Abrasive water jet drilling of flax fibre metal laminates: effect of drilling approach on interlayer delamination and abrasive contamination

The current study investigates the influence of two drilling approaches namely direct drilling and predrilling on the structural integrity, interlayer delamination and abrasive contamination of holes machined in flax fibre metal laminates (FFMLs). Abrasive water jet drilling (AWJD) process was used to create holes in the FFML by varying the water pressure (WP) 1000,3000 bars, traverse speed (TS) 20,100 mm/min, abrasive mass flow rate (AMFR) 300 g/min and standoff distance (SD) 2,4 mm. Direct drilling approach involved using AWJD process to create 5-mm holes in the FFML. Pre-drilling approach involved drilling a 3-mm hole size using a twist drill followed by enlargement of the hole to 5-mm using AWJD. The hole integrity was evaluated under scanning electron microscopy (SEM) and computerised tomography (micro-CT) scan to assess delamination, damage, fracture and failure mechanisms in the FFML. Using the direct drilling approach, the holes suffered from severe interlayer delamination and abrasive contamination. In addition, peel-up and push out delamination were observed regardless of the drilling parameters used while pre-drilling approach proved to be successful in eliminating them.