Showing papers on "Stress–strain curve published in 1994"

Complete stress — strain behaviour of high-strength concrete under compression

Abstract: A series of compression tests were conducted on 3 × 6 in (76·2 × 152·4 mm) cylindrical specimens using a modified testing method that gave the complete stress–strain behaviour for high-strength concrete with or without tie confinements. Empirical equations are proposed to represent the complete stress–strain relationships of unconfined and confined high-strength concretes with compressive strength exceeding 10 kip/in2 (69 MPa). Various parameters were studied and their relationships were experimentally determined. me proposed empirical stress–strain equations are compared with actual cylinder tests under axial compression, and are found to agree well.

Beam-column behaviour of steel tubes filled with high strength concrete

Abstract: The results of an investigation into the behaviour of thin-walled steel tubes filled with high strength concrete are presented. The main emphasis is placed on the level of ductility that can be ach...

Stress and strain in liquid and solid foams

Abstract: Both liquid and solid foams, together with analogous cellular materials, have distinctive mechanical or rheological properties which find many applications. This review concentrates on the search for a basic understanding of the underlying mechanisms, in terms of specific structural models. Computer simulations play an increasing role and are beginning to be applied to three-dimensional models.

Effect of strain rate on the fracture behaviour of skin

Abstract: The effect of strain rate on the stress-strain behaviour of skin is studied. It is observed that the plastic set in the skin is dependent on strain rate. The scanning electron micrographs of the fractured skin sample shows thicker fibrils and thinner one at low strain rates. The plastic flow is clearly brought out in the stress-strain curves at different strain rates. The stress relaxation behaviour at any given strain is clearly brought out in the 3-dimensional plot.

Elastic and viscoelastic properties of trabecular bone by a compression testing approach.

Abstract: In this review the advantages and disadvantages of different variants of compression testing of trabecular bone are discussed. Factors affecting the precision and the accuracy of mechanical properties of trabecular bone derived from such tests are analysed. Below are listed some of the important conclusions which can be drawn. Conclusions based on the author's previous studies (I-IX) are shown in italic. 1) Trabecular bone is a viscoelastic solid. 2) Stiffness, strength, ultimate strain, and failure energy are derived from a standard compression test to failure. Viscoelastic properties such as energy dissipation and the relative energy loss (loss tangent) can be obtained from non-destructive cyclic tests. 3) A non-destructive test conducted between a lower load level (zero strain) and an upper strain limit of about 0.8% specimen strain has been developed. The reproducibility of such a test technique has been assessed at different conditions. The reproducibility was best after a number of conditioning cycles in order to achieve a viscoelastic steady state. Orthotropic properties can be determined by non-destructive testing in different directions of cubic specimens. The reproducibility of such testing has been established. 4) The stiffness derived from non-destructive tests will be lower than that obtained from a destructive test because of the non-linearity of the load-deformation curve, but the stiffnesses will be strongly correlated. 5) Stiffnesses derived from destructive and non-destructive tests have an elastic and a viscoelastic contribution. Since the viscoelastic contribution is time dependent, the results will be dependent on strain rate and loading frequency in cyclic tests. 6) Standard testing of small trabecular bone specimens is associated with systematic errors. The most significant of these errors are believed to be related to trabecular disintegrity at the surface of the specimen and to friction at the specimen-platen interface. Structural disintegrity causes an axial strain inhomogeneity resulting in a overestimation of axial strain and a corresponding underestimation of specimen stiffness. Friction at the interface causes an uneven stress and strain distribution in the layer nearest to the test platen resulting in a overestimation of stiffness. The net result of these systematic errors is a 20-40 per cent underestimation of stiffness. 7) The specimen geometry has a highly significant influence on mechanical properties such as stiffness, ultimate strain and energy absorption. A cube with a side length of 6.5 mm and a cylindrical specimen with a length of 6.5 mm and a diameter of 7.5 mm are suggested as standard geometries providing comparable results.

Effect of internal heating during hot compression on the stress-strain behavior of alloy 304L

Abstract: The temperature change due to the conversion of mechanical deformation to internal heat and its effect on the as-measured stress-strain behavior of alloy 304L was investigated by means of initially isothermal (compression specimen, dies, and environment at same temperature at initiation of test), constant strain rate, uniaxial compression of laboratory-sized cylindrical specimens. Strain rate was varied in the range 0.01 to 1 s−1, where the thermal state of the test specimen varied from nearly isothermal to nearly adiabatic, respectively. Specimens were deformed in the temperature range of 750 °C to 1150 °C to a strain of 1. The change in specimen temperature with applied strain was calculatedvia finite-element analysis (FEA) from the asmeasured stress-strain data. Selected predictions were confirmed with embedded thermocouples to verify the model employed. Temperature was found to increase monotonically with strain at a strain rate of 1 s-1, consistent with what is theoretically expected for the adiabatic case. At the 0.1 and 0.01 s-1 rates, the sample temperature initially increased, peaked, and then decreased as the sample thinned and the contact area between the sample and the cooler dies increased. As-measured stress was corrected for softening associated with deformational heating by interpolation between the various instantaneous stress-temperature behaviors. The resulting isothermal flow data are compared to those predicted by a conventional method that employs an empirical estimate of the heat retention efficiency of the test specimen, assumed dependent on strain rate but independent of strain, to reduce the increase in temperature calculated for the adiabatic case. Differences between the calculated isothermal stress-strain data from the two methods are discussed. Values for the apparent activation energy of deformation and the strain to the peak in the flow curve, which is associated with the onset of dynamic recrystallization, determined from isothermal stress-strain data differed significantly from those obtained from the as-measured compression test data.

An Analytical Approach to Elastic-Plastic Stress Analysis of Rolling Contact

Abstract: Based on a stress invariant hypothesis and a stress/strain relaxation procedure, an analytical approach is forwarded for approximate determination of residual stresses and strain accumulation in elastic-plastic stress analysis of rolling contact. For line rolling contact problems, the proposed method produces residual stress distributions in favorable agreement with the existing finite element findings. It constitutes a significant improvement over the Merwin-Johnson and the McDowell-Moyar methods established earlier. The proposed approach is employed to study combined rolling and sliding for selected materials, with special attention devoted to 1070 steel behavior. Normal load determines the subsurface residual stresses and the size of the subsurface plastic zone. On the other hand, the influence of tangential force penetrates to a depth of 0.3a, where a is the half width of the contact area, and has diminishing influence on the residual stresses beyond this thin layer. A two-surface plasticity model, commensurate with nonlinear kinematic hardening, is utilized in solution of incremental surface displacements with repeated rolling. It is demonstrated that a driven wheel undergoes greater plastic deformation than the driving wheel, suggesting that the driven wheel experiences enhanced fatigue damage. Furthermore, the calculated residual stresses are compared with the existing experimental data from the literature with exceptional agreements.

Near surface microstructures developing under large sliding loads

Abstract: The subsurface zones of copper developed during the application of large sliding loads were observed using TEM and SEM. Differences in microstructural development as a function of load and sliding velocity are assessed. The observed microstructural changes, such as the development of a dislocation substructure and a mechanically mixed layer, are used to estimate the stress and strain-state of the near surface zone during sliding. These estimates of local stress and strain were compared to the applied stresses to show that large stress concentrations develop at and below a sliding interface. Thus, the stresses which develop locally within the near surface zone can be many times larger than those predicted from the applied load and the friction coefficient. It is postulated that these stress concentrations arise from two sources: (1) asperity interactions and (2) local and momentary bonding between the two surfaces. These results are compared to various friction models.

Deviatoric stress measurement under uniaxial compression by a powder x‐ray diffraction method

Abstract: The complete stress field in a polycrystalline sample compressed in a modified Drickamer‐type apparatus was determined from x‐ray diffraction data. The incident x rays, from a synchrotron source, were perpendicular to the compression axis, and the diffracted energy‐dispersive signals were simultaneously determined for two directions relative to the compression axis. The two sets of d values measured by this system were analyzed by making use of a new equation derived by Singh, and the uniaxial stress component σ1−σ3 and the parameter α, which describes the stress and strain conditions across the grain boundaries of the sample, were obtained. This method was applied to NaCl and the results give the important information on the stress state and the pressure determination method under direct compression of a solid sample.

Modeling the Stress-Strain Response of Continuous Fber Reinforced Cement Composites

Abstract: This paper describes a theoretical model of stress transfer between polypropylene fibrillated fibers and the matrix in fiber cement composites. The model is based on microscopic observations of the tensile fracture process, which demonstrate that slip occurs within the polymer due to shear stress during multiple cracking as well as at the fiber-matrix interface. Therefore, the proposed model allows for frictional stress transfer at two different interfaces (i.e., the matrix-fiber interface and the polymer slip surface within the fibers). The tensile stress-strain curve predicted by this model has two different slopes in the multiple-cracking region (i.e., a horizontal part and a rising stress part). Also, the predictions of this model provide reasonable agreement with the experimental results of fibrillated polypropylene fiber cement composites.

Ultrasonic imaging of the stress distribution in elastic media due to an external compressor.

Abstract: We describe an experimental ultrasonic method capable of imaging the two-dimensional distribution of longitudinal stress in an elastic, tissue-like material due to an external compressor of arbitrary size or shape and boundary conditions. The method involves the use of a compressor and an opposing ultrasonic transducer. Local strains are derived from the ultrasonic backscatter signals before and after compression using cross correlation analysis. The strain distribution is converted to a stress map by assuming a linear stress-strain relationship. The technique is useful for quantifying the corrections that must be made to images of the elastic modulus of tissue (elastograms) due to the effects of compressor size and shape, depth and boundary conditions. It is also useful for experimental modeling of stress distributions in elastic media.

Analysis of thermally induced stress and strain in continuous fiber-reinforced composites

Abstract: An axisymmetric model for the thermally induced stresses and strains in a deformable matrix continuous fiber-reinforced composite is developed. The model allows for a temperature- and strain-dependent matrix flow stress and is numerically implemented using a von Mises flow law. The model implementation permits the study of an arbitrary number of temperature cycles. This model is compared to a simple one-dimensional model that has been used in several pre-vious analyses. The models show good qualitative agreement, but there are important differ-ences, and the magnitude of the discrepancy depends sensitively on the properties of the composite. These models can be applied in analyzing experimentally measured strainvs tem-perature hysteresis loops to reveal thein situ mechanical properties of the deformable matrix. The models can also be applied to the design of continuous fiber-reinforced composites that will not suffer thermally induced cyclic-plastic deformation.

Mechanics of Solids: An Introduction

Abstract: 1: Introduction to Stress and Strain 2: Uniaxial Loading and Deformation 3: Torsion of Circular Shafts 4: Shear Forces and Bending Moments in Beams 5: Stresses due to Bending 6: Deflections of Statically Determinate Beams 7: Deflections of Statically Indeterminate Beams 8: Stress and Strain 9: Analysis of Combined States of Stress 10: Buckling and Stability. Appendix: solutions to selected problems.

Uniaxial Stress-Strain Behavior of Unsaturated Soils at High Strain Rates

Abstract: : The Split-Hopkinson Pressure Bar was used to study the uniaxial stress-strain behavior of compacted moist soils under one-dimensional, undrained, confined compression loading at high strain rates (1000/sec and 2000/ sec. Three soils, Eglin Sand, Tyndall sand and Ottawa 20-20 sand were tested. The results suggest that the stress strain response is dominated by the water- phase from the lock-up strain and beyond. The soil skeleton dominates the response from the start of loading up to the lock-up strain. It appears that there may be some strain-rate effects, however, the data arc insufficient to adequately demonstrate this and further investigation is suggested. The research described in this report has demonstrated that the Split-Hopkinson Bar System is a viable technique for high strain rate dynamic geotechnical testing of unsaturated, saturated, and dry soils, and provides a framework for conducting further studies. Split-Hopkinson pressure bar, Tyndall sand, Ottawa 20-20 sand, Uniaxial stress strain

Torsional Motion Monitoring System for Small-Strain (10 −5 to 10 −3 %) Soil Testing

Abstract: For accurate measurements of stress-strain hysteresis loops at strains below 10−3%, a torsional motion monitoring system was modified to incorporate micro-proximitors. A micro-proximitor system with enlarged target arms resulted in about 50 times higher resolution in motion monitoring than previously possible. The four proximitor signals (instead of two) were measured, compared, and averaged to insure that pure torsion of the system was generated and that any bending did not enter the measurement. Ambient noise was controlled by using a low-pass filter and/or a vibration isolation table. With this new system, shear modulus was measured at strains as low as 2 · 10−5%, and hysteretic damping was measured at strains as low as 6 · 10−5%. Below the elastic threshold strain, shear modulus of dry sand measured in the cyclic torsional shear test is independent of strain amplitude. Hysteretic damping exists below the elastic threshold and is independent of strain amplitude, even though the value is quite small.

Tensile Stress-Strain Characteristics of Lightly Cemented Sand

Abstract: Laboratory tensile and unconfined compression test results on lightly cemented sand specimens are reported. Type I portland cement was mixed with sand in proportions of 4, 6, and 8% by weight to prepare the specimens. Tensile strength was determined by indirect tensile strength testing and direct tension testing. The variation of tensile strain with stress in indirect tensile strength tests was measured by a computer-aided image analysis method. Based on the test results, tensile and compressive strengths and strain levels at failure have been determined and compared. Nondimensional tensile stress-strain relationships in the form of a rectangular hyperbola as obtained from the indirect tensile strength tests and direct tension tests have been developed.

Basic role of a hard particle in a metal matrix subjected to tensile loading

Abstract: The present study is mainly devoted to clarifying the basic role of a hard particle in a metal matrix based on Eshelby's theory of an inhomogeneity. Firstly, the stress and strain distribution around an isolated spherical particle has been visualized instead of leaving the classic fundamental approach as an analytical form. Secondly, the features of the matrix-particle interfacial stress characteristics have been examined. Thirdly, the work answers the question of how the misfit of the elastic constant affects stress transfer to the inhomogeneity. Finally, a verification has been made that the stress concentration in the matrix is normalized by the size of the inhomogeneity.

Fracture criteria for hydrogen and temper embrittlement in 9Cr1Mo steel

Abstract: A reduction in ductility and toughness is observed on thermal ageing of 9Cr1Mo steels in the temperature range 400–650°C. Previous investigations using tensile tests have shown a synergistic effect of hydrogen on such temper embrittlement. To investigate the mechanisms underlying this effect of hydrogen a series of fracture tests have been undertaken on a commercially produced 9Cr1Mo steel using blunt-notched (SENB) specimens tested in four-point-bend. The results were analysed to determine the maximum local tensile stress σ F ∗ and the local stress and strain levels at the point of crack initiation as a function of test temperature, hydrogen content and thermal ageing. Local fracture stress, rather than σ F ∗ , was relatively constant with test temperature, and it is proposed that this parameter, together with local fracture strain, controls the failure mechanism. A dual stress/strain criteria model is proposed, and it is suggested that both hydrogen and temper embrittlement reduce the local fracture stress, indicating an influence on cohesive strength for both mechanisms of embrittlement.

Effect of nonuniform stresses on measured dss stress-strain behavior

Abstract: This paper presents results of a laboratory investigation of the influence of the nonuniform stresses imposed by the Geonor direct simpleshear (DSS) apparatus on measured stressstrain behavior. The...