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.

Abstract

Abstract

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

Guided wave-based structural health monitoring (SHM) systems using piezoelectric sensors for composite parts face challenges due to the weight of copper wiring. This study developed lightweight, 3D-printed conductive paths using silver ink (Dycotec Materials) and epoxy (Epolam 8052) doped with carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs). The inks were characterized for their weight and conductivity with a Keithley 2410. Following which they were evaluated for signal transmission of guided waves and easy integration with induction heating. Nanoparticle-doped epoxy inks demonstrated increased viscosity and controlled circuit dimensions, though dispersion issues led to voids and agglomerates. Unmodified silver inks did not show good printing quality; however, the quality was improved significantly with the adding of GNPs. Circuits from both inks were evaluated for conductivity and signal transmission. Silver inks achieved conductivity levels comparable to copper and effective signal transmission, while nanoparticle-doped epoxy had significantly lower conductivity and signal loss (2-3 times), even at its best formulation. A lightweight film integrating silver circuits was successfully bonded to a composite panel using induction heating, demonstrating a rapid integration method for SHM systems. These findings highlight the potential of metallic and nanoparticle-doped inks to replace traditional copper wiring, offering significant weight reduction, and easier integration capabilities for SHM applications.

Abstract

Structural health monitoring is essential to ensure safety and extend the service life of critical components in renewable energy systems, such as repaired wind turbine blades. This study presents the development of strain gauges printed using advanced functional printing techniques, optimized for integration into composite materials and tailored to the mechanical characteristics of repaired areas to assess the effectiveness and durability of structural repairs. The integration of these sensors would enable real-time monitoring of key parameters, such as microstrains, during the operation of the blade after repair. 
The experimental work included the printing of strain gauges, evaluation of different substrates, and cyclic loading tests under controlled conditions to assess the accuracy and sensitivity of the printed gauges. Additionally, composite material coupons were characterized under tensile and compressive loads to analyse the impact of gauge integration on the mechanical properties of the composite. Preliminary results demonstrate the feasibility of this approach, although full validation is required, including aging studies, testing in real operational environments, and exposure to extreme temperature variations prior to industrial implementation.

Abstract

Soft magnetic materials are excellent candidates as sensors for monitoring materials, applications and processes, having already found application in multiple sectors [1]. Moreover, their ability to be configured as microwires ensures excellent integration within composite structures, making them ideally suited for reinforced material monitoring.

At GAIKER, within the INFINITE and MOSINCO projects, required equipment and characterization techniques have been developed to evaluate the behavior of electromagnetic properties under various stimuli (stress, temperature...) These investigations have enabled the analysis of both hysteresis loops and scattering parameters in transmission and reflection within the microwave range, under conditions such as composite matrix polymerization or when subjecting specimens to different stress states [2]. Consequently, a clear dependency of scattering parameters and impedance on applied stress, which can be monitored, has been demonstrated [3].

However, despite the repeatability of the phenomenon, modeling this behavior is challenging due to the dispersion of results caused by multiple factors and varying conditions that influence outcomes in a conventional environment. This study analyzes the influence of the relative sample position on these measurements and presents results obtained by modifying the position and orientation of microwires through rotation and flipping movements of the test specimen.

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.