Strength Degradation of Glass Fibre Reinforced Polymer Sandwich Composites Under Hygrothermal Loading Conditions

Abstract

Glass fibre-reinforced polymer (GFRP) have been used as an alternative to steel in concrete due to high strength-to-weight ratio, high stiffness-to-weight ratio, and corrosion and fatigue resistance. The main environmental factors for the deterioration of GFRP sandwich composites are temperature, sunshine, water/moisture, alkalinity and load. Most of the early durability tests were carried out with reference to application of FRP (Fibre Reinforced Polymer) in aerospace industries. In this thesis an experimental investigation has been carried out to study combined effect of chosen parameters moisture and temperature & also to study the rate & magnitude of damage of GFRP sandwich structure composites under hygrothermal loading conditions. For achieving this objective an experimental setup was prepared. The sandwich structure composed of E-glass fibre, polystyrene (thermocol core) and epoxy resin were subjected to three point bending test to assess bending strength. Two thermocol cores with different thickness (8mm and 16mm) were investigated. The effect of core thickness and different bending pre-loads was assessed. It has been observed that the sandwich structure with higher core thickness withstand a higher bending load show less flexural stress and flexure modulus when compared with low core thickness. The bending pre-load also affect the degradation. Higher percent bending pre-loads lead to higher degradation in maximum flexure load as well as flexure modulus and flexure stress. The macroscopic and microscopic behaviour of sandwich structure immersed in water has been examined. Moisture uptake was monitored for up to 50 days showing percentage weight gain curves for samples of pure epoxy and sandwich structure with different core thickness. The apparent diffusivity values extracted from the weight gain were significantly greater for initial days for higher core thickness sandwich structure. Micro hardness (Vickers’s Hardness Number) is also found to be decreasing with respect to time for both pure epoxy and sandwich structures. An attempt to make relation between macroscopic and microscopic behaviour of sandwich structure has been made. Area fraction and circularity measurement of fibre using Image-J software on SEM-images have also been carried out.