The effects of mechanical degradation on the quasi static and dynamic stiffness of polyester yarns

Offshore moorings have been extensively researched in recent decades, and since the introduction of Taut-Leg systems made with synthetic polyester fibers as an alternative to steel catenaries, several fibers have gained significant prominence. High modulus polyethylene (HMPE) stands out due to its superior mechanical resistance and linear tenacity compared to many other fibers. However, it shows challenging behavior in creep, showing high strain rates and low creep resistance. Consequently, manufacturers have focused on developing HMPE fibers typified as "Low Creep," aiming to achieve satisfactory creep behavior and enable offshore mooring systems made entirely of HMPE. Such advancements could lead to the use of HMPE in offshore installations in ultra-deep waters, given its low elongation. The goal of this study is to evaluate the creep behavior of 6 HMPE fibers, including both European and Asian manufactures, with 3 fibers designated as "Low Creep." The evaluation encompasses different load temperature conditions. The experimental approach uses HMPE multifilaments, which serve as the base material for making mooring ropes. The results are compiled in tables, providing initial characterization results and average creep results, including creep strain rates. Creep graphs are drawn to facilitate understanding and comparison of the behaviors, along with a generalized statistical modeling of the creep-rupture surface for each fiber. The results show that the fibers designated as "Low Creep" indeed exhibit significantly better behavior than others, with lower strain rates. Among them, Fibers A and D emerge as the most promising for offshore mooring, showing greater resistance to creep. From a commercial standpoint, Fiber D offers the lowest cost per kg and presents favorable constitutive behaviors in specific operational contexts, as well as better stability with increasing temperature. In terms of future directions, other methodologies linked to the acquired experimental database should be explored, including analytical models and numerical simulations. Additionally, an investigation into sub-ropes and a detailed study of thermal degradation decoupling in the studied phenomenon should be considered for further research.

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The effects of mechanical degradation on the quasi static and dynamic stiffness of polyester yarns

Melito¹,

Cruz²,

Belloni³

et al. 2023

10.5267/j.esm

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Polyester fibers are the most used in the manufacture of ropes for mooring systems and offshore operation, thus being constantly subjected to different situations. Such requests are implicated in a variety of load conditions, and their effects must be studied. This work presents data referring to an experimental study on the behavior of the quasi-static and dynamic stiffness of polyester yarns considering different mechanical levels of degradation and use. The study is performed with five different types of multifilament samples, these were extracted from a virgin spool and sub-ropes tested for tension and fatigue. The experimental procedure is carried out through an initial characterization where the linear density, the Yarn Break Load - YBL and the linear tenacity of the samples are determined. Continuing with the experimental tests, a procedure standardized by ISO 18962-2 is then carried out, consisting of three quasi-static stages and three dynamic stages, where the data acquired in the tests allow the determination of a dimensionless stiffness value. The results showed an increase in the quasi-static stiffness, tending to a plateau, and a linear increase in the dynamic stiffness, but with somewhat similar behavior between the samples. The results related to the total quasi-static stiffness also show that the specimens extracted from sub-ropes that underwent fatigue present greater total non-dimensionalized stiffness, this is indicative of the mechanical fatigue procedure as an improvement of the specimens, giving them greater stiffness, and consequently greater stresses rupture, a behavior that should be explored in future studies.

show abstract

The effects of mechanical degradation on the quasi static and dynamic stiffness of polyester yarns

Cited by 3 publications

References 1 publication

Numerical simulation of multi-material hybrid lines for offshore mooring

Numerical simulation of multi-material hybrid lines for offshore mooring

Experimental Study of Creep Behavior at High Temperature in Different HMPE Fibers Used for Offshore Mooring

The effects of mechanical degradation on the quasi static and dynamic stiffness of polyester yarns

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