Mechanical compression behavior of reinforced and unreinforced thermoplastic film materials as high-performance core layer for semi-finished sandwich products

Thermoplastic honeycomb cores for sandwich structures offer, in addition to high stiffness and low weight, further advantages such as recyclability, chemical resistance, and suitability for large-scale processing. These properties, combined with the broad range of characteristics offered by high-performance thermoplastics such as polyetherimide (PEI), polyphenylene sulfide (PPS), and polyether ether ketone (PEEK), make these materials promising for use in the aerospace industry. With this focus, this paper examined PEI films and carbon fiber-reinforced non-woven materials with PEI and PPS matrices to assess their potential as thermoplastic cores in sandwich structures. Assessing the performance of new material combinations requires adapted testing methods, since conventional characterization of sandwich structures is complex due to their multi-layered nature, especially with regard to the structured core layer. This work introduces a simplified test method for determining the compressive stiffness of film-like and paper-like non-woven thermoplastic core materials. The approach is based on curved compression tests at the coupon level and complemented by in situ computed tomography (CT) analysis of the thermoplastic sandwich at the substructure level, enabling the extraction of mechanical properties and the evaluation of failure mechanisms. Using ThermHex® honeycombs as an example and in comparison to Nomex® structures, the study demonstrates that thermoplastic sandwich semi-finished products hold high potential for efficient, sustainable, and high-performance lightweight applications in aviation.