Transition of Part-Through Cracks at Holes into Through-the-Thickness Flaws

This paper describes results of a numerical and experimental study of the behavior of part-through cracks located at holes as they transition into uniform through-the-thickness flaws. Fatigue crack growth tests are conducted with transparent polymer specimens which allow the crack plane to be photographed during the fatigue test. Stress intensity factors are computed by the three-dimensional finite-element-alternating method for the measured crack shapes. Both analysis and experiment indicate that the crack growth rate varies along the flaw perimeter in a manner which encourages the trailing edge of crack advance to “catch up” with the leading edge. Once a uniform through-thickness configuration is achieved, the trailing point then slows down to the growth rate occurring at the point of maximum crack advance.