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材料的超塑性可以由流变应力敏感性指数(m)来量度。m值和表示超塑性程度的总延伸率(即拉断时的延伸率)之间存在一定的依赖关系。当m值在某一定的范围之内时,试棒在拉伸期间具有缩颈抗力,不产生加工硬化,能够均匀地拉伸到几倍,甚至几十倍于原始长度的长度才发生断裂,而显示出超塑性。Backofen等认为:在超塑性流动过程中,因拉伸试棒的截面减小而引起的几何上的弱化是通过应变速率的作用引起的“硬化效果”来抵销的。他将这种作用称为“应变速率硬化作用”。然而只有当m值在一定的范围内时,“应变速率硬化”才能够对材料显示超塑性特征产
The superplasticity of a material can be measured by the rheological stress sensitivity index (m). There is a certain dependency between the value of m and the total elongation (ie, the elongation at break) that represents the degree of superplasticity. When the value of m is within a certain range, the test bar has constrictive resistance during stretching, does not produce work hardening, can be uniformly stretched several times, or even several times the original length of the length of the fracture occurred, And show superplasticity. According to Backofen et al., The geometric weakening caused by the reduction of the cross-section of the tensile test bar during superplastic flow is offset by the “hardening effect” caused by the strain rate. He calls this effect “strain rate hardening.” However, “strain rate hardening” can show superplastic characteristics of the material only when the value of m is within a certain range