Interface Chemistry Dependent Mechanical Properties in Energetic Materials Using Nano-Scale Impact Experiment

Abstract

Energetic materials are sensitive to mechanical shock and defects caused by a high velocity impact, which may result in unwanted detonation due to hot-spot formation. In order to understand the underlying mechanism, characterization of high strain rate mechanical properties needs to be studied. One of the key factors that can contribute to this type of defect is the failure initiated at the interfaces such as those between Hydroxyl-terminated polybutadiene (HTPB)-HMX (or HTPB-Ammonium Perchlorate (AP)). In this work, interface mechanical properties of HTPB-HMX (and HTPB-AP) interfaces are characterized using nano-scale impact experiments at strain rates up to 100 s⁻¹. The experiments were conducted with impactor of radius 1 μm on the interfaces with varying amount of binding agent. For HTPB-AP samples, Tepanol is used as the binding agent. The impact response is determined in the bulk HTPB, HMX, and AP as well as at the HTPB-HMX and HTPB-AP interfaces. A power law viscoplastic constitutive model is fitted to experimental stress-strain-strain rate data which can be used in Finite Element Model simulation to predict the shock behavior of energetic materials. An in-situ mechanical Raman spectroscopy (MRS) setup was used to analyze the effect of interface chemistry on interface level stress variation. The stress distribution near the interface captures the effect of interface chemistry variation.