Effect of fiber orientation and stress level on creep behavior of glass fiber reinforced epoxy composites

Glass fiber reinforced polymer (GFRP) composites, made of glass fiber and plastic, are widely used in structural applications because of their high strength and resistance to corrosion. But the orientation of the fibers and the level of stress have a major effect on their performance characteristics when subjected to constant stress. This paper experimentally investigates the flexural and flexural creep behavior of glass fiber-reinforced epoxy composites with varying fiber orientations. Composite laminates were made using the vacuum-assisted resin transfer molding (VARTM) process. The specimens with fiber orientations of 0°, 30°, 45°, and 60° were prepared and tested. Initially, static three-point bending tests were conducted to determine the ultimate flexural strength values. Creep tests were conducted at stress levels of 25%, 50%, and 75% of the maximum flexural strength for 120 minutes, based on these values. The results showed that the fiber orientation significantly affected both flexural strength and creep response. The specimens with a 0° fiber orientation showed the highest flexural strength as 133.1 ± 17.8 MPa and the lowest creep deformations which are 0.78 mm, 1.48 mm, and 2.69 mm for 25%, 50%, and 75% stress levels, respectively after two hours. On the contrary, the 45° fiber orientation showed the lowest strength as 63.2 ± 8.9 MPa and hence highest creep deformations which are 1.01 mm, 2.53 mm, and nearly 10 mm for 25%, 50%, and 75% stress levels, respectively. The 45° fiber-oriented sample was failed after nearly 2000 seconds which could not reach the two hours under 75% stress level. With an increase in the fiber orientation angle, the stiffness reduced and the displacement increased due to the dominance of matrix-dominated deformation mechanisms. As stress levels rose, the impact of fiber orientation intensified, leading to unstable creep behavior, especially in 45° specimens at a 75% stress level. The findings demonstrate that both fiber orientation and applied stress level must be considered in the design of GFRP components subjected to long-term loading conditions.