A phenomenological approach is proposed to model the influence of texture-induced anisotropy in the variation of strain hardening characteristics of a sheet material. The variation of uniaxial strain hardening exponent with rolling direction is modelled using existing anisotropic yield criteria assuming power law strain hardening behaviour. The model is extended to the biaxial region to predict the effective strain hardening exponent with the assumption of constant plastic work. The prediction of both uniaxial and biaxial strain hardening is compared with the experimental data available in the literature. It is observed that a variable strain hardening exponent provided greater accuracy of numerical prediction than the existing isotropic model. The accuracy of the proposed model is dependent on the yield criteria and the flow rule used for the modelling. © IMechE 2012.

K Hariharan

Department of Mechanical Engineering

Raghu V. Prakash

ANISOTROPIC SHEET METALS

Effective strain

Experimental data

FLOW RULES

ISOTROPIC MODELS

Numerical predictions

Phenomenological approach

PLASTIC WORK

POWER LAW STRAIN HARDENING

Rolling direction

SHEET MATERIAL

STRAIN HARDENING MODEL

Strain-hardening exponent

Uni-axial strains

YIELD CRITERIA

Anisotropy

Textures

Strain hardening

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

A variable strain hardening model for anisotropic sheet metals

Journal of Strain Analysis for Engineering Design

In this study, Hill 48 and Barlat 89 yield criteria are evaluated by simulating the Limiting Dome Height test of the Numisheet 96 benchmark problem [1] for a commercial D-grade steel and the results are validated with experimental data. Three strain modes, viz. biaxial, plane strain, and uniaxial strain modes, are used in the simulation studies. The yield criteria are evaluated based on the strain distribution in forming and residual stress distribution after springback. The results show that the Hill 48 and Barlat 89 yield criteria do not show a good match with predicted results of strain distribution in the plane strain mode. The difference between predicted results and experiments can be attributed to the combined influence of friction coefficient and draw bead boundary condition. The prediction of residual stress distribution differed considerably with the yield criteria. The residual stress predicted is validated for selected locations using X-ray diffraction techniques. Copyright © Taylor &amp; Francis Group, LLC.

Materials and Manufacturing Processes

Influence of yield criteria in the prediction of strain distribution and residual stress distribution in sheet metal formability analysis for a commercial steel

Process induced anisotropy in sheet metal is accounted for in analytical modeling by anisotropic yield criteria. The suitability of a yield criterion for predicting sheet metal forming process is generally validated by way of its ability to predict surface strains. However, the sensitivity of surface strains to yield criteria is dependent upon strain modes, with plane strain mode exhibiting higher sensitivity. To eliminate dependency on strain modes, stresses are used to evaluate yield criteria, since forming stresses are less sensitive to strain modes. In the study, the residual stresses remaining in a hemispherical cup formed in plain strain mode is predicted using Hill48 and Barlat89 criteria. The residual stresses are experimentally characterized by using X-Ray diffraction method. Suitable yield criterion for forming simulation is validated based on the correlation of theoretical predictions with experimental residual stress values. © 2010 Springer-Verlag France.

International Journal of Material Forming

Evaluation of yield criteria for forming simulations based on residual stress measurement

Engineering Materials and Processes Crystallographic Texture of Materials

Annealing Texture

Sheet Metal Forming Processes

Numerical Simulation of the Sheet Metal Forming Processes

Forming Limit Curves (FLCs) were determined experimentally through limiting dome height (LDH) tests in AA1050, AISI 316L and AISI 304L. FLCs were also simulated through FE (finite element) analysis. Simulations involved both constant and varying (with strain and strain path) material properties - namely, strain hardening exponent (n) and normal anisotropy (r̄).Varying n values were estimated from limited experimental data (from tensile tests) and the implicit assumption that n scales with in-grain misorientation developments and formation of strain induced martensite. r̄, on the other hand, could be estimated from crystallographic texture only for AA1050. Simulations with varying r̄ in AA1050 had shown a clear, though numerically marginal, improvement. On the other hand, varying n could remarkably improve the FLC predictability in 316L and 304L, especially in the biaxial region. © 2009 Springer/ESAFORM.

Improved predictability of forming limit curves through microstructural inputs

Journal	Journal of Strain Analysis for Engineering Design
ISSN	03093247
Open Access	No