Mixed-mode crack growth: An experimental and computational study

The surface integral method, an indirect boundary element method which represents a crack as a distribution of force dipoles, has been developed to model 3D nonplanar crack growth in complex structures. The finite body was effectively modeled by superposition of specialized stress influence functions or by meshing the free surface with surface integral elements. This procedure has proven to be accurate for a variety of cracks in semi-infinite and finite regions through convergence studies and comparison to published 2D and 3D results. Crack propagation was accomplished using the maximum circumferential stress theory to predict crack direction and the Forman fatigue equation to predict extension. A fully automated meshing/remeshing system was developed to propagate the crack through a complex structure.;An experimental method was developed to produce three-dimensional mixed-mode fatigue crack growth data. This was accomplished using a surface crack specimen, with an off-axis EDM notch, in a standard tension-tension machine. A marker banding technique was also developed to identify the crack geometry with the fatigue cycle count without affecting the overall fatigue behavior of the test. The growth laws used to predict fatigue crack growth in the computational models did not properly account for mode mixity. Therefore, a fatigue crack growth model using an effective stress intensity factor was implemented in the surface integral model to accurately predict both the trajectory and fatigue life of the specimen data.