PSI - Issue 25

P. Santos et al. / Procedia Structural Integrity 25 (2020) 370–377 P. Santos../ Structural Integrity Procedia 00 (2019) 000–000

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4. Conclusions This study analysed the hybridization effect on the viscoelastic behaviour of flax laminates. It was possible to conclude that the maximum bending stress increases with the number of glass fibres layers added to the flax laminates. From the stress relaxation tests, it became evident that stress decreases over time, but laminates with a higher number of glass fibres are less prone to stress relaxation. Moreover, for bending stresses greater than 50% of the maximum bending stress, the stress relaxation is very similar regardless of the applied displacement. In terms of creep behaviour, the displacement increases with the time, and higher bending stresses are responsible for higher creep displacements. One more time, the hybridization decreases, in this case, the creep displacements. Therefore, the hybridization is an efficient way to decrease the viscoelastic behaviour of natural fibre reinforced composites. Finally, the Kohlrausch-Williams-Watts (KWW) equation and the Findley model were used to predict the stress relaxation time and the creep displacement, respectively, and good accuracy was obtained between experimental and theoretical results. Acknowledgements This work was supported by the project Centro-01-0145-FEDER-000017 - EMaDeS - Energy, Materials and Sustainable Development, co-financed by the Portugal 2020 Program (PT 2020), within the Regional Operational Program of the Center (CENTRO 2020) and the European Union through the European Regional Development Fund (ERDF). References Almeida, José Humberto S., Heitor L. Ornaghi, Natália P. Lorandi, Bernardo P. Bregolin, Sandro C. Amico. 2018. Creep and Interfacial Behavior of Carbon Fiber Reinforced Epoxy Filament Wound Laminates. Polymer Composites 39, 2199–2206. Altin Karataş, Meltem, Hasan Gökkaya. 2018. A Review on Machinability of Carbon Fiber Reinforced Polymer (CFRP) and Glass Fiber Reinforced Polymer (GFRP) Composite Materials. Defence Technology 14, 318–26. ASTM. 2003. D790-03-Standard Test Method for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulation Materials. ASTM Standards, 1–11. ASTM. 2008. E328-02(2008) Standard Test Methods for Stress Relaxation for Materials and Structures. ASTM Standards 02, 1–13. Bouafif, Hassine, Ahmed Koubaa, Patrick Perré, and Alain Cloutier. 2013. Creep Behaviour of HDPE/Wood Particle Composites. International Journal of Microstructure and Materials Properties 8, 225. Campilho, R. D.S.G. 2015. Natural Fiber Composites. Edited by R.D.S.G. Campilho. Natural Fiber Composites. CRC Press. Fakirov, Stoyko. 2015. Composite Materials – Is the Use of Proper Definitions Important? Materials Today 18, 528–29. Fancey, Kevin S. 2005. A Mechanical Model for Creep, Recovery and Stress Relaxation in Polymeric Materials. Journal of Materials Science 40, 4827–31. Georgiopoulos, Panayiotis, Evagelia Kontou, Aggelos Christopoulos. 2015. Short-Term Creep Behavior of a Biodegradable Polymer Reinforced with Wood-Fibers. Composites Part B: Engineering 80, 134–44. Hsu, C. F., H. Y. Tsai, T. H. Chen. 2018. The Effect of Manufacturing Parameters and Environmental Factors on Mechanical Properties of Carbon Fiber/Epoxy Composites. Journal of Mechanics 34, 839–46. Jayaraman, Krishnan. 2003. Manufacturing Sisal–Polypropylene Composites with Minimum Fibre Degradation. Composites Science and Technology 63, 367–74. Razavi-Nouri, M. 2012. Creep and Stress Relaxation Behavior of Polypropylene, Metallocene-Prepared Polyethylene and Their Blends. Iranian Journal of Chemcial Engineering 9, 60–68. Reis, P. N. B., J. A. M. Ferreira, P. A. A. Silva. 2011. Mechanical Behaviour of Composites Filled by Agro-Waste Materials. Fibers and Polymers 12, 240–46. Reis, P. N. B., M. P. Silva, P. Santos. 2019. Stress Relaxation in Delaminated Carbon/Epoxy Composites. Fibers and Polymers 20, 1284–89. Reis, P.N.B., J.A.M. Ferreira, Z.Y. Zhang, T. Benameur, M.O.W. Richardson. 2014. Impact Strength of Composites with Nano-Enhanced Resin after Fire Exposure. Composites Part B: Engineering 56, 290–95. Reis, P.N.B., L. Gorbatikh, J. Ivens, S.V. Lomov. 2019. Strain-Rate Sensitivity and Stress Relaxation of Hybrid Self-Reinforced Polypropylene Composites under Bending Loads. Composite Structures 209, 802–10.