On single-edge-crack tension specimens for tension-compression fatigue crack growth testing

Single-edge-crack (SEC) specimens with rigid threaded ends are well suited for fatigue crack growth testing in extreme environments and for conducting tests at negative load ratios. Stress intensity parameter, K, and crack mouth opening displacement, CMOD, solutions as a function of crack size for this geometry are derived using 3-D finite element analyses using multiple codes. Both K and CMOD values obtained are shown to be comparable between the various finite element codes used. The solutions are sensitive to the height (2H) to width (W) ratio of the specimen, as well as to the aggregate bending stiffness of the members of the loading train. A procedure utilizing the computational results for various 2H/W values and a set of specially designed fatigue crack growth experiments is described to develop custom solutions for estimating K and CMOD values that account for both, the 2H/W ratio and the bending stiffness of the loading train.