1,721,941 research outputs found
Thermography for defect detection and structural integrity analysis: comparison of new and established methods and novel procedures for a robust quantitative assessment
No full textSubsurface defects can be detected by pulsed thermography, starting from the evaluation of the temperature response at the surface. However, it is necessary a post-processing of the raw thermal data, in order to provide quantitative information, such as defect depth and size. In the past, many algorithms have been developed to localize defects with a very good contrast and also to estimate their depths such as Thermal Signal Reconstruction (TSR®) and Pulsed Phase Thermography (PPT). There are also different numerical models, one, two or three dimensional, that describe the thermal behavior after a pulsed test of a certain duration that help to have an estimation about the correct thermographic parameter to perform a quantitative analysis. Therefore, a lot of very important parameters, such as the acquisition frequency, the power of the heat sources, the truncation window size in terms of analysis window and also the required geometrical resolution change with the used material, the sample geometry and also the type of expected defect (delamination, crack, porosity, flat bottom hole); for this reason the same have to be selected carefully. Even if many publications have been already dealing with these topics, within this dissertation a new approach is proposed for performing a quantitative and correct analysis after a pulsed test. In particular, a very critical type of material has been studied, such as the aluminum one, because of the major part of the past works regards the composite materials, which are not affected by the problems due to the high diffusivity when a pulsed test is performed. A very large investigation concern the possibility to detect the defects in an aluminum sample with different flat bottom holes, having also very critical aspect ratio values less than 2, by applying different post-processing algorithms such as Principal Component Thermography (PCT), Pulsed Phase Thermography (PPT), Thermal Signal Reconstruction (TSR®), Slope and Square Correlation Coefficient (R2). The influence of the truncation window size, the flash power, and the acquisition frequency has been investigated and also different set-ups, with very different peculiarities, have been used in order to compare the possible achieved results. The new proposed quantitative approach starts from the evidence that exists a linear correlation between the defect aspect ratios and their relative contrasts, shown after the application of different post-processing algorithms and a suitable truncation window size. This experimental evidence has been also explained by simulating the thermal behavior with different well-established models. In this way, the possibility to have an estimation of defect depth and size is however demonstrated by using a very low-cost set-up with very competitive acquisition parameters. The limits of PPT and TSR® algorithms are shown when the aim is to have quantitative information in very high diffusivity materials. An important part of this dissertation regards the application of the pulsed thermography to investigate the thermal behavior of different materials and typical defects involved within several industrial and research applications. In this part of the dissertation, the results in terms of “how to analyze a thermographic data to characterize a defect and quantify it” obtained within the first part, will be used and further studies to solve and investigate components with real and particular types of defects. Finally, new procedures very similar to the one proposed in the first part to quantify imposed defects, will be outlined and described, for evaluating the quality of industrial processes of spread interest, that require not only the identification of the defect, but the control of decisive process parameters . In particular, a lot of pulsed tests, by using different energy sources and IR cameras, and also different thermographic parameters in terms of frame rate and pulse duration have been performed to detect typical defects in a Metal Additive Manufacturing process. This particular type of defects is not simple to detect because they are very small and superficial and also their typical irregular 3D shape involves small air pockets air pockets inside the material. A new and suitable approach has been proposed to control the integrity of a real component by using the thermography as a non-destructive technique. The starting point of this procedure is the comparison between the results reached by using two very different non-destructive techniques, such as the pulsed thermography in terms of Pulsed Phase Thermography and the ultrasonic one in terms of C-scan map with a Phased Array Technology, in the estimation of delamination depth in a composite material. The proposed approach allows for extracting the sound area from the same real component to get information about defect size and depth of a defective part having the same its geometry. Novel procedures for a robust quantitative assessment have been carried out. The first one regards the application of a very simple transmission set-up in order to perform pulsed tests to control the quality of different RSW (Resistance Spot Welding) joints. Different steel joints were obtained from the RSW process by varying the main process parameters such as current and time. By studying the thermal behavior in correspondence of the nugget of these welded joints, it is possible to find different thermographic “indexes”, capable of assessing the quality of joints. A further investigation regards the possibility to use a thermographic method for estimating the coating thickness by using a calibration curve, like the approach shown in the case of an aluminum sample with different flat bottom holes. The investigation regards a coating and a basic material in steel with very close thermophysical properties. For this reason, also in this sac, the limits that shown the classical methods to do a quantitative analysis in this type of application are shown in detail. However, by using a very low-cost equipment, mainly for the used infrared camera, that is a microbolometer one, it will be shown how these limits can be overcome, by developing a new thermographic procedure capable to provide an estimation of the coating thickness from 1 to 10 mm. All the investigated applications are related by a main topic: the possibility and also the necessity to use the thermography as a quantitative control in a lot of industrial and research applications. It is worth to underline that, it is necessary to have a standard as a reference, such as a sample with different imposed defects, or a sample with quality feature well known, or again another type of non destructive technique, in order to calibrate pre and post-processing thermographic parameters before to move on to the analysis of a real component. The variety of the treated real problems such as the detection of typical metal additive manufacturing defects, shows once again as thermography is a versatile and competitive type of non destructive control in terms of time and costs and as a more that promising technique to talk about of “integrity analysis” in the field of engineering
Non-destructive thermographic methods for quality evaluation of thin joints
Full text linkQuesto lavoro mira a sviluppare procedure di controllo non distruttivo, automatizzate o semi-automatizzate, per valutare la qualità di giunti saldati sottili utilizzando tecniche di termografia stimolata. Dopo un'analisi approfondita dello stato dell'arte dei metodi tradizionali di controllo non distruttivo per giunti sottili, si è riscontrato che le tecniche termografiche possono essere utilizzate sia per una valutazione quantitativa della regione fusa nelle saldature RPW che per la verifica di cambiamenti microstrutturali attraverso la misura della diffusività termica. Dopo aver sviluppato una procedura di prova di termografia pulsata per misurare la zona fusa nei giunti RPW, questa è stata validata utilizzando controlli ben consolidati come ultrasuoni e tomografia computerizzata come riferimenti. Inoltre, utilizzando modelli a elementi finiti e metodologie di Design of Experiment (metodo delle superfici di risposta), è stato condotto uno studio sull'influenza dei parametri di test sull'errore nella misura della diffusività termica, identificando una procedura di test per la selezione dei parametri più adatti. Si è anche scoperto che la tecnica laser pulsata è capace di distinguere diverse microstrutture in acciai al boro attraverso la misura della diffusività termica, che è stata successivamente correlata con la resistenza a trazione monoassiale, consentendo una stima di quest'ultima attraverso la misura della diffusività termica.This work aimed to develop non-destructive control procedures, either automated or semi- automated, for evaluating the quality of thin welded joints using active thermography techniques. After a thorough analysis of the state of the art of traditional non-destructive control methods for thin joints, it was found that thermographic techniques can be used both for a quantitative evaluation of the fusion region in RPW welds and for verifying microstructural changes through the measurement of thermal diffusivity. After developing a pulsed thermography testing procedure to measure the fused zone in RPW joints, this was validated using well-established controls such as ultrasound and computed tomography as references. In addition, using finite element models and Design of Experiment (Response surface method) methodologies, a study was conducted on the influence of test parameters on the error in the thermal diffusivity measurement, identifying a testing procedure for selecting the most suitable parameters. It was also found that the pulsed laser thermographic technique can distinguish different microstructures in boron steels through thermal diffusivity, which was subsequently correlated with the ultimate tensile strength, allowing for an estimation of the latter through the measurement of thermal diffusivity
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
On the Micro-Macro limit in traffic flow
Full text linkWe investigate the relations between a macroscopic Lighthill-Whitham and Richards model and a microscopic follow-the-leader model for traffic flow. Solutions to the microscopic model are proved to tend to those to the macroscopic one in a sort of kinetic limit, i.e. as the number of individuals tends to +∞ while their total mass is constant. Based on this convergence result, we approximately compute the solutions to a conservation law by means of the integration of an ordinary differential system
Avocado (Persea americana Mill.) by-products and their impact: from bioactive compounds to biomass energy and sorbent material for removing contaminants. A Review
No full textAvocado industry produces enormous by-products and represents an important source of raw material in
food and non-food applications. This review aims to focus the attention on the valorisation of avocado
wastes recycling to produce different materials with important industrial and environmental impacts. In
fact, peels and seeds can be reused in food and cosmetic fields due to the presence of bioactive ingredients
such as polyphenols; thanks to their antioxidant and antinflammatory activities. In addition, both peels
and seeds can be reused in the production of carbonaceous materials with important consequences for
environmental pollution in the removal of contaminants from water. Interesting applications of avocado
wastes in photocatalysis and biofuel production are also discussed. All the utilisations attest the great
potential of recycling avocado by-products, a little known resource
Recensione a: Fortier, V. (ed.), La circoncision rituelle. Enjeux de droit, enjeux de vérité
No full textEpidemiologia della malattia in Italia. Cosa ècambiato? Territorio, le professioni e lo stile di vita. E' giunto il tempo dello screening?
No full textEpidemiology of disease conditions in Italy. Has anything changed? Environment, professional
exposure, and lifestyle. Is time for screening?
Risk factors analysis in bladder cancer should consider not only the clinical and pathological features
of the tumor but also environmental and lifestyle factors. They may play, in fact, a relevant role not only
in the pathogenesis but also in the biological behavior of the tumor. The association between cigarette
smoking and bladder cancer has been consistently confirmed in several case-control and cohort studies.
The risk of bladder cancer seems to increase with duration and intensity of smoking. Another environmental
risk factor, although not definitively proved, is water supply. Chlorination or water pollution
by pesticides and other chemical factors is considered a relevant risk factor. Familiarity and genetic
predisposition, diet and individual risk factors should be taken into account
MEMORIA DI SHAKESPEARE, 8, ON AUTHORSHIP
No full textThis monographic number of the Journal "Memoria di Shakespeare" is dedicated to the problem of apocrypha and authorship, and it includes articles both in English and Italian by major experts in the field
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