超塑性拉伸变形应变速率敏感性指数的试验测量及其精细分析

EXPERIMENTAL MEASUREMENT AND ELABORATE ANALYSIS OF STRAIN-RATE SENSITIVITY EXPONENT IN TENSILE FORMING

从理论上导出不同典型变形路径下用试验参数F(变形载荷 )、v(十字头速度 )和l(试样标距长度 )表达的应变速率 ( ε)敏感性指数m的一组公式 ,并由此建立了在一组恒 ε试验、恒v试验和定F试验曲线上测量定长度应变速率敏感性指数ml、恒速度应变速率敏感性指数mv 和定载荷应变速率敏感性指数mF 的统一方法。在同一组恒 ε(恒v或定F)曲线上测得ml、mv 和mF,而且测得的ml、mv 和mF 是不相同的 ,这说明超塑性变形具有较强的结构敏感性。但是在不同组的恒 ε、恒v和定F试验曲线上用相同的测量公式测得的ml、mv 或mF 的值也各不相同 ,便是应分析的问题 ,于是又对m值的结构敏感性作了精细分析。

A set of formulae of strain rate sensitivity exponent m are deduced from theories in different typical deforming path by using experimental parameters F (forming load), v (velocity of cross head) and l (gauge length of specimen), through which the uniform method for measuring m l (strain rate sensitivity exponent under constant length), m v (strain rate sensiti vity exponent under constant velocity) and m F (strain rate sensitivity exponent under fixed load) is established on experimental curves of constant , constant v and fixed F respectively. m l,m v and m F are measured on the same group of curves of constant (constant v or fixed F ) and their results are different, which is shown that there exists structure sensitivity in superplastic forming. Whereas,it should be analyzed why the results of m l , m v and m F are different, which are measured with the same measuring formulae on different group of curves under constant , constant v and fixed F .Furthermore the structure sensitivity of m value is analyzed subtly.