Preliminary analysis of the effects of thermal cycling on the mechanical properties of Kevlar®/Epoxy tubular braided composites for use in satellite components

Satellites in low Earth orbit (LEO) are exposed to several hazardous conditions including large temperature fluctuations. Materials with non-zero coefficients of thermal expansion (CTE) can develop thermal stresses that lead to failure. Tubular braided composites (TBCs) are a customizable type of fiber reinforced polymer composite (FRPC) and are manufactured with high-strength fibers and polymer resins to create a cylindrical structure optimal for load bearing applications with a near-zero CTE. Despite this, TBCs have not been used in satellites, nor have they had the effects of thermal cycling on their mechanical behaviour evaluated. This preliminary work studied the effect of relatively low amounts of thermal cycling on the mechanical performance of Kevlar®/Epoxy TBCs to pre-emptively assess their viability in satellite structural applications. Samples made with one of three braid angles (35°,45°, and 55°) were exposed to either zero, five, or 10 cycles between −50 ℃ and 120 ℃ , before being tensile tested to find their elastic modulus and ultimate tensile strengths (UTS). Thermal cycling decreased the average elastic modulus and UTS of the 35° TBCs by 16.6% and 13.8% after five cycles, and 17.0% and 33.5% after 10 cycles respectively. The 45-degree TBC’s average elastic modulus and UTS increased by 8.9% and 7.3% after five cycles, then decreased by 25.8% and 22.2% after 10 cycles. The 55° TBC’s average elastic modulus and UTS decreased by 9.3% and 25.1% after five cycles, and 30.7% and 36.2% after 10 cycles. Normality and equal variance of the data were verified with Kolmogorov-Smirnov and Bartlett’s tests respectively. Single factor ANOVA tests were also used to verify the significance of change between the mechanical property averages and were succeeded by Tukey’s test to determine which specific pairs of averages were significantly different. Before TBCs can be used in satellites, further evaluation must be performed. This may include variation in materials, greater cycle counts, alternate cycle durations, or different temperature change rates.