Date of Award
Open Access Dissertation
Polymer bonded explosives (PBX) are heterogeneous granular composites with a high-volume fraction of solid. Typically, they contain 80-95% explosive crystals and 5- 20% soft polymer binder. These materials are subjected to different loading conditions during their service life. The main function of the soft binder is to reduce shock sensitivity to prevent an accidental explosion. However, there have been inadvertent detonations in these materials during transportation and handling. The reason for such unintentional explosion is not well understood. It is commonly accepted that the formation of local hightemperature regions, called ‘hot spots’, is the primary cause. Hotspot formation is associated with the local energy dissipation mechanisms in the material system during dynamic loading. There is a large knowledge gap in understanding the dynamics of local failure mechanisms in polymer bonded explosives subjected to loading at different time scales. The primary focus of the present work is to understand the local deformation mechanisms in polymer bonded explosives subjected to high rate and impact loading. An experimental method is developed based on high-speed photography and digital image correlation (DIC). The experimental setup helps to observe and quantify the deformation mechanisms in-situ at a spatial and temporal resolution of 10.66 µm/pixel and 200 ns, respectively. The capability of the experimental setup is validated in two heterogeneous materials system at strain rates varying from 150-1000 s-1. v In this study, polymer bonded sugar (PBS), a mechanical simulant of PBX is used. PBS contains sugar solid crystals and plasticized hydroxyl-terminated polybutadiene (HTPB) as the soft binder. Two different dynamic loading configurations are studied, simulating high strain rate and high impact loading conditions. The first loading configuration involves the dynamic loading of PBS specimens at a strain rate from 150 to 1000 s-1. High temporal resolution dynamic deformation measurements are conducted at macro and meso (local) length scales. From these experiments, global and local deformation mechanisms and failure behavior are studied in detail. The effects of strain rate and particle volume fraction on the deformation mechanisms are studied for a comprehensive understanding of the material behavior. These experiments reveal the link between the macroscale shear band formation and its microscopic origin. The second case involves, a direct impact loading utilizing a gas-gun with impact velocity varying from 50 to 100 m/s. From the images captured during loading, a quantitative analysis of the compaction wave dynamics is performed at two length scales. The particle velocity, compaction wave velocity, and wave thickness are calculated from the macroscale experiments. In addition. spatial stress distribution is determined from the equilibrium equations using the full displacement data obtained from DIC. From stress and strain rates, the total energy dissipated during compaction wave propagation is estimated. Finally, mesoscale experimental observations are used to identify the main local failure and deformation mechanisms associated with the energy dissipation.
Ravindran, S.(2018). Multiscale Deformation And Failure Behavior Of Polymer Bonded Explosives Subjected To High Rate Loading. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/4935