Experimental and numerical investigations on microstructures and mechanical properties of hybrid fiber reinforced thermoplastic polymer

Organic sheet overmolding injection (OSOI) is an integrated manufacturing process in which thermoplastics or composites are injected directly on the back of thermoformed organic sheets. It is one of the most promising processes to obtain lightweight structures with excellent mechanical properties and complex geometry. Microstructures, mechanical properties and bonding mechanisms of the interface between injection and thermoformed composites were investigated using SEM analysis, nano-indentation tests and molecular dynamics simulation, because the interface may be the weakest layer due to the pores, inclusions and thermal-expansion coefficient mismatch. SEM results show that the interface microstructures can be categorized into three kinds of features, that are wavy, bubble, and diffusion configurations, respectively, and they are greatly influenced by the preheating temperature of laminates. By appropriate preheating, the equivalent interface elastic modulus increases approximately 2.3 times. Moreover, the bonding mechanisms of the interface of preheated specimen include micro/nano scale mechanical interlocks, diffusion reaction, Van der Waals force and electrostatic interaction. This research could serve as a foundation for the application of hybrid fiber reinforced thermoplastic polymer.