Modelling the compression strength of polymer laminates in fire

A theoretical and experimental study is presented into the thermal decomposition, softening and failure of polymer matrix laminates under combined compressive loading and one-sided heating to high temperature. A thermo-mechanical model is presented for predicting the time-to-failure of laminates supporting a static compressive stress during one-sided heating. The thermal component of the model predicts the mass loss due to polymer decomposition and through-thickness temperature profile of the hot laminate. The mass loss and temperature predictions are validated against measured data, and the agreement is good. The thermal analysis is coupled to a mechanics-based model that calculates the loss in compressive strength with increasing temperature. The model can also predict the time-to-failure of the hot laminate supporting a static compressive load. The accuracy of the model is evaluated using failure times measured in fire-under-compression load tests on a woven E-glass/vinyl ester laminate. The experimental time-to-failure values decreased with increasing heat flux (temperature) and applied compressive stress, and the model can accurately predict these failure times. The paper also examines the dimensional expansion, out-of-plane distortion and failure mechanism of laminates under combined compressive loading and heating. It is envisaged that the thermo-mechanical model is a useful tool to estimate the failure time of compressively loaded composite structures exposed to high temperature or fire.