Overall thermal conductivity of carbon fiber polymer matrix composites undergoing thermal decomposition

The objective of this work is micromechanics-based prediction of the effective longitudinal and transverse thermal conductivity of carbon fiber reinforced polymer (CFRP) composites at high temperatures, when pyrolytic thermal decomposition of the polymer matrix takes place. Microstructure of the composite evolves with temperature and consists of polymer phase, growing pores, which represent pyrolytic gaseous phase, and continuous carbon fibers. Volume fractions of polymer and pores at different temperatures are obtained from the Arrhenius-type equation describing decomposition of the polymer matrix. The char residue produced during pyrolytic thermal decomposition is not considered in this study. Microstructure generation algorithms are developed to create densely packed, randomly distributed, poly-dispersed, particle filled microstructures consisting of circular (representing fibers) and elliptic (representing pores) inclusions. Statistical analysis of the generated microstructures is discussed to demonstrate their suitability. A two-step numerical homogenization technique is used to compute the effective directional thermal conductivities of the composite. The computational results for the effective transverse and longitudinal thermal conductivities are obtained for the AS4/3501-6 composite in a temperature range up to 700 K.