Thermoplastic sandwich cylindrical structure with hierarchical honeycomb core: Dynamic/static compression and compression-after-impact behavior

Abstract

Sandwich cylindrical structures, appreciated for their lightweight, high specific strength, excellent energy absorption, and crash resistance, are gaining popularity in aerospace, automotive, and marine industries. Initially, these structures were mainly made of metal or thermosetting composites. Using thermoplastic composites in fabrication highlights a significant step towards better performance. However, constructing thermoplastic sandwich cylindrical structures meets some challenges due to the difficulties in joining thermoplastic composites and the limited reshaping options before curing. In this research, we develop a method that includes a snap-fit technique and a self-reinforced technique to produce thermoplastic sandwich cylindrical structures with a hierarchical honeycomb core. The snap-fit technique uses 2D chips and constructs them into a 3D structure. Additionally, a self-reinforced technique that uses rods made from the same material as the composite matrix enhances the structural connectivity without adding any extra compounds, thus keeping the structures recyclable. The mechanical properties of these sandwich cylindrical structures were evaluated using quasi-static compression, low-speed impact, and compression after impact (CAI) tests. The results show that these structures have exceptional energy absorption ability, with an average specific energy absorption exceeding 4 J/g. Most notably, after impacts of 300, 600, and 900 J, the structure's energy absorption ability and crush force efficiency were pleasantly improved. This demonstrates the difference between thermoplastic and thermoset composites. Unlike brittle fractures, the thermoplastic composite structure undergoes plastic deformation upon impact, presenting a benefit in energy absorption, especially in situations involving secondary impacts.