Chuang-qi Zhao

Effect of temperature on bending properties and failure mechanism of three-dimensional multiaxial warp-knitted carbon/epoxy composites

The three-point bending experiments on three-dimensional multiaxial warp-knitted carbon/epoxy composites with two fiber architectures are performed at room and elevated temperatures. Macro-fracture morphology and scanning electron microscopic micrographs are examined to understand the deformation and failure mechanism. The results show that the load–deflection curves are significantly different for different temperatures and the bending properties decrease significantly with increasing the temperature. Meanwhile, bending properties can be affected greatly by the fiber architecture and these increase significantly with the decrease of the fiber orientation angle at different temperatures. The results also show that the damage and failure patterns of composites vary with the test temperature. At room temperature, the composite exhibits brittle feature, and it damages with the breakage and tearing of fibers. At elevated temperature, the composite becomes more softened and exhibits plasticity. The damage of matrix plastic and cracking, interface debonding, and fiber layer delaminating become prominent. Moreover, the failure mechanism at room and elevated temperatures can be significantly affected by the fiber architecture.

Static and dynamic mechanical behavior of 3D integrated woven spacer composites with thickened face sheets

Abstract3D integrated woven spacer composites with thickened face sheets are fabricated successfully. Static compression and impact behavior are analyzed to evaluate the effect of thickened face sheets. The results show that thickened face sheet is an important influence parameter, warp compression and impact properties have been improved significantly than those of composite without thickened face sheets. Moreover, the damage and failure mechanism is significantly different. The main failure mode under flat compression is an abrupt rigid breakage of core fiber bundles. However, the thickened face sheets reduce the shear stress that transfer to core fibers. For warp compression, there is no face sheets fracture or dislocation, the local shear fracture occurs on the thickened face sheets. In regard to low-velocity impact, the strength of thickened face sheets dominates the failure, the damage is mainly manifested as the penetration of the top and bottom face sheets, matrix cracking, interface debonding, micro-buckling, as well as tearing and breakage of core fibers.

Experimental study on the charpy impact failure of 3D integrated woven spacer composite at room and liquid nitrogen temperature

The charpy impact experiments on the 3D integrated woven spacer composites with six types of core heights are performed at room and liquid nitrogen temperatures (as low as −196 °C). Macro-fracture morphology and SEM micrographs are examined to understand the deformation and failure mechanism. The results show that the impact energy increase with the increase of the core height at both room and liquid nitrogen temperatures. Meanwhile, the impact properties at liquid nitrogen temperature have been improved significantly than that at room temperature. Moreover, at room temperature, the penetration fracture of the face sheets, the tearing and pulling out of the core fibers as well as the cracking of the matrix is the main damage and failure patterns. However, at liquid nitrogen temperature, the matrix crushing dominates the failure. Less fibers fracture and brittle fracture feature becomes more obvious. In addition, with the increase of the core heights, the damage of composites has been reduced significantly at room and liquid nitrogen temperatures.

Charpy Transverse Impact Failure Mechanisms of 3D MWK Composites at Room and Liquid Nitrogen Temperatures

AbstractThe 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 d...