Three-dimensional, inelastic response of single-edge notch bend specimens subjected to impact loading

Many significant problems in fracture mechanics of ductile metals involve surface breaking defects (cracks) located in structures that are 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 research examines the interaction of impact loading, inelastic material deformation and crack geometry with the goal of improving procedures for the engineering assessment of flaws located in critical structures. The work focuses on the bending-type test specimen employed to measure the inherent fracture toughness of a material. A thorough understanding of the test specimen behavior is a prerequisite to the application of measured material properties in structural applications.; Three-dimensional dynamic analyses are performed for three different specimen configurations (a/W = 0.5, 0.15, 0.0725) of single edge bend, SE(B), fracture specimens subjected to impact loading. Loading rates obtained in routine drop tower tests (terminal load-line velocity of 100 in/sec) are applied in the analyses. The quarter-symmetric finite element models have 2000-3000, 8-node elements. Such models are refined sufficiently to provide detailed information about overall load-displacement response, Crack Tip Opening Displacement values and J-integral values. The mesh refinement provides only a coarse prediction of crack tip stress fields over distances of a few CTODs. Explicit time integration coupled with an efficient element integration scheme is used 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 same SE(B) specimens provide baseline results from which inertial effects are assessed. Similarly, dynamic analyses using a strain-rate insensitive material provide a reference for the assessment of strain rate effects. Strains at key locations and the support reactions 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 acceleration component of J.