Title: Investigation of a cohesive zone model for simulating void nucleation and its connection to nuclear safety assessmen

Date/Time: Tuesday, August 29, 2006, 10:00 – 10:30 (PT)

Location: Building 980 Room 95 (Sandia NM), Building 940 Auditorium (Sandia-CA)

Brief Abstract: Nuclear safety assessments have been the focus of abnormal mechanical environment modeling efforts for multiple weapons systems over the last few years (i.e., W80-3, W76 and W87).  The modeling efforts are aimed at predicting metal failure of common engineering materials such as steel and aluminum in order to determine if exclusion regions with the weapon are breeched during abnormal mechanical events such as a drop during handling or a crash during transport.  Simulations of the W80-3 subjected to drops have been performed using the Sandia-developed EMMI (Evolving Microstructure Model of Inelasticity) plasticity and failure model.  EMMI accounts for void nucleation and growth in an elastic-plastic material with failure parameters derived from calibration with tensile and shear material characterization tests.  It was observed during determination of these failure parameters that it was difficult to obtain a single set of material parameters that maintained good correlation across the entire suite of material characterization test geometries.  Also, it is not well understood how well the model captures the portion of damage due to nucleation.  Therefore, to better understand the mechanisms associated with ductile failure (void nucleation, growth, and coalescence) and their relative importance, micromechanical models of these phenomena are investigated.  For void nucleation specifically, the decohesion of a metal matrix from an elastic particle in varying tensile loading conditions is modeled with the use of a cohesive zone model based on a traction-displacement relation.  The responses obtained from the cohesive zone model are then qualitatively compared with those from a simpler critical stress model to help direct future work on this topic.

CSRI POC: Jay Dike, (925) 294-1352