Inverse Identification of the Ductile Failure Law for Ti6Al4V Based on Orthogonal Cutting Experimental Outcomes

Despite the prevalence of machining, tools and cutting conditions are often chosen based on empirical databases, which are hard to be made, and they are only valid in the range of conditions tested to develop it. Predictive numerical models have thus emerged as a promising approach. To function correctly, they require accurate data related to appropriate material properties (e.g., constitutive models, ductile failure law). Nevertheless, material characterization is usually carried out through thermomechanical tests, under conditions far different from those encountered in machining. In addition, segmented chips observed when cutting titanium alloys make it a challenge to develop an accurate model. At low cutting speeds, chip segmentation is assumed to be due to lack of ductility of the material. In this work, orthogonal cutting tests of Ti6Al4V alloy were carried out, varying the uncut chip thickness from 0.2 to 0.4 mm and the cutting speed from 2.5 to 7.5 m/min. The temperature in the shear zone was measured through infrared measurements with high resolution. It was observed experimentally, and in the FEM, that chip segmentation causes oscillations in the workpiece temperature, chip thickness and cutting forces. Moreover, workpiece temperature and cutting force signals were observed to be in counterphase, which was predicted by the ductile failure model. Oscillation frequency was employed in order to improve the ductile failure law by using inverse simulation, reducing the prediction error of segmentation frequency from more than 100% to an average error lower than 10%

Behaviour of a biocompatible titanium alloy during orthogonal micro-cutting employing green machining techniques

The sustainability of a process is the objective of modern industries aiming to reduce waste in production, since consumers require high quality and efficiency with fair price. Thus, a good understanding of the process should be its starting point. The manufacture of dental implants is an example in which waste reduction is important for the reduction of prices due to the demand for great quality and accuracy. This study observed the behaviour of sustainable micro-cutting applied to the Ti-6Al-7Nb titanium alloy, considering the ploughing effect on minimum quantity lubrication (MQL) and high-speed machining (HSM) conditions. When compared with dry condition and low-speed cutting in orthogonal micro-cutting, the use of HSM in dry cutting was more efficient than using MQL. The dry condition presented lower surface roughness, whilst the cooled/lubricated condition presented lower burr formation.publishe

Recent treatment perspectives in lipidology

peer reviewedClinical lipidology has gained its recognition with the publication of numerous clinical trials since the 4S study in 1994. Since that time statins have fully confirmed their promises and play now a crucial role in the battle against cardiovascular diseases. The last decade has been dominated by two demonstrations that apparently are discordant: (1) the lower the cholesterol level with the pharmacological intervention, the lower the risk of cardiovascular complications, arguing for the use of very efficacious cholesterol-lowering therapies; and (2) the cardiovascular protection provided by statins is present whatever the baseline cholesterol level, supporting the concept of pleiotropic effects of statins. As a consequence, statin treatment should be prescribed and intensified according to the high individual cardiovascular risk rather than because of the cholesterol level stricto sensu. Statin therapy should be completed by the addition of ezetimibe when LDL cholesterol level remains above target values or by the addition of fenofibrate when triglyceride levels are high and/or HDL cholesterol level is low. New pharmacological approaches aiming at further improving lipid profile, especially by targeting low HDL cholesterol levels, are currently in clinical development

Recommendations of the Belgian Lipid Club for the diagnosis and treatment of hyperlipidemias: summary for the practitioner

peer reviewedThe present paper summarizes the last recommendations of the Belgian Lipid Club for the diagnosis and treatment of hyperlipidaemias which were published in 1999. These guidelines are in agreement with the "Recommendations of the second Task Force of European and other societies on Coronary Protection", published in 1998. We will briefly describe the evidence supporting the treatment of dyslipidaemias, especially hypercholesterolaemia, to improve coronary prognosis of at high risk subjects as well as the general strategies, lipid objectives and therapeutic means, in a practical way for the clinician

Données nouvelles sur la lipoprotéine (a) : une curiosité biochimique ou un facteur de risque cardiovasculaire important ?

La lipoprotéine (a) est une molécule intéressant à la fois les chercheurs et les cliniciens qui s’occupent de l’évaluation du risque cardiovasculaire. La Lp(a) est une particule hybride, composée d’une moitié indistinguable du LDL, liée par un pont disulfure à un composant glycoprotéique particulier, l’apolipoprotéine (a). Beaucoup d’arguments épidémiologiques arrivent à la conclusion que l’élévation de la Lp(a) est un facteur de risque cardiovasculaire indépendant. L’apolipoprotéine(a) présente des homologies avec le plasminogène car elle contient de nombreux motifs en boucle appelés « kringle » semblables à ceux du plasminogène. Le nombre des kringles de l’apo(a) explique l’hétérogénéité de taille des isoformes de la Lp(a). Les similitudes entre la Lp(a) et le LDL d’une part et le plasminogène d’autre part ont conduit à formuler l’hypothèse que la Lp(a) joue un rôle à la fois dans l’athérogenèse et la thrombogenèse. De plus, l’apo(a) possède des propriétés spécifiques qui expliquent que la Lp(a) peut affecter la fonction plaquettaire et aussi contribuer à la dysfonction endothéliale. De nouvelles données récentes ont mis en évidence un rôle de la Lp(a) dans l’élimination des phospholipides oxydés. Les futurs développements dans ce domaine comprendront la détermination du rôle de la taille des isoformes de l’apo(a), la mise en évidence des rôles physiologiques de la Lp(a) ainsi que l’élaboration de recommandations cliniques pour la meilleure prise en charge d’un taux élevé de Lp(a)

Place of fibrates for the treatment of patients with atherogenic dyslipidemia

peer reviewedThe demography of dyslipidemia has changed towards a more complex atherogenic dyslipidemia involving increased levels of LDL cholesterol, in particular highly atherogenic small dense particles, hypertriglyceridemia and low HDL cholesterol, together with increased levels of markers of inflammation, thrombogenesis and endothelial dysfunction. Statins were shown to significantly lower cardiovascular morbidity and mortality, but treated patients are still left with a high residual risk, in particular for those with metabolic syndrome, type 2 diabetes, or low HDL cholesterol levels. Fibrates have been shown to reduce plasma triglycerides and increase HDL cholesterol, while improving inflammation, thrombogenesis and endothelial dysfunction. Clinical trials with fibrates have demonstrated their potential to reduce cardiovascular morbidity and mortality too, often through other mechanisms than those of statins. Combination trials of statins with fibrates have shown a more complete improvement of lipid profile and risk markers than each class separately. In contrast with gemfibrozil, fenofibrate does not interact significantly with the pharmacokinetics of statins, and its combination with statins has been shown to have a low risk of muscular side-effects or liver toxicity. The ACCORD outcome trial is exploring possible benefits of the combination of fenofibrate with statins on morbidity and mortality of patients with type 2 diabetes