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Effect of Crystal Density on Dynamic Deformation Behavior of PBX Suraj Ravindran, Addis Tessema, and Addis Kidane

Abstract Polymer bonded explosives (PBX) are heterogeneous materials that contain solid loading varying from 80 to 95 % and bound together by 5–20 % soft binder. An experimental investigation is performed to study the effect of crystal solid loading on the failure process of PBX subjected to dynamic loading at different strain rates. Model materials, with sugar crystals and binder, are fabricated with solid loading varying from 80 to 95 %. Then dynamic compression experiments are performed on each specimens using split Hopkinson pressure bar. During loading, the deformation is captured using the high-speed camera at 1 million frames/s. Digital image correlation technique is used to obtain the local and full field deformation and strain fields at each strain rate. Based on the local deformation field and the load data, the failure process of each sample are investigated, and the effect of solid loading on the strain localization and failure mode of the PBX is discussed. Keywords Polymer bonded explosive • Dynamic • DIC • Meso-scale • Strain localization

11.1

Introduction

Polymer bonded explosives (PBX) are heterogeneous composites, which contains 80–95 % of polycrystalline explosives crystals such as, RDX, HMX, etc. bound together by 5–20 % of rubbery polymer binder such as hydroxyl-terminated polybutadiene (HTPB), Estane, etc. These materials are subjected to a dynamic loading of strain rate varying from 102 to 105 s 1, during manufacturing, machining, transportation and service [1–3]. This can cause severe damage and formation of hot spots that can lead to deflagration of the material, which in turn affects the safety and chemical stability of the PBX. It is believed that the grain scale strain localization due to heterogeneity in the microstructure, material property mismatch between the binder and explosive crystal, defects such as voids, cracks, and inclusions play a major role in the local failure and formation of hot spots [3, 4]. Experimentally it is shown, at intermediate strain rates, the strain localization mainly occurs in the polymer binder whereas crystals realign themselves without deformation to accommodate the high deformation in the binder [5, 6]. In this work, the effect of the amount of solid loading on the local deformation behavior of polymer bonded sugar under dynamic loading is investigated using in situ digital image correlation [7].

11.2

Materials Preparation

The material used in this study is polymer bonded sugar (PBS) a well-known simulant of polymer bonded explosives (PBX). The composition of the simulant material is given Table 11.1. To fabricate the samples, first, the HTPB is mechanically mixed with the dioctyl sebacate (DOS) plasticizer in the proportion shown in Table 11.1. Subsequently, curing agent toluene diisocyanate (TDI) has been added and mixed thoroughly. This mixture is further blended with the sugar crystal and partially cured at 70  C for 8 h. After th