Microstructural characterization of pressure-induced cracking in melamine/F2311 composites and crack-healing behavior via thermal-pressure aging treatment

The effects of F2311 content on the crack morphology and crack healing behavior of melamine/F2311 composites, a safe polymer-bonded explosive analog, were systematically studied in terms of its microstructure and mechanical properties. Scanning electron microscopy and CT analysis were used to quantitatively characterize the microcrack zone. The results demonstrated that thermal-pressure aging treatment could eliminate cracks and further improve the density and mechanical properties. The density and mechanical properties of the M-10F samples improved by the largest margin, its density increased by 1.9% and its tensile and compressive strength increased by >100%. The improvement of the density and mechanical properties were related to the processing parameters, the initial density, and the binder content. The thermal energy and compressive stress provided to the system during thermal-pressure aging treatment can promote the binder migration at the interface. In addition, small melamine particles that are prone to displacement and rotation may migrate with F2311 to fill cracks. These processes could collectively reduce damage and defects, partially or completely heal cracks, and restore the structure and properties of the material. Crack healing under pressure and temperature indicates that thermal-pressure aging treatment has high potential for damage repair of composites with a thermoplastic binder.