Experimental investigation of fiber orientation on quasi-static and dynamic mode-I fracture in woven intra-ply carbon/Kevlar hybrid composites

Woven hybrid composites demonstrate significant rate-dependent fracture behaviour under impact and elevated loading conditions. This becomes crucial for design of light-weight structures in various sectors including aerospace, defence, transportation, and sports utilities. The current study experimentally investigates the quasi-static and dynamic Mode-I fracture response of woven carbon, woven Kevlar, and intra-ply carbon/Kevlar (C/K) hybrid composites. Initiation and propagation fracture toughness values are determined over different fiber orientations i.e. 0°, 45°, and 90° under quasi-static and dynamic loading conditions. Attention is also given to analysing the crack growth behaviour and corresponding occurred failure mechanisms under both loading conditions. Quasi-static fracture experiments are carried out on a universal testing machine, integrated with 3D-DIC, whereas the dynamic fracture experiments utilize a modified Hopkinson pressure bar in conjunction with ultra high-speed 3D-DIC setup. Orthotropic crack-tip displacement analysis is used for determining fracture initiation toughness, while the fracture propagation toughness is computed using an energy-based approach. The obtained outcomes indicate that fracture initiation is predominantly influenced by the high stiffness of carbon fibers, whereas the fracture propagation fracture toughness is mostly governed by fiber bridging, fiber rotation and induced energy absorption related to kevlar fibers. Comparisons based on fiber orientation-dependent fracture toughness indicated that the 0° fiber orientation contributes the highest initiation fracture toughness, while the superior propagation fracture toughness is exhibited in 45° fiber orientation among all the considered woven composites. The 0° fiber-oriented CFRP composites exhibit 15% higher dynamic propagation fracture toughness as compared to quasi-static counterpart. Conversely, the W-KFRP composites exhibit approximately 18% higher propagation fracture toughness. Intra-ply hybridization improves the crack growth resistance At 45° fiber orientation, propagation fracture toughness of intra-ply W-C/K FRP composites is 22% higher than W-CFRP composites. The maximum hybrid effectiveness ratio (HER) is observed in the C/K 45° oriented specimen, in which the crack propagates at the intersection of both the carbon and kevlar fibers. SEM fractography analysis reveal the most predominant toughening response is observed in the C/K 45° oriented specimen, in which the crack interacts concurrently with both carbon and kevlar fibers.