Two-Dimensional Cure Simulation of Thick Thermosetting Composites

Abstract

An investigation into the two-dimensional cure simulation of thick thermosetting composites is presented. Temperature and degree of cure distributions within arbitrary cross-sectional geometries are predicted as a function of the autoclave temperature history. The heat conduction equation for two-dimensional, transient anisotropic heat transfer is coupled to the cure kinetics of the thermosetting composite material. A heat generation term, expressed as a function of cure rate and the total heat of reaction, is introduced to account for the heat liberated during the curing process. A generalized boundary condition formulation is employed, enabling arbitrary temperature boundary conditions to be enforced straightforwardly. An incremental, transient finite difference solution scheme is implemented to solve the pertinent governing equations and boundary conditions. The boundary-fitted coordinate system (BFCS) transformation technique is combined with the Alternating Direction Explicit (ADE) finite difference method in the solution strategy. Complex gradients in temperature and degree of cure are predicted and the influence of the tool on the curing process is demonstrated. Correlation between experimentally measured and predicted through-the-thickness temperature profiles in glass/polyester laminates are presented for various arbitrary temperature cure cycle histories. Several typical glass/polyester and graphite/epoxy structural elements of arbitrary cross-section (ply-drop and angle bend) are analyzed to provide insight into the non-uniform curing process unique to thick-sections. Spatial gradients in degree of cure are shown to be strongly dependent on part geometry, thermal anisotropy, cure kinetics and the temperature cure cycle. These spatial gradients directly influence the quality and in-service performance of the finished component by inducing warpage and residual stress during the curing process.