Determination of Heat Deflection Temperature under a Load and Vicat Softening Temperature of Powder Composites used for Ablative Shields

This paper presents the results of a study to determine the heat deflection temperature (HDT) and Vicat softening temperature (VST) of polymer matrix powder composites used for ablative shielding. The issue is of particular importance since, during ablative tests, the composite material is partially burnt (ablative layer). However, its remaining parts are additionally heated to a higher temperature, which is consequently associated with a change in the visco-elastic properties that depend, among other things, on the VST and HDT temperatures. In the conducted research, the authors used different mass percentages of powder modifiers (montmorillonite, halloysite, mullite, carbon nanotubes, silicon carbide) matrix base epoxy resin LH 145 Havel with the hardener H147 in the experiments. Apart from observing thermal properties that may change due to a modification of the composition of the composites, the effect of conditioning of the samples on the test results was also noticed. It is preheating a composite at a temperature as low as 55°C was observed to increase the HDT and VST by approximately 20°C and the composite hardness by approximately 3-7%.