Computational study of laser-induced heating of PVDF/nAl composites

Optical sources such as lasers provide a means for precise temporal and spatial control of the ignition of energetic materials through customized deposition of excitation energy. Using coupled microscale electromagnetic (EM) and thermal simulations, we analyze the interactions between the EM waves and the microstructures of PVDF/nAl composites with weight fractions of nAl particles (or solids loadings), w(f), ranging from 10 to 40 wt. %. Statistically equivalent microstructure sample sets with multiple random microstructure instantiations are generated and used for each solid loading, thereby allowing the statistical variations in the material heating behavior due to microstructure randomness to be analyzed. Maxwell's equations are solved to characterize the interactions between the materials and EM waves at wavelengths of 266, 532, and 1064 nm. The resulting energy deposition rate is calculated, accounting for Joule heating, dielectric heating, and magnetic induction heating. The coupled thermal analysis accounts for the energy deposition and thermal diffusion, yielding the temperature fields in the materials. The energy deposition and heating are characterized using three measures: the skin depth of the EM wave, the depth of the significant temperature increase in the material, and the average temperature. An empirical relation is developed for the average temperature increase in the heated layer of the material as a function of the intensity of the input laser, solids loading, and time. It is found that trends in the average temperature and depth of significant heating correlate well with the ignition trends observed in experiments.

Automated summary

By using coupled microscale electromagnetic and thermal simulations, the interactions between PVDF/nAl composites and EM waves are analyzed. The energy deposition rate and temperature fields in the materials are calculated, and it is found that the average temperature and depth of significant heating correlate well with the ignition trends.