Three-dimensional and K-dominance effects in isotropic and anisotropic cracked solids

In this study, the three-dimensional and K-dominant nature of the stress and deformation fields in the vicinity of crack tips in isotropic and composite materials has been investigated. Optical experimental technique coupled with two and three-dimensional finite element analysis has been used to achieve this goal. The finite element methods have been used to obtain the inner and outer bounds of the region of K-dominance. The lateral shearing interferometer of Coherent Gradient Sensing (CGS) was used to experimentally extract fracture parameters such as stress intensity factors, K_I and K_II and crack tip phase angle, ω. The data points used to obtain these quantities were taken from the regions of K-dominance previously determined from the experiments and finite element analysis. This methodology provided a means of extracting much reliable values of the fracture parameters.; The effect of mode mixity on crack tip stress fields in isotropic materials is studied using CGS and finite element analysis. Two and three-dimensional finite analysis was utilized to study the effect of mode mixity on the extent of K-dominance. It was noted that increasing mode mixity leads to an increased rotation of the three-dimensional zone, keeping its shape and size unchanged. In contrast, the region of K-dominance is seen to dramatically depend on mode mixity, both in shape and size. In addition, an analysis of the CGS interferograms was conducted to obtain an estimate of the regions of K-dominance experimentally.; For composite materials, in addition to mode mixity, additional parameters such as fiber orientation and amount of orthotropy (β = E ₁₁/E₂₂) also affect the extent of three-dimensionality and K-dominance. Using finite element analyses the effect of fiber orientation, amount of orthotropy, plate thickness, Poisson's ratio, ν₂₃ on the three-dimensional zone has been studied and an estimate of the region of K-dominance has been obtained. The technique of CGS in reflection has been used to experimentally extract fracture parameters for specimens where the fibers are parallel and perpendicular to the crack under pure mode I and mixed mode loading conditions.