In Situ Joining of Unidirectional Tapes on Long Fiber Reinforced Thermoplastic Structures by Thermoplastic Automated Fiber Placement for Scientific Sounding Rocket Applications

Automated Fiber Placement allows the automated lay-up of tailored laminates in aerospace quality. For thermoplastic matrix materials, the use of closed-loop temperature control enables an in situ consolidation. This makes autoclave curing superfluous and increases the overall process efficiency. Scientific sounding rockets typically consist of several aluminum modules carrying the scientific payload. The design of a module includes a cylindrical outer shell and two load input rings with a defined assembly interface. Reducing the structural weight would allow higher payloads, higher apogees or reduced fuel consumption. A new manufacturing concept using the Thermoplastic Automated Fiber Placement (TP-AFP) process was developed to manufacture a lightweight composite module. This paper presents the developed concept and focuses on the characterization of an in situ joint of TP-AFP tapes on a long fiber reinforced thermoplastic (LFT) structure. This represents the joint of the cylindrical shell on the load input rings of the rocket module. The joint was characterized with single lap shear tests for two different sample extraction areas at room temperature and at elevated temperature on pre-treated and untreated LFT surface. The variations did not show significant effects on the resulting shear strength. The results were considered for the design of the composite module allowing a weight reduction of more than 40 % compared to the aluminum modules. The new module proved its airworthiness as part of the sounding rocket mission REXUS-23 in March 2019. Beyond sounding rockets, the concept of in situ bonded TP-AFP tapes on complex LFT structures has many potential applications within aerospace but also automotive structures.