College of Engineering
Materials Engineering Department
BS in Materials Engineering
Epoxy matrix composites are widely used in aerospace industry for lighter aircraft while thermoplastic-matrix composites have traditionally been underutilized despite their excellent fracture resistance, impact strength, and the ability to be recycled. Toray Advanced Composites (Morgan Hill, CA) wants to investigate the structural integrity of thermoplastic matrices in common aircraft operating environments. An experiment was conducted to observe the effect of moisture absorption on thermoplastic composites’ mechanical strength. PEEK, PPS, and PEI matrices were compared to an epoxy matrix in this experiment. Samples were submerged in 160ºF distilled water to accelerate moisture absorption. For two months, the changes in mass and dimension were recorded at frequent intervals to compare the absorption characteristics of each matrix. Short-beam shear tests were conducted weekly to examine moisture’s effect on interlaminar shear strength. Results indicated that epoxy had significantly higher saturation point and dimensional strain compare to the thermoplastics. At saturation, epoxy also had a greater decrease in interlaminar shear strength (34.0%) than the thermoplastics (PEEK: 9.11%, PPS: 16.24%, PEI: 10.18%). The coefficient of moisture expansion (CME) for each material was the slope of a linear trendline through a percent moisture content versus percent strain plot. Epoxy had the highest CME of 1.075, followed by PPS: 1.012, PEI: 0.532, and PEEK: 0.192. Although not directly proportional, higher CME seemed to correlate with higher strength loss.