Compression Failure of Carbon Fiber-Epoxy Laminates in Fire

This paper investigates the compression failure of carbon fiber-epoxy laminates when exposed to fire. The investigation gives insights into the softening and failure of carbon-epoxy laminates supporting compression loads in the event of aircraft fire. A thermomechanical model is presented for calculating the compression properties and failure of polymer matrix laminates under combined loading and one-sided heating by fire. The accuracy of the model to predict the failure time of carbon-epoxy laminates at different compression load levels and fire temperatures is determined with structural fire tests performed on woven carbon-epoxy panels. The model predicts a gradual increase in the failure time of the laminate with decreasing compression stress (down to 10% of the room temperature buckling load) and decreasing heat flux (or temperature) of the fire. This was confirmed by the fire tests, which showed good agreement between the calculated and measured failure times. Compression failure of the laminate usually occurred within relatively short times (less than a few minutes) by viscous softening of the polymer matrix. For long failure times, matrix decomposition was shown to influence the failure process. Parametric analysis using the model reveals that raising the glass transition temperature of the polymer matrix increases the compression failure time of laminates in fire. However, only small improvements to the failure time are achieved by raising the glass transition temperature of laminates exposed to high-temperature fires typical of postcrash aircraft accidents.