Influence of heat treatment and KIc/HRc ratio on the dynamic wear properties of coated high speed steel

The aim of this work was to determine the impact of various heat treatments on the KIc/HRc ratio and subsequently on the wear properties of coated high-speed steel under dynamic impact loading. The results showed that hardness and improvement in the fracture toughness have significant influence on the adhesion and impact wear properties of the coated high-speed steel

Influence of heat treatment and KIc/HRc ratio on the dynamic wear properties of coated high speed steel

The aim of this work was to determine the impact of various heat treatments on the KIc/HRc ratio and subsequently on the wear properties of coated high-speed steel under dynamic impact loading. The results showed that hardness and improvement in the fracture toughness have significant influence on the adhesion and impact wear properties of the coated high-speed steel

Biocompatibility of poly(lactic acid) with incorporated graphene-based materials

The incorporation of graphene-based materials has been shown to improve mechanical properties of poly(lactic acid) (PLA). In this work, PLA films and composite PLA films incorporating two graphene-based materials – graphene oxide (GO) and graphene nanoplatelets (GNP) – were prepared and characterized regarding not only biocompatibility, but also surface topography, chemistry and wettability. The presence of both fillers changed the films surface topography, increasing the roughness, and modified the wettability – the polar component of surface free energy increased 59% with GO and decreased 56% with GNP. Mouse embryo fibroblasts incubated with both fillers exceeded the IC50 in both cases with a concentration of 10 μg mL−1. No variations in cell proliferation at the surface of the composite films were observed, except for those containing GO after 24 h incubation, which presented higher cell proliferation than pristine PLA films. Platelet adhesion to PLA and PLA/GNP films was lower in the presence of plasma proteins than when no proteins were present. Furthermore, incorporation of GNP into PLA reduced platelet activation in the presence of plasma proteins. The results indicated that low concentrations of GO and GNP may be incorporated safely in PLA to improve aspects relevant for biomedical applications, such as mechanical properties.Funding for this work was partially provided by FEDER, through Programa Operacional Factores de Competitividade - COMPETE, and by National Funding through FCT - Fundacao para a Ciencia e a Tecnologia, in the framework of project PTDC/EME-PME/114808/2009 and of grant SFRH/BPD/63722/2009

Effect of segregations on mechanical properties and crack propagation in spring steel

Considerable efforts have been made over the last decades to improve performance of spring steels, which would increase the service time of springs and also allow vehicles weight reduction. There are different possibilities of improving properties of spring steels, from modifying the chemical composition of steels to optimizing the deformation process and changing the heat treatment parameters. Another way of improving steel properties is through refining the microstructure and reducing amount of inclusions. Therefore, the focus of the current investigation was to determine the effect of more uniform and cleaner microstructure obtained through electro-slag remelting (ESR) of steel on the mechanical and dynamic properties of spring steel, with special focus on the resistance to fatigue crack propagation. Effect of the microstructure refinement was evaluated in terms of tensile strength, elongation, fracture and impact toughness, and fatigue resistance under bending and tensile loading. After the mechanical tests the fracture surfaces of samples were analyzed using scanning electron microscope (SEM) and the influence of microstructure properties on the crack propagation and crack propagation resistance was studied. Investigation was performed on hot rolled, soft annealed and vacuum heat treated 51CrV4 spring steel produced by conventional continuous casting and compared with steel additional refined through ESR. Results shows that elimination of segregations and microstructure refinement using additional ESR process gives some improvement in terms of better repeatability and reduced scattering, but on the other hand it has negative effect on crack propagation resistance and fatigue properties of the spring steel

Clinical Sports Medicine

Problem: Lower altitude stay (1250m) and extensive recreational aerobic activity like skiing at lower to moderate altitude (1250-2000m) and its effect on oxygen transport parameters had not been thoroughly investigated.Methods: The experimental group (N=17) underwent an intervention, a typical 10-day ski-trip. They slept at 1250 m and performed 5-6 hours of aerobic activity (skiing) at 1250-2000m altitude. The control group (N=15) stayed at sea level and performed their regular activities. The ferritin levels, reticulocyte count, RBC parameters and erythropoietin before and 48 h after the trip were measured in both groups.Results: The reticulocyte count increased (44.516.6 to 67.919.18 G/L) and somewhat surprisingly erythropoietin decreased in experimental group (6.042.39 to 4.911.54 IU/L, ANOVA p=<0.001). Ferritin levels decreased and reticulocyte count increased in 88% of all experimental group subjects while in control group it changed in both directions. The initial erythrocyte concentration was foundto be a good predictor of reticulocyte increase changes,while ferritin reserveswasdid not. No significant changes after intervention were observed in other parameters.Discussion: In recreational population, sleeping at lower altitudes in combination with aerobic activity of longer daily duration like skiing, elicits changes in erythropoiesis.KEY WORDS: Altitude, Training, Hypoxia, Ferritin, Reticulocyte, Erythropoieti

Influence of heat treatment and K_Ic/HRc ratio on the dynamic wear properties of coated high speed steel

The aim of this work was to determine the impact of various heat treatments on the KIc/HRc ratio and subsequently on the wear properties of coated high-speed steel under dynamic impact loading. The results showed that hardness and improvement in the fracture toughness have significant influence on the adhesion and impact wear properties of the coated high-speed steel