Effect of Applied Pressure on Induction Welded Thermoplastic Composite Joint Quality and Performance

Abstract

Growing demand for the next generation of aircraft used for commercial and defense applications has motivated the adoption of novel strategies to reduce airframe weight, manufacturing process cycle time, and overall cost. The solution for decreasing weight, cycle time, and cost often relies on the inclusion of automation and the implementation of new materials that allow advanced processing techniques to be leveraged. Reinforced thermoplastic composites are an attractive material solution for many aerospace applications due to their ability to reduce manufacturing cycle time and cost. Additionally, thermoplastic composites have superior toughness and environmental resistance compared to thermoset composites and offer the ability to eliminate or decrease the use of mechanical fasteners at joints by fusion welding. Out of various approaches, induction welding of unidirectional reinforced thermoplastic composites offers the most robust solution for scaling-up the technology for developing automated process for large structures. Due to the conductive nature of the carbon fiber reinforcement in each substrate, the material itself can be heated and welded without the addition of any foreign material at the interface of a joint to generate heat. Several critical processing parameters were identified during the initial induction welding trials, with the applied pressure playing a significant role in the quality and performance of the weld. When the material is heated, the joint must be held under enough pressure to prevent deconsolidation of the substrate, while preventing application of excessive pressure that may cause fiber distortions or resin bleed out. After the appropriate applied pressure was established, induction welded single lap shear strengths were compared to autoclave consolidated baseline strengths.