Fracture toughness determination of adhesive and co-cured joints in natural fibre composites

摘要

Adhesive bonding has become more efficient in the last few decades due to the adhesives developments,granting higher strength and ductility. On the other hand, natural fibre composites have recently gainedinterest due to the low cost and density. It is therefore essential to predict the fracture behavior of jointsbetween these materials, to assess the feasibility of joining or repairing with adhesives. In this work, thetensile fracture toughness (Gcn) of adhesive joints between natural fibre composites is studied, by bondingwith a ductile adhesive and co-curing. Conventional methods to obtain Gcn are used for the co-cured specimens,while for the adhesive within the bonded joint, the J-integral is considered. For the J-integral calculation,an optical measurement method is developed for the evaluation of the crack tip opening andadherends rotation at the crack tip during the test, supported by a Matlab sub-routine for the automatedextraction of these quantities. As output of this work, an optical method that allows an easier and quickerextraction of the parameters to obtain Gcn than the available methods is proposed (by the J-integral technique),and the fracture behaviour in tension of bonded and co-cured joints in jute-reinforced naturalfibre composites is also provided for the subsequent strength prediction. Additionally, for the adhesively-bonded joints, the tensile cohesive law of the adhesive is derived by the direct method.