Charpy transverse impact failure mechanisms of 3D MWK composites at room and liquid nitrogen temperatures

The Charpy transverse impact experiments on the three-dimensional (3D) multiaxial warp knitted (MWK) composites with four fiber architectures are performed at room and liquid nitrogen temperatures (-196°C). Macrofracture morphology and scanning electron microscope (SEM) micrographs are examined to understand the impact deformation and failure mechanism. The results show that the transverse impact properties can be affected greatly by the fiber architecture and decrease significantly with the increase of 90° fibers at room and liquid nitrogen temperatures. Meanwhile, the impact energy at liquid nitrogen temperature has been improved significantly than that at room temperature. Moreover, the fiber architecture is an important parameter affecting the transverse impact damage and failure patterns of composites at room and liquid nitrogen temperatures. At liquid nitrogen temperature, the matrix solidification and interfacial bonding is enhanced significantly. However, more local microcracks occur and damage accumulation increase, especially for the materials with 90° fibers. In addition, the brittle failure feature becomes more obvious at liquid nitrogen temperature.