基于CJP模型的疲劳裂纹扩展率曲线及应用方法

Fatigue Crack Growth Rate Curve Based on the CJP Model and Its Application Method

利用数字图像相关技术开展工业纯钛5种不同高宽比CT试样的疲劳裂纹扩展率试验,分别采用传统应力强度因子范围ΔK和基于CJP模型理论框架的新应力强度因子范围ΔKCJP对数据进行分析,得到的da/d N-ΔK和da/d N-ΔKCJP曲线均有效反映了试验数据分布规律,具有良好的拟合效果。相较于传统参量ΔK,ΔKCJP直接由裂尖位移场求解,无需进行修正即可用于材料疲劳裂纹扩展率描述,具有与CT试样高宽比无关的特性;作为ΔKCJP的两个组成参量,ΔKF、ΔKR与传统ΔK数据间均呈现出某种总体变化趋势,分别可用二次多项式和线性方程表征。构造了ΔKCJP与ΔK的关联函数,并由此推导出ΔKCJP表达式,为da/d N-ΔKCJP曲线在材料与结构的失效分析和安全评价中的应用提供了有效途径,拓宽了CJP模型的工程应用范围。

Fatigue crack growth rate tests of commercial pure titanium specimens with 5 different height-width ratios of CT specimens using the digital imagine correlation technique are carried out. The traditional stress intensity factor range, ΔK, and the new definition of the stress intensity factor range, ΔKCJP, which is under the theory of the CJP model, are utilized in the analysis of the test data. Both the da/d N-ΔK curve and the da/d N-ΔKCJP curve reflect the distribution of the test data effectively and show good fitting effects. Compared to the traditional ΔK, the ΔKCJP is obtained directly from the displacement fields near the crack tip and can be utilized without correction, and has a characteristic of height-width ratio-independent for CT specimens. Furthermore, as two component parameters of ΔKCJP, both ΔKF and ΔKR show some certain general change trends with the traditional ΔK, which can be described by using the quadratic polynomial and the linear equation respectively. Based on this, a correlation curve is constructed to determine the expression of ΔKCJP. Thus, an effective approach is established for using the da/d N-ΔKCJP curve in the failure analysis and the safety assessment of materials and structures, which extends the engineering applications of the CJP model.