Estudo das propriedades mecânicas da fibra rami para aplicações de amarração e ancoragem

Abstract

With the worldwide trend of replacing synthetic materials from non-renewable sources, with more environmentally friendly materials, the use of natural fibers, especially ramie, has become a possible viable option. Ramie fiber is a renewable, low-cost material with ultraviolet light blocking properties. The present experimental work aimed to analyze the mechanical behavior of the natural fiber ramie, when submitted to dynamic and static stresses, due to the use in the manufacturing of ropes for the mooring of offshore platforms. In order to generate knowledge about the behavior of these fibers, the following tests were carried out: chemical characterization, linear density (ABNT NBR 8427:2015), tension test (ASTM D885:2014), creep without rupture (15, 30 and 45% YBL with dead weight), creep with rupture (70, 80 and 90% YBL), fatigue (10% to 50%, 10% to 60%, 10% to 70%, 10% to 80%, 10% to 90% YBL), impact (dead weight at 300 mm height), quasi-static and dynamic stiffness (ABNT NBR ISO 18692:2013), hydrolysis (80ºC for 7, 14, 21 and 28 days) and Yarn-on-Yarn abrasion (Standard CI 1503- 99). The natural ramie fiber showed interesting chemical characteristics for offshore mooring applications, as it showed a low moisture content, which represents a good resistance to degradation due to microorganisms. Ramie fiber also showed lower percentage of impurities compared to other natural fibers. The dynamic behavior evaluated by creep and fatigue tests showed that the fiber has a good mechanical performance, compared to polyester for low percentages of the breaking load. But with the increase of the loads applied, rami showed way superior results than all the other fibers in which it was compared in this work with the exception of the Polyester fiber for 90% YBL. Still in this load level, in comparison with HMPESK75, the rami fiber had a 26,7 times better performance. Ramie showed superior results also for the quasi-static stiffness tests when compared to the HMPE and PET fibers researched, which can reach up to 102,1% more stiffness than the HMPE 3. As for dynamic stiffness, the ramie fiber also showed a higher stiffness than all the other fibers. These results indicate that if the fiber would be used in mooring ropes, it would provide a greater stability of the rig. When the fiber was submitted to hydrolysis tests, ramie showed a significant increase on its tension results, reaching up to 20% higher after 21 days of sea water immersion, at 80ºC. For the yarn-on-yarn abrasion tests, the ramie fiber showed results close to the polyamide fiber. With the proposed study, it was concluded that ramie fiber has the potential to be applied as a mooring rope for short periods of time of high stresses, it also can be used as rope covers, but its use still requires further studies in order to fill a gap in understanding the behavior of the fiber as a part of a rope.