PSI - Issue 25

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Dalbir Singh et. al. Structural Integrity Procedia 00 (2019) 000 – 000

Dalbir Singh et al. / Procedia Structural Integrity 25 (2020) 159–171

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resistance to corrosion, good static and dynamic properties, competitive cost and simplified fabrication. Nowadays, due to their high corrosion and fatigue resistance, reparability and customizability to the desired design shape, laminate composites are replacing traditional materials such as steel and aluminium alloys. During i t’s working life, these materials are exposed to different environmental conditions, which significantly affect their mechanical properties. In terms of moisture, the flexural strength and interlaminar shear strengths continue to degrade due to the water uptake effects on the vinyl ester and polyester samples. The water uptake effects were first noticed by suppression from the fi bre barrier and then later by enhancement from the interface (Gellert and Turley, 1999). (José-Trujillo et al., 2019) studied the effects on the mechanical properties of composites of different fibre/matrix when aged in seawater and reported that there is significant strength reduction due to seawater ageing on composites with epoxy and polyester matrices. On further analysis, it was concluded that the seawater severely affected the fibre/matrix interface. (Davies et al., 2017) Analysed the influence of seawater aging on the mechanical behaviour of acrylic matrix composites. They concluded that the thermoplastic acrylic resin under study was stable when immersed seawater at 60 0 C for up to one year. The drop in properties were found to fully recover after drying. Degradation of fibre/matrix interface was due to the non-optimization of fibre reinforcement to acrylic matrix. Carbon fibre/acrylic composites showed minimal change in tensile properties and the drop in properties of ± 45 0 composites was recovered after drying. The above conclusions suggest that acrylic resins are suitable for marine applications (Lb et al., 2008a). The Influence of immersion in different solutions deteriorates the mechanical properties and three factors, i.e. the test period, concentration and temperature are playing a key role. The most important factor among these is the temperature of the solution (Lb et al., 2008b). However, (Kaushal et al., 1991) observed that the concentration of water, temperature and types of matrix and fibre decides the rate of water absorption. When the samples were exposed to moisture, it reduced the interlaminar shear stress at higher rate fibre volume fraction, which ultimately resulted in the interfacial strength reduction. The glass-transition temperature decreases significantly due to penetration of water into the matrix at the interface between the fibre and resin it acts as a plasticizer. The presence of the plasticizer makes the matrix pliable and this phenomenon makes the composite softer (Reis et al., 2013). The higher temperature accelerates the diffusion process. In addition, a study of the effects of environmental conditions on fibre orientation angle and aging degradation of E-glass/epoxy, when exposure time increased, the flexural modulus and the flexural strength decrease. The authors also reported that the alkaline solution further decreased the flexural properties when compared to that of the acid solution (A. Amaro et al., 2013; Bookhound et al., 2006). (Mansouri et al., 2019) studied the effect of hygrothermal aging in distilled and saline water on the mechanical behaviour of mixed short fibre/woven composites. They observed that temperature aging and water absorption are important parameters that degrade the composites. Despite the unique mechanical properties of short fibre/ woven composites, their sensitivity to temperature and water; influences elastic properties and stiffness of laminate, gives them a huge disadvantage. (Selzer and Friedrich, 1997) investigated the effect of moisture on the mechanical properties of fibre reinforced polymer composites. For evaluating this effect these authors performed Tensile, Compression, Fatigue and Compression after-impact tests on two thermosetting matrices. They concluded that the mechanical properties decrease with the absorption of moisture with epoxy resin-based composite; this decrease mainly being controlled by the fibre/matrix interface and thermoplastic material was not affected by moisture. On this issue, (Akay et al., 1997) reported on the influence of moisture on the thermal and mechanical property of Kevlar -49/epoxy-resin laminates. They observed that the compression, inter- laminar shear and flexural strength had reduced around 5%, 4% and 2% respectively for every 1% of absorbed moisture. (Reis et al., 2012) found that the addition of cork powder significantly decreased of static and fatigue strengths of Kevlar/epoxy composites. In-service condition, the composite materials are also subjected to the effects of alkaline and acidic solutions along with the exposure to moisture. Evidence of this study can also be found in the following literature. (Banna et al., 2011) exposed composite materials to aggressive solutions and reported that the final mechanical properties are determined by the type resin used. They observed that the polyester resin has lower modulus value than the bis-phenol-A epoxy