Experimental Investigation on the effect of water ingress on the flexural and interlaminar properties of glass/vinylester composite for marine applications

Abstract

Fibre-reinforced polymer (FRP) composite materials find increasing acceptance and application in a number of transport sectors due to their lightweight nature, which provides a significant advantage in terms of lower fuel consumption and greenhouse gas emissions, in line with relevant EU directives. Particularly in the marine industry, FRPs are currently dominating the manufacture of vessels up to 50 m in length, with liquid resin infusion (LRI) being the most frequently used manufacturing technique and vacuum-assisted resin transfer moulding (VARTM) in particular the most widely adopted LRI variant. The wide-scale adoption of FRPs into large marine structures is often hindered by the lack of guidelines available for qualification of these materials by classification societies, particularly in relation to fire safety. FIBRESHIP is a Horizon 2020 funded EU project that aims to further the use of FRPs in long-length ship construction by addressing this issue in addition to tackling numerous other challenges associated with manufacturing FRP composite ships. It is important to characterise fully the performance of new commercially available marine resin systems as a potential candidates for selection in composite ship construction. This needs to be done under a wide range of environmental conditions, as durability of composites and their ability to exhibit unchanged performance and stability in a marine context and environment is a crucial factor in their selection. Ideally, a composite would retain its mechanical and thermo-mechanical profile even when exposed to a marine environment for extended periods. During the service life of marine composites (typically 20-25 years), water uptake is inevitable. This may cause plasticization, swelling, matrix hydrolysis or debonding of fibres from the matrix. As a result, the mechanical and thermal properties degrade accordingly, and the service life is shortened. This work represents part of a selection process for materials for the construction of long-length ships from FRPs and focuses on a commercially available fireretardant composite system (SAERTEX LEO®). The aim of the study is, therefore, to compare the flexural (ISO 14125) and interlaminar shear (ISO 14130) properties of the SAERTEX LEO® composite system under dry conditions and under “wet” conditions where the specimens have been immersed in deionised water at 35°C for varying durations (28 days, two months, three months). The flexural and interlaminar properties will also be assessed after soaking for 28 days, two months and three months followed by a drying process to remove all ingressed water. This will give an indication of the reversibility of the effects of water ingress and highlight the point at which permanent alteration of the properties begins to occur. Unidirectional laminates are manufactured by VARTM using the Saertex LEO Glass/Vinyl ester system (the system includes a fire-retardant gel coat, however the gel coat was not applied for the purpose of obtaining the mechanical properties of the FRP component of the system only). Dynamic Mechanical Analysis (DMA) is performed to establish that the laminates have been fully cured and fracture mechanisms are examined using scanning electron microscopy.

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