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An elastic-perfectly plastic finite-element analysis has been conducted of plasticity-induced crack closure under plane strain conditions. At a load ratio R ( = Kmin/Kmax) of zero, crack closure was observed in a center-cracked panel but not in a bend specimen. Crack closure in the center-cracked panel occurred for a transient period of growth as the crack evolved from the state of a stationary crack to the steady state of a growing fatigue crack. The influence of specimen geometry upon closure response was rationalized in terms of the “T-stress.” This stress is the nonsingular constant second term in the near tip series expansion of the normal stress parallel to the crack plane. No closure was observed in the center-cracked panel for R ≧ 0.3. The crack opening response and plastic zone distribution of a growing fatigue crack were compared with those of a cyclically loaded stationary crack and a statically loaded tearing crack. Some of the features of the solution for the growing fatigue crack were similar to the solution for a stationary crack, while other features bore more resemblance to those of a tearing crack.
crack closure, crack propagation, elastic-plastic fracture, fatigue, finite-element analysis, fracture, plane strain
Lecturer, University of Cambridge, Cambridge,
Senior research scientist, NASA Langley Research Center, Hampton, VA