Energy loss in a unidirectional flax-polyester composite subjected to multiple tensile load–unload cycles

• Published in: Journal of materials science 2012-02, Vol.47 (3), p.1164-1170
• Main Authors: Newman, Roger H., Battley, Mark A., Carpenter, James E. P., Le Guen, Marie Joo
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Composite materials industry; Crystallography and Scattering Methods; Cycle ratio; Deformation; Deformation mechanisms; Energy dissipation; Failure; Fibers; Fibres; Flax; Internal energy; Kink bands; Load; Materials in New Zealand; Materials Science; Polyester resins; Polyesters; Polymer matrix composites; Polymer Sciences; Solid Mechanics; Straightening; Strain; Tensile stress; Vegetable fibers; Vibration damping; Yarns; Yield point
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-011-5713-3

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 × 10 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.