Cure kinetics and the dimensional control of composite structure

Manufacturers of composite parts are challenged to precisely control part dimensions, or rather maintain tight dimensional control. The dimensional control of composites is a problem having its roots in the basic anisotropic nature of fiber reinforced materials. Our approach is to use a finite-element-based process model that captures all significant aspects of the autoclave process. This process model is called COMPRO, and is described in previous work (1, 2, 3), COMPRO has been shown to accurately predict deformations, such as the spring-in of an angle, for any arbitrary processing cycle. Cure kinetics is a mathematical description of how fast the cure reaction happens with respect to both temperature and the degree of cure. Cure kinetics, which are unique for each resin system, is one of the key input parameters for our process models. This paper describes the relationship of accurate kinetics modeling to the prediction of the spring-in angle of a laminate. The kinetics of YLA's RS 3 cyanate ester resin system is modeled using a series of isothermal and dynamic (ramping temperature) experiments. A method of residual exotherms is used in conjunction with isothermal experiments to generate reaction rate data. Finally, an RS-3 kinetics model that uses a simple lookup table is shown to be highly accurate when compared to the experimental data. The accuracy of the lookup table is a significant advantage over the more-standard chemical kinetics equation approach. Two companion papers, associated with this work are also presented. One paper, authored by Madhukar and Karkkainen, et, al. describes the cure shrinkage behavior of curing epoxies. The second, authored by Fernlund and Poursartip, et. al. describes the analysis of three-dimensional composite structure using the process models described here.