Showing papers on "Strain hardening exponent published in 1982"
TL;DR: In this paper, the lattice misorientation across the shear band, which is such to cause geometrical softening of the bands, is not sensitive to the imperfection form for high strength, low hardening crystals a comparison with existing experimental data shows remarkably good qualitative and quantitative agreement between the calculations and observations.
1,237 citations
TL;DR: In this paper, the von Mises effective strain criterion was used to measure the progress of the γ→α transformation in 304 stainless steel sheet loaded in uniaxial and biaxially tension at both low (10-3 per second and high (103 per second) strain rates.
Abstract: The γ→α transformation in 304 stainless steel can be induced by plastic deformation at room temperature. The kinetics of strain-induced transformations have been modeled recently by Olson and Cohen. We used magnetic techniques to monitor the progress of the γ→α transformation in 304 stainless steel sheet loaded in uniaxial and biaxial tension at both low (10-3 per second) and high (103 per second) strain rates. We found that using the von Mises effective strain criterion gives a reasonable correlation of transformation kinetics under general strain states. The principal effect of increased strain rate was observed at strains greater than 0.25. The temperature increase resulting from adiabatic heating was sufficient to suppress the γ→α transformation substantially at high rates. The consequences of the γ→α transformation on mechanical behavior were noted in uniaxial and biaxial tension. Uniaxial tension tests were conducted at temperatures ranging from 50 to -80°C. We found that both the strain hardening and transformation rates increased with decreasing temperature. However, the martensite transformation saturates at ≈85 pct volume fraction α. This can occur at strains less than 0.3 for conditions where the transformation is rapid. Once saturation occurs, the work hardening rate decreases rapidly and premature local plastic instability results. In biaxial tension, the same tendency toward plastic instability associated with high transformation rates provides a rationale for the low biaxial ductility of 304 stainless steel.
529 citations
TL;DR: In this article, a modified Jaumann derivative based on the spin of specific material directions associated with the kinematic hardening is proposed, which eliminates the spurious oscillation. But it does not consider the effect of rotational effects.
Abstract: : Kinematic hardening represents the anisotropic component of strain hardening by a shift of the center of the yield surface in stress space. The current approach in stress analysis at finite deformation includes rotational effects by using the Jaumann derivatives of the shift and stress tensors. This procedure generates the unexpected result that oscillatory shear stress is predicated for monotonically increasing simple shear strain. A theory is proposed which calls for a modified Jaumann derivative based on the spin of specific material directions associated with the kinematic hardening. This eliminates the spurious oscillation. General anisotropic hardening is shown to require a similar approach. (Author)
188 citations
TL;DR: Frictional sliding experiments at confining pressures from 50 to 400 MPa were performed on thin layers of clay-rich fault gouges from locations along the San Andreas and Hayward faults in California as well as pure clays from other locations.
Abstract: Frictional sliding experiments at confining pressures from 50 to 400 MPa were performed on thin layers of clay-rich fault gouges from locations along the San Andreas and Hayward faults in California as well as pure clays from other locations. Both dry and saturated, drained samples exhibited a strain hardening that increased systematically with increasing confining pressure for the each particular gouge. In addition, the amount of strain hardening was greater with progressively stronger gouges among the suite of different samples. Tests using various lubricating mediums at the sample ends and different jacketing materials all showed that these possible constraints on frictional sliding had no effect on the strain-hardening process. Therefore, the observed strain hardening was a material property of the fault gouges. The presence of water lowered the strength, coefficient of friction, and amount of strain hardening of the samples. The coefficient of friction ranged from around 0.21 to 0.58 under saturated, drained conditions at 200-MPa confining pressure with the exception of pure montmorllonite. This sample had anomalously low strength and friction (t " 0.13) in relation to the other specimens. The strength of the gouges did not correlate well with mineral composition, grain size distribution, or location along the San Andreas fault; in Particular, gouge samples from creeping and 'locked' sections of the fault showed no systematic differences in strength.
114 citations
TL;DR: In this paper, an extensive experimental investigation comprising tensile testing and high voltage electron microscopy studies of interstitial-free α-Fe was carried out and the results were compared with the empirically derived Ludwik-Hollomon and Ludwik relationships for the σ-ϵ behaviour of metals.
71 citations
TL;DR: In this paper, the effect of solutes on the yield strength and strain hardening behavior of a wide variety of alloys is considered, and several explanations based on thermally activated mechanisms are found to provide superior flexibility in modelling the strength versus temperature behavior shown by the available data.
57 citations
56 citations
TL;DR: In this paper, an upper-bound type analysis is presented for predicting the shear plane angle, φ, in machining, using work material strain-hardening characteristics, which is quantified by referring to standard reference tables for yield strength and ultimate strength.
Abstract: An upper-bound type analysis is presented for predicting the “shear plane angle,” φ, in machining, using workmaterial strain-hardening characteristics. The degree of strain-hardening is quantified by referring to standard reference tables for yield strength and ultimate strength. In the model, the first step is to formulate the lowest amount of plastic work needed to cause a shear instability (collapse) in severely strain-hardened material. (In an upper-bound analysis this occurs on a plane at (φ = 45 + α/2.) However, due to work-hardening, this deformation zone geometry is nonunique and the shear plane can “rotate” into the softer material ahead of this initial instability. Using the proposition that the plastic work input remains constant, an equation is then derived which can be used to calculate the degree of shear plane rotation and hence the final position that the shear plane adopts for various workmaterials. In discussion, it is emphasized that this is an introductory analysis which ignores friction at the rake face and the high strain rates and temperatures that arise in practice; however, the agreement between this new, predictive model and experimental data is exceptionally good.
51 citations
TL;DR: In this article, the authors studied the deformation of sapphire (α-Al23) by slip on the prism planes in compression and showed that deformation occurs in three stages.
39 citations
TL;DR: In this paper, the sagging rotation capacity of composite beams consisting of a concrete slab attached to a steel beam by a shear connection is studied and expressions for the minimum inelastic rotation and deflection available at collapse are proposed.
Abstract: The sagging rotation capacity of composite beams consisting of a concrete slab attached to a steel beam by a shear connection is studied. Tests are reported on four full scale beams in the range of ductility parameter chi from 0.65 To 3.0. This parameter is an index of the degree of strain hardening developed in the steel beam at collapse. Expressions are proposed for the minimum inelastic rotation and deflection available at collapse. Examples are given of the application of these expressions to design problems with continuous composite beams. It is shown that, with a minimum value of chi equal to 1.4, Sufficient sagging rotation should be available to develop the conventional plastic design collapse load under the worst combinations of spans and loading (a).
39 citations
TL;DR: The hardening of supersaturated Cu-Fe alloys (0.28 ≤ c ≤ 1.15 at.% Cu) in the as-quenched state and after isothermal aging at 500°C is investigated in this article.
TL;DR: Different stress-strain characteristics of single crystals of copper lere deformed by rolling at room temperature in different orientations were found in this paper, where a dynamical recovery process (D.R.t-2) was identified.
TL;DR: In this paper, the simulation of forming schedules by several techniques, tension, compression and torsion, are compared and their results described, which show that the amount of softening between passes increases with inverse temperature, strain rate and strain during the pass (accumulated strain if no recrystallization in previous arrests) and with temperature and duration of arrest.
TL;DR: In this article, the effects of strain hardening on the post-collapse behavior of frame structures were analysed using a model which incorporates strain hardens in an approximate fashion and it was shown how the discrepancies between the experiments and the simple theory arise.
01 Apr 1982
TL;DR: In this article, a modified Jaumann derivative was proposed to predict oscillating shear stress for monotonically increasing simple shear strain, but this anomaly can be eliminated by adopting a physically more meaningful modifiedJaumann derivative.
Abstract: : The non-linear kinematics of the combination of elastic and plastic deformations at finite strain provides the mathematical structure to examine aspects of elastic-plastic analysis more succinctly than is possible with the approach based on infinitesimal elastic strain. Kinematic hardening represents the anisotropic component of strain hardening by a back stress alpha. Application of current theory for finite deformation incorporates the effect of finite rotation by using the Jaumann derivative in the evolution equation for alpha. This approach predicts oscillating shear stress for monotonically increasing simple shear strain but this anomaly can be eliminated by adopting a physically more meaningful modified Jaumann derivative. (Author)
01 Jan 1982
TL;DR: In this article, shot peening is a widely used method to improve the behavior of materials as for instance fatigue behavior or corrosion resistance The improvement of fatigue behavior is for example a consequence of either the strain hardening of surface layers or of the compressive residual stresses in surface layers induced by shot-peening or of both.
Abstract: Shot peening is a widely used method to improve the behavior of materials as for instance fatigue behavior or corrosion resistance The improvement of fatigue behavior is for example a consequence of either the strain hardening of surface layers or of the compressive residual stresses in surface layers induced by shot peening or of both It depends upon the strength or hardness of the material and upon the geometry of the workpiece which of these influencing factors is the predominant one In a high strength material, or in any notched workpiece residual stresses have an appreciable effect on the fatigue behavior and compressive residual stresses can enhance the fatigue strength (1,15,16)
TL;DR: In this article, the authors proved that Taylor hardening, the simple theory of rotation-dependent, anisotropic latent hardening and a 2-parameter hardening rule introduced in the metallurgical literature are all correct for tensile loading in 6-fold symmetry.
TL;DR: In this article, an analysis of the consequence of this observation is presented, and it leads to an expression for the plastic potential function as composed of two functions, a yield function and another dependent only on the hydrostatic pressure.
Abstract: For many soils experimental evidence suggests that deviation from normality between the plastic strain increments and the yield function is exhibited mainly in the volumetric behaviour, whereas the deviatoric behaviour exhibits normality. An analysis of the consequence of this observation is presented, and it leads to an expression for the plastic potential function as composed of two functions, a yield function and another dependent only on the hydrostatic pressure; the latter is considered to constitute the concept of correction functions presented recently by Desai and Siriwardane13.
01 Jan 1982
TL;DR: In this paper, it was shown that the von Mises effective stress strain criterion cannot explain axisymmetric deformation in torsion, whereas linear hardening is observed for axismmetric extension. But the simple analysis does not fully explain the hardening response following deformation path changes and multidirectional loading.
Abstract: It is demonstrated that strain hardening in torsion cannot be correlated with axisymmetric deformation by the von Mises effective stress strain criterion. In fcc materials, the flow stress levels and strain hardening rates are typically lower in torsion and saturation, only at lower stress levels. In bcc iron, a low saturtion stress is observed for torsion, whereas linear hardening is observed for axisymmetric extension. Much of the discrepancy in flow curves can be explained by texture. It is demonstrated that a crystallographic effective stress-strain criterion based on evolving average Taylor factors provides the proper magnitude correction for torsional flow curves in fcc materials. The simple crystallographic analysis does not fully explain the hardening response following deformation path changes and multidirectional loading. 96 references, 42 figures.
TL;DR: A finite strain elasto-plastic deformation theory based on Hill's new anisotropic flow theory was used in this paper to determine the stress concentration factor at a circular hole embedded in an infinite sheet subjected to remote uniform tension.
Abstract: The classical problem of determining the stress concentration factor at a circular hole embedded in an infinite sheet subjected to remote uniform tension is investigated. A finite strain elasto-plastic deformation theory based on Hill's new anisotropic flow theory [7] is used. It is shown that the governing field equations can be reduced to a single first order differential equation from which the stress concentration factor is obtained by a standard numerical method. The solution covers the entire elasto-plastic range and is valid for any strain hardening function. Comparison with experimental results, for a few materials, shows good agreement. With a pure power hardening law and within the framework of small strain plasticity, our results agree with those obtained from a more general solution discovered by Budiansky [8].
01 Jan 1982
TL;DR: A survey of slipline field theory techniques for solving boundary value problems for rigid/plastic solids undergoing plane strain deformations can be found in this paper, where the problems involved in trying to include strain hardening in the analyses are discussed.
Abstract: This article is a state of the art survey of slipline field theory techniques for solving boundary value problems for rigid/plastic solids undergoing plane strain deformations. Attention is concentrated on developments in the last 15 years, such as the use of computers to construct complex solutions to problems of “indirect type” which lead to integral equations, and of visioplastic techniques for constructing experimental slipline fields. Applications to several important forming operations such as strip rolling, extrusion, and machining are described. The problems involved in trying to include strain hardening in the analyses are discussed.
TL;DR: In this paper, the authors used elasticnplastic finite element analyses incorporating both a non-strain hardening and a power law hardening behavior to describe stress strain conditions at crack tips for short cracks.
Abstract: Stress and strain distributions and crack opening displacement characteristics of short cracks have been studied in single edge notch bend and centre cracked panel specimens using elasticnplastic finite element analyses incorporating both a non strain hardening and a power law hardening behaviour. J contour integral solutions to describe stress strain conditions at crack tips for short cracks differ from those for long cracks. The analyses show that (i) short cracks can propagate at stress levels lower than those required for long cracks and (ii) a two-parameter description of crack tip fields is necessary for crack propagation.
TL;DR: The limitations of power-law strain hardening and'strain-rate hardening' descriptions are reviewed in this article, and significant advantages can be gained by using, instead, the Voce relation, especially in the proposed modification that accounts for the rate sensitivities of flow stress and of strain hardness.
Abstract: The limitations of power-law strain hardening and 'strain-rate hardening' descriptions are reviewed. It is found that significant advantages can be gained by using, instead, the Voce relation, especially in the proposed modification that accounts for the rate sensitivities of flow stress and of strain hardening. Considerable further predictive value can be derived from differential constitutive relations, which can be integrated over arbitrary paths. The material parameters to be measured are the (linear) strain-hardening rate and the rate sensitivity of the flow stress, both as a function of (pre)stress and (current) strain rate. These are history independent over substantial regimes of unidirectional deformation, where a mechanical equation of state exists.
TL;DR: In this paper, nonlinear constitutive equations for varying stress histories are developed and used to predict the creep behavior of 304 stainless steel at 593°C (1100°F) under variable tension or torsion stresses including reloading, complete unloading, step-up, and step-down stress changes.
Abstract: Nonlinear constitutive equations for varying stress histories are developed and used to predict the creep behavior of 304 stainless steel at 593°C (1100°F) under variable tension or torsion stresses including reloading, complete unloading, step-up, and step-down stress changes. The strain in the constitutive equations (a viscous-viscoelastic model) consists of: linear elastic, time-independent plastic, time-dependent-recoverable viscoelastic, and time-dependent-nonrecoverable viscous components. For variable stressing, the modified superposition principle, derived from the multiple integral representation, and the strain hardening theory were used to represent the recoverable and nonrecoverable components, respectively, of the time-dependent strain. Time-independent plastic strains were described by a flow rule of similar form to that for nonrecoverable, time-dependent strains. The material constants of the theory were determined from constant stress creep and creep recovery data. Considerable aging effects were found and the effects on the strain components were incorporated in each strain predicted by the theory. Some modifications of the theory for the viscoelastic strain component under step-down stress changes were made to improve the predictions. The final predictions combining the foregoing features made satisfactory agreements with the experimental creep data under step stress changes.
TL;DR: The effect of hydrogen on the stress-strain curve of iron whiskers is considered to be a result of the interaction of hydrogen with dislocations, the hydrogen induced modification of dislocation motion, and changes in dislocation structure as mentioned in this paper.
TL;DR: In this paper, the effect of morphology, particle size, β grain size and volume fraction of β, from 0.025 to 1.0, on the low cycle fatigue life of α-β Ti-Mn alloys, have been studied under total strain control.
Abstract: The effect of morphology, particle size, β grain size and volume fraction of β, from 0.025 to 1.0, on the low cycle fatigue life of α-β Ti-Mn alloys, have been studied under total strain control. In general, Widmanstatten plus grain boundary (W+GB) α structures show shorter fatigue lives than equiaxed (E) α structures, and this has been ascribed to the formation of much larger surface cracks and ease of transfer of slip from α to β. For Eα structures, fatigue life increases with decreasing α particle size and when the alloy is single phase β fatigue life increases with decreasing grain size. At high total strains the nearly all α alloy had the longest fatigue life and at lower strains the β alloy, with the higher yield strength, had the longest fatigue life. Fatigue life was correlated with strain hardening. The nearly all α alloy which had the highest strain hardening, over the plastic strains encountered, had the highest fatigue life, while the β alloy, with the lowest strain hardening, had the lowest fatigue life. For a portion of the fatigue life curves, it was found that as the average Baushinger strain (ABS) increased, the Coffin-Manson exponentc decreased. The results are discussed.
TL;DR: In this article, two viscoplastic flow rules were developed using constant stress creep and strain recovery data, one based on accumulated strain (strain hardening), and the other based on a tensorial state variable (kinematic hardening).
Abstract: : Creep data of 2618-T61 aluminum alloy under multistep multiaxial proportional loadings at 200 degrees C (392 degrees F) are reported. Two viscoplastic flow rules were developed using constant stress creep and strain recovery data. One was based on the accumulated strain (strain hardening), and the other on a tensorial state variable (kinematic hardening). Data were represented by two models: a nonrecoverable viscoplastic model and a viscous-viscoelastic model in which the time-dependent strain was resolved into resolved into recoverable (viscoelastic) and nonrecoverable components. The modified superposition principles was used to predict the viscoelastic strain component under variable stress states for both models. The experiments showed that the viscous-viscoelastic model with either strain-hardening or kinematic hardening gave very good predictions of the material responses. Strain hardening was best in some step-down stress states. The viscoelastic component accounted for not only the recovery strain but also the transient creep strain upon reloadings and step-up loadings.
TL;DR: The mechanical behavior of dual-phase steels depends on a broad range of metallurgical phenomena, such as deformation, fracture, and deformation of the ferrite-martensite interface as discussed by the authors.
Abstract: The mechanical behavior of dual-phase steels depends on a broad range of metallurgical phenomena. The initial hardening reflects the volume fraction of the martensitic phase via a back stress, but this also depends on the local strength of the martensite. Formability is related not only to strain hardening and other continuum properties such as normal plastic anisotropy, but may also be influenced by fracture phenomena associated with discrete microstructural events such as decohesion of the ferrite-martensite interface. Various micromechanisms of duplex systems are discussed and the influence of the related mechanical behavior in determining formability in different technological forming process is described. The low yield-to-tensile-strength ratio of dual-phase steels is of particular benefit in stamping shallow components such as autobody skin panels; however, denting resistance requires a high yield strength emphasizing the importance of aging after forming.
TL;DR: In this article, a plane stress constitutive relation for rigid-plastic sheets under biaxial stretching is presented, in which the yield surface expansion models the behaviour of a solid carrying a rounded vertex at the loading point.
TL;DR: In this article, the isotropic hardening rule with homogeneous yield functions of the form f (J9 2, J9 3 ) was examined in terms of the plastic behavior of a range of engineering metals and alloys under proportionate loading.
Abstract: Test results on the plastic behaviour of a range of engineering metals and alloys under proportionate loading are examined in terms of the isotropic hardening rule with homogeneous yield functions of the form f ( J9 2 , J9 3 ). It is shown that the inclusion of J9 3 accounts for the differences observed between experiment and the Levy-Mises flow rule, that is in the associated constitutive relations, Lode parameter equality and equivalent stress–plastic strain correlations. Non-symmetrical functions account for nonlinear plastic strain paths and the presence of second-order strain under torsional loading. Alternative yield functions are presented where deformation behaviour has been identified with initially anisotropic material. The distinction between isotropic and anisotropic yield functions is clarified by an examination of component plastic strain paths in a tension test. It is shown that anisotropy due to plastic strain can be modelled by combining the rules of isotropic and kinematic hardening. Functions describing the model are consistent with experimental observations in that they display a marked Bauschinger effect and an absence of cross-hardening.