The Effect of Thermal Processing on Residual Strain Development in Unidirectional Graphite Fibre Reinforced PEEK

Abstract

The effect of annealing on residual strain development in amorphous graphite fibre reinforced PEEK (APC-2) is studied experimentally. A method is presented for embedding strain gauges in a unidirectional laminate at the time of manufacture and then quenching the laminate into the amorphous state. With this method, thermal and crys tallization strains are measured directly during quasi-isothermal heating of the laminate. Both longitudinal and transverse lamina strains resulting from contraction during crystallization are measured. Longitudinal crystallization strains are found to be negligible due to fibre stiffness. Transverse contraction due to crystallization is large and increases with anneal temperature. A coefficient of crystalline expansion (CCE) is defined which is analogous to the CTE. This coefficient describes the permanent crystallization strain as a function of anneal tem perature and is determined experimentally.