Strength of Thermoplastic Carbon Fibre-PEEK Composite Tubes Under Combined Compression-Torsion Loading

Composite hollow cylindrical tubes can provide superior design advantages in engineering structures due to their geometric versatility added with reduced weight. However, the response of such components especially failure prediction under combined, compressive, and torsional loading poses a long-standing challenge for the structural engineering community. With the advancement of automated fibre placement (AFP), thermoplastic tubular components can be manufactured accurately at a faster rate to optimize production efficiency. Moreover, the discontinuities such as cut-outs for inlets and service openings are often included in the design of composite structures, which can experience strength reduction along the process. This chapter presents the numerical analysis and experimental demonstration of thermoplastic Carbon Fibre-PEEK composite (CF-PEEK) tubes including cut-outs under simultaneous compression and torsional loading. A set of thermoplastic tubes with different sizes (length to diameter ratio) and stack up sequences were manufactured using a hot gas torch (HGT) assisted fibre placement machine. The specimens then were tested using a servo-hydraulic testing machine capable of applying compression as well as torsional loading both independently and concurrently. The experimental results were compared with numerical simulation carried out using the Ansys Composite PrepPost (ACP) package. Deflections and surface strains were measured for the test articles using digital image correlation (DIC), distributed optical fibre sensor (DOFS) and electro resistive strain gauges, which were compared with the finite element analysis (FEA) estimates. Numerical interaction diagrams for the tubes were developed based on maximum stress criteria in the laminate to demonstrate the effect of fibre orientations on the ply-wise failure initiation under axial-torsion loading combinations.