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Hot-Air Forming of Al-Mg-Cr Alloy and Prediction of Failure Based on Zener-Holloman Parameter
김우진,W. Y. Kim,H. K. Kim 대한금속·재료학회 2010 METALS AND MATERIALS International Vol.16 No.6
The microstructure of an Al-Mg-Cr alloy tube fabricated through indirect extrusion at 673 K showed elongated grains with a mean size of ~26 μm. The strain rate-stress relationship at high temperatures (753 K to 793K) revealed that dislocation climb creep was the rate-controlling deformation mechanism. The hot-air forming process was successful at a pressure of 70 bar. The Zener-Hollomon parameter based failure criterion was 3602+, and was used to explain the failure behavior of a deforming body. The forming and fracture behavior of the Al-Mg-Cr alloy tube was analyzed with the aid of finite element (FE) simulation, into which the failure criterion was incorporated. Comparison of the simulation and the experimental results indicated that the proposed fracture criterion was useful in predicting the fracture behavior of aluminum tube deforming by means of gas pressure.
AZ31판재 온간 성형의 파단 예측을 위한 한계응력 모델
김흥규(H. K. Kim),김우진(W. J. Kim) 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.5
Magnesium alloy sheet has a relatively low formability compared to other commercial structural metals though it is press-formed at elevated temperatures to improve the press formability. In general, the formability of magnesium alloy sheet is known to depend on temperature as well as strain-rate imposed on the material, and the accurate prediction of the formability considering the dependence is crucial to design the forming process of magnesium alloy sheet parts. In the recent work, we proposed the failure models based on the critical damage work as well as the critical strain for warm forming of AZ31 sheet. However, it is to be examined whether the criterion is capable of predicting the forming limits for various strain paths of sheet metal before applying the failure model to the sheet forming process under complex strain modes. In this paper, we propose a simple stress-based failure criterion for warm forming of AZ3l sheet motivated by the stress-based FLD concept suggested by Stoughton (2000). The predictability of the stress-based failure criterion will be examined compared with the previous damage work- or strain-based failure models.