Abstract

This work proposes a calibration procedure to obtain the material parameters required by the Serial/Parallel Mixing Theory for the analysis of composites. A set of experimental tests are defined to obtain the main composite failure modes. Then, it is proposed to calculate the parameters required by the formulation using the experimental results. The procedure proposed is validated by comparing the numerical results, with those obtained from the experimental campaign. This comparison shows that the Serial/Parallel mixing theory is capable of representing the failure modes of the composite for different loading scenarios as well as the material toughness.

Abstract

Glass-fibre reinforced polymer (GFRP) laminates were manufactured using Vacuum assisted Resin Transfer Moulding (VaRTM) with a range of thermosetting resins and a novel infusible thermoplastic resin as part of a comprehensive down-selection to identify suitable commercially available resin systems for the manufacture of marine vessels greater than 50 m in length. The effect of immersion in deionised water and in an organic liquid (diesel) on the interlaminar shear strength (ILSS) and glass transition temperature (Tg) was determined. The thermoplastic had the highest Tg of all materials tested and comparable ILSS properties to the epoxy. Immersion in water, however, caused larger reductions in ILSS properties of the thermoplastic compared to the other systems. SEM showed a transition from matrix-dominated failure in the dry condition to failure at the fibre-matrix interface in the wet and organic-wet specimens. The overall performance of the infusible thermoplastic is good when compared to well-established marine resin systems; however, the environmental performance could be improved if the thermoplastic resin is used in conjunction with a fibre sizing that is tailored for use with acrylic-based resin systems.

Abstract

Glass-fibre reinforced polymer (GRP) composite materials are the most widely adopted amongst fibrereinforced polymer composites globally, with approximately 1 million tons produced annually in the EU alone. GRP’s find very wide use and application in a number of industrial sectors (e.g. land & waterborne transport1 , marine, construction) due to their excellent balance between good performance and low cost compared to fibre reinforced polymers utilising other commercially available fibres (e.g. carbon, aramid). Particularly in marine applications, durability of composites and their ability to exhibit unchanged performance and stability in a marine context and environment is a crucial factor in order to select the most appropriate combination of polymer matrix and reinforcement. Ideally, a composite would retain its mechanical and thermo-mechanical profile even when exposed to a marine environment for extended periods. In this work, we conducted an extensive comparative study of the water absorption behavior and retention of mechanical properties of a group of GRP composite laminates manufactured with a range of infusible thermosetting and thermoplastics resins. Sample preparation for water immersion studies was according to ASTM D5229. This study was part of a comprehensive down-selection of commercially available resins in terms of their suitability for shipbuilding applications, as part of the EU H2020 project FIBRESHIP2 . All laminates were manufactured by Vacuum-Assisted Resin Transfer Moulding (VARTM; the most relevant manufacturing technique in shipbuilding) with a range of state-of-the-art thermosetting resins (Urethane acrylate Crestapol 1210, Epoxy SR1125, Bio-epoxy Supersap CLR, Phenolic Cellobond J2027X) and a novel infusible acrylic thermoplastic resin (Acrylic Elium 150). The reinforcement of choice for each laminate was a unidirectional glass fabric of 996 gsm. A selection of relevant properties of the laminates with different resin systems is presented in this paper including fibre volume fraction, apparent interlaminar shear strength (dry and wet condition), flexural strength (dry and wet condition) and flexural modulus (dry and wet condition). For the wet condition, samples were immersed in distilled water for 28 days at 35 oC (wet state) in accordance with classification society guidelines. The quality of the laminates (void content, fibre-matrix adhesion) was examined by scanning electron microscopy on fracture surfaces. The effects of water absorption on the microstructure, mechanical, thermal & thermomechanical properties of the laminates were studied. The average water absorption percentage varied across all resins systems from 0.19 to 1.37% in the interlaminar-shear specimens, and from 0.25 to 1.59% in the flexure specimens. The phenolic laminate was the one absorbing most water in both cases but the mechanical properties were relatively unaffected. Fibre volume fraction was in the range 0.56 to 0.6 for all of the laminates. The majority of the tested GRP laminates showed good retention of their flexural properties and interlaminar shear strength under the testing conditions. The laminate that appeared to be most adversely affected was the infusible thermoplastic, showing a reduction in flexural strength and interlaminar shear strength of 17.3% and 37.5%, respectively (in comparison to the dry state values). However, the water absorption for the Elium 150 was not excessive, ranging from 0.40 to 0.42% for the ILSS and flexure samples, respectively. References: 1 Summerscales J, Marine applications of advanced fibre reinforced composites, Woodhead Publishing, Cambridge, 2016 2 H2020 project FIBRESHIP, funded by the European Commission under GA 723360 (www.fibreship.eu)

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.

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/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 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.

Abstract

In the marine industry, Fibre-reinforced polymers (FRP) are currently dominating the manufacture of vessels up to 50m in length, with liquid resin infusion (LRI) being the most frequently used manufacturing technique, of which vacuum-assisted liquid resin infusion is the most widely adopted LRI variant. However, current regulations restrict the use of composite materials in vessels over 50m in length. FIBRESHIP is a Horizon 2020 funded EU project that aims to further the use of FRPs in vessels over 50m in length by addressing the regulatory restrictions and the numerous other challenges associated with manufacturing long-length FRP composite ships. The mechanical performance of new commercially available composite material constituents as potential candidates for selection in composite ship construction is central to this work. This paper provides an overview of selected work performed as part of the FIBRESHIP project in terms of evaluating various mechanical properties of selected laminates under dry and wet conditions. The laminates were immersed in seawater at 35°C for durations of one to three months. Three-point bend and interlaminar shear strength tests were undertaken in order to investigate the change in the mechanical properties of composite laminates subject to immersion. Finally, tested specimens were observed using micro-computed tomography (μCT) to evaluate the failure morphology.

Abstract

One of the main restrictions in adopting polymer composite materials for primary and secondary structural applications in marine vessels over 50 meters in length is concerns regarding fire retardancy and also a lack of design guidelines in general. The aim of this study is to evaluate the edgewise compression strength and core-shear strength of a fire retardant sandwich structure reinforced with through thickness composite ‘bridges’ under ambient conditions. These properties are important for structural components subjected to in-plane loads such as bulkheads. Core shear strength of the through-thickness reinforced sandwich far exceeded non-reinforced sandwich. However, edgewise compression strength and stiffness of the reinforced case was found to be similar to the unreinforced case.