The Relationship between Tensile Strain and Residual Stress of High Strength Dual Phase Steel Sheet

Maoyu Zhao A,Chunyan Tian,Ping Li,Zhengzheng Meng,Wen-Pei Sung,Tao-Yun Han

doi:10.1051/matecconf/201817501033

Abstract

The relation between residual stress and tensile strain is an important factor for evaluating plastic formation grade of steel sheet. The degree of plastic deformation (Δl) and elastic recovery (δ) were obtained by measuring the length of DP600 steel sheet sample under different tensile test conditions, i.e. five tensile strains (ε). Furthermore, the average residual stress value in the surface middle (the diameter of 10 mm) region of above tensile samples was analyzed by x-ray diffraction (XRD) in the crystal plane of (211). By processing the diffraction peak angle (2θ) with half width high method (FWHM), the relationship between sin2(ψ) and diffraction angle is attained by least squares method. On this basis, a mathematical model was established to correlate the tensile strain with the residual stress in the present study. The results show that the residual stress decreases and the elastic recovery increases with the increase of tensile strain (ε≤0.205). The relation between residual stress and tensile strain can be described with an exponential function . Finally, a function of tensile strain, elastic recovery and surface residual stress is established, by which a reasonable forming condition, viz. ε=0.205, δ=2.65 mm is determined for achieving the smallest σψ.

Highlights

The residual stress is a kind of internal deformation coordination of materials, which is caused by constraints or non-uniform deformation, and influences the account of springback
With the increase of tensile strain, in experiment 1, the maximum stress σ equals 180 MPa when the tensile stress ε is 0.001, which is less than the yield strength σs (300 MPa) of experimental DP600 steel
The material is subjected to plastic deformation in this stage, and the elastic energy stored in the specimen will release and elastic recovery will occur after unloading

Summary

INTRODUCTION

The residual stress is a kind of internal deformation coordination of materials, which is caused by constraints or non-uniform deformation, and influences the account of springback. Residual stress is an important factor for evaluating the deformation materials[2]. Owing to the uneven dislocations and slip, a residual stress is generated inside the material in order to balance the non-uniform deformation force after unloading[4]. Detailed X-ray diffraction (XRD) studies of residual stresses of a multilayer or films material are presented[7]. The residual stress affects forming springback that can depict plastic deformation mechanism. Residual stress is an important factor for evaluating the materials deformation, the variation inside the DP steel material can cause greater strain gradient in ferrite phases. The model about strain and residual stress can effectively promote residual stress prediction when DP steel (consists of the martensitic and ferrite phase) was tested on the condition of different strains

Materials

Scheme

Computational theory

Calculation of the Residual Stress

Results and Discussion

CONCLUSION