Showing papers on "Stress–strain curve published in 1980"

Fatigue of metallic materials

Abstract: 1. Introduction. 2. Cyclic Stress-Strain Response. Mechanical properties. Microstructure. Theories of hardening and softening. 3. Fatigue-Crack Nucleation. Stress near surface. Sites of crack initiation. Near-surface dislocation structures. Surface relief and its relation to near-surface dislocation structures. Mechanisms of crack nucleation. Factors influencing crack nucleation. 4. Fatigue-Crack Propagation. Kinetics of crack growth. Fracture mechanics for fatigue cracks. Quantitative description of fatigue-crack propagation rate and threshold. Properties of plastic zone. Models of fatigue-cracks propagation and thresholds. Effects of miscellaneous factors on the crack-propagation rate. 5. Fatigue-Life Curves. Fatigue-life curve a versus f. Fatigue-life curve a versus f. Transformation of fatigue-life curves. Influence of cycle asymmetry. Hysteresis energy and fatigue life. Fatigue limit. Curves of constant damage. S/N curves of precracked bodies. Influence of temperature on fatigue life. 6. Notched Behaviour. Stress and strain concentration. Influence of notches on fatigue life. 7. Fatigue Life for Random Loading. Cyclic plasticity. Analysis of random variations of stress and strain. Prediction of fatigue life. References. Subject Index.

Hysteretic Fracturing Endochronic Theory for Concrete

Abstract: An improved endochronic nonlinear triaxial constitutive relation for concrete is developed: (1)In addition to plastic strain increments proportional to stress tensor, fracturing strain increments proportional to strain tensor are used to model strain-softening; (2)the plastic and fracturing inelastic strain increments are characterized by different intrinsic times; (3)degradation of the elastic shear modulus is determined by the intrinsic time for the fracturing strain increments, and degradation of the bulk modulus is related to that of the shear modulus using Budianski-O'Connell's expressions for the elastic moduli of randomly microcracked material; (4)jump-kinematic hardening, in which the center of the loading surface jumps into the current stress and strain point whenever loading reverses to unloading or vice versa, is introduced. The theory also exhibits hydrostatic pressure sensitivity, inelastic dilatancy, initial shear compaction in triaxial loading, and inelastic strain due to hydrostatic pressure.

Micromechanisms of crack growth in composite materials under corrosive environments

Abstract: The nucleation and propagation of cracks in aligned continuous glass fibre reinforced polyester composites in the presence of hydrochloric acid have been studied using ring specimens subjected to parallel plate compression. The appearance of the fracture surfaces depends on the initial strain but is characterized by planar cracks normal to the fibre direction with little fibre pull-out. The planar cracks are separated by interlaminar cracks. A model is presented for the nucleation and growth of cracks in stress and strain corrosion conditions.

The effect of chain structure on the annealing and deformation behaviour of polymers

Abstract: In a tensile test ductile thermoplastics may give either uniform deformation or necking. Recently it has been found that those giving uniform deformation either, are known to have extended chain configurations in solution, or have chemical formulae with linear structures and relatively few flexible bonds. The observed differences in behaviour can be predicted from a viscosity retarded rubber elasticity model in which a constant related to chain flexibility is introduced, which quantifies the strain hardening of the material. It is argued that the early development of strain hardening generally interferes with the localization of plastic strain in shear bands or crazes (as well as in a neck) and correlates with the stress cracking performance of high density polythenes.

Optimized stress and strain distribution diaphragms

Abstract: A stress distribution plate, such as a diaphragm for a pressure transducer, has a central plane and a neutral stress plane. According to the invention, the neutral stress plane is displaced from the central plane, providing for a mechanical advantage or amplification in the operation of the stress plate or transducer. The stress plate or diaphragm may be provided with a lacunose surface region or with a predetermined and preferably symmetrical pattern of mesas and recesses for a displacement of the neutral stress plane relative to the central plane.

Dislocation theories of work hardening and yield surfaces of single crystals

Abstract: The nature of existing dislocation hardening mechanisms are analyzed. This analysis shows that the hardening mechanisms can be classified into two categories: isotropic and kinematic; consequently a general physical hardening law, which incorporates the concept of the degree of isotropy in work hardening, is proposed. The corresponding motions of yield surface in both stress and strain space are examined on the basis of this general hardening law and its two extreme cases: isotropic and kinematic hardening.

Total strain theory and path - dependence of concrete

Abstract: The nonlinear triaxial behavior of plane concrete that is free of continuous cracks is modeled by an algebraic relation between total strains and stresses, analogous to deformation theory of plasticity. Unloading is not modeled. Good agreement with numerous test data is achieved. The formulation implies algebraic expressions for failure envelopes and some stress-strain curves, which make data fitting easier. The model is enhanced by corrective path-dependent terms that vanish for proportional loading so as extend it for highly nonproportional loading. The principal directions of stress and strain then cease to coincide. In contrast to previous models, the present one applies to much largest atrains, gives the peak stress points, failure envelopes, strain softening, inelastic dilatancy, etc. A tangential incremental form for structural analysis is also indicated.

A fundamental study of the stress-strain characteristics of a bituminous material

Abstract: This paper reports on tests of the stress-strain characteristics of bituminous materials that provided good quality data on the relationships between applied stress and the resulting permanent and resilient strain. The results are expressed in a manner which enables general conclusions to be reached about the mix behavior under three-dimensional stress conditions. Both repeated load and creep tests were used and the results may have applications in other design situations such as asphaltic concrete cores for rockfill dams.

Mechanical properties of Stycast-1266 at low temperatures

Abstract: Young’s modulus, the critical tensile stress, and the fracture stress of Stycast‐1266 have been determined by the tension test as functions of temperature between room temperature and 2.2 K.

There is no hookean region in the stress-strain curve of keratin (Or other viscoelastic polymers)

Abstract: Viscoelastic polymers exhibit stress relaxation, and it is therefore predicted that their stress-strain curves will be nonlinear at all strains. It is shown in this report that this behavior is observed only with straight and properly clamped specimens; when a specimen is crimped or badly clamped, the initial part of the curve exhibits “toe-in” (caused by straightening of the specimen), which obscures the viscoelastic curvature. In this case, a pseudo-linear region, strictly an inflection region, is observed at low strains, which arises from opposing viscoelastic and toe-in curvatures. There is thus no Hookean region in the stress-strain curve of (straight or crimped) viscoelastic polymers, and the concept of a Young's modulus is inapplicable; however, the inflection modulus, derived from the slope of the inflection region has limited applicability, particularly when the toe-in is not excessive. Instead of a Young's modulus, a unique stiffness parameter is proposed, termed the initial secant modu...

Analysis of Free Forging by Rigid-Plastic Finite Element Method Based on the Plasticity Equation for Porous Metals

Abstract: The rigid-plastic finite element method based on the plasticity equation for porous metals has been extended and applied for the analysis of plastic deformation of ordinary pore-free metals. The relative density is assumed to be very close 100%, eg. 99.5% or 99.95% in the calculation. The stress and strain states can be calculated with this method up to large deformation. Upsetting of a cylindrical billet with grooved dies and compression of square and rectangular thin plates with flat dies without lubrication are analysed. The analytical results of stress, load and deformed shape show good agreements with experimental results.

Stress and Strain Concentrations in Perforated Structures Under Steady Creep Conditions

Abstract: Steady creep solutions are obtained for perforated materials under various loading conditions. Norton’s creep power law is used and the plane stress problem is analyzed for both the triangular and square penetration patterns of circular holes. Maximum local stresses at the hole boundaries are obtained for calculating creep rupture damage. Local creep strain concentration factors are also obtained. The interrelations between the elastic, plastic and creep solutions are investigated.

Stress - strain relationships for confined concrete: rectangular sections

Abstract: An experimental investigation into the behaviour of square, confined, reinforced concrete columns was undertaken. Thirty 450 mm square, 1200 mm high units were cast with varying amounts of longitudinal and lateral steel. These were subjected to concentric or eccentric axial loads to failure at slow or dynamic loading rates. Confinement requirements of reinforced concrete columns are discussed and the results and analyses of experimental work presented. Results include an assessment of the significance of loading rate, eccentricity, amount and distribution of longitudinal steel, and the amount of confining steel. A general stress-strain curve for rectangular concrete sections loaded at seismic rates is proposed and compared with existing curves based on previous static loading tests.

Nucleation and propagation of cracks during strain corrosion of grp

Abstract: The mechanisms of crack nucleation and propagation in ± 55° angle ply sections of glass fibre polyester resin filament wound pipe tested in both stress and strain corrosion conditions have been studied using optical microscopy and scanning electron microscopy. The failure processes are compared with similar tests in hoop wound pipe. Four distinct stages of deformation and fracture have been identified. Stress and strain corrosion failure is associated with fibre fracture and characteristic planar fracture surfaces are obtained. The main difference between ± 55° sections and hoop wound sections is the occurrence of transverse cracking in the ± 55° sections in the initial loading stage. These cracks allow acid to penetrate through the inner lamina and lead to an enhanced stress corrosion cracking effect. The results are interpreted in terms of the stress acting parallel and perpendicular to the fibres.

Comparison of elastic and elastic-plastic structural analyses for cooled turbine blade airfoils

Abstract: Elastic plastic stress strain states in cooled turbine blade airfoils were calculated by three methods for the initial takeoff transient of an advanced technology aircraft engine. The three analytical methods compared were a three dimensional elastic plastic, finite element analysis, a three dimensional, elastic, finite element analysis, and a one dimensional, elastic plastic, beam theory analysis. Structural analyses were performed for eight cases involving different combinations of mechanical and thermal loading on impingement cooled airfoils with and without leading edge film cooling holes. The von Mises effective total strains at maximum takeoff computed from the elastic and elastic plastic finite element analyses agreed with 9 percent for rotating airfoils and 28 percent for stationary airfoils with the elastic results on the conservative side.

The spherical vessel with anisotropic creep properties considering large strains

Abstract: The effect of material anisotropy on creep of pressurized thick-walled spherical vessel has been discussed considering the large strain theory It is found that the creep strain varies with varying anisotropy of the material The results obtained for the anisotropic case have been compared with those obtained for the isotropic case and it is observed that the stress and strain distribution in the wall of the vessel is strikingly different for the two cases