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

UNE ONTOLOGIE SIMONIENNE DU MONDE DE L'ARTIFICIEL

International audienceThis tutorial puts Herbert Simon's (1916-2001) work on design into perspective. In fact, in the 1960s, this economist has tried to build a general theory of design. This tutorial gives some biographical references explaining why this decision theorist had an interest in design, which is not a usual object for an economist. Then we propose an ontology that synthesizes Simon's conceptualization of the world of the artificial. This last one integrates three key entities: the artefact, the design process defined as a form of problem-solving involving a specific rationality, and the sciences of the artificial seen as different from the natural sciences. A scientific balance of this ontology is made in order to establish its interests for design researchers. A bibliometrical study based on articles published in Design Studies is then realized. The researchers who edit this journal went further into the analysis of design process as a form of problem-solving. They however failed to explore some issues of Simon's design theory. The first one is related to the empirical foundations of the sciences of the artificial. The second one refers to the creative rationality underlying the designer's activity. Simon's work can still inspire new research issues in design theory.L'objectif du présent tutoriel est de porter un regard rétrospectif et critique sur les travaux de Herbert Simon (1916-2001). Après avoir expliqué comment cet économiste spécialiste de la décision en est venu à s'intéresser à la conception, ce tutoriel présentera une ontologie synthétisant la façon dont il conceptualisait le monde de l'artificiel. Trois entités clefs seront explicitées. Il s'agit de l'artefact, de la conception vue comme un processus de résolution de problèmes impliquant, chez le concepteur, la mise en œuvre d'une rationalité spécifique, et des sciences de l'artificiel pensées comme distinctes des sciences de la nature. Une fois cette ontologie présentée, un bilan de son appropriation par les chercheurs en conception sera dressé. Pour ce faire, nous nous appuierons sur une étude bibliométrique réalisée à partir de la littérature produite par la communauté réunie autour de la revue Design Studies. Si celle-ci a multiplié les études sur la résolution de problème de conception, elle n'a toutefois pas approfondi les points relatifs aux fondements empiriques des sciences de l'artificiel ou encore la rationalité créative du concepteur. De ce fait, l'œuvre de Simon peut encore inspirer les recherches en matière de théorie de la conception

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