MULTIDISCIPLINARY EFFECTS OF AGING FACTORS ONDAMAGE IN STRUCTURAL COMPOSITES

摘要

The increasing use of structural composites made from carbon fiber and organic matrix leads us toinvestigate thermo-mechanical quality and aging relationships. Multidisciplinary effects of agingfactors introduce complex phenomena which can substantially alter mechanical properties ofcomposite laminates and reduce their lifetime. After a review of aging effects, the main parametersintroduced within ordinary environmental conditions subjected to thermo-structural composites aredescribed. The combination of two parameters, temperature and oxygen diffusion, makes it extremelycomplex to study combined aging effects and understand corresponding mechanical results. A singlesurface thermo-oxidation gives rise to corrosion, surface stress state, and microcracking which areresponsible for degradation of mechanical properties. Each effect can be modeled separately. Thispaper predicts an oxidized layer using an oxygen diffusion-reaction method. This technique iscomplex, however a combined study incorporating all multidisciplanary effects is significantly moreso. To date, there has been no attempt to incorporate all these effects into a mechanical behaviormodel. As to degradation in the whole volume of the composite, it seems easier if only viscousbehavior of the matrix is considered (without cracking or interface problems). For thermal aging, thereexists a dynamic compromise between crosslinking and chain degradation which can be representedby a displacement of the glass transition temperature (Tg). The paper presents a multiscale mechanicalapproach including this Tg internal variable in order to understand the evolution of the viscoelasticbehavior of composite laminates aged under various conditions.