부산대학교 도서관

Composites reinforced with plant fibres show inelastic deformation under tensile loads. This property can be exploited in vibration-damping applications. Inelastic deformation was characterised for composites made from unsaturated polyester resin reinforced with unidirectional flax yarns. The primary yield point was found at a strain of 0.17%, with additional minor yielding events to a strain of 1.0% and then linear deformation to failure at a strain of 1.9%. Inelastic deformation accounted for approximately half of the total deformation across the final half of the stress-strain curve. Energy loss was greatest in the first load-unload cycle, with little change beyond the second cycle. The ratio of lost energy to stored energy settled to values between 0.23 and 0.40 for load-unload cycles peaking at between 15 and 75% of predicted maximum load. Failure stress remained unchanged after 2 x [10.sup.4] load-unload cycles to approximately 50% of the breaking load. Results were consistent with kink bands straightening when fibres were first loaded, causing partial debonding at the fibre-matrix interface. Energy loss in subsequent cycles was attributed to friction between microfibrils within the kink bands as they twisted and untwisted.
Introduction When unmodified flax (Linum usitatissimum) fibres are used to reinforce thermosetting resins, the composites show non-linear tensile stress-strain curves [1]. Loading-unloading experiments have demonstrated a degree of irreversibility in [...]