The Role of Adhesion and Elastic Modulus on the Sensitivity of Energetic Materials to Vibration and Impact

The transformation of mechanical energy into thermal energy within composite energetic materials through various thermomechanical mechanisms is thought to lead to the creation of localized areas of intense heating. The growth of these “hot spots” is responsible for the bulk reaction or decomposition of the energetic material. Understanding the formation and growth of these hot spots has been an active area of research particularly for high-speed impact and shock conditions, but further work remains to be done in particular with respect to hot spot formation due to periodic mechanical excitation. Previous literature has established that many potential thermomechanical mechanisms may act at the interface between the constituent components of a composite energetic material. In order to provide further insight and guidance into the design of safer and more resilient energetic materials, the role of adhesion on hot spot formation for polymer bonded explosives (PBXs), a subset of composite energetic materials, was explored. Single HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane) crystals in polymer blocks were subjected to ultrasonic excitation and subsequent heating was captured via infrared thermography. Subsequent testing of HMX PBXs using a drop weight tower captured changes in the sensitivity of the energetic material. Variation of the polymer binder allowed for a range of adhesive and mechanical properties to be examined. These experiments on the role of adhesion under these kinds of excitations provided insight into how mechanical energy is being transformed into localized heating.