Fibre reinforced polymer composite materials are extensively used for manufacturing piping, tanks, boats, bridge decks, under water cable terminations and other products used in wet and moist environment. The applications include marine, defence and oil and gas industry. Glass fibre reinforced plastics (GFRP) are one of the most commonly used composite materials due to their availability and cost effectiveness. Glass fibre composites are more durable and chemically stable in corrosive environments compared to other conventional materials like metals. They also provide high strength to weight ratio which is crucial in certain applications.The use of Glass fibre reinforced plastics (GFRP) in under water applications has been increasing in recent times. Due to its superior durability and chemical stability in corrosive environments, GFRP has been successfully replacing conventional materials like metals in such applications. But the penetration of moisture in to the polymer matrix can adversely affect the mechanical properties of composite materials. In this study, the effect of exposure to water and salt water on the mechanical properties of GFRP specimens has been analyzed. Tensile and 3 point bend tests were conducted on composite specimens with different moisture contents to characterize the mechanical degradation due to moisture absorption. Gravimetric tests were conducted on specimens to calculate the moisture absorption parameters. The results indicate that water is absorbed at a faster rate compared to salt water. Using these parameters, a transient moisture diffusion model was developed using commercial finite element software ABAQUS®. Further, a coupled hygro-mechanical model was developed in ABAQUS® and the simulation results were compared with actual test results. Scanning electron Microscopy was used to examine the fracture surface of failed specimens. The reason for mechanical degradation seems to be the deterioration of fibre-matrix interface due to the penetration of water molecules.The specimens were exposed to water and salt water separately and mass gain due to moisture absorption was plotted. It was observed that water was absorbed at a faster rate compared to salt water by the GFRP specimens. The maximum amount of moisture absorbed at saturation condition was also higher for water (1.8%) compared to salt water (1.5%). The reason for this observation could be the presence of massive ionic species in salt water and are in conformity with results published in literature. The moisture absorption in both the media seems to follow a Fickian model. The diffusion coefficient and moisture absorbed at saturation point values were calculated from experimental results. These values were used to develop a transient moisture absorption model in finite element software ABAQUS. The modelling results were in agreement with experimental values. The model also gave moisture distribution through the specimen. Tensile tests and 3 point bend tests were conducted on specimens with different moisture contents to characterize the mechanical degradation due to moisture absorption. The results indicate that both tensile and flexural properties of composite specimens degrade with exposure to moisture. The specimens soaked in water and salt water showed comparable degradation in properties for the equal amount of moisture absorbed even though exposure durations were different. This indicates that for both water and salt water media the degradation mechanism is the same. This observation is in agreement with literature. A coupled hygro-mechanical model was developed using finite element software ABAQUS. The moisture distribution obtained from the transient mass diffusion analysis was used as a predefined field variable and the modulus value was defined as a field dependent material property. Tensile and 3 point bend tests were simulated in ABAQUS. The Stress-Stress curves from the simulation are in good agreement with experimental curves in the linear region. Therefore the method can satisfactorily model stiffness degradation of composites due to moisture absorption. Scanning electron microscopy (SEM) of fracture surface revealed that the degradation in properties could be due to the deterioration of interfacial bond between fibre and the matrix.

Effect of Moisture Absorption on the Tensile and Flexural Properties of Glass Fiber Reinforced Composite Materials

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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