Concept of Placement of Fiber-Optic Sensor in Smart Energy Transport Cable under Tensile Loading.

Due to the exponential growth in offshore renewable energies and structures such as floating offshore wind turbines and wave power converters, the research and engineering in this field is experiencing exceptional development. This emergence of offshore renewable energy requires power cables which are usually made up of copper to transport this energy ashore. These power cables are critical structures that must withstand harsh environmental conditions, handling, and shipping, at high seas which can cause copper wires to deform well above the limit of proportionality and consequently break. Copper, being an excellent electric conductor, has, however, very weak mechanical properties. If plasticity propagates inside copper not only will the mechanical properties be affected, but the electrical properties are also disrupted. Constantly monitoring such large-scale structures can be carried out by providing continuous strain using fiber-optic sensors (FOSs). The embedding of optical fibers within the cables (not within the phase) is practiced. Nevertheless, these optical fibers are first introduced into a cylinder of larger diameter than the optical fiber before this same fiber is embedded within the insulator surrounding the phases. Therefore, this type of embedding can in no way give a precise idea of the true deformation of the copper wires inside the phase. In this article, a set of numerical simulations are carried-out on a single phase (we are not yet working on the whole cable) with the aim of conceptualizing the placement of FOSs that will monitor strain and temperature within the conductor. It is well known that copper wire must never exceed temperatures above 90 °C, as this will result in shutdown of the whole system and therefore result in heavy maintenance, which would be a real catastrophe, economically speaking. This research explores the option of embedding sensors in several areas of the phase and how this can enable obtaining strain values that are representative of what really is happening in the conductor. It is, therefore, the primary objective of the current preliminary model to try to prove that the principle of embedding sensors in between copper wires can be envisaged, in particular to obtain an accurate idea about strain tensor of helical ones (multi-parameter strain sensing). The challenge is to ensure that they are not plastically deformed and hence able to transport electricity without exceeding or even becoming closer to 90 °C (fear of shutdown). The research solely focuses on mechanical aspects of the sensors. There are certainly some others, pertaining to sensors physics, instrumentation, and engineering, that are of prime importance, too. The upstream strategy of this research is to come up with a general concept that can be refined later by including, step by step, all the aspects listed above.

An Experimental Study on the Thermomechanical Coupling Effects of Carbon-Fiber-Reinforced Polyetheretherketone under Dynamic Impact.

Carbon-fiber-reinforced polyetheretherketone (CF/PEEK) composites are widely utilized in aerospace, medical devices, and automotive industries, renowned for their superior mechanical properties and high-temperature resistance. Despite these advantages, the thermomechanical coupling behavior of CF/PEEK under dynamic loading conditions is not well understood. This study aims to explore the thermomechanical coupling effects of CF/PEEK at elevated strain rates, employing Hopkinson bar impact tests and scanning electron microscopy (SEM) for detailed characterization. Our findings indicate that an increase in temperature led to significant reductions in the yield strength, peak stress, and specific energy absorption of CF/PEEK, while fracture strain had no significant effect. For instance, at 200 °C, the yield strength, peak stress, and specific energy absorption decreased by 39%, 37%, and 38%, respectively, compared to their values at 20 °C. Furthermore, as the strain rate increased, the yield strength, peak stress, specific energy absorption, and fracture strain all exhibited strain-hardening effects. However, as the strain rate further increased, above 4000 s-1, the enhancing effect of the strain rate on the yield strength and peak stress gradually diminished. The interaction of the temperature and strain rate significantly affected the mechanical performance of CF/PEEK under high-speed impact conditions. While the strain rate generally enhanced these properties, the strain-hardening effect on the yield strength weakened as the temperature increased, and both the temperature and strain rate contributed to the increase in specific energy absorption. Microdamage mechanism analysis revealed that interface debonding and sliding between the fibers and the matrix were more pronounced under static compression than under dynamic compression, thereby diminishing the efficiency of stress transfer. Additionally, higher temperatures caused the PEEK matrix to soften and exhibit increased viscoelastic behavior, which in turn affected the material's toughness and the mechanisms of stress transfer. These insights hold substantial engineering significance, particularly for the optimization of CF/PEEK composite design and applications in extreme environments.

A Novel Measurement Approach to Experimentally Determine the Thermomechanical Properties of a Gas Foil Bearing Using a Specialized Sensing Foil Made of Inconel Alloy.

Modern approaches dedicated to controlling the operation of gas foil bearings require advanced measurement techniques to comprehensively investigate the bearings' thermal and thermomechanical properties. Their successful long-term maintenance with constant operational characteristics may be feasible only when the allowed thermal and mechanical regimes are rigorously kept. Hence, an adequate acquisition of experimental readings for the critical physical quantities should be conducted to track the actual condition of the bearing. The above-stated demand has motivated the authors of this present work to perform the thermomechanical characterization of the prototype installation of a gas foil bearing, applying a specialized sensing foil. This so-called top foil is a component of the structural part of the bearing's supporting layer and composed of a superalloy, Inconel 625. The strain and temperature distributions were identified based on the readings from the strain gauges and integrated thermocouples mounted on the top foil. The measurements' results were obtained for the experiments that represent the arbitrarily selected operational conditions of the tested bearing. Specifically, the considered measurement scenario relates to the operation at a nominal rotational speed, i.e., during the stable process, as well as to the run-up and run-out stages. The main objectives of the work are: (a) experimental proof for the described functionalities of the designed and manufactured specialized sensing foil that allow for the application of a novel approach to the bearing's characterization, and (b) qualitative investigation of the relation between the mechanical and thermal properties of the tested bearing, using the measurements conducted with the newly proposed technical solution.

Thermomechanical Studies of Yielding and Strain Localization Phenomena of Gum Metal under Tension.

This paper presents results of investigation of multifunctional ß-Ti alloy Gum Metal subjected to tension at various strain rates. Digital image correlation was used to determine strain distributions and stress-strain curves, while infrared camera allowed for us to obtain the related temperature characteristics of the specimen during deformation. The mechanical curves completed by the temperature changes were applied to analyze the subsequent stages of the alloy loading. Elastic limit, recoverable strain, and development of the strain localization were studied. It was found that the maximal drop in temperature, which corresponds to the yield limit of solid materials, was referred to a significantly lower strain value in the case of Gum Metal in contrast to its large recoverable strain. The temperature increase proves a dissipative character of the process and is related to presence of ω and α″ phases induced during the alloy fabrication and their exothermic phase transformations activated under loading. During plastic deformation, both the strain and temperature distributions demonstrate that strain localization for higher strain rates starts nucleating just after the yield limit leading to specimen necking and rupture. Macroscopically, it is exhibited as softening of the stress-strain curve in contrast to the strain hardening observed at lower strain rates.

Avoiding/inducing dynamic buckling in a thermomechanically coupled plate: a local and global analysis of slow/fast response.

The nonlinear response of a reduced model of an orthotropic single-layered plate with thermomechanical coupling is investigated in the presence of thermal excitations, in addition to mechanical ones. Different issues are addressed via accurate and extended local and global analyses. (i) Assessing the possible occurrence, disappearance or modification of mechanical buckling as a result of thermal aspects; (ii) exploiting global dynamics to unveil the effects of coupling; (iii) highlighting the crucial role played by the slow thermal transient evolution in modifying the fast steady mechanical response; (iv) framing the influence of coupling and underlining the need to use a thermomechanical model to grasp the actual plate dynamics; and (v) getting hints of technical interest as to the outcome robustness with respect to variations in the external/internal thermal parameters.