Fracture simulation for zirconia toughened alumina microstructure

Purpose - The purpose of this paper is to describe finite element modelling for fracture and fatigue behaviour of zirconia toughened alumina microstructures. Design/methodology/approach - A two-dimensional finite element model is developed with an actual $Al{_2}O{_3}$ - 10 vol% $ZrO{_2}$ microstructure. A bilinear, time-independent cohesive zone law is implemented for describing fracture behaviour of grain boundaries. Simulation conditions are similar to those found at contact between a head and a cup of hip prosthesis. Residual stresses arisen from the mismatch of thermal coefficient between grains are determined. Then, effects of a micro-void and contact stress magnitude are investigated with models containing residual stresses. For the purpose of simulating fatigue behaviour, cyclic loadings are applied to the models. Findings - Results show that crack density is gradually increased with increasing magnitude of contact stress or number of fatigue cycles. It is also identified that a micro-void brings about the increase of crack density rate. Social implications - This paper is the first step for predicting the lifetime of ceramic implants. The social implications would appear in the next few years about health issues. Originality/value - This proposed finite element method allows describing fracture and fatigue behaviours of alumina-zirconia microstructures for hip prosthesis, provided that a microstructure image is available

Influence of proteins from physiological solutions on the electrochemical behaviour of the Ti-6Al-4V alloy: reproducibility and time-frequency dependence. ---- Influence de la teneur en prot\'eines de solutions physiologiques sur le comportement \'electrochimique du Ti-6Al-4V : reproductibilit\'e et repr\'esentation temps-fr\'equence

The electrochemical behaviour of the biomedical and metallic alloys, especially in the orthopaedic implants fields, raises many questions. This study is dedicated for studying the Ti-6Al-4V alloy, by electrochemical impedance spectroscopy, EIS, in various physiological media,: Ringer solution, phosphate buffered solution (PBS), PBS solution and albumin, PBS solution with calf serum and PBS solution with calf serum and an antioxidant (sodium azide). Moreover, the desionised water was considered as the reference solution. The tests reproducibility was investigated. The time-frequency-Module graphs highlighted that the desionised water is the most protective for the Ti-6Al-4V alloy. This biomedical alloy is the less protected in the solution constituted by PBS and albumin. The time-frequency graph allows pointing out the graphic signatures of adsorption for organic and inorganic species (differences between the modules means in studied solution and the modules mean in the reference solution). --- Le comportement \'electrochimique des alliages m\'etalliques biom\'edicaux, notamment dans le domaine des implants orthop\'ediques, pose encore de nombreuses questions. Ce travail propose d'\'etudier l'alliage de titane Ti-6Al-4V, par spectroscopie d'imp\'edance \'electrochimique, SIE, dans diff\'erents milieux physiologiques : solution de Ringer, solution \`a base d'un tampon phosphate (PBS), solution PBS avec de l'albumine, solution PBS avec du s\'erum bovin et une solution PBS avec du s\'erum bovin et un antioxydant (azoture de sodium). De plus, une solution d'eau ultra-pure servira de r\'ef\'erence. La reproductibilit\'e des tests a \'et\'e \'etudi\'ee. Les repr\'esentations temps-fr\'equence des modules ont mis en \'evidence que l'eau d\'esionis\'ee est la solution qui pr\'esente le caract\`ere le plus protecteur pour le Ti-6Al-4V. Cet alliage de titane est le moins prot\'eg\'e dans la solution de PBS contenant de l'albumine. Cette repr\'esentation permet de mettre en \'evidence des signatures graphiques d'adsorption des esp\`eces inorganiques et organiques (diff\'erences entre les moyennes des modules dans les solutions \'etudi\'ees et la moyenne des modules dans la solution de r\'ef\'erence)

Fretting-corrosion between 316L SS and PMMA: Influence of ionic strength, protein and electrochemical conditions on material wear. Application to orthopaedic implants

International audienceIn biomedical field, fretting-corrosion between 316L SS femoral stem and bone cement is one of the significant causes of the hip prosthesis loosening. This article investigates wear by fretting-corrosion at the contact between 316L and PMMA. The influences of the ionic strength (NaCl solutions from 10−3 to 1 mol L−1), a model protein (albumin) and electrochemical conditions on contact behaviour are studied. At OCP (open circuit potential) conditions, the chlorides concentration, i.e. the ionic strength, increases the 316L wear; and albumin, concentration of 1 g L−1, does not play a significant role in total 316L wear. At cathodic applied potential E = −400 mV(SCE), a threshold concentration of 10−1 mol L−1 (NaCl solution), Cth, indicates two behaviours: a protective effect below Cth, and an additional anodic dissolution above Cth. One might suggest that, beyond Cth, the passive layer is not efficient for protecting against the corrosion. At this potential, albumin reduces wear due to corrosion and amplifies mechanical wear induced by corrosion. Albumin seems to act as an anodic inhibitor. To determine the mechanisms of synergism, a "more cathodic" potential is applied, E = −800 mV(SCE), during fretting-corrosion experiments. Consequently, the corrosive wear can be neglected and the mechanical wear can be only measured

Friction-corrosion of AISI 316L/bone cement and AISI 316L/PMMA contacts : ionic strength effect on tribological behaviour

International audienceWear phenomena understanding of implants is a challenge: friction-corrosion of biomaterials, which constitute orthopaedic implants, is a significant issue concerning the aseptic loosening. This work aims at studying AISI 316L/bone cement friction which is a tribological problem related to hip joint cemented prostheses. This study focuses on the ionic strength effect on the tribological behaviour of 316L/bone cement and 316L/PMMA contacts. PMMA, poly(methylmethacrylate), can be considered as a model material for bone cement because of vicinity of mechanical properties and PMMA transparency. Pin on disk friction tests were investigated, in different media with NaCl concentration increasing. Friction coefficient and free corrosion potential of 316L sample were monitored. Moreover, SEM-FEG and microraman spectroscopy analyses were investigated on samples surfaces. Friction coefficient evolution according to ionic strength, for 316L/bone cement and 316L/PMMA contacts, are opposite. Indeed, when the ionic strength increases, the friction coefficient growths (decreases), for 316L/PMMA contact (for 316L/bone cement contact). The free corrosion potential decreases in both cases but more drastically for 316L/PMMA contact with ionic strength increasing. One might suggest that ions adsorption on 316L and PMMA surfaces involves attraction between surfaces in contact. On the contrary, ions adsorption on bone cement has no effect in terms of surface attraction forces, the gap between surfaces is too big due to roughness of bone cement. If ions concentration increases, the tribofilm viscosity between 316L and bone cement could increase. Attraction forces between surfaces are the less significant phenomenon compared to lubricant effect of tribofilm, 316L/bone cement contact. SEM-FEG analysis highlighted principally deep grooves on 316L surface, corrosive wear after destruction of passive film by friction. Finally microraman spectroscopy results, on metal surface, show principally Fe3O4 and Cr2O3 oxides deposits. Further investigations are in progress for understanding surfaces interactions during friction

Wear of poly (methyl methacrylate) against a metallic surface in dry conditions

International audienceWear of Poly (methyl methacrylate), PMMA, against a metallic surface, AISI 316L stainless steel (SS) has been investigated in dry conditions. These materials have been used to simulate the degradation of the contact, femoral stem-bone cement in the field of hip prosthesis. First of all, no significant wear was observed on the 316L SS. PMMA wear has been quantified: the energy wear coefficient, slope of the line, and wear volume according to the cumulated dissipated energy, don't depend on the normal load, FN. This energy analysis allows predicting the PMMA wear depth. According to the comparison between the measured dissipated energy and the energy breaking polymer chains, mechanical dissipated energy is used essentially to transform third body structure and to expel it from the contact between the two materials. Moreover, the experimental results have highlighted the stick-slip phenomenon. Lastly, Attenuated Total Reflectance-Fourier Transform InfraRed and Reflection Absorption-Fourier Transform InfraRed have shown that PMMA debris configuration and conformation have changed after wear against 316L SS. The driving force of these changes seems to be the acid-base interactions between PMMA and hydroxyl groups of the SS surface

Atomic force microscopy investigations on pits and debris related to fretting-corrosion between 316L SS and PMMA

International audienceIn the case of hip prostheses, debris generation, due to the fretting-corrosion phenomenon between the femoral stem and the bone cement is one of the most significant causes of reintervention. In this study we use atomic force microscopy (AFM) to analyze PMMA particles and pitting corrosion on 316L SS as a function of chlorides and albumin concentration. Without albumin, the number of pits increases with the chlorides concentration. Contrary to the protective effect of albumin on global corrosive wear, albumin tends to increase the number of pits. The number of ejected particles highly depends on electrochemical conditions and the in vivo conditions, Open Circuit Potential, seem to lead to a small number of particles. This work has also explored atomic force microscopy as a "new" characterization technique for wear debris and demonstrates that 80% of particles have a size inferior to 100 nm, which is the 'critical size' for tissues response

Shock Induced Damages on alumina and zirconia hip prostheses

International audienceCeramics mostly used in orthopaedics are alumina (Al²O³) and zirconia (ZrO²), the rate of fracture bioceramics hip prostheses being around 0.01% [1]. Some in vivo fractures have been reported and some of them have occurred in overweight patients [2]. One may suggest that prostheses may fail because of important repeated mechanical shocks. Moreover, the microseparation between the head and cup that may occur in vivo [3,4] seems to be another key parameter influencing the lifetime of the prostheses. Only few walking hip simulators have been modified to take into account this phenomenon and it has been shown that microseparation increases the wear and creates the so-called wear bands that have been observed in vivo on ceramic heads [5,6]. The main goal of this work was to use a specially designed shock machine to test bioceramics heads and cups under microseparation

Durées de vie de prothèses de hanche en biocéramiques soumises à des dégradations par chocs

National audienceLes prothèses de hanche visent à remplacer l'articulation coxo-fémorale. Les céramiques, notamment l'alumine, sont très utilisées pour la réalisation des têtes fémorales et des cupules cotyloïdiennes. Grâce à une machine unique en Europe, on peut tester dans des conditions sévères, le comportement des prothèses de hanche soumises aux chocs, afin d'estimer leur durée de vie. Le cycle de force appliqué est un pic de force de 9 kN pendant 30 ms à une fréquence de 2 Hz. Les essais ont été menés à sec, articulation non lubrifiée, ou en solution (sérum bovin). L'ensemble tête-cupule est incliné à 45° pour respecter la position anatomique. Les prothèses étudiées sont en alumine. Les essais, doublés ou triplés selon le milieu, sont conduits jusqu'à 800000 cycles ou jusqu'à la rupture de la cupule. A sec, la rupture est intervenue pour 254000 ± 43000 cycles. En solution, aucune rupture n'a été observée après 800000 cycles. Des ruptures intergranulaire et intragranulaire ont été observées au Microscope Electronique à Balayage (MEB). Pour tous les essais, on met en évidence des bandes d'usure sur la tête, analogues à celles observées ex vivo. Cette dégradation est plus rapide pour les essais à sec qu'en solution. La rupture de la cupule se produit lorsque la bande d'usure supérieure est voisine de 4 mm. Les analyses de rugosité par Microscopie à Force Atomique (AFM) ont montré que, pour les zones non usées, Ra-3D (rugosité 3D) = 9,1 ± 5,1 nm et pour les zones usées Ra-3D = 277,9 ± 29,4 nm ; ces valeurs sont comparables avec celles mesurées ex vivo. Ces résultats valident la machine de chocs comme un dispositif qui permet de reproduire et de comprendre les mécanismes d'endommagement des prothèses de hanche en biocéramique. Enfin, ces travaux expérimentaux nous permettront d'obtenir des résultats de référence et de les comparer à ceux qui découleront d'investigations autour de la modélisation multi-échelles

Higher-order calculations of electron-deuteron scattering in nuclear effective theory

Motivated by recent advances in the application of effective field theory techniques to light nuclei we revisit the problem of electron-deuteron scattering in these approaches. By sidestepping problems with the description of electron-nucleon scattering data in effective field theories, we show that the effective theory expansion for deuteron physics converges well over a wide range of momentum transfers. The resultant description of the physics of the two-nucleon system is good up to virtual photon momenta of order 700 MeV.Comment: 18 pages, 7 figure

Dictionnaire portatif de l'ingénieur, 1755

O documento foi acessado pela base de dados archive.org e está disponível no endereço https://archive.org/details/bub_gb_3iEPAAAAQAAJ/mode/2up.O documento apresentado em 354 páginas contendo a descrição resumida de uma série de termos e conceitos próprios da aritmética, álgebra e geometria