非对称载荷下TC17合金超高周疲劳试验

通过试验研究了110Hz和20kHz两种频率正弦式非对称载荷作用下TC17合金材料的疲劳失效行为,结果表明:载荷频率对TC17合金的疲劳强度和疲劳失效机理影响不明显,两种频率载荷作用下TC17合金的疲劳失效均存在表面诱发疲劳失效和内部诱发疲劳失效。表面诱发的疲劳失效主要是由循环载荷作用下试样机械加工缺陷和表面滑移所导致的,内部诱发的疲劳失效主要是由于材料初生α相在非对称循环载荷作用下发生解理断裂而导致的,失效形式的不同使得材料的应力-疲劳寿命（S-N）曲线呈双线性。萌生于TC17合金试样内部的疲劳裂纹可分为3个阶段:初生α相的解理断裂阶段、短裂纹扩展阶段和长裂纹扩展阶段。由裂纹萌生区特征可以确定室温条件下,应力比为0.1时,TC17合金疲劳长裂纹扩展门槛值为3.3MPa·m1/2。 

Very high cycle fatigue test of TC17 alloy under asymmetric loading

The fatigue failure of TC17 alloy was investigated under asymmetric loading with the help of piezoelectric fatigue tester (20kHz) and electromagnetic resonance fatigue tester (110Hz), and could be divided into surface induced failure mode and interior induced failure mode. Micro cracks near the center cross section of the specimen surface caused by slip trace under cyclic loading and the machine defects were the main reasons that caused the surface induced fatigue failure. The interior induced failure was mainly caused by the cleavage fracture of primary α phase. The frequency effect on the fatigue strength and fatigue failure mechanism was not obvious. And the variation of the failure mode resulted in a bilinear stree-fatigue life (S-N) curve of TC17 alloy. The formation of interior fracture could be divided into three stages: cleavage fracture of primary α phase, short crack propagation and long crack propagation. The critical stress intensity range of long crack propagation can be determined as 3.3MPa·m1/2 under the stress ratio of 0.1 at room temperature.