Tensile-shear transition in mixed mode I/III fracture

The propensity of the transition of fracture type in either brittle or ductile cracked solid under mixed-mode I and III loading conditions is investigated. A fracture criterion based on the competition of the maximum normal stress and maximum shear stress is utilized. The prediction of the fracture type is determined by comparing tau(max)/sigma(max) at a critical distance from the crack tip to the material strength ratio tau(C)/sigma(C), i.e., (tau(max)/sigma(max)) < (tau(C)/sigma(C)) for tensile fracture and (tau(max)/sigma(max)) > (tau(C)/sigma(C)) for shear fracture, where sigma(C) (tau(C)) is the fracture strength of materials in tension (shear). Mixed mode I/III fracture tests were performed using circumferentially notched cylindrical bars made of PMMA and 7050 aluminum alloy. Fracture surface morphology of the specimens reveals that: (1) for the brittle material, PMMA, only tensile type of fracture occurs, and (2) for the ductile material, 7050 aluminum alloy, either tensile or shear type of fracture occurs depending on the mode mixity. The transition (in ductile material) or non-transition (in brittle material) of the fracture type and the fracture path observed in experiments were properly predicted by the theory. Additional test data from open literature are also included to validate the proposed theory. (C) 2004 Elsevier Ltd. All rights reserved.