SPECKLE PHOTOGRAPHY DURING DYNAMIC IMPACT OF AN ENERGETIC MATERIAL USING LASER-INDUCED FLUORESCENCE

Laser and white light speckle photography have been used to observe su rface displacement in a number of materials and over a varied range of strain rates. However, each suffers from limitations. We have develop ed a novel application of speckle photography in very difficult enviro nments by using laser-induced fluorescence to generate the speckle pat tern. This permits confinement of the free surface without undue degra dation of the correlation upon which speckle methods are based. We hav e applied this method to measure the surface displacement of a reactiv e material during dynamic deformation at moderate strain rates. Conven tional methods were tried but were unsuccessful, necessitating a novel approach. To the best of our knowledge, neither high-speed laser nor white light speckle photography has been performed using energetic mat erials. These measurements are very difficult because of the low mater ial strength (yield strength similar to 8-80 MPa), and because signifi cant out-of-plane motion and surface disruption occur during fracture, and early during the deformation process. We report results from expe riments in which these major problems have been overcome. (C) 1997 Ame rican Institute of Physics.