Publications

Predicting failure of thin-walled structures from explosive loading is a very complex task. The problem can be divided into two parts; the detonation of the explosive to produce the loading on the structure, and secondly the structural response. First, the factors that affect the explosive loading include: size, shape, stand-off, confinement, and chemistry of the explosive. The goal of the first part of the analysis is predicting the pressure on the structure based on these factors. The hydrodynamic code CTH is used to conduct these calculations. Secondly, the response of a structure from the explosive loading is predicted using a detailed finite element model within the explicit analysis code Presto. Material response, to failure, must be established in the analysis to model the failure of this class of structures; validation of this behavior is also required to allow these analyses to be predictive for their intended use. The presentation will detail the validation tests used to support this program. Validation tests using explosively loaded aluminum thin flat plates were used to study all the aspects mentioned above. Experimental measurements of the pressures generated by the explosive and the resulting plate deformations provided data for comparison against analytical predictions. These included pressure-time histories and digital image correlation of the full field plate deflections. The issues studied in the structural analysis were mesh sensitivity, strain based failure metrics, and the coupling methodologies between the blast and structural models. These models have been successfully validated using these tests, thereby increasing confidence of the results obtained in the prediction of failure thresholds of complex structures, including aircraft.

Catastrophic failure of a Reusable Launch Vehicle (RLV) during launch poses a significant engineering problem in the context of crew escape. The explosive hazard potential of the RLV changes during the various phases of the launch. The hazard potential in the on-pad environment is characterized by release and formation of a gas phase mixture in an oxidizer rich environment, while the hazard during the in-flight phase is dominated by the boundary layer and wake flow formed around the vehicle and the interaction with the exhaust gas plume. In order to address more effectively crew escape in these explosive environments a computational analysis program was undertaken by Lockheed Martin, funded by NASA JSC, with simulations and analyses completed by Southwest Research Institute and Sandia National Laboratories. This paper presents then the details of the methodology used in this analysis, results of the study, and important conclusions that came out of the study. Copyright © 2005 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.