保载时间和应力比对Ti6242合金应力应变响应影响

Effects of dwell time and stress ratio on stress and strain responses of Ti6242 alloy

Ti6242等一些近α和α+β型钛合金存在保载疲劳行为,研究结果显示其保载疲劳失效内在机制主要与周期载荷作用下材料内部微区不均匀变形行为密切相关。本研究在对钛合金保载疲劳现有软−硬取向模型的理解基础上,通过设计Ti6242合金在不同保载时间和应力比载荷作用下的保载疲劳试验,验证保载时间和应力比对保载疲劳寿命影响规律,更长的保载时间引起Ti6242合金保载疲劳寿命单调衰减并趋于稳定,更高的应力比则引起其保载疲劳寿命呈指数增长。从应力−应变曲线分析角度表征Ti6242合金在保载疲劳载荷下的应力、应变响应特征,分析显示保载时间主要影响材料内部局部应力、应变的重新分布和累积变形协调过程,应力比则主要加剧材料在循环载荷中内部软相和硬相的微区应变差别。

These nearαandα+βtitanium alloys,such as Ti6242 alloy,usually exhibit dwell fatigue failure characteristic.The investigation results show that the dwell fatigue failure internal mechanism of these titanium alloy is mainly related to the inhomogeneous plastic deformation and local stress concentration under the dwell fatigue load.In this study,the dwell fatigue tests with different dwell time and stress ratio were designed to verify their influences on dwell fatigue life based on the understanding of the soft-hard orientation models.It is found that the dwell fatigue life of Ti6242 titanium alloy decreases monotonously with the increase of dwell time and tends to stabilize,but increases exponentially with stress ratio.According to the detailed analysis of stress and strain curves of Ti6242 alloy under dwell fatigue load,the dwell time mainly affects the redistribution and accumulative coordination processes of local stress and strain,while the stress ratio can intensify the local strain difference between the soft phase and the hard phase in the material.