Strain-rate-dependent interlaminar shear properties of 3D FWP-C/C composites

Three-dimensional fine weave pierced carbon/carbon (3D FWP-C/C) composites are widely employed in critical aerospace thermal structures due to their exceptional high-temperature mechanical properties. However, these structures inevitably operate in complex dynamic environments, where the relatively weak interlaminar mechanical properties of 3D FWP-C/C composites make them particularly susceptible to dynamic interlaminar shear (ILS) failure. In this study, a double-shear specimen is specifically designed and size-optimized to evaluate the ILS properties of 3D FWP-C/C composites. Quasi-static and dynamic experiments are conducted using an electromechanical universal testing machine and a servo-hydraulic high-speed testing machine, respectively. The fracture surfaces are subsequently analyzed via scanning electron microscopy (SEM) to reveal the strain-rate-dependent ILS failure mechanism. Results demonstrate that the ILS failure in 3D FWP-C/C composites is primarily governed by pierced fiber bundles. Under quasi-static loading, the ILS failure occurs due to the tensile rupture of the pierced fiber bundles, whereas at high strain rate loading, failure is primarily governed by the shear fracture of the pierced fiber bundles. With increasing strain rate, the ILS strength improves, rising from 22.738 MPa at 0.001/s to 30.859 MPa at 1000/s, while the initial ILS modulus remains nearly unchanged. This enhancement is attributed to the suppressed propagation of matrix cracks at higher strain rates. The ILS failure process of 3D FWP-C/C composites exhibits two distinct stages: the matrix-dominated first damage stage and the fiber-dominated second damage stage. Additionally, the two damage stages gradually converge with increasing strain rate. Based on these findings, a novel strain-rate-dependent dual-damage ILS constitutive model, incorporating both damage stages, is proposed and validated against experimental data. The proposed constitutive model provides precise predictive capabilities for both dynamic ILS responses and progressive failure modes in aerospace 3D FWP-C/C composite structures under operational dynamic loading conditions.