Nanoindentation Behavior of Two-Dimensional Energetic Polymer-Reinforced Hybrid HMX Crystals

Insensitive hybrid 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) crystals could be prepared by intercalating with a two-dimensional (2D) energetic material, the so-called triaminoguanidine-glyoxal polymer (TAGP), with different contents. The resulting hybrid HMX crystals have a higher density and better thermal stability due to a strong interaction between the TAGP skeleton and HMX molecules. There should also be a coherent relationship between the mechanical strength and the initiation capability of these modified HMX crystals (qy-HMX). Therefore, in this paper, the dependence of the mechanical behavior of qy-HMX crystals on the content of TAGP has been evaluated. Nanoindentation measurements were performed, based on which hardness and modulus were obtained. The TAGP content ranged from 1 to 14%, making the hardness and modulus change in the ranges of 0.60 to 0.74 and 16.0 to 17.9 GPa, respectively. For each 1% increase in TAGP content, the hardness and modulus of qy-HMX crystals were found to be increased by about 0.02 and 0.28 GPa, respectively. The higher modulus values of the qy-HMX crystals imply that the intercalation of TAGP with the conjugation structure may lead to increased rigidity and stiffness. It means that qy-HMX crystals can withstand more stress without deformation, resulting in a much lower mechanical sensitivity. Their hardness increase also indicates higher resistance to localized plastic deformation, such as scratching or denting, implying an inherently more robust bond formation within qy-HMX crystals.