Influence of Hole Diameter on Hole Quality and Tensile Strength of Woven Flax Fiber Laminates

This work primarily evaluates the effect of abrasive waterjet (AWJ) drilling variables on the machinability and residual tensile strength (σrts) of open-hole flax laminates. The primary purpose is to improve drilling quality and tensile performance. The AWJ drilling (AWJD) variables include waterjet pressure (WP), transverse speed (TS), and hole diameter (HD). HD exerts the highest impact on mean roughness (Ra) and hole size (D), while TS has a substantial effect on all response parameters except D and Ra. σrts decreases with increasing D for a constant specimen width. σrts at minimal delamination is higher than at maximal damage for the same D, particularly for small holes. Considering all holes, σrts for the worst-quality hole is 104.91 MPa, which is much higher than 83.09 MPa for the optimal-quality hole, indicating that σrts under optimal-quality conditions is less than that under worst-quality conditions. The failure of open-hole flax composites originates from transverse matrix cracking perpendicular to the tensile axis, causing the separation of the fibers from the matrix and ultimately leading to the specimens breaking. The fracture mechanisms are independent of AWJD parameters. In summary, the AWJD parameters can markedly affect the hole quality and residual tensile strength of flax fiber composites.