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International Journal of Automotive Technology > Volume 20(S); 2019 > Article
International Journal of Automotive Technology 2019;20(S): 19-30.
CONSTITUTIVE MODELING OF ASYMMETRIC HARDENING BEHAVIOR OF TRANSFORMATION-INDUCED PLASTICITY STEELS
Jaebong Jung1, Yong Chan Hur1, Sungwook Jun2, Hyun-Seok Lee3, Byung-Min Kim1, Ji Hoon Kim1
1Pusan National University
2LG Electronics
3NARA Mold & Die Co., Ltd.
PDF Links Corresponding Author.  Ji Hoon Kim , Email. kimjh@pusan.ac.kr
ABSTRACT
Transformation-induced plasticity (TRIP) steels are part of advanced high strength steels capable of phase transformation, having good strength and ductility. The transformation rate is known to be dependent on the stress state, which may lead to asymmetric hardening behaviour for TRIP steels with compressive flow stresses larger than tensile ones. Sheet stamping products of TRIP steels show complex springback because of the asymmetry in addition to the large strength, which will complicate the analysis of sheet metal forming processes. In this work, the asymmetric hardening behaviour of a TRIP steel with a tensile strength of 1180 MPa was measured using the sheet tension–compression tester. An asymmetric hardening model was developed by introducing an off-centred bounding surface for the kinematic back-stress evolution, to depict the asymmetric hardening behaviour. The model parameters of the proposed constitutive equations were obtained from the stress– strain curves under tension followed by compression. The stress–strain curves were well captured by the developed constitutive model, whereas the conventional symmetric model fails to describe the asymmetric hardening behaviour of the TRIP steel. For validation, load-displacement curve and springback angles of three-point bending test were compared with the predictions by the proposed model.
Key Words: Transformation-induced plasticity (TRIP), Asymmetry, Combined isotropic–kinematic hardening rule, Springback, Phase transformation
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