Prepreg technology generates air pockets at the interface of laminates under heating and pressurization. The air pockets cause defects in the through-thickness direction. This includes poor adhesion between layers, which degrades material properties. Therefore, in this study, cryogenic mechanical properties were compared to obtain uniform properties by using prepreg laminated and resin film infused glass fiber reinforced plastic (GFRP) composites (“PP-only” and “RF-only”, respectively) while maintaining the constituent contents of the fiber and polymer. Moreover, stepped repair was applied to extend the life of composites. The results demonstrated that the stiffness of the composites improved, and the brittleness increased in cryogenic environments. In the case of PP-only, numerous voids were observed inside the polymer, which showed higher bending strength than RF-only; however, it exhibited significantly lower interfacial bonding strength. When applied to secondary bonding of stepped repair, RF-only as repair layers showed high strength recovery rate in homogeneous materials, and not in heterogeneous materials. In contrast, the high strength PP-only as a parent material and RF-only as repair layers showed relatively good interfacial bonding strength due to primary damage in the PP of a parent material. Hence, the RF-only can be considered useful as a repair material.
The Impact of Surface Treatment and Degree of Vacuum on the Interface and Mechanical Properties of Stainless Steel Clad Plate