Tensile and bending properties of sandwich films of carbon fiber reinforced thermoplastics‐polypropylene sheet processed by a simple hot‐press method

Abstract To develop a material with strong impact resistance, bending direction and in‐plane direction, the tensile and bending properties of sandwich films obtained by placing and re‐pressing a compression‐molded polypropylene sheet between two sheets of carbon‐fiber‐reinforced thermoplastics (CFRTPs) were evaluated. Three types of CFRTP were investigated, and thermoplastic nylon 66, polyurethane, and polyphenylene sulfite were used as the resin base materials to wrap the carbon fiber. Regarding the tensile properties of the sandwich films, the Young's modulus and maximum stress values were lower compared with those of the CFRTP sheets, regardless of the resin base material. However, improvements in elongation properties of 97%, 109%, and 156%, respectively were found, transforming the film into a softer and stronger film. Regarding the bending properties of the sandwich films, the Young's modulus and maximum stress values were higher compared with those of the CFRTP sheet. To examine the influence of the number of layers, the five‐layer sheet, in which the sandwich film was placed in two CFRTP sheets, exhibited inferior elongation properties to the three‐layer sheet during the tensile test. However, the results of the bending test found a significant improvement in Young's modulus of approximately 2.5 times and final strength of approximately three times. We anticipate that this material could be applicable to components requiring specific mechanical properties in both bending and in‐plane directions in future applications. Highlights CFRTP sandwich sheets were fabricated using a simple hot‐press method. The sandwich sheet showed improved mechanical properties in the in‐plane directions. Both the tensile modulus and the bending modulus have reached the GPa‐order. The sandwich film in question had particularly excellent bending properties. The sandwich film showed dependence on the number of layers. In‐plane elasticity of the films was evaluated using a falling ball test.