Effect of machining processes on the damage response and surface quality of open hole hybrid carbon/flax composites: An experimental study

The influence of conventional drilling (CD) and abrasive water jet (AWJ) machining on the mechanical behavior of hybrid carbon/flax composites was investigated. The specimens were manufactured using woven carbon fiber (C) and unidirectional flax fiber (F) in three configurations: unidirectional [0-90(C2)/0(F6)](S), cross-ply [0-90(C2)/(0/90)(F6)](S), and angle-ply [0-90(C2)/(+/- 45)(F6)](S) laminates. The examination of the hole surface revealed severe damage in the form of peel-up, push-out, and secondary delamination of AWJ machined holes, and only push-out delamination at the exit side of the CD drilled hole. A delamination factor was developed to quantify the delamination at the hole surface. The specimens were subjected to quasi-static load-unload tensile tests to assess their damage response and surface fracture. Unidirectional and angle-ply specimens drilled with AWJ accumulated a higher damage compared to CD specimens. This correlates with the delamination factor, indicating that the delamination at the entry and exit of the hole and secondary delamination greatly affect the damage evolution of the laminates.