Constraint effect on three-dimensional elastic-plastic fracture

This dissertation contains four papers whose common topic is three-dimensional (3D) constraint effect on elastic-plastic fracture. The purpose of the first paper was to examine whether 3D crack-front constraint effect can be characterized by the J-A2 three-term solution under small scale yielding condition. A 3D modified boundary layer analysis was performed with the finite element method. Results show that the in-plane stress fields at the crack front possess the plane-strain nature throughout the thickness except in the region near the free surface and can be characterized by the J-A2 solution.; The second paper presents results from the study of crack-front constraint in finite-sized, thin plates under large scale yielding condition. It was found that the in-plane stress fields near the crack front exhibit the plane strain nature throughout the thickness except in the region near the free surfaces, and can be characterized by the three-term solution. The transition of the stress field from the far field to the near crack-front field was explained by the iso-effective stress contours.; The third paper describes the relation between the crack-front constraint and the cleavage fracture toughness for thick SENB specimens. This study employed the 3D finite element analyses to compare the constraint effect of specimen size and crack depth on fracture toughness data. Rectangular and square-cross-section specimens with a deep crack of a/W = 0.5 and square-cross-section specimen with a shallow crack of a/ W = 0.15 were analyzed. Results indicate that the minimum fracture toughness and scatter bands for different specimens are well captured by the failure curves based on the J-A2 solution.; The last paper is concerned with the prediction of stable crack growth in plate made of Aluminum 7050 alloy. In order to simulate the crack extension, the surface-cracked plate was analyzed by quasi-static elastic-plastic finite strain analysis. The node release method and reloading technique were used with the Crack Tip Opening Angle (CTOA) fracture criterion. It was shown that numerical predictions are in general agreement with experimental observations and constant CTOA fracture criteria show a good promise for simulating 3D ductile crack growth.