Modelling the surface roughness influence on the hole expansion ratio of multiphase steel

S Münstermann,P Wechsuwanmanee,J Lian

doi:10.1088/1757-899x/651/1/012006

S Münstermann, P Wechsuwanmanee + Show 1 more

Open Access

https://doi.org/10.1088/1757-899x/651/1/012006

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Abstract

There exist both extrinsic manufacturing process-related and intrinsic material-immanent effects on the edge crack sensitivity of dualphase steels. Extrinsic influences can be further divided into effects of residual damage as well as roughness-induced effects. A new simulation framework is applied to quantitatively assess the surface roughness-induced influences on the edge crack sensitivity of cold rolled dualphase steel of grade DP1000. Hole expansion ratios are numerically predicted for four different edge manufacturing processes, including drilling, milling, waterjet cutting, and wire cutting. The simulation framework applies the idea to make use of a ductile damage mechanics model. It employs realistic material parameters for all elements situated in the bulk, whereas those elements situated at the edge to be expanded during the test apply artificial model parameters. These are identified with the help of sub-models with geometrical surface representation. For the sub-model construction, roughness profiles are experimentally characterized by white light confocal microscopy. With the new simulation framework, numerical predictions of hole expansion ratios can be significantly improved, even though a remarkable overestimation still remains. Among others, this general overestimation can be attributed to local strain hardening, residual stresses, and microstructural modifications.

Highlights

For dualphase steels, the edge crack sensitivity belongs to the limiting factors for the materials applicability in the automotive sector [1]
Hole expansion ratios are numerically predicted for four different edge manufacturing processes, including drilling, milling, waterjet cutting, and wire cutting
External influences can be named which promote ductile damage evolution. These external influencing factors can mainly be categorized into two different groups: residual damage from previous edge manufacturing processes [5] as well surface roughness effects [6]

Summary

Introduction

For dualphase steels, the edge crack sensitivity belongs to the limiting factors for the materials applicability in the automotive sector [1]. The ductile failure locus (DFL) defines the equivalent plastic strain to ductile failure ε4a as a function of stress triaxiality and normalized Lode angle according to the following function: ε4a With these criteria at hand, a damage evolution law can be designed. It has to be noted that the MBW model in its current release [20] is able to consider the effect of non-proportional loading by relying on indicators for ductile damage initiation and ductile fracture, respectively These indicators still rely on DIL and DFL, but they evaluate the loading path in the 3D space of stress triaxiality, Lode angle parameter, and equivalent plastic strain. The MBW parameters used in this study are summarized in table 1 [11]

Methods and approaches

Results

80 Macroscopic simulation without roughness consideration