Showing papers on "Stress–strain curve published in 1970"

On the Structure of Stress-Strain Relations for Time-Dependent Plastic Deformation in Metals

Abstract: The paper is concerned with the structure of multiaxial stress-strain relations in timedependent metal plasticity, as for transient creep and rate sensitive yielding. First. a general kinematical relation is developed between the macroscopic inelastic strain tensor and microstructural slip displacements, as modeled either by continuum shearing on crystallographic planes of individual grains or by the motion of discrete dislocation lines. It is assumed that at any given slipped state, the rate of slipping on a particular system is governed by the resolved shear stress on that system (or by the local \"forces\" on dislocation lines). 'This leads to the primary result of the paper: Components of the macroscopic inelastic strain rate tensor are deriz!able, at each instant in the course of deformation, from a potential function of stress, General features of the flow potential surfaces in stress space are discussed, and some specific functional forms are examined, Linear viscoelasticity and tirre-independent plasticity are developed as limiting cases of the flow potential formulatic!, and the appropriateness of a potential function for stationary creep is discussed,

Determination of stress-strain characteristics at very high strain rates

Abstract: A modified version of the Kolsky thin-wafer technique is described. The method permits one to obtain the dynamic plastic properties of materials at strain rates as high as 105 sec−1. Data obtained from compression tests on high-purity aluminum are presented for strain rates ranging from 4000 to 120,000 sec−1 at room temperature. Specimen-size effects and the effect of lateral inertia are taken into account in analyzing the data. The results plotted as stress vs. strain rate at constant strains (5 to 20 percent) show that, at the highest strain rates, the stress rises very rapidly with strain rate suggesting that a limiting strain rate is being reached. At the lower strain rates (103 to 104 sec−1), the stress is linearly proportional to the strain rate indicating that the material is deforming in a viscous manner.

A criterion for inhomogeneous plastic deformation

Abstract: A model has been developed to describe the tendency of a material that exhibits strain softening to develop regions of high local strain. It is shown that large inhomogeneities in strain tend to develop if the negative slope of the true stress-strain curve after the upper yield point is large, if the variation of the yield stress of the material with strain rate is small, and if the material contains large local inhomogeneities to begin with. In the next paper the model is used to discuss shear-band formation in a number of polymers.

Stress-strain characteristics of concrete confined in steel binders

Abstract: Synopsis The ductility of concrete can be increased by confinement in steel binders but, for a proper analysis of the ultimate strength of structures utilizing this gain, an undertsanding of the st...

Deformability of schistous rocks

Abstract: THE RESULTS OF LABORATORY AND IN SITU UNIAXIAL COMPRESSION TESTS OF SCHISTOUS ROCKS ARE PRESENTED, ALONG WITH AN ANALYSIS BEING MADE OF THE VARIATION OF THE MODULUS OF ELASTICITY, OF THE POISSON'S RATIO, OF THE COEFFICIENT OF UNIT VOLUME EXPANSION AND THE RELATION BETWEEN PRINCIPAL DIRECTIONS OF STRESS AND STRAIN WITH THE ANGLE BETWEEN A GIVEN DIRECTION AND THE NORMAL TO THE SCHISTOSITY. FOR THE PURPOSE OF THIS STUDY, THE SCHISTOUS ROCKS WERE ASSUMED TO BEHAVE LIKE THE TRANSVERSELY ISOTROPIC BODY WHICH THEY RESEMBLE. /AUTHOR/

Effect of Paste-Aggregate Bond Strength on Behavior of Concrete

Abstract: COARSE AGGREGATE WAS COATED WITH A THIN LAYER OF POLYSTYRENE TO REDUCE PASTE-AGGREGATE BOND STRENGTH. THE RESULTING CONCRETE WAS COMPARED TO CONCRETE CONTAINING UNCOATED CONTROL AGGREGATE FOR STRENGTH, STIFFNESS AND TYPE AND AMOUNT OF MICROCRACKING. LARGE CHANGES IN INTER-FACIAL PASTE-AGGREGATE BOND STRENGTH CAUSED ONLY SMALL CHANGES IN COMPRESSIVE STRENGTH, STIFFNESS, AND MICROCRACKING. /JM/

On the theory of fibre strengthening

Abstract: A new method of analysing stress and strain in the matrix of a fibre-reinforced material within the elastic region is demonstrated. To this end, a single long elastic fibre is considered which is embedded in and bonded to a plane matrix. The problem is reduced to the solution of an integral equation; this equation is derived and solved for two shapes of fibres. The calculated interface shear stress for a rectangular fibre is compared with experiment and good agreement is found. The effect of the fibre shape and the elastic constants on the interface shear stress is discussed. A general curve that can be used to estimate the interface shear stress reasonably far away from the end region is given.

31—observations on the mechanical behaviour of lincoln-wool fibres supercontracted in lithium bromide solution

Abstract: A brief summary of certain phenomena associated with the two stages of supercontraction in aqueous lithium bromide solution is given; in particular, the mechanical properties, in the cold solution, of wool fibres at the end of each stage are discussed. Results previously obtained by Feughelman and Haly are reinterpreted in terms of the simple two-phase model of crystalline microfibril embedded in a less ordered matrix. On the basis of certain assumptions, it is possible to obtain an estimate of the Stress–Strain curve of the matrix in LiBr solution. The matrix Stress–Strain curve so obtained compares well with the theoretical inverse Langevin rubber-elasticity curve up to a certain strain level. A value for the number of random links between cross-links is obtained.

On the Relation Between Stress and Strain-Concentration Factors in Notched Members in Plane Stress

Abstract: The validity of the relationship between stress and strain-concentration factors proposed by Neuber, i.e., the geometric mean of the stress and strain-concentration factors is equal to the linear elastic-stress-concentration factor, is investigated for plane-stress problems. The physically nonlinear plane-stress problem of an infinite plate with a circular hole is solved by a perturbation method. Applicability of the solution and the restrictions on the relationship are discussed with reference to theoretical and experimental results.

Behavior of Concrete under Varying Strain Gradients

Abstract: Stress-strain relationships developed for concrete subjected to concentric compressive loadings are used to predict the response of concrete subjected to eccentric loadings. The computed response is compared with the results of 19 test specimens subjected to strain gradients in which the strain at one face of the specimen was held at zero and the strain at the other face was varied. The results indicate that under monotonic loading to failure, the stress strain curve for concrete subjected to strain gradients is essentially the same as for concrete subjected to uniform strains. The response of concrete under repeated eccentric loading is reliably predicted using the stress-strain relations developed for concrete under repeated concentric loading.

The relationship between discontinuous yielding and cyclic behavior in polycrystalline molybdenum

Abstract: The fatigue properties of polycrystalline molybdenum at room temperature have been determined by axial tension-compression tests in both stress and strain control modes to give lives of up to 106 cycles. Under the appropriate conditions, the endurance limit can be considerably reduced,e.g., the stress to cause failure in 106 cycles decreases from ∼42,000 psi at 5 cps to ∼28,000 psi at 0.5 cps. The fatigue resistance as assessed by either strain control or by stress control is discussed in relation to the tensile and creep behavior, and it is concluded that the reduction in the long life fatigue resistance with decrease in the cyclic frequency is due to the time dependent generation of a mobile dislocation population. The previously accepted value of 0.6 for the ratioFL/UTS for bcc metals can be attributed to this frequency effect. A lower value for this ratio, 0.4, can be derived from the high frequency data by the use of an extrapolation technique. This lower value is confirmed by long life, low frequency tests, in agreement with the value for fcc metals. The importance of obtaining fatigue data under comparable states of mobile dislocation density is emphasized, particularly for materials exhibiting pronounced tensile yield points, in order that meaningful comparisons can be made between different materials.

Strength Characteristics of Glass Fibers Under Dynamic Loading

Abstract: The main purpose of the present investigation was to characterize the behavior of S‐glass fibers at quasistatic strain rates. The experimental results presented herein, representing over 1600 individual tests, are a first step in the statistical characterization of fiber properties. It has been established that fiber strength decreases with increasing strain rate. Moreover, the experimental results demonstrate that Weibull distribution can adequately represent fiber strength distribution for quasistatic strain rates. For the type of glass tested, strength was observed to be maximum at or near room temperature (+75°F). The strength dependence on strain rate is greatest at room temperature. At higher or lower temperatures the dependence on strain‐rate is not so marked. Tests were also performed to determine the elastic modulus at various temperatures and strain rates. The elastic modulus increases with both an increase in strain rate and a decrease in temperature.

The role of dislocations in damping

Abstract: According to the classical theory of elasticity, stress and strain are uniquely related. However, as early as 1825 small deviations from perfect elasticity were observed in galvanometer suspensions. Upon release of the couple the suspension did not at once return to its zero point but approached the zero asymptotically. This behaviour, which was termed the elastic after-effect, is one of several effects, caused by the lack of uniqueness between stress and strain in the preplastic range generally known as anelasticity.

Stress-Strain Curves for Oxygen-Free High Conductivity Copper at Shear Strain Rates of up to 103s-1:

Abstract: Shear stress-shear strain curves for o.f.h.c. copper at room temperature have been obtained at constant shear strain rates in the range 1 to 103s-1, using thin walled tubular specimens in a flywheel type torsion testing machine. Results show that, for a given value of strain, the stress decreases when the rate of strain is increased. Moreover, the elastic portion of the stress-strain curve tends to disappear as the rate of strain is increased. It is postulated that these effects are due to the formation of adiabatic shear bands in the material when the given rate of strain is impressed rapidly enough. A special feature of the design of the testing machine used is the rapid application of the chosen strain rate.

An Explicit Damage Model For Dynamic ConcreteBehaviour. Numerical Simulations AndComparisons With Experimental Results OnReinforced Concrete Plates Under Blast Loading

Abstract: Under severe mechanical loading, brittle materials, like concrete, can be described favourably using damage models. In order to determine the vulnerability of reinforced concrete structures submitted to accidental loading, the Centre d'Etudes de Gramat has developed an explicit damage model. This new concrete model uses two internal scalar variables to represent the material stiffness with opened or closed Inelastic tensile and inelastic compressive strains are introduced. Strain rate effects are also taking into account in order to separately increase the dynamic tensile and compressive material strength. Friction stresses are added to simulate stress strain hysteresis during unloading and reloading path. The Hillerborg regularisation concept is applied to reduced mesh size effects on failure process. The explicit model allows computation of the stress tensor directly and exactly, without any iterative process. Computation time are reduced drastically and convergence difficulties of the iterative procedure are suppressed. The model has been implemented in an explicit finite element program. Numerical simulations has been done to simulate experimental results obtained on a reinforced concrete circular plates under shock wave loading. The concrete plates have a diameter of 1.3 meter and a thickness of 8 or 10 centimetres. The plates are supported on it external edge. Calibrated shock wave loading inducing static overpressure between 100 Kpa and 500 Kpa are applied successively to the reinforced concrete plates. Large and permanent deflections are obtained on the concrete structure. Strain gage measurements are recorded on the steel reinforcement. Comparisons between numerical and experimental results are presented and discussed.

Effect of reactor irradiation on ductile- brittle transition and stress-strain behavior of tungsten

Abstract: Reactor irradiation effects on ductile brittle transition and stress-strain behavior of tungsten

Stress/Strain Distribution in Triaxial Compression Tests on a Sand,

Abstract: : The influence of nonuniform stress and strain distribution, caused by end platen effects, on analysis of triaxial tests is studied through finite element calculations. End effects are found to affect significantly the homogeneity of stress in the specimen. (Author)