Thermal response during volumetric ablation of carbon fiber composites under a high intensity continuous laser irradiation

Abstract

Abstract The phenomenon of volumetric ablation of carbon fiber composites by a continuous high power density laser was investigated theoretically and numerically. The main goal of this study was to investigate the thermal responses of the heat shields of re-entry vehicles in the extreme thermal environment. The composite was considered as a homogenized block in geometry. And a one-dimensional transient model was proposed. The laser power density varied from 50W/cm2 to 500W/cm2 and the laser irradiation time varied from 0 to 5 s. During volumetric ablation, the composite could be separated into three zones: the virgin zone, the pyrolysis zone and the char zone. It was found that a higher laser power density led to a smaller pyrolysis zone. The peak pressure of pyrolysis gases in the composite appeared in the region with a low degree of pyrolysis reaction, which had a significantly low porosity and permeability. When the initial porosity of the composite was low, a small amount of gas generation might lead to a high gas pressure, causing mechanical failure of the composite. And the magnitude of the peak pressure decreased quickly with the initial porosity increasing. Therefore, the porous structure and the honeycomb sandwich structure used inside of the composite should decrease the internal gas pressure to prevent the material from mechanical damage. The simulation result of this study was helpful for the design of high temperature thermal protection systems.