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An experimental study is described in this paper dealing with the tension–tension fatigue and failure mechanism of 3D MWK composites with different fiber architectures and material sizes. Macroscopic fracture morphology and SEM micrographs are examined to understand the fatigue damage and failure mechanism. The results show the fatigue properties and failure mechanism of composites can be affected significantly by the fiber architecture and material size. The fatigue life of material A(0°/0°/0°/0°) with small fiber orientation angle is significantly longer than that of material B(+45°/−45°/+45°/−45°). For material A, the fatigue properties of the long composite are better than that of the short one. It is 0° fiber bundles fracture under fatigue stress which cause the material failure and the long composite provides more space for the formation and propagation of local fatigue micro-cracks. However, for material B, the short composites have better fatigue properties. Moreover, the materials show typical ±45° zigzag fatigue fracture and obvious shear behavior. The fatigue cracks for the long composite can be spread more quickly along the fiber/matrix interface due to the fiber bundles realignment.

Three-point bending tests at room and liquid nitrogen temperature (as low as −196 °C) are conducted on the 3D integrated woven spacer composites with different core heights. Macrofracture morphology and SEM micrographs are examined to understand the deformation and failure mechanism. The results show that the bending properties at liquid nitrogen temperature are improved significantly than those at room temperature. Meanwhile, the bending properties both at room and liquid nitrogen temperature can be affected greatly by the core height. Moreover, the damage and failure patterns of composites vary with the core height and test temperature. At room temperature, three typical failure mechanism have been obtained for composites with different core heights. At liquid nitrogen temperature, the composites show gradual failure process which extends from the external layers of the compression face to the interior core layers. Furthermore, the brittle failure feature becomes more obvious and the interfacial adhesion capacity is enhanced significantly.

•Obtain impact properties of 3D MWK composites at room and cryogenic temperature.•The impact damage and failure mechanism is demonstrated at different temperatures.•Analyze the influence of fiber architecture on the properties and failure modes.•Analyze the influence of testing temperature on the properties and failure modes.The charpy impact experiments on the 3D MWK (Multi-axial warp knitted) composites with four different fiber architectures are performed at room (20 °C) and liquid nitrogen temperatures (as low as −196 °C). Macro-Fracture morphology and SEM micrographs are examined to understand the impact deformation and failure mechanism. The results show that the impact properties decrease significantly with the increase of the fiber ply angle at both 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 has remarkable effect on the impact damage and failure patterns of composites at room and liquid nitrogen temperatures. At liquid nitrogen temperature, the matrix solidification and the interfacial adhesion capacity increase greatly, which effectively hinders the stress wave propagation. However, more micro-cracks appear and the brittle failure feature becomes more obvious.

The compressive experiments on the 3D braided composites with different braiding parameters are performed in three directions (longitudinal, in-plane and transverse) at room and liquid nitrogen temperature (low as −196 °C). Macro-Fracture morphology and SEM micrographs are examined to understand the deformation and failure mechanism. The results show that the stress–strain curves and the compression properties are significantly different in the longitudinal, in-plane and transverse direction. Meanwhile, the compression properties at liquid nitrogen temperature are improved significantly than that at room temperature. Moreover, the damage and failure patterns of composites vary with the loading directions and test temperature. At liquid nitrogen temperature, the brittle failure feature becomes more obvious and the interfacial adhesion capacity is enhanced significantly. In addition, the compressive properties and failure mechanism at room and liquid nitrogen temperature can be significantly affected by the braiding angle and the fiber volume fraction.