Daniel Magalhães da Cruz

This study investigates the constitutive behavior and tangent modulus of polyamide multifilaments in post-impact rupture. Polyamide is widely used in applications such as offshore mooring systems due to its excellent mechanical properties. However, its performance under dynamic conditions, especially after impact events, has not been extensively studied. The research presents an experimental approach to evaluate the mechanical response of polyamide multifilaments, focusing on the constitutive behavior during the rupture test after impact preconditioning. The impact pre-loads were applied under 4 impact load conditions and 4 impact cycle ratios, totaling 16 groups in the study. The impact pre-loads aim to prepare the samples for rupture without causing failure during the preconditioning phase. The results show that polyamide exhibits good stabilization and resilience in the impact tests. In the tangent modulus, polyamide fibers show a decrease in the initial modulus on the constitutive curve as the impact load increases, but the maximum tangent modulus values remain consistent across all samples, ≈10,000 MPa. The study highlights the importance of understanding the material’s constitutive behavior under such conditions for accurate predictions of its performance. The findings suggest that post-impact behavior should be a key consideration in the design and selection of materials for dynamic load scenarios, particularly in offshore mooring systems. Future work should explore other material construction levels, improved models, and enhancements in the testing method, tested samples, and data analysis.

This study presents a numerical approach for simulating the stress-strain behavior of high-modulus polyethylene (HMPE) and polyester (polyethylene terephthalate, PET) multifilaments subjected to progressive dynamic tensile loading cycles. Experimental tests were performed under force-controlled conditions, with a fixed frequency of 0.1 Hz and sinusoidal waveform, considering five successive zero-tension loading cycles with increasing amplitudes from 0 to 50% of the Yarn Break Load (YBL). The numerical modeling was carried out using a phenomenological hyperelastic Modified Yeoh model, implemented within a tensor-based formulation grounded in continuum mechanics and calibrated through parametric optimization based on experimental data. The simulations demonstrated a satisfactory ability to reproduce the constitutive response of both fibers across different load levels, even under non-stabilized hysteresis conditions. The results showed that the mean simulation error varied between cycles, with the largest discrepancies observed for the first cycle at the lowest load amplitude (0 to 10% of the YBL). Conversely, the highest load amplitude cycle (0 to 50% of the YBL) exhibited the best visual agreement between numerical and experimental curves for both HMPE and PET. Overall, a general trend of decreasing mean error was observed with increasing load amplitude and number of cycles. The identified phenomenological parameters remained consistent throughout the simulations, indicating the robustness of the implemented numerical code, although these parameters do not possess direct physical or mechanical meaning. The results highlight the exploratory nature of the study and support the potential of the proposed methodology for future extensions, including other synthetic fibers, higher structural levels, and investigations involving different loading frequencies, rates, and non-stabilized single-cycle loading conditions.

This study evaluates the mechanical performance and hydrolytic lifetime of four commercial aramid fibers (A, B, C, and D) subjected to accelerated seawater aging at 70°C and 80°C for exposure times of up‐to approximately days. Aramid A and B exhibit progressive degradation with increasing exposure time and temperature, with reductions of approximately and in rupture force, and up to and in rupture strain at 80°C, respectively. In contrast, Aramid C and D maintain stable mechanical behavior, with rupture force increases of approximately and at 80°C, respectively under maximum hydrolysis exposure condition. Mathematical 2D‐models, predominantly based on reciprocal formulations, show good agreement with experimental results (), both for rupture force and rupture strain. While three‐dimensional response surfaces describe the coupled effects of temperature and hydrolysis time for rupture force. Arrhenius‐type lifetime prediction models are developed for the degrading fibers (Aramid A and B), indicating predicted hydrolytic lifetimes exceeding typical offshore operational periods for Aramid A under marine service temperatures ( years at 16°C, and years at 4°C), whereas Aramid B becomes dominant above approximately 81.5°C. The proposed experimental and modeling framework contributes to the understanding of hydrolytic degradation in aramid fibers for marine applications.

This study experimentally investigated the effect of testing speed on the mechanical behaviour of five types of synthetic fibres – aramid, high-modulus polyethylene (HMPE), liquid crystal polymer (LCP), polyamide, and polyester – through yarn break load (YBL) tests, ISO 2062. Twelve different speeds were evaluated, ranging from 50 to 1 000 mm min−1. The discrete rupture force and rupture strain results were stable and showed no statistically significant variations as a function of speed, which was reflected in the fitted mathematical models exhibiting stabilised curves across the studied range. The stress-strain curves also showed a high degree of similarity, with a particular emphasis on LCP, which demonstrated extremely consistent behaviour across all tested speeds. For HMPE, a slight trend of increased strain at lower speeds was observed, attributed to its viscoelastic nature. The tangent modulus curves revealed more noticeable variations in the initial tangent modulus response for each fibre, where lower speeds resulted in steeper slopes, indicating a greater instantaneous stiffness. It is concluded that, although the testing speed does not affect the overall rupture parameters (rupture force and strain), it can influence the behaviour in the initial regions, particularly regarding the determination of modulus and stiffness.

This paper presents a study on the stress-strain simulation of offshore mooring fibers using the Modified Yeoh model. It incorporates the mathematical descriptions (linear, quadratic, cubic, and exponential), also examining the dependence on the strain invariants (I1 and I2), thus aiming to improve the accuracy of the numerical description of the constitutive behavior of the fibers. The research methodology includes computational simulations validated by experimental data, focusing on the mathematical construction based on the Modified Yeoh model for representing the constitutive behavior in mechanical hysteresis (loading-unloading), addressing two fibers: high modulus polyethylene (HMPE) and polyester (PET). The simulation results demonstrate the models' ability to describe the stress-strain behavior, but it is clear that a description solely through I2 is not sufficient for the convergence of the simulation with the experimental data. For the mathematical models, the linear term dependent on I1 (principal strains) is the most important for the good fitting of experimental data. The smallest error concerning the simulations is obtained for a model with a complete mathematical description and dependence on both invariants, presenting an average error of 0.52% for HMPE and 1.77% for PET. This work provides a framework for simulating and understanding the mechanical responses of mooring fibers in mechanical hysteresis, highlighting the relevance of the mathematical model and invariant dependence coupled with numerical simulation.

The offshore industry faces significant challenges in the dynamic energy and maritime domain, necessitating robust engineering solutions for mooring systems. This study investigates the impact of ultraviolet radiation A (UV-A) on the mechanical strength of high-strength multifilaments, crucial for offshore mooring. Five fibre types: Aramid, High-modulus polyethylene (HMPE), Liquid crystal polymers (LCP), Polyamide and Polyester, are exposed to UV-A for up to 28 days. Initial mechanical characterisation provides baseline data, while subsequent tests reveal varying degrees of degradation. Polyamide and polyester exhibit superior stability, while Aramid and HMPE show restrained degradation. LCP experiences substantial degradation. Mathematical modelling reveals distinct degradation patterns, emphasising the need for comprehensive understanding in ensuring the safety and efficiency of offshore operations. There are indications that degradation by ultraviolet exposure for Aramid, HMPE, polyamide, and polyester fibres, restricts the constitutive behaviour in terms of strength and extension, but without changing the shape of the curve. These findings provide valuable insights for the offshore industry and guidance future research and development efforts.

Polyester (polyethylene terephthalate, PET) and high-modulus polyethylene (HMPE) fibers are currently among the most commonly used materials in the manufacturing of ropes for offshore operations. Several studies have been conducted in analytical, experimental, and numerical domains, addressing various factors such as tensile tests, fatigue, creep, and environmental exposure conditions that influence their mechanical behavior. This work presents data from an experimental study on rupture resistance in semi-finished products (rope yarns) of PET and HMPE fibers subjected to different ultraviolet (UV) radiation exposure durations. The experimental procedure involved UV exposure for up to 84 days, followed by tensile rupture tests based on ISO 2062. The results showed that UV degradation occurs in a monotonic manner for PET, whereas HMPE exhibits relative stability for rope yarns.