Study the Mechanical Properties and Fatigue Effect of Multilayer Woven E-Glass/Epoxy Composite under Constant and Variable Loading

Abstract

The present work studies the effect of adding woven E-glass fibers [0°/90°], 16 layers with 50% weight fraction to pure epoxy (matrix) on fatigue behavior under constant and variable loadings. The CNC water jet cutting machine was used to cut the composite samples with five fiber direction angles, such as (0°, 5°, 15°, 30°, and 45°). The tensile test was used to determine the composite material’s mechanical properties. The results showed that the composite material with 5° of fiber direction had the highest ultimate tensile stress, i.e., 353 MPa, and the highest Young's Modulus, i.e., 11940 MPa, compared to other samples with angles of (0°, 15°, 30°, 45°) of fiber direction. The sample with 5° angle was adopted in constant and variable fatigue loading tests. The fatigue test results under constant loading showed a 24.8 times fatigue strength improvement for composite material at 107 cycles compared to pure epoxy. The fatigue test under variable loading was conducted with two types of sequence loading program tests at a constant number of cycles at each stress level: high-low sequence loading with stress of 170-130 MPa with 10,000 and 20,000 cycles for each stress level and low-high sequence loading with stress 130-170 MPa with 10,000 and 20,000 cycle for each stress level loading and so on to failure. The results showed that the fatigue life under high-low sequence loading for both 10,000 and 20,000 cycles was less than that of the low-high sequence loading. Also, the results showed that Miner's rules were safe to calculate the damage of composite material used in this work where the damage was above one (D > 1).