With the future use of thermoplastic composite (TPC) helicopter parts, recycling, repairing and reuse of used composite parts become within reach. In order to recycle used parts of an assembly group the joints have to be detachable.
Disacop investigated a thermoplastic separation scenario that allowed disassembling the parts of a structure by fusion debonding for recycling. Due to the thermoplastic behavior of the TPC components, the fusion zone can be weakened by temperature. To ensure component separation at the joining interface between the components a special separation layer was investigated if necessary. The separation was intended to be without degradation of the TPC parts. For economic and environmental reasons the heating was limited to local heating of the joining zone. The possible joining and separation layer was intended to be used as a heating element as well.
Based on the available demonstrators, Disacop identified a method to locally apply heat and to debond the assemblies. An energy-efficient technology is induction heating.
The approach was to perform first trials on available coupons and subcomponents from the industrial partners to understand the process effects on real joints. Then the technology was fine-tuned based on the requirements coming from the industrial partners, first on coupon level. Subsequently, the technology were scaled up to subcomponents/ validation articles and the demonstrators.
To prove the environmental benefits of the Disacop separation method data for life cycle assessment was collected, for economic assessment a cost analysis for evaluation has to be made.
Thermoplastic matrices for fibre reinforced polymers have become very popular. So-called thermoplastic composite materials (TPC) offer great potential regarding weldability, thermoformability and recyclability when compared to thermosets. Consequently, the manufacturing costs of such parts are reduced hence augmenting their economic value. Furthermore, their storage life is not restricted and they are known for their excellent toughness and chemical resistibility.
For mainly these reasons, a rising attention for aerospace applications can be noted. Typical shell constructions, in which many stiffeners and panels are joined to complex structures, can be built in a much more integral and weight efficient way with the help of fusion bonding techniques. The advantage of fiber reinforcement can be fully exploited, as holes and rivets become unnecessary.
This study investigated the possibility of disassembling such integral structures for recycling purposes. By inverting the fusion bonding process, single elements can be detached from the main structure and in the best-case scenario reused in a refurbished component. The focus lied hereby on the assessment of the best suitable heating method. Preliminary tests on coupon level had been conducted to gather the main drivers. Hereby, the resistance heating method in which a conducting material is placed within the interface region of the bond had been identified as most promising technique. Fracture mechanical tests were conducted as well in order evaluate the impact of the separation process on the parts. Finally, the separation process was adapted on demonstrator level, where an omega-stringer-stiffened panel is disassembled.