Mechanical Characterization of High-Elongation Polyester and Polyamide Fibers for FOWT Mooring

Abstract This study examines the mechanical properties of high-elongation polyester (HE PET) and polyamide (PA) fibers, focusing on their potential for shallow water mooring applications in Floating Offshore Wind Turbines (FOWT). Synthetic fibers are widely employed in offshore mooring systems due to their lightweight, high flexibility, and excellent fatigue resistance. Among these, PA is commonly chosen for shallow waters, valued for its shock absorption and dynamic performance. However, its higher cost and limited availability pose significant challenges. HE PET presents itself as a cost-effective alternative, offering comparable mechanical performance at a lower specific cost. To evaluate these materials, experimental testing was conducted at the multifilament level. Key parameters assessed include tensile strength, elongation at break, creep resistance, loading-unloading hysteresis, abrasion resistance, and stiffness under both quasi-static and dynamic conditions. The results demonstrate that HE PET outperforms PA in several critical areas, such as higher tenacity, greater breaking stress, superior creep resistance, and better abrasion resistance in yarn-on-yarn contact. However, PA exhibits better elastic recovery, particularly in cyclic loading tests. These findings underscore HE PET's suitability for dynamic environments with wave-induced loads, making it a strong candidate for shallow water mooring systems in offshore renewable energy applications. Its lower cost and mechanical resilience enhance its appeal as an alternative to PA. These advantages translate into practical benefits for the offshore industry, including potential cost reductions and/or enhanced safety in mooring systems for renewable energy applications. Nevertheless, the study highlights the need for long-term evaluations under fluctuating stress levels near working loads to fully assess fatigue performance and material longevity. By exploring the intrinsic mechanical properties of HE PET and PA, this research lays the groundwork for optimizing mooring solutions in FOWT and Marine Renewable Energy (MRE) systems. The insights gained contribute to the advancement of synthetic fiber technologies, supporting the growth of offshore renewable energy infrastructure. Future research should focus on higher-level structural elements, such as sub-ropes and full-scale mooring lines. These investigations would provide a more comprehensive understanding of how construction complexities affect performance under real-world conditions.