Simulation of the effects of thermal history on the morphology of thermoplastic composites

This paper concerns the simulation of the development of the degree of crystallinity and the size of spherulites that arise during the cooling of a slab of a semicrystalline polymer reinforced with long, continuous carbon fibers. This situation is commonly found during the processing of semicrystalline thermoplastic composites. Whereas published attempts at simulating this process have treated the composite as a continuum, and thereby used mass averaged physical properties (such as thermal conductivity, density, and specific heat), we use a quasicontinuum approach in which we consider the properties of the matrix and fiber separately. Once a temperature distribution is calculated using the continuum approach, the finite element method is applied locally at various points in the slab to calculate the degree of crystallinity and the size of the developing spherulites. This is done by using the Avrami equation and the Hoffman and Lauritzen radial growth equation. The degree of crystallinity and the spherulite size are predicted as a function of fiber spacing and packing geometry, and the predictions are in good agreement with experimental results obtained on poly(phenylene sulfide)/carbon fiber composites. The advantages of our approach over the continuum approach is that a relatively accurate prediction of the spherulite size is possible owing to constraints imposed by the fiber on the spherulitic growth.