Heat flux evaluation in high temperature ring-on-ring contacts

A comprehensive methodology to investigate heat flux in a ring-on-ring tribometer is presented. Thermal fluxes under high contact pressures and temperature differences were evaluated through an experimental campaign and by a numerical procedure of inverse analysis applied to surface temperature measurements. An approximation of a two-dimensional time-dependent analytical solution for the temperature distribution was first developed and subsequently adapted to mimic the specific testing configuration characteristics; the problem was finally simplified to enable further inverse analysis. Experiments were performed using an innovative high temperature ring-on-ring tribometer. The evaluated contact heat transfer rates were reported as a function of normal load and temperature difference between the discs under steady-state conditions; the results reported here show that, in the present test configuration, the temperature difference has stronger influence than the applied load in terms of heat transfer induced by contact

Reliability of Real-Time Kinematic (RTK) Positioning for Low-Cost Drones’ Navigation across Global Navigation Satellite System (GNSS) Critical Environments

UAVs are nowadays used for several surveying activities, some of which imply flying close to tall walls, in and out of tunnels, under bridges, and so forth. In these applications, RTK GNSS positioning delivers results with very variable quality. It allows for centimetric-level kinematic navigation in real time in ideal conditions, but limitations in sky visibility or strong multipath effects negatively impact the positioning quality. This paper aims at assessing the RTK positioning limitations for lightweight and low-cost drones carrying cheap GNSS modules when used to fly in some meaningful critical operational conditions. Three demanding scenarios have been set up simulating the trajectories of drones in tasks such as infrastructure (i.e., building or bridges) inspection. Different outage durations, flight dynamics, and obstacle sizes have been considered in this work to have a complete overview of the positioning quality. The performed tests have allowed us to define practical recommendations to safely fly drones in potentially critical environments just by considering common software and standard GNSS parameters

How do cardiologists select patients for dual antiplatelet therapy continuation beyond 1 year after a myocardial infarction? Insights from the EYESHOT Post-MI Study

Background: Current guidelines suggest to consider dual antiplatelet therapy (DAPT) continuation for longer than 12 months in selected patients with myocardial infarction (MI). Hypothesis: We sought to assess the criteria used by cardiologists in daily practice to select patients with a history of MI eligible for DAPT continuation beyond 1 year. Methods: We analyzed data from the EYESHOT Post-MI, a prospective, observational, nationwide study aimed to evaluate the management of patients presenting to cardiologists 1 to 3 years from the last MI event. Results: Out of the 1633 post-MI patients enrolled in the study between March and December 2017, 557 (34.1%) were on DAPT at the time of enrolment, and 450 (27.6%) were prescribed DAPT after cardiologist assessment. At multivariate analyses, a percutaneous coronary intervention (PCI) with multiple stents and the presence of peripheral artery disease (PAD) resulted as independent predictors of DAPT continuation, while atrial fibrillation was the only independent predictor of DAPT interruption for patients both at the second and the third year from MI at enrolment and the time of discharge/end of the visit. Conclusions: Risk scores recommended by current guidelines for guiding decisions on DAPT duration are underused and misused in clinical practice. A PCI with multiple stents and a history of PAD resulted as the clinical variables more frequently associated with DAPT continuation beyond 1 year from the index MI

The dilatometric technique for studying sigma phase precipitation kinetics in F55 steel grade

Sigma phase precipitation occurring during the exposure of duplex stainless steels in the temperature range from 800 to 900 °C deeply affects the material toughness and corrosion resistance. σ-Phase precipitation process is strongly influenced by many physical parameters, such as the specific chemical composition, the ferrite amount and its average grain size, and the entity of plastic deformation due to the previous technological process. The strong dependencies of σ-phase precipitation on all these factors justify the continuous study of the process kinetics. This paper focuses on the σ-phase precipitation kinetics in F55 steel grade. The investigation has been performed by an innovative experimental method, such as the anisothermal dilatometric technique. The application of the Kissinger’s method has been used for deriving the process activation energy and kinetics. The results have been compared with the ones obtained by metallographic analysis and hardness tests performed on isothermally aged samples, heat-treated in a laboratory furnace at 850 °C

Heat treatment and impact toughness of the f55-grade steel

Low-temperature impact tests are commonly performed to test the quality of industrial forgings in Duplex Stainless Steels (DSS). The F55 grade is a highly alloyed Super DSS characterized by excellent low-temperature toughness in the solution annealed condition. Because of the rich chemical composition, it is very prone to precipitation phenomena during quenching. This research investigates the effect of the material cooling rate on the impact toughness of a water-quenched F55 steel, characterized by the absence of s-phase. Furthermore, by elaborating the impact test data, the T45J [°C] and the KV-46°C [J] parameters have been identified. They are two indicators based on the austenite/ferrite ratio and the material cooling rate, useful for predicting the material impact behavior prior to testing

High-temperature mechanical properties of P91 weld metal

Increasing temperature is one of the key factors for improving the efficiency of steam power plants. Important metallurgical phenomena are activated at such high temperatures and creep resistance becomes a driving criterion for the material selection. Ferritic steels, including 2Cr, 9Cr, and 12Cr steels, are among the best candidates; their continuous development and optimization with the addition of Mo, V, Nb, and W have resulted in a significant improvement in creep strength together with a good weldability. This study investigates the high-temperature mechanical properties of two Grade 91 welded plates and focuses on the creep behavior, proposing a modified expression of the Larson-Miller parameter for the estimation of critical combinations of temperature, stress, and time, which could lead to rupture. The suggested parameter, which is highly sensitive to temperature, is able to outline the criticality of the welding and it is useful for predicting the duration of a creep test with the specimen rupture

Super-resolution of thermal images using an automatic total variation based method

The relatively poor spatial resolution of thermal images is a limitation for many thermal remote sensing applications. A possible solution to mitigate this problem is super-resolution, which should preserve the radiometric content of the original data and should be applied to both the cases where a single image or multiple images of the target surface are available. In this perspective, we propose a new super-resolution algorithm, which can handle either single or multiple images. It is based on a total variation regularization approach and implements a fully automated choice of all the parameters, without any training dataset nor a priori information. Through simulations, the accuracy of the generated super-resolution images was assessed, in terms of both global statistical indicators and analysis of temperature errors at hot and cold spots. The algorithm was tested and applied to aerial and terrestrial thermal images. Results and comparisons with state-of-the-art methods confirmed an excellent compromise between the quality of the high-resolution images obtained and the required computational time