Effect of Elastic Module Degradation Measurement in Different Sizes of the Nonlinear Isotropic–Kinematic Yield Surface on Springback Prediction

Baara Baara,Ismail Ismail,Baharudin Baharudin,Anuar Anuar

doi:10.3390/met9050511

Abstract

Commercial finite element software that uses default hardening model simulation is not able to predict the final shape of sheet metal that changes its dimensions after removing the punch due to residual stress (strain recovery or springback). We aimed to develop a constitutive hardening model to more accurately simulate this final shape. The strain recovery or balancing of residual stress can be determined using the isotropic hardening of the original elastic modulus and the hardening combined with varying degrees of elastic modulus degradation and the size of the yield surfaces. The Chord model was modified with one-yield surfaces. The model was combined with nonlinear isotropic–kinematic hardening models and implemented in Abaqus user-defined material subroutine for constitutive model (UMAT). The Numisheet 2011 benchmark for springback prediction for DP780 high-strength steel sheet was selected to verify the new model, the Chord model, the Quasi Plastic-Elastic (QPE) model, and the default hardening model using Abaqus software. The simulation of U-draw bending from the Numisheet 2011 benchmark was useful for comparing the proposed model with experimental measurements. The results from the simulation of the model showed that the new model more accurately predicts springback than the other models.

Highlights

Lightweight materials in the passenger vehicle manufacturing process have been widely used to reduce the cost of consumption and reduce deformability
Accurate constitutive models enable the accurate determination of the stress distribution during the loading process and of the residual stress relaxation during the unloading process, which occur during the springback stage
The result of the Quasi Plastic-Elastic (QPE) model shows that the strain recovery is positive, instead of there being zero residual stress, at the center of the bounding yield surface

Summary

Introduction

Lightweight materials in the passenger vehicle manufacturing process have been widely used to reduce the cost of consumption and reduce deformability. The dimensions of the final shape of the deformed part change after removing the punch guide due to residual stress. This phenomenon is called springback, which is challenging to predict using constitutive models. Simulating springback requires an accurate hardening model to describe the stress and strain curve history in the complex loading and unloading process that occurs during sheet-stamping operations. Accurate constitutive models enable the accurate determination of the stress distribution during the loading process and of the residual stress relaxation during the unloading process, which occur during the springback stage. Researchers have attempted to improve constitutive models and increase the accuracy of springback simulations

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Conclusion