不同加载条件对TC4钛合金后继高温应力松弛及其力学行为的影响规律

Effect laws of different loading conditions on high-temperature stress relaxation of TC4 titanium alloy and its mechanical behavior

针对TC4钛合金,在700℃条件下,分别开展了单向拉伸、剪切拉伸和平面应变拉伸后的高温应力松弛与二次加载实验,分析了上述3种条件下的应力松弛行为差异,并结合有限元数值仿真,探讨了应力松弛对不同加载条件下力学行为的影响。结果表明:应力松弛初始阶段的松弛速率与初始应力大小成正相关,引入塑性变形将提高应力松弛速率;在相同的初始应力条件下,单向拉伸后的应力松弛速率比另外两种条件下的应力松弛速率高;剪切变形和高温应力松弛后,TC4钛合金的流动应力峰值变化不大,单向拉伸和高温应力松弛后,TC4钛合金的流动应力降低,而平面应变拉伸和高温应力松弛后,TC4钛合金的流动应力明显提高;应力松弛显著减弱了剪切变形后材料的高温软化,增加了平面应变拉伸后材料的加工硬化,这两种条件下TC4钛合金的伸长率均得到提高。

For TC4 titanium alloy,the experiments of high-temperature stress relaxation and reloading under three loading conditions,including uniaxial tension,shear tension and plane strain tension,were conducted sequentially at 700 C.The differences of stress relaxation behaviors under three conditions were analyzed,and the influences of different loading conditions under stress relaxation on mechanical behaviors were explored by finite element numerical simulation.The results demonstrate that the stress relaxation rate at the beginning stage is positively correlated with the initial stress,which can be improved by the introduction of plastic deformation.At the same initial equivalent stress,the stress relaxation rate after uniaxial tension is faster than that under shear tension or plane stress tension.After shearing deformation and high-temperature stress relaxation,the flow stress peak of TC4 titanium alloy has no obvious change,and the flow stress decreases after uniaxial tension and high-temperature stress relaxation,but increases significantly after plane strain tension and hightemperature stress relaxation.In conclusion,the elongation of TC4 titanium alloy is increased by stress relaxation,which decreases the softening of material at high temperature after shearing deformation and increases the work hardening of material after plane strain tension.