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

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

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

Assessment of digital image correlation measurement errors: methodology and results

Optical full-field measurement methods such as Digital Image Correlation (DIC) are increasingly used in the field of experimental mechanics, but they still suffer from a lack of information about their metrological performances. To assess the performance of DIC techniques and give some practical rules for users, a collaborative work has been carried out by the Workgroup “Metrology” of the French CNRS research network 2519 “MCIMS (Mesures de Champs et Identification en Mécanique des Solides / Full-field measurement and identification in solid mechanics, http://www.ifma.fr/lami/gdr2519)”. A methodology is proposed to assess the metrological performances of the image processing algorithms that constitute their main component, the knowledge of which being required for a global assessment of the whole measurement system. The study is based on displacement error assessment from synthetic speckle images. Series of synthetic reference and deformed images with random patterns have been generated, assuming a sinusoidal displacement field with various frequencies and amplitudes. Displacements are evaluated by several DIC packages based on various formulations and used in the French community. Evaluated displacements are compared with the exact imposed values and errors are statistically analyzed. Results show general trends rather independent of the implementations but strongly correlated with the assumptions of the underlying algorithms. Various error regimes are identified, for which the dependence of the uncertainty with the parameters of the algorithms, such as subset size, gray level interpolation or shape functions, is discussed

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

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

Assessment of digital image correlation measurement accuracy in the ultimate error regime: main results of a collaborative benchmark

We report on the main results of a collaborative work devoted to the study of the uncertainties associated with Digital image correlation techniques (DIC). More specifically, the dependence of displacement measurement uncertainties with both image characteristics and DIC parameters is emphasised. A previous work [Bornert et al. (2009) Assessment of digital image correlation measurement errors: methodology and results. Exp. Mech. 49, 353-370] dedicated to situations with spatially fluctuating displacement fields demonstrated the existence of an ultimate error' regime, insensitive to the mismatch between the shape function and the real displacement field. The present work is focused on this ultimate error. To ensure that there is no mismatch error, synthetic images of in-plane rigid body translation have been analysed. Several DIC softwares developed by or in use in the French community have been used to explore the effects of a large number of settings. The discrepancies between DIC evaluated displacements and prescribed ones have been statistically analysed in terms of random errors and systematic bias, in correlation with the fractional part of the displacement component expressed in pixels. Main results are as follows: (i) bias amplitude is almost always insensitive to subset size, (ii) standard deviation of random error increases with noise level and decreases with subset size and (iii) DIC formulations can be split up into two main families regarding bias sensitivity to noise. For the first one, bias amplitude increases with noise while it remains nearly constant for the second one. In addition, for the first family, a strong dependence of random error with is observed for noisy images

In-situ Analysis of Laminated Composite Materials by X-ray Micro-Computed Tomography and Digital Volume Correlation

The complex mechanical behaviour of composite materials, due to internal heterogeneity and multi-layered composition impose deeper studies. This paper presents an experimental investigation technique to perform volume kinematic measurements in composite materials. 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 create contrast during X-ray acquisition. A specific in situ loading device is presented for three-point bending tests, which enables the visualization of transverse shear effects in composite structures

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