Développement de techniques de mesure dans le volume : photoélasticimétrie 3D pardécoupage optique et corrélation volumique par tomographie optique et rayons X.Application à l’étude des effets mécaniques 3D dans les structures et les biomatériaux.

This work is about developments of volume measurement techniques. Three approaches have been developed tostudy 3D mechanical effects in materials and structures. The first approach is the 3D photoelasticity technique byoptical slicing which enables us to observe principal stress or strain differences in transparent structures. Thesecond approach is the digital volume correlation (DVC) coupled with optical scanning tomography. DVC,which is the 3D extension of the Digital Image correlation (DIC), gives full 3D displacement and strain fields.Optical scanning tomography is a technique which generates volume images in transparent materials. The lastapproach is the DVC method coupled with X-ray micro-computed tomography. With this technique, it ispossible to generate volume images in non-transparent materials.Several mechanical tests with imposed displacement or deformation are presented in order to compare thesethree methods and to determine their application fields, theirs performances, their advantages and disadvantages.Concerning applications, 3D photoelasticity and DVC by optical slicing have been used for the experimentalanalysis of aeronautical spherical plain bearing behaviour in order to make more realistic a numerical simulation.Concerning non transparent materials, DVC and X-ray micro-computed tomography have been employed tostudy mechanical behaviour of cancellous bone.Le travail présenté dans ce mémoire concerne le développement de techniques de mesures dans le volume. Troisapproches ont été développées pour étudier les effets mécaniques 3D dans les matériaux et les structures. Lapremière est la photoélasticimétrie 3D par découpage optique qui permet d’observer les différences decontraintes ou de déformations principales au coeur de structures fabriquées dans un matériau transparent. Ladeuxième approche est la Corrélation d’Images Volumiques (CIV) associée à la tomographie par découpageoptique. La CIV, qui est l’extension en 3D de la corrélation d’images numériques, fournit les champsvolumiques des déplacements et des déformations. La tomographie par découpage optique est une techniqued’acquisition d’images volumiques dans les matériaux transparents. La dernière approche est la CIV associée àla microtomographie par rayons X. Celle-ci permet d’acquérir des images volumiques dans les matériaux nontransparents.Plusieurs essais expérimentaux de déplacements et de déformations sont présentés dans le but de confronter cestrois méthodes et afin de déterminer leurs champs d’applications, leurs performances, leurs avantages etinconvénients.En termes d’applications, la photoélasticimétrie 3D et la CIV par découpage optique sont utilisées pour l’analyseexpérimentale du comportement mécanique de rotules aéronautiques dans le but de rendre plus réaliste lamodélisation numérique des éléments rotulés. Concernant les matériaux non-transparents, la corrélationvolumique et la microtomographie par rayons X sont employées pour étudier le comportement mécanique de l’osspongieux

3D mechanical analysis of aeronautical plain bearings: Validation of a finite element model from measurement of displacement fields by digital volume correlation and optical scanning tomography

On Airbus aircraft, spherical plain bearings are used on many components; in particular to link engine to pylon or pylon to wing. Design of bearings is based on contact pressure distribution on spherical surfaces. To determine this distribution, a 3D analysis of the mechanical behaviour of aeronautical plain bearing is presented in this paper. A numerical model has been built and validated from a comparison with 3D experimental measurements of kinematic components. For that, digital volume correlation (DVC) coupled with optical scanning tomography (OST) is employed to study the mechanical response of a plain bearing model made in epoxy resin. Experimental results have been compared with the ones obtained from the simulated model. This comparison enables us to study the influence of various boundary conditions to build the FE model. Some factors have been highlighted like the fitting behaviour which can radically change contact pressure distribution. This work shows the contribution of a representative mechanical environment to study precisely mechanical response of aeronautical plain bearings

Corrélation volumique par tomographie optique et photoélasticimétrie 3D pour l'étude des effets mécaniques tridimensionnels

On présente deux méthodes d'investigation en volume pour l'analyse de la réponse mécanique tridimensionnelle (3D) de structures modèles transparentes : la photoélasticimétrie 3D par découpage optique et la corrélation volumique par tomographie optique. Ces deux techniques sont basées sur le phénomène de la lumière diffusée provoqué par des marqueurs aléatoirement répartis dans le matériau. Chacune de ces deux techniques utilise des propriétés particulières de la lumière diffusée, ce qui implique des champs d'application spécifiques et d'éventuelles limitations. On présente une première comparaison de ces deux techniques sur un test de compression localisée avec un appui sphérique sur un bloc parallélépipédique. Les résultats montrent que la corrélation volumique est mieux adaptée que la photoélasticimétrie 3D pour la mesure de grandes déformations. Dans le cas de petites déformations où la corrélation est limitée par son incertitude de mesure (0,1%), la photoélasticimétrie 3D s'avère plus performante

X-μCT and DVC use for composite materials analysis

The complex mechanical behaviour of composite materials, due to internal heterogeneity and multi-layered composition imposes deeper studies. This paper presents an experimental protocol to perform volume kinematic measurements in composite materials. This work is centered on the transverse shear effects in relation with the composite materials mechanical behaviour. A lot of theories exist in literature to consider the existing warping section during high transverse shear stresses, but very few studies have been realized in the experimental way. The association of X-ray micro-computed tomography acquisitions and Digital Volume Correlation (DVC) technique allows the measurement of displacements and deformations in the whole volume of composite specimen. To elaborate the latter, composite fibres and epoxy resin are associated with metallic particles to make contrast in X-μCT acquisitions. A specific in-situ loading device is presented for three-point bending tests, which enables the visualization of transverse shear effects in composite structures

Etude de la répartition des efforts dans les rotules aéronautiques

Pour étudier le comportement des éléments rotulés de mât-réacteur d'avions, AIRBUS cherche à construire un outil de simulation numérique par la méthode des éléments finis, permettant d'analyser l'influence de leur géométrie sur leur performance. Cet article présente le travail de comparaison entrepris pour valider la simulation numérique du comportement statique à l'aide d'une technique expérimentale d'investigation dans le volume : la photoélasticimétrie tridimensionnelle. Cette technique permet d'analyser la répartition 3D des contraintes dans des structures modèles fabriquées en résine époxy. Ces premières observations nous ont permis de faire évoluer le modèle numérique afin de le rendre plus réaliste

Analyse à cœur des champs de déplacement obtenus sur une éprouvette fissurée

La méthode de corrélation d’images volumiques (nommée DVC, Digital Volume Correlation) couplée avec la microtomographie à rayons X permet de déterminer les trois composantes de déplacement au cœur des matériaux. Ces techniques ont été employées pour étudier des éprouvettes fissurées SEN (Single Edge Notch) sollicitées en mode I afin de réaliser une comparaison et de quantifier les différences dans le volume entre les résultats expérimentaux et ceux obtenus à partir d’un modèle théorique

Warping section analysis by numerical modelling and volume measurements techniques

The transverse shear effects is a important phenomenon which have to be taken into account in the composite structures studies. This paper deals whith the use of differents kind of transverse shear functions for the analytical displacement fields calculations of composite materials. Since the old models of Kirchhoff-Love and Reissner-Mindlin to consider the transverse shear stresses, litterature gives a very large number of functions wich can be used to concider the transverse shear effects, especially the warping sections

Study of mechanical effects of lumbar disc arthroplasty on facet joints at the index level/adjacent levels by using a validated finite element analysis

Introduction: Lumbar disc arthroplasty is a surgical procedure designed to treat degenerative disc disease by replacing the affected disc with a mobile prosthesis. Several types of implants fall under the term total disc replacement, such as balland-socket, mobile core or elastic prostheses. Some studies have shown that facet arthritis can develop after arthroplasty, without much precision on the mechanical impact of the different implant technologies on the facet joints. This study aims to create validated patient-specific finite element models of the intact and post-arthroplasty lumbar spine in order to compare the mechanical response of ball-and-socket and elastic prostheses. Methods: Intact models were developed from CT-scans of human lumbar spine specimens (L4-S1), and arthroplasty models were obtained by replacing the L4-L5 disc with total disc replacement implants. Pure moments were applied to reproduce physiological loadings of flexion/extension, lateral bending and axial rotation. Results: Models with ball-and-socket prosthesis showed increased values in both range of motion and pressure at the index level and lower values at the adjacent level. The mechanical behaviour of the elastic prosthesis and intact models were comparable. The dissipated friction energy in the facet joints followed a similar trend. Conclusion: Although both implants responded to the total disc replacement designation, the mechanical effects in terms of range of motion and facet joint loads varied significantly not only between prostheses but also between specimens. This confirms the interest that patient-specific surgical planning using finite element analysis could have in helping surgeons to choose the appropriate implant for each patient

Study of mechanical effects of lumbar disc arthroplasty on facet joints at the index level/adjacent levels by using a validated finite element analysis

Introduction: Lumbar disc arthroplasty is a surgical procedure designed to treat degenerative disc disease by replacing the affected disc with a mobile prosthesis. Several types of implants fall under the term total disc replacement, such as ball-and-socket, mobile core or elastic prostheses. Some studies have shown that facet arthritis can develop after arthroplasty, without much precision on the mechanical impact of the different implant technologies on the facet joints. This study aims to create validated patient-specific finite element models of the intact and post-arthroplasty lumbar spine in order to compare the mechanical response of ball-and-socket and elastic prostheses.Methods: Intact models were developed from CT-scans of human lumbar spine specimens (L4-S1), and arthroplasty models were obtained by replacing the L4-L5 disc with total disc replacement implants. Pure moments were applied to reproduce physiological loadings of flexion/extension, lateral bending and axial rotation.Results: Models with ball-and-socket prosthesis showed increased values in both range of motion and pressure at the index level and lower values at the adjacent level. The mechanical behaviour of the elastic prosthesis and intact models were comparable. The dissipated friction energy in the facet joints followed a similar trend.Conclusion: Although both implants responded to the total disc replacement designation, the mechanical effects in terms of range of motion and facet joint loads varied significantly not only between prostheses but also between specimens. This confirms the interest that patient-specific surgical planning using finite element analysis could have in helping surgeons to choose the appropriate implant for each patient