Resistance Welding of Carbon Fiber Reinforced Thermoplastic Composites for Repurposable Applications

We propose to develop resistance welding (RW) technology for carbon fiber reinforced thermoplastic composites (CFR-TCs) based on innovative heating element technology. A proposed target for these innovations is repurposable aerospace applications. Historically, CFR-TCs were not considered as the material of choice for aerospace applications despite their excellent specific strength and modulus. Instead, CFR- epoxy composites have been extensively used primarily for their ease of manufacture and excellent specific properties. However, they pose a great challenge to be recycled, reused, and repurposed. However, CFR-TCs can be reheated and remelted which makes it possible for them to be reshaped, repaired, recycled, and repurposed. Structures must be joined together and fusion welding of CFR-TCs is a method that takes advantage of the reheatable nature of thermoplastics. Bonding is achieved by heating the CFR-TC surfaces to above the melting or glass transition temperature while applying a clamping pressure. RW involves placement of a resistive material (heating element) between two workpieces and heating it with an electric current while applying a clamping pressure to ensure good contact and efficient thermal conduction. The localized heating melts the workpiece’s surfaces and mixes materials through diffusion, penetration, entanglement of thermoplastic polymer chains, and carbon fiber migration at the interface. However, poor shear strength between the bonded surfaces has been a continuing problem. The proposed project will seek to create a 3D strength pattern at the bonded surface to increase shear strength in the joint. RW, with the proposed improvements, offers unique advantages, such as 3D joint strength, less requirement of equipment, direct conversion from electricity to heat, and efficient localized heating, all of which can be significant for an application like repurposing materials for deep space exploration applications in which resources are very limited.

Resistance welding of thermoplastic composites, with the proposed improvements, offers unique advantages, such as 3D joint strength, less requirement of equipment, direct conversion from electricity to heat, and efficient localized heating, all of which can be significant for an application like repurposing materials for deep space exploration applications in which resources are very limited. The proposed work offers NASA opportunities for unique structural designs both on mission startup and mission evolution.

The fabrication of thermoplastic composite structural elements such as beams, trusses, and columns require a means of connecting to other structural elements. Companies whose business is the manufacture and/or construction of composite structures would have immediate need of connection technologies such as resistance welding as proposed herein.

This is early/mid-stage (TRL 4) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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