High-Speed DIC on flat panels subjected to ballistic impacts

Abstract

Over the past several years, Southwest Research Institute® (SwRI®) has developed and applied DIC to measure back-face deflection and strain response on hundreds of flat panel test articles subjected to ballistic impacts from both small arms fire and bird-strike. The data collected has been used to develop new composite panel layups and validate material models to a level that no previous measurement technique was able to achieve. Getting consistent, high-quality DIC data during a ballistic impact test, however, presents some unique challenges not present in lower-rate testing methods. Proper pattern application techniques to avoid spalling during impact and protection of the expensive stereo high-speed camera pair must be considered and are addressed here. For small arms tests, the required image exposure time to avoid motion blur is on the order of 1, μs, requiring appropriate illumination methods. Bird strike presents a separate set of challenges including an outdoor environment, larger measurement area, and biohazard. The methods used to address these will also be presented. Materials tested include metals, transparent plastics, and composites including carbon, aramid, and polyethylene. Target sizes range from 6, ×, 6 to 36, ×, 36, in. and data rates from 10,000 to 50,000, Hz. Comparison of the DIC data with traditional measurement techniques such as strain gauges and calipers was also made. Agreement proved to be good, prompting the most recent series of tests to be run with DIC as the exclusive data collection method.