A fracture mechanics analysis of a crack in a variable thickness plate having a fillet (thin-to-thick type)

A 3D finite-element analysis is employed to analyze crack-tip stress-intensity factor F in plates of variable thickness with fillets. The analysis is complemented by the investigation of crack-growth behavior near and at the thickness interface by means of fatigue testing on these types of specimens cut from an aluminum plate. The correction factor for the stress-intensity factor is based on the variables for the dimensionless fillet ratio, the width ratio, the thickness ratio, and the dimensionless crack length. The crack-propagation characteristics are similar to those of a crack in a plate of uniform thickness when the crack tip is located far enough from the thickness interfaces. The fatigue-crack propagation rate varies indirectly with the width ratio and the thickness ratio. Both F and the crack-propagation rate increase as the crack tip approaches the thickness interface when the fillet ratio is large compared to the thickness ratio.