Co-authors​ :

 Soma NISHIMURA (JAPAN), Daiki TANABE (JAPAN), Takeshi EGUCHI , Kazuaki NISHIYABU (JAPAN), Tetsusei KURASHIKI (JAPAN) 

Carbon fiber reinforced thermoplastic (CFRTP) composites which can be manufactured by press molding, hybrid injection molding and automated tape laying are attracting attention recently in next generation aircraft and automobile applications. However, CFRTP components have rather simple geometry due to the limited deformation allowed for the reinforcing fibers and high melt viscosity of thermoplastic. To enhance the stiffness property of these components, adding reinforcement ribs has been explored, particularly in the ubiquitous skin and stringer joints of the aerospace industry for fuselage structures [1]. Furthermore, higher strength and stiffness requirements in launch vehicles have prompted the consideration of an anisotropic grid namely anisogrid for improved load transfer [2]. Traditionally, manufacturing grid structures and rib structures using CFRP grids involves a time-intensive process of filament winding around a mandrel followed by curing process of thermosetting plastics. However, such methods require long manufacturing times and have problems with moldability.
Therefore, in this study, to solve these problems, authors proposed a new approach to fabricate CFRTP grid structures that can be manufactured in a short time using pultruded rods of thermoplastic CFRP [3]. To manufacture rib structures using CFRTP pultruded rods, it is necessary to join rods and laminates. Various welding technologies such as ultrasonic welding, resistance welding and induction welding have been proposed so far to weld high performance CFRTP members with high welding strength and reliability [4]. Among them, the ultrasonic welding has some advantages such as short welding time, low power consumption and ease of automation.
This study aims to development of CFRTP pultruded square bar reinforcement method for CFRTP laminates using ultrasonic welding and evaluation of welding strength. The materials used for welding experiment were UD-CF/PP pultruded rods and UD-CF/PP laminates. In this study, the ultrasonic welding parameters of CF/PP rods and laminates were investigated and evaluated to optimize the welding conditions. The ultrasonic welding device consists of a servo press unit that can precisely control load and displacement, and a 20kHz ultrasonic heating unit. A fillet was formed using a sonotrode made of silicone rubber and metal to reduce stress concentration at the welded part between the CF/PP rib structure and the laminate, To evaluate the joint interface after welding, the condition of the welding part was evaluated by cross-sectional observation and microscopic observation. In addition, the mechanical properties of the welded parts were evaluated using the tensile shear strength using a single lap shear strength test and the interlaminar shear strength using a short beam shear test. Furthermore, FEM was performed using structural analysis software to examine the validity of the values obtained from various mechanical tests.