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Many significant problems in fracture mechanics of ductile metals involve surface breaking defects (cracks) located in structures subjected to short-duration loading caused by impact or blast. When the severity of impact loads is sufficient to produce large inelastic deformations, the assessment of crack-tip conditions must include the effects of plasticity, strain rate and inertia. This work examines the interaction of impact loading, inelastic material deformation and rate sensitivity with the goal of improving the interpretation of ductile fracture toughness values measured under dynamic loading. We focus on shallow and deeply notched bend test specimens, SE(B)s, employed routinely to measure the static fracture toughness of a material. A thorough understanding of the test specimen's dynamic behavior is a prerequisite to the application of measured fracture properties in structural applications.
Three-dimensional, nonlinear dynamic analyses are performed for SE(B) fracture specimens (a/W= 0.5, 0.15, 0.0725) subjected to impact loading. Loading rates obtained in conventional drop tower tests (impact load-line velocities of = 6 m/sec) are applied in the analyses. An explicit time integration procedure coupled with an efficient (one-point) element integration scheme is employed to compute the dynamic response of the specimen. Strain-rate sensitivity is introduced via a new, efficient implementation of the Bodner-Partom viscoplastic constitutive model. Material properties for A533B steel (a medium strength pressure vessel steel) are used in the analyses. Static analyses of the SE(B) specimens provide baseline responses for assessment of inertial effects. Similarly, dy namic analyses using a strain-rate insensitive material provide reference responses for the assess ment of strain rate effects. Strains at key locations on the specimens and the support reactions (ap plied load) are extracted from the analyses to assess the accuracy of static formulas commonly used to estimate applied J values. Inertial effects on the applied J are quantified by examining the accelera tion component of J evaluated through a domain integral procedure
inertial effects, strain rate sensitivity, impact loading, J, constraint
Senior Research Engineer, Exxon Production Research, Houston, Texas
Professor, University of Illinois, Urbana, IL