基于DIC与Irwin模型的工业纯钛疲劳裂纹尖端循环应变场表征

为了实现工业纯钛TA2疲劳裂纹尖端循环应变场的表征,采用数字图像相关(digital image correlation, DIC)方法并结合Irwin模型,研究了TA2紧凑拉伸试样在多级疲劳载荷下的裂纹扩展规律、循环应变场的实验划分方法以及循环应变环的演化规律。首先通过多级载荷试验获得了TA2紧凑拉伸试样的疲劳裂纹扩展规律,在此基础上结合DIC和Irwin模型,建立了疲劳裂纹尖端循环应变场的实验划分方法,实现了循环塑性区、单调塑性区和弹性区的划分。另一方面,采用DIC获得不同区域的滞回应变环,讨论了不同区域应变环的差异,从而论证了划分方法的有效性,并且揭示了裂纹扩展过程中裂纹尖端应变场从弹性区、单调塑性区到循环塑性区的演化规律。研究工作实现了TA2疲劳裂纹扩展过程中裂纹尖端循环应变场的表征,能够满足疲劳裂纹扩展研究的需要。

Characterization of Cycle Strain Field of Commercial Pure Titanium at Fatigue Crack Tip Based on DIC and Irwin model

In order to realize the characterization and regional division of cyclic strain field at fatigue crack tip, digital image correlation (DIC) method and Irwin model were used to study the crack growth law, experimental division method of cyclic strain field and the evolution law of cyclic strain loops of commercial pure titanium TA2 compact tensile specimen under continuous fatigue loads. Firstly, the fatigue crack growth law of TA2 compact tensile specimen was obtained by the continuous fatigue experiment. On this basis, combining DIC method and Irwin model, the experimental division method of cyclic strain field at fatigue crack tip was established, and the division of cyclic plastic zone, monotonic plastic zone and elastic zone was realized. On the other hand, the hysteresis loops in different regions were obtained by DIC method, and the differences of strain loops in different regions were discussed. Thus the effectiveness of the division method was demonstrated, and the evolution law of strain field at crack tip from elastic zone, monotonic plastic zone to cyclic plastic zone during crack growth was revealed. The research work in this paper provides an experimental method to characterize the cyclic strain field at crack tip for the study of fatigue crack growth behavior, which can meet the needs of the experimental study of fatigue crack growth.