TC18钛合金应力松弛行为及其本构关系

The Stress relaxation behavior of TC18 alloy and its constitutive equation

本文利用高温环状等距弯曲应力松弛试样研究了TC18合金应力松弛行为。研究发现TC18应力松弛行为分为明显的两个阶段:第一阶段应力松弛速度较快,第二阶段松弛速度较慢,最后趋于一定值,存在应力松弛极限。应力松弛行为受应力松弛温度和初应力的影响,低温应力松弛慢,应力松弛极限高;高温应力松弛快,应力松弛极限低,松弛极限只与应力松弛试验的温度有关。初应力只影响应力松弛速率,初应力越高,松弛越快。根据达到应力松弛极限的时间及应力松弛极限的大小,初步选定650℃作为热校形的温度。采用MAXWELL方程拟合获得其剩余应力与初应力、松弛时间的关系方程,并得到TC18钛合金蠕变塑性应变与瞬时剩余应力的本构方程。

The stress relaxation behaviors of TC18 alloy were investigated in this paper by using high temperature iso- moment bending specimen. Theresults showed that the stress relaxation behavior can be divided into two stages. The first one shows a high relaxation rate,and the second one shows a low rate. A certain value called relaxation limit can be obtained at final stage. The stress relaxation behavior is affected by temperature and initial stress. A high temperature shows a small value in stress rate and a high value in relaxation limitation. The relaxation limitation is only determined by relaxation temperature,and has no relationship with initial stress. The initial stress affects relaxation rate.A high initial stress results in a high relaxation rate. 650℃ is determined as hot- sizing temperature according relaxation time and limitation. The fitted equation which is used to describe the relationships among remaining stress- time,initial stress and relaxation time are ontained. And the constitute equation of plastic creep strain- remaining stress is gotten.