Showing papers on "Stress–strain curve published in 1974"

Quasi-static extension of a tensile crack contained in a viscoelastic-plastic solid

Abstract: Final stretch criterion of failure is applied to the problem of quasi-static extension of a crack embedded in an elastic-plastic or viscoelastic-plastic matrix. The slow growth under subcritical conditions in a rate-sensitive Tresca solid is shown to be a superposition of creep rupture and McClintock's ductile growth. This type of growth occurs at subcritical magnitude of the imposed K-factor and can be accounted for only through a recognition of inelastic properties of solids. In the subcritical range there is no unique value for K sub c independent of geometrical configuration and flaw size. Not only the produced states of stress and strain are dependent on the loading path, but also the material resistance to fracture turns out to be a function of the history of loading that precedes catastrophic failure. A nonlinear integro-differential equation of motion is derived for a crack progressing through a viscoelastic medium with some limited ability to plastic flow. Examples of numerical integration are given incorporating both monotonic and cyclic loading programs.

An analysis of strain accumulation on a strike slip fault

Abstract: An analysis of strain accumulation on a strike slip fault is given. The fault between two lithospheric plates is assumed to be locked to a finite depth; owing to plastic flow the fault is free to slide at greater depths. The base of each plate is also a free boundary. The periodic stress accumulation and stress release associated with the elastic rebound hypothesis are modeled. A solution for the two-dimensional stress and strain field near the fault is obtained. It is shown that significant strain accumulation extends to distances of the order of the length of the fault break. The rates of accumulation of stress and strain energy for the San Andreas fault are obtained. Predicted distributions of shear strain are compared with observations. Because of the scatter in the data and possible complexities where observations have been obtained, poor agreement with theory is found.

Fracture and Stress-Strain Relationship of Concrete under Triaxial Compression

Abstract: Specimens of paste, mortar, and concrete were tested to failure when subjected to different amounts of lateral confining pressure. Two distinct modes of behavior were observed. Under low confining pressures, failure was accompanied by splitting, by large axial compressive and lateral tensile strains, significant internal microcracking and by a reduction in pulse velocity. For high lateral pressures, the axial strains at failure were smaller, lateral strains were compressive, and very little cracking and reduction in pulse velocity occurred at failure. This transition in behavior is explained in terms of the relative values of maximum deviatoric and hydrostatic components of failure stress, and the strengths of porous matrix and sliding interfaces. A stress-strain relationship includes two basic material constraints: bulk modulus and Poisson’s ratio. These material properties are considered functions of invariants of stresses; the appropriate functions are derived from test results.

Uniaxial tensile creep and failure of concrete

Abstract: Synopsis This paper describes a series of experiments carried out on concrete under uniaxial tensile stress, using a test method developed previously. The properties assessed include the effect of mix proportions and curing conditions upon the short-term failure stress and strain and upon the tensile creep under a load of 35% of the ultimate short-term strength. The effect of variable humidity states upon the tensile creep was also investigated, and the results interpreted from the viewpoint of creep hypotheses for compressive loading. Where possible, the observed effects are related to the microstructure of cement gel. Finally, the effects upon creep of the level of loading and of the long-term strength of concrete in tension have been determined, and compared with the established behaviour in compression.

The relevance of tensile properties to sheet formability

Abstract: Perhaps the area in which a detailed knowledge of stress/strain relations is most important is that of sheet forming. It is true that the precise form of the stress/strain equation should be known to assist analyses of sheet-forming processes. However, in the present context, the proposition is that such data can be obtained from a tensile test. This contribution examines that proposition especially under the circumstance likely to prevail in sheet forming that the material is anisotropic. The anisotropy may be crystallographic in origin or may otherwise arise from the pre-strain history. It is concluded that the differences between any of the empirical stress/strain equations represent the least significant of the errors in describing the actual stress/strain behaviour of an element of material under sheet-forming conditions. The importance of considering the total states of stress and strain is illustrated by analysing an example from the literature due to Richards.

On stress rates in solid mechanics with application to elasticity theory

Abstract: The efficacy of making a careful choice of strain measure in problems of solid mechanics was recognized and fully exploited by Hill(1–4). He brought coherence to fundamental stress and strain analysis by the introduction of the idea of conjugate pairs of stress and strain measures, and provided a platform for the further development of constitutive relations for solid materials.

Brazilian Tensile Test for Soils

Abstract: Analysis and design of impermeable cores of earth dams against cracking require knowledge of the tensile strengths and tensile stress–strain relationships of the concerned soils. The same is needed for any stress and deformation analysis of an earth structure when a portion of it is expected to be in tension. In order to investigate behavior of soils in tension the Brazilian tensile test has been employed and found advantageous over other methods. However the interpretation of results of this test is involved because of the biaxial stress conditions existing at the center of the test specimen. Neglecting this fact leads to erroneous evaluation of the test results, particularly if the moduli in tension and compression differ. A numerical stress solution which considers the difference between compressive and tensile moduli with respect to tensile strength and tensile stress–strain relationship is developed. The magnitude of errors associated with the incorrect assumption of equal modulus in tension and comp...

A Comparison of Tensile Stress-Strain Data from Dumbbell, Ring, and Oval Specimens

Abstract: Our study has shown that the tensile bar or dumbbell gives higher values for failure stress and strain than does either the ring or oval specimen. This should be expected since the tensile bar permits a primarily uniaxial test and one without the stress-concentrating pins used for the ring and oval. However, it is very difficult to obtain accurate low-strain data with the tensile bar. Also, the strain rate is not constant because of tab deformation. The ring, oval, and tensile bar show agreement for values of stress and strain above 100 per cent strain but below failure. For soft, low modulus stocks the ring and oval agree at low strains. For stock with tensile modulus values above 1000 psi, the bending stress and strain, required to straighten the ring to its in-test configuration, significantly affect the data. There is less ambiguity in reducing the data from tests run with the oval than from those run with the ring, whether reduction is done manually or through direct acquisition by computer....

Stress-Strain Properties of Compacted Clays

Abstract: It is pointed out that if the 70 percent and 95 percent points are used in fitting, the laboratory curve and the hyperbolic curve will compare vary well in this region but may differ seriously at low stress levels. The best overall fit between laboratory curves and hypergolas is obtained using the 50 percent and 95 percent points but the user should use points appropriate to the stress levels of major interest. Comment is made on the values of R sub f, and compaction conditions, and a linear failure equation. The use is unidacted of the log-log relationship to obtain a single analytic relationship through the stress range from 10 psi-1,000 psi. Both the tangent Poisson ration model and the hyperbolic model work well for samples compocted wet of optimum because they involve essentially constant values of Poissons ratio and thus degenerated into linear models in both cases. It is pointed out that the use of average axial strain and averate radial strain (derived from average values of volumetric and axial strains) is more likely to yield accurate results than the use of an average axial strain with the radial strain measured at a single point.

Measurement of the dynamic elastic modulus of short staple fibers

Abstract: A description is given of the equipment and measurement techniques which have been developed for the determination of the dynamic elastic modulus of staple fibers of length 25 mm or less. The dynamic elastic modulus, often called the sonic modulus, is determined by means of the pulse propagation method with the aid of a specially designed constant fiber-strain device. The modulus values are obtained for different fiber strain levels and are used to construct the dynamic stress–strain curve of the fibers. Results obtained for cotton, jute, and wool fibers are presented and discussed. In general, two points of inflexion on the constructed fiber stress–strain curves are determined without ambiguity, by the maximum and minimum values of the fiber dynamic modulus. The region between these two inflexion points is interpreted as the yield region of the fiber.

The Stress vactor and the Subsequent Yield Surface in Loading along the Strain Path with a Corner

Abstract: The stress strain relation and the subsequent yield surface in loading along the strain path with a corner are experimentally investigated in the deviatoric stress and strain space by subjecting thin-walled brass specimens to combined axial load, internal pressure and torsion. The change in direction of the stress vector can be uniquely associated with the length of strain path irrespective of the amount of prestrain and the corner angle of strain path, if the change in direction of the stress vector is represented by a nondimensional value divided by the corner angle. The minimum value of the magnitude of stress vector after turning the corner is independent of the amount of prestrain, if it is reduced to a nondimensional value divided by the magnitude of stress vector at the corner. The subsequent yield surface after preloading along the strain pat with a corner is not symmetric with respect to the direction of coresponding prestress. But, with an increase of prestrain, the symmetry of the yield surface is found and the shape is congruent with the subsequent yield surface after radial preloading to the same amount of prestrain.

Nonlinear Stress-Strain Formulation for Soils

Abstract: The basic principles of hypoelasticity are used to develop an incremental theory that is capable of describing the nonlinear stress-strain behavior of soils when compacted to different densities and loaded along various axisymmetric stress paths. Specific relationships are determined from experimental data for two types of soils. The results indicate that the modulus and Poission's ratio may either increase or decrease, depending on the ratio of the principal stress increments. A computer analysis of a buried reinforced concrete pipe is compared with actual experimental measurements to illustrate application of the method.

The effects of pressurization on the microstructure and mechanical properties of magnesium oxide

Abstract: Changes in microstructure in single crystals of MgO, containing elastic discontinuities, which result from pressurization treatments in the range 0.2 to 2 GN m−2 have been studied using an etch-pitting technique. Complex dislocation arrays have been observed around cubical and spherical cavities and precipitates. The observations are discussed in terms of stress and strain criteria. Production of {100} and {110} cracks at high pressure is also described. Following a 1 GN m−2 pressurization the flow stress was observed to decrease by < 10% and this has been related to the induced dislocation density. In polycrystalline MgO the fracture strength was unaltered by pressurization but the critical temperature difference of thermal shock,ΔTC, was increased by 55K. This has similarly been attributed to the movement of pressurization-induced dislocations.

Stress Analysis of Coldworked Fastener Holes.

Abstract: : The stress and strain distributions around an initially coldworked hole in a plate and the subsequent redistribution of the stresses and strains when the plate is subjected to a uniform tensile loading are evaluated both analytically and experimentally. An elastic-plastic finite element idealization is developed for a one-quarter inch diameter hole in a 7075-T6 aluminum alloy plate one-quarter inch thick. Stress and strain distributions are provided for a 6 mil radial expansion of the hole and at tensile load levels of 10,000 lb., 25,000 lb., 37,500 lb., and 42,500 lb. Moire interferometry was used to verify that the elastic-plastic finite element analysis is representative of the strain distributions in an actual fastener coldworking procedure which involves inserting a cylindrical sleeve into a nominal one-quarter inch diameter hole and then drawing an oversized mandrel through the hole to produce a symmetrical distribution of residual stresses around the hole. Previous experimental strain evaluations of holes in plates involved hole diameters of at least one inch. The moire mismatch technique and photographic enlargements of the moire patterns provided the accuracy required. The conditions in the vicinity of the hole associated with the sleeve insertion procedure did not reflect the idealized conditions used in the finite element analysis which prohibited a valid comparison between the experimental and computed results. (Author)

Stress and strain distributions beyond general yield in the Charpy V-notched specimen

Abstract: T he visioplasticity method has been used to obtain the stress and strain distributions during planestrain bending in a standard Charpy V-notched specimen of low carbon steel. The specimen was slit longitudinally through the notch with a square grid inscribed on the interface. The instantaneous grid distortion was obtained during a three-point incremental bending test. A computer program was developed for the calculation of the instantaneous stress and strain distributions using the experimentally determined displacement field and the true stress-strain curve of the steel.

STRESS-STRAIN RELATIONSHIPS OF CHEMICALLY IMPROVED UNFERMENTED DOUGHS: I: The Evaluation of Data Obtained at Large Deformations in Simple Tensile Mode

Abstract: The rheological behaviour of doughs prepared from flours treated with potassium bromate, azodicarbonamide and ascorbic acid was studied at large deformations in simple tension The results were interpreted in terms of isochronal constant strain rate modulus F(t*), and exponent n characterizing the time dependence of modulus F(t) The exponent n can be calculated from the equation: F(t) =F(t*)·(t/t*)n; n= -1 indicates a purely viscous response, n= 0 a purely elastic one The strengthening effect of the improvers at different moisture absorptions and temperatures was demonstrated by the drifting of the exponent n closer to 0, which indicated that the behaviour of the dough was becoming more similar to that of an elastic body The stress-strain relation measurements as well as the evaluation of the ultimate properties of the doughs in terms of ‘failure envelopes’ reflected the combined effect of the temperature on both the reaction rate of the improver and the consistency of the dough

A precise stress-strain relation of mild steel in the proportional deformation under combined loading

Abstract: With the appearance of electronic computer, more ditailed theories which can simulate accurately actual phenomena are evolved by taking into account the secondary effect hitherto neglected for avoiding mathematical difficalties in analyzing phenomena. In the plastic deformation, such a theory will be needed also for making precise estimations in the structural analysis and the deformation analysis of plastic work. According to the recent experiments, it has been made clear that the conventional plastic flow theory cannot simulate acculately the plastic deformation of metals under complex loading. In the present paper, as a first step of formulating in detail the plastic features of real materials under complex loading, an experiment is performed on the proportional deformation by applying a combined load of axial force and torsion to a thin-walled tube of mild steel. The stress-strain relation is formulated by using a fundamental tensorial equation from the experimental result.