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

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/dN-ΔK curve and the da/dN-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/dN-ΔKCJP curve in the failure analysis and the safety assessment of materials and structures, which extends the engineering applications of the CJP model.