A combined computational and experimental fracture mechanics approach for modeling fatigue crack growth

This work is a combination of numerical and experimental fracture mechanics aimed at the development of a general technique for the improved simulation of Fatigue Growth for arbitrarily shaped embedded cracks.; The first part of this work involves the development of a special fracture specimen called a constant-K specimen. This type of specimen allows an eased and improved determination of fatigue parameters due to the specimen's shape that is optimized in this work by achieving a linear compliance while varying the specimen's curvature.; The second part of this work involves using the constant-K specimen to obtain da/dN vs. ΔK curves for steel and aluminum. The experimental procedure is a newly developed procedure that uses an optimized constant-K specimen. The newly developed Paris Law expressions are comparable to existing literature expression, but are different and more applicable to the batches of steel and aluminum used in the experiment. To validate the Paris Law expressions, a crack growth experiment in an aluminum compact specimen is set-up using the same batch of aluminum as used to determine the Paris Law constants using the constant-K specimens. The crack growth is also simulated using both new Paris Law constants and existing literature Paris Law constants for aluminum. As expected, the simulation using the new Paris showed a better agreement to the experimental results.; The last part of this experiment involved the exploration of tetrahedral element meshes set-up for use in the domain integral method to obtain mode I, II, and III stress intensity factors along the crack front of arbitrarily shaped cracks. A requirement for the use of the domain integral method is information related to the crack front and crack surface geometry. In an arbitrarily shaped crack the geometry has to be approximated. A Bezier curve and surface is used for this approximation. The accuracy of the method is obtained by testing the new methodology on certain benchmark problems for which analytical expressions exist. With the method validated, stress intensity factors are obtained for an embedded warped ellipse shaped crack surface.