Abstract

The structural monitoring, which is becoming increasingly common, makes it necessary to choose one or more methods of processing and analyzing the obtained data. This choice is key to meeting the objectives of this monitoring. Considering that there are many methods with different capacities and requirements, this choice is a complex problem. This paper presents a methodology for the assessment and selection of methods for the identification of dynamic response properties of buildings using vibration monitoring. In this work, well-known methods based on time domain analysis (subspace-state) and non-parametric methods based on the frequency domain are studied when applied to seismic vibration records for a reinforced concrete building instrumented with a network of tri-axial force-balance accelerometers. For two and a half years, the sensor network has recorded close to 500 sensitive earthquakes. Nonetheless, it only includes those with a magnitude higher than 4.8 (M_L or M_W) and that occurred between September, 2015 and September, 2016. Using six versions of identification methods, modal response parameters are determined for each of the two main directions of the building, considering different levels of information acquired by the sensor network (floor information). An assessment of the performance of each method is conducted based on the number of identified modal frequencies and damping ratios; their variability (coefficient of variation); and the processing time of each method. As a result and conclusion regarding the use of this methodology, it is not only possible to choose the most convenient method for processing vibration records applied to structural health monitoring (SHM) according to its own objective, but also to progressively improve the design of the sensor network.

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Abstract

Structural health monitoring (SHM) by means of embedded fibre optic (FO) sensors is able to perform diagnosis and prognosis of structural damages and defects. SHM system monitor structural status based on the acquired data resulting in the detection and characterization of damages and defects without necessity for the aircraft to be on ground. Optical fibre sensors are permanently installed in the structure and trigger maintenance actions only when a damage or defect of a particular size is detected. To demonstrate the potential of FO sensors technology and their application by means of embedded sensors to composite material aerostructures, manufacturing trials have been performed and the influence in mechanical behaviour of the sensors’ embedding has been studied by performing tests campaings, at coupon level, for experimental validation. This study is within the scope of SHERLOC, a project belonging to the Clean Sky 2 JU aeronautical research and development program, and of which main objective is to combine advanced Structural Health Monitoring (SHM) and smart repair technologies with a probabilistic design philosophy, and hence to develop new maintenance concepts to reduce the direct operative costs without lowering the operational safety of a composite fuselage.

Abstract

In the present work, a model of electrical properties of composites with inherent sensing properties is proposed. More specifically, the effect of both geometry and dispersion procedure is analyzed for carbon nanostructured polimers, exploring their influence in its electromechanical properties by developing simple analytical methods. In this context, it is observed that a better CNT distribution (by reducing the aggregate ratio) leads to a higher electrical conductivity as well as a higher electrical sensitivity to mechanical deformation. Therefore, the proposed model allows to get a deepr knoweledge about the influence of different processing parametrs in the final electrical properties of the nanocomposite. Moreover, the experimetal testing of self-sensing structures has been carried out by using a carbon nanotube doped adhesive film. More specifically, it has been observed that the proposed nanostructured adhesive presnts an outstanding capability for early damage detection and propagation, being a promising technique in order to complement other available inspection methods. This tests have been validated at coupon level, as well as a subelement one, by using stiffened panels. In addition, it has been proved a higher capability for detecting the presence of possible weak interfaces, demonstrating the applicability of the developed technique.

Abstract

Fibre-Reinforced Polymer (FRP) materials are widely used in the construction of small-length vessels due to their light weight and high strength to weight ratio. However, the use of FRP materials in vessels above 50 m length is only allowed to secondary structural elements of the vessel. Hence, it is necessary to promote the creation of new regulatory frameworks to permit the construction of large-length vessels using composite laminates in all parts of the vessel structure to enable the development of this interesting technology for the reduction of weight. FIBRESHIP proposes to create a new market focused on the construction of large-length vessels based uniquely on lightweight composites. The results of this project are attracting considerable interest within the shipping industry as the extensive use of FRP materials in large-length vessels induces an important reduction of the weight with respect to the conventional steel ships. This significant weight reduction decreases the vessel bunkering consumption, increases the payload cargo capacity, and avoids the corrosion phenomena in the vessel among other identified benefits.

Abstract

Optical fibre Bragg grating (FBG) sensors are commonly used for structural health monitoring in composite materials, since their small dimensions, high sensitivity and multiplexing capacity are a good match with the structures to be monitored. We present a method for making a low-loss connection to an FBG optical fibre sensor that is integrated in a fibre reinforced composite structure. The method allows to both manufacture composite structure without taking special precautions to prevent damage to the connecting fibre and (if needed) to repair the connecting fibre, while optimizing the optical connection efficiency even if both fibres have dissimilar mode field diameters.

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