Fracture behaviour of epoxy biocomposite reinforced with short coconut fibres (Cocos nucifera) and walnut particles (Juglans regia L.)

Mixed-mode fracture characteristics of epoxy-based biocomposite reinforced with 20 wt% walnut shell particle and 10 wt% coconut fibres are investigated. The biocomposite is fabricated using the squeeze casting method. The positive aspect of hybrid combination of fibre and particle reinforcement is advocated by comparing mode I, mode II and mixed-mode I/II fracture surfaces under a scanning electron microscope. An edge-cracked semicircular arc specimen subjected to symmetric three-point bend (TPB) loading is suggested for fracture toughness testing of biocomposite material. A series of fracture tests are conducted on hybrid biocomposite using the proposed semicircular bend (SCAB) specimen geometry, TPB and four-point bend (FPB) specimens. The average mode I and II fracture toughness obtained from semicircular arc bend (SCAB) specimen are 1.319 MPa and 1.219 MPa m, respectively. The average values of modes I and II toughness obtained from TPB and FPB specimens are 1.267 and 0.754 MPa m. The overall ratio of mode I and mode II fracture toughness is found to be 0.762, which is very close to the predicted value of 0.87 by maximum tangential stress criterion. The results obtained from new SCAB geometry are validated with the results obtained from TPB and FPB specimen geometries by statistical significance test. Very good agreement is found between the experimental results obtained from TPB, FPB and the proposed SCAB specimens.