Abstract: 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, ΔK_CJP, 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-ΔK_CJP curve reflect the distribution of the test data effectively and show good fitting effects. Compared to the traditional ΔK, the ΔK_CJP 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 ΔK_CJP, both ΔK_F and ΔK_R 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 ΔK_CJP. Thus, an effective approach is established for using the da/dN-ΔK_CJP curve in the failure analysis and the safety assessment of materials and structures, which extends the engineering applications of the CJP model.

Key words: CJP model, commercial pure titanium, crack growth rate, crack tip displacement fields, digital imagine correlation