High-strain-rate compression behavior and failure mechanism of 3D MWK carbon/epoxy composites

The high-strain-rate compression experiments were performed on the three-dimensional multiaxial warp knitted (3D MWK) carbon/epoxy composites with different fiber architectures at room and elevated temperature using a split Hopkinson pressure bar apparatus. Macro-fracture and scanning electron microscope (SEM) micrographs were examined to understand the deformation and failure mechanism. The results show that 3D MWK carbon/epoxy composites have excellent high-strain-rate compression properties. The dynamic properties increase significantly with the strain rate and the composites show a high-strain-rate sensitivity. Meanwhile, composites with multidirectional symmetric fiber architecture have higher dynamic properties. Moreover, the composites show temperature sensitivity at high strain rates and the dynamic strength decreases significantly. The results also indicate the composites take on more serious damage and failure with the increase of strain rate. The failure of material with [0°/0°/0°/0°] behaves as binding fibers fracture in shear, 0° fibers tearing, overall expansion, and multiple 45°angle shear fracture, while the material with [0°/90°/+45°/-45°] is mainly interlaminar delaminating, and the local fibers tearing and shear on different fiber layers. In addition, with the increase of temperature, the composite shows less fracture and becomes more softened and plastic. The damages of matrix falling off, plasticity, and fiber/matrix interface debonding increase significantly.