Environmental Effects on Fiber Reinforced Polymer Composites Fluid and Temperature Effects on Mechanical Performance

Abstract

In several applications, like offshore, marine, wind energy and aerospace industry, fiber reinforced polymer composites are exposed to mechanical loads and environmental effects: fluid exposure and high temperature. The interaction between environmental effects and the composite materials can cause both reversible and non-reversible degradation of the mechanical strength and performance. In this work, the fluid interaction with the material is analyzed using fickian diffusion theory. Analytical solutions are developed for the identification of the orthotropic diffusion constants from the most common composite structures: plates, cylinders and pipes, by using samples with different geometrical aspect ratios. The effect of static and fatigue loads on the rate of fluid diffusion in composite laminates is studied using a theoretical model. The proposed model accounts for the accelerating effect of matrix cracks and delaminations on fluid diffusion by defining a periodic representative volume element based on the crack density. A new I-beam shear test method is introduced to study the environmental effects on the interlaminar shear strength of the material, which accelerates fluid saturation. The method is analyzed by means of elastoplastic Finite Element (FE) analysis, comparing it to the conventionally adopted short-beam-shear configuration. The dry and conditioned shear deformation characteristics are predicted from the matrix constitutive behavior. The dry and immersed fatigue behavior were measured experimentally at different temperatures. The different failure mechanisms observed were explained and schematized. A theoretical model based on the activation energy concepts is proposed to explain the fatigue behavior’s dependence on the environment.