拉伸应变硬化指数的解析测定及力学分析

Analytical measurement and mechanical study on the tensile strain hardening exponent

基于Hollomon公式σ=kεn所定义的有关应变硬化指数 (n值 )力学本质 ,本文提出了求解金属材料均匀变形阶段n值的新的测试手段 ,包括差分平均法 (DAM)与解析拟合法 (APM)。以国标线性回归法所得结果为参考基准 ,DAM与APM在规定应变范围 (以 10 %～ 2 0 %为例 )内所测出的n值具有极高的准确度和可靠性。借助解析拟合法单点n值测定技术和高分辨率的Zwick材料拉伸试验机 ,本文详细论述了载荷极值点上应变硬化指数与均匀延伸率的相关特性 ,并从实验上证实了关联公式n =ln (1+Agt)。此外 ,本文也探讨了差分法具有数据处理方便、计算结果可靠的特点 ,以及能够在拉伸试验过程中动态实时地显示n值随应变量变化的半定量关系曲线。

Based on the mechanical principle of strain hardening exponent (i.e. n Value) described by Hollomon equation σ=kε n, new measurement methods were introduced in the paper such as Difference Average Method (DAM) and Analytical Polynominal-fitting Method (APM). When concerning the measurement of n value for the strain scale from 10% to 20%, coincidence of results generated by DAM and APM with that determined by the Linear Regression Method recommended by GB/T 5028-1999 was found to be satisfactory. Benefiting from the advantage of APM to monitor the accurate variation of n value versus the increase of strain during tensile uniform plastic deformation and with the help of high-frequency data acquisition equipped with Zwick Z100 tensile testing machine, relationship between n value at the point of tensile strength and ultimate uniform elongation was experimentally proved accordable to the equation n=ln(1+A gt). Moreover, DAM was discussed for it's efficient data processing, high results accuracy and the ability to monitor the quasi tendency of n value against strain variation during tensile test.