Identification of accelerated wet-ageing cycles
Abstract
The increasing use of polymer-matrix composites in aircraft structural parts calls for a better knowledge of the long-term properties in cyclic hygro-thermal conditions. For example, the new A380 aircraft is composed of composite structural parts that are more than 20 thick. In such cases, wet-ageing, partially characterized as a through-the-thickness water concentration profile, evolves over several decades. Wetageing is, typically, so slow that characterization experiments based on direct reproduction of the hygro-thermal cycles are not possible within the development time of the aircraft. The identification of cycles leading to comparable through-the-thickness water concentrations in shorter times has been proposed using a Fickian water diffusion model in [7, 8]. This article presents a rigorous methodology and software development for the identification of accelerated wet-ageing cycles. Depending on the formulation, identification time and water concentration profiles are treated either as objective functions or as constraints. The results of the different identifications exhibit the trade-offs that exist between water profile accuracy and experiment time. The numerical implementation is performed in the LAMKIT c software ([3]), which is an object oriented platform for the analysis and optimization of composite laminates ([4]). An application is given for a thick and humid laminate.