| Theodore von Kármán Professor of Aeronautics and Mechanical Engineering |
Research Interests Concepts of Dynamic Fracture Mechanics Applied to the Analysis of Blast-Induced Failures in Pressurized Structures Collaborator: G. Ravichandran, Caltech Conventional numerical studies of failure mechanisms in full-scale structures loaded by explosive loading often utilize simplistic failure criteria based on the attainment of critical levels of stress corresponding to failure initiation. Such stress levels are often arbitrarily chosen to be fractions of the yield stress and are assumed to be uniform through the structure, irrespective of the rate of loading experienced at different locations. In the present work, we use basic concepts of dynamic fracture mechanics to rationalize and refine this simple approach. An explosively loaded, full scale structure (e.g. an airplane fuselage) is subdivided into smaller elements containing pre-existing fatigue cracks emanating from rivet holes. These elements are then subjected to the transient loads predicted by a global stress analysis of the dynamically loaded structure. The dynamic fracture problem is then solved "locally" (numerically and, when possible, analytically) and the resulting time histories of dynamic stress intensity factor are obtained at different locations. These time variations are compared to the dynamic fracture toughness of the material to determine crack initiation. Experimental data of the dependence of fracture toughness on loading rate are utilized. This comparison determines the times and critical stress levels for crack initiation as functions of loading rate. The approach provides a simple, fracture mechanic based, relation between the failure stress and local stress rate, to be used in structural codes modeling the response of aircraft and other pressurized structures to dynamic loading.
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last
update:
05/31/2016