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

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

Crack initiation and propagation in Chromium pre-alloyed PM-steel under cyclic loading

Powder metallurgy processing of steels typically results in materials characterized by residual porosity, whose sizes and morphology, together with the microstructure, strongly affect the fatigue crack growth behaviour of the materials. Prismatic specimens were pressed at 7.0 g/cm3 density from Astaloy CrM powder and sintered under different conditions, varying the sintering temperature and the cooling rate after sintering. Optical observations allowed us to evaluate the sizes and the morphology of the porosity and the microstructural characteristics for all the investigated conditions. Fatigue tests were performed at R-ratio equal to 0.1 to investigate the threshold zone and to calculate the coefficients of the Paris law. All the tests were carried out according to the compliance method, and the crack length was evaluated during the tests. Moreover, KIC tests were performed in order to complete the investigation. On both fatigue and KIC samples, a fractographic analysis was carried out to investigate the crack path and the fracture surface features. The results show that the exponent of the Paris law is about 6.0 for 1120°C sintered and about 4.7 for 1250°C sintered materials. Interesting data have been also found for the threshold values

Influence of prior microstructure on the mechanical and microstructural properties of C–Mn–B steel after spheroidizing annealing

During spheroidizing annealing of steels, the carbide shape is modified from lamellar to spheroidal for increasing cold deformability. The aim of this work is to study the kinetics and the mechanical properties of a C–Mn–B steel grade after spheroidizing annealing, varying the prior microstructure produced by industrial conventional and thermo-mechanical hot rolling with different Stelmor cooling rates. Moreover, different prior microstructures were also produced by laboratory heat treatments. Microstructural analysis, hardness tests, and tensile tests were carried out at different soaking times. The results show that a better distribution of the carbon in the metal matrix obtained in bainitic and martensitic microstructures results in a more uniform dispersion of the carbides with higher mechanical resistance and deformability. The ferritic and pearlitic microstructures obtained by thermo-mechanical hot rolling are able to produce more homogeneous carbides when compared with the traditional hot rolling

Prompt and safe femoral hemostasis with a collagen device after intracoronary implantation of Palmaz-Schatz stents

We report the safety and efficacy of sealing the femoral puncture site with percutaneously applied collagen after Palmaz-Schatz stent implantation in 100 consecutive patients. Patients were anticoagulated with continuous heparin infusion, overlapping oral anticoagulants, and antiplatelet therapy by dextran, aspirin, and dipyridamole. At the time of sheath removal and collagen application, the mean activated partial thromboplastin time and prothrombin time values expressed as international normalized ratio were 3.2 +/- 2.1 and 1.6 +/- 0.7, respectively. The hemostasis time ranged from 1 to 8 minutes (mean 2.18 +/- 2.08 minutes). Only two (2%) patients had major puncture-site bleeding (not seal related in one case) that required surgery and blood transfusions. Small (< 6 cm) and medium (6 to 10 cm) hematomas observed in 12 (12%) and 2 (2%) patients, respectively, resolved spontaneously without sequelae. Local infection developed in 2 (2%) patients, who were successfully treated with antibiotics without clinical consequences. Subacute stent thrombosis was observed in only 1 (1%) patient. Repeat catheterization through the same femoral artery was performed at 6-month follow-up in 55 patients without difficulty or vascular complications. These findings suggest that percutaneous collagen application after coronary stenting is a secure method of achieving prompt and effective femoral hemostasis with a low incidence of major vascular bleeding complications despite intense anticoagulation. Stable hemostasis may allow continued full-dose anticoagulation, reducing the risk of stent subacute thrombosis