Effect of CNT on Welding Strength of Resistance Welded CFRTP Using Carbon Fiber as Heating Element

Abstract

One of the joining methods of carbon fiber reinforced thermoplastics (CFRTP) is a direct resistance heating method and we have reported that the tensile lap-shear strength and flexural strength were improved by using carbon nanotube (CNT) grafted carbon fibers as the heating element for welding. In order to reduce the weight of CFRTP structural parts, further improvement of welding strength is needed to reduce the welding area where materials overlap. CNT/polyamide 6 (PA6) composite nanofibers in which CNTs are dispersed in PA6 nanofibers had successfully been fabricated. By using this CNT/PA6 composite nanofibers as the matrix resin of the heating element for welding, further improvement of welding strength can be achieved. In this study, the tensile lap-shear test and flexural test were carried out by using carbon fibers and CNT grafted carbon fibers as the heating element and CNT/PA6 composite nanofibers as the matrix resin for welding; in order to clarify the effect of CNT on the welding strength of resistance welded CFRTP. The welding strength was improved by using CNT/PA6 composite nanofibers with the decrease of void content in the welded zone of resistance welded CFRTP. Moreover, the lower void content and the higher welding strength were obtained when CNT grafted carbon fibers and CNT/PA6 composite nanofibers were used for the heating element and the matrix resin for welding. Due to the reinforced resin by CNTs in CNT/PA6 composite nanofibers and the improvement of the fiber/matrix interfacial shear strength by CNT grafting on the surface of the carbon fibers, the welding strength of resistance welded CFRTP was improved.