Thermal cycling of composite laminates made of out-of-autoclave materials

Abstract

Carbon fiber-reinforced polymer material has been widely used in space/aerospace industries for manufacturing of spacecraft structures, satellite panels and antennas. In space, composites can be subjected to periodic thermal cycling (TC) in which temperature ranges from −196°C to 180°C, depending on the operational condition. The effect of TC on the properties of flat laminates made of unidirectional (UD) and fabric out-of-autoclave (OOA) material will be presented. Flat laminates were made using the recommended cure cycle by the material supplier. Then, the samples were cut and subjected to the thermal cycle. To do so, the samples were dipped into liquid nitrogen (−196°C) and then transferred to the oven (140°C). After different numbers of cycles (30, 60, 100, 150 and 200), the cross section of the specimens was examined under a microscope for microcrack detection. Other mechanical and physical properties including interlaminar shear strength, storage modulus and coefficient of thermal expansion (CTE) were measured. It was identified that TC can affect the examined properties by two competing factors: (i) more cross-linking in the polymer chain due to post-curing at high temperature during TC and (ii) microcrack formation due to the induced thermal stresses as a result of the matrix/fiber CTE mismatch. It was found that TC can cause microcrack formation and propagation around the voids in the laminate and affect its properties. Depending on the size and shape of the void, microcracks can form at different stages of TC.

Keywords

• microcracks
• out-of-autoclave composite material
• thermal cycling