Damage mechanisms of 2.5D SiO2f/SiO2 woven ceramic matrix composites under compressive impact

Fiber-reinforced SiO_2f/SiO₂ woven ceramic matrix composites (CMCs) are widely applied in the aeronautics and astronautics field due to their many physical and chemical advantages. However, compressive impact loads affect many application scenarios; thus, the damage morphologies and failure modes of these composites under compressive impact should be studied, particularly in the through-thickness direction. In this study, a comparative analysis using the split Hopkinson pressure bar (SHPB) experiment and finite element analysis (FEA) model revealed the damage mechanisms. The compressive impact was simulated in Abaqus/Explicit, and the cohesive element was selected to simulate cohesion of the interface according to the Hashin criterion for multi-mode failure. The results show that 2.5-dimensional SiO_2f/SiO₂ woven CMCs do not have sufficient plasticity to restrain the propagation of micro-cracks under high strain rates after the elastic stage under compressive impact. Many micro-cracks propagated and formed large cracks in the adiabatic shear zone. The adiabatic shear zones were generated when a compressive impact load was applied to the SiO_2f/SiO₂ CMCs at a high strain rate, and these impacts deformed the SiO_2f/SiO₂ CMCs. The adiabatic shear zone occurred at a high strain rate at the weakest point inside the fields of the SiO_2f/SiO₂ CMCs. The micro-cracks propagated and accumulated in this zone. Plastic fracture is the major failure mode for the SiO_2f/SiO₂ CMC specimens; this failure was characterized by fiber yarn fracture and the formation of micro-voids and micro-cracks due to matrix fracture. The large cracks, new voids, and interfacial debonding lead to the failure of the SiO_2f/SiO₂ CMCs. Combined action due to micro-crack formation and its propagation in the adiabatic shear band leads to a softening mechanism of the strain rate.