NASA-LLIS-0508

Abstract

<strong>Description of Driving Event:</strong> <br>Currently, only one method is available for determining an object's angle of impact against a structure: high speed photography. This method requires a great deal of equipment and produces data, which requires a great deal of time to analyze. Presently, the acoustic emission technique is being used to assess damage caused by the impact of an object. As now used, this technique does not provide information concerning the angle of impact. However, a patent was granted on 3-2-93 for a method for determining the angle of impact of an object on a thin-walled structure through analysis of the acoustic waves which result when the object impacts. Transducers are placed on and in the surface of the structure which sense the impact waves caused in the structure. The waves are recorded and saved for analysis. For source motion normal to the surface, the antisymmetric mode has a large amplitude while that of the symmetric mode is very small. <br>As the source angle increases with respect to the surface normal, the symmetric mode amplitude increases while the antisymmetric mode amplitude decreases. Thus, the angle of impact is determined by measuring the relative amplitudes of these two lowest order modes.