Characterization of the effects of hygrothermal-aging on mechanical performance and damage progression of fiberglass epoxy composite

Abstract

Marine Hydro-Kinetic Devices (MHK) are a developing renewable energy technology that allows energy to be harvested from the natural flow of water due to tides, currents, and waves. Fiber Reinforced Polymers (FRP), which have been extensively used in wind energy applications, offer favorable mechanical properties as well as low costs and manufacturability making them a viable option for construction of MHK devices. However, exposure to a harsh marine environment results in moisture uptake into the FRP, often degrading mechanical properties. A study of a fiberglass-epoxy FRP was conducted to characterize the effects of moisture on mechanical properties and damage behavior of the material as well as classify the degradation mechanisms responsible for changes in performance. Environmental exposure was simulated through hygrothermal aging, exposing the FRP samples to distilled water and elevated temperature (50 °C) to accelerate the environmental effects. Quasi-static tension tests of both unidirectional and cross-ply laminates were conducted to classify the effects of moisture on mechanical properties of constituent and multi-angle laminates. Cross-ply laminates experienced 54% reduction in strengths due to moisture absorption, while unidirectional laminates strengths were reduced by 40%. Constitutive stress-strain response in conjunction with Acoustic Emission (AE) monitoring describe changes in damage behavior due to hygrothermal aging. This work also characterizes hygrothermal effects on pure/neat epoxy material to aid in interpreting hygrothermal degradation mechanisms in the composite as well as guided ultrasonic evaluation of composite specimens to characterize effects of moisture on AE signals.