Effects of Cooling Rate on the Crystallinity and Mechanical Properties of Thermoplastic Composites

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Abstract
Tests were performed to evaluate the effects of crystallinity on the mechanical properties of PEEK 150P polymer and APC-2 graphite/PEEK composite. The tensile strengths, ten sile moduli and fracture toughnesses of the polymer, and the mixed mode I and mode II fracture toughnesses of the composite were measured at crystallinities ranging from 27 to 43 percent by weight. The results show that, in the crystallinity range studied, the tensile properties are not affected significantly by changes in crystallinity, while the fracture toughness depends strongly on the crystallinity. A model is also described which can be used to calculate the crystallinity from the known applied cooling rate. The validity of the model was verified by tests performed with PEEK 150P polymer.