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利用标识载荷试验技术,将具有两种不同显微组织TC4钛合金分别在三种应力水平下进行疲劳试验,在光学显微镜下对疲劳裂纹扩展断口进行观察,获得裂纹扩展过程中不同循环周次下的裂纹长度,以此建立了表征TC4钛合金原始疲劳质量的通用EIFS分布。研究结果显示钛合金双态组织比片层组织具有更好的原始疲劳质量,双态组织具有较高的疲劳裂纹萌生寿命及裂纹扩展系数。此外还分析了双态组织中添加标识载荷的疲劳断口形貌,认为其疲劳断口标识线的形成是由于加入标识载荷后,应力强度因子范围发生变化,导致疲劳裂纹扩展过程中断裂模式发生改变,从而在断口上形成了可判读的标识线。
The fatigue test of TC4 titanium alloy with two different microstructures at three stress levels was carried out by using the mark load test technique. The fatigue crack propagation fracture was observed under an optical microscope to obtain the fracture propagation under different cyclic cycles Of the crack length, in order to establish a common EIFS distribution TC4 titanium alloy fatigue quality of the original. The results show that the biomorphic titanium alloy has better initial fatigue quality than the lamellar structure, and the bimodal microstructure has higher fatigue crack initiation life and crack propagation coefficient. In addition, the fatigue fracture morphology with added load is analyzed. It is considered that the formation of fatigue fracture line is due to the change of the stress intensity factor after the load is added, resulting in the change of the fracture mode during fatigue crack growth, Thus forming a legible mark on the fracture.