Session: 01-07: Nonlinear Problems in Aerospace Structures

Paper Number: 137503

137503 - Manufacturing of Ultra-Thin Thermoplastic Composites for Deployable Space Structures 

Current projects for space structures envision ever larger and more sophisticated architectures which, due to the available launch vehicles, require in-orbit deployment. To reduce weight and complexity of the deployment system, Carbon Fiber Reinforced Polymers (CFRPs) have been employed in several successful missions, namely NASA's DART and ROSA. More ambitious applications of the technology, in particular the Caltech-based space solar power project, conceive hundreds of deployable composite components. The required flexibility for packaging and rigidity for deployment are achieved by layering only a few laminas, each tens of microns in thickness. As a result of the restricted design space caused by the small number of layers in the laminate, the choice of matrix phase greatly influences the material properties of the composite shell. These factors have sparked increased interest in less-conventional polymers phases, such as thermoplastics.

Aerospace-grade thermoplastics, such as Poly Ether Ether Ketone (PEEK), have many advantages compared to thermosetting resins. Some of the benefits include the ability to be shaped and bonded after crystallization in the reinforcement phase, improved ultimate strength, enhanced fracture toughness, and indefinite reprocessing cycles. However, these polymers entail the drawbacks of higher cost and, more crucially, manufacturing challenges. Indeed, the manufacturing temperature of thermoplastics is two to three times larger than most thermosets (for PEEK 360-400C) and their viscosity is also orders of magnitude greater than thermosets. As a result, impregnation of fibers during the compaction of laminas is challenging and commonly used techniques and equipment for composite fabrication are not suitable due to these higher temperatures.

Considering the objective of high-quality flexible composites, this presentation illustrates the manufacturing processes to laminate a novel thermoplastic-carbon fiber Uni-Directional (UD) pre-preg produced by Sakai Ovex. Common thermoplastic pre-pregs have an aerial weight of 145gsm, while this PEEK-CF lamina is one of the thinnest available on the market, with an aerial weight of 67.6gsm and compacted thickness of 50 microns. A staggered stacking sequence of the UD tapes, along with spot-welding of the matrix at the laminate's corners helps maintain the fibers orientation during compaction, while sandwiching the composite between kapton layers provides remarkable surface finish. A symmetric vacuum bagging sequence and thin steel shims are also shown to achieve equal layer thicknesses and uniform compaction, thus reducing voids. Standard mechanical testing and micro-CT scanning of the produced specimens are used to evaluate material properties and assess the final quality of the laminates. In addition, to gain more insight in the stacking sequences of PEEK-CF laminates that could be used for deployable structures, the Triangular Rollable And Collapsible (TRAC) boom geometry is selected as an example. To this regard, both analytical calculations and finite element simulations are employed to perform failure analyses and confirm the applicability of the thermoplastic polymer phase to the technology. 

Presenting Author: Federico Benazzo California Institute of Technology

Presenting Author Biography: Federico Benazzo is a graduate student at Caltech's department of Aerospace engineerig, working on ultra-thin thermoplastic composites for deployable space structures. He graduated from the Univeristy of Michigan, where he worked on a joint research project between UofM and the Politecnico of Milan on self-healing composite materials. The research, which was published in a number of papers, focused on enhancing the fiber-matrix interfacial properties of the mendable composite system and creating a multifunctional material by incorporating optical fiber sensors to monitor the degree of self-healing. His focus has now shifted towards the manufacturing techniques of carbon fiber reinforced PEEK pre-pregs to enhance the design space of thin flexible shells for space deployables.