Abstract: The pyrolysis reaction of polymer matrix composites will occur at high temperature. With the production of pyrolysis gas, the gas pressure will be formed in the material. In this paper, through the secondary development of UMATHT subroutine, the numerical simulation of matrix pyrolysis and pyrolysis product diffusion of composites in high temperature environment is carried out, the prediction model of internal pressure of composites is established, the coupling calculation of heat transfer equation, Arrhenius equation, Darcy’s law and ideal gas state equation is realized, and the change of internal pressure of glass fiber/vinyl ester composites under 75 kW/ m² heat flow is simulated. The results show that the pressure prediction value obtained by this method is in good agreement with the experimental value, and the maximum pressure peak error is about 4.68%, which can effectively predict the internal pressure change trend of glass fiber/vinyl ester. The pressure at each location begins to decrease after reaching its peak, and the influencing factors are different. The pressure decreasing at the 3 mm position is affected by the decomposition rate, permeability and porosity; the 6 mm position is caused by the increase of the porosity and the initial permeability; the 9 mm position is only affected by the initial permeability.

Key words: internal pressure, thermal decomposition, glass fiber/vinyl ester, thermal response, overlapping grid technology