559 research outputs found
An acoustic emission approach to the structural health monitoring of historical metallic tie-rods
The application of Non-Destructive Testing and Structural Health Monitoring systems in historical
buildings is of great interest due to the need to guarantee safety and conservation. The present
memory focuses on the case study of the historical wrought iron tie-rods of Duomo di Milano,
Italy. In recent years, two of these elements presented critical failures. Consequently, a monitoring
methodology based on acoustic emission was defined. First, the fracture toughness of wrought
iron was characterized by employing standard small-scale specimens taken from one of the failed
tie-rods. Meanwhile, acoustic emission was acquired to define a methodology for detecting and
localizing the damage events, separating those due to background noise by applying suitable
pattern recognition algorithms. Subsequently, a tensile test was performed on a full-scale section
of the same tie-rod. Before and after the test, phased-array ultrasonic testing and magnetic particle
inspections were carried out to identify and map defects and their possible development due to
load application. Finally, it was possible to conclude that magnetic inspections allow identifying
the presence of surface defects effectively, phased-array testing estimates the geometry of the
defect accurately, and acoustic emission is a promising technique for monitoring the structural
integrity of historical metallic tie-rods
Analysis of peel and shear strains in cracked lap shear specimens subjected to fatigue loading using digital image correlation
Adhesive bonding presents many advantages, such as efficient manufacturing and improved structural performance [1]. However, in structures subjected to fatigue, cracks might initiate and propagate in joints, leading to in-service failure [2]. Most adhesively bonded joints are subjected to combination of peel and shear loads, so mixed I+II mode loading conditions are present [3]. In this work, Cracked Lap Shear specimens, which feature mixed I+II mode loading conditions, were tested under fatigue loading. During tests, crack growth was monitored using Visual Testing and Digital Image Correlation. With Digital Image Correlation, opening and sliding displacements in the bondline were extracted from the substratesâ displacement fields and compared against a Finite Element Model, revealing a highly strained process zone ahead of the crack tip. Results highlight the usefulness of DIC in capturing the deformation behaviour of adhesive joints under mixed mode loading conditions
Acoustic emission applied to mode I fatigue damage monitoring of adhesively bonded joints
The use of adhesively bonded joints has increased considerably due to their lightweight, relevant
strength-weight ratio and possibility to join multi-materials. Nevertheless, there are still some
challenges in the application of this kind of joints in primary structures, such as guaranteeing their
reliability during the componentsâ useful life.
Structural health monitoring methods are suggested to ensure in-service safety and reliability of
adhesive joints. The acoustic emission appears promising because it can detect the elastic waves
produced within the material when it is under damage or straining.
This research focuses on mode I fatigue damage monitoring metallic double cantilever beam
adhesively bonded joints using the acoustic emission method. Digital image correlation and visual
evaluation were applied during fatigue interruptions to track the crack-tip position within the
adhesive and correlate them with the acoustic emission outcomes.
The acoustic emission method is susceptible and different kinds of waves (background, friction
and damage) can be easily assessed during the tests, producing an immense amount of data. So,
unsupervised artificial neural networks for patterning recognition were proposed. Self-organising
maps and k-means algorithms were used for data clustering and then classified regarding their
sources. Finally, the acoustic emission results, digital image correlation and visual evaluations
were compared
Analysis of peel and shear strains in cracked lap shear specimens subjected to fatigue loading using digital image correlation
Adhesive bonding presents many advantages, such as efficient manufacturing and improved structural performance [1]. However, in structures subjected to fatigue, cracks might initiate and propagate in joints, leading to in-service failure [2]. Most adhesively bonded joints are subjected to combination of peel and shear loads, so mixed I+II mode loading conditions are present [3]. In this work, Cracked Lap Shear specimens, which feature mixed I+II mode loading conditions, were tested under fatigue loading. During tests, crack growth was monitored using Visual Testing and Digital Image Correlation. With Digital Image Correlation, opening and sliding displacements in the bondline were extracted from the substratesâ displacement fields and compared against a Finite Element Model, revealing a highly strained process zone ahead of the crack tip. Results highlight the usefulness of DIC in capturing the deformation behaviour of adhesive joints under mixed mode loading conditions
A multi-sensor approach for volcanic ash cloud retrieval and eruption characterization: the 23 November 2013 Etna lava fountain
Volcanic activity is observed worldwide with a variety of ground and space-based
remote sensing instruments, each with advantages and drawbacks. No single system can give
a comprehensive description of eruptive activity, and so, a multi-sensor approach is required. This
work integrates infrared and microwave volcanic ash retrievals obtained from the geostationary
Meteosat Second Generation (MSG)-Spinning Enhanced Visible and Infrared Imager (SEVIRI),
the polar-orbiting Aqua-MODIS and ground-based weather radar. The expected outcomes are
improvements in satellite volcanic ash cloud retrieval (altitude, mass, aerosol optical depth and
effective radius), the generation of new satellite products (ash concentration and particle number
density in the thermal infrared) and better characterization of volcanic eruptions (plume altitude,
total ash mass erupted and particle number density from thermal infrared to microwave). This
approach is the core of the multi-platform volcanic ash cloud estimation procedure being developed
within the European FP7-APhoRISM project. The Mt. Etna (Sicily, Italy) volcano lava fountaining
event of 23 November 2013 was considered as a test case. The results of the integration show the
presence of two volcanic cloud layers at different altitudes. The improvement of the volcanic ash
cloud altitude leads to a mean difference between the SEVIRI ash mass estimations, before and after
the integration, of about the 30%. Moreover, the percentage of the airborne âfineâ ash retrieved from
the satellite is estimated to be about 1%â2% of the total ash emitted during the eruption. Finally,
all of the estimated parameters (volcanic ash cloud altitude, thickness and total mass) were also
validated with ground-based visible camera measurements, HYSPLIT forward trajectories, Infrared
Atmospheric Sounding Interferometer (IASI) satellite data and tephra deposits
Hydrogen Refueling Stations: Prevention and Scenario Management. Large Scale Experimental Investigation of Hydrogen Jet-Fires
Hydrogen is becoming an attractive alternative for energy storage and transportation, because of the elevated energy content per unit of mass and possibility to have zero carbon-emission vehicles. For these reasons, hydrogen's share in global market is expected to grow substantially in the coming years. Today, hydrogen-fueled buses and cars are already available, and several refueling stations are operating in different countries around the world. A key role of the deployment of hydrogen fueled-vehicles is the presence of a widespread network of refueling stations, especially close to residential and industrial areas. This fact poses attention to the safety aspects related to hydrogen, with particular interest to its high flammability that can lead to catastrophic consequences for personnel and equipment. As a matter of fact, hydrogen is a comparatively less safe fuel compared to conventional fuels such as gasoline and diesel. Hydrogen infrastructures are characterized by operating pressure up to 1000 bar that, in case of an unintended loss of containments, produce a highly under expanded turbulent jet. If ignited, this hydrogen jet may give rise to very severe scenarios, mainly related to high temperatures and the oriented flows. As recently suggested by Moradi and Groth (Moradi and Groth, 2019), there is a lack of experimental and on-site data for almost all of the storage and delivery technologies relevant to the hydrogen infrastructures. Experimental data is vital to support model validation, especially in the case of the very peculiar combustion process of hydrogen. In this way, a real-scale experimental campaign is proposed to investigate the main characteristic of the hydrogen jet fire resulting from its rapid fired depressurizations. Focus of the experimental campaign is evaluation of safety distance for person and device (i.e. pressurized tanks) in order to avoid critical conditions and domino effects in real refueling station. Different initial conditions, i.e., storage pressures, are exploited, and the resulting jet across specified orifice is investigated. More specifically, temperatures at various locations are measured through an arrangement of thermocouples. Values up to 1200 °C were obtained in the core of the jet. Moreover, it was found that the recorded temperatures, especially those at the outer portion of the jet, are very sensitive to the initial conditions
The influence of subsurface geology on the distribution of earthquakes during the 2016â-2017 Central Italy seismic sequence
Abstract In 2016â2017, a destructive sequence of earthquakes affected a wide portion of Central Italy, activating a complex, 80-km long system of SW-dipping normal faults and causing impressive surface faulting and widespread damage. Former studies providing reconstructions of the fault systems activated during this sequence, are mostly based on high-resolution seismological and geodetic data. In this paper, we integrate surface and subsurface geological data with the ones obtained by an irregular network of seismic reflection profiles, aimed at providing a comprehensive reconstruction of the subsurface lithologies and structures in this area. We have constructed a set of five geological cross-sections, passing through the mainshock epicentral areas (Mw > 5.5) of the seismic sequence. The cross-sections are extrapolated down to a depth of ca. 12 km, along which we have plotted relocated seismicity. Combined geological and seismological data support a new 3D seismotectonic model, illustrating the propagation through time and space of the seismic ruptures during the sequence. Our results show that the litho-mechanical stratigraphy exerted a primary control on the distribution of seismicity, as it is mostly hosted in the more competent lithologies (i.e. the Late Triassic-Paleogene succession, consisting of carbonates and evaporites). In addition, we illustrate the crucial role played by the inherited compressional structures in determining the lateral and vertical variations of the rheological properties of the upper crust and, eventually, the overall geometry and segmentation of the seismogenic extensional system. The workflow proposed here can be applied to other seismogenic zones throughout the world, since reliable seismotectonic models require an accurate reconstruction of the subsurface geological setting, based on a close integration of geological, geophysical and seismological data
Tamm Plasmon Resonance as Optical Fingerprint of Silver/Bacteria Interaction
Incorporation of responsive elements into photonic crystals is an effective
strategy for building up active optical components to be used as sensors,
actuators and modulators. In these regards, Tamm Plasmon (TP) modes have arisen
recently as powerful optical tools for the manipulation of light-matter
interaction and for building sensors/actuators. These emerge at the interface
between a dielectric mirror and a plasmonic layer and, interestingly, can be
excited at normal incidence angle with relatively high quality factors.
Although its field is located at the interface between the dielectric mirror
and the metal, recent studies have demonstrated that corrugation at the
nanoscale permits to access the TP mode from the outside, opening new exciting
perspectives for many real-life applications. Here, we show that the TP
resonance obtained by capping a distributed Bragg reflector with a
nanostructured layer of silver is sensitive to the presence of bacteria. We
observed that nanoscale corrugation is essential for accessing the TP field,
while the well-known bio-responsivity of silver nanostructures renders such a
localised mode sensible to the presence of Escherichia Coli. Electrodoping
experiments confirm the pivotal role of nanostructuration, as well as
strengthening our hypothesis that the modifications of the TP mode upon
exposure to bacteria are related to the accumulation of negative charge due to
the bacterial-driven removal of Ag+ ions from its lattice. Finally, we devised
a case study in which we disentangled optically the presence of proliferative
and non-proliferative bacteria using the TP resonance as a read-out, thus
making these devices as promising simple all-optical probes for bacterial
metabolic activity, including their response against drugs and antibiotics
Lipidomics analysis of juveniles' blue mussels (Mytilus edulis L. 1758), a key economic and ecological species
Blue mussels (Mytilus edulis L. 1758) are important components of coastal ecosystems and in the economy of rural and coastal areas. The understanding of their physiological processes at key life stages is important both within food production systems and in the management of wild populations. Lipids are crucial molecules for bivalve growth, but their diversity and roles have not been fully characterized. In this study, traditional lipid profiling techniques, such as fatty acid (FA) and lipid class analysis, are combined to un-targeted lipidomics to elucidate the lipid metabolism in newly settled spat fed on a range of diets. The evaluated diets included single strains treatments (Cylindrotheca fusiformis CCAP 1017/2 âCYL, Isochrysis galbana CCAP 927/1â ISO, Monodopsis subterranean CCAP 848/1 âMONO, Nannochloropsis oceanica CCAP 849/10â NANNO) and a commercial algae paste (SP). Spat growth was influenced by the diets, which, according to their efficacy were ranked as follows: ISO>NANNO/CYL>SP>MONO. A higher triacylglycerols (TG) content, ranging from 4.23±0.82 ÎŒg mgashfree Dry weight (DW)-1 at the beginning of the trial (T0) to 51±15.3 ÎŒg mgashfreeDW-1 in ISO, characterised significant growth in the spat, whereas, a reduction of TG (0.3±0.08 ÎŒg mgashfreeDW-1 in MONO), mono unsaturated FAâMUFA (from 8.52±1.02 ÎŒg mgFAashfreeDW-1 at T0 to 2.81±1.02 ÎŒg mgFAashfreeDW-1 in MONO) and polyunsaturated FAâPUFA (from 17.57±2.24 ÎŒg mgFAashfreeDW-1 at T0 to 6.19±2.49 ÎŒg mgFAashfreeDW-1 in MONO) content characterised poor performing groups. Untargeted lipidomics evidenced how the availability of dietary essential PUFA did not influence only neutral lipids but also the membrane lipids, with changes in lipid molecular species in relation to the essential PUFA provided via the diet. Such changes have the potential to affect spat production cycle and their ability to respond to the surrounding environment. This study evidenced the advantages of coupling different lipid analysis techniques, as each technique disclosed relevant information on nutritional requirements of M. edulis juveniles, expanding the existing knowledge on the physiology of this important species
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