Investigation of Crack-Wake Effects on Fracture Toughness of Geological Materials Spandan Maiti, Department of Mechanical Engineering-Engineering Mechanics, Michigan Technological University Microstructural features at the crack level are operative at the wake of the propagating crack and it significantly alters the effective fracture toughness of the material. We proposed to test it by evaluating the effect of both grain bridging and presence of pre-existing flaws on crack propagation, and quantify their effect on the fracture toughness. This endeavor resulted in two computational challenges: (1) A computational technique for arbitrary fast crack propagation in a domain, and (2) development of sensitivity analysis technique to study the effect of microstructural features on fracture toughness. To address the first challenge, we developed a new technique called Generalized Çohesive Element (GCE) method within the framework of finite element analysis that can nucleate and propagate a fast crack in an arbitrary direction. A graph representation of the mesh has been developed to handle changing topology of the mesh. For the second challenge, we have developed an ANOVA decomposition based algorithm that can compute the sensitivity indices for input parameters for a given output. Crack propagation from a notch Simulation of arbitrary crack path through finite elements Graph representation of finite element