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Crystal Plasticity Finite Element Analysis of Loading-Unloading Behaviour in Magnesium Alloy Sheet
Takayuki Hama,Hitoshi Fujimoto,Hirohiko Takuda 한국소성가공학회 2010 기타자료 Vol.2010 No.6
Magnesium alloy sheets exhibit strong inelastic response during unloading. In this study crystal plasticity finite element analysis of loading-unloading behaviour during uniaxial tension in a rolled magnesium alloy sheet was carried out, and the mechanism of this inelastic response was examined in detail in terms of macroscopic and mesoscopic deformations. The unloading behaviour obtained by the simulation was in good agreement with the experiment in terms of variation with stress of instantaneous tangent modulus during unloading. Variations of activities of each family of slip systems during the deformation showed that the activation of basal slip systems is the largest during unloading, and the slip direction during unloading is opposite from during loading. These results indicated that one of the factors of the inelastic behaviour during unloading is the fact that the basal slip systems are easily activated during unloading because of their low strengths.
Prediction of Yield Loci for a Magnesium Alloy Sheet using Crystal-Plasticity Finite-Element Method
Takayuki HAMA,Hitoshi FUJIMOTO,Hirohiko TAKUDA 한국소성가공학회 2011 기타자료 Vol.2011 No.8
This paper presents the prediction of yield loci for an AZ31 magnesium alloy sheet using a rate-dependent crystal-plasticity finite-element method. A differential work-hardening behavior was clearly observed; the contour of plastic work was initially rather flattened in the vicinity of equi-biaxial tension, but thereafter severely bulged. The variation of the relative activity of each family of slip systems was examined to investigate the mechanism of the differential work-hardening behavior. During uniaxial tension, the work hardening was determined mainly by the basal slip in the very beginning, while by both the prismatic slip and the basal slip in the subsequent deformation. On the other hand, during equi-biaxial tension, the activity of the basal slip systems was predominant throughout the deformation, while the relative activity of the prismatic slip systems was smaller than that in the uniaxial tension. We concluded that this difference in the relative activities of the slip systems depending on the biaxial-stress ratio eventually resulted in the differential work-hardening behavior of the contour of plastic work. The mechanism that the activity of the prismatic slip systems decreased as the biaxial-stress ratio approached to one was also discussed using a simple analytical model.