在室温下,通过压剪试件(SCS)法对AZ91铸造镁合金进行不同加载速率下(4.8、48、480 mm/min)的复合压剪实验,研究AZ91铸造镁合金复杂应力状态下的力学行为.结合单轴拉伸实验、单轴压缩实验和"帽型"试件剪切实验的结果,得到AZ91铸造镁合金的实验初始屈服面.通过实验,以及实验屈服面、Ellipse准则理论屈服面和极限应变能强度理论(LESET)屈服面的比较,可以发现:在研究的应变速率范围内(0.01~1 s-1),AZ91铸造镁合金弹性阶段具有明显的应变率负敏感性,初始屈服强度随着应变速率的增大而减小;Ellipse准则对AZ91镁合金屈服的判定优于LESET,可以比较准确地描述AZ91铸造镁合金在复合压剪应力状态下的屈服行为;由实验屈服面和Ellipse准则理论屈服面可以初步判断,正应力对AZ91铸造镁合金的屈服具有促进作用,而静水压力对其有抑制作用.%The combined shear-compression experiments of cast magnesium alloy AZ91 under three different loading rates (4.8,48,480 mm·min) were realized by the test method of shear-compression specimen (SCS) at room temperature. Then,combined with the test result of compression,tensile and shear,the initial yield loci of cast AZ91 can be plotted.Through comparing the proposed initial yield surfaces of Ellipse criterion and limiting strain energy strength theory (LESET) with the experimental initial yield loci,the initial yield behavior of cast AZ91 was studied.The cast AZ91 shows strong strain rate negative sensitivity at elastic stage and its initial yield loci shrink in-wardly when the strain rate increase from 0.01 s-1to 1 s-1.Ellipse criterion is more suitable for explaining the ini-tial yielding of cast AZ91 than LSEST. The yielding of cast AZ91 is inhibited by hydrostatic pressure and promoted by normal stress according to the proposed of Ellipse criterion and the experimental initial yield loci.
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