Stress intensity factor computations for general curvilinear cracks in complex components

Stress intensity factor (SIF) calculation for general curvilinear cracks in complex components presents unique challenges. One of the challenges is mesh construction for three-dimensional complex geometries having arbitrary non-planar crack fronts. Another challenge is accurate extraction of mixed mode SIFs. In the past, domain integral methods have been used for calculating mixed mode SIFs in conjunction with structured meshing. Structured meshing (mostly using brick elements) usually involves manual interaction and becomes difficult for complex component geometries and for general curvilinear crack fronts.; Many commercially available CAD packages can create complex three-dimensional solid models and then generate detailed unstructured meshes with tetrahedral elements. During the course of this research, new techniques were developed so that domain integral methods can be used for tetrahedral elements. We have used the domain representation of the J-integral for arbitrary in-plane cracks. The domain integral representations of the interaction energy integrals have been used to extract mixed mode SIFs for non-planar cracks. These are also valid for planar cracks. A special integration procedure based on geometric properties of tetrahedral elements is implemented that permits the use of powerful automatic mesh generators. To illustrate this, I-DEAS, a commercial software, is used for solid modeling, mesh generation, and finite element analysis of the numerical examples in this thesis. It is emphasized here that no singular elements are used at the crack tip.; To obtain accurate results, parametric cubic splines are used for smooth representations of the crack front. A cubic spline has a continuous radius of curvature and is the lowest degree curve that allows a point of inflection and has the ability to twist through space. To access the accuracy, results are compared for penny-shaped, elliptical, and cap-shaped cracks in infinite solids subjected to remote tension. Excellent agreement is obtained between the numerical and analytical results (the maximum error is less than 1%).; A modified Direct Integration Method for fatigue reliability and the optimization of inspection times is presented and compared with Monte Carlo Simulation and the First Order Reliability Method. Results are compared for edge cracks and semi-elliptical surface breaking cracks.