Experimental Investigation on the effect of thickness on the flexural properties of glass/vinyl-ester composite laminates for marine applications

Abstract

Fibre-reinforced polymer (FRP) composite materials find increasing acceptance and application in a number of transport sectors (aviation, land & waterborne transport) 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 waterborne transport and shipbuilding, FRP composites 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 FRP composites into large marine structures is often hindered by the lack of guidelines available for qualification of these materials by classification societies. FIBRESHIP is a Horizon 2020 funded EU project that aims to further the use of FRP composites in long-length ship construction by addressing this issue in addition to tackling numerous other challenges associated with manufacturing FRP composite ships. This work represents part of a selection process for materials for the construction of long-length ships from FRP composites and focuses on a commercially available fire-retardant composite system (SAERTEX LEO®). As part of the selection procedure for these materials, material properties, such as the flexural strength and modulus, are obtained using coupon-sized test-pieces and are subsequently used as the basis for numerical models for ship design. However, the actual material that is used in the final ship structure is significantly thicker than the coupons from which the original material properties were derived. Additionally, the scale of the manufacturing process of laminates for the extraction of coupons is drastically different to that of the manufacturing process of a ship’s hull. The aim of the study is, therefore, to compare the flexural properties obtained from a thin monolithic laminate manufactured in a research laboratory (University of Limerick, Ireland) to the flexural properties obtained from a thick monolithic laminate representative of the thickness of a ship hull manufactured in a shipyard (iXBlue Division H2x, Marseille, France) using the same material under investigation. This will give an indication of how representative the thin test coupons are of the material manufactured by the shipyards at the thickness used in the final structure. Unidirectional laminates are manufactured in both the research and shipyard facilities by VARTM using the Saertex LEO Glass/Vinylester 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 on specimens from the thin and thick laminates to establish that the laminates have been fully cured. Three-point-bend tests in accordance with ISO 14125 are performed on 0° and 90° specimens extracted from thin and thick laminates. Another set of 0° and 90° specimens extracted from thin and thick laminates are tested according to Bureau Veritas guidelines (NR456) in order to investigate the comparison between the properties obtained using both methods. Fracture mechanisms in thick and thin specimens are examined using scanning electron microscopy.

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