Analysis of the formation mechanism under different grinding conditions on the machining defects of needle-punched quartz fibre reinforced hybrid polymer matrix composites

To understand the defect forms of needle-punched quartz fibres reinforced hybrid polymer matrix composites, this study adopt end face and side face grinding and selected down and up grinding to conduct experiments. The results show that the macroscopic defects are mainly burrs and the microscopic defects are mainly fibre pull-out, fibre debonding, fibre bending and matrix interface broken. And it is found that the 90° fibre pull-out degrees of end face down grinding (EFDG) and end face up grinding (EFUG) were similar, which were 7.82 μm and 7.34 μm respectively, significantly lower than 53.57 μm of side face up grinding (SFUG) and 82.10 μm of side face down grinding (SFDG). The pull-out degree of the 0° fibre bundle showed the same variation pattern as that of the 90° fibre bundle, but its pull-out degree is significantly higher than that of the 90° fibre bundle, which were 34.92 μm (EFDG), 33.13 μm (EFUG), 61.46 μm (SFUG), and 256.56 μm (SFDG) respectively. By analyzing different grinding conditions, the effective action distance that plays a crucial role in defect formation is obtained, and the effective action distances of end face grinding and side face grinding are different. The grits of the internal end face play an important role in the formation of defects under EFUG and EFDG conditions. In addition, the support effects also vary under different grinding conditions. The joint support effect formed between the grits and the material > the separate support effect of the material > almost no support effect and only the grinding effect of grits.