A model for the structural integrity of composite laminates in fire

Abstract

This thesis describes a model for the integrity of composite laminates in fire. The model was based on laminate theory analysis and a one dimensional heat transfer model, and was validated for three materials; glass reinforced polyester, glass reinforced vinyl ester and glass reinforced polypropylene. A small-scale fire resistance test, based on a simple burner, is also described.

A propane burner was used to produce a constant heat flux for testing composite laminates. The thermal response was measured at the rear face of the sample in a 50kW/m2 fire. A one dimensional thermal model was used to make predictions of the temperature profile and residual resin content through the material’s cross-section. The measured thermal response was then used to validate these predictions.

Fire tests were also conducted on small-scale samples under a constant load. The samples were loaded in either tension or compression and then exposed to a 50kW/m2 heat flux, provided by the propane burner. The time to failure was recorded and used to validate the laminate failure model predictions. Very little work had been conducted on the fire testing of loaded composites prior to this research.

Temperature dependent material properties were measured for each material. An empirical relationship was used to describe the variation of flexural modulus, tensile strength and compressive strength from room temperature, through the glass transition temperature and up to 400°C.

Ply constitutive equations were constructed using the predicted temperature and resin content profiles, and the temperature dependent material property information. These equations provided input for the laminate analysis model. Predictions are presented for the variation of the laminate A, B and D matrices in a 50kW/m2 fire. The model produced very accurate strength predictions for all three laminate systems, and would therefore be a useful tool for the initial stages of composite structure design.