Modelling and simulation of cure in pultrusion processes

Trial and error approach is not a suitable method to optimize the pultrusion process because of the high times required for the start up and the wide range of possible combinations of matrix and reinforcement. On the other hand, numerical approaches can be a suitable solution to test different parameter configuration. One of the main tasks in pultrusion processes is to obtain a complete and homogeneous resin polymerization. The formation of cross-links between polymeric chains is thermally induced but it leads to a strong exothermic heat generation, hence the thermal and the chemical phenomena are mutually affected. It requires that the two problems have to be modelled in coupled way. The mathematical model used in this work considers the composite as a lumped material, whose thermal and mechanical properties are evaluated as function of resin and fibers properties. The numerical pattern is based on a quasi-static approach in a threedimensional Eulerian domain, which describes both thermal and chemical phenomena. The data obtained are used in a simplified C.H.I.L.E. (Cure Hardening Instantaneous Linear Elastic) model to compute the mechanical properties of the resin fraction in the pultruded. The two combined approaches allow to formulate a numerical model which takes into account the normal (no-penetration) and tangential (viscosity/friction) interactions between die and profile, the pulling force and the hydrostatic pressure of the liquid resin to evaluate the stress and strain fields induced by the process within the pultruded. The implementation of the numerical models has been carried out using the ABAQUS finite element suite, by means of several user subroutines (in Fortran language) which improve the basic software potentialities.