155 research outputs found
Passive and Active Thermography for surface treatments characterization in spur gears
No full textL'abstract è presente nell'allegato / the abstract is in the attachmen
An active thermography approach for materials characterisation of thermal management systems for Lithium-ion batteries
No full textThe aim of this work is an alternative non destructive technique for estimating the thermal properties of four different Thermal Management System (TMS) materials. More in detail, a thermographic setup realized with the Active Thermography approach (AT) is utilized for the purpose and the data elaboration follows the ISO 18755 Standard.
As well known, Phase Changes Materials (PCMs) represent an innovative solution in the Thermal Management System (TMS) of Lithium-Ion batteries and, during the years, many solutions were developed to improve its thermal properties. As a matter of fact, parameters such as the internal temperature or heat exchanges impact on both efficiency and safety of the
whole battery system. Consequently, the thermal conductivity was often chosen as a performance indicator of Thermal Management System (TMS) materials.
In this work, both thermal diffusivity and thermal conductivity were estimated in two different testing conditions, respectively at room temperature and higher temperature conditions. The Active Thermography (AT) technique proposed in this activity has satisfactory estimated both thermal diffusivity and thermal conductivity of Thermal Management System (TMS)
materials. An analytical model was also developed to reproduce the temperature experimental profiles. Finally, results obtained with AT approach were compared to those available from commercial datasheet and literature
Thermographic approach for a rapid fatigue limit estimation of gears
No full textGear resistance is an important mechanical aspect to ensure the proper functioning of power transmission systems. It is well
known that one of the most dangerous failures in gears refers to tooth root fillet cracks, generally caused by bending fatigue.
Standards help engineers in the gear design phase by providing material resistance data arranged on the basis of chemical
composition, manufacturing process and surface treatment. The execution of experimental campaigns involving bending fatigue
tests can be approached through two classical methodologies: meshing gears (MG) and Single Tooth Bending Fatigue (STBF)
test approaches. However, it is important to note that both approaches necessitate a significant amount of time and effort. In this
work, the STBF approach was adopted in combination with a Thermographic monitoring. This way, a full superficial acquisition
of the tooth root thermal emission was performed during the fatigue test at different loads. So, the fatigue limit was estimated by
an iterative analysis of thermal parameters evolution (Two Curves Method, TCM). The proposed Thermographic approach
(TCM), already well-established in the literature for classical samples, allowed in this work to obtain fatigue limit data in the
specific case of gears. Gears made of C45 and 20MnCr5 with surface treatments as induction hardening and case hardening
respectively were tested. The obtained results in terms of bending fatigue limit values were compared with those evaluated by
using consolidated approaches as the Staircase Method and with the indications available in ISO 6336 Standard for that material
Active Thermography for residual stresses identification in gears by using different heating sources
No full textThe application of Non-Destructive Techniques (NDTs) in mechanical research is becoming significant since there is a growing demand for non-invasive research methodologies that also consider the environmental impact. An innovative configuration of Thermography, called Active Thermography (AT), meets this demand and is already used in industrial areas to investigate defects within the material. Recent studies have also explored the potentialities of AT in other mechanical fields such as material characterisation or damage investigation, extending its applicability to other industrial research fields. The aim of this work is to expand the application of AT in the field of surface treatment analysis. In particular, an alternative Non-Destructive approach based on AT was proposed for the identification of residual stresses by means of thermal responses, and the thermal results obtained with two different heating sources are presented and compared with classical X‐Ray residual stress measurements. A laser and a lamp were used to generate localised and distributed heating over the surface of the investigated specimens. Dedicated data elaboration procedures and thermal indexes were proposed for the surface treatment identification based on the heating source adopted during the Active Thermography tests. The results are illustrated for samples and gears, made of 20MnCr5 steel, subjected to carburizing and shot peening surface treatments. A detailed analysis of both mechanical and physical properties was also carried out to verify the AT results
Application of NDT active thermography for the characterization of the cold spray process of high entropy alloys
No full textA Non-Destructive technique (NDT) based on Active Thermography (AT) is proposed to correlate mechanical properties, process parameters and thermal response for High Entropy Alloys (HEA) coatings. More in detail, the Pulsed technique is utilized to investigate thermal responses generated by different High Entropy Alloys (HEA) coatings. In particular, specimens tested in this work are made of several chemical compositions (AlxCoCrCuFeNi and MnCoCrCuFeNi) and are realized by using different Cold Spray temperatures (650 °C, 750 °C and 850 °C), generating coatings with various mechanical properties. This way, results in terms of thermal responses obtained with a Non-Destructive technique are correlated, by means of ANOVA, with the corresponding chemical compositions and process parameters of each specimen. The impact of both roughness and emissivity on the process characterization was also investigated
Value-at-Risk dynamics: a copula-VAR approach
No full textIn financial research and among risk management practitioners the estimation of a correct measure of the Value-at-Risk still proves interesting. A current approach, the multivariate CAViaR allows to provide an accurate measure of VaR modelling the joint dynamics in the Values-at-Risk by capturing the quantile conditional dependence structure to take into account financial contagion risk. The parameter estimates are based on multiple quantile regressions which assume linear combinations of sample quantiles. In this paper we argue that the analysis of multiple time-series aimed to model the time-varying quantile dependence can require non-linear and flexible estimation procedures. To this end, we examine the conditional quantile behaviour of some assets included in the Eurostoxx50 with respect to the quantile of a portfolio representing the market with a new copula-based quantile Vector AutoRegressive approach, and compare the results with the bivariate CAViaR model. Findings show that the copula approach is highly competitive, providing a time-varying model aimed to give a better specification of the Value-at-Risk, especially in terms of loss functions
Tribo-thermo-electrical investigation on lubricating grease enriched with graphene nano-platelets as an additive
No full textMany efforts are being made in recent years to boost the performance of traditional lubricants with innovative nano-additive, like graphene. In this paper, long-term lubricated pin-on-disc tests were performed with four grease compounds filled with 0.5 %–5 % graphene nano-platelets. Severe contact conditions were explored to investigate the impact of graphene on the performance and thermal properties of grease. The temperature of the sliding contact and the in-situ electric contact resistance were monitored and correlated to friction and wear. Results of the tribo-thermo-electrical tests indicated that a moderate quantity of graphene reduce both friction and wear because graphene strengthened the lubricating film against scuffing. However, an excessive quantity was detrimental and interfered with lubrication. Graphene also affected the thermal properties of grease, but it did not directly affect the overall thermal behaviour of the tribopair
Experimental and Numerical Wear Characterization by Means of Active Thermography Technique
No full textThermography is a non-contact technique used to obtain thermal maps
of a component surface. Active Thermography (AT) has gained a lot of interest
in recent years as a tool to characterize thermal properties and fatigue damage
in materials, coatings, and components. Hidden flaws can also be detected based
on the surface thermal map in a non-destructive way . This paper presents a preliminary
experimental procedure where Lock-in AT is exploited to characterize
wear damages of a flat steel surface featuring a series of linear wear traces from
pin-on-flat wear tests. A dedicated temperature data processing route was set up to
correlate thermal signals to the characteristic parameters which may identify the
amount of material loss by wear. The results suggest that AT may be a promising,
fast, and alternative method to detect and quantify wear on surfaces. An exponential
law correlates the wear track width, depth, and area with the intensity peaks
of the fundamental harmonics of the pulsed thermal response. Although the sensitivity
and reliability of this method is still to be assessed, this preliminary work
might pave the way to significant implications for AT in industry in the case of
wear on hidden surfaces
Metodologia di identificazione delle tensioni residue su materiali e componenti mediante tecniche di termografia attiva
No full textLa termografia attiva applicata allo studio della fatica nei materiali metallici: un caso studio
No full textLa fatica in campo elastico o ad alto numero di cicli nei materiali metallici viene generalmente associata alla dissipazione intrinseca, espressa come dissipazione di energia associata alla sollecitazione meccanica a cui il materiale viene sottoposto. Lo smorzamento interno viene descritto generalmente come un indicatore dello stato microstrutturale, diretta conseguenza del danneggiamento irreversibile in corso nei materiali in seguito al fenomeno della fatica meccanica. In letteratura è ormai consolidato l’uso della termografia passiva come tecnica non distruttiva per caratterizzare il danneggiamento a fatica di materiali e componenti e non solo.
Questo lavoro si propone di confrontare l’approccio termografico attivo e passivo nell’indagine del danneggiamento a fatica e della sua evoluzione.
Il caso studio indaga provini in C45 sottoposti a diversi livelli di cicli di fatica meccanica.
I risultati mostrano come la risposta termica del materiale varia al variare del danneggiamento
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