Dynamic Mechanical Behavior Characterization of Epoxy-Cast Al + Fe2O3 Thermite Mixture Composites

The dynamic mechanical behavior characterization of epoxy-cast stoichiometric mixtures of nano- or micron-scale aluminum and hematite (Fe2O3) powders is investigated in this work. Experiments conducted on rod-shaped samples, using instrumented reverse Taylor impact tests employing high-speed imaging and velocity interferometry, show that these composites exhibit viscoelastic deformation and brittle fracture behaviors. Upon impact, the samples display significant elastic and plastic deformation during both the loading and unloading stages, as determined from quantitative high-speed camera measurements of the transient deformation states. Approximately 50 pct elastic recovery of total axial strain was observed to occur rapidly (within tens of microseconds) after impact. A one-dimensional elastic-plastic wave propagation analysis was used for estimating the composite’s dynamic average yield stress and total plastic strain. The results reveal that the nano-Al + Fe2O3-containing epoxy composite is most resilient, has the highest strength, and is more capable of absorbing impact energy. The analysis additionally provides detailed information about elastic and plastic wave interactions for discrete times, up to the final state of the material. Calculations and observations through the coupling of high-speed camera images and velocity interferometry (VISAR) measurements show that the elastic recovery coincides with peak axial strain and the interaction of elastic and plastic waves propagating within the rod-shaped specimen. Hence, such an instrumented Taylor test provides a detailed view of the general wave structure within the material upon impact and, at the same time, enables a complete description of the stress-strain response.