A numerical investigation of the fatigue crack closure phenomenon has been performed by an elastic-plastic finite element analysis. Computer software was developed to consider many aspects affecting plasticity-induced crack closure. Linear and power-law hardening models are considered in the finite element analysis. The paper presents results from the study carried out on compact tension (CT) coupons at various crack lengths corresponding to different loading conditions. Finally the results of the analysis are compared with the experimental estimates of fatigue crack closure levels obtained from laser interferometry, scanning-electron and transmission-electron fractography presented in Part I of this paper on identical specimens. NOMENCLATURE a, ai = length of the crack, initial crack length E = modulus of elasticity 2h = height of the specimen P = applied load level R = stress ratio S,, = applied stress level at which crack starts closing S, = applied stress level at which crack starts opening S,, = ratio of closure and maximum applied stress level gOp = ratio of opening and maximum applied stress level { U } = nodal displacement vector [ K , ] , [Re] = elastic stiffness matrix and modified elastic stiffness matrix S,,,,,, Smin = maximum and minimum applied stress levels t = thickness of the specimen W = width of the specimen Aa = smallest element length along crack plane A& = total strain increment A&e,, Acp1 = elastic and plastic strain increment go = yield stress in tension, i.e. effective yield stress ox, oy, uz = normal stress components E* = distortional strain E, = volumetric strain 963 964 N. E. ASHBAUGH et al.
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