OFP. A further development of the model can also represent the primary and secondary stage of creep curves. The model is compared to stress strain curves in compression and tension for Cu-OFP. The compression tests were performed at room temperature for strain rates between 5 × 10 −5 and 5 × 10 −3 s −1 . The tests in tension covered the temperature range 20–175 °C for strain rates between 1 × 10 −7 and 1 × 10 −4 s −1 . Consequently, it is demonstrated that the model can represent mechanical test data that have been generated both at constant load and at constant strain rate without the use of any fitting parameters.

Error estimation and adaptivity for incompressible hyperelasticity

KAUST Repository

Whiteley, J.P.; Tavener, S.J.

2014-01-01

SUMMARY: A Galerkin FEM is developed for nonlinear, incompressible (hyper) elasticity that takes account of nonlinearities in both the strain tensor and the relationship between the strain tensor and the stress tensor. By using suitably defined

PRINCIPAL STRESSES IN NON-LINEAR ANALYSIS OF BAKUN CONCRETE FACED ROCKFILL DAM

Directory of Open Access Journals (Sweden)

Mohd Hilton Ahmad

2017-11-01

Full Text Available With rapid population growth and accelerating economic development, much of the world’s WATER which requires urgent attention to ensure sustainable use. Nowadays, Concrete Faced Rockfill Dam (CFRD is preferred among dam consultant due to its advantages. They are designed to withstand all applied loads; namely gravity load due to its massive weight and hydrostatic load due to water thrust from the reservoir. Bakun CFRD, which ranks as the second highest CFRD in the world when completed, is analyzed to its safety due to both loads mentioned earlier by using Finite Element Method. 2-D plane strain finite element analysis of non-linear Duncan-Chang hyperbolic Model which formulated by Duncan and Chang is used to study the structural response of the dam in respect to the deformation and stresses of Main dam of Bakun’s CFRD project. Dead-Birth-Ghost element technique was used to simulate sequences of construction of the dam as well as during reservoir fillings. The comparison of rigid and flexible foundation on the behaviour of the dam was discussed. The maximum and minimum principal stresses are the maximum and minimum possible values of the normal stresses. The maximum principal stress controls brittle fracture. In the finite element modeling the concrete slab on the upstream was represented through six-noded element, while the interface characteristic between dam body and concrete slab was modeled using interface element. The maximum settlement and stresses of the cross section was founded and the distribution of them were discussed and tabulated in form of contours.

Modeling of stress-strain diagram on the basis of magnetic measurements

International Nuclear Information System (INIS)

Gorkunov, Eh.S.; Fedotov, V.P.; Bukhvalov, A.B.; Veselov, I.N.

1997-01-01

The model of a stress-strain diagram with taking into account the strain hardening and the growth of metal damageing is proposed. The model is applied to calculate a stress-strain curve for continuous cast 45 steel using the results of magnetic properties measuring. The latter permits predicting the durability of construction elements with the use of nondestructive magnetic testing

Stress markers in relation to job strain in human service organizations.

Science.gov (United States)

Ohlson, C G; Söderfeldt, M; Söderfeldt, B; Jones, I; Theorell, T

2001-01-01

Workers in human service organizations are often confronted with conflicting demands in providing care or education. The aim of this cross-sectional study was to relate levels of endocrine stress markers to perceived job strain in two human service organizations. Employees in two local units of the social insurance organization and two local units of the individual and family care sections of the social welfare in Sweden were selected and 103 employees participated (56% participation rate). The perceived job strain was assessed with a standardized questionnaire containing questions of the demand-control model. Questions specially designed to measure emotional demands were also included. The stress markers cortisol, prolactin, thyroid-stimulating hormone, testosterone and IgA and IgG were analysed in blood samples. The main finding was an association between high emotional strain and increased levels of prolactin. The levels of cortisol, but none of the other four stress markers, increased slightly with emotional strain. Emotional strain experienced in human service work may cause psychological stress. The increase in prolactin was modest but consistent with findings in other published studies on stress-related endocrine alterations. Copyright 2001 S. Karger AG, Basel.

Resistance of functional Lactobacillus plantarum strains against food stress conditions.

Science.gov (United States)

Ferrando, Verónica; Quiberoni, Andrea; Reinhemer, Jorge; Suárez, Viviana

2015-06-01

The survival of three Lactobacillus plantarum strains (Lp 790, Lp 813 and Lp 998) with functional properties was studied taking into account their resistance to thermal, osmotic and oxidative stress factors. Stress treatments applied were: 52 °C-15 min (Phosphate Buffer pH 7, thermal shock), H2O2 0.1% (p/v) - 30 min (oxidative shock) and NaCl aqueous solution at 17, 25 and 30% (p/v) (room temperature - 1 h, osmotic shock). The osmotic stress was also evaluated on cell growth in MRS broth added of 2, 4, 6, 8 and 10% (p/v) of NaCl, during 20 h at 30 °C. The cell thermal adaptation was performed in MRS broth, selecting 45 °C for 30 min as final conditions for all strains. Two strains (Lp 813 and Lp 998) showed, in general, similar behaviour against the three stress factors, being clearly more resistant than Lp 790. An evident difference in growth kinetics in presence of NaCl was observed between Lp 998 and Lp 813, Lp998 showing a higher optical density (OD570nm) than Lp 813 at the end of the assay. Selected thermal adaptation improved by 2 log orders the thermal resistance of both strains, but cell growth in presence of NaCl was enhanced only in Lp 813. Oxidative resistance was not affected with this thermal pre-treatment. These results demonstrate the relevance of cell technological resistance when selecting presumptive "probiotic" cultures, since different stress factors might considerably affect viability or/and performance of the strains. The incidence of stress conditions on functional properties of the strains used in this work are currently under research in our group. Copyright © 2014 Elsevier Ltd. All rights reserved.

Resonant Column Tests and Nonlinear Elasticity in Simulated Rocks

Science.gov (United States)

Sebastian, Resmi; Sitharam, T. G.

2018-01-01

Rocks are generally regarded as linearly elastic even though the manifestations of nonlinearity are prominent. The variations of elastic constants with varying strain levels and stress conditions, disagreement between static and dynamic moduli, etc., are some of the examples of nonlinear elasticity in rocks. The grain-to-grain contact, presence of pores and joints along with other compliant features induce the nonlinear behavior in rocks. The nonlinear elastic behavior of rocks is demonstrated through resonant column tests and numerical simulations in this paper. Resonant column tests on intact and jointed gypsum samples across varying strain levels have been performed in laboratory and using numerical simulations. The paper shows the application of resonant column apparatus to obtain the wave velocities of stiff samples at various strain levels under long wavelength condition, after performing checks and incorporating corrections to the obtained resonant frequencies. The numerical simulation and validation of the resonant column tests using distinct element method are presented. The stiffness reductions of testing samples under torsional and flexural vibrations with increasing strain levels have been analyzed. The nonlinear elastic behavior of rocks is reflected in the results, which is enhanced by the presence of joints. The significance of joint orientation and influence of joint spacing during wave propagation have also been assessed and presented using the numerical simulations. It has been found that rock joints also exhibit nonlinear behavior within the elastic limit.

Simulation of tensile stress-strain properties of irradiated type 316 SS by heavily cold-worked material

International Nuclear Information System (INIS)

Muto, Yasushi; Jitsukawa, Shiro; Hishinuma, Akimichi

1995-07-01

Type 316 stainless steel is one of the most promising candidate materials to be used for the structural parts of plasma facing components in the nuclear fusion reactor. The neutron irradiation make the material brittle and reduces its uniform elongation to almost zero at heavy doses. In order to apply such a material of reduced ductility to structural components, the structural integrity should be examined and assured by the fracture mechanics. The procedure requires a formulated stress-strain relationship. However, the available irradiated tensile test data are very limited at present, so that the cold-worked material was used as a simulated material in this study. Property changes of 316 SS, that is, a reduction of uniform elongation and an enhancement of yield stress are seemingly very similar for both the irradiated 316 SS and the cold-worked one. The specimens made of annealed 316 SS, 20% (or 15%) cold worked one and 40% cold worked one were prepared. After the formulation of stress strain behavior, the equation for the cold-worked 316 SS was fitted to the data on irradiated material under the assumption that the yield stress is the same for both materials. In addition, the upper limit for the plastic strain was introduced using the data on the irradiated material. (author)

Nonlinear constitutive relations for anisotropic elastic materials

Science.gov (United States)

Sokolova, Marina; Khristich, Dmitrii

2018-03-01

A general approach to constructing of nonlinear variants of connection between stresses and strains in anisotropic materials with different types of symmetry of properties is considered. This approach is based on the concept of elastic proper subspaces of anisotropic materials introduced in the mechanics of solids by J. Rychlewski and on the particular postulate of isotropy proposed by A. A. Il’yushin. The generalization of the particular postulate on the case of nonlinear anisotropic materials is formulated. Systems of invariants of deformations as lengths of projections of the strain vector into proper subspaces are developed. Some variants of nonlinear constitutive relations for anisotropic materials are offered. The analysis of these relations from the point of view of their satisfaction to general and limit forms of generalization of partial isotropy postulate on anisotropic materials is performed. The relations for particular cases of anisotropy are written.

A finite element model for nonlinear shells of revolution

International Nuclear Information System (INIS)

Cook, W.A.

1979-01-01

A shell-of-revolution model was developed to analyze impact problems associated with the safety analysis of nuclear material shipping containers. The nonlinear shell theory presented by Eric Reissner in 1972 was used to develop our model. Reissner's approach includes transverse shear deformation and moments turning about the middle surface normal. With these features, this approach is valid for both thin and thick shells. His theory is formulated in terms of strain and stress resultants that refer to the undeformed geometry. This nonlinear shell model is developed using the virtual work principle associated with Reissner's equilibrium equations. First, the virtual work principle is modified for incremental loading; then it is linearized by assuming that the nonlinear portions of the strains are known. By iteration, equilibrium is then approximated for each increment. A benefit of this approach is that this iteration process makes it possible to use nonlinear material properties. (orig.)

Computer modeling of the stress-strain state of welded construction

Science.gov (United States)

Nurguzhin, Marat; Danenova, Gulmira; Akhmetzhanov, Talgat

2017-11-01

At the present time the maintenance of the welded construction serviceability over normative service life is provided by the maintenance system on the basis of the guiding documents according to the concept of "fail safe". However, technology factors relating to welding such as high residual stresses and significant plastic strains are not considered in the guiding documents. The design procedure of the stressed-strained state of welded constructions is suggested in the paper. The procedure investigates welded constructions during welding and the external load using the program ANSYS. In this paper, the model of influence of the residual stress strain state on the factor of stress intensity is proposed. The calculation method of the residual stressed-strained state (SSS) taking into account the phase transition is developed by the authors. Melting and hardening of a plate material during heating and cooling is considered. The thermomechanical problem of heating a plate by a stationary heat source is solved. The setup of the heating spot center on distance (190 mm) from the crack top in a direction of its propagation leads to the fact that the value of total factor of stress intensity will considerably decrease under action of the specified residual compressing stresses. It can lower the speed of the crack propagation to zero. The suggested method of survivability maintenance can be applied during operation with the purpose of increasing the service life of metal constructions up to running repair of technological machines.

Mechanical stresses and strains in superconducting dipole magnets for high energy accelerators

International Nuclear Information System (INIS)

Greben, L.I.; Mironov, E.S.; Moustafin, H.H.

1979-01-01

Stress and strain distributions in superconducting dipole magnets were investigated numerically. A finite element computer program was developed to calculate stresses and displacements due to thermal stress, electromagnetic forces and prestressing of structural elements. Real mechanical and thermal properties of superconducting dipole elements are taken into account. Numerical results of stress and strain patterns in dipole magnets are presented

Inverse strain rate effect on cyclic stress response in annealed Zircaloy-2

Energy Technology Data Exchange (ETDEWEB)

Sudhakar Rao, G.; Verma, Preeti [Center of Advanced Study, Department of Metallurgical Engineering, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005 (India); Chakravartty, J.K. [Mechanical Metallurgy Group, Bhabha Atomic Research Center, Trombay 400 085, Mumbai (India); Nudurupati, Saibaba [Nuclear Fuel Complex, Hyderabad 500 062 (India); Mahobia, G.S.; Santhi Srinivas, N.C. [Center of Advanced Study, Department of Metallurgical Engineering, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005 (India); Singh, Vakil, E-mail: vsingh.met@itbhu.ac.in [Center of Advanced Study, Department of Metallurgical Engineering, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005 (India)

2015-02-15

Low cycle fatigue behavior of annealed Zircaloy-2 was investigated at 300 and 400 °C at different strain amplitudes and strain rates of 10{sup −2}, 10{sup −3}, and 10{sup −4} s{sup −1}. Cyclic stress response showed initial hardening with decreasing rate of hardening, followed by linear cyclic hardening and finally secondary hardening with increasing rate of hardening for low strain amplitudes at both the temperatures. The rate as well the degree of linear hardening and secondary hardening decreased with decrease in strain rate at 300 °C, however, there was inverse effect of strain rate on cyclic stress response at 400 °C and cyclic stress was increased with decrease in strain rate. The fatigue life decreased with decrease in strain rate at both the temperatures. The occurrence of linear cyclic hardening, inverse effect of strain rate on cyclic stress response and deterioration in fatigue life with decrease in strain rate may be attributed to dynamic strain aging phenomena resulting from enhanced interaction of dislocations with solutes. Fracture surfaces revealed distinct striations, secondary cracking, and oxidation with decrease in strain rate. Deformation substructure showed parallel dislocation lines and dislocation band structure at 300 °C. Persistent slip band wall structure and development of fine Corduroy structure was observed at 400 °C.

Inverse strain rate effect on cyclic stress response in annealed Zircaloy-2

International Nuclear Information System (INIS)

Sudhakar Rao, G.; Verma, Preeti; Chakravartty, J.K.; Nudurupati, Saibaba; Mahobia, G.S.; Santhi Srinivas, N.C.; Singh, Vakil

2015-01-01

Low cycle fatigue behavior of annealed Zircaloy-2 was investigated at 300 and 400 °C at different strain amplitudes and strain rates of 10 −2 , 10 −3 , and 10 −4 s −1 . Cyclic stress response showed initial hardening with decreasing rate of hardening, followed by linear cyclic hardening and finally secondary hardening with increasing rate of hardening for low strain amplitudes at both the temperatures. The rate as well the degree of linear hardening and secondary hardening decreased with decrease in strain rate at 300 °C, however, there was inverse effect of strain rate on cyclic stress response at 400 °C and cyclic stress was increased with decrease in strain rate. The fatigue life decreased with decrease in strain rate at both the temperatures. The occurrence of linear cyclic hardening, inverse effect of strain rate on cyclic stress response and deterioration in fatigue life with decrease in strain rate may be attributed to dynamic strain aging phenomena resulting from enhanced interaction of dislocations with solutes. Fracture surfaces revealed distinct striations, secondary cracking, and oxidation with decrease in strain rate. Deformation substructure showed parallel dislocation lines and dislocation band structure at 300 °C. Persistent slip band wall structure and development of fine Corduroy structure was observed at 400 °C

X-ray study of residual stress distribution of ground ceramics

International Nuclear Information System (INIS)

Sakaida, Yoshihisa; Tanaka, Keisuke; Ikuhara, Yuichi; Suzuki, Kenzi.

1997-01-01

The residual stress distribution of ground ceramics was determined from the eigen strain existing in the ground surface. The eigen strain of ground ceramics was tensile, and exponentially decreased with the distance from the surface. The residual stress distribution is given as a superposition of an exponential function of compression and a linear function. It is found that the actual residual stress distribution can be approximated by a compressive exponential function because the magnitude of tensile residual stress is negligibly small compared to the compressive residual stress. In the experiments, the diffraction angle was measured on ground silicon nitride for a wide range of sin 2 ψ using the glancing incidence X-ray diffraction technique. A strong nonlinearity was found in the 2θ-sin 2 ψ diagram at very high ψ-angles. From the analysis of nonlinearity, the residual stress distribution was determined. The residual stress distribution of silicon nitride coincided with the distribution calculated from the eigen strain distribution. Transmission electron microscopy was used to clarify the origin of generation of the residual stress. Both strain contrasts and microcracks were observed below the ground surface ; straight dislocations were also observed within silicon nitride grains near the ground surface. (author)

Approximate methods and working rules for peak stress effects

International Nuclear Information System (INIS)

Jobson, D.A.

1983-01-01

In order to assess stress concentration effects and associated strain intensification at notches, Neuber's work on this subject is used frequently. Neuber refers to a particular nonlinear stress-strain relation which, he observed, led to the same deferential equation for the lateral displacements as that found by Chaplygin for the velocity potential of compressible flow. for a linearized adiabatic law. This finding has been examined by studying torsion problems, which Involve warping displacements. Although a deformation law of the type τ(γ) has been assumed, the shear strain components remain 'proportional' to the corresponding stress components for problems of the type considered. It has been found that the governing equations and boundary conditions for φ may be made completely analogous to those for the velocity potential of a corresponding compressible flow in a prismatic cylinder of the same shape as that of the solid bar, provided that the constitutive equation. for the solid and the gas correspond in a defined sense. This embodied Neuber's observation, which was restricted to a particular stress strain law, namely that which corresponded to a linear adiabatic gas relationship. The above finding also assimilates a well-known hydrodynamic analogy, to which it reduces for linearly elastic materials. Corresponding governing equations have further been established for the stress function and these have similarly been related to those for an analogous stream function, defined by reference to the flow density of the corresponding compressible fluid

Relating high-temperature flow stress of AISI 316 stainless steel to strain and strain rate

International Nuclear Information System (INIS)

Matteazzi, S.; Paitti, G.; Boerman, D.

1982-01-01

The authors have performed an experimental determination of tensile stress-strain curves for different strain rates (4.67 x 10 - 5 , 4.67 x 10 - 2 s - 1 ) and for a variety of temperature conditions (773-1073 K) of AISI 316H stainless steel (annealed conditions) and also a computer analysis of the experimental curves using a fitting program which takes into consideration different constitutive relations describing the plastic flow behaviour of the metals. The results show that the materials tested are clearly affected by strain rate only at the highest temperature investigated (1073 K) and that the plastic strain is the more significant variable. Of the constitutive equations considered, Voce's relation gives the best fit for the true stress-time-strain curves. However, the Ludwik and Ludwigson equations also provide a description of the experimental data, whereas Hollomon's equation does not suitably characterize AISI 316H stainless steel and can be applied with some accuracy only at 1073 K. (author)

Work-family conflict as a mediator of the work stress - mental health relationship

OpenAIRE

Poelmans, Steven

2001-01-01

The relationship between work stressors and mental health outcomes has been demonstrated in a whole range of work stress models and studies. But less has been written about factors outside the work setting that might predict or moderate the relationship between work stressors and strain. In this exploratory study, we suggest a model linking work stressors and "time-based" work-family conflict (TWFC) with mental health, with the intention to contribute to the refinement of the traditional work...

Annealing effects on strain and stress sensitivity of polymer optical fibre based sensors

DEFF Research Database (Denmark)

Pospori, A.; Marques, C. A. F.; Zubel, M. G.

2016-01-01

The annealing effects on strain and stress sensitivity of polymer optical fibre Bragg grating sensors after their photoinscription are investigated. PMMA optical fibre based Bragg grating sensors are first photo-inscribed and then they were placed into hot water for annealing. Strain, stress...... fibre tends to increase the strain, stress and force sensitivity of the photo-inscribed sensor....

Ethnic variations in the relationship between multiple stress domains and use of several types of tobacco/nicotine products among a diverse sample of adults

Directory of Open Access Journals (Sweden)

Christopher J. Rogers

2018-06-01

Full Text Available Introduction: Financial strain and discrimination are consistent predictors of negative health outcomes and maladaptive coping behaviors, including tobacco use. Although there is considerable information exploring stress and smoking, limited research has examined the relationship between patterns of stress domains and specific tobacco/nicotine product use. Even fewer studies have assessed ethnic variations in these relationships. Methods: This study investigated the relationship between discrimination and financial strain and current tobacco/nicotine product use and explored the ethnic variation in these relationships among diverse sample of US adults (N = 1068. Separate logistic regression models assessed associations between stress domains and tobacco/nicotine product use, adjusting for covariates (e.g., age, gender, race/ethnicity, and household income. Due to statistically significant differences, the final set of models was stratified by race/ethnicity. Results: Higher levels of discrimination were associated with higher odds of all three tobacco/nicotine product categories. Financial strain was positively associated with combustible tobacco and combined tobacco/nicotine product use. Financial strain was especially risky for Non-Hispanic Whites (AOR:1.191, 95%CI:1.083–1.309 and Blacks/African Americans (AOR:1.542, 95%CI:1.106–2.148, as compared to other groups, whereas discrimination was most detrimental for Asians/Pacific Islanders (AOR:3.827, 95%CI:1.832–7.997 and Hispanics/Latinas/Latinos (AOR:2.517, 95%CI:1.603–3.952. Conclusions: Findings suggest discrimination and financial stressors are risk factors for use of multiple tobacco/nicotine products, highlighting the importance of prevention research that accounts for these stressors. Because ethnic groups may respond differently to stress/strain, prevention research needs to identify cultural values, beliefs, and coping strategies that can buffer the negative consequences of

Nonlinear Heart Rate Variability features for real-life stress detection. Case study: students under stress due to university examination.

Science.gov (United States)

Melillo, Paolo; Bracale, Marcello; Pecchia, Leandro

2011-11-07

This study investigates the variations of Heart Rate Variability (HRV) due to a real-life stressor and proposes a classifier based on nonlinear features of HRV for automatic stress detection. 42 students volunteered to participate to the study about HRV and stress. For each student, two recordings were performed: one during an on-going university examination, assumed as a real-life stressor, and one after holidays. Nonlinear analysis of HRV was performed by using Poincaré Plot, Approximate Entropy, Correlation dimension, Detrended Fluctuation Analysis, Recurrence Plot. For statistical comparison, we adopted the Wilcoxon Signed Rank test and for development of a classifier we adopted the Linear Discriminant Analysis (LDA). Almost all HRV features measuring heart rate complexity were significantly decreased in the stress session. LDA generated a simple classifier based on the two Poincaré Plot parameters and Approximate Entropy, which enables stress detection with a total classification accuracy, a sensitivity and a specificity rate of 90%, 86%, and 95% respectively. The results of the current study suggest that nonlinear HRV analysis using short term ECG recording could be effective in automatically detecting real-life stress condition, such as a university examination.

Microstructure and strain-stress analysis of the dynamic strain aging in inconel 625 at high temperature

Science.gov (United States)

Maj, P.; Zdunek, J.; Mizera, J.; Kurzydlowski, K. J.; Sakowicz, B.; Kaminski, M.

2017-01-01

Serrated flow is a result of unstable plastic flow, which occurs during tensile and compression tests on some dilute alloys. This phenomenon is referred as the Portevin Le-Chatelier effect (PLC effect). The aim of this research was to investigate and analyze this phenomenon in Inconel 625 solution strengthened superalloy. The tested material was subjected to tensile tests carried out within the temperature range 200-700 °C, with three different strain rates: 0.002 1/s, 0.01/s, and 0.05 1/s and additional compression tests with high deformation speeds of 0.1, 1, and 10 1/s. The tensile strain curves were analyzed in terms of intensity and the observed patterns of serrations Using a modified stress drop method proposed by the authors, the activation energy was calculated with the assumption that the stress drops' distribution is a direct representation of an average solute atom's interaction with dislocations. Subsequently, two models, the standard vacancy diffusion Bilby-Cottrell model and the realistic cross-core diffusion mechanism proposed by Zhang and Curtin, were compared. The results obtained show that the second one agrees with the experimental data. Additional microstructure analysis was performed to identify microstructure elements that may be responsible for the PLC effect. Based on the results, the relationship between the intensity of the phenomenon and the conditions of the tests were determined.

On Maximally Dissipative Shock Waves in Nonlinear Elasticity

OpenAIRE

Knowles, James K.

2010-01-01

Shock waves in nonlinearly elastic solids are, in general, dissipative. We study the following question: among all plane shock waves that can propagate with a given speed in a given one-dimensional nonlinearly elastic bar, which one—if any—maximizes the rate of dissipation? We find that the answer to this question depends strongly on the qualitative nature of the stress-strain relation characteristic of the given material. When maximally dissipative shocks do occur, they propagate according t...

The Non-Linear Relationship Between Fiscal Deficits And Inflation: Evidence From Africa

Directory of Open Access Journals (Sweden)

Abu Nurudeen

2015-12-01

Full Text Available Although, there is abundant research on the fiscal deficit-inflation relationship, little has been done to investigate the non-linear association between them, particularly in Africa. This study employs fixed-effects and GMM estimators to examine the non-linear relationship between deficits and inflation from 1999 to 2011 in 51 African economies, which are further grouped into high-inflation/low-income countries and moderate-inflation/middle-income countries. The results indicate that the deficit-inflation relationship is non-linear for the whole sample and sub-groups. For the whole sample, a percentage point increase in deficit results in a 0.25 percentage point increase in inflation rate, while the relationship becomes quantitatively greater once deficits reach 23% of GDP. The subsamples report different relationships. Although our results cannot be used as the base for generalization, we identify importance of grouping African countries according to their levels of inflation and/or income, rather than treating them as a homogeneous entity.

Linear and nonlinear characterization of low-stress high-confinement silicon-rich nitride waveguides.

Science.gov (United States)

Krückel, Clemens J; Fülöp, Attila; Klintberg, Thomas; Bengtsson, Jörgen; Andrekson, Peter A; Torres-Company, Víctor

2015-10-05

In this paper we introduce a low-stress silicon enriched nitride platform that has potential for nonlinear and highly integrated optics. The manufacturing process of this platform is CMOS compatible and the increased silicon content allows tensile stress reduction and crack free layer growth of 700 nm. Additional benefits of the silicon enriched nitride is a measured nonlinear Kerr coefficient n(2) of 1.4·10(-18) m(2)/W (5 times higher than stoichiometric silicon nitride) and a refractive index of 2.1 at 1550 nm that enables high optical field confinement allowing high intensity nonlinear optics and light guidance even with small bending radii. We analyze the waveguide loss (∼1 dB/cm) in a spectrally resolved fashion and include scattering loss simulations based on waveguide surface roughness measurements. Detailed simulations show the possibility for fine dispersion and nonlinear engineering. In nonlinear experiments we present continuous-wave wavelength conversion and demonstrate that the material does not show nonlinear absorption effects. Finally, we demonstrate microfabrication of resonators with high Q-factors (∼10(5)).

Biaxial Stress Tests of Plain Concrete

Energy Technology Data Exchange (ETDEWEB)

Lee, S.K.; Cho, M.S.; Song, Y.C. [Korea Electric Power Research Institute, Taejon (Korea)

2001-07-01

Containment concrete specimens(4000, 5000psi) were tested under biaxial stress and presented basic physical properties and biaxial failure envelops for the concrete specimens. Failure behaviors of concrete under biaxial stress were assessed with stress-strain responses and failure modes. Here provided real test data to develop nonlinear finite element concrete models. (author). 15 refs., 46 figs., 4 tabs.

The study of stress-strain state of stabilized layered soil foundations

Directory of Open Access Journals (Sweden)

Sokolov Mikhail V.

2017-01-01

Full Text Available Herein presented are the results of modeling and analysis of stress-strain state of layered inhomogeneous foundation soil when it is stabilised by injection to different depths. Produced qualitative and quantitative analysis of the components of the field of isolines of stresses, strains, stress concentration and the difference between the strain at the boundary of different elastic horizontal layers. Recommendations are given for the location of stabilised zones in relation to the border of different elastic layers. In particular, it found that stabilization of soil within the weak layer is inappropriate, since it practically provides no increase in the stability of the soil foundation, and when performing stabilisation of soil foundations, it is recommended to place the lower border of the stabilisation zone below the border of a stronger layer, at this the distribution of stresses and strains occurs more evenly, and load-bearing capacity of this layer is used to the maximum.

Nonlinear cosmological consistency relations and effective matter stresses

International Nuclear Information System (INIS)

Ballesteros, Guillermo; Hollenstein, Lukas; Jain, Rajeev Kumar; Kunz, Martin

2012-01-01

We propose a fully nonlinear framework to construct consistency relations for testing generic cosmological scenarios using the evolution of large scale structure. It is based on the covariant approach in combination with a frame that is purely given by the metric, the normal frame. As an example, we apply this framework to the ΛCDM model, by extending the usual first order conditions on the metric potentials to second order, where the two potentials start to differ from each other. We argue that working in the normal frame is not only a practical choice but also helps with the physical interpretation of nonlinear dynamics. In this frame, effective pressures and anisotropic stresses appear at second order in perturbation theory, even for ''pressureless'' dust. We quantify their effect and compare them, for illustration, to the pressure of a generic clustering dark energy fluid and the anisotropic stress in the DGP model. Besides, we also discuss the effect of a mismatch of the potentials on the determination of galaxy bias

Effects of strain rate, mixing ratio, and stress-strain definition on the mechanical behavior of the polydimethylsiloxane (PDMS) material as related to its biological applications.

Science.gov (United States)

Khanafer, Khalil; Duprey, Ambroise; Schlicht, Marty; Berguer, Ramon

2009-04-01

Tensile tests on Polydimethylsiloxane (PDMS) materials were conducted to illustrate the effects of mixing ratio, definition of the stress-strain curve, and the strain rate on the elastic modulus and stress-strain curve. PDMS specimens were prepared according to the ASTM standards for elastic materials. Our results indicate that the physiological elastic modulus depends strongly on the definition of the stress-strain curve, mixing ratio, and the strain rate. For various mixing ratios and strain rates, true stress-strain definition results in higher stress and elastic modulus compared with engineering stress-strain and true stress-engineering strain definitions. The elastic modulus increases as the mixing ratio increases up-to 9:1 ratio after which the elastic modulus begins to decrease even as the mixing ratio continues to increase. The results presented in this study will be helpful to assist the design of in vitro experiments to mimic blood flow in arteries and to understand the complex interaction between blood flow and the walls of arteries using PDMS elastomer.

Application of Nonlinear Elastic Resonance Spectroscopy For Damage Detection In Concrete: An Interesting Story

Energy Technology Data Exchange (ETDEWEB)

Byers, Loren W. [Los Alamos National Laboratory; Ten Cate, James A. [Los Alamos National Laboratory; Johnson, Paul A. [Los Alamos National Laboratory

2012-06-28

Nonlinear resonance ultrasound spectroscopy experiments conducted on concrete cores, one chemically and mechanically damaged by alkali-silica reactivity, and one undamaged, show that this material displays highly nonlinear wave behavior, similar to many other damaged materials. They find that the damaged sample responds more nonlinearly, manifested by a larger resonant peak and modulus shift as a function of strain amplitude. The nonlinear response indicates that there is a hysteretic influence in the stress-strain equation of state. Further, as in some other materials, slow dynamics are present. The nonlinear response they observe in concrete is an extremely sensitive indicator of damage. Ultimately, nonlinear wave methods applied to concrete may be used to guide mixing, curing, or other production techniques, in order to develop materials with particular desired qualities such as enhanced strength or chemical resistance, and to be used for damage inspection.

Time, stress, and temperature-dependent deformation in nanostructured copper: Stress relaxation tests and simulations

International Nuclear Information System (INIS)

Yang, Xu-Sheng; Wang, Yun-Jiang; Wang, Guo-Yong; Zhai, Hui-Ru; Dai, L.H.; Zhang, Tong-Yi

2016-01-01

In the present work, stress relaxation tests, high-resolution transmission electron microscopy (HRTEM), and molecular dynamics (MD) simulations were conducted on coarse-grained (cg), nanograined (ng), and nanotwinned (nt) copper at temperatures of 22 °C (RT), 30 °C, 40 °C, 50 °C, and 75 °C. The comprehensive investigations provide sufficient information for the building-up of a formula to describe the time, stress, and temperature-dependent deformation and clarify the relationship among the strain rate sensitivity parameter, stress exponent, and activation volume. The typically experimental curves of logarithmic plastic strain rate versus stress exhibited a three staged relaxation process from a linear high stress relaxation region to a subsequent nonlinear stress relaxation region and finally to a linear low stress relaxation region, which only showed-up at the test temperatures higher than 22 °C, 22 °C, and 30 °C, respectively, in the tested cg-, ng-, and nt-Cu specimens. The values of stress exponent, stress-independent activation energy, and activation volume were determined from the experimental data in the two linear regions. The determined activation parameters, HRTEM images, and MD simulations consistently suggest that dislocation-mediated plastic deformation is predominant in all tested cg-, ng-, and nt-Cu specimens in the initial linear high stress relaxation region at the five relaxation temperatures, whereas in the linear low stress relaxation region, the grain boundary (GB) diffusion-associated deformation is dominant in the ng- and cg-Cu specimens, while twin boundary (TB) migration, i.e., twinning and detwinning with parallel partial dislocations, governs the time, stress, and temperature-dependent deformation in the nt-Cu specimens.

Can an Internal Locus of Control and Social Support Reduce Work-Related Levels of Stress and Strain?: A Comparative Study Between Spanish Owners and Managers.

Science.gov (United States)

Ariza-Montes, Antonio; Leal-Rodríguez, Antonio L; Rodríguez-Félix, Lucía; Albort-Morant, Gema

2017-09-01

The aim of this article is to assess the role played by both individual and contextual factors in reducing the manager's levels of stress and strain within the workplace setting. This article also highlights the manager's locus of control (LOC) as an internal factor and emphasizes the social support variable as a contextual factor. We use a sample of 332 respondents belonging to Spanish manufacturing and services firms and a structural equation modeling technique (partial least squares path modeling). The results reveal that there are significant differences between managers and owners about stress-strain relationship. The study provides support for the literature on stress management, which emphasizes the importance of a LOC and social support in influencing stress and strain between managers and owners.

Linear analysis using secants for materials with temperature dependent nonlinear elastic modulus and thermal expansion properties

Science.gov (United States)

Pepi, John W.

2017-08-01

Thermally induced stress is readily calculated for linear elastic material properties using Hooke's law in which, for situations where expansion is constrained, stress is proportional to the product of the material elastic modulus and its thermal strain. When material behavior is nonlinear, one needs to make use of nonlinear theory. However, we can avoid that complexity in some situations. For situations in which both elastic modulus and coefficient of thermal expansion vary with temperature, solutions can be formulated using secant properties. A theoretical approach is thus presented to calculate stresses for nonlinear, neo-Hookean, materials. This is important for high acuity optical systems undergoing large temperature extremes.

Confidence bounds for nonlinear dose-response relationships

DEFF Research Database (Denmark)

Baayen, C; Hougaard, P

2015-01-01

An important aim of drug trials is to characterize the dose-response relationship of a new compound. Such a relationship can often be described by a parametric (nonlinear) function that is monotone in dose. If such a model is fitted, it is useful to know the uncertainty of the fitted curve...... intervals for the dose-response curve. These confidence bounds have better coverage than Wald intervals and are more precise and generally faster than bootstrap methods. Moreover, if monotonicity is assumed, the profile likelihood approach takes this automatically into account. The approach is illustrated...

Effect of nitrogen concentration and temperature on the critical resolved shear stress and strain rate sensitivity of vanadium

International Nuclear Information System (INIS)

Rehbein, D.K.

1980-08-01

The critical resolved shear stress and strain rate sensitivity were measured over the temperature range from 77 to 400 0 K for vanadium-nitrogen alloys containing from 0.0004 to 0.184 atom percent nitrogen. These properties were found to be strongly dependent on both the nitrogen concentration and temperature. The following observations were seen in this investigation: the overall behavior of the alloys for the temperature and concentration range studied follows a form similar to that predicted; the concentration dependence of the critical resolved shear stress after subtracting the hardening due to the pure vanadium lattice obeys Labusch's c/sup 2/3/ relationship above 200 0 K and Fleischer's c/sup 1/2/ relationship below 200 0 K; the theoretical predictions of Fleischer's model for the temperature dependence of the critical resolved shear stress are in marked disagreement with the behavior found; and the strain rate sensitivity, par. delta tau/par. deltaln γ, exhibits a peak at approximately 100 0 K that decreases in height as the nitrogen concentration increases. A similar peak has been observed in niobium by other investigators but the effect of concentration on the peak height is quite different

Nonlinear morphoelastic plates I: Genesis of residual stress

KAUST Repository

McMahon, J.

2011-04-28

Volumetric growth of an elastic body may give rise to residual stress. Here a rigorous analysis is given of the residual strains and stresses generated by growth in the axisymmetric Kirchhoff plate. Balance equations are derived via the Global Constraint Principle, growth is incorporated via a multiplicative decomposition of the deformation gradient, and the system is closed by a response function. The particular case of a compressible neo-Hookean material is analyzed, and the existence of residually stressed states is established. © SAGE Publications 2011.

Nonlinear morphoelastic plates I: Genesis of residual stress

KAUST Repository

McMahon, J.; Goriely, A.; Tabor, M.

2011-01-01

Volumetric growth of an elastic body may give rise to residual stress. Here a rigorous analysis is given of the residual strains and stresses generated by growth in the axisymmetric Kirchhoff plate. Balance equations are derived via the Global Constraint Principle, growth is incorporated via a multiplicative decomposition of the deformation gradient, and the system is closed by a response function. The particular case of a compressible neo-Hookean material is analyzed, and the existence of residually stressed states is established. © SAGE Publications 2011.

Nonequilibrium and Nonlinear Dynamics in Geomaterials I : The Low Strain Regime

OpenAIRE

Pasqualini, Donatella; Heitmann, Katrin; TenCate, James A.; Habib, Salman; Higdon, David; Johnson, Paul A.

2006-01-01

Members of a wide class of geomaterials are known to display complex and fascinating nonlinear and nonequilibrium dynamical behaviors over a wide range of bulk strains, down to surprisingly low values, e.g., 10^{-7}. In this paper we investigate two sandstones, Berea and Fontainebleau, and characterize their behavior under the influence of very small external forces via carefully controlled resonant bar experiments. By reducing environmental effects due to temperature and humidity variations,...

Nonlinear primary resonance of micro/nano-beams made of nanoporous biomaterials incorporating nonlocality and strain gradient size dependency

Science.gov (United States)

Sahmani, S.; Aghdam, M. M.

2018-03-01

A wide range of biological applications such as drug delivery, biosensors and hemodialysis can be provided by nanoporous biomaterials due to their uniform pore size as well as considerable pore density. In the current study, the size dependency in the nonlinear primary resonance of micro/nano-beams made of nanoporous biomaterials is anticipated. To accomplish this end, a refined truncated cube is introduced to model the lattice structure of nanoporous biomaterial. Accordingly, analytical expressions for the mechanical properties of material are derived as functions of pore size. After that, based upon a nonlocal strain gradient beam model, the size-dependent nonlinear Duffing type equation of motion is constructed. The Galerkin technique together with the multiple time-scales method is employed to obtain the nonlocal strain gradient frequency-response and amplitude-response related to the nonlinear primary resonance of a micro/nano-beam made of the nanoporous biomaterial with different pore sizes. It is indicated that the nonlocality causes to decrease the response amplitudes associated with the both bifurcation points of the jump phenomenon, while the strain gradient size dependency causes to increase them. Also, it is found that increasing the pore size leads to enhance the nonlinearity, so the maximum deflection of response occurs at higher excitation frequency.

Cyclic behavior of Ta at low temperatures under low stresses and strain rates

International Nuclear Information System (INIS)

Stickler, C.; Knabl, W.; Stickler, R.; Weiss, B.

2001-01-01

The cyclic stress-strain response of recrystallized technically pure Ta was investigated in the stress range well below the technical flow stress, for temperatures between 173 K and 423 K, at loading rates between 0.042 Mpa/s and 4.2 Mpa/s with resulting plastic strains between -5 up to 1X10 -2 . Cyclic hardening-softening curves were recorded in multiple step tests. Cyclic stress strain curves exhibit straight portions associated with microplastic, transition range and macroplastic deformation mechanisms. The microstructure of the deformed specimens was characterized by SEM and TEM techniques which revealed typical dislocation arrangements related to plastic strain amplitudes and test temperatures. A mechanism of the microstrain deformation of Ta is proposed. (author)

Effect of Nonlinear Hardening of Lead Rubber Bearing on Long Term Behavior of Base Isolated Containment Building

International Nuclear Information System (INIS)

Park, Junhee; Choun, Young-Sun; Kim, Min-Kyu

2015-01-01

The rubber material used in laminated rubber bearings is the hyper elastic material whose stress-strain relationship can be defined as nonlinearly elastic. From the previous research, it was presented that the rubber hardness and stiffness was increased by the aging of LRB. The mechanical properties of LRB changed by aging can directly affect a nonlinear hardening behavior. Therefore it is needed to consider the nonlinear hardening effect for exactly evaluating the seismic safety of base isolated structure during the life time. In this study, the seismic response analysis of base isolated containment building was performed by using the bilinear model and the hardening model to identify the effect of structural response on the nonlinear hardening behavior of isolator. Moreover the floor response spectrum of base isolated structure considering the aging was analyzed by according to the analysis model of LRB.. The hardening behavior of lead rubber bearing occurs at high strain. Therefore it is reasonable to assume that the hysteretic model of LRB is the nonlinear hardening model for exactly evaluating the seismic response of base isolated structure. The nonlinear analysis of base isolated containment was performed by using the nonlinear hardening variables which was resulted from the test results and finite element analysis. From the analysis results, it was represented that the FRS was higher about 40% with nonlinear hardening model than with the bilinear model. Therefore the seismic response of base isolated structure with bilinear model can be underestimated than the real response. It is desired that the nonlinear hardening model of LRB is applied for the seismic risk evaluation requiring the ultimate state of LRB

Stress Induced in Periodontal Ligament under Orthodontic Loading (Part II): A Comparison of Linear Versus Non-Linear Fem Study.

Science.gov (United States)

Hemanth, M; Deoli, Shilpi; Raghuveer, H P; Rani, M S; Hegde, Chatura; Vedavathi, B

2015-09-01

Simulation of periodontal ligament (PDL) using non-linear finite element method (FEM) analysis gives better insight into understanding of the biology of tooth movement. The stresses in the PDL were evaluated for intrusion and lingual root torque using non-linear properties. A three-dimensional (3D) FEM model of the maxillary incisors was generated using Solidworks modeling software. Stresses in the PDL were evaluated for intrusive and lingual root torque movements by 3D FEM using ANSYS software. These stresses were compared with linear and non-linear analyses. For intrusive and lingual root torque movements, distribution of stress over the PDL was within the range of optimal stress value as proposed by Lee, but was exceeding the force system given by Proffit as optimum forces for orthodontic tooth movement with linear properties. When same force load was applied in non-linear analysis, stresses were more compared to linear analysis and were beyond the optimal stress range as proposed by Lee for both intrusive and lingual root torque. To get the same stress as linear analysis, iterations were done using non-linear properties and the force level was reduced. This shows that the force level required for non-linear analysis is lesser than that of linear analysis.

Dynamical heterogeneities and mechanical non-linearities: Modeling the onset of plasticity in polymer in the glass transition.

Science.gov (United States)

Masurel, R J; Gelineau, P; Lequeux, F; Cantournet, S; Montes, H

2017-12-27

In this paper we focus on the role of dynamical heterogeneities on the non-linear response of polymers in the glass transition domain. We start from a simple coarse-grained model that assumes a random distribution of the initial local relaxation times and that quantitatively describes the linear viscoelasticity of a polymer in the glass transition regime. We extend this model to non-linear mechanics assuming a local Eyring stress dependence of the relaxation times. Implementing the model in a finite element mechanics code, we derive the mechanical properties and the local mechanical fields at the beginning of the non-linear regime. The model predicts a narrowing of distribution of relaxation times and the storage of a part of the mechanical energy --internal stress-- transferred to the material during stretching in this temperature range. We show that the stress field is not spatially correlated under and after loading and follows a Gaussian distribution. In addition the strain field exhibits shear bands, but the strain distribution is narrow. Hence, most of the mechanical quantities can be calculated analytically, in a very good approximation, with the simple assumption that the strain rate is constant.

Development of stress-modified fracture strain criterion for ductile fracture of API X65 steel

International Nuclear Information System (INIS)

Oh, Chang Kyun; Kim, Yun Jae; Park, Jin Moo; Kim, Woo Sik; Baek, Jong Hyun

2005-01-01

This paper presents a stress-modified fracture strain for API X65 steel used for gas pipeline, as a function of stress triaxiality. To determine the stress-modified fracture strain, tension test of bars with four different notch radii, made of API X65 steel, is firstly performed, from which true fracture strains are determined as a function of notch radius. Then detailed elastic-plastic, large strain Finite Element (FE) analyses are performed to estimate variations of stress triaxiality in the notched bars with load. Combining experimental with FE results provides the true fracture strain as a function of stress triaxiality, which is regarded as a criterion of ductile fracture. Application of the developed stress-modified fracture strain to failure prediction of gas pipes made of API X65 steel with various types of defects is discussed

Stresses and strains in thick perforated orthotropic plates

Science.gov (United States)

A. Alshaya; John Hunt; R. Rowlands

2016-01-01

Stress and strain concentrations and in-plane and out-of-plane stress constraint factors associated with a circular hole in thick, loaded orthotropic composite plates are determined by three-dimensional finite element method. The plate has essentially infinite in-plane geometry but finite thickness. Results for Sitka Spruce wood are emphasized, although some for carbon...

Extrinsic contribution to the non-linearity in a PZT disc

Energy Technology Data Exchange (ETDEWEB)

Perez, Rafel [Departament de Fisica Aplicada, Universitat Politecnica de Catalunya, Jordi Girona 1-3, Campus Nord, 08034 Barcelona (Spain); Albareda, Alfons [Departament de Fisica Aplicada, Universitat Politecnica de Catalunya, Jordi Girona 1-3, Campus Nord, 08034 Barcelona (Spain); Garcia, Jose E [Departament de Fisica Aplicada, Universitat Politecnica de Catalunya, Jordi Girona 1-3, Campus Nord, 08034 Barcelona (Spain); Tiana, Jordi [Departament de Fisica Aplicada, Universitat Politecnica de Catalunya, Jordi Girona 1-3, Campus Nord, 08034 Barcelona (Spain); Ringgaard, Erling [Ferroperm Piezoceramics A/S, Hejreskovvej 18, DK-3490 Kvistgaard (Denmark); Wolny, Wanda W [Ferroperm Piezoceramics A/S, Hejreskovvej 18, DK-3490 Kvistgaard (Denmark)

2004-10-07

Non-linear increases in elastic, piezoelectric (direct and reverse) and dielectric coefficients have been measured under a high electrical field or under high mechanical stress. The permittivity and reverse piezoelectric coefficient can be measured by applying a high voltage at a low frequency, while the elastic compliance and direct piezoelectric coefficient can be measured at the first radial resonance frequency in order to apply a high stress. The non-linear behaviour has been analysed at the radial resonance of a disc. In all the materials tested, the results show that there is a close relation between the non-linear increments of the different coefficients. An empirical model has been proposed in order to describe and understand these relations. It is assumed that either the strain or the electrical displacement is produced by intrinsic and extrinsic processes, but only the latter, which consist mainly in the motion of domain walls, contribute to the non-linearity. The model enables us to find the domain wall contribution to elastic, piezoelectric and dielectric non-linearities, and allows us to compare the amplitudes of the fields and stresses that produce the same displacement of domain walls.

Relationship of trehalose accumulation with ethanol fermentation in industrial Saccharomyces cerevisiae yeast strains.

Science.gov (United States)

Wang, Pin-Mei; Zheng, Dao-Qiong; Chi, Xiao-Qin; Li, Ou; Qian, Chao-Dong; Liu, Tian-Zhe; Zhang, Xiao-Yang; Du, Feng-Guang; Sun, Pei-Yong; Qu, Ai-Min; Wu, Xue-Chang

2014-01-01

The protective effect and the mechanisms of trehalose accumulation in industrial Saccharomyces cerevisiae strains were investigated during ethanol fermentation. The engineered strains with more intercellular trehalose achieved significantly higher fermentation rates and ethanol yields than their wild strain ZS during very high gravity (VHG) fermentation, while their performances were not different during regular fermentation. The VHG fermentation performances of these strains were consistent with their growth capacity under osmotic stress and ethanol stress, the key stress factors during VHG fermentation. These results suggest that trehalose accumulation is more important for VHG fermentation of industrial yeast strains than regular one. The differences in membrane integrity and antioxidative capacity of these strains indicated the possible mechanisms of trehalose as a protectant under VHG condition. Therefore, trehalose metabolic engineering may be a useful strategy for improving the VHG fermentation performance of industrial yeast strains. Copyright © 2013 Elsevier Ltd. All rights reserved.

Effects of deviatoric stress and radial strain on the shock-induced diffusionless transformation in boron nitride

International Nuclear Information System (INIS)

Sekine, T.; Kobayashi, T.; Nameki, H.

1997-01-01

The phase transformation of graphitelike BN (h-BN) to wurtzite-type high-pressure BN (w-BN) was investigated through shock-recovery techniques under quasihydrodynamic and nonhydrodynamic shock compressions and under various strain conditions. The experimental results support a diffusionless mechanism, by which the hydrodynamic c-axis compression of h-BN is preferred. This mechanism is topologically considered based on the relationship of crystal structures between h-BN and w-BN. The presence of deviatoric stress and strain depresses the yield of w-BN and the development of w-BN (100) relative to (002). copyright 1997 American Institute of Physics

Reconstruction of the residual stresses in a hyperelastic body using ultrasound techniques

KAUST Repository

Joshi, Sunnie; Walton, Jay R.

2013-01-01

This paper focuses on a novel approach for characterizing the residual stress field in soft tissue using ultrasound interrogation. A nonlinear inverse spectral technique is developed that makes fundamental use of the finite strain nonlinear response

Ratchetting strain prediction

International Nuclear Information System (INIS)

Noban, Mohammad; Jahed, Hamid

2007-01-01

A time-efficient method for predicting ratchetting strain is proposed. The ratchetting strain at any cycle is determined by finding the ratchetting rate at only a few cycles. This determination is done by first defining the trajectory of the origin of stress in the deviatoric stress space and then incorporating this moving origin into a cyclic plasticity model. It is shown that at the beginning of the loading, the starting point of this trajectory coincides with the initial stress origin and approaches the mean stress, displaying a power-law relationship with the number of loading cycles. The method of obtaining this trajectory from a standard uniaxial asymmetric cyclic loading is presented. Ratchetting rates are calculated with the help of this trajectory and through the use of a constitutive cyclic plasticity model which incorporates deviatoric stresses and back stresses that are measured with respect to this moving frame. The proposed model is used to predict the ratchetting strain of two types of steels under single- and multi-step loadings. Results obtained agree well with the available experimental measurements

Stress tolerance and growth physiology of yeast strains from the Brazilian fuel ethanol industry.

Science.gov (United States)

Della-Bianca, B E; Gombert, A K

2013-12-01

Improved biofuels production requires a better understanding of industrial microorganisms. Some wild Saccharomyces cerevisiae strains, isolated from the fuel ethanol industry in Brazil, present exceptional fermentation performance, persistence and prevalence in the harsh industrial environment. Nevertheless, their physiology has not yet been systematically investigated. Here we present a first systematic evaluation of the widely used industrial strains PE-2, CAT-1, BG-1 and JP1, in terms of their tolerance towards process-related stressors. We also analyzed their growth physiology under heat stress. These strains were evaluated in parallel to laboratory and baker's strains. Whereas the industrial strains performed in general better than the laboratory strains under ethanol or acetic acid stresses and on industrial media, high sugar stress was tolerated equally by all strains. Heat and low pH stresses clearly distinguished fuel ethanol strains from the others, indicating that these conditions might be the ones that mostly exert selective pressure on cells in the industrial environment. During shake-flask cultivations using a synthetic medium at 37 °C, industrial strains presented higher ethanol yields on glucose than the laboratory strains, indicating that they could have been selected for this trait-a response to energy-demanding fermentation conditions. These results might be useful to guide future improvements of large-scale fuel ethanol production via engineering of stress tolerance traits in other strains, and eventually also for promoting the use of these fuel ethanol strains in different industrial bioprocesses.

Synergistic relationships among stress, depression, and troubled relationships: insights from psychoneuroimmunology.

Science.gov (United States)

Jaremka, Lisa M; Lindgren, Monica E; Kiecolt-Glaser, Janice K

2013-04-01

Stress and depression consistently elevate inflammation and are often experienced simultaneously, which is exemplified by people in troubled relationships. Troubled relationships also elevate inflammation, which may be partially explained by their ability to engender high levels of stress and depression. People who are stressed, depressed, or in troubled relationships are also at greater risk for health problems than their less distressed counterparts. Inflammation, a risk factor for a variety of age-related diseases including cardiovascular disease, Type II diabetes, metabolic syndrome, and frailty, may be one key mechanistic pathway linking distress to poor health. Obesity may further broaden the health implications of stress and depression; people who are stressed or depressed are often overweight, and adipose tissue is a major source of proinflammatory cytokines. Stress, depression, and troubled relationships may have synergistic inflammatory effects: loneliness, subclinical depression, and major depression enhance inflammatory responses to an acute stressful event. The relationship between distress and inflammation is bidirectional; depression enhances inflammation and inflammation promotes depression. Interesting questions emerge from this literature. For instance, some stressors may be more potent than others and thus may be more strongly linked to inflammation. In addition, it is possible that psychological and interpersonal resources may buffer the negative inflammatory effects of stress. Understanding the links among stress, depression, troubled relationships, and inflammation is an exciting area of research that may provide mechanistic insight into the links between distress and poor health. © 2013 Wiley Periodicals, Inc.

Microscopic origin of nonlinear non-affine deformation in metallic glasses

NARCIS (Netherlands)

Zaccone, A.; Schall, P.; Terentjev, E.M.

2014-01-01

The atomic theory of elasticity of amorphous solids, based on the nonaffine response formalism, is extended into the nonlinear stress-strain regime by coupling with the underlying irreversible many-body dynamics. The latter is implemented in compact analytical form using a qualitative method for the

Dynamical System and Nonlinear Regression for Estimate Host-Parasitoid Relationship

Directory of Open Access Journals (Sweden)

Ileana Miranda Cabrera

2010-01-01

Full Text Available The complex relationships of a crop with the pest, its natural enemies, and the climate factors exist in all the ecosystems, but the mathematic models has studied only some components to know the relation cause-effect. The most studied system has been concerned with the relationship pest-natural enemies such as prey-predator or host-parasitoid. The present paper shows a dynamical system for studying the relationship host-parasitoid (Diaphorina citri, Tamarixia radiata and shows that a nonlinear model permits the estimation of the parasite nymphs using nymphs healthy as the known variable. The model showed the functional answer of the parasitoid, in which a point arrives that its density is not augmented although the number host increases, and it becomes necessary to intervene in the ecosystem. A simple algorithm is used to estimate the parasitoids level using the priori relationship between the host and the climate factors and then the nonlinear model.

The effect of hydrogen on the multiaxial stress-strain behavior of titanium tubing

International Nuclear Information System (INIS)

Lentz, C.W.; Hecker, S.S.; Koss, D.A.; Stout, M.G.

1983-01-01

The influence of internal hydrogen on the multiaxial stress-strain behavior of commercially pure titanium has been studied. Thin-walled specimens containing either 20 or 1070 ppm hydrogen were tested at constant stress ratios in combined tension and internal pressure. Hydrogen lowers the yield strength but has no significant effect on strain hardening behavior at strains epsilon greater than or equal to 0.02. Thus, hydrogen embrittlement under plain strain or equibiaxial loading is not a consequence of changes of flow behavior. The yielding behavior is described well by Hill's quadratic yield criterion. As measured mechanically and pole figure analysis, the plastic anisotropy changes with deformation in a manner which depends on stress state. A strain dependent, texture-induced strengthening effect in equibiaxial tension an enhanced strain hardening rate

Application of the Generalized Nonlinear Complementary Relationship for Estimating Evaporation in North China

Science.gov (United States)

Yu, M.; Wu, B.

2017-12-01

As an important part of the coupled Eco-Hydrological processes, evaporation is the bond for exchange of energy and heat between the surface and the atmosphere. However, the estimation of evaporation remains a challenge compared with other main hydrological factors in water cycle. The complementary relationship which proposed by Bouchet (1963) has laid the foundation for various approaches to estimate evaporation from land surfaces, the essence of the principle is a relationship between three types of evaporation in the environment. It can simply implemented with routine meteorological data without the need for resistance parameters of the vegetation and bare land, which are difficult to observed and complicated to estimate in most surface flux models. On this basis the generalized nonlinear formulation was proposed by Brutsaert (2015). The daily evaporation can be estimated once the potential evaporation (Epo) and apparent potential evaporation (Epa) are known. The new formulation has a strong physical basis and can be expected to perform better under natural water stress conditions, nevertheless, the model has not been widely validated over different climate types and underlying surface patterns. In this study, we attempted to apply the generalized nonlinear complementary relationship in North China, three flux stations in North China are used for testing the universality and accuracy of this model against observed evaporation over different vegetation types, including Guantao Site, Miyun Site and Huailai Site. Guantao Site has double-cropping systems and crop rotations with summer maize and winter wheat; the other two sites are dominated by spring maize. Detailed measurements of meteorological factors at certain heights above ground surface from automatic weather stations offered necessary parameters for daily evaporation estimation. Using the Bowen ratio, the surface energy measured by the eddy covariance systems at the flux stations is adjusted on a daily scale

The Strain and Grain Size Dependence of the Flow Stress of Copper

DEFF Research Database (Denmark)

Hansen, Niels; Ralph, B.

1982-01-01

Tensile stress strain data for 99.999% copper at room and liquid nitrogen temperature as a function of grain size are presented together with some microstructural observations made by transmission electron microscopy. It is shown that the flow stress data, at constant strain may be expressed...

Stress and strain fluctuations in plastic deformation of crystals with disordered microstructure

International Nuclear Information System (INIS)

Kapetanou, O; Zaiser, M; Weygand, D

2015-01-01

We investigate the spatial structure of stress and strain patterns in crystal plasticity. To this end, we combine theoretical arguments with plasticity simulations using three different models: (i) a generic model of bulk crystal plasticity with stochastic evolution of the local microstructure, (ii) a 2D discrete dislocation simulation assuming single-slip deformation in a bulk crystal, and (iii) a 3D discrete dislocation model for deformation of micropillars in multiple slip. For all three models we investigate the scale-dependent magnitude of local fluctuations of internal stress and plastic strain, and we determine the spatial structure of the respective auto- and cross-correlation functions. The investigations show that, in the course of deformation, nontrivial long range correlations emerge in the stress and strain patterns. We investigate the influence of boundary conditions on the observed spatial patterns of stress and strain, and discuss implications of our findings for larger-scale plasticity models. (paper)

Cyclic Elastoplastic Performance of Aluminum 7075-T6 Under Strain- and Stress-Controlled Loading

Science.gov (United States)

Agius, Dylan; Wallbrink, Chris; Kourousis, Kyriakos I.

2017-12-01

Elastoplastic investigations of aerospace aluminum are important in the development of an understanding of the possible cyclic transient effects and their contribution to the material performance under cyclic loading. Cyclic plasticity can occur in an aerospace aluminum component or structure depending on the loading conditions and the presence of external and internal discontinuities. Therefore, it is vital that the cyclic transient effects of aerospace aluminum are recognized and understood. This study investigates experimentally the cyclic elastoplastic performance of aluminum 7075-T6 loaded in symmetric strain control, and asymmetric stress and strain control. A combination of cyclic hardening and softening was noticed from high strain amplitude symmetric strain-controlled tests and at low stress amplitude asymmetric stress-controlled tests. From asymmetric strain control results, the extent of mean stress relaxation depended on the size of the strain amplitude. Additionally, saturation of the ratcheting strain (plastic shakedown) was also found to occur during asymmetric stress control tests. The experimental results were further analyzed using published microstructure research from the past two decades to provide added explanation of the micro-mechanism contribution to the cyclic transient behavior.

Cyclic stress-strain behavior of polymeric nonwoven structures for the use as artificial leaflet material for transcatheter heart valve prostheses

Directory of Open Access Journals (Sweden)

Arbeiter Daniela

2017-09-01

Full Text Available Xenogenic leaflet material, bovine and porcine pericardium, is widely used for the fabrication of surgically implanted and transcatheter heart valve prostheses. As a biological material, long term durability of pericardium is limited due to calcification, degeneration and homogeneity. Therefore, polymeric materials represent a promising approach for a next generation of artificial heart valve leaflets with improved durability. Within the current study we analyzed the mechanical performance of polymeric structures based on elastomeric materials. Polymeric cast films were prepared and nonwovens were manufactured in an electrospinning process. Analysis of cyclic stress-strain behavior was performed, using a universal testing machine. The uniaxial cyclic tensile experiments of the elastomeric samples yielded a non-linear elastic response due to viscoelastic behavior with hysteresis. Equilibrium of stress-strain curves was found after a specific number of cycles, for cast films and nonwovens, respectively. In conclusion, preconditioning was found obligatory for the evaluation of the mechanical performance of polymeric materials for the use as artificial leaflet material for heart valve prostheses.

Effects of mean strain on the random cyclic stress-strain relations of 0Cr18Ni10Ti pipe steel

International Nuclear Information System (INIS)

Zhao Yongxiang; Yang Bing

2005-01-01

Experimental study is performed for the effects of the mean strain on the random cyclic stress-strain relations of the new nuclear material, 0Cr18Ni10Ti pipe steel. From saving the size of specimens, an improved maximum likelihood fatigue test method is proposed to operate the present strain-controlled fatigue tests. Six straining ratios, -1, -0.52, -0.22, 0.029, 0.18, and 0.48, respectively, are applied to study the effects. Fatigue test has been carried out on totally 104 specimens. The test results reveal that the material exhibits a Masing behaviour and the saturation hysteresis loops under the six ratios hold an entirely relaxation effect of mean stress. There is no effectively method for the description of the mean straining effects under this case. Previous Zhao's random stress-strain relations are therefore applied to characterizing effectively the scattering test data under the six ratios on a basis of Ramberg-Osgood equation. Then the effects of the ratios are analyzed respectively on the average stress amplitudes, the standard deviations of the stress amplitudes, and the stress amplitudes under different survival probabilities and confidences. The results reveal that the ratios act a relatively decreasing effect to the stress amplitudes under higher survival probabilities and confidences. The strongest effect appears at the ratio of 0.029, and a weaker effect acts as the distance increase of the ratio from the zero. In addition, it is indicated that the effects from the sense of average fatigue lives might result in a wrong conclusion. The effects can be appropriately assessed from a probabilistic sense to take into account the scattering regularity of test data and the size of sampling. (author)

Effects of strain rate, stress condition and environment on iodine embrittlement of Ziracloy-2

International Nuclear Information System (INIS)

Une, K.

1979-01-01

Iodine stress corrosion cracking (SCC) susceptibility of Zircaloy became higher with decreasing strain rate. Critical strain rate, below which high SCC severity was observed, substantially depended on Zircaloy stress condition. This strain rate (7 x 10 -3 min -1 ) under plane strain condition was about 3.5 times as fast as that (2 x 10 -3 min -1 ) under uniaxial condition. The maximum iodine embrittlement in Zircaloy was found in stress ratio α (axial/tangential stress) range of 0.5 to 0.7. No embrittlement occurred at α = infinity because of its texture effect. The SCC fracture stresses were about 39 kg/mm 2 for unirradiated and stress-relieved material, and about 34 kg/mm 2 for recrystallized material, whose ratios to yield strength of each material were 0.8 and 1.2. Impurity gases of oxygen and moisture in the iodine had the effects of reducing Zircaloy SCC susceptibility. Stress-relieved material was more sensitive to environmental impurities than recrystallized material

Relationship between occupational stress and job burnout among rural-to-urban migrant workers in Dongguan, China: a cross-sectional study.

Science.gov (United States)

Luo, Hao; Yang, Hui; Xu, Xiujuan; Yun, Lin; Chen, Ruoling; Chen, Yuting; Xu, Longmei; Liu, Jiaxian; Liu, Linhua; Liang, Hairong; Zhuang, Yali; Hong, Liecheng; Chen, Ling; Yang, Jinping; Tang, Huanwen

2016-08-17

In China, there have been an increasing number of migrant workers from rural to urban areas, and migrant workers have the highest incidence of occupational diseases. However, few studies have examined the impact of occupational stress on job burnout in these migrant workers. This study aimed to investigate the relationship between occupational stress and job burnout among migrant workers. This study used a cross-sectional survey. This investigation was conducted in Dongguan city, Guangdong Province, China. 3806 migrant workers, aged 18-60 years, were randomly selected using multistage sampling procedures. Multistage sampling procedures were used to examine demographic characteristics, behaviour customs and job-related data. Hierarchical linear regression and logistic regression models were constructed to explore the relationship between occupational stress and burnout. Demographics, behaviour customs and job-related characteristics significantly affected on burnout. After adjusting for the control variable, a high level of emotional exhaustion was associated with high role overload, high role insufficiency, high role boundary, high physical environment, high psychological strain, high physical strain, low role ambiguity, low responsibility and low vocational strain. A high level of depersonalisation was associated with high role overload, high role ambiguity, high role boundary, high interpersonal strain, high recreation, low physical environment and low social support. A low level of personal accomplishment was associated with high role boundary, high role insufficiency, low responsibility, low social support, low physical environment, low self-care and low interpersonal strain. Compared to the personal resources, the job strain and personal strain were more likely to explain the burnout of rural-to-urban migrant workers in our study. The migrant workers have increased job burnouts in relation to occupational stress. Relieving occupational stress and maintaining

Stress-Dilatancy of Cambria Sand for Triaxial Tests at High Pressures

Science.gov (United States)

Szypcio, Zenon

2017-12-01

In this paper, the stress-dilatancy relationship of Cambria sand for drained triaxial compression and extension tests at high stress level is investigated. The stress dilatancy relationship is obtained by use of frictional state theory and experimental tests data published in literature. It is shown that stress-dilatancy relationship is bilinear, described by three parameters of frictional state theory: critical frictional angle and two other parameters. It is accepted that critical friction angle is independent of confining pressure. The two additional parameters are strongly dependent on confining pressure and different for initial and advanced stages. The point at which the values of these parameters change is termed as Transformation Shear Point. This point is not simply visible either in stress ratio-strain or the volume strain-shear strain relationship which are traditionally shown in soil mechanics papers. Transformation Shear Point is very characteristic in stress ratio-plastic dilatancy plane. Thus, stress ratio- plastic dilatancy is very important for describing stress-strain behaviour of soils. The relationship shown in the paper can be used in soil modelling in the future.

New Insights into the Relationship Between Network Structure and Strain Induced Crystallization in Unvolcanized Natural Rubber by Synchrotron X-ray Diffraction

International Nuclear Information System (INIS)

Toki, S.; Hsiao, B.; Amnuaypornsri, S.; Sakdapipanich, J.

2009-01-01

The relationship between the network structure and strain-induced crystallization in un-vulcanized as well as vulcanized natural rubbers (NR) and synthetic poly-isoprene rubbers (IR) was investigated via synchrotron wide-angle X-ray diffraction (WAXD) technique. It was found that the presence of a naturally occurring network structure formed by natural components in un-vulcanized NR significantly facilitates strain-induced crystallization and enhances modulus and tensile strength. The stress-strain relation in vulcanized NR is due to the combined effect of chemical and naturally occurring networks. The weakness of naturally occurring network against stress and temperature suggests that vulcanized NR has additional relaxation mechanism due to naturally occurring network. The superior mechanical properties in NR compared with IR are mainly due to the existence of naturally occurring network structure.

Dynamic stress relaxation due to cyclic variation of strain at elevated temperature

International Nuclear Information System (INIS)

Suzuki, F.

1975-01-01

The relaxation of stress which occurs when low amplitude alternating strains are superimposed on constant mean total strains is studied in this paper. Experiments were carried out on a 0.16 per cent carbon steel and an AISI 347 stainless steel at 450 0 C and 650 0 C respectively in which the decrease of axial mean stress was measured as a function of time. When even a low amplitude alternating strain was applied, the rate of stress relaxation was observed to increase. Analytical predictions based on creep and static relaxation data show fairly good agreement with experiments in the period corresponding to transient creep. (author)

Superelastic stress-strain behavior in ferrogels with different types of magneto-elastic coupling

Science.gov (United States)

Cremer, Peet; Löwen, Hartmut; Menzel, Andreas M.

Colloidal magnetic particles embedded in an elastic polymer matrix constitute a smart material called ferrogel. It responds to an applied external magnetic field by changes in elastic properties, which can be exploited for various applications like dampers, vibration absorbers, or actuators. Under appropriate conditions, the stress-strain behavior of a ferrogel can display a fascinating feature: superelasticity, the capability to reversibly deform by a huge amount while barely altering the applied load. In a previous work, using numerical simulations, we investigated this behavior assuming that the magnetic moments carried by the embedded particles can freely reorient to minimize their magnetic interaction energy. Here, we extend the analysis to ferrogels where restoring torques by the surrounding matrix hinder rotations towards a magnetically favored configuration. For example, the particles can be chemically cross-linked into the polymer matrix and the magnetic moments can be fixed to the particle axes. We demonstrate that these systems still feature a superelastic regime. As before, the nonlinear stress-strain behavior can be reversibly tailored during operation by external magnetic fields. Yet, the different coupling of the magnetic moments causes different types of response to external stimuli. For instance, an external magnetic field applied parallel to the stretching axis hardly affects the superelastic regime but stiffens the system beyond it. Other smart materials featuring superelasticity, e.g. metallic shape-memory alloys, have already found widespread applications. Our soft polymer systems offer many additional advantages like a typically higher deformability and enhanced biocompatibility combined with high tunability.

Stress and Strain State Analysis of Defective Pipeline Portion

Science.gov (United States)

Burkov, P. V.; Burkova, S. P.; Knaub, S. A.

2015-09-01

The paper presents computer simulation results of the pipeline having defects in a welded joint. Autodesk Inventor software is used for simulation of the stress and strain state of the pipeline. Places of the possible failure and stress concentrators are predicted on the defective portion of the pipeline.

A thermodynamic approach to nonlinear ultrasonics for material state awareness and prognosis

Science.gov (United States)

Chillara, Vamshi Krishna

2017-11-01

We develop a thermodynamic framework for modeling nonlinear ultrasonic damage sensing and prognosis in materials undergoing progressive damage. The framework is based on the internal variable approach and relies on the construction of a pseudo-elastic strain energy function that captures the energetics associated with the damage progression. The pseudo-elastic strain energy function is composed of two energy functions—one that describes how a material stores energy in an elastic fashion and the other describes how material dissipates energy or stores it in an inelastic fashion. Experimental motivation for the choice of the above two functionals is discussed and some specific choices pertaining to damage progression during fatigue and creep are presented. The thermodynamic framework is employed to model the nonlinear response of material undergoing stress relaxation and creep-like degradation. For each of the above cases, evolution of the nonlinearity parameter with damage as well as with macroscopic measurables like accumulated plastic strain is obtained.

Influence of stress, temperature, and strain on calcite twins constrained by deformation experiments

Science.gov (United States)

Rybacki, E.; Evans, B.; Janssen, C.; Wirth, R.; Dresen, G.

2013-08-01

A series of low-strain triaxial compression and high-strain torsion experiments were performed on marble and limestone samples to examine the influence of stress, temperature, and strain on the evolution of twin density, the percentage of grains with 1, 2, or 3 twin sets, and the twin width—all parameters that have been suggested as either paleopiezometers or paleothermometers. Cylindrical and dog-bone-shaped samples were deformed in the semibrittle regime between 20 °C and 350 °C, under confining pressures of 50-400 MPa, and at strain rates of 10- 4-10- 6 s- 1. The samples sustained shear stresses, τ, up to 280 MPa, failing when deformed to shear strains γ > 1. The mean width of calcite twins increased with both temperature and strain, and thus, measurement of twin width provides only a rough estimation of peak temperature, unless additional constraints on deformation are known. In Carrara marble, the twin density, NL (no of twins/mm), increased as the rock hardened with strain and was approximately related to the peak differential stress, σ (MPa), by the relation σ=19.5±9.8√{N}. Dislocation tangles occurred along twin boundaries, resulting in a complicated cell structure, which also evolved with stress. As previously established, the square root of dislocation density, observed after quench, also correlated with peak stress. Apparently, both twin density and dislocation cell structure are important state variables for describing the strength of these rocks.

Analytical Modeling of the High Strain Rate Deformation of Polymer Matrix Composites

Science.gov (United States)

Goldberg, Robert K.; Roberts, Gary D.; Gilat, Amos

2003-01-01

The results presented here are part of an ongoing research program to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to high strain rate impact loads. State variable constitutive equations originally developed for metals have been modified in order to model the nonlinear, strain rate dependent deformation of polymeric matrix materials. To account for the effects of hydrostatic stresses, which are significant in polymers, the classical 5 plasticity theory definitions of effective stress and effective plastic strain are modified by applying variations of the Drucker-Prager yield criterion. To verify the revised formulation, the shear and tensile deformation of a representative toughened epoxy is analyzed across a wide range of strain rates (from quasi-static to high strain rates) and the results are compared to experimentally obtained values. For the analyzed polymers, both the tensile and shear stress-strain curves computed using the analytical model correlate well with values obtained through experimental tests. The polymer constitutive equations are implemented within a strength of materials based micromechanics method to predict the nonlinear, strain rate dependent deformation of polymer matrix composites. In the micromechanics, the unit cell is divided up into a number of independently analyzed slices, and laminate theory is then applied to obtain the effective deformation of the unit cell. The composite mechanics are verified by analyzing the deformation of a representative polymer matrix composite (composed using the representative polymer analyzed for the correlation of the polymer constitutive equations) for several fiber orientation angles across a variety of strain rates. The computed values compare favorably to experimentally obtained results.

Exchange Rate – Relative Price Nonlinear Cointegration Relationship in Malaysia

OpenAIRE

Venus Khim-Sen Liew; Chee-Keong Choong; Evan Lau; Kian-Ping Lim

2005-01-01

The finding of exchange rate–relative price nonlinear cointegration relationship in Malaysia, among others, suggests that nonlinear Purchasing Power Parity (PPP) equilibrium may be regarded as reference point in judging the short run misalignment of the Ringgit currency and thereby deducing effective policy actions. Moreover, economists who wish to extend the simple PPP exchange rate model into the more complicated monetary exchange models may do so comfortably, at least in the text of Malays...

A non-linear kinematic hardening function

International Nuclear Information System (INIS)

Ottosen, N.S.

1977-05-01

Based on the classical theory of plasticity, and accepting the von Mises criterion as the initial yield criterion, a non-linear kinematic hardening function applicable both to Melan-Prager's and to Ziegler's hardening rule is proposed. This non-linear hardening function is determined by means of the uniaxial stress-strain curve, and any such curve is applicable. The proposed hardening function considers the problem of general reversed loading, and a smooth change in the behaviour from one plastic state to another nearlying plastic state is obtained. A review of both the kinematic hardening theory and the corresponding non-linear hardening assumptions is given, and it is shown that material behaviour is identical whether Melan-Prager's or Ziegler's hardening rule is applied, provided that the von Mises yield criterion is adopted. (author)

Strained Silicon Photonics

Directory of Open Access Journals (Sweden)

Ralf B. Wehrspohn

2012-05-01

Full Text Available A review of recent progress in the field of strained silicon photonics is presented. The application of strain to waveguide and photonic crystal structures can be used to alter the linear and nonlinear optical properties of these devices. Here, methods for the fabrication of strained devices are summarized and recent examples of linear and nonlinear optical devices are discussed. Furthermore, the relation between strain and the enhancement of the second order nonlinear susceptibility is investigated, which may enable the construction of optically active photonic devices made of silicon.

Inversion of the strain-life and strain-stress relationships for use in metal fatigue analysis

Science.gov (United States)

Manson, S. S.

1979-01-01

The paper presents closed-form solutions (collocation method and spline-function method) for the constants of the cyclic fatigue life equation so that they can be easily incorporated into cumulative damage analysis. The collocation method involves conformity with the experimental curve at specific life values. The spline-function method is such that the basic life relation is expressed as a two-part function, one applicable at strains above the transition strain (strain at intersection of elastic and plastic lines), the other below. An illustrative example is treated by both methods. It is shown that while the collocation representation has the advantage of simplicity of form, the spline-function representation can be made more accurate over a wider life range, and is simpler to use.

Dynamic pull-in instability of geometrically nonlinear actuated micro-beams based on the modified couple stress theory

Directory of Open Access Journals (Sweden)

Hamid M. Sedighi

Full Text Available This paper investigates the dynamic pull-in instability of vibrating micro-beams undergoing large deflection under electrosatically actuation. The governing equation of motion is derived based on the modified couple stress theory. Homotopy Perturbation Method is employed to produce the high accuracy approximate solution as well as the second-order frequency- amplitude relationship. The nonlinear governing equation of micro beam vibrations predeformed by an electric field includes both even and odd nonlinearities. The influences of basic non-dimensional parameters on the pull-in instability as well as the natural frequency are studied. It is demonstrated that two terms in series expansions are sufficient to produce high accuracy solution of the micro-structure. The accuracy of proposed asymptotic approach is validated via numerical results. The phase portrait of the system exhibits periodic and homoclinic orbits.

A nonlinear beam model to describe the postbuckling of wide neo-Hookean beams

Science.gov (United States)

Lubbers, Luuk A.; van Hecke, Martin; Coulais, Corentin

2017-09-01

Wide beams can exhibit subcritical buckling, i.e. the slope of the force-displacement curve can become negative in the postbuckling regime. In this paper, we capture this intriguing behaviour by constructing a 1D nonlinear beam model, where the central ingredient is the nonlinearity in the stress-strain relation of the beams constitutive material. First, we present experimental and numerical evidence of a transition to subcritical buckling for wide neo-Hookean hyperelastic beams, when their width-to-length ratio exceeds a critical value of 12%. Second, we construct an effective 1D energy density by combining the Mindlin-Reissner kinematics with a nonlinearity in the stress-strain relation. Finally, we establish and solve the governing beam equations to analytically determine the slope of the force-displacement curve in the postbuckling regime. We find, without any adjustable parameters, excellent agreement between the 1D theory, experiments and simulations. Our work extends the understanding of the postbuckling of structures made of wide elastic beams and opens up avenues for the reverse-engineering of instabilities in soft and metamaterials.

Intraspecies diversity of Lactobacillus sakei response to oxidative stress and variability of strain performance in mixed strains challenges.

Science.gov (United States)

Guilbaud, Morgan; Zagorec, Monique; Chaillou, Stéphane; Champomier-Vergès, Marie-Christine

2012-04-01

Lactobacillus sakei is a meat-borne lactic acid bacterium species exhibiting a wide genomic diversity. We have investigated the diversity of response to various oxidative compounds, between L. sakei strains, among a collection representing the genomic diversity. We observed various responses to the different compounds as well as a diversity of response depending on the aeration conditions used for cell growth. A principal component analysis revealed two main phenotypic groups, partially correlating with previously described genomic clusters. We designed strains mixes composed of three different strains, in order to examine the behavior of each strain, when cultured alone or in the presence of other strains. The strains composing the mixtures were chosen as diverse as possible, i.e. exhibiting diverse responses to oxidative stress and belonging to different genomic clusters. Growth and survival rates of each strain were monitored under various aeration conditions, with or without heme supplementation. The results obtained suggest that some strains may act as "helper" or "burden" strains depending on the oxidative conditions encountered during incubation. This study confirms that resistance to oxidative stress is extremely variable within the L. sakei species and that this property should be considered when investigating starter performance in the complex meat bacterial ecosystems. Copyright © 2011 Elsevier Ltd. All rights reserved.

Unconstrained Finite Element for Geometrical Nonlinear Dynamics of Shells

Directory of Open Access Journals (Sweden)

Humberto Breves Coda

2009-01-01

Full Text Available This paper presents a positional FEM formulation to deal with geometrical nonlinear dynamics of shells. The main objective is to develop a new FEM methodology based on the minimum potential energy theorem written regarding nodal positions and generalized unconstrained vectors not displacements and rotations. These characteristics are the novelty of the present work and avoid the use of large rotation approximations. A nondimensional auxiliary coordinate system is created, and the change of configuration function is written following two independent mappings from which the strain energy function is derived. This methodology is called positional and, as far as the authors' knowledge goes, is a new procedure to approximated geometrical nonlinear structures. In this paper a proof for the linear and angular momentum conservation property of the Newmark algorithm is provided for total Lagrangian description. The proposed shell element is locking free for elastic stress-strain relations due to the presence of linear strain variation along the shell thickness. The curved, high-order element together with an implicit procedure to solve nonlinear equations guarantees precision in calculations. The momentum conserving, the locking free behavior, and the frame invariance of the adopted mapping are numerically confirmed by examples.

Nonlinear response of dense colloidal suspensions under oscillatory shear: mode-coupling theory and Fourier transform rheology experiments.

Science.gov (United States)

Brader, J M; Siebenbürger, M; Ballauff, M; Reinheimer, K; Wilhelm, M; Frey, S J; Weysser, F; Fuchs, M

2010-12-01

Using a combination of theory, experiment, and simulation we investigate the nonlinear response of dense colloidal suspensions to large amplitude oscillatory shear flow. The time-dependent stress response is calculated using a recently developed schematic mode-coupling-type theory describing colloidal suspensions under externally applied flow. For finite strain amplitudes the theory generates a nonlinear response, characterized by significant higher harmonic contributions. An important feature of the theory is the prediction of an ideal glass transition at sufficiently strong coupling, which is accompanied by the discontinuous appearance of a dynamic yield stress. For the oscillatory shear flow under consideration we find that the yield stress plays an important role in determining the nonlinearity of the time-dependent stress response. Our theoretical findings are strongly supported by both large amplitude oscillatory experiments (with Fourier transform rheology analysis) on suspensions of thermosensitive core-shell particles dispersed in water and Brownian dynamics simulations performed on a two-dimensional binary hard-disk mixture. In particular, theory predicts nontrivial values of the exponents governing the final decay of the storage and loss moduli as a function of strain amplitude which are in good agreement with both simulation and experiment. A consistent set of parameters in the presented schematic model achieves to jointly describe linear moduli, nonlinear flow curves, and large amplitude oscillatory spectroscopy.

PNNL Stress/Strain Correlation for Zircaloy

Energy Technology Data Exchange (ETDEWEB)

Geelhood, Kenneth J.; Beyer, Carl E.; Luscher, Walter G.

2008-07-18

Pacific Northwest National Laboratory (PNNL) was tasked with incorporating cladding mechanical property data into the Nuclear Regulatory Commission (NRC) fuel codes, FRAPCON-31 and FRAPTRAN2, by the NRC Office of Nuclear Reactor Research. The objective of that task was to create a mechanical model that can calculate true stress, true strain, and the possible failure of the fuel rod cladding based on uniaxial test data.

Strain, Stress and Seismicity pattern in Switzerland

Science.gov (United States)

Houlié, Nicolas; Woessner, Jochen; Villiger, Arturo; Deichmann, Nicholas; Rothacher, Markus; Giardini, Domenico; Geiger, Alain

2013-04-01

Switzerland lies across one of the most complex plate boundary in the world. With a 100 Ma of deformation history, and a wide diversity of deformation mechanism, it is an ideal place to study the link(s) between small strain rates measured at the surface and stress dissipated at depth. The link is of genuine interest for seismic hazard assessment as it provides an independent estimate for moment release within the seismogenic volume. We use geodetic (GPS velocities, shortening axes, strain maps) and seismic (anisotropy, P-axes, focal mechanisms) datasets in order to assess whether the stress accumulated at depth due to the continental collision reflects the deformation rates measured at the surface and correlates with the seismic activity as well as the stress directions deduced from earthquake focal mechanisms throughout the area - or not. While the deformation amplitudes of the area are small (less than 10-7 yr-1) in some areas of Switzerland, we can relate long- and short-term features of the tectonic processes occurring over the last 10+ Ma. Preliminary results suggest that while deformation rates measured by GPS are large in the Ticino compared to the Valais region - its seismic activity rate is lower. This implies other processes might play important roles in the generation of seismicity.

Simulation of creep effects in framework of a geometrically nonlinear endochronic theory of inelasticity

Science.gov (United States)

Zabavnikova, T. A.; Kadashevich, Yu. I.; Pomytkin, S. P.

2018-05-01

A geometric non-linear endochronic theory of inelasticity in tensor parametric form is considered. In the framework of this theory, the creep strains are modelled. The effect of various schemes of applying stresses and changing of material properties on the development of creep strains is studied. The constitutive equations of the model are represented by non-linear systems of ordinary differential equations which are solved in MATLAB environment by implicit difference method. Presented results demonstrate a good qualitative agreement of theoretical data and experimental observations including the description of the tertiary creep and pre-fracture of materials.

The effects of strain induced martensite on stress corrosion cracking in AISI 304 stainless steel

International Nuclear Information System (INIS)

Lee, W. S.; Kwon, S. I.

1989-01-01

The effects of strain induced martensite on stress corrosion cracking behavior in AISI 304 stainless steel in boiling 42 wt% MgCl 2 solution were investigated using monotonic SSRT and cyclic SSRT with R=0.1 stress ratio. As the amount of pre-strain increased, the failure time of the specimens in monotonic SSRT test decreased independent of the existence of strain induced martensite. The strain induced martensite seems to promote the crack initiation but to retard the crack propagation during stress corrosion cracking

Nonlinear tension-bending deformation of a shape memory alloy rod

International Nuclear Information System (INIS)

Shang, Zejin; Wang, Zhongmin

2012-01-01

Based on the measured shape memory alloy (SMA) stress–strain curve and the nonlinear large deformation theory of extensible beams (or rods), the first-order nonlinear governing equations of a SMA cantilever straight rod are established. They consist of a boundary-value problem of ordinary differential equations with a strong nonlinearity, in which seven unknown functions are contained and the arc length of the deformed axis is considered as one of the basic unknown functions. The shooting method combining with the Newton–Raphson iteration method is applied to solve the equations numerically. For a SMA cantilever rod subjected to a transverse uniformly distributed force, the deformation characteristics curves, the maximum strain and the maximum stress distribution curves along the longitudinal direction of rod, and the relation curves between deformation characteristic parameters and transverse uniformly force under different slenderness ratios are obtained. The effects of material nonlinearity, geometrical nonlinearity and slenderness ratio on the tension-bending deformation of the SMA cantilever rod are investigated. The numerical simulation results are in good agreement with the experimental data from the literature, verifying the soundness of the entire numerical simulation scheme. (paper)

Elevated nonlinearity as an indicator of shifts in the dynamics of populations under stress.

Science.gov (United States)

Dakos, Vasilis; Glaser, Sarah M; Hsieh, Chih-Hao; Sugihara, George

2017-03-01

Populations occasionally experience abrupt changes, such as local extinctions, strong declines in abundance or transitions from stable dynamics to strongly irregular fluctuations. Although most of these changes have important ecological and at times economic implications, they remain notoriously difficult to detect in advance. Here, we study changes in the stability of populations under stress across a variety of transitions. Using a Ricker-type model, we simulate shifts from stable point equilibrium dynamics to cyclic and irregular boom-bust oscillations as well as abrupt shifts between alternative attractors. Our aim is to infer the loss of population stability before such shifts based on changes in nonlinearity of population dynamics. We measure nonlinearity by comparing forecast performance between linear and nonlinear models fitted on reconstructed attractors directly from observed time series. We compare nonlinearity to other suggested leading indicators of instability (variance and autocorrelation). We find that nonlinearity and variance increase in a similar way prior to the shifts. By contrast, autocorrelation is strongly affected by oscillations. Finally, we test these theoretical patterns in datasets of fisheries populations. Our results suggest that elevated nonlinearity could be used as an additional indicator to infer changes in the dynamics of populations under stress. © 2017 The Author(s).

Strain-rate effect on initial crush stress of irregular honeycomb under dynamic loading and its deformation mechanism

Science.gov (United States)

Wang, Peng; Zheng, Zhijun; Liao, Shenfei; Yu, Jilin

2018-02-01

The seemingly contradictory understandings of the initial crush stress of cellular materials under dynamic loadings exist in the literature, and a comprehensive analysis of this issue is carried out with using direct information of local stress and strain. Local stress/strain calculation methods are applied to determine the initial crush stresses and the strain rates at initial crush from a cell-based finite element model of irregular honeycomb under dynamic loadings. The initial crush stress under constant-velocity compression is identical to the quasi-static one, but less than the one under direct impact, i.e. the initial crush stresses under different dynamic loadings could be very different even though there is no strain-rate effect of matrix material. A power-law relation between the initial crush stress and the strain rate is explored to describe the strain-rate effect on the initial crush stress of irregular honeycomb when the local strain rate exceeds a critical value, below which there is no strain-rate effect of irregular honeycomb. Deformation mechanisms of the initial crush behavior under dynamic loadings are also explored. The deformation modes of the initial crush region in the front of plastic compaction wave are different under different dynamic loadings.

Mathematical description for the stress-strain behavior of annealed 21/4 Cr--1 Mo steel

International Nuclear Information System (INIS)

Klueh, R.L.; Hebble, T.L.

1976-01-01

We have conducted a detailed series of tensile tests on one heat of annealed 2 1 / 4 Cr-1 Mo steel over the range 25 to 593 0 C (75 to 1100 0 F) and at nominal strain rates of 0.4, 0.04, 0.004, and 0.0004/min. To determine an empirical relationship to represent the flow behavior, we fitted the true-stress true-strain data from these tests to several proposed models. The models fit were those proposed by Holloman, Ludwik, Ludwigson, and Voce. From a comparison of the standard error of estimate, the Voce equation was concluded to be the best mathematical description of the data under most test conditions and the best single representation over the wide range of test conditions

Nonlinear aspects of structural fatigue damage assessment and accumulation

International Nuclear Information System (INIS)

Leis, B.N.

1977-01-01

The present paper reviews a recently developed concept for structural fatigue analysis which is capable of accounting for nonlinearities in both the above noted transformations. It is shown that, for cases where the local stressing and straining is proportional, the multiplicity of initiation sites and mechanisms observed to dominate structural fatigue resistance can be explained in terms of these additional nonlinearities. The ability of current concepts for structural fatigue analysis which account for nonlinear action to handle situaions where nonproportional stressing occurs in fatigue critical locations is next examined. Limitations in the assumptions made in fatigue analysis are shown to essentially preclude the application of present technology to that class of problems. A new approach whereby the present fatigue analysis procedures based on a deformation-type plasticity analysis can be extended to handle the nonproportional cycling by their application on a 'memory event' by 'memory event' basis is postulated and discussed in the context of a simple component

CYCLIC PLASTIC BEHAVIOUR OF UFG COPPER UNDER CONTROLLED STRESS AND STRAIN LOADING

Directory of Open Access Journals (Sweden)

Lucie Navrátilová

2012-01-01

Full Text Available The influence of stress- and strain-controlled loading on microstructure and cyclic plastic behaviour of ultrafine-grained copper prepared by equal channel angular pressing was examined. The stability of microstructure is a characteristic feature for stress-controlled test whereas grain coarsening and development of bimodal structure was observed after plastic strain-controlled tests. An attempt to explain the observed behaviour was made.

Nonlinear analysis of 0-3 polarized PLZT microplate based on the new modified couple stress theory

Science.gov (United States)

Wang, Liming; Zheng, Shijie

2018-02-01

In this study, based on the new modified couple stress theory, the size- dependent model for nonlinear bending analysis of a pure 0-3 polarized PLZT plate is developed for the first time. The equilibrium equations are derived from a variational formulation based on the potential energy principle and the new modified couple stress theory. The Galerkin method is adopted to derive the nonlinear algebraic equations from governing differential equations. And then the nonlinear algebraic equations are solved by using Newton-Raphson method. After simplification, the new model includes only a material length scale parameter. In addition, numerical examples are carried out to study the effect of material length scale parameter on the nonlinear bending of a simply supported pure 0-3 polarized PLZT plate subjected to light illumination and uniform distributed load. The results indicate the new model is able to capture the size effect and geometric nonlinearity.

Tolerance to winemaking stress conditions of Patagonian strains of Saccharomyces eubayanus and Saccharomyces uvarum.

Science.gov (United States)

Origone, A C; Del Mónaco, S M; Ávila, J R; González Flores, M; Rodríguez, M E; Lopes, C A

2017-08-01

Evaluating the winemaking stress tolerance of a set of both Saccharomyces eubayanus and Saccharomyces uvarum strains from diverse Patagonian habitats. Yeast strains growth was analysed under increasing ethanol concentrations; all of them were able to grow until 8% v/v ethanol. The effect of different temperature and pH conditions as well as at SO 2 and hexose concentrations was evaluated by means of a central composite experimental design. Only two S. uvarum strains (NPCC 1289 and 1321) were able to grow in most stress conditions. Kinetic parameters analysed (μ max and λ) were statistically affected by temperature, pH and SO 2 , but not influenced by sugar concentration. The obtained growth model was used for predicting optimal growth conditions for both strains: 20°C, 0% w/v SO 2 and pH 4·5. Strains from human-associated environments (chichas) presented the highest diversity in the response to different stress factors. Two S. uvarum strains from chichas demonstrated to be the most tolerant to winemaking conditions. This work evidenced the potential use of two S. uvarum yeast strains as starter cultures in wines fermented at low temperatures. Saccharomyces eubayanus was significantly affected by winemaking stress conditions, limiting its use in this industry. © 2017 The Society for Applied Microbiology.

Annealing and etching effects on strain and stress sensitivity of polymer optical fibre Bragg grating sensors

DEFF Research Database (Denmark)

Pospori, A.; Marques, C. A.F.; Sáez-Rodríguez, D.

2017-01-01

Thermal annealing and chemical etching effects on the strain and stress sensitivity of polymer optical fibre based sensors are investigated. Bragg grating sensors have been photo-inscribed in PMMA optical fibre and their strain and stress sensitivity has been characterised before and after any...... annealing or etching process. The annealing and etching processes have been tried in different sequence in order to investigate their impact on the sensor's performance. Results show with high confidence that fibre annealing can improve both strain and stress sensitivities. The fibre etching can also...... provide stress sensitivity enhancement, however the strain sensitivity changes seems to be random....

Assessing Lifetime Stress Exposure Using the Stress and Adversity Inventory for Adults (Adult STRAIN): An Overview and Initial Validation

Science.gov (United States)

Slavich, George M.; Shields, Grant S.

2018-01-01

ABSTRACT Objective Numerous theories have proposed that acute and chronic stressors may exert a cumulative effect on life-span health by causing biological “wear and tear,” or allostatic load, which in turn promotes disease. Very few studies have directly tested such models, though, partly because of the challenges associated with efficiently assessing stress exposure over the entire life course. To address this issue, we developed the first online system for systematically assessing lifetime stress exposure, called the Stress and Adversity Inventory (STRAIN), and describe its initial validation here. Methods Adults recruited from the community (n = 205) were administered the STRAIN, Childhood Trauma Questionnaire—Short Form, and Perceived Stress Scale, as well as measures of socioeconomic status, personality, social desirability, negative affect, mental and physical health complaints, sleep quality, computer-assessed executive function, and doctor-diagnosed general health problems and autoimmune disorders. Results The STRAIN achieved high acceptability and was completed relatively quickly (mean = 18 minutes 39 seconds; interquartile range = 12–23 minutes). The structure of the lifetime stress data best fit two latent classes overall and five distinct trajectories over time. Concurrent associations with the Childhood Trauma Questionnaire—Short Form and Perceived Stress Scale were good (r values = .147–.552). Moreover, the STRAIN was not significantly related to personality traits or social desirability characteristics and, in adjusted analyses, emerged as the measure most strongly associated with all six of the health and cognitive outcomes assessed except current mental health complaints (β values = .16–.41; risk ratios = 1.02–1.04). Finally, test-retest reliability for the main stress exposure indices over 2–4 weeks was excellent (r values = .904–.919). Conclusions The STRAIN demonstrated good usability and acceptability; very good concurrent

Assessing Lifetime Stress Exposure Using the Stress and Adversity Inventory for Adults (Adult STRAIN): An Overview and Initial Validation.

Science.gov (United States)

Slavich, George M; Shields, Grant S

2018-01-01

Numerous theories have proposed that acute and chronic stressors may exert a cumulative effect on life-span health by causing biological "wear and tear," or allostatic load, which in turn promotes disease. Very few studies have directly tested such models, though, partly because of the challenges associated with efficiently assessing stress exposure over the entire life course. To address this issue, we developed the first online system for systematically assessing lifetime stress exposure, called the Stress and Adversity Inventory (STRAIN), and describe its initial validation here. Adults recruited from the community (n = 205) were administered the STRAIN, Childhood Trauma Questionnaire-Short Form, and Perceived Stress Scale, as well as measures of socioeconomic status, personality, social desirability, negative affect, mental and physical health complaints, sleep quality, computer-assessed executive function, and doctor-diagnosed general health problems and autoimmune disorders. The STRAIN achieved high acceptability and was completed relatively quickly (mean = 18 minutes 39 seconds; interquartile range = 12-23 minutes). The structure of the lifetime stress data best fit two latent classes overall and five distinct trajectories over time. Concurrent associations with the Childhood Trauma Questionnaire-Short Form and Perceived Stress Scale were good (r values = .147-.552). Moreover, the STRAIN was not significantly related to personality traits or social desirability characteristics and, in adjusted analyses, emerged as the measure most strongly associated with all six of the health and cognitive outcomes assessed except current mental health complaints (β values = .16-.41; risk ratios = 1.02-1.04). Finally, test-retest reliability for the main stress exposure indices over 2-4 weeks was excellent (r values = .904-.919). The STRAIN demonstrated good usability and acceptability; very good concurrent, discriminant, and predictive validity; and excellent test

AC loss characteristics of Bi2223/Ag sheathed tape wires subjected to mechanical strains and stresses

International Nuclear Information System (INIS)

Tsukamoto, Osami; Li, Z

2007-01-01

The influence of uniaxial tensile stress-strain on the AC loss characteristics of multifilamentary Bi2223/Ag sheathed tape wires was investigated. The uniaxial tensile stress-strain was applied to the sample wire in liquid nitrogen at atmospheric pressure, and the AC losses (transport, magnetization and total losses) were measured by an electric method. Two kinds of wire, oxide-dispersion strengthened Ag-alloy sheathed and Ag-alloy sheathed wires, were tested. The stress-strain curves of the tested wires were divided in three regions, i.e. elastic deformation, continuous plastic deformation and serrated-like plastic deformation regions, though the ranges of those regions were different for different kinds of wire. In the elastic and continuous plastic regions, the stress-strain curve was smooth and continuous, and in the serrated-like plastic region, the curve was rough. In the serrated-like plastic region, the wires kept elongating, while increase of the tensile stress was suspended. Dependences of the critical currents on the stress-strain were generally as follows. While decreases of the wire critical currents were in the range of less than 4% of the original values of the no-stress condition, the critical currents of the wires were reversible, that is, the critical currents recovered the original values at zero stress when the stress were released, regardless of whether the wires were in the elastic or continuous plastic region. In the continuous plastic region, the critical currents decreased up to 10%-15% of the original values and the critical currents were irreversible when the degradations of the critical currents exceeded about 4%. In the serrated-like plastic regions, the critical currents were more severely degraded. The AC loss characteristics of the wires are different in those regions. In the elastic and continuous plastic regions, the absolute values of AC losses were dependent on the stress-strain. However, the dependences of those normalized

Stress Tolerance Variations in Saccharomyces cerevisiae Strains from Diverse Ecological Sources and Geographical Locations.

Directory of Open Access Journals (Sweden)

Yan-Lin Zheng

Full Text Available The budding yeast Saccharomyces cerevisiae is a platform organism for bioethanol production from various feedstocks and robust strains are desirable for efficient fermentation because yeast cells inevitably encounter stressors during the process. Recently, diverse S. cerevisiae lineages were identified, which provided novel resources for understanding stress tolerance variations and related shaping factors in the yeast. This study characterized the tolerance of diverse S. cerevisiae strains to the stressors of high ethanol concentrations, temperature shocks, and osmotic stress. The results showed that the isolates from human-associated environments overall presented a higher level of stress tolerance compared with those from forests spared anthropogenic influences. Statistical analyses indicated that the variations of stress tolerance were significantly correlated with both ecological sources and geographical locations of the strains. This study provides guidelines for selection of robust S. cerevisiae strains for bioethanol production from nature.

Creep strain accumulation in a typical LMFBR piperun

International Nuclear Information System (INIS)

Johnstone, T.L.

1975-01-01

The analysis described allows the strain concentrations in typical LMFBR two anchor point uniplanar piperuns to be calculated. Account is taken of the effect of pipe elbows in attracting creep strain to themselves as well as possible movements of the thrust line due to strain redistribution. The influence of the initial load conditions is also examined. The stress relaxation analysis is facilitated by making the assumption that a cross-sectional stress distribution determined by the asymptotic fully developed state of creep exists at all times. Use is then made of Hoff(s) analogy between materials with a creep law of the Norton type and those with a corresponding non-linear elastic stress strain law, to determine complementary strain energy rates for straight pipes and bends. Ovalisation of the latter produces an increased strain energy rate which can be simply calculated by comparison with an equal length of straight pipe through employing a creep flexibility factor due to Spence. Deflection rates at any location in the pipework can then be evaluated in terms of the thermal restraint forces at that location by an application of Castigliano's principle. In particular for an anchor point the deflection rates are identically zero and this leads to the generation of 3 simultaneous differential equations determining the relaxation of the anchor reactions. Indicative results are presented for the continuous relaxation at 570 deg C of the thermally induced stress in a planar approximation to a typical LMFBR pipe run chosen to have peak elbow stresses close to the code maximum. The results indicate a ratio, after 10 5 hours, of 3 for creep strain concentration relative to initial peak strain (calculated on the assumption of fully elastic behavior) in the most severely affected elbow, when either austenitic 316 or 321 creep properties are employed

Flow stress and dynamic strain-ageing of β-transformed Zircaloy-4

International Nuclear Information System (INIS)

Woo, O.T.; Tseng, D.; Tangri, K.; MacEwen, S.R.

1979-01-01

The 0.2% yield stress of β-transformed Zircaloy-4 was found to be independent of prior-β grain size but varied as the inverse of the transformed β plate width. A dislocation loop expansion model originally proposed by Langford and Cohen (1969) for cold-drawn iron wires is used to explain the inverse plate width dependence. Both air-cooled and water-quenched samples exhibited dynamic strain-ageing effects in approximately the same temperature range of 573 to 673 K: (a) a local minimum in strain-rate sensitivity is associated with a peak or an inflection point in the temperature dependence of the 0.2% yield stress for water-quenched or air-cooled samples respectively, and (b) yield drops were observed in strain rate change tests. (Auth.)

An analytical nonlinear magnetoelectric coupling model of laminated composites under combined pre-stress and magnetic bias loadings

International Nuclear Information System (INIS)

Zhou, Hao-Miao; Qu, Shao-Xing; Ou, Xiao-Wei; Xiao, Ying; Wu, Hua-Ping

2013-01-01

Based on the equivalent circuit method, this paper adopts the nonlinear magnetostrictive constitutive relations to establish an analytical nonlinear magnetoelectric coefficient model for magnetostrictive/piezoelectric/magnetostrictive laminated magnetoelectric composites. When the pre-stress is set to zero in the model, the predicted results of the magnetoelectric coefficient coincide well with the available experimental results both qualitatively and quantitatively. Using the model, we can qualitatively predict the influence of the pre-stress, magnetic bias fields and the volume fraction of the magnetostrictive material on the magnetoelectric coefficient. The predicted results show that the influences of the pre-stress on the magnetoelectric coefficient, which varies with the magnetic bias field, before and after reaching the magnetoelectric coefficient maximum, are opposite. That is, the influence of the pre-stress on curves of the magnetoelectric coefficient reverses when the magnetoelectric coefficient reaches its maximum. Therefore, the correct setting of the pre-stress can lower the applied magnetic bias field and improve the magnetoelectric coefficient. The established nonlinear magnetoelectric effect model can provide a theoretical basis for regulating the magnetoelectric coefficient by the pre-stress and magnetic bias field and make it possible to design high-precision miniature magnetoelectric devices. (paper)

Method and analysis for determining yielding of titanium alloy with nonlinear Rayleigh surface waves

Energy Technology Data Exchange (ETDEWEB)

Guo, Shifeng; Zhang, Lei; Mirshekarloo, Meysam Sharifzadeh; Chen, Shuting; Chen, Yi Fan; Wong, Zheng Zheng; Shen, Zhiyuan; Liu, Huajun; Yao, Kui, E-mail: k-yao@imre.a-star.edu.sg

2016-07-04

Methods for determining yielding of titanium (Ti) alloy material with second harmonic Rayleigh ultrasonic wave are investigated. Both piezoelectric angle beam transducers and high frequency laser scanning vibrometer (LSV) are used to detect ultrasonic signals in the Ti alloy specimens with different plastic strain levels. Technical features and outcomes with use of piezoelectric transducers and LSV are compared. The method using piezoelectric transducers, with much higher signal-to-noise ratio than LSV, has been further improved by deploying two transducers with central frequencies corresponding to the fundamental and second order harmonic signals respectively to improve the testing reliability and accuracy. Both the techniques using piezoelectric transducer and LSV demonstrate consistently that the acoustic nonlinearity increases with plastic strain, and the second harmonic Rayleigh ultrasonic wave can be utilized for effective determination of yielding in Ti alloy. Our experiments further show that the acoustic nonlinearity increases gradually with plastic strain at small plastic strain level, and there is a more significant increase of acoustic nonlinearity when the plastic strain reaches a higher level. Microscopic investigations using scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) are conducted for clarifying the relationship between the observed acoustic nonlinearity and micro-structural changes.

Stress relaxation in viscous soft spheres.

Science.gov (United States)

Boschan, Julia; Vasudevan, Siddarth A; Boukany, Pouyan E; Somfai, Ellák; Tighe, Brian P

2017-10-04

We report the results of molecular dynamics simulations of stress relaxation tests in athermal viscous soft sphere packings close to their unjamming transition. By systematically and simultaneously varying both the amplitude of the applied strain step and the pressure of the initial condition, we access both linear and nonlinear response regimes and control the distance to jamming. Stress relaxation in viscoelastic solids is characterized by a relaxation time τ* that separates short time scales, where viscous loss is substantial, from long time scales, where elastic storage dominates and the response is essentially quasistatic. We identify two distinct plateaus in the strain dependence of the relaxation time, one each in the linear and nonlinear regimes. The height of both plateaus scales as an inverse power law with the distance to jamming. By probing the time evolution of particle velocities during relaxation, we further identify a correlation between mechanical relaxation in the bulk and the degree of non-affinity in the particle velocities on the micro scale.

Influence of local microplastic strains on stress corrosion of 08Kh18N10T steel

International Nuclear Information System (INIS)

Moskvin, L.N.; Efimov, A.A.; Sherman, Ya.I.; Fedorova, T.I.

1987-01-01

Study on specific features of microhomogeneous strain in the process of plastic strain development and their role in stress corrosion of 08Kh18N10T steel sheet specimens subject to preliminary strain by 1, 3, 6, 16 and 23% and subsequent tests of stress corrosion in magnesium chloride solution at 150 deg C 140 MPa has been carried out. Analysis of test results has shown that microplastic strain is distributed over a specimen nonuniformly and is accompanied with the slip bands formation which are sources of corrosion crack origination and development. 08Kh18N10T steel manifests the highest trend to stress corrosion under 1% microplastic strain

Nonlinear and anisotropic tensile properties of graft materials used in soft tissue applications.

Science.gov (United States)

Yoder, Jonathon H; Elliott, Dawn M

2010-05-01

The mechanical properties of extracellular matrix grafts that are intended to augment or replace soft tissues should be comparable to the native tissue. Such grafts are often used in fiber-reinforced tissue applications that undergo multi-axial loading and therefore knowledge of the anisotropic and nonlinear properties are needed, including the moduli and Poisson's ratio in two orthogonal directions within the plane of the graft. The objective of this study was to measure the tensile mechanical properties of several marketed grafts: Alloderm, Restore, CuffPatch, and OrthADAPT. The degree of anisotropy and non-linearity within each graft was evaluated from uniaxial tensile tests and compared to their native tissue. The Alloderm graft was anisotropic in both the toe- and linear-region of the stress-strain response, was highly nonlinear, and generally had low properties. The Restore and CuffPatch grafts had similar stress-strain responses, were largely isotropic, had a linear-region modulus of 18MPa, and were nonlinear. OrthADAPT was anisotropic in the linear-region (131 MPA vs 47MPa in the toe-region) and was highly nonlinear. The Poisson ratio for all grafts was between 0.4 and 0.7, except for the parallel orientation of Restore which was greater than 1.0. Having an informed understanding of how the available grafts perform mechanically will allow for better assessment by the physician for which graft to apply depending upon its application. Copyright 2010 Elsevier Ltd. All rights reserved.

Material law for concrete under multiaxial stress

International Nuclear Information System (INIS)

Geistefeldt, H.

1977-01-01

In this paper a general triaxial set of finite strain-stress relations is derived, which can include in a step-by-step way nearly all known factors and curves of material response. The finite constitutive equations representing the behavior of concrete are related to the main strain-directions. The elastic part, the functions for uniaxial behavior, those for biaxial response and finally the relation-parts, nonzero only in triaxial stress-state, can be reset separately by suitable functions which have been adjusted to the material response of actual concrete known from special tests. In nonlinear incremental analysis a potential is usually assumed in incremental material behavior to keep incremental stiffness matrices symmetric. If the proposed generalized set of constitutive equations is restricted to special types of functions, the resulting tangent stiffness is symmetric. Special functions for the various parts are presented, the tangent stiffness of which can easily be derived explicitly by partial differentiation of the related strain-stress relations. Thus the application of the proposed constitutive equations in incremental nonlinear analysis is very effective. The free coefficients of one general set of equations are adjusted step by step to the results of Kupfer's biaxial tests under shorttime loading. With a new and very short bixial failure criterion for concrete, which has been stated and compared with test results, the analytic description of the biaxial behavior of Kupfer's concrete is completed. With some additional assumptions the proposed failure criteria and the strain-stress equations for concrete are extended to the biaxial response of uncracked othogonally reinforced concrete response

Consistent stress-strain ductile fracture model as applied to two grades of beryllium

International Nuclear Information System (INIS)

Priddy, T.G.; Benzley, S.E.; Ford, L.M.

1980-01-01

Published yield and ultimate biaxial stress and strain data for two grades of beryllium are correlated with a more complete method of characterizing macroscopic strain at fracture initiation in ductile materials. Results are compared with those obtained from an exponential, mean stress dependent, model. Simple statistical methods are employed to illustrate the degree of correlation for each method with the experimental data

Simulation of Stress-Strain State of Shovel Rotary Support Kingpin

Science.gov (United States)

Khoreshok, A. A.; Buyankin, P. V.; Vorobiev, A. V.; Dronov, A. A.

2016-04-01

The article presents the sequence of computational simulation of stress-strain state of shovel’s rotary support. Computation results are analyzed, the kingpin is specified as the most loaded element, maximum stress zones are identified. Kingpin design modification such as enhancement of fillet curvature radius to 25 mm and displacement of eyebolt holes on the diameter of 165 mm are proposed, thus diminishing impact of stress concentrators and improving reliability of the rotary support.

Relationship between strain and central deflection in small punch creep specimens

International Nuclear Information System (INIS)

Yang Zhen; Wang Zhiwen

2003-01-01

Acquiring information about creep strain directly from small punch creep tests is difficult because the deformation behaviour of the small punch specimen is complicated. A routine is suggested in the present paper to treat this problem indirectly. Based on a finite element analysis, it is proposed that the relationship of central deflection δ to central creep strain ε c of a specimen subjected to creep can be represented approximately by the relationship of central deflection δ to central (elastic-plastic) strain ε of a specimen not subjected to creep. With this hypothesis, the δ∼ε c relation of the small punch creep specimen is obtained by resorting to a rigid-plastic membrane stretch forming model. Finally, small punch creep test results are used to evaluate creep strain and creep strain rate by taking advantage of this δ∼ε c relation

Microstructural Origins of Nonlinear Response in Associating Polymers under Oscillatory Shear

Directory of Open Access Journals (Sweden)

Mark A. Wilson

2017-10-01

Full Text Available The response of associating polymers with oscillatory shear is studied through large-scale simulations. A hybrid molecular dynamics (MD, Monte Carlo (MC algorithm is employed. Polymer chains are modeled as a coarse-grained bead-spring system. Functionalized end groups, at both ends of the polymer chains, can form reversible bonds according to MC rules. Stress-strain curves show nonlinearities indicated by a non-ellipsoidal shape. We consider two types of nonlinearities. Type I occurs at a strain amplitude much larger than one, type II at a frequency at which the elastic storage modulus dominates the viscous loss modulus. In this last case, the network topology resembles that of the system at rest. The reversible bonds are broken and chains stretch when the system moves away from the zero-strain position. For type I, the chains relax and the number of reversible bonds peaks when the system is near an extreme of the motion. During the movement to the other extreme of the cycle, first a stress overshoot occurs, then a yield accompanied by shear-banding. Finally, the network restructures. Interestingly, the system periodically restores bonds between the same associating groups. Even though major restructuring occurs, the system remembers previous network topologies.

Simple quasi-analytical holonomic homogenization model for the non-linear analysis of in-plane loaded masonry panels: Part 1, meso-scale

Science.gov (United States)

Milani, G.; Bertolesi, E.

2017-07-01

A simple quasi analytical holonomic homogenization approach for the non-linear analysis of masonry walls in-plane loaded is presented. The elementary cell (REV) is discretized with 24 triangular elastic constant stress elements (bricks) and non-linear interfaces (mortar). A holonomic behavior with softening is assumed for mortar. It is shown how the mechanical problem in the unit cell is characterized by very few displacement variables and how homogenized stress-strain behavior can be evaluated semi-analytically.

Mental Strain and Chronic Stress among University Students with Symptoms of Irritable Bowel Syndrome

Directory of Open Access Journals (Sweden)

Marco D. Gulewitsch

2013-01-01

Full Text Available Aim. To investigate the degree of mental strain and chronic stress in a German community sample of students with IBS-like symptoms. Methods and Materials. Following an internet-based survey about stress, this study recruited 176 German university students (23.45±2.48 years; 48.3% males with IBS-like symptoms according to Rome III and 181 students without IBS (23.55±2.82 years; 50.3% males and compared them regarding current mental strain (SCL-90-R and the extend of chronic stress. Beyond this, IBS subtypes, IBS severity, and health care utilization were assessed. Results. Students fulfilling IBS criteria showed significantly elevated values of mental strain and chronic stress. Nearly 40% of the IBS group (versus 20% of the controls reached a clinically relevant value on the SCL-90-R global severity scale. IBS subtypes did not differ in terms of mental distress or chronic stress. Somatization, anxiety, and the chronic stressors “work overload,” “social tension,” and “dissatisfaction with job” were most closely connected to IBS symptom severity. Regarding health care utilization, our results show that consulting a physician frequently was not associated significantly with elevated mental strain or chronic stress but with IBS symptom severity. Conclusion. Our data contribute additional evidence to the distinct association between psychological stress and IBS in community samples.

Gene Cloning, Expression and Activity Analysis of Manganese Superoxide Dismutase from Two Strains of Gracilaria lemaneiformis (Gracilariaceae, Rhodophyta under Heat Stress

Directory of Open Access Journals (Sweden)

Lu Zhang

2012-04-01

Full Text Available Manganese superoxide dismutase (Mn-SOD plays a crucial role in antioxidant responses to environmental stress. To determine whether Mn-SOD affects heat resistance of Gracilaria lemaneiformis, we cloned Mn-SOD cDNA sequences of two strains of this red alga, wild type and cultivar 981. Both cDNA sequences contained an ORF of 675 bp encoding 224 amino acid residues. The cDNA sequences and the deduced amino acid sequences of the two strains shared relatively high identity (more than 99%. No intron existed in genomic DNA of Mn-SOD in G. lemaneiformis. Southern blotting indicated that there were multiple copies, possibly four, of Mn-SOD in both strains. Both in the wild type and cultivar 981, SOD mRNA transcription and SOD activity increased under high temperature stress, while cultivar 981 was more heat resistant based on its SOD activity. This research suggests that there may be a direct relationship between SOD activity and the heat resistance of G. lemaneiformis.

Stress strain modelling and analysis of a piezo-coated optical fibre sensor

Science.gov (United States)

Al-Raweshidy, H.; Ali, H.; Obayya, S. S. A.; Langley, R.; Batchelor, J.

2005-02-01

A finite element model, using commercially available software, is presented to simulate the piezoelectrically induced stresses and strains in an optical fibre to be used as antenna. These stresses and strains are generated by a layer of piezoelectric polymer deposited on the cladding of a short fibre sample. The theoretical basis for the work is briefly explained and the modelling process is emphasised. Two types of fibre are investigated - circular fibre and D-fibre, and the results compared, analysed and discussed. It is shown that in the D-fibre, the stress and displacement increased by 1.46 and 115 times, respectively, in comparison with the circular fibre.

Occupational stress and strain in the Royal Navy 2007.

Science.gov (United States)

Bridger, R S; Brasher, K; Dew, A; Kilminster, S

2008-12-01

Previous surveys of psychological strain in the Naval Service (NS) have shown higher than expected levels of strain when compared to the general population. To repeat the survey last carried out in 2004 and to obtain further information on the nature of the occupational stressors associated with strain. General Health Questionnaire-12 strain rates and job/life stressors were measured using a Work and Well-Being Questionnaire. Models of strain were developed for male and female personnel in the Royal Navy (RN) and males in the Royal Marines (RM). The response rate was 57%. The psychological strain rate was 31.5% overall. Personnel suffering from strain tended to be 'overcommitted' to work, had low levels of commitment to the NS and had suffered stressful life events (SLEs) in the previous 12 months. Strain rates declined with age and rank in males, but not in females. Strain was significantly positively correlated with levels of overcommitment, effort-reward imbalance (ERI), role conflict, work-family conflict, organizational commitment and exposure to SLEs. Models of strain in the males and females in the RN and in the RM accounted for between 37 and 44% of the variance in strain. The survey provides evidence for both the demand control and ERI models-components of these models contribute independently to strain. High levels of commitment to the organization were associated with lower strain and exposure to SLEs to higher strain.

Development of a quick and easy-to-install strain measurement tool for piping stress evaluation

International Nuclear Information System (INIS)

Takahama, Tsunemichi; Nishimura, Kazuma; Ninomiya, Seiichiro; Matsumoto, Yoshihiro; Harada, Yutaka

2015-01-01

To avoid failures of small bore piping connections caused by high cycle fatigue, it is important to measure the stresses around the connections. To measure such stresses, the authors have developed an easily-attachable and detachable strain measurement tool which utilizes strain gauges in combination with our patented strain gauge holder. Traditionally, strain gauges have been bonded to piping surfaces using adhesive; however, with the newly-developed measurement tool, bonding adhesive is no longer necessary. The tool can be installed quickly and easily on a piping surface and measure the strains on the piping as accurately as adhesively-bonded strain gauges. Accordingly, the new strain measurement tool significantly reduces the work time without affecting the measurement accuracy. (author)

Non-linear calculation of PCRV using dynamic relaxation

International Nuclear Information System (INIS)

Schnellenbach, G.

1979-01-01

A brief review is presented of a numerical method called the dynamic relaxation method for stress analysis of the concrete in prestressed concrete pressure vessels. By this method the three-dimensional elliptic differential equations of the continuum are changed into the four-dimensional hyperbolic differential equations known as wave equations. The boundary value problem of the static system is changed into an initial and boundary value problem for which a solution exists if the physical system is defined at time t=0. The effect of non-linear stress-strain behaviour of the material as well as creep and cracking are considered

Type of faulting and orientation of stress and strain as a function of space and time in Kilauea's south flank, Hawaii

Science.gov (United States)

Gillard, D.; Wyss, M.; Okubo, P.

1996-01-01

Earthquake focal mechanisms of events occurring between 1972 and 1992 in the south flank of Kilauea volcano, Hawaii, are used to infer the state of stress and strain as a function of time and space. We have determined 870 fault plane solutions from P wave first motion polarities for events with magnitudes ML ??? 2.5 and depth ranging between 6 and 12 km. Faulting is characterized by a mixture of decollement, reverse, and normal faults. Most large earthquakes with magnitude M 7 rupture the decollement plane, since it is the only surface large enough to generate magnitude 7 or larger earthquakes. The percentage of reverse faulting events is high compared to the decollement and normal faulting mechanisms for the period 1972-1983. The percentage of decollement type focal mechanisms becomes dominant after 1983. This pattern of faulting activity suggests that pressure was building up within Kilauea's rift zone prior to the 1983 Puu'Oo eruption. Overall, a single stress orientation with the maximum compressive stress oriented SE perpendicular to the rift and dipping at 45?? is compatible with the coeval existence of decollement, reverse, and normal faults. However, in a crustal volume east of longitude 155??10'W, we find a change of the orientation of ??1 from nearly horizontal to plunging 45?? SE occurring in 1979. This stress rotation suggests magma movements within the aseismic part of Kilauea's east rift zone. The strain and stress orientations are coaxial in the south flank except within the volume where the stress rotation is observed. We observe a change in the relationship between stress and strain directions caused either by the shifting of seismic activity from reverse faults to decollements, while stress stays constant, or by a rotation of stress, while strain remains constant. Assuming that the model of a noncohesive Coulomb wedge is appropriate for Kilauea's south flank, we find that high pore pressures are prevalent along the decollement and within the wedge

A new constitutive equation for strain hardening and softening of fcc metals during severe plastic deformation

International Nuclear Information System (INIS)

Wei, W.; Wei, K.X.; Fan, G.J.

2008-01-01

The stress-strain relationship for strain hardening and softening of high-purity aluminum and copper, which were deformed by equal channel angular pressing (ECAP) at ambient temperature, was analyzed by combining the Estrin and Mecking (EM) model and an Avrami-type equation with experimental data during severe plastic deformation. The initial strain hardening can be described by the EM model, while the flow stress arrives at the peak stress after it was saturated. However, strain softening similar to plastic deformation at high temperatures is observed after the peak stress. Moreover, the peak strain at the maximum flow stress is ∼4 for copper and ∼2 for aluminum. A new constitutive equation was developed to describe strain softening at high strain levels, which was supported well by tensile, compression and microhardness tests at room temperature and low strain rate. It was observed that dynamic recovery and recrystallization occurs in copper, and recrystallized grains and their growth in aluminum. The results indicate that dynamic recovery and recrystallization was the dominant softening mechanism, which was confirmed by scanning electron microscopy-electron channeling contrast observations and the abnormal relationship between the imposed strain during ECAP and subsequent recrystallization temperature after ECAP

Development of serial measurement system for three-dimensional stress determination by over-coring the strains on borehole wall

International Nuclear Information System (INIS)

Itamoto, Masaharu; Kuwabara, Kazumichi; Tanno, Takeo; Nakayama, Yoshiki; Mizuta, Yoshiaki

2007-01-01

In order to determine the three-dimensional stress state in serial order, the authors developed the serial measurement system for three-dimensional stress determination by over-coring the strains on the borehole wall. The serial stress measurements give the value of the stresses with high accuracy and bring the regional stress variations. In this paper, the authors describe the studies through FEM analysis on the effect of over-coring diameter, the influence of strain gauge length and the behavior of strain on the borehole wall, induced by biaxial external loading. We developed the multi-strain gauge mounted packer and examined it by measuring the strains on the borehole wall through biaxial loading test. The Laboratory tests showed its applicability to practical use. (author)

The relationship between crude oil spot and futures prices: Cointegration, linear and nonlinear causality

International Nuclear Information System (INIS)

Bekiros, Stelios D.; Diks, Cees G.H.

2008-01-01

The present study investigates the linear and nonlinear causal linkages between daily spot and futures prices for maturities of one, two, three and four months of West Texas Intermediate (WTI) crude oil. The data cover two periods October 1991-October 1999 and November 1999-October 2007, with the latter being significantly more turbulent. Apart from the conventional linear Granger test we apply a new nonparametric test for nonlinear causality by Diks and Panchenko after controlling for cointegration. In addition to the traditional pairwise analysis, we test for causality while correcting for the effects of the other variables. To check if any of the observed causality is strictly nonlinear in nature, we also examine the nonlinear causal relationships of VECM filtered residuals. Finally, we investigate the hypothesis of nonlinear non-causality after controlling for conditional heteroskedasticity in the data using a GARCH-BEKK model. Whilst the linear causal relationships disappear after VECM cointegration filtering, nonlinear causal linkages in some cases persist even after GARCH filtering in both periods. This indicates that spot and futures returns may exhibit asymmetric GARCH effects and/or statistically significant higher order conditional moments. Moreover, the results imply that if nonlinear effects are accounted for, neither market leads or lags the other consistently, videlicet the pattern of leads and lags changes over time. (author)

Modeling of the stress-strain state of the ground mass contaminated with peracetic acid

Directory of Open Access Journals (Sweden)

Levenko Anna

2017-01-01

Full Text Available None of the methods described previously provides a solution to the problem that deals with the SSS evaluation of the ground mass which is under the influence of chemically active substances and, in particular, under the influence of peracetic acid. The stress-strain state of the ground mass contaminated with peracetic acid was estimated. Stresses occurring in the ground mass in the natural state were determined after the entry of acid into it and after the chemical fixation of it with sodium silicate. All the parameters of the stress-strain state of the ground mass were obtained under a number of physical and mechanical conditions. It was determined that following the work on the silicatization of the ground mass contaminated with peracetic acid the quantity of strain decreased by 26.11 to 48.9%. The comparison of the results of stress calculations indicates the stress reduction in the ground mass in 1.8 – 2.6 times after its fixing.

Applications and algorithms for mixed integer nonlinear programming

International Nuclear Information System (INIS)

Leyffer, Sven; Munson, Todd; Linderoth, Jeff; Luedtke, James; Miller, Andrew

2009-01-01

The mathematical modeling of systems often requires the use of both nonlinear and discrete components. Discrete decision variables model dichotomies, discontinuities, and general logical relationships. Nonlinear functions are required to accurately represent physical properties such as pressure, stress, temperature, and equilibrium. Problems involving both discrete variables and nonlinear constraint functions are known as mixed-integer nonlinear programs (MINLPs) and are among the most challenging computational optimization problems faced by researchers and practitioners. In this paper, we describe relevant scientific applications that are naturally modeled as MINLPs, we provide an overview of available algorithms and software, and we describe ongoing methodological advances for solving MINLPs. These algorithmic advances are making increasingly larger instances of this important family of problems tractable.

Non-Linear Behaviour Of Gelatin Networks Reveals A Hierarchical Structure

KAUST Repository

Yang, Zhi; Hemar, Yacine; Hilliou, loic; Gilbert, Elliot P.; McGillivray, Duncan James; Williams, Martin A. K.; Chaieb, Saharoui

2015-01-01

We investigate the strain hardening behaviour of various gelatin networks - namely physically-crosslinked gelatin gel, chemically-crosslinked gelatin gels, and a hybrid gels made of a combination of the former two - under large shear deformations using the pre-stress, strain ramp, and large amplitude oscillation shear protocols. Further, the internal structures of physically-crosslinked gelatin gel and chemically-crosslinked gelatin gels were characterized by small angle neutron scattering (SANS) to enable their internal structures to be correlated with their nonlinear rheology. The Kratky plots of SANS data demonstrate the presence of small cross-linked aggregates within the chemically-crosslinked network, whereas in the physically-crosslinked gels a relatively homogeneous structure is observed. Through model fitting to the scattering data, we were able to obtain structural parameters, such as correlation length (ξ), cross-sectional polymer chain radius (Rc), and the fractal dimension (df) of the gel networks. The fractal dimension df obtained from the SANS data of the physically-crosslinked and chemically crosslinked gels is 1.31 and 1.53, respectively. These values are in excellent agreement with the ones obtained from a generalized non-linear elastic theory we used to fit our stress-strain curves. The chemical crosslinking that generates coils and aggregates hinders the free stretching of the triple helices bundles in the physically-crosslinked gels.

Non-Linear Behaviour Of Gelatin Networks Reveals A Hierarchical Structure

KAUST Repository

Yang, Zhi

2015-12-14

We investigate the strain hardening behaviour of various gelatin networks - namely physically-crosslinked gelatin gel, chemically-crosslinked gelatin gels, and a hybrid gels made of a combination of the former two - under large shear deformations using the pre-stress, strain ramp, and large amplitude oscillation shear protocols. Further, the internal structures of physically-crosslinked gelatin gel and chemically-crosslinked gelatin gels were characterized by small angle neutron scattering (SANS) to enable their internal structures to be correlated with their nonlinear rheology. The Kratky plots of SANS data demonstrate the presence of small cross-linked aggregates within the chemically-crosslinked network, whereas in the physically-crosslinked gels a relatively homogeneous structure is observed. Through model fitting to the scattering data, we were able to obtain structural parameters, such as correlation length (ξ), cross-sectional polymer chain radius (Rc), and the fractal dimension (df) of the gel networks. The fractal dimension df obtained from the SANS data of the physically-crosslinked and chemically crosslinked gels is 1.31 and 1.53, respectively. These values are in excellent agreement with the ones obtained from a generalized non-linear elastic theory we used to fit our stress-strain curves. The chemical crosslinking that generates coils and aggregates hinders the free stretching of the triple helices bundles in the physically-crosslinked gels.

Molecular characteristics of stress overshoot for polymer melts under start-up shear flow.

Science.gov (United States)

Jeong, Sohdam; Kim, Jun Mo; Baig, Chunggi

2017-12-21

Stress overshoot is one of the most important nonlinear rheological phenomena exhibited by polymeric liquids undergoing start-up shear at sufficient flow strengths. Despite considerable previous research, the fundamental molecular characteristics underlying stress overshoot remain unknown. Here, we analyze the intrinsic molecular mechanisms behind the overshoot phenomenon using atomistic nonequilibrium molecular dynamics simulations of entangled linear polyethylene melts under shear flow. Through a detailed analysis of the transient rotational chain dynamics, we identify an intermolecular collision angular regime in the vicinity of the chain orientation angle θ ≈ 20° with respect to the flow direction. The shear stress overshoot occurs via strong intermolecular collisions between chains in the collision regime at θ = 15°-25°, corresponding to a peak strain of 2-4, which is an experimentally well-known value. The normal stress overshoot appears at approximately θ = 10°, at a corresponding peak strain roughly equivalent to twice that for the shear stress. We provide plausible answers to several basic questions regarding the stress overshoot, which may further help understand other nonlinear phenomena of polymeric systems.

Discussion on accuracy of weld residual stress measurement by neutron diffraction. Influence of strain free reference

International Nuclear Information System (INIS)

Suzuki, Hiroshi; Akita, Koichi

2012-01-01

It is required to evaluate a strain-free reference, α 0 , to perform accurate stress measurement using neutron diffraction. In this study, accuracy of neutron stress measurement was quantitatively discussed from α 0 evaluations on a dissimilar metal butt-weld between a type 304 austenitic stainless steel and an A533B low alloy ferritic steel. A strain-free standard specimen and a sliced specimen with 10 mm thickness taken from the dissimilar metal butt-weld were utilized. In the lattice constant evaluation using the standard specimen, average lattice constant derived from multiple hkl reflections was evaluated as the stress-free reference with cancelling out an intergranular strain. Comparing lattice constant distributions in each reflection with average lattice constant distribution in the standard specimen, αFe211 and γFe311 reflections were judged as a suitable reflection for neutron strain measurement to reduce intergranular strain effects. Residual stress distribution in the sliced specimen evaluated using α 0 measured here exhibited higher accuracy than that measured using strain gauges. On the other hand, α 0 distributions were evaluated using the sliced specimen under the plane-stress condition. Existence of slight longitudinal residual stresses near the weld center decreased accuracy of the α 0 evaluations, which means that it is required to optimize the thickness of the sliced specimen for accurate α 0 evaluation under plane strain condition. As a conclusion of this study, it was confirmed that procedures of accurate α 0 evaluation, optimization of the measurement condition, and multiple evaluations on the results play an important role to improve accuracy of the residual stress measurement using neutron diffraction. (author)

Relationship between anelastic and non-linear visco-plastic behavior of 316 stainless steel at low homologous temperature

International Nuclear Information System (INIS)

Nir, N.; Huang, F.H.; Hart, E.W.; Li, C.Y.

1976-05-01

At low homologous temperature the plastic strain rate seems to be controlled largely by dislocation glide friction. However, since a sizeable fraction of the applied stress sigma is dissipated in overcoming the strong barriers due to dislocation tangles generated by strain hardening, only a portion of the applied stress is actually expended against the frictional resistance. A recent model for this process includes the role of dislocation pile-ups at the strong barriers. The pile-ups provide a mechanism for producing the internal back stresses that limit the effective frictional stress. The also appear in the deformation as a stored anelastic strain component. The resultant behavior at low temperature and high stress is similar to that proposed by Grupta and Li. The same model also predicts an anelastic behavior at low stress. Measurements at both high and low stress levels on 316 Stainless Steel have now shown that the predictions of the model are quantitatively consistent at both stress levels

Micromechanical modelling of the cyclic stress-strain behaviour of nickel polycrystals

International Nuclear Information System (INIS)

Steckmeyer, A.; Sauzay, M.; Weidner, A.; Hieckmann, E.

2012-01-01

A crystalline elasto-plasticity model is proposed to describe the cyclic behaviour of face-centred cubic crystals. It is based on many experimental observations correlating the observed dislocation structures with the orientations of corresponding crystals. The model distinguishes between two families of crystals. The first family gathers crystals for which the tension-compression loading axis is located in the centre of the standard stereo-graphic triangle. These crystals, in which bundle and/or slip band dislocation structures are usually observed, are subjected to single slip deformation. The second family gathers crystals in which labyrinths or wall dislocation structures develop. These crystals are subjected to multiple slip deformation. Crystalline plasticity parameters are adjusted using only the single crystal cyclic stress strain curves measured for one orientation of each of the two families. The relevance of the model is evaluated through finite elements calculations of the uniaxial cyclic deformation of texture-free nickel polycrystals at room temperature. The macroscopic predictions are in reasonable agreement with experimental data concerning both the cyclic stress-strain curve and the hysteresis loops provided either large grain sizes or intermediate to high plastic strains are considered. By construction, the modelling is unable to predict grain size effect observed at low plastic strain. The distributions of the mean grain plastic strains become narrower as the macroscopic plastic strain amplitude increases, which appears consistent with the large scattering in high-cycle fatigue lifetimes usually observed. On the contrary, the distributions of mean grain axial stresses get broader, in agreement with neutron and X-ray diffraction measurement values published in the literature. The influence of the material parameters is then discussed. Finally, the cumulative probability curves of the number of cycles to fatigue microcrack nucleation are deduced

Intra-species Genomic and Physiological Variability Impact Stress Resistance in Strains of Probiotic Potential.

Science.gov (United States)

Arnold, Jason W; Simpson, Joshua B; Roach, Jeffrey; Kwintkiewicz, Jakub; Azcarate-Peril, M Andrea

2018-01-01

Large-scale microbiome studies have established that most of the diversity contained in the gastrointestinal tract is represented at the strain level; however, exhaustive genomic and physiological characterization of human isolates is still lacking. With increased use of probiotics as interventions for gastrointestinal disorders, genomic and functional characterization of novel microorganisms becomes essential. In this study, we explored the impact of strain-level genomic variability on bacterial physiology of two novel human Lactobacillus rhamnosus strains (AMC143 and AMC010) of probiotic potential in relation to stress resistance. The strains showed differences with known probiotic strains ( L. rhamnosus GG, Lc705, and HN001) at the genomic level, including nucleotide polymorphisms, mutations in non-coding regulatory regions, and rearrangements of genomic architecture. Transcriptomics analysis revealed that gene expression profiles differed between strains when exposed to simulated gastrointestinal stresses, suggesting the presence of unique regulatory systems in each strain. In vitro physiological assays to test resistance to conditions mimicking the gut environment (acid, alkali, and bile stress) showed that growth of L. rhamnosus AMC143 was inhibited upon exposure to alkaline pH, while AMC010 and control strain LGG were unaffected. AMC143 also showed a significant survival advantage compared to the other strains upon bile exposure. Reverse transcription qPCR targeting the bile salt hydrolase gene ( bsh ) revealed that AMC143 expressed bsh poorly (a consequence of a deletion in the bsh promoter and truncation of bsh gene in AMC143), while AMC010 had significantly higher expression levels than AMC143 or LGG. Insertional inactivation of the bsh gene in AMC010 suggested that bsh could be detrimental to bacterial survival during bile stress. Together, these findings show that coupling of classical microbiology with functional genomics methods for the

Intra-species Genomic and Physiological Variability Impact Stress Resistance in Strains of Probiotic Potential

Directory of Open Access Journals (Sweden)

Jason W. Arnold

2018-02-01

Full Text Available Large-scale microbiome studies have established that most of the diversity contained in the gastrointestinal tract is represented at the strain level; however, exhaustive genomic and physiological characterization of human isolates is still lacking. With increased use of probiotics as interventions for gastrointestinal disorders, genomic and functional characterization of novel microorganisms becomes essential. In this study, we explored the impact of strain-level genomic variability on bacterial physiology of two novel human Lactobacillus rhamnosus strains (AMC143 and AMC010 of probiotic potential in relation to stress resistance. The strains showed differences with known probiotic strains (L. rhamnosus GG, Lc705, and HN001 at the genomic level, including nucleotide polymorphisms, mutations in non-coding regulatory regions, and rearrangements of genomic architecture. Transcriptomics analysis revealed that gene expression profiles differed between strains when exposed to simulated gastrointestinal stresses, suggesting the presence of unique regulatory systems in each strain. In vitro physiological assays to test resistance to conditions mimicking the gut environment (acid, alkali, and bile stress showed that growth of L. rhamnosus AMC143 was inhibited upon exposure to alkaline pH, while AMC010 and control strain LGG were unaffected. AMC143 also showed a significant survival advantage compared to the other strains upon bile exposure. Reverse transcription qPCR targeting the bile salt hydrolase gene (bsh revealed that AMC143 expressed bsh poorly (a consequence of a deletion in the bsh promoter and truncation of bsh gene in AMC143, while AMC010 had significantly higher expression levels than AMC143 or LGG. Insertional inactivation of the bsh gene in AMC010 suggested that bsh could be detrimental to bacterial survival during bile stress. Together, these findings show that coupling of classical microbiology with functional genomics methods for the

Microstructure and temperature dependence of intergranular strains on diffractometric macroscopic residual stress analysis

Energy Technology Data Exchange (ETDEWEB)

Wagner, J.N., E-mail: Julia.Wagner@kit.edu [KNMF, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Hofmann, M. [Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRM II), TU München, Lichtenbergstr. 1, 85747 Garching (Germany); Wimpory, R. [Helmholtz-Zentrum Berlin für Materialien und Energie, D-14109 Berlin Wannsee (Germany); Krempaszky, C. [Christian-Doppler-Labor für Werkstoffmechanik von Hochleistungslegierungen, TU München, Boltzmannstr. 15, 85747 Garching (Germany); Lehrstuhl für Werkstoffkunde und Werkstoffmechanik, TU München, Boltzmannstr. 15, 85747 Garching (Germany); Stockinger, M. [Böhler Schmiedetechnik GmbH and Co KG, Mariazeller Straße 25, 8605 Kapfenberg (Austria)

2014-11-17

Knowledge of the macroscopic residual stresses in components of complex high performance alloys is crucial when it comes to considering the safety and manufacturing aspects of components. Diffraction experiments are one of the key methods for studying residual stresses. However a component of the residual strain determined by diffraction experiments, known as microstrain or intergranular residual strain, occurs over the length scale of the grains and thus plays only a minor role for the life time of such components. For the reliable determination of macroscopic strains (with the minimum influence of these intergranular residual strains), the ISO standard recommends the use of particular Bragg reflections. Here we compare the build-up of intergranular strain of two different precipitation hardened IN 718 (INCONEL 718) samples, with identical chemical composition. Since intergranular strains are also affected by temperature, results from room temperature measurement are compared to results at T=550 °C. It turned out that microstructural parameters, such as grain size or type of precipitates, have a larger effect on the intergranular strain evolution than the influence of temperature at the measurement temperature of T=550 °C. The results also show that the choice of Bragg reflections for the diffractometric residual stress analysis is dependent not only on its chemical composition, but also on the microstructure of the sample. In addition diffraction elastic constants (DECs) for all measured Bragg reflections are given.

Simulation of cyclic stress-strain relation under non proportional loading

International Nuclear Information System (INIS)

Chen, X.; Zhu, Q.X.; Abel, A.

1995-01-01

A series of cyclic constitutive experiments have been conducted on 42 Cr Mo steel on MTS809 machine under tension-torsional loading. Thin-walled tube specimen were used. Two kinds of cruciform strain path have been investigated. The paper suggests a simple method for the calculation of stable cyclic stress and strain values based on a modified endochronic constitutive theory by redefined intrinsic time scale. (author). 6 refs., 3 figs

Modeling of Nonlinear Mechanical Response in CFRP Angle-Ply Laminates

Science.gov (United States)

Ogihara, Shinji

2014-03-01

It is known that the failure process in angle-ply laminate involves matrix cracking and delamination and that they exhibit nonlinear stress-strain relation. There may be a significant effect of the constituent blocked ply thickness on the mechanical behavior of angle-ply laminates. These days, thin prepregs whose thickness is, for example 50 micron, are developed and commercially available. Therefore, we can design wide variety of laminates with various constituent ply thicknesses. In this study, effects of constituent ply thickness on the nonlinear mechanical behavior and the damage behavior of CFRP angle-ply laminates are investigated experimentally. Based on the experimental results, the mechanical response in CFRP angle-ply laminates is modeled by using the finite strain viscoplasticity model. We evaluated the mechanical behavior and damage behavior in CFRP angle-ply laminates with different constituent ply thickness under tensile loading experimentally. It was found that as the constituent ply thickness decreases, the strength and failure strain increases. We also observed difference in damage behavior. The preliminary results of finite strain viscoplasticity model considering the damage effect for laminated composites are shown. A qualitative agreement is obtained.

Modeling stress/strain-dependent permeability changes for deep geoenergy applications

Science.gov (United States)

Rinaldi, Antonio Pio; Rutqvist, Jonny

2016-04-01

Rock permeability is a key parameter in deep geoenergy systems. Stress and strain changes induced at depth by fluid injection or extraction may substantially alter the rock permeability in an irreversible way. With regard to the geoenergies, some applications require the permeability to be enhanced to improve productivity. The rock permeability is generally enhanced by shearing process of faults and fractures (e.g. hydroshearing for Enhanced and Deep Geothermal Systems), or the creation of new fractures (e.g. hydrofracturing for shale gas). However, such processes may, at the same time, produce seismicity that can be felt by the local population. Moreover, the increased permeability due to fault reactivation may pose at risk the sealing capacity of a storage site (e.g. carbon sequestration or nuclear waste disposal), providing then a preferential pathway for the stored fluids to escape at shallow depth. In this work we present a review of some recent applications aimed at understanding the coupling between stress (or strain) and permeability. Examples of geoenergy applications include both EGS and CO2 sequestration. To investigate both "wanted" and "unwanted" effects, THM simulations have been carried out with the TOUGH-FLAC simulator. Our studies include constitutive equations relating the permeability to mean effective stress, effective normal stress, volumetric strain, as well as accounting for permeability variation as related to fault/fracture reactivation. Results show that the geomechanical effects have a large role in changing the permeability, hence affecting fluids leakage, reservoir enhancement, as well as the induced seismicity.

Low-temperature strain ageing in In-Pb alloys under stress relaxation conditions

International Nuclear Information System (INIS)

Fomenko, L.S.

2000-01-01

The dynamic strain ageing (DSA) of In-Pb (6 and 8 at. % Pb) substitutional solid solution single crystals is studied at temperatures 77-205 K under stress relaxation conditions. The dependences of the stress increment after relaxation connected with DSA on stress relaxation time, stress relaxation rate at the end of the relaxation, temperature, alloy content, flow stress, and strain are determined. It is shown that the DSA kinetic is described by a Harper-type equation with the exponent equal to 1/3 and a low activation energy value (0.3-0.34 eV). This provides a low temperature of the DSA onset (∼ 0.17 T m , where T m is the melt temperature) and is evidence of pipe-mode diffusion. It is supposed that the obstacles to dislocation motion in the crystals studied consist of the groups of solutes, and the strength of the obstacles increases during the DSA due to the pipe diffusion of the solute atoms along the dislocations

Biaxial failure criteria and stress-strain response for concrete of containment structure

International Nuclear Information System (INIS)

Lee, S. K.; Woo, S. K.; Song, Y. C.; Kweon, Y. K.; Cho, C. H.

2001-01-01

Biaxial failure criteria and stress-strain response for plain concrete of containment structure on nuclear power plants are studied under uniaxial and biaxial stress(compression-compression, compression-tension, and tension-tension combined stress). The concrete specimens of a square plate type are used for uniaxial and biaxial loading. The experimental data indicate that the strength of concrete under biaxial compression, f 2 /f 1 =-1/-1, is 17 percent larger than under uniaxial compression and the poisson's ratio of concrete is 0.1745. On the base of the results, a biaxial failure envelope for plain concrete that the uniaxial strength is 5660 psi are provided, and the biaxial failure behaviors for three biaxial loading areas are plotted respectively. And, various analytical equations having the reliability are proposed for representations of the biaxial failure criteria and stress-strain response curves of concrete

Under which climate and soil conditions the plant productivity-precipitation relationship is linear or nonlinear?

Science.gov (United States)

Ye, Jian-Sheng; Pei, Jiu-Ying; Fang, Chao

2018-03-01

Understanding under which climate and soil conditions the plant productivity-precipitation relationship is linear or nonlinear is useful for accurately predicting the response of ecosystem function to global environmental change. Using long-term (2000-2016) net primary productivity (NPP)-precipitation datasets derived from satellite observations, we identify >5600pixels in the North Hemisphere landmass that fit either linear or nonlinear temporal NPP-precipitation relationships. Differences in climate (precipitation, radiation, ratio of actual to potential evapotranspiration, temperature) and soil factors (nitrogen, phosphorous, organic carbon, field capacity) between the linear and nonlinear types are evaluated. Our analysis shows that both linear and nonlinear types exhibit similar interannual precipitation variabilities and occurrences of extreme precipitation. Permutational multivariate analysis of variance suggests that linear and nonlinear types differ significantly regarding to radiation, ratio of actual to potential evapotranspiration, and soil factors. The nonlinear type possesses lower radiation and/or less soil nutrients than the linear type, thereby suggesting that nonlinear type features higher degree of limitation from resources other than precipitation. This study suggests several factors limiting the responses of plant productivity to changes in precipitation, thus causing nonlinear NPP-precipitation pattern. Precipitation manipulation and modeling experiments should combine with changes in other climate and soil factors to better predict the response of plant productivity under future climate. Copyright © 2017 Elsevier B.V. All rights reserved.

Acquirement of true stress-strain curve using true fracture strain obtained by tensile test and FE analysis

International Nuclear Information System (INIS)

Lee, Kyoung Yoon; Kim, Tae Hyung; Lee, Hyung Yil

2009-01-01

In this work, we predict a true fracture strain using load-displacement curves from tensile test and Finite Element Analysis (FEA), and suggest a method for acquiring true Stress-Strain (SS) curves by predicted fracture strain. We first derived the true SS curve up to necking point from load-displacement curve. As the beginning, the posterior necking part of true SS curve is linearly extrapolated with the slope at necking point. The whole SS curve is then adopted for FE simulation of tensile test. The Bridgman factor or suitable plate correction factors are applied to pre and post FEA. In the load-true strain curve from FEA, the true fracture strain is determined as the matching point to test fracture load. The determined true strain is validated by comparing with test fracture strain. Finally, we complete the true SS curve by combining the prior necking part and linear part, the latter of which connects necking and predicted fracture points.

Acquirement of true stress-strain curve using true fracture strain obtained by tensile test and FE analysis

Energy Technology Data Exchange (ETDEWEB)

Lee, Kyoung Yoon; Kim, Tae Hyung; Lee, Hyung Yil [Sogang University, Seoul (Korea, Republic of)

2009-07-01

In this work, we predict a true fracture strain using load-displacement curves from tensile test and Finite Element Analysis (FEA), and suggest a method for acquiring true Stress-Strain (SS) curves by predicted fracture strain. We first derived the true SS curve up to necking point from load-displacement curve. As the beginning, the posterior necking part of true SS curve is linearly extrapolated with the slope at necking point. The whole SS curve is then adopted for FE simulation of tensile test. The Bridgman factor or suitable plate correction factors are applied to pre and post FEA. In the load-true strain curve from FEA, the true fracture strain is determined as the matching point to test fracture load. The determined true strain is validated by comparing with test fracture strain. Finally, we complete the true SS curve by combining the prior necking part and linear part, the latter of which connects necking and predicted fracture points.

Acquirement of True Stress-strain Curve Using True Fracture Strain Obtained by Tensile Test and FE Analysis

Energy Technology Data Exchange (ETDEWEB)

Lee, Kyoung Yoon; Lee, Hyung Yil [Sogang University, Seoul (Korea, Republic of); Kim, Tae Hyung [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2009-10-15

In this work, we predict a true fracture strain using load-displacement curves from tensile test and finite element analysis (FEA), and suggest a method for acquiring true stress-strain (SS) curves by predicted fracture strain. We first derived the true SS curve up to necking point from load-displacement curve. As the beginning, the posterior necking part of true SS curve is linearly extrapolated with the slope at necking point. The whole SS curve is then adopted for FE simulation of tensile test. The Bridgman factor or suitable plate correction factors are applied to pre and post FEA. In the load-true strain curve from FEA, the true fracture strain is determined as the matching point to test fracture load. The determined true strain is validated by comparing with test fracture strain. Finally, we complete the true SS curve by combining the prior necking part and linear part, the latter of which connects necking and predicted fracture points.

Slow strain rate stress corrosion cracking under multiaxial deformation conditions: technique and application to admiralty brass

International Nuclear Information System (INIS)

Blanchard, W.K.; Heldt, L.A.; Koss, D.

1984-01-01

A set of straightforward experimental techniques are described for the examination of slow strain rate stress corrosion cracking (SCC) of sheet deforming under nearly all multiaxial deformation conditions which result in sheet thinning. Based on local fracture strain as a failure criterion, the results contrast stress corrosion susceptibility in uniaxial tension with those in both plane strain and balanced biaxial tension. These results indicate that the loss of ductility of the brass increases as the stress state changes from uniaxial toward balanced biaxial tension

Heat stress and strain in exercise and sport.

Science.gov (United States)

Brotherhood, John R

2008-01-01

Heat stress arising from the thermal environment is of concern to sports medicine and to sports administration because of the perceived risk of heat casualties, in particular heat stroke. Many sports organizations recommend environmental indices such as the WBGT for assessing risk and setting environmental limits for training and competition. But the limits are not justified by evidence. This article describes the nature of heat stress in sport and how it may be assessed objectively. Heat stress and the principal human responses to exercise heat stress are reviewed briefly. Metabolic heat production and the thermal environment provoke separate and largely independent physiological strains. Metabolic heat production drives body core temperature, and the thermal environment drives skin temperature; the combined stresses are integrated to drive sweat rate. Control of core temperature depends on adequate sweat production and the capacity of the environment to evaporate the sweat. The nature of exercise heat stress is demonstrated by rational analysis of the physical heat exchanges between the body and the environment. The principles of this analysis are applied to critical review of current practice in the assessment of heat stress in sport. The article concludes with discussion of research to establish methods for objective sport-specific assessment of heat stress.

Non-linear analysis and the design of Pumpkin Balloons: stress, stability and viscoelasticity

Science.gov (United States)

Rand, J. L.; Wakefield, D. S.

Tensys have a long-established background in the shape generation and load analysis of architectural stressed membrane structures Founded upon their inTENS finite element analysis suite these activities have broadened to encompass lighter than air structures such as aerostats hybrid air-vehicles and stratospheric balloons Winzen Engineering couple many years of practical balloon design and fabrication experience with both academic and practical knowledge of the characterisation of the non-linear viscoelastic response of the polymeric films typically used for high-altitude scientific balloons Both companies have provided consulting services to the NASA Ultra Long Duration Balloon ULDB Program Early implementations of pumpkin balloons have shown problems of geometric instability characterised by improper deployment and these difficulties have been reproduced numerically using inTENS The solution lies in both the shapes of the membrane lobes and also the need to generate a biaxial stress field in order to mobilise in-plane shear stiffness Balloons undergo significant temperature and pressure variations in flight The different thermal characteristics between tendons and film can lead to significant meridional stress Fabrication tolerances can lead to significant local hoop stress concentrations particularly adjacent to the base and apex end fittings The non-linear viscoelastic response of the envelope film acts positively to help dissipate stress concentrations However creep over time may produce lobe geometry variations that may

Exchange Rate – Relative Price Nonlinear Cointegration Relationship in Malaysia

OpenAIRE

Venus Khim-Sen Liew; Chee-Keong Choong; Evan Lau; Kian-Ping Lim

2005-01-01

The finding of exchange rate–relative price nonlinear cointegration relationship in Malaysia, among others, suggests that nonlinear Purchasing Power Parity (PPP) equilibrium may be regarded as reference point in judging the short run misalignment of the Ringgit currency and thereby deducing effective policy actions. Moreover, economists who wish to extend the simple PPP exchange rate model into the more complicated monetary exchange models may do so comfortably, at least in the text of Mala...

Bioethanol strains of Saccharomyces cerevisiae characterised by microsatellite and stress resistance

Directory of Open Access Journals (Sweden)

Vanda Renata Reis

Full Text Available Abstract Strains of Saccharomyces cerevisiae may display characteristics that are typical of rough-type colonies, made up of cells clustered in pseudohyphal structures and comprised of daughter buds that do not separate from the mother cell post-mitosis. These strains are known to occur frequently in fermentation tanks with significant lower ethanol yield when compared to fermentations carried out by smooth strains of S. cerevisiae that are composed of dispersed cells. In an attempt to delineate genetic and phenotypic differences underlying the two phenotypes, this study analysed 10 microsatellite loci of 22 S. cerevisiae strains as well as stress resistance towards high concentrations of ethanol and glucose, low pH and cell sedimentation rates. The results obtained from the phenotypic tests by Principal-Component Analysis revealed that unlike the smooth colonies, the rough colonies of S. cerevisiae exhibit an enhanced resistance to stressful conditions resulting from the presence of excessive glucose and ethanol and high sedimentation rate. The microsatellite analysis was not successful to distinguish between the colony phenotypes as phenotypic assays. The relevant industrial strain PE-2 was observed in close genetic proximity to rough-colony although it does not display this colony morphology. A unique genetic pattern specific to a particular phenotype remains elusive.

Relationship between Job Stress and Hypo-high-density Lipoproteinemia of Chinese Workers in Shanghai: The Rosai Karoshi Study.

Science.gov (United States)

Muratsubaki, Tomohiko; Hattori, Tomomi; Li, Jue; Fukudo, Shin; Munakata, Masanori

2016-10-20

Karoshi, or death due to overwork, has now become a serious social problem in China. Worsening of cardiovascular risks by stress might initiate karoshi. Many studies have examined the relationship between job stress and obesity, hypertension, and type 2 diabetes mellitus, but less evidence exists for dyslipidemia like hypo-high-density lipoproteinemia (hypo-HDL). The aim of this study was to investigate the relationship between job stress and hypo-HDL of Chinese workers in Shanghai. We studied 2219 Chinese workers in Shanghai, who participated in the Japan-China cooperative study for the prevention of karoshi. A questionnaire was administered to examine the lifestyle characteristics, job category, weekly working hours, and job stress. Job demand and job control were quantified using the National Institute for Occupational Safety and Health questionnaire. Modified job strain measure was defined by the combination of low job control and high demand. Hypo-HDL was defined as plasma high-density lipoprotein cholesterol concentration of <1.04 mmol/L (40 mg/dl). Multivariate logistic regression analysis was performed for hypo-HDL as a dependent variable. Modified job strain was not related to hypo-HDL either in men or women. In men, multivariate adjusted odds ratio (OR) for having hypo-HDL was significantly higher in the lowest job control tertile compared with the highest job control tertile (OR = 1.39, 95% confidence interval [CI] 1.03-1.87, P = 0.034). In the same model, a similar trend was observed for women, but it did not reach a statistically significant level (OR = 1.51, 95% CI, 0.88-2.56, P = 0.132). A low level of job control but not modified job strain was significantly related to higher prevalence of hypo-HDL of Chinese workers in Shanghai.

Experimental determination of the micro-scale strength and stress-strain relation of an epoxy resin

DEFF Research Database (Denmark)

Zike, Sanita; Sørensen, Bent F.; Mikkelsen, Lars Pilgaard

2016-01-01

An approach is developed for determining the stress-strain law and a failure stress appropriate for micro-mechanical models of polymer materials. Double cantilever beam test specimens, made of an epoxy polymer with notches having finite root radius, were subjected to pure bending moments in an en......An approach is developed for determining the stress-strain law and a failure stress appropriate for micro-mechanical models of polymer materials. Double cantilever beam test specimens, made of an epoxy polymer with notches having finite root radius, were subjected to pure bending moments......-scale (5–6%). The hardening exponent of a power law hardening material was obtained by the use of the J-integral, estimating the strain energy density around the notch. The hardening exponent was found to be within the range of 5–6 and the corresponding micro-scale failure stress was in the range of 220...

Strain and stress tensors of rolled uranium plate by Rietveld refinement of TOF neutron-diffraction data

International Nuclear Information System (INIS)

Balzar, D.; Popa, N.C.; Vogel, S.

2010-01-01

We report the complete macroscopic average strain and stress tensors for a cold-rolled uranium plate, based on the neutron TOF measurements. Both tensors were determined by the least-squares refinement of the interplanar spacings of 19 Bragg reflections. Based on the pole figures, as determined by GSAS, a triclinic sample symmetry of the uranium plate was assumed. Strain and stress are tensile in both the transverse and rolling directions and very small in the normal direction (through the thickness of the plate). Shear strain and stress components are compressive and of significant magnitude.

Gene Transcription and Virulence Potential of Listeria monocytogenes Strains After Exposure to Acidic and NaCl Stress

DEFF Research Database (Denmark)

Olesen, Inger; Vogensen, Finn Kvist; Jespersen, Lene

2009-01-01

transcription were observed both after exposure to shock (six genes) and after long-term adaptation to stress (18 genes). In the shock experiments, a transient induction of clpC and clpE was seen for both strains, while transient induction of sigB, inlA, and inlB was observed for strain 4140 only; actA was only...... induced in EGD-e after NaCl shock. The longterm stress experiments were included to imitate the stress conditions encountered by L. monocytogenes when present in food products. Long-term adaptation of EGD-e to acidic stress induced transcription of iap and repressed flaA, while genes related to stress......Gene transcription and virulence potential of two strains of Listeria monocytogenes, EGD-e and 4140, were compared by quantitative real-time polymerase chain reaction and in a Caco-2 in vitro model after exposure to acidic (pH 5.5) and NaCl (4.5% w=v) stress. Strain-dependent differences in gene...

Analysis of Thermal Stresses and Strains Developing during the Heat Treatment of Windmill Shaft

Directory of Open Access Journals (Sweden)

Cebo-Rudnicka A.

2017-06-01

Full Text Available In the paper the results of evaluation of the temperature and stress fields during four cycles of the heat treatment process of the windmill shaft has been presented. The temperature field has been calculated from the solution to the heat conduction equation over the whole heat treatment cycles of the windmill shaft. To calculate the stress field an incremental method has been used. The relations between stresses and strains have been described by Prandtl-Reuss equation for the elastic-plastic body. In order to determine the changes in the temperature and stress fields during heat treatment of the windmill shaft self-developed software utilizing the Finite Element Method has been used. This software can also be used to calculate temperature changes and stress field in ingots and other axially symmetric products. In the mathematical model of heating and cooling of the shaft maximum values of the strains have been determined, which allowed to avoid the crack formation. The critical values of strains have been determined by using modified Rice and Tracy criterion.

Influence of anisotropic hardening on longitudinal welding strains and stresses

International Nuclear Information System (INIS)

Gatovskij, K.M.; Revutskij, M.N.

1981-01-01

The algorithm and program for estimation of longitudinal welding strains and stresses with account of hardening and Bauschinger effect, which expand the possibilities of more complete description of stress change during thermodeformation welding cycles at bead surfacing on plate made of the 06Kh18N9T steel and AMg61 alloy. It is shown that for metals, deformation curves which are characterized by considerable yield moduli (Esub(T)/E>=0.05) hardening effect is considerable and its account leads to the decrease of stress level in the heataffected zone (down to 20%) [ru

Analytical solution for stress, strain and plastic instability of pressurized pipes with volumetric flaws

International Nuclear Information System (INIS)

Cunha, Sérgio B.; Netto, Theodoro A.

2012-01-01

The mechanical behavior of internally pressurized pipes with volumetric flaws is analyzed. The two possible modes of circumferentially straining the pipe wall are identified and associated to hypothesized geometries. The radial deformation that takes place by bending the pipe wall is studied by means of axisymmetric flaws and the membrane strain developed by unequal hoop deformation is analyzed with the help of narrow axial flaws. Linear elastic shell solutions for stress and strain are developed, the plastic behavior is studied and the maximum hoop stress at the flaw is related to the undamaged pipe hoop stress by means of stress concentration factors. The stress concentration factors are employed to obtain equations predicting the pressure at which the pipe fails by plastic instability for both types of flaw. These analytical solutions are validated by comparison with burst tests on 3″ diameter pipes and finite element simulations. Forty-one burst tests were carried out and two materials with very dissimilar plastic behavior, carbon steel and austenitic stainless steel, were used in the experiments. Both the analytical and the numerical predictions showed good correlation with the experimentally observed burst pressures. - Highlights: ► An analytical model for the burst of a pipe with a volumetric flaw is developed. ► Deformation, strain and stress are modeled in the elastic and plastic domains. ► The model is comprehensively validated by experiments and numerical simulations. ► The burst pressure model’s accuracy is equivalent to finite element simulations.

Characterizations of Stress and Strain Variation in Three-Dimensional Forming of Laser Micro-Manufacturing

International Nuclear Information System (INIS)

Ming, Zhou; Guo-Huan, Zhao; Tao, Huang; Hua, Ding; Lan, Cai

2010-01-01

A micro-manufacturing technology is presented to form three-dimensional metallic micro-structures directly. Micro grid array structures are replicated on a metallic foil surface, with high spatial resolution in micron levels. The numerical simulation results indicate that the material deformation process is characterized by an ultrahigh strain rate. With increasing pulse duration, the sample absorption strain energy increases, and the sample deformation degree enlarges. The stress state of the central point fluctuates between tensile stress and compression stress. The stress state of the angular point is altered from compressive stress to tensile stress due to geometry and loading conditions. The duration length of pulse stress has an effect on the stress state, as with the increase of pulse duration, fluctuation in the stress state decreases. Therefore, laser micro-manufacturing technology will be a potential laser micro forming method which is characterized by low cost and high efficiency. (fundamental areas of phenomenology(including applications))

Unpredictable chronic mild stress differentially impairs social and contextual discrimination learning in two inbred mouse strains.

Science.gov (United States)

van Boxelaere, Michiel; Clements, Jason; Callaerts, Patrick; D'Hooge, Rudi; Callaerts-Vegh, Zsuzsanna

2017-01-01

Alterations in the social and cognitive domain are considered important indicators for increased disability in many stress-related disorders. Similar impairments have been observed in rodents chronically exposed to stress, mimicking potential endophenotypes of stress-related psychopathologies such as major depression disorder (MDD), anxiety, conduct disorder, and posttraumatic stress disorder (PTSD). Data from numerous studies suggest that deficient plasticity mechanisms in hippocampus (HC) and prefrontal cortex (PFC) might underlie these social and cognitive deficits. Specifically, stress-induced deficiencies in neural plasticity have been associated with a hypodopaminergic state and reduced neural plasticity persistence. Here we assessed the effects of unpredictable chronic mild stress (UCMS) on exploratory, social and cognitive behavior of females of two inbred mouse strains (C57BL/6J and DBA/2J) that differ in their dopaminergic profile. Exposure to chronic stress resulted in impaired circadian rhythmicity, sociability and social cognition in both inbred strains, but differentially affected activity patterns and contextual discrimination performance. These stress-induced behavioral impairments were accompanied by reduced expression levels of brain derived neurotrophic factor (BDNF) in the prefrontal cortex. The strain-specific cognitive impairment was coexistent with enhanced plasma corticosterone levels and reduced expression of genes related to dopamine signaling in hippocampus. These results underline the importance of assessing different strains with multiple test batteries to elucidate the neural and genetic basis of social and cognitive impairments related to chronic stress.

Specific strain work as a failure criterion in plane stress state

International Nuclear Information System (INIS)

Zuchowski, R.; Zietkowski, L.

1985-01-01

An experimental verification of failure criterion based on specific strain work was performed. Thin-walled cylindrical specimens were examined by loading with constant force and constant torque moment, assuming different values for particular tests, at the same time keeping stress intensity constant, and by subjecting to thermal cycling. It was found that the critical value of failure did not depend on axial-to-shearing stresses ratio, i.e., on the type of state of stress. Thereby, the validity of the analysed failure criterion in plane stress was confirmed. Besides, a simple description of damage development in plane stress was suggested. (orig./RF)

Energetic stress: The reciprocal relationship between energy availability and the stress response.

Science.gov (United States)

Harrell, C S; Gillespie, C F; Neigh, G N

2016-11-01

The worldwide epidemic of metabolic syndromes and the recognized burden of mental health disorders have driven increased research into the relationship between the two. A maladaptive stress response is implicated in both mental health disorders and metabolic disorders, implicating the hypothalamic-pituitary-adrenal (HPA) axis as a key mediator of this relationship. This review explores how an altered energetic state, such as hyper- or hypoglycemia, as may be manifested in obesity or diabetes, affects the stress response and the HPA axis in particular. We propose that changes in energetic state or energetic demands can result in "energetic stress" that can, if prolonged, lead to a dysfunctional stress response. In this review, we summarize the role of the hypothalamus in modulating energy homeostasis and then briefly discuss the relationship between metabolism and stress-induced activation of the HPA axis. Next, we examine seven mechanisms whereby energetic stress interacts with neuroendocrine stress response systems, including by glucocorticoid signaling both within and beyond the HPA axis; by nutrient-induced changes in glucocorticoid signaling; by impacting the sympathetic nervous system; through changes in other neuroendocrine factors; by inducing inflammatory changes; and by altering the gut-brain axis. Recognizing these effects of energetic stress can drive novel therapies and prevention strategies for mental health disorders, including dietary intervention, probiotics, and even fecal transplant. Copyright © 2015 Elsevier Inc. All rights reserved.

Stress-strain effects in alumina-Cu reinforced Nb3Sn wires fabricated by the tube process

International Nuclear Information System (INIS)

Murase, Satoru; Nakayama, Shigeo; Masegi, Tamaki; Koyanagi, Kei; Nomura, Shunji; Shiga, Noriyuki; Kobayashi, Norio; Watanabe, Kazuo.

1997-01-01

In order to fabricate a large-bore, high-field magnet which achieves a low coil weight and volume, a high strength compound superconducting wire is required. For those demands we have developed the reinforced Nb 3 Sn wire using alumina dispersion strengthened copper (alumina-Cu) as a reinforcement material and the tube process of the Nb 3 Sn wire fabrication. The ductility study of the composites which consisted of the reinforcement, Nb tube, Cu, and Cu clad Sn brought a 1 km long alumina-Cu reinforced Nb 3 Sn wire successfully. Using fabricated wires measurements and evaluations of critical current density as parameters of magnetic field, tensile stress, tensile strain, and transverse compressive stress, and those of stress-strain curves at 4.2 K were performed. They showed superior performance such as high 0.3% proof stress (240 MPa at 0.3% strain) and high maximum tolerance stress (320 MPa) which were two times as large as those of conventional Cu matrix Nb 3 Sn wire. The strain sensitivity parameters were obtained for the reinforced Nb 3 Sn wire and the Cu matrix one using the scaling law. Residual stress of the component materials caused by cooling down to 4.2 K from heat-treatment temperature was calculated using equivalent Young's modulus, equivalent yield strength, thermal expansion coefficient and other mechanical parameters. Calculated stress-strain curves at 4.2 K for the reinforced Nb 3 Sn wire and the Cu matrix one based on calculation of residual stress, had good agreement with the experimental values. (author)

Fabrication and characterization of THUNDER actuators—pre-stress-induced nonlinearity in the actuation response

International Nuclear Information System (INIS)

Kim, Younghoon; Jiang, Qing; Cai, Ling; Usher, Timothy

2009-01-01

This paper documents an experimental and theoretical investigation into characterizing the mechanical configurations and performances of THUNDER actuators, a type of piezoelectric actuator known for their large actuation displacements, through fabrication, measurements and finite element analysis. Five groups of such actuators with different dimensions were fabricated using identical fabrication parameters. The as-fabricated arched configurations, resulting from the thermo-mechanical mismatch among the constituent layers, and their actuation performances were characterized using an experimental set-up based on a laser displacement sensor and through numerical simulations with ANSYS, a widely used commercial software program for finite element analysis. This investigation shows that the presence of large residual stresses within the piezoelectric ceramic layer, built up during the fabrication process, leads to significant nonlinear electromechanical coupling in the actuator response to the driving electric voltage, and it is this nonlinear coupling that is responsible for the large actuation displacements. Furthermore, the severity of the residual stresses, and thus the nonlinearity, increases with increasing substrate/piezoelectric thickness ratio and, to a lesser extent, with decreasing in-plane dimensions of the piezoelectric layer

Stress-strain effects on powder-in-tube MgB2 tapes and wires

International Nuclear Information System (INIS)

Katagiri, Kazumune; Takaya, Ryuya; Kasaba, Koichi; Tachikawa, Kyoji; Yamada, Yutaka; Shimura, Satoshi; Koshizuka, Naoki; Watanabe, Kazuo

2005-01-01

The effects of stress-strain on the critical current, I c , of ex situ powder-in-tube (PIT)-processed Ni-sheathed MgB 2 tapes and round wires as well as in situ PIT-processed Cu-sheathed wires at 4.2 K in a magnetic field up to 5 T have been studied. The effect of In powder addition on the Ni-sheathed MgB 2 wire was not so clear compared with that in the tape, in which the irreversible strain, ε irr , for the I c degradation onset increases significantly by the addition. This is attributed to the difference in the microstructure of the core associated with cold workings. A peak and gradual degradation behaviour of I c with strain beyond ε irr was found in the wire, whereas no evident peak and a steep degradation behaviour was found in the tape. As a possible reason, the difference in the triaxial residual stress state at 4.2 K due to the difference in geometry of the cross-section is suspected. The transverse compression tests revealed that I c of the wire did not degrade up to 270 MPa. Again, the effect of In addition was minimal. The Young's modulus of MgB 2 , 31-41 GPa, at room temperature was estimated by a tensile test of Cu sheath wire using a high-accuracy extensometer and the law of mixtures. The tensile strain dependence of I c in the Cu sheath wire was similar to that in the Ni-sheathed wire, ε irr being 0.4%. However, the stress corresponding to ε irr , 50 MPa, was about 1/10 of that for the Ni-sheath wire and the irreversible transverse compressive stress, 150 MPa, was also lower. The effect of bending strain on the I c in Cu-sheathed wire was compared with that of the tensile strain

Childhood Adversity, Daily Stress, and Marital Strain in Same-Sex and Different-Sex Marriages

Science.gov (United States)

Donnelly, Rachel; Umberson, Debra; Kroeger, Rhiannon A.

2017-01-01

Childhood adversity has enduring consequences for individuals throughout life, including increased reactivity to stress that may contribute to marital strain in adulthood. Past research on gendered experiences of heterosexual spouses raises questions about how the influence of childhood adversity might differ for men and women in same-sex marriages. We analyze dyadic diary data from 756 individuals in 106 male same-sex, 157 female same-sex, and 115 different-sex marriages to consider how childhood adversity moderates the association between daily stress and marital strain. Results suggest that the negative consequences of daily stress for marital strain are amplified by past childhood adversity with variation for men and women in same- and different-sex unions, such that women and those in same-sex marriages may experience some protection from the adverse consequences of childhood adversity.

Relationships Among Nightly Sleep Quality, Daily Stress, and Daily Affect.

Science.gov (United States)

Blaxton, Jessica M; Bergeman, Cindy S; Whitehead, Brenda R; Braun, Marcia E; Payne, Jessic D

2017-05-01

We explored the prospective, microlevel relationship between nightly sleep quality (SQ) and the subsequent day's stress on positive (PA) and negative affect (NA) as well as the moderating relationships between nightly SQ, subsequent stress, and subsequent PA on NA. We investigated whether age moderated these relationships. We collected 56 days of sleep, stress, and affect data using daily diary questionnaires (N = 552). We used multilevel modeling to assess relationships at the between- and within-person levels. Daily increases in SQ and decreases in stress interacted to predict higher daily PA and lower daily NA. Better SQ in older adults enhanced the benefits of PA on the stress-NA relationship more during times of low stress, whereas better sleep in younger adults enhanced the benefits of PA more during times of high stress. Between-person effects were stronger predictors of well-being outcomes than within-person variability. The combination of good SQ and higher PA buffered the impact of stress on NA. The moderating impact of age suggests that sleep and stress play different roles across adulthood. Targeting intervention and prevention strategies to improve SQ and enhance PA could disrupt the detrimental relationship between daily stress and NA. © The Author 2015. Published by Oxford University Press on behalf of The Gerontological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Exercise-induced heat stress disrupts the shear-dilatory relationship.

Science.gov (United States)

Ives, Stephen J; Lefferts, Wesley K; Wharton, Margret; Fehling, Patricia C; Smith, Denise L

2016-12-01

What is the central question of this study? Although heat stress is known to increase cardiovascular strain, no study, to date, had explored the potential impact of exercise-induced heat stress on vascular function. What is the main finding and its importance? We found that acute exercise tended to reduce flow-mediated dilatation (FMD), owing in part to reduced reactive hyperaemia/shear stimulus; thus, when FMD is normalized to shear no postexercise deficit exists. Exercise-induced heat stress increased reactive hyperaemia, shear rate, coupled with a sustained FMD postexercise, suggests that exercise-induced heat stress increases the amount of shear stimulus to elicit a similar response, indicating reduced vascular responsiveness, or reserve, which might increase cardiovascular susceptibility. Heat stress increases cardiovascular strain and is of particular concern in occupations, such as firefighting, in which individuals are required to perform strenuous work while wearing personal protective equipment. Sudden cardiac events are associated with strenuous activity and are the leading cause of duty-related death among firefighters, accounting for ∼50% of duty-related fatalities per year. Understanding the acute effects of exercise-induced heat stress (EIHS) on vascular endothelial function may provide insight into the mechanisms precipitating acute coronary events in firefighters. The purpose of this study, therefore, was to determine the effects of EIHS on vascular endothelial function. Using a balanced crossover design, 12 healthy men performed 100 min of moderate-intensity, intermittent exercise with and without EIHS (personal protective equipment or cooling vest, respectively). Measurements of flow-mediated dilatation (FMD), reactive hyperaemia and shear rate area under the curve (SR AUC ) were performed pre- and postexercise. During EIHS, core temperature was significantly higher (38 ± 0.1 versus 37 ± 0.1°C). Postexercise FMD tended to be suppressed

Structure/property relationships in non-linear optical materials

Energy Technology Data Exchange (ETDEWEB)

Cole, J M [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France); [Durham Univ. (United Kingdom); Howard, J A.K. [Durham Univ. (United Kingdom); McIntyre, G J [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France)

1997-04-01

The application of neutrons to the study of structure/property relationships in organic non-linear optical materials (NLOs) is described. In particular, charge-transfer effects and intermolecular interactions are investigated. Charge-transfer effects are studied by charge-density analysis and an example of one such investigation is given. The study of intermolecular interactions concentrates on the effects of hydrogen-bonding and an example is given of two structurally similar molecules with very disparate NLO properties, as a result of different types of hydrogen-bonding. (author). 3 refs.

Multiphase-field model of small strain elasto-plasticity according to the mechanical jump conditions

Science.gov (United States)

Herrmann, Christoph; Schoof, Ephraim; Schneider, Daniel; Schwab, Felix; Reiter, Andreas; Selzer, Michael; Nestler, Britta

2018-04-01

We introduce a small strain elasto-plastic multiphase-field model according to the mechanical jump conditions. A rate-independent J_2 -plasticity model with linear isotropic hardening and without kinematic hardening is applied exemplary. Generally, any physically nonlinear mechanical model is compatible with the subsequently presented procedure. In contrast to models with interpolated material parameters, the proposed model is able to apply different nonlinear mechanical constitutive equations for each phase separately. The Hadamard compatibility condition and the static force balance are employed as homogenization approaches to calculate the phase-inherent stresses and strains. Several verification cases are discussed. The applicability of the proposed model is demonstrated by simulations of the martensitic transformation and quantitative parameters.

A numerical study of stress/strain response to oil development in reservoir rocks-a case study in Xingshugang area of Daqing Anticline

International Nuclear Information System (INIS)

Li Zian; Ma Teng; Yi Jin; Zhu Jiangjian; Lin Ge; Zhang Lu; Zhu Yan; Sun Yaliang; Zhu Jun

2010-01-01

Formation pressure and the underground stress field will be disturbed by high pressure injection and production activities during oilfield development. Such disturbance will induce the deformation of formation rock, sometimes causing formation to slip. As a result, production wells and/or injection wells will encounter sanding, casing deformation, or even casing shear problems. This article introduced a simulation study on formation pressure and the underground stress field variation during injection and production activities in the Xingshugang area of the Daqing Anticline, Songliao Basin, China. The relationships of injection pressure to formation pressure, underground stress field variation, and strain variation were investigated in this paper.

Strain-dependent electrical resistance of multi-walled carbon nanotube/polymer composite films

International Nuclear Information System (INIS)

Park, Myounggu; Kim, Hyonny; Youngblood, Jeffrey P

2008-01-01

The strain-dependent electrical resistance characteristics of multi-walled carbon nanotube (MWCNT)/polymer composite films were investigated. In this research, polyethylene oxide (PEO) is used as the polymer matrix. Two representative volume fractions of MWCNT/PEO composite films were selected: 0.56 vol% (near the percolation threshold) and 1.44 vol% (away from the percolation threshold) of MWCNT. An experimental setup which can measure electrical resistance and strain simultaneously and continuously has been developed. Unique and repeatable relationships in resistance versus strain were obtained for multiple specimens with different volume fractions of MWCNT. The overall pattern of electrical resistance change versus strain for the specimens tested consists of linear and nonlinear regions. A resistance change model to describe the combination of linear and nonlinear modes of electrical resistance change as a function of strain is suggested. The unique characteristics in electrical resistance change for different volume fractions imply that MWCNT/PEO composite films can be used as tunable strain sensors and for application into embedded sensor systems in structures

Raman measurements of Kevlar-29 fiber pull-out test at different strain levels

Science.gov (United States)

Wang, Quan; Lei, Zhenkun; Kang, Yilan; Qiu, Wei

2008-11-01

This paper adopted Kevlar-29 fiber monofilament embedding technology to prepare fiber/ epoxy resin tensile specimen. The specimen was pulled on a homemade and portable mini-loading device. At the same time micro-Raman spectroscopy is introduced to detect the distributions of stress on the embedded fiber at different strain levels. The characteristic peak shift of the 1610 cm-1 in Raman band has a linear relationship with the strain or stress. The experimental results show that the fiber axial stress decreases gradually from the embedded fiber-start to the embedded fiber-end at the same strain level. At different strain levels, the fiber axial stress increases along with the applied load. It reveals that there is a larger fiber axial stress distribution under a larger strain level. And the stress transfer is realized gradually from the embedded fiber-start to the fiber-end. Stress concentration exists in the embedded fiber-end, which is a dangerous region for interfacial debonding easily.

Unpredictable chronic mild stress differentially impairs social and contextual discrimination learning in two inbred mouse strains.

Directory of Open Access Journals (Sweden)

Michiel van Boxelaere

Full Text Available Alterations in the social and cognitive domain are considered important indicators for increased disability in many stress-related disorders. Similar impairments have been observed in rodents chronically exposed to stress, mimicking potential endophenotypes of stress-related psychopathologies such as major depression disorder (MDD, anxiety, conduct disorder, and posttraumatic stress disorder (PTSD. Data from numerous studies suggest that deficient plasticity mechanisms in hippocampus (HC and prefrontal cortex (PFC might underlie these social and cognitive deficits. Specifically, stress-induced deficiencies in neural plasticity have been associated with a hypodopaminergic state and reduced neural plasticity persistence. Here we assessed the effects of unpredictable chronic mild stress (UCMS on exploratory, social and cognitive behavior of females of two inbred mouse strains (C57BL/6J and DBA/2J that differ in their dopaminergic profile. Exposure to chronic stress resulted in impaired circadian rhythmicity, sociability and social cognition in both inbred strains, but differentially affected activity patterns and contextual discrimination performance. These stress-induced behavioral impairments were accompanied by reduced expression levels of brain derived neurotrophic factor (BDNF in the prefrontal cortex. The strain-specific cognitive impairment was coexistent with enhanced plasma corticosterone levels and reduced expression of genes related to dopamine signaling in hippocampus. These results underline the importance of assessing different strains with multiple test batteries to elucidate the neural and genetic basis of social and cognitive impairments related to chronic stress.

Relationship between the Pedaling Biomechanics and Strain of Bicycle Frame during Submaximal Tests

Directory of Open Access Journals (Sweden)

Aneliya V. Manolova

2015-06-01

Full Text Available The aim of this study was to analyse the effect of forces applied to pedals and cranks on the strain imposed to an instrumented bicycle motocross (BMX frame. Using results from a finite element analysis to determine the localisation of highest stress, eight strain gauges were located on the down tube, the seat tube and the right chain stay. Before the pedaling tests, static loads were applied to the frame during bench tests. Two pedaling conditions have been analysed. In the first, the rider was in static standing position on the pedals and applied maximal muscular isometric force to the right pedal. The second pedaling condition corresponds to three pedaling sprint tests at submaximal intensities at 150, 300 and 550 W on a cycle-trainer. The results showed that smaller strain was observed in the pedaling condition than in the rider static standing position condition. The highest strains were located in the seat tube and the right chain stay near the bottom bracket area. The maximum stress observed through all conditions was 41 MPa on the right chain stay. This stress was 11 times lower than the yield stress of the frame material (460 MPa. This protocol could help to adapt the frame design to the riders as a function of their force and mechanical power output. These results could also help design BMX frames for specific populations (females and rider morphology.

Effect of salt stress on the physiology of Frankia sp strain CcI6

Indian Academy of Sciences (India)

2013-10-01

Oct 1, 2013 ... the strain is closely related to Frankia sp. strain CcI3. ... [Oshone R, Mansour SR and Tisa LS 2013 Effect of salt stress on the physiology of Frankia sp strain CcI6. .... This work was supported in part by US-Egypt Joint Research.

Bioethanol strains of Saccharomyces cerevisiae characterised by microsatellite and stress resistance.

Science.gov (United States)

Reis, Vanda Renata; Antonangelo, Ana Teresa Burlamaqui Faraco; Bassi, Ana Paula Guarnieri; Colombi, Débora; Ceccato-Antonini, Sandra Regina

Strains of Saccharomyces cerevisiae may display characteristics that are typical of rough-type colonies, made up of cells clustered in pseudohyphal structures and comprised of daughter buds that do not separate from the mother cell post-mitosis. These strains are known to occur frequently in fermentation tanks with significant lower ethanol yield when compared to fermentations carried out by smooth strains of S. cerevisiae that are composed of dispersed cells. In an attempt to delineate genetic and phenotypic differences underlying the two phenotypes, this study analysed 10 microsatellite loci of 22 S. cerevisiae strains as well as stress resistance towards high concentrations of ethanol and glucose, low pH and cell sedimentation rates. The results obtained from the phenotypic tests by Principal-Component Analysis revealed that unlike the smooth colonies, the rough colonies of S. cerevisiae exhibit an enhanced resistance to stressful conditions resulting from the presence of excessive glucose and ethanol and high sedimentation rate. The microsatellite analysis was not successful to distinguish between the colony phenotypes as phenotypic assays. The relevant industrial strain PE-2 was observed in close genetic proximity to rough-colony although it does not display this colony morphology. A unique genetic pattern specific to a particular phenotype remains elusive. Copyright © 2016 Sociedade Brasileira de Microbiologia. Published by Elsevier Editora Ltda. All rights reserved.

Analytical solution for stress, strain and plastic instability of pressurized pipes with volumetric flaws

Energy Technology Data Exchange (ETDEWEB)

Cunha, Sergio B., E-mail: sbcunha@petrobras.com.br [PETROBRAS/TRANSPETRO, Av. Pres. Vargas 328 - 7th floor, Rio de Janeiro, RJ 20091-060 (Brazil); Netto, Theodoro A., E-mail: tanetto@lts.coppe.ufrj.br [COPPE, Federal University ot Rio de Janeiro, Ocean Engineering Department, PO BOX 68508, Rio de Janeiro - RJ (Brazil)

2012-01-15

The mechanical behavior of internally pressurized pipes with volumetric flaws is analyzed. The two possible modes of circumferentially straining the pipe wall are identified and associated to hypothesized geometries. The radial deformation that takes place by bending the pipe wall is studied by means of axisymmetric flaws and the membrane strain developed by unequal hoop deformation is analyzed with the help of narrow axial flaws. Linear elastic shell solutions for stress and strain are developed, the plastic behavior is studied and the maximum hoop stress at the flaw is related to the undamaged pipe hoop stress by means of stress concentration factors. The stress concentration factors are employed to obtain equations predicting the pressure at which the pipe fails by plastic instability for both types of flaw. These analytical solutions are validated by comparison with burst tests on 3 Double-Prime diameter pipes and finite element simulations. Forty-one burst tests were carried out and two materials with very dissimilar plastic behavior, carbon steel and austenitic stainless steel, were used in the experiments. Both the analytical and the numerical predictions showed good correlation with the experimentally observed burst pressures. - Highlights: Black-Right-Pointing-Pointer An analytical model for the burst of a pipe with a volumetric flaw is developed. Black-Right-Pointing-Pointer Deformation, strain and stress are modeled in the elastic and plastic domains. Black-Right-Pointing-Pointer The model is comprehensively validated by experiments and numerical simulations. Black-Right-Pointing-Pointer The burst pressure model's accuracy is equivalent to finite element simulations.

Formation of stress/strain cycles for analytical assessment of fatigue crack initiation and growth

International Nuclear Information System (INIS)

Tashkinov, A.V.

2005-01-01

This paper discusses standard techniques for setting up cycles of stresses, strains and stress intensity factors (SIF) for use in analysing the fatigue characteristics of crack-free components or the fatigue crack growth if crack-like flaws are present. A number of improved techniques are proposed. An enhanced procedure for analytical description of true metal stress-strain curves, covering plastic effects, is presented. This procedure involves standard physical and mechanical properties of the metal in question, such as ultimate stress, yield stress and elasticity modulus. It is emphasized that the currently practiced rain-flow method of design cycle formation, which is effective for an actual (truly known) cyclic loading history, is not suitable for a projected (anticipated) history, as it leaves out of account possible variations in the sequence of operating conditions. Improved techniques for establishing design stress/strain and SIF cycles are described, which make allowance for the most unfavourable sequence of events in the projected loading history. The paper points to a basic difference in the methods of design cycle formation, employed in assessment of the current condition of a component (with the actual history accounted for) and in estimation of the residual lifetime or life extension (for a projected history). (authors)

Prediction of stress- and strain-based forming limits of automotive thin sheets by numerical, theoretical and experimental methods

Science.gov (United States)

Béres, Gábor; Weltsch, Zoltán; Lukács, Zsolt; Tisza, Miklós

2018-05-01

Forming limit is a complex concept of limit values related to the onset of local necking in the sheet metal. In cold sheet metal forming, major and minor limit strains are influenced by the sheet thickness, strain path (deformation history) as well as material parameters and microstructure. Forming Limit Curves are plotted in ɛ1 - ɛ2 coordinate system providing the classic strain-based Forming Limit Diagram (FLD). Using the appropriate constitutive model, the limit strains can be changed into the stress-based Forming Limit Diagram (SFLD), irrespective of the strain path. This study is about the effect of the hardening model parameters on defining of limit stress values during Nakazima tests for automotive dual phase (DP) steels. Five limit strain pairs were specified experimentally with the loading of five different sheet geometries, which performed different strain-paths from pure shear (-2ɛ2=ɛ1) up to biaxial stretching (ɛ2=ɛ1). The former works of Hill, Levy-Tyne and Keeler-Brazier made possible some kind of theoretical strain determination, too. This was followed by the stress calculation based on the experimental and theoretical strain data. Since the n exponent in the Nádai expression is varying with the strain at some DP steels, we applied the least-squares method to fit other hardening model parameters (Ludwik, Voce, Hockett-Sherby) to calculate the stress fields belonging to each limit strains. The results showed that each model parameters could produce some discrepancies between the limit stress states in the range of higher equivalent strains than uniaxial stretching. The calculated hardening models were imported to FE code to extend and validate the results by numerical simulations.

FLEXURAL STRESS ANALYSIS OF RIGID PAVEMENTS USING AXI-SYMMETRIC AND PLANE STRAIN FEM

Directory of Open Access Journals (Sweden)

V.A. Sawant

2017-11-01

Full Text Available The design of pavement involves a study of soils and paving materials, their response under load for different climatic conditions. In the present study, an attempt has been made to compare stresses predicted using two finite element analyses. First analysis is based on the twodimensional plane strain assumption where as in second approach axi-symmetric condition is assumed to consider three-dimensional behavior of rigid pavement. The results are compared with flexural stresses obtained from conventional Portland Cement Association method. The computed flexural stresses obtained from axi-symmetric condition are found to be in close agreement with PCA method. Results of plane strain analysis show a fair agreement after application of an appropriate multiplication factor

Stress-Strain Law for Confined Concrete with Hardening or Softening Behavior

Directory of Open Access Journals (Sweden)

Piero Colajanni

2013-01-01

Full Text Available This paper provides a new general stress-strain law for concrete confined by steel, fiber reinforced polymer (FRP, or fiber reinforced cementitious matrix (FRCM, obtained by a suitable modification of the well-known Sargin’s curve for steel confined concrete. The proposed law is able to reproduce stress-strain curve of any shape, having both hardening or softening behavior, by using a single closed-form simple algebraic expression with constant coefficients. The coefficients are defined on the basis of the stress and the tangent modulus of the confined concrete in three characteristic points of the curve, thus being related to physical meaningful parameters. It will be shown that if the values of the parameters of the law are deduced from experimental tests, the model is able to accurately reproduce the experimental curve. If they are evaluated on the basis of an analysis-oriented model, the proposed model provides a handy equivalent design model.

Analysis of stress and strain in a rotating disk mounted on a rigid shaft

Directory of Open Access Journals (Sweden)

Alexandrova Nelli N.

2006-01-01

Full Text Available The plane state of stress in an elastic-perfectly plastic isotropic rotating annular disk mounted on a rigid shaft is studied. The analysis of stresses, strains and displacements within the disk of constant thickness and density is based on the Mises yield criterion and its associated flow rule. It is observed that the plastic deformation is localized in the vicinity of the inner radius of the disk, and the disk of a sufficiently large outer radius never becomes fully plastic. The semi-analytical method of stress-strain analysis developed is illustrated by some numerical examples. .

Stress and strain in the contractile and cytoskeletal filaments of airway smooth muscle.

Science.gov (United States)

Deng, Linhong; Bosse, Ynuk; Brown, Nathan; Chin, Leslie Y M; Connolly, Sarah C; Fairbank, Nigel J; King, Greg G; Maksym, Geoffrey N; Paré, Peter D; Seow, Chun Y; Stephen, Newman L

2009-10-01

Stress and strain are omnipresent in the lung due to constant lung volume fluctuation associated with respiration, and they modulate the phenotype and function of all cells residing in the airways including the airway smooth muscle (ASM) cell. There is ample evidence that the ASM cell is very sensitive to its physical environment, and can alter its structure and/or function accordingly, resulting in either desired or undesired consequences. The forces that are either conferred to the ASM cell due to external stretching or generated inside the cell must be borne and transmitted inside the cytoskeleton (CSK). Thus, maintaining appropriate levels of stress and strain within the CSK is essential for maintaining normal function. Despite the importance, the mechanisms regulating/dysregulating ASM cytoskeletal filaments in response to stress and strain remained poorly understood until only recently. For example, it is now understood that ASM length and force are dynamically regulated, and both can adapt over a wide range of length, rendering ASM one of the most malleable living tissues. The malleability reflects the CSK's dynamic mechanical properties and plasticity, both of which strongly interact with the loading on the CSK, and all together ultimately determines airway narrowing in pathology. Here we review the latest advances in our understanding of stress and strain in ASM cells, including the organization of contractile and cytoskeletal filaments, range and adaptation of functional length, structural and functional changes of the cell in response to mechanical perturbation, ASM tone as a mediator of strain-induced responses, and the novel glassy dynamic behaviors of the CSK in relation to asthma pathophysiology.

Strain-dependent partial slip on rock fractures under seismic-frequency torsion

Science.gov (United States)

Saltiel, Seth; Bonner, Brian P.; Ajo-Franklin, Jonathan B.

2017-05-01

Measurements of nonlinear modulus and attenuation of fractures provide the opportunity to probe their mechanical state. We have adapted a low-frequency torsional apparatus to explore the seismic signature of fractures under low normal stress, simulating low effective stress environments such as shallow or high pore pressure reservoirs. We report strain-dependent modulus and attenuation for fractured samples of Duperow dolomite (a carbon sequestration target reservoir in Montana), Blue Canyon Dome rhyolite (a geothermal analog reservoir in New Mexico), and Montello granite (a deep basement disposal analog from Wisconsin). We use a simple single effective asperity partial slip model to fit our measured stress-strain curves and solve for the friction coefficient, contact radius, and full slip condition. These observations have the potential to develop into new field techniques for measuring differences in frictional properties during reservoir engineering manipulations and estimate the stress conditions where reservoir fractures and faults begin to fully slip.

Non-Linear Dose Response Relationships in Biology, Toxicology, and Medicine (June 8-10, 2004). Final Report

International Nuclear Information System (INIS)

Calabrese, Edward J.

2004-01-01

The conference attracts approximately 500 scientists researching in the area of non-linear low dose effects. These scientists represent a wide range of biological/medical fields and technical disciplines. Observations that biphasic dose responses are frequently reported in each of these areas but that the recognition of similar dose response relationships across disciplines is very rarely appreciated and exploited. By bringing scientist of such diverse backgrounds together who are working on the common area of non-linear dose response relationships this will enhance our understanding of the occurrence, origin, mechanism, significance and practical applications of such dose response relationships

Damage detection methodology under variable load conditions based on strain field pattern recognition using FBGs, nonlinear principal component analysis, and clustering techniques

Science.gov (United States)

Sierra-Pérez, Julián; Torres-Arredondo, M.-A.; Alvarez-Montoya, Joham

2018-01-01

Structural health monitoring consists of using sensors integrated within structures together with algorithms to perform load monitoring, damage detection, damage location, damage size and severity, and prognosis. One possibility is to use strain sensors to infer structural integrity by comparing patterns in the strain field between the pristine and damaged conditions. In previous works, the authors have demonstrated that it is possible to detect small defects based on strain field pattern recognition by using robust machine learning techniques. They have focused on methodologies based on principal component analysis (PCA) and on the development of several unfolding and standardization techniques, which allow dealing with multiple load conditions. However, before a real implementation of this approach in engineering structures, changes in the strain field due to conditions different from damage occurrence need to be isolated. Since load conditions may vary in most engineering structures and promote significant changes in the strain field, it is necessary to implement novel techniques for uncoupling such changes from those produced by damage occurrence. A damage detection methodology based on optimal baseline selection (OBS) by means of clustering techniques is presented. The methodology includes the use of hierarchical nonlinear PCA as a nonlinear modeling technique in conjunction with Q and nonlinear-T 2 damage indices. The methodology is experimentally validated using strain measurements obtained by 32 fiber Bragg grating sensors bonded to an aluminum beam under dynamic bending loads and simultaneously submitted to variations in its pitch angle. The results demonstrated the capability of the methodology for clustering data according to 13 different load conditions (pitch angles), performing the OBS and detecting six different damages induced in a cumulative way. The proposed methodology showed a true positive rate of 100% and a false positive rate of 1.28% for a

Study on the stress and strain during welding of plate-to-pipe joint

Energy Technology Data Exchange (ETDEWEB)

Na, S.J.; Kim, H.W.

1986-09-01

In manufacturing of pipe walls for boiler units, distortion can result in pipe-to-pipe joints from the nonuniform expansion and contraction of the weld metal and the adjacent base metal during heating and cooling cycle of the welding process. In this study, the stresses and strains during longitudinal welding of the plate-to-pipe joint were investigated. Using the method of sucessive elastic solution, longitudinal stresses and strains during and after welding were calculated from the information of temperature distributions obtained by Rosenthal's equations. In order to confirm the validity of the numerical results, the temperature and residual stress distributions were measured and compared with the calculated results. In spite of some assumptions, the one-dimensional analytical results of residual stresses were in fairly good agreement with the experimental ones. The residual stresses due to welding of plate-to-pipe joints are tensile near the weld line and compressive in the base metal as in the welding of plates. The amount and distribution of residual stresses were deeply dependent on the heat input ratio of the plate and pipe.