Work-hardening Stagnation Research Articles

Anisotropic work-hardening behaviour of structural steels and aluminium alloys at large strains

Sheet metal forming processes may often involve intense forming sequences, leading to large strains and severe strain-path changes. Optimizing such technologies requires a good understanding and description of the anisotropic plastic behaviour of the deformed material, in connection with the evolution of its texture and microstructure. In this paper, we present the predictions provided by a model involving isotropic and kinematioc hardening and by a physically-based microstructural model, which introduces additional internal variables taking into account the directional strength of dislocation structures and their polarity. These models have been identified by using sequences of uniaxial traction and simple shear experiments, carried out on various steels (DC06, DP600, HSLA340) and aluminium alloys (AA5182-O, AA60l6-T4). The microstructural model proved able predict the complex hardening behaviour displayed, especially by the ferritic steels, namely the transient work-hardening stagnation during reversed deformation in Bauschinger tests, the temporary work-softening during orthogonal tests, and the grain fragmentation at large monotonic strains.

A Model of Large-Strain Cyclic Plasticity and its Application to Springback Simulation

This paper presents a framework of constitutive modeling of large-strain cyclic plasticity which describes both the deformation- and texture-induced anisotropies of materials. In this model, the transient Bauschinger effect is described accurately by a new equation of the backstress evolution, and the strain-range and mean-strain dependencies of cyclic strain hardening are expressed by a model of workhardening stagnation. For the description of texture-induced anisotropy, any of widely accepted yield criteria of orthotropic anisotropy is easily incorporated into this model. This paper demonstrates the advantage of the present model in the springback analysis over other classical models by comparing the FE simulations of draw bending with the corresponding experimental results.

A model of large-strain cyclic plasticity describing the Bauschinger effect and workhardening stagnation

Abstract This paper presents a constitutive model that has a high capability of describing the deformation behavior of large-strain cyclic plasticity and also the stress–strain responses at small-scale re-yielding after large prestrain. A new equation of backstress evolution is proposed for an accurate simulation of the transient Bauschinger effect. Furthermore, an original idea of a non-isotropic-hardening surface defined in the stress space is presented for the description of the workhardening stagnation appearing under reverse deformation, as well as the strain-range and mean-strain dependencies of cyclic hardening characteristics. The validity of this model is confirmed by comparing the cyclic stress–strain responses calculated by the model with the experimental observations on some steel sheets and an aluminum sheet.

Elastic–plastic behavior of steel sheets under in-plane cyclic tension–compression at large strain

Abstract Elastic–plastic behavior of two types of steel sheets for press-forming (an aluminum-killed mild steel and a dual-phase high strength steel of 590 MPa ultimate tensile strength) under in-plane cyclic tension–compression at large strain (up to 25% strain for mild steel and 13% for high strength steel) have been investigated. From the experiments, it was found that the cyclic hardening is strongly influenced by cyclic strain range and mean strain. Transient softening and workhardening stagnation due to the Bauschinger effect, as well as the decrease in Young's moduli with increasing prestrain, were also observed during stress reversals. Some important points in constitutive modeling for such large-strain cyclic elasto-plasticity are discussed by comparing the stress–strain responses calculated by typical constitutive models of mixed isotropic–kinematic hardening with the corresponding experimental observations.

A Constitutive Equation for Description of Large-Strain Cyclic Plasticity.

This paper presents a constitutive model of plasticity that describes the cyclic stress-strain responses at large strain. A new equation of backstress evolution is proposed for an accurate simulation of the transient Bauschinger effect. An original idea of a non-isotropic-hardening surface defined in the stress space is presented for the description of the workhardening stagnation appearing under reverse deformation, as well as the strain-range and mean-strain dependencies of cyclic hardening characteristics. The validity of this model is confirmed by comparing the cyclic stress-strain responses calculated by the model with the experimental observations on two types of steel sheets (an aluminum-killed steel and a dual-phase high strength steel of 590 MPa tensile strength).

Work-hardening behavior of mild steel under cyclic deformation at finite strains

The work-hardening behavior of mild steel under monotonic deformation at large shears and cyclic deformation under a wide range of shear amplitudes (from 3 to 34%) has been experimentally investigated and modeled. The influence of shear amplitude, the effect of the amount of pre-shear and that of pre-cyclic deformation have been studied. Considering the evolution of both polarized persistent dislocation structures and no-polarized low-energy dislocation configurations, a physically-based phenomenological model with four internal variables has been proposed. The model explains the cyclic hardening behavior at large strains, the work-hardening stagnation followed by a resumption of work-hardening under Bauschinger deformation with large pre-strains and under cyclic deformation with moderate strain amplitudes. A good qualitative and quantitative agreement has been achieved between experimental results and model predictions.

Bauschinger effect and dislocation structure in stainless steel during cyclic deformation: Xia, Y., Wang, Z. and Du, X. Acta Metall. Sin. (China) Aug. 1988 24, (4), A221–A227 (in Chinese)

This paper presents a constitutive model that has a high capability of describing the deformation behavior of large-strain cyclic plasticity and also the stress–strain responses at small-scale re-yielding after large prestrain. A new equation of backstress evolution is proposed for an accurate simulation of the transient Bauschinger effect. Furthermore, an original idea of a non-isotropic-hardening surface defined in the stress space is presented for the description of the workhardening stagnation appearing under reverse deformation, as well as the strain-range and mean-strain dependencies of cyclic hardening characteristics. The validity of this model is confirmed by comparing the cyclic stress–strain responses calculated by the model with the experimental observations on some steel sheets and an aluminum sheet.