Effects of moisture absorption on damage progression and strength of unidirectional and cross-ply fiberglass–epoxy composites

Abstract

Abstract. Fiber-reinforced-polymer composites (FRPs) possess superior mechanical properties and formability, making them a desirable material for construction of large optimized mechanical structures, such as aircraft, wind turbines, and marine hydrokinetic (MHK) devices. However, exposure to harsh marine environments can result in moisture absorption into the microstructure of the FRPs comprising these structures and often degrading mechanical properties. Specifically, laminate static and fatigue strengths are often significantly reduced, which must be considered in design of FRP structures in marine environments. A study of fiberglass epoxy unidirectional and cross-ply laminates was conducted to investigate hygrothermal effects on the mechanical behavior of a common material system used in wind applications. Several laminates were aged in 50 ∘C distilled water until maximum saturation was reached. Unconditioned control and the saturated samples were tested in quasi-static tension with the accompaniment of acoustic emission (AE) monitoring. Cross-ply laminates experienced a 54 % reduction in strength due to moisture absorption, while unidirectional laminate strengths were reduced by 40 %. Stress–strain curves and AE activity of the samples were analyzed to identify changes in damage progression due to aging.

Subcomponent Validation of Composite Joints for the Marine Energy Advanced Materials Project

“…The specimens conditioned at FAU were soaked in tanks at an elevated temperature of 58°C to accelerate the aging process. Periodic mass measurements were taken for some of the T-bolt specimens to track the water absorption process (Nunemaker et al 2018).…”

Static and Fatigue Characterization of Large Composite T-Bolt Connections in Marine Hygrothermal Environments

“…It is well known that FRPs suffer from varying degrees of degradation when subjected to marine environments [5][6][7][8][9]. Degradation is initiated through water diffusion into the polymeric matrix materials, which is analogous to heat diffusion, and typically presents itself as static and fatigue strength degradation.…”

“…These diffusion mechanisms and resulting strength degradation are well understood [10][11][12][13], but extensive mechanical characterization at the coupon scale is required to properly design large FRP structures for marine environments. However, most coupon-scale studies mainly focus on comparing only dry and fully saturated laminates [9], with little focus on partially saturated laminates. Also, little to no research has been performed to understand how coupon-scale degradation data translate into larger-scale structures with thick FRP laminates [3,14].…”

Leveraging the Advantages of Additive Manufacturing to Produce Advanced Hybrid Composite Structures for Marine Energy Systems

“…Composite materials, such as fiberglass/epoxy, are an attractive material choice for marine energy systems because of their low cost, high stiffness and strength, and resistance to environmental degradation [2]. Material density and structural mass are of lower importance because the structures are submerged underwater where buoyancy forces offset gravity-induced forces.…”