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The tensile experiments on the three-dimensional (3D) multi-axial warp knitted (MWK) composites with four types of fiber architecture were performed at room and liquid nitrogen temperatures (as low as -196°C). Macroscopic fracture morphology and SEM micrographs both are examined to understand the deformation and failure mechanism. The results showed that the tensile properties can be affected greatly by the fiber architecture and these decrease significantly with the increase of the fiber orientation angle at room and liquid nitrogen temperatures. Meanwhile, the tensile properties at liquid nitrogen temperature have improved significantly than that of those at room temperature. Moreover, the damage and failure patterns of composites vary with the test temperature. At liquid nitrogen temperature, more microcracks appear and the brittle failure feature becomes more obvious; however, the interfacial adhesion capacity is enhanced significantly. In addition, the fiber architecture has remarkable effect on the failure mechanism at room and liquid nitrogen temperatures. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Highlights: [•] Obtain flat and warp compression properties of 3D integrated woven spacer composite. [•] The damage and failure mechanism is demonstrated under flat and warp compression. [•] Analyze the influence of core height on compressive properties and failure modes. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

In this letter, 3D integrated woven spacer composites with thickened face sheets were fabricated successfully by 3D integrated woven technology and VARIM process. The three-point bending properties and failure mechanism were first analyzed to evaluate the effect of thickened face sheets. The results show that the thickness of face sheets is an important parameter influencing the mechanical properties of 3D integrated woven spacer composite. The bending load-bearing ability is improved significantly than that of composite without thickened face. Moreover, the strength of thickened face sheets dominates the failure of composite, and the destruction is a gradual process from external layers of the compression face to the interior “8”-shaped core layers. The better mechanical properties of this new composite indicate it has a good potential application in many engineering fields. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]