Shape Optimization of Plates to Mitigate the Effects of Air Blast Loading
Final rept. 1 Jul 2006-21 Jun 2009
PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF MECHANICAL AND NUCLEAR ENGINEERING
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This report presents a formal approach for optimizing the shape of freely supported isotropic plates to withstand air blast loading. Unique difficulties are presented by the nature of short-duration dynamic loading, viz. transient dynamic response, monitoring of maximum plastic strain failure at every point in the panel over time, optimizers that can handle non-differentiable, nonconvex and computationally expensive functions, and mesh distortion. LS-DYNA is used as the finite element software. The finite element model has been developed to reflect experimental test conditions and observed structural response. The goal has been to minimize dynamic displacement relative to the fixture, while monitoring plastic strain values, mass, and envelope constraints. A Fortran code has been developed to implement the methodology. Sinusoidal basis shapes are used to obtain an optimized double-bulge shape. Importantly, the flat plate is associated with a concentration of plastic strain at its center while for the optimized bulge shape, the plastic strain is smeared around the support showing greater utilization of material. Results show that much superior structural systems can be designed compared to ad-hoc techniques that sometimes fail to improve even the baseline design of a flat plate. Change in optimized shape with increasing offset in charge location is studied. A methodology for optimizing honeycomb sandwich structures is presented, utilizing a novel technique for linking honeycomb core geometry with its stress-strain curve.