Abstract

Carbon fiber reinforced polymer composites have been widely used in space industries for manufacturing of spacecraft structures, satellite‐panels and antennas. Composite materials in space undergo harsh environmental conditions. One of the most environmental effects during the life of a satellite antenna is thermal cycling during which the composite endures a large temperature difference between −196°C and +180°C, depending on operational condition. On the other hand, composite structures for space applications are often cured in an autoclave to achieve the required space grade quality which is limited and expensive. Therefore, fabrication of large structures using out‐of‐autoclave (OOA) with the same performance as autoclave with lower costs is of interest of many industries. Composite parts cured inside an oven have higher void content than the ones cured in the autoclave. This thesis aims to study the effect of thermal cycling on the mechanical and thermal properties of flat laminates made of unidirectional (UD) and woven fabric OOA materials as well as a sandwich panel. A toughened epoxy prepreg reinforced by carbon fibers was used to manufacture flat laminates by the hand layup and cured inside the oven. Coupon samples were cut and subjected to different number of thermal cycles (30, 60, 100, 150, 200, 350) by dipping into the liquid nitrogen (−196°C) and then transferring to the oven (+140°C). Afterwards, different material properties were measured including: interlaminar shear strength (ILSS) in three-point bending, viscoelastic properties (loss and storage modulus and tan δ) and glass transition temperature (Tg) in DMA, and coefficient of thermal expansion (CTE) in TMA. Besides, optical microscope was utilized to identify damages within the resin. It was identified that the thermal cycling can affect the examined properties by two competing factors: (i) excessive cross-linking in polymer chain due to post-curing at high temperature; (ii) micro-cracks formation due to the induced thermal stresses as a result of matrix/fiber CTE mismatch. It was found that the thermal cycling can cause microcrack formation and propagation around the voids in the laminate and affect its properties.