Assessment of Thermoplastic Composite Joining by Resistance, Induction, and Ultrasonic Welding

The NASA Game Changing Development (GCD) program, Thermoplastic Development for Exploration Applications (TDEA) project was initiated to advance NASA’s capabilities to manufacture, model, and design with thermoplastic composites in support of future exploration missions. Recognizing that joints are a challenge area in many NASA applications using thermoset matrix composites, the project worked to develop structurally efficient joints for large scale thermoplastic composite space structures.

Thermoplastic composites are well suited for manufacturing large, lightweight aerospace structures through fusion bonding processes. Fusion bonding, or welding, refers to heating a thermoplastic joint at the bondline, providing time and pressure as required for polymer chain reptation across the weld interface, and cooling under pressure to solidify the joint. Several methods for welding thermoplastic composites are available however the three often used in aerospace include resistance, induction, and ultrasonic welding. The goal of this work is to evaluate the requirements, benefits, and constraints of these three welding methods to join four candidate thermoplastic composite material systems. Lap shear coupons were welded by each method on a per coupon basis. The weld area was limited to the 2.54 cm by 2.54 cm coupon overlap region to provide an assessment of the reproducibility of each weld process and the influence of edge effects. The outcome of this work includes the apparent lap shear strength of each material and weld method, an assessment of the reproducibility of lap shear strength produced by each method, material effects, and examination of edge effects through non-destructive evaluation.