Achieving record-high tensile strength in SLS-fabricated CF/PEEK composites: multiscale insights into fibre reinforcement mechanisms via dual-scale XCT and DEM-FEA

Selective laser sintering (SLS) of carbon fibre reinforced polyetheretherketone (CF/PEEK) holds significant promise for load-bearing applications, yet the fibre reinforcement mechanisms governing this material system remain insufficiently understood. To address this gap, an integrated investigation is conducted that combines dual-scale X-ray computed tomography (XCT) characterisation and discrete element method-finite element analysis (DEM-FEA) modelling of CF/PEEK composites reinforced with three carbon fibre T300, T800, and T1100 grades. The optimal process achieves an ultimate tensile strength of 160.5 MPa, among the highest reported values for SLS-fabricated CF/PEEK composites. To characterise microstructural features that remain unresolved by conventional industrial XCT, synchrotron radiation computed tomography (SR-CT) and X-ray microcomputed tomography (micro-XCT) are combined. The dual-scale characterisation reveals preferential fibre alignment along the powder-spreading direction and quantifies the fibre orientation distribution. A coupled DEM-FEA framework is then developed to capture the links among powder spreading, fibre orientation, and composite performance, using the fibre orientation tensor predicted by DEM simulations of powder spreading as input to the FEA models. The results show that fibre modulus affects load sharing and stress distribution, providing insight into its role in composite reinforcement. This work establishes a direct mechanistic link between fibre reinforcement and mechanical performance for SLS-fabricated CF/PEEK composites.