Laminate Theory Analysis of Composites under Load in Fire

Abstract

Laminate analysis is used to model a loaded composite plate under one-sided heat flux. The input to the laminate analysis comes from a thermal/ablative model, which predicts the temperature evolution through the thickness. It also gives the profile of residual resin content, which reflects the extent of thermal damage. Relationships are proposed to enable the computation of the elastic constants and other mechanical properties as functions of temperature and resin content. The model was applied to a 12 mm thick woven glass/polyester laminate exposed to a heat flux of 75 kW m 2. The laminate A, B, and D matrices were modeled, along with the variation of failure loads in compression and tension. The predictions agreed well with experimental values for compression of a constrained plate. Both the local buckling load, which is proportional to √D1 D2, and the compressive failure load fall rapidly on exposure to heat flux. The bending/tensile coupling matrix, B, which is zero initially, becomes finite due to the asymmetric thermal profile, then declines as the thermal front progresses. For tensile loading, the residual properties after fire were accurately modeled, but the fall in tensile failure load was somewhat over-predicted.