Characterization of Kerf Surface Using Complementary Roughness Descriptors in Abrasive Waterjet Cutting of Kevlar Fiber-Reinforced Polymers

Abrasive waterjet cutting (AWJC) is widely used for processing Kevlar-reinforced polymer composites; however, surface quality is typically assessed using amplitude-based roughness parameters like Ra and Rz, which offer limited insight into the overall morphology of the machined surface. This study investigates four complementary roughness descriptors—profile peak height, distribution, spacing, and slope—to characterize kerf wall morphology. Measurements were performed in two zones of the kerf wall under varied cutting conditions: traverse speed (100; 500 mm/min), focusing tube diameter (0.76; 1.00 mm), and abrasive grain size (100; 200 mesh). All investigated process parameters significantly influenced the descriptors. The bottom zone was rougher than the smooth top zone, with the maximum profile peak height (Rp), skewness (Rsk), and mean width of profile elements (RSm) increasing on average by 42.13%, 57.85%, and 45.80%, respectively, while the mean profile slope (Rda) showed a moderate average increase of 6.33%. Pearson correlation analysis showed strong relationships between the complementary descriptors and the conventional amplitude parameters (Ra, Rz, Rz1max, Rt) in the top zone (r ≥ 0.790), whereas in the bottom zone the correlations were lower (r = 0.421–0.798). This suggests that the behavior of the complementary descriptors changes with kerf depth.