Kinetics, evolving thermal properties, and surface ignition of carbon fiber reinforced epoxy composite during laser-induced decomposition

The decomposition kinetics, heats of reaction, evolving thermal conductivity and emissivity, and surface ignition conditions of carbon fiber reinforced polymer (CFRP) composites during laser-induced polymer matrix decomposition were investigated. Woven carbon fiber-epoxy panels of different thicknesses were irradiated with a 1.07-μm, 2-kW ytterbium fiber laser at irradiances of 5-525 W/cm2. The changing front and backside surface temperatures were measured using a mid-wave infrared camera, adjusted using measured emissivity of irradiated and un-irradiated CFRP samples. The evolving temperature maps were fit to a 3D, explicit, finite difference, thermal model to estimate Arrhenius kinetic rate parameters, heats of reaction, and thermal conductivity during a two-step epoxy decomposition reaction and a single stage char oxidation reaction. The kinetics is not strongly dependent on heating rates of 20-700 °C/sec and parameters determined at lower laser powers extrapolate well to higher powers. Surface ignition occurs at critical surface temperatures of 1198 ± 50 °C.