In situ measurement of the fragmentation behavior of Al/PTFE reactive materials subjected to explosive loading, Part 1: Fragment size measurements

Abstract

AbstractHigh‐speed optical diagnostics and image analysis methods are applied here to measure the size, velocity, and trajectory of Al/PTFE fragments produced by explosively loading cylindrical specimens. The imaging utilizes high‐speed digital cameras and focused shadowgraphy to capture time‐resolved images of the accelerated fragment field. In Part 1, high‐fidelity fragment size distributions are measured from visual timelines assembled from the high‐speed images through a phase correlation stitching process. The in situ measurements are compared to fragment size distributions measured from images of fragments recovered using a traditional snow soft catch. The two methods show similar size distributions, with the in situ measurement capturing essentially all of the fragment mass whereas the soft catch recovered less than 70 % of the initial sample mass. The fragment mass‐size distributions were fit to a fragmentation model. The model fit showed consistency across tests and a value of the scaling parameter approximately equal to the proposed universal value. In Part 2, a two‐dimensional Kalman filter‐based automated tracking methodology is presented that is used to determine trajectories and velocities of fragments greater than 1 mm. The measured velocities are compared to velocity estimates from the bulk fragment displacement calculated using a phase correlation routine. Bivariate histograms describing the diameter‐velocity variations are presented for the explosive fragmentation and acceleration of these Al/PTFE samples.