Three-dimensional effects in elastic-plastic fracture
Abstract
Fifteen ductile fracture tests on grooved specimens are simulated to investigate ductile fracture under plane strain deformation. Stresses, especially, equivalent stresses within a critical distance from the crack tip are found to remain at constant values during steady static crack growth. The constant values of the crack tip stresses are specimen size independent. Ductile fracture criteria using stresses at the crack tip as characterization parameters are thus suggested for ductile fracture under plane strain deformation. Ductile fractures of flat plates are studied by simulating fracture tests on ungrooved specimens. 3D effects on the stress distribution at the crack tip must be considered in such cases. A 2D moving plane strain core model is used to account for the 3D effects. With the plane strain core model, it is found that stresses, especially, equivalent stresses at the crack tip remain constant during steady quasi-static crack growth for ungrooved specimens. Stresses at the crack tip are specimen size independent. Plane strain core is proved to exist at the crack tip for an elastic plate by analytical solution of 3D stresses at the crack tip of an elastic plate. Numerical results on the plane strain nature of the crack tip singular stresses for ductile fracture are discussed. 1T compact tension specimens of 2024-T3 aluminum are tested. Specimens of three different thicknesses are compared. Tunneling effects are found to be important for all cases. Equivalent crack length is introduced to account for the tunneling effects and is used together with the moving plane strain core model to simulate the experimental tests. Ductile fracture criterion based on the critical equivalent stress at the crack tip is used together with plane strain strip model, a simple version of plane strain core model, to study the interaction of a leading crack and small cracks. Special attention is paid on the development of yielding zones of the interacting cracks. Swift's postulation that the leading crack and a small crack coalesce if the yielding zones of the two cracks overlap is shown to be good approximation at least for 2024-T3 aluminum.
Degree
Ph.D.
Advisors
Sun, Purdue University.
Subject Area
Aerospace materials|Mechanical engineering
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