Impact of Predrilling on Machinability and Open-Hole Tensile Properties of Woven Flax Composites

The applications of flax fiber composites typically relate to their machinability. Although several investigations on mechanical and abrasive waterjet (AWJ) drilling have detailed this aspect, some issues persist. The first issue is that perpendicularity is high when using AWJ drilling (AWJD). The second issue is thermal distortion when using mechanical drills to produce holes. This work employed mechanical drilling to create pilot holes in woven flax laminates and enlarged them utilizing AWJ. Several hole-quality parameters were measured, the influence of the drilling approach on hole quality was evaluated, AWJ processing damage was examined, open-hole tensile tests were conducted, and the material-cutting mechanisms involved in predrilling were assessed. This study also used the same parameters to produce holes directly for comparison. The processing damage with predrilling is similar to that without it. However, the voids with predrilling are larger, and the fiber-matrix detachment is more severe than that without it. The quality of the optimal hole with predrilling is higher than that of the untreated case. The tensile strength of open-hole specimens with predrilling is higher than that without it. Overall, predrilling followed by AWJ enlarging can improve the quality of the optimal hole.