Optimized and validated prediction of plastic yielding supported by cruciform experiments and crystal plasticity
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REVIEW
Optimized and validated prediction of plastic yielding supported by cruciform experiments and crystal plasticity Holger Hippke1
· Sebastian Hirsiger1 · Bekim Berisha2 · Pavel Hora1
Received: 24 December 2019 / Accepted: 19 May 2020 © Springer-Verlag France SAS, part of Springer Nature 2020
Abstract The predictability of strain distributions and the related prediction of hardening and failure plays a central role in tool and process design for any metal forming process. Studying yielding behaviour, it was discovered that for various well established yield loci no satisfying agreement between DIC (digital image correlation) measurement of strain distribution and simulation result could be obtained, even after optimization of parameters based on associated flow assumption. In parallel, crystal plasticity simulations were investigated with the objective to predict the relation between stress and strain ratios for a large number of load cases based on texture measurement. To include macroscopic data, a secondary strategy uses cruciform tension specimen as defined in ISO16842 to obtain strain and stress ratios. The resulting relations were then applied separately as input parameters for the plastic yield description. Both approaches reach high agreement between forming experiment and simulation. Against the previous assumption, the output can be obtained with either anisotropic or free shape yield loci and associated flow description. The methodology discussed provides an alternative and challenges to rethink the definition of yielding for aluminium alloys on the example of an AA6014-T4 aluminium alloy. Keywords Cruciform · Crystal plasticity · Vegter yield locus · YLD2000-2D · m-value
Introduction This contribution investigates the predictive performance of yield locus definitions. Instead of yield loci based on tensile and biaxial experimental data, it is proposed to model yield loci based on crystal plasticity (CP) [1, 2] or cruciform tension (CT) experiments [3]. The two approaches are compared with the industrial standard for aluminium alloys, a YLD2000-2D [4, 5] yield locus with flow exponent of m = 8. It becomes apparent, that a precise modelling of either CP or CT results leads to a very detailed reproduction of strain distributions in Nakajima specimen. Yield locus models for plane stress materials are under investigation with rising popularity of developments like the use of non-associated flow as suggested by Stoughton [6] and Stoughton and Yoon [7] and free shape yield loci Holger Hippke
[email protected] 1
ETH Zurich, Institute of Virtual Manufacturing, Tannenstrasse 3, 8092, Zurich, Switzerland
2
inspire AG, Institute of Virtual Manufacturing (inspire-ivp), Tannenstrasse 3, 9092, Zurich, Switzerland
such as the Vegter model [8], or the FAY model [9]. Hao and Xianghuai [10] recently presented an additional yield locus based on B´ezier interpolation. Cazacu et al. [11] have advanced the modelling for asymmetric yielding of titanium alloys and [12] have provided an alternative model fo
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