金属的后继屈服面研究—单试样与多试样测试

STUDY ON SUBSEQUENT YIELD SURFACES TESTED BY USING SINGLE AND MULTIPLE SPECIMEN

采用退火45号钢薄壁试样进行拉扭组合试验,测试材料经历预拉伸后的系列后继屈服面.试验采用平移应变法定义屈服应力,讨论了不同的平移应变、预变形程度对后继屈服面测试结果的影响;试验分别用单试样法和多试样法进行,分析讨论了两种方法的合理性与局限性.试验研究得到以下结果:(1)单试样法和多试样法确定的初始屈服面的形状与Mises圆很接近;(2)单试样法屈服点的测试顺序对所测得的屈服面的形状有很大影响,第一测试点与预加载方向相反时,所得屈服面会出现"内凹"现象,而若改变测试顺序,可不再出现"内凹";(3)单试样法测得的后继屈服面与测试的屈服点数密切相关,当测试的屈服点数较多时,所得结果因累积塑性应变引起的应变强化作用而出现较大的偏离;(4)单试样法与多试样法测得的后继屈服面形状和大小有较明显的差异,测试过程中塑性变形的积累对单试样法的测试结果有明显影响,采用多试样法研究屈服面演化更为合理;(5)多试样法若采用较小目标平移应变定义屈服,测得的后继屈服面也出现轻微内凹.

In order to study the subsequent yield surfaces at different pre-tension strains, a series of tension-torsion tests of thin-walled tubular specimens of 45 annealing steel were carried. Considering the yield of material can be defined by the offset strain,the effects of the chosen plastic strain offsets and the prescribed pre-strain levels on subsequent yield surface were explored. The initial and the subsequent yield surfaces are determined by multiple-specimens method and single-specimen method, respectively, and their rationality and limitations were discussed. The experimental results showed： （1） the shape of initial yield surface obtained by using multiple-specimens and single-specimen method were close to the von-Mises surface; （2） the shape of yield surface was strongly affected by test sequence for the single-specimen method, the first yield point was tested in opposite directions of preloading,the yield surface was ＇inner concave＇, however,if the test sequence was changed,no ＇inner concave＇ was observed; （3） the shape of yield surface was affected by the number of yield tests for the single-specimen method, when the number of yield tests was larger,the subsequent yield point deviated from the yield surface due to increasing strain hardening caused by the plastic strain cumulated each time; （4） the shape and size of subsequent yield surfaces tested by the single-specimen method and the multiple-specimen method were obviously different, the shape of yield surface was greatly influenced by the plastic strain cumulated each time for the single-specimen meth- od thus the multiple-specimens method was a better choice; （5） if a small offset strain was used to define the subsequent yield surface for the multiple-specimen method,the ＇inner concave＇ appeared but was negligible.