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关于板料的成形性能,有两个重要参数,一个是应变硬化率n值,另一个就是塑性应变比r值(又称厚向异性指数)。 r值来自薄板的单向拉伸试验。它被表示为:r=ε_2/ε_3。其中ε_2、ε_3分别为薄板单向拉伸试样的宽向真应变和厚向真应变。在测试薄板r值的试验中,人们经常关心r值的测试误差问题。一般说来,在均匀塑性变形阶段,试样的纵向应变ε_1越大,测试r值的最大相对误差|dr|max/r就越小。那么,当ε_1大于多少时,才能保证|dr|max/r小于某一给定的百分数M呢?这就是本文所要讨论的问题。 r值的测试方法有两种:直接法和间接法。两种
On sheet forming performance, there are two important parameters, one is the value of the strain hardening rate n, the other is the plastic strain ratio r value (also known as the anisotropy index). The value of r comes from a one-way tensile test of the sheet. It is expressed as: r = ε_2 / ε_3. Among them, ε_2 and ε_3 are the true strain and the true strain in the width direction of the specimen. In testing the value of the sheet r test, people often concerned about r value of the test error. In general, at the stage of uniform plastic deformation, the larger the longitudinal strain ε_1 of the specimen, the smaller the maximum relative error of the test r value | dr | max / r. So, when ε_1 is greater than how much, can we guarantee | dr | max / r is less than a given percentage M? This is the problem to be discussed in this article. There are two test methods for r value: direct method and indirect method. Two kinds