Application of digital speckle photography to flash x-ray studies of internal deformation fields in impact experiments

A technique to measure two-dimensional deformation fields of a layer inside materials during dynamic events such as impact experiments is presented. E ven optically opaque materials like cement can be evaluated when flash x ra ys are used. Blocks of polyester and cement were prepared with a layer of x -ray-absorbing lead particles. The specimens were then hit by a 9-mm-diamet er steel sphere (ball bearing) fired from a 9-mm-bore gas gun at a velocity of 373.5 +/- 3.0 ms(-1). A 30-ns-long x-ray pulse exposed one radiograph b efore impact; another radiograph was exposed a short time after the impact on the specimen. The two-dimensional displacement field was obtained when t he x-ray radiographs were digitized by a conventional flatbed scanner, and a digital speckle photography algorithm was used to calculate the displacem ents. The flash x-ray technique allowed examination of the deformation at t he layer inside the material during failure, thus giving interesting data a bout the material flow field around the impactor. (C) 1999 Optical Society of America.