A highly efficient joining method using ultrasonic welding is required for the manufacturing and processing of thermoplastic carbon fiber-reinforced plastic (CFRP) structures. Herein, the application of resin mesh as a sheet-like energy director is proposed, and its feasibility is assessed. The relationship between the welding conditions and the tensile shear strength was investigated using single lap joint specimens prepared by ultrasonic welding. The fracture surface observations indicated that resin mesh melting occurred from the end of the specimen, whereas the unmelted zone remained at the center of the welding surface. It was necessary to supply a sufficient amount of resin to the welding surface and select a resin mesh suitable for the welding conditions to minimize variations in the bonding strength. Under the welding conditions used herein, the specimens with the coarsest resin mesh showed an average tensile shear strength of 34 MPa and a coefficient of variation of 0.1. From these results, it was concluded that the application of a sheet-like energy director for the ultrasonic welding of thermoplastic CFRP is a promising method to achieve a practical level of bonding strength.
This study aims to propose a new joint technique to improve the static and fatigue durability of the bolted joint of a carbon fiber reinforced thermoplastic (CFRTP) plate. A pair of steel plates called “bite plates” was prepared; the plate surfaces were machined using a V-shaped cutter. Three types of polypropylene (PP) film were pressed, which included normal PP film and PP film modified by the addition of 0.5 or 1.0 wt% sub-micron glass fiber. A CFRTP plate and pair of bite plates were used to assemble the joint specimen using heat pressing with the paired PP film. Specimens of each bite plate and PP film were used for tensile shear and tensile-tensile fatigue tests. Test results demonstrated that the joint efficiency and fatigue durability were improved by using a bite plate and modified PP film. A detailed investigation of the joint under a loading condition revealed that the load transfer along the width direction of the specimen was enhanced by using a bite plate. The fractured surface observation also revealed that the interfacial shear strength between the PP and carbon fiber was improved. As such, our joint efficiency improvement mechanism was validated by the enhancement in the load transfer to the surface of the CFRTP due to the increase in its interfacial shear strength.
The effect of molding condition on the resin impregnation behavior and associated mechanical properties were investigated for plain woven carbon fabric reinforced thermoplastic polyimide composites. Resin impregnation was accelerated with increasing molding temperature and pressure. At molding temperatures above 410ºC, resin impregnation remained unchanged with change in temperature. Tensile test results indicated that modulus and strength increased with resin impregnation. Resin impregnation was predicted using analytical models and it was found that the analysis could successfully predict the impregnation behavior, despite the difference in molding pressure and temperature.
Mechanical properties of semi-crystalline polymers and composites with a semi-crystalline thermoplastic matrix are highly dependent on the crystallinity and crystalline morphology. The cooling rate from the melt has the greatest effect on this along with other processing conditions. The objective of this study is to evaluate the effects of the cooling rate on the mode I and II fracture toughnesses of the composites with the semi-crystalline thermoplastic matrix. Carbon fiber/polyphenylene sulfide (CF/PPS) composites were fabricated using varying cooling rates. These rates ranged from 1 to 300ºC/min. The degree of crystallinity in the CF/PPS composites was determined using differential scanning calorimetry (DSC). Double cantilever beam (DCB) and end-notched flexure (ENF) tests were performed on the specimens to evaluate the fracture toughnesses of the CF/PPS composites with different cooling rates. Furthermore, the effect of the cooling rate on the mode I and II fracture morphologies of the CF/PPS composites is discussed.