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The aim of this study was to describe the behaviour of a shock machine designed for testing hip prostheses. A microseparation between head and cup occurs inducing a shock of several times the body weight, leading to fracture of ceramic femoral components. Femoral heads and cups of diameter 32 mm manufactured from alumina were tested in dry and wet conditions. Implants were subjected to shocks with a load profile of 9 kN load at 2 Hz and various microseparations. Position is monitored and force is measured with two acquisition systems. The working range and the device capabilities were investigated. Only cups tested in dry conditions failed. Observations by scanning electron microscopy revealed intergranular and transgranular fractures. Two wear stripes were observed on the heads. Three-dimensional roughness of wear stripes was measured. Since experimental results are in good agreement with retrieved femoral heads, the shocks machine reproduces the in vivo degradations. Copyright © 2011 John Wiley & Sons, Ltd.

International audience; 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 électrochimique des alliages métalliques biomédicaux, notamment dans le domaine des implants orthopédiques, pose encore de nombreuses questions. Ce travail propose d'étudier l'alliage de titane Ti-6Al-4V, par spectroscopie d'impédance électrochimique, SIE, dans différents milieux physiologiques : solution de Ringer, solution à base d'un tampon phosphate (PBS), solution PBS avec de l'albumine, solution PBS avec du sérum bovin et une solution PBS avec du sérum bovin et un antioxydant (azoture de sodium). De plus, une solution d'eau ultra-pure servira de référence. La reproductibilité des tests a été étudiée. Les représentations temps-fréquence des modules ont mis en évidence que l'eau désionisée est la solution qui présente le caractère le plus protecteur pour le Ti-6Al-4V. Cet alliage de titane est le moins protégé dans la solution de PBS contenant de l'albumine. Cette représentation permet de mettre en évidence des signatures graphiques d'adsorption des espèces inorganiques et organiques (différences entre les moyennes des modules dans les solutions étudiées et la moyenne des modules dans la solution de référence).

National audience; Des films de tetrahedral amorphous-Carbon (ta-C) ont été déposés, sous vide poussé, par ablation d'une cible de graphite avec un laser Ti : saphir (durée d'impulsion 170 fs, fréquence de répétition 1 kHz, énergie maximale par impulsion 1,5 mJ, longueur d'onde 800 nm) sur substrats standard et sur biomatériaux (acier AISI 316L, polyéthylène à très haut poids moléculaire). Les propriétés de ces couches (structure, propriétés nanomécaniques et tribologiques) ont été caractérisées, en fonction des conditions d'élaboration, en examinant l'intérêt de l'utilisation d'un laser femtoseconde et leur capacité à satisfaire aux exigences spécifiques du domaine biomédical. Les propriétés d'adhérence des films ont été considérablement améliorées lors du dépôt sur des substrats en acier inoxydable préalablement préparés par décapage ionique in situ sous atmosphère d'argon. La surface hémisphérique d'une tête fémorale, en acier inoxydable, de prothèse de hanche de diamètre 22,2 mm a été revêtue d'un film de DLC adhérent et homogène en épaisseur. La résistance à l'usure de ce revêtement sera quantifiée à l'aide d'un simulateur de marche durant un million de cycles (correspondant à une année d'activité physique d'un être humain).

International audience; 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 Al2O3-10 vol% ZrO2 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.

In 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), C th , indicates two behaviours: a protective effect below C th , and an additional anodic dissolution above C th . One might suggest that, beyond C th , 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.

The aim of this work was to simulate the behaviour of hip prostheses under mechanical shocks. When hip joint is replaced by prosthesis, during the swing phase of the leg, a microseparation between the prosthetic head and the cup could occur. Two different sizes of femoral heads were studied: 28 and 32 mm diameter, made, respectively, in alumina and zirconia. The shock-induced stress was determined numerically using finite element analysis (FEA), Abaqus software. The influence of inclination, force, material, and microseparation was studied. In addition, an algorithm was developed from a probabilistic model, Todinov's approach, to predict lifetime of head and cup. Simulations showed maximum tensile stresses were reached on the cup's surfaces near to rim. The worst case was the cup-head mounted at 30°. All simulations and tests showed bulk zirconia had a greater resistance to shocks than bulk alumina. The probability of failure could be bigger than 0.9 when a porosity greater than 0.7% vol. is present in the material. Simulating results showed good agreement with experimental results. The tests and simulations are promising for predicting the lifetime of ceramic prostheses.

This paper describes a two-dimensional (2D) finite element simulation for fracture and fatigue behaviours of pure alumina microstructures such as those found at hip prostheses. Finite element models are developed using actual Al2O3 microstructures and a bilinear cohesive zone law. Simulation conditions are similar to those found at a slip zone in a dry contact between a femoral head and an acetabular cup of hip prosthesis. Contact stresses are imposed to generate cracks in the models. Magnitudes of imposed stresses are higher than those found at the microscopic scale. Effects of microstructures and contact stresses are investigated in terms of crack formation. In addition, fatigue behaviour of the microstructure is determined by performing simulations under cyclic loading conditions. It is shown that crack density observed in a microstructure increases with increasing magnitude of applied contact stress. Moreover, crack density increases linearly with respect to the number of fatigue cycles within a given contact stress range. Meanwhile, as applied contact stress increases, number of cycles to failure decreases gradually. Finally, this proposed finite element simulation offers an effective method for identifying fracture and fatigue behaviours of a microstructure provided that microstructure images are available.

Wear 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. POLYM. ENG. SCI., 47:633–648, 2007. © 2007 Society of Plastics Engineers.

International audience; Ceramic hip prostheses are very reliable with respect to wear, however, there has been evidence of brittleness problems. Microseparation is likely to occur between the head and the cup during human gait and the mechanical shocks transmitted to these elements are believed to enhance the risk of potential failure of the prosthesis. A finite element model has been developed and, based on its results, fracture probabilities for zirconia cups have been simulated over time. The results show good agreement with experimental work, nevertheless, additional work is in progress to take into account the wear occuring at the surface of the elements.; Les prothèses de hanche en biocéramiques sont résistantes à l’usure mais, du fait de leur fragilité intrinsèque, sont susceptibles de casser. Le phénomène de décoaptation (séparation de la tête et de la cupule) a été mis en évidence lors de la marche, et le choc mécanique en résultant peut fortement augmenter les risques de rupture. Un modèle par éléments finis a été développé et les résultats ont été exploités afin de simuler l’évolution de la probabilité de rupture de cupules en zircone au cours du temps. Les résultats s’accordent bien avec l’expérience, même si des améliorations sont en cours afin de prendre en compte l’usure des surfaces de contact.

Publié suite au congrès : 15th International Conference on Wear of Materials, July-August 2005; International audience; In the biomedical field, about 6% of hip total joint prostheses have to be replaced after 9 years because of a loosening of the femoral stem. One of the main causes of a new surgical intervention is attributed to the phenomenon of fretting-corrosion, i.e. wear under small movements (lower than 100 µm) in corrosive aqueous medium. To understand this degradation, the fretting between 316L steel and PMMA has been investigated to simulate the fretting between femoral stem and bone cement. First, fretting in air has been studied as a reference environment. No significant wear was observed on the stainless steel. PMMA suffers a wear that exhibits a linear evolution as a function of the cumulated dissipated energy. Third body evolution could explain the particular W shape of the active wear track in PMMA, in dry conditions. In aerated Ringer's solution, at free corrosion potential, stainless steel suffers significant wear damage, and the wear volume increases linearly with time but not with dissipated energy. Moreover the optical observations and three-dimensional (3-D) profilometry show a 'W' shape of the wear track of 316L. A corrosion mechanism involving a crevice effect enhanced by fretting allows to explain the location of the maximum damage zones. Finally, the effect of electrochemical potential on the behaviour of 316L/PMMA contacts has been studied by recording current intensity and cumulated dissipated energy under potentiodynamic conditions. Dissipated energy exhibited a reproducible variation with potential. Lubrication regimes and effect of potential on the surface charges could account for such a behaviour.

Copia digital. Madrid : Ministerio de Cultura. Subdirección General de Coordinación Bibliotecaria, 2008

Дело Бернарда Форест де Белидора (1697-1761), француског војног и грађевинског инжењера, који је био значајан у развоју науке о хидраулици. Илустровано многим преклопљеним гравурама хидрауличних машина које управљају ветрењачама, пумпама, бунарима, фонтанама итд, као и плановима и прорачунима. Ово је био први рад те врсте који је применио интегрални рачун на практичне проблеме. Преведено са француског на немачки. Обрађују се следеће области: вештина коришћења вода мора и река у корист одбране тврђава, трговине и пољопривреде. The work of Bernard Forest de Bélidor (1697-1761), a French military and civil engineer, who was important in the development of the science of hydrology. Illustrated by many folded engravings of hydraulic machines that control windmills, pumps, wells, fountains, etc, as well as plans and calculations. This was the first work of its kind to apply an integral calculus to practical problems. Translated from French into German. Contains: the skill of using the waters of the sea and rivers in favor of the defense of fortresses, trade and agriculture.

Дело Бернарда Форест де Белидора (1697-1761), француског војног и грађевинског инжењера, који је био значајан у развоју науке о хидраулици. Илустровано многим преклопљеним гравурама хидрауличних машина које управљају ветрењачама, пумпама, бунарима, фонтанама итд, као и плановима и прорачунима. Ово је био први рад те врсте који је применио интегрални рачун на практичне проблеме. Преведено са француског на немачки. Дело се бави следећим областима: механика, трење; основе хидраулике; тестере, резачи мермерног камена, млинови за бушење цеви; млинови за прах; водени точкови, машине за вађење воде; пумпе за воду, машине за ветар, теорија пумпи за воду; опис и прорачун машине за воду у Паризу; црпљење, вођење и дистрибуција воде, нове машине; дубоки бунари и употреба ватре / парне машине; проналажење и усмеравање воде, фонтана. The work of Bernard Forest de Bélidor (1697-1761), a French military and civil engineer, who was important in the development of the science of hydrology. Illustrated by many folded engravings of hydraulic machines that control windmills, pumps, wells, fountains, etc, as well as plans and calculations. This was the first work of its kind to apply an integral calculus to practical problems. Translated from French into German. Contains: mechanics, friction; basics of hydraulics; saws, marble stone cutters, pipe drills; powder mills; water wheels, water extraction machines; water pumps, wind machines, water pump theory; description and calculation of a water machine in Paris; water pumping, directing and distribution, new machines; deep wells and use of fire / steam engines; finding and directing water, fountain

Дело Бернарда Форест де Белидора (1697-1761), француског војног и грађевинског инжењера, који је био значајан у развоју науке о хидраулици. Илустровано многим преклопљеним гравурама хидрауличних машина које управљају ветрењачама, пумпама, бунарима, фонтанама итд, као и плановима и прорачунима. Ово је био први рад те врсте који је применио интегрални рачун на практичне проблеме. Преведено са француског на немачки. Дело обрађује области које се тичу: својстава ваздуха потеклих из многих емпиријских узорака; темељних теорија њихових водених сметњи; сила и снаге ветра; израчунавања највећег могућег утицаја различитих машина које ветар може покренути; темељних описа свих врста чепова за воду и опсежне теорије о томе како са великом прецизношћу израчунати њихове ефекте. The work of Bernard Forest de Bélidor (1697-1761), a French military and civil engineer, who was important in the development of the science of hydrology. Illustrated by many folded engravings of hydraulic machines that control windmills, pumps, wells, fountains, etc, as well as plans and calculations. This was the first work of its kind to apply an integral calculus to practical problems. Translated from French into German. Contains: features of air which originated from many empirical samples; basic theory of water disturbances; wind force and power; calculating the maximum possible impact of different machines that can be driven by the wind; basic descriptions of all types of water plugs and a comprehensive theory of how to calculate their effects with great precision

Дело Бернарда Форест де Белидора (1697-1761), француског војног и грађевинског инжењера, који је био значајан у развоју науке о хидраулици. Илустровано многим преклопљеним гравурама хидрауличних машина које управљају ветрењачама, пумпама, бунарима, фонтанама итд, као и плановима и прорачунима. Ово је био први рад те врсте који је применио интегрални рачун на практичне проблеме. Преведено са француског на немачки. Садржане су следеће области: вештина коришћења вода мора и река у корист одбране тврђава, трговине и пољопривреде The work of Bernard Forest de Bélidor (1697-1761), a French military and civil engineer, who was important in the development of the science of hydrology. Illustrated by many folded engravings of hydraulic machines that control windmills, pumps, wells, fountains, etc, as well as plans and calculations. This was the first work of its kind to apply an integral calculus to practical problems. Translated from French into German. Contains:the skill of using the waters of the sea and rivers in favor of the defense of fortresses, trade and agriculture