1,720,997 research outputs found
Guided wave propagation and interaction with ice layers in marine structures
No full textReliable and autonomous monitoring systems have been increasingly considered to enhance metal and composite-based maritime structures. The main goal is to continuously assess the overall condition of the structure using several nodes of sensors to ensure safety and cost-effective maintenance during the lifetime. To achieve the detection of small emerging flaws, ultrasound wave propagation in thin sheets is successfully adopted to interrogate both metallic and composite structures. However, ships are operating in water environment and even in polar regions, making the correct extraction of damage parameters from ultrasound signals quite challenging. An interesting and practically important aspect deals with icing problems, where thin layers of ice emerge in direct contact with the ship’s hull. This may lead to misinterpretations of measured signals, inducing false alarms and potentially missing damage detection. Guided wave propagation should be investigated in this contribution accounting for these aspects to prevent misleading interpretation. A finite element model has been considered including ice models to address the effect of an emerging ice layer on wave propagation using both pitch-catch and pulse-echo approaches. Numerical results show that reflections generated at the discontinuity raise with the thickness and length of ice layer. The ice accretion affects the transmitted energy, whose result is even more visible in the direct propagation analysis. The outcomes definitely prove the ability of guided waves to detect ice and the modeling is well suited for preliminary design of further experiments
Investigation on guided waves propagation across ice layers
No full textIcing conditions are threatening for a variety of engineering applications. When accreting on the aircraft surface, ice may lead to catastrophic accidents while its deposition on turbine blades can overload the components reducing power and inducing damage. The first way to protect engineering constructions from icing issues deals with early detection of ice. Ultrasound has been demonstrated to be effective for detecting changes of the structure which it is propagating through. Guided waves interact with emerging flaw and discontinuity, including ice accreting on the surface. This paper introduces an experimental campaign carried out on composite structures subject to icing. The building up of planar ice onto surface structure is analysed. Furthermore, a parametric investigation is carried out by finite element modelling to look into the interaction between wave and ice while varying its dimension. Experimental findings demonstrate the ability of guided waves to detect ice layers accreting onto surface. In addition, the ice is likely to be identified from the scattering of guided waves resulting in different transmission and reflection characteristics. Instead, numerical outcomes show how the interaction of guided waves depends upon the thickness and length of the ice
Surface ice detection on composite plates with ultrasonic guided waves
No full textThe paper presents an integrated active system for ice detection on composite plates with ultrasonic guided waves. The aim is to efficiently detect ice formation and growing on complex structures to ensure safety in transportation vehicles. Ice may lead to serious hazards and its early detection is crucial to avoid catastrophic events. In addition, structural health monitoring based on wave propagation benefits from its early detection preventing misleading interpretation of ultrasound signals. Guided wave propagation, likely adopted for damage monitoring in complex structures, can be likewise adopted to reveal the presence of the ice and characterize its dimension. Experimental tests have been carried out in this work to investigate the effect of an emerging ice layer on wave propagation using the pitch-catch approach. Different measurements have been carried out on a glass fiber composite panel integrated with light piezoelectric actuators. The icing condition is simulated using a climate chamber where water is used to trigger the ice formation. The ultrasonic data have been recorded with a dedicated acquisition system. Results show that reflections generated at the ice location are quite visible in the propagating waves indicating waves as ice sensitive. In addition waterfall diagram and RMS analysis show that ice significantly changes the signals. The outcomes and their post-processing analysis definitely prove the ability of guided waves to detect ice
Experimental characterization of a damage detection and localization system for composite structures
No full textStructural health monitoring aims to reduce life-cycle costs as well as design constraints of composites due to unforeseen events like impacts with objects. Guided waves are effectively employed in this process because they show a great sensitivity to flaws in the structure and are able to provide a continuous monitoring. However, the complexity of wave propagation in composites suggests a detailed analysis of the diagnostic methodology in every critical aspect to achieve an effective and reliable implementation of the monitoring system.
This paper presents the results of the experimental characterization of a methodology for damage identification and localization where permanently-installed sensors are employed to create a network for structural health monitoring. A statistical approach is adopted to select the nodes in the network that are affected by the emerging flaw. Different techniques have then been compared to locate the damage. Results are generally in good agreement with the actual location of the damage, although the best performance is obtained with a density-based algorithm applied to the nodes affected by the damage. Furthermore, measurement uncertainty strongly affects measurement of the damage position, and it is shown that its value depends on the specific detection and localization strategy. Moreover, we show the effect of the identification threshold on the localization procedure, and provide an optimal value
Sensor integration within composite structures for continuous load monitoring
No full textComposite structures show a very complex mechanics and requires to pass trough a very strict design and challenging maintenance tasks. To relax design and maintenance constraints, structural health monitoring and load monitoring have been increasingly investigating for decades. Nonetheless, there is still a gap between scientific results and industry deployment due to different aspects such as sensors' equipment costs, manufacturing costs, durability and reliability of the integrated structure. This paper deals with the integration of commercially available strain gauges within coposite structures in view of low cost system for continuous load monitoring. The manufacturing process has been controlled opportunely to succesfully embed sensors among different plies. Several tests have been carried out to investigate the effect of the insert on the durability of components and the reliability of the monitoring system approaching linear and non-linear behaviour of structures. The results shows that integrating sensors in composite specimen could even benefit the stiffness of the overall section. However, the thoughness of the material is affected negatively, compromising the durability. Nonetheless, the changes respect to pristine configuration are compensated by the benefit of integrating sensors within the structure. In addition data can be stored to fatigue record and may also be used to warn the occurrence of a damage whether due to the insert induced discontiuity or to the excessive load achieved
Interaction of guided electromagnetic waves with defects emerging in metallic plates
No full textUltra-wideband guided electromagnetic waves have been recently adopted to detect damage in structures. Transmission and reflection coefficients are indeed sensitive to any defect within the waveguide and can potentially warn the presence of hidden failures. Within this context, the paper shows a detection and localization approach for a structural health monitoring system based on elctromagnetic sensors permanently integrated with the structure to be monitored. A metallic plate is equipped with a dielectric waveguide patch attached to the structure's surface and a multi-input multi-output approach is adopted to interrogate the host component characterized by a reversible defect in different position. The findings show the sensitivity of transmission and reflection loss to the defect presence in between 3-20 GHz. Furthermore, an optimal frequency band beyond 12-15 GHz can be generally found. Based on wave spectrum changes, damage indicators result reliable means of detection. On top of that, they can be further elaborated to reconstruct and localize the defect. Both the amplitude and the phase of the signals are worth being investigated as detection and localization features
Simultaneous load and structural monitoring of a carbon fiber rudder stock: Experimental results from a quasi-static tensile test
No full textCarbon-fiber-reinforced plastics are widely used in lightweight marine structures due to their high strength and superior fatigue behavior. In this article, we will present an innovative methodology for simultaneous load and structural monitoring of a carbon-fiber-reinforced plastic rudder stock as part of a big commercial vessel. Experimental results are presented here from a quasi-static tensile test in which the load monitoring is performed using embedded strain sensors. Structural monitoring is based on high-frequency electromechanical impedance spectroscopy combined with dedicated signal processing and surface-mounted piezoelectric transducers. We have achieved the following results: (1) the demonstration of a hybrid monitoring system including load and structural monitoring, (2) successful embedding of strain gauges during composite manufacturing of the carbon-fiber-reinforced plastic rudder stock, (3) development of instrumentation hardware for multichannel electromechanical impedance measurements, and (4) successful damage detection by means of electromechanical impedance spectroscopy in thick carbon-fiber-reinforced plastic rudder stock samples exploiting strain data
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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