Study of the frictional contact conditions in the hole expansion test

D M Neto,M C Oliveira,L F Menezes,P D Barros,J L Alves

doi:10.1088/1742-6596/1063/1/012139

D M Neto, M C Oliveira + Show 3 more

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https://doi.org/10.1088/1742-6596/1063/1/012139

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Abstract

The adoption of advanced high-strength steels is growing in the automotive industry due to their good strength-to-weight ratio. However, the frictional contact conditions differ from the ones arising in mild steels due to the high values of contact pressure. The objective of this study is the detailed numerical analysis of the frictional contact conditions in the hole expansion test. The Coulomb friction law is adopted in the finite element model, using different values for the (constant) friction coefficient, as well as a pressure dependent friction coefficient. The increase of the friction coefficient leads to an increase of the punch force and a slight decrease of the hole expansion. The results show that increasing the friction coefficient postpones the onset of necking, but the localization does not change.

Highlights

The hole expansion test is commonly adopted to study the formability of metallic sheets, allowing the study of fracture occurrence in stretch-flanging areas [1]
Since the contact pressure is relatively high from the beginning (>30 MPa) and the saturated friction coefficient given by the pressure dependent friction model is about 0.1, the punch force evolution is identical to the one obtained with a constant friction coefficient μ=0.10
Since the hoop stress is approximately constant in the hole edge and the material yield stress is lower near the diagonal direction, the hole diameter is slightly larger around the diagonal direction

Summary

Introduction

The hole expansion test is commonly adopted to study the formability of metallic sheets, allowing the study of fracture occurrence in stretch-flanging areas [1]. The accurate prediction of thinning and localization of fracture by numerical simulation requires an accurate modelling of the plastic deformation behavior, namely the anisotropic yield function [2]. Some authors suggest that the friction model may play a role because of its interaction with the material flow, since the strain distribution in the hole expansion test is not uniform [1]. The objective of the present study is the detailed numerical analysis of the frictional contact conditions in the hole expansion test, the influence of the friction coefficient on the fracture prediction (location and instant)

Objectives

Results

Conclusion