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Fatigue crack growth behavior of Ti-62222 mill-annealed material in sheet form was examined as a function of specimen geometry. The geometries investigated were the eccentrically loaded single edge-notch tension (ESE(T)), the compact tension (C(T)), and the middle tension (M(T)). Tests were conducted at room temperature at two load ratios (R=0.1 and 0.7) and covered a broad range of crack growth rates ranging from 10-7 to 10-2 mm/cycle. The same precracking and threshold test procedures were used for all geometries as each threshold test was started at the same crack length and continuous load shedding was applied at a K-gradient of C=-0.08 mm-1. As a result, the same stress intensity-crack length (K-a) history was maintained throughout all of the threshold tests. Experimental results showed differences in fatigue crack growth behavior at the lowest crack growth rates while higher crack growth rates were similar. Surface roughness differences at lower crack growth rates were observed at the same nominal ΔK for the three geometries, suggesting differing crack growth mechanisms. Discrepancies observed in specimen behavior are assessed in terms of the crack tip stress field distribution which include both y-direction and T-stresses. In addition, supplemental fatigue crack growth tests showed a dependence on crack length and load reduction procedure.
fatigue crack growth, near threshold, load ratio, roughness, geometry, crack closure, T, -stress, biaxiality, y, -stresses, titanium, load history
Graduate Assistant, Mechanical Engineering, University of Idaho, Moscow, ID
Associate Professor, Mechanical Engineering, University of Idaho, Moscow, ID