Philippe Sainsot

• Institut National des Sciences Appliquées de Lyon

Physical phenomena at various scales are involved in energy dissipation and material degradation induced by mechanical contacts. Stress computation at the microstructural level is particularly valuable for the study of rolling contact fatigue or wear. For this purpose, a new efficient and versatile numerical model based on the Green-FFT method is p...

A commercial composite powder was used to develop a new paste for stereolithography processing (SLA) of dense 11Ce-TZP-based composites containing 8 vol.% of alumina and 8 vol.% of strontium aluminate. The same powder was used to prepare reference ceramics by conventional Cold Isostatic Pressing (CIP) and sintering. The use of SLA gave rise to a mi...

A numerical model for rolling contact fatigue has been developed using finite element method and the Tanaka-Mura micromechanical model to calculate fatigue crack threshold. Two different approaches are compared: macroscopic modeling and mesoscopic modeling which considers a Voronoi polycrystalline geometry. Smooth and dented surface contacts are co...

Rolling Contact Fatigue (RCF) is the result of crack initiation and propagation leading to surface damages. This study proposes a mesoscopic model for RCF crack initiation simulation. Finite Element Method (FEM) is used to obtain stresses using cubic elasticity. Persistent Slip Bands (PSBs) are modeled using polycrystalline geometry and grain orien...

A thorough review and analysis of the classic contact deflection formulae in gear simulations are presented. Based on extensive analytical developments, it is shown that the scatter in the results given by the classic formulations is mainly due to their respective displacement datum (either explicit or implicit) where contact deflections are suppos...

X-ray tomography techniques give researchers the full access to material inner structures. With such ample information, employing numerical simulation on real material images becomes more and more common. Material behavior, especially, of heterogeneous materials, e.g. polycrystalline, composite, can be observed at the microscopic scale with the com...

As a result of its high capacity to absorb neutrons, boron carbide (B4C) is a ceramic widely used in control rods of nuclear reactors. Its behavior under irradiation is of importance especially in order to predict the lifetime of this material in future (Generation IV) reactors. In that context, we used ion irradiation to create damage in B4C at th...

Transformation-induced plasticity in a ceria-stabilized-zirconia based composite was studied in four-point bending, with particular emphasis on nucleation and growth of tetragonal-to-monoclinic transformation bands. They initiated on the side in tension at a given value of stress and grow in size and number with increased applied load. The spacing...

The use of tomographic images of materials as an input for numerical simulations is becoming more and more common. The main difficulty is the computational cost, mesh generations of finite element simulations and the large discontinuities of material properties. This work proposes a strategy to use a MultiGrid method coupled with homogenization tec...

The contact problem of a semi-infinite elastic body with a rigid rough surface with adhesive forces is modeled using a boundary element method (BEM). An original theoretical framework for this problem is presented. Four original BEM algorithms are studied, for both prescribed normal pressure and prescribed penetration, in primal and dual forms. The...

The Tooth Flank Fracture, TFF, is a failure mode observed in the surface-hardened of gear tooth flanks. There is a fatigue phenomenon which initiates from a subsurface crack that occurs in the transition zone between the hardened layer and the core structure of the tooth. It is substantially initiated close to the mid-height of the tooth in the sin...

This paper summarizes the submissions to a recently announced contact-mechanics modeling challenge. The task was to solve a typical, albeit mathematically fully defined problem on the adhesion between nominally flat surfaces. The surface topography of the rough, rigid substrate, the elastic properties of the indenter, as well as the short-range adh...

The contact problem of a rough, rigid surface with an elastic or viscoelastic incompressible semi-infinite body is studied in this paper. The problem is solved using a Boundary Element Method coupled with a conjugate gradient method. Viscoelasticity is taken into account with a ‘State Variable’ approach, making it possible to tackle the transient p...

Since the development of X-ray tomography, it has been possible to obtain 3D images of the micro-structure of materials. These data are extremely useful for analysing of the morphology of heterogeneous materials. More recently, using diffraction contrast tomography in polycrystalline materials, not only the morphology of grains but also their orien...

The prediction of brittle fracture initiation and propagation in heterogeneous structures is one of the main challenging problems in the field of solid failure mechanics. Nowadays with the development of X-Ray tomography, it is possible to account for the real micro structure in a computational model. Recently, a new phase field method proposed by...

Graphite finds widespread use in many areas of nuclear technology based on its excellent moderator and reflector qualities as well as its strength and high temperature stability. Thus, it has been used as moderator or reflector in CO2 cooled nuclear reactors such as UNGG, MAGNOX, and AGR. However, neutron irradiation of graphite results in the prod...

Approximate formulae are presented which give the time-varying mesh stiffness function for ideal solid narrow-faced spur and helical gears. The corresponding results compare very well with those obtained by using 2D finite element models and specific benchmark software codes thus validating the proposed analytical approach. More deviations are repo...

Approximate formulae are presented which give the time-varying mesh stiffness function for ideal solid spur and helical gears. The corresponding results compare very well with those obtained by using two-dimensional (2D) finite element (FE) models and specific benchmark software codes thus validatingthe proposed analytical approach. More deviations...

Graphite is used in many types of nuclear reactors due to its ability to slow down fast neutrons without capturing them. Whatever the reactor design, the irradiated graphite waste management has to be faced sooner or later regarding the production of long lived or dose determining radioactive species such as 14C, 3H or 36Cl. The first carbon dioxid...

The dismantling of the 1st French generation UNGG (Uranium Naturel Graphite Gas) nuclear reactors operated by the French utility, EDF (Electricité de France) will generate around 17,000 tons of irradiated graphite wastes that have to be disposed of. 14C is one of the main radioactive dose contributors over 10,000 years. For the management of this w...

This paper deals with the thermal behaviour of 36Cl in nuclear graphite used in UNGG French reactors (graphite moderated and CO2 cooled reactors). Implanted 37Cl simulates 36Cl displaced from its original structural site by recoil. The implanted nuclear graphite samples were annealed in the 200–1600 °C temperature range and the 6–50 h time range. S...

Quantifying the surface roughness evolution in contacts is a crucial step in the fatigue prediction process. Surfaces are initially conditioned by the running-in process and later altered by surface fatigue. The aim of this study is to understand and predict the evolution of the micro-geometry in the first few over-rolling cycles. Numerical predict...

The performance and reliability of machine elements are the central topic of tribology. In these highly loaded contacts a specific lubrication regime exists named elastohydrodynamic lubrication. This type of lubrication is encountered in rolling element bearings, gears and in cam contacts. The high pressures, and occasionally the high temperatures,...

The degradation of zirconia-based ceramic components for total hip arthroplasty (head and cup) has been the topic of many works. However, the correlation between what is measured in vivo and what is expected from in vitro simulations on hip simulators may be sometimes feeble, especially where zirconia component are concerned, mainly due to a lack o...

This work studies the influence of the cross-hatching groove parameters on a model piston ring load carrying capacity. Over 2000 transient calculations were performed varying all parameters (groove depth, groove width, groove angle, and the distance between cross-overs) to obtain the average load carrying capacity. It is shown that the load carryin...

This paper is part of a project aiming at optimizing the cylinder-liner/piston-ring contact performance: oil consumption, friction and wear. The surface micro-geometry has a major influence on these characteristics. Classical cylinder-liners display cross-hatched patterns. Grooves modify contact pressure distributions and act as lubricant reservoir...

Surface roughness plays an important role in the performance of soft elastohydrodynamically lubricated contacts. When a soft and smooth body is in contact with a very rigid and rough one, the roughness creates pressure fluctuations, resulting in the deformation of the soft body. As the contact pressure is low, the fluid can be considered isoviscous...

The prediction of both the tribological behaviour and mechanical analysis of the wear resistance are still of great research interest in order to improve the lifetime of material surfaces. This concerns both bulk and coated materials although coating processes have been often developed in order to protect substrates from tribological solicitations....

Rolling contacts are a major topic in scientific studies as they are highly exposed to fatigue damage. Indeed, the applied loads generate periodic stresses and the surface roughness generates stress concentrations close to the surface. The combination of these two phenomena facilitates fatigue damage. Many multi-axial criteria have been created to...

La tenue des surfaces des contacts rugueux lubrifiés est un problème crucial dans l'évaluation de la durée de vie des mécanismes, durée de vie conditionnée dès les premiers cycles par le rodage puis par les mécanismes de fatigue des surfaces. La difficulté de ce type d'analyse est liée à la réalisation d'un suivi en continu de l'évolution de l'état...

The knowledge of the gas fission product behavior is mandatory when assessing the performance of the LWR fuel. In this study, Xenon is implanted at two fluences (1015 and 1016 at.cm−2) in two batches of UO2 sintered pellets differing only from the grain size (7 μm and 22 μm). The evolution of Xenon depth profiles versus thermal treatments (1673 K a...

A 3D graded coating/substrate model based on multigrid techniques within a finite difference frame work is presented. Localized refinement is implemented to optimize memory requirement and computing time. Validation of the solver is performed through a comparison with analytical results for (i) a homogeneous material and (ii) a graded material. The...

The actual contact between solid surfaces is generally rough and time dependent. This roughness can only be correctly described using a 3D model. Moreover, severe thermo-mechanical loading induces high stress and temperature gradients within a thin subsurface layer. Even higher gradients are obtained in the case of surface coatings. Consequently, t...

Numerical tools are required to improve our understanding of tribological experiments. In order to represent all the details of rough surface contacts, such calculations require many grid points. Hence, high-performance tools are necessary to obtain precision and limit computing time and memory requirement. This article compares the precision, conv...

The pressure distribution generated by rough surfaces contact induces high stresses just beneath the surface. These stresses are at the origin of several failure mechanisms such as wear, crack initiation, etc. Therefore, it is important to be able to predict these stresses. This article describes an analytical model to evaluate the near surface str...

The actual contact between solid surfaces is generally rough and time dependent. The stresses induced by the rough contact can only be correctly described using a detailed 3D model. Even finer details are required in the case of surface coatings. Consequently, the rough coated contact problem is strongly multi-scale: the characteristic dimensions o...

In this paper, we present the study of thermal behaviour of 36Cl in nuclear graphite used in the St. Laurent A2 UNGG reactor (graphite moderated and CO2 cooled reactor). 37Cl, used to simulate 36Cl displaced from its original structural site by recoil, has been implanted into nuclear graphite samples (energy=250keV, fluence=5×1013 at cm−2). The sam...

On s'intéresse à la représentation de surfaces rugueuses aléatoires par des analogues auto-affines pour décrire les propriétés mécaniques et de transport (écoulement visqueux et diffusion) du contact de ces surfaces avec un plan lisse indéformable. En s'appuyant sur des textures rodées et sablées réelles, des textures équivalentes sont synthétisées...

In this work, we are interested in the contact between a self-affine fractal surface pressed against a smooth and perfectly rigid plane. The purpose is to analyse the influence of both sampling interval delta and sampling length L, on the determination of surface roughness parameters, contact areas and viscous and diffusive flow through the apertur...

In this work, we analyze diffusion and viscous flow through the aperture field of a contact between rough surfaces pressed against each other. The purpose of our study is to validate the use of synthesized rough surfaces instead of real ones for surfaces exhibiting fractal properties. Models for mechanical deformation of asperities as well as for t...

Poster présenté au congrès Interpore 2009, Kaiserslautern, Allemagne

In this work, we adress the issue of sealing performance of metal gaskets using a deterministic approach that allows the analysis of creeping viscous flow and diffusion through a tight contact between rough surfaces taking into account surface deformation. Our analysis is focused on rough surfaces exhibiting fractal properties, and our purpose is t...

Starvation combined with surface roughness drastically reduces fatigue life. On the basis of the results obtained earlier, concerning the effect of sinusoidal surface roughness on rolling contact fatigue under elastic dry contact assumptions and relations established by Venner et al. and Morales-Espejel et al., the authors have developed an analyti...

La fatigue de contact est essentiellement initiée en surface. Un modèle analytique a été développé afin de déterminer les surpressions dues aux rugosités en condition de contact sec élastique. Une analyse du champ de contrainte a été conduite ensuite afin d'identifier le cisaillement maximum. Enfin, un abaque de risque en fonction des paramètres de...

The radiation enhanced diffusion of chlorine in UO2 during heavy ion irradiation is studied. In order to simulate the behaviour of 36Cl, present as an impurity in UO2, 37Cl has been implanted into the samples (projected range 200 nm). The samples were then irradiated with 63.5 MeV 127I at two fluxes and two temperatures and the chlorine distributio...

Metallic gaskets are frequently used in applications operating under extreme conditions (very high or low temperatures). The elastic-plastic contact conditions between a layered toroidal seal and its seat are presented in this paper using a bi-dimensional finite element method. This problem is similar to the contact between an elastic cylinder and...

Résumé : La technologie des joints métalliques utilise des surfaces revêtues. En effet, les portées de joint n'étant pas parfaitement lisses, on interpose entre les surfaces des revêtements mous dont l'écoulement plastique sous charge permet de gommer les inégalités des surfaces. L'objectif de ce papier est de montrer l'influence de l'épaisseur du...

An approximate hydrodynamic model of the air-lubricant pumping by spur and helical gears, which makes it possible to predict the compression-expansion process by the meshing teeth, is presented. The simulated pressure patterns correlate well with the experimental evidence obtained from a specific test rig for both spur and helical gears. Finally, i...

This paper deals with the comparison between thermal and Fission Enhanced Diffusion (FED) of uranium into zirconia, representative of the inner face of cladding tubes. The experiments under irradiation are performed at the Institut Laue Langevin (ILL) in Grenoble using the Lohengrin spectrometer. A thin $^{235}UO\_2$ layer in direct contact with an...

The magnitude and variation of tooth pair compliance affects tooth loading and gear dynamics significantly. This paper presents an improved fillet/foundation compliance analysis based on the theory of Muskhelishvili applied to circular elastic rings. Assuming linear and constant stress variations at root circle, the above theory makes it possible t...

A strain approach for the design of coated contacts is described, allowing a simple evaluation of the risk of coating failure, once the elastic modulus of the coating and the substrate and the coating thickness are known. Examples are provided for hard and soft coatings. The approach is shown to be particularly useful for hard coatings, where failu...

Because of deflections under load, contacts on tooth flanks can occur outside the theoretical plane of action between nonconjugated profiles especially when tooth modifications are not appropriate. The main objective of the present paper is to introduce an original model of the dynamic behavior of spur gears when submitted to these particular meshi...

Today, Rolling Contact Fatigue (RCF) is essentially caused by surface originated failures. This failure mode is often linked to surface defects like dents due to oil contamination [1, 2, 3] or surface finishing [4]. For example, the surface roughness has an influence on both the risk of EHL film collapse and the stress level in the contacting bodie...

Static seal is of major concern in spatial technology and because of severe thermodynamic conditions, direct metal/metal contact is often used. This work is a contribution to the study of liquid leakage through a rough metal contact resulting from the tightening of two machined surfaces. Our approach is based on experimental measurements of leak-ra...

Based upon a Coulomb model, an original analytical analysis of tooth friction excitations in errorless spur and helical gears is presented. Upon averaging the contributions of bending angles at pinion and gear centres and using a constant mesh stiffness per unit of contact length, it is shown that the intensity of tooth friction excitations compare...

Pressure distributions calculated in the simulation of rough contacts show high values and induce high stresses just beneath the surface. These stresses often exceed the yield strength of the material, therefore, a purely elastic contact model is restrictive. Plastic flow occurs and modifies the surface shape and consequently modifies the surface p...

Five different types of machines are commonly used to study elastohydrodynamic lubrication: four-ball, ball on disc, FB2, gear and the disc machines.The two-disc machine available at the Laboratoire de Mécanique des Contacts (LMC) was originally designed 30 years ago. Using this test rig, traditional tests are possible: traction curve measurement t...

The aim of this work is to characterise the retention properties of apatites, studied as potential inert matrices, towards the long-lived fission product 99Tc (T=210000 years) in radioactive waste disposal. The study was made using two stable homologous elements of Tc: molybdenum which has the same mass as technetium, and rhenium which is the chemi...

During the reactor processing fission products, among which iodine is one, are implanted by recoil inside the Zircaloy cladding tube, most of them being distributed within the first 2 μm. At the same time, oxidation of the cladding tubes occurs and therefore in the waste disposal phase zirconia will act as the first migration barrier. In order to a...

One of the solutions to store high level nuclear wastes (actinides and fission products) is deep geological repository. Since some of these radionuclides have extremely long half-lives, they require an appropriate durable immobilisation system. Several materials, including apatites, are studied as potential inertial matrices. One of the most fed lo...

Pressure distributions due to surface roughness in contact induce high stresses just beneath the surface. These stresses can bring on crack initiation and micro-pitting. A purely elastic contact model to account for these effects is restrictive because stress fields often exceed the yield strength of the material. Plastic flow occurs and modifies t...

A new ball bearing behavior model which predicts and locates power losses in a high-speed gearbox angular contact ball bearing, operating under axial and radial loads, is presented. Its new features come from the consideration of both cage action and effect of lubricant film thickness in the computation of bearing kinematics at equilibrium. Lubrica...

In real hertzian contacts, surface roughness modifies strongly the pressure field compared to the Hertz theory (smooth surfaces). Highly loaded zones then appear in the first layers of contacting bodies. These zones are exposed to a distinct class of damages (micro-pitting) and constitute potential points for fatigue cracks initiation. An analysis...

An experimental study of particulate metallic contaminant deformation and of the effect on surface indentation in high speed ball bearing is presented. Particles are initially spherical and are composed of M50 high carbon steel powder. A high speed rig with a controled level of oil contamination was built. Information concerning initial and final p...

A 2D simulation of a rough elastic cylinder normally loaded on a plane coated elastic medium is presented. The effect of soft and hard coatings on the rough contact pressures and on Von Mises stresses associated is shown. The hertzian contact pressure field is significantly altered by the surface roughness. The presence of a soft coating greatly re...

This paper presents an evaluation of the influence of misalignments on tooth load distribution in gear systems. Static and dynamic analyses are conducted using a normal contact algorithm including local and global effects. This algorithm is shown to be well adapted to determine the pressure field between surfaces with any manufacturing errors, inve...

During the reactor operation, fission products are implanted by recoil inside the zircaloy cladding tube. Most of them are distributed in the first 2 Jlm. At the same time oxidation of the cladding tube occurs, hence in the waste storage phase zirconia will act as a migration barrier. In order to analyse the mechanism involved in iodine migration,...