3D crack growth monitoring in wood-based materials by means of X-ray computed microtomography and 2D DIC analysis method

Crack initiation and growth in wood-based materials, commonly employed in buildings and civil engineering structures, still generate considerable inspection and repair costs besides the fact that is one of the most important factors involved in structural failure. X-ray computed microtomography (X-ray CT), which provides 3D images with a high level of detail at both the micro- and macro-scales, is frequently used as a non-destructive technique. In this work, the propagation of a 20 mm initial crack in Mixed-Mode Crack Growth (MMCG) wood samples was tracked using high-energy X-ray CT. Crack growth data were then determined from 3D tomography reconstructions. 2D crack tracking data measurements from fracture surface were performed using 2D Digital Image Correlation (DIC) analysis method. The collected 3D measurements were compared to those obtained from 2D DIC analysis and conventional mechanical tests in order to measure long and small crack growth. The observed results demonstrates that X-ray CT and surface tracking analysis usingDICgrid methodcan be successfully combined to study the crack propagatio

Comportement local des enrobés recyclés : apport des mesures de champs cinématiques

Asphalt mixtures are complex composite materials constituted of several phases, namely aggregates, bituminous binder and voids. The assembly of these phases defines a highly complex microstructure, which drives the macroscopic response of asphalt mixtures. Classically, both the mechanical and the thermal responses of asphalt materials are characterized by using experiments at the scale of the mixture assuming that the material is homogeneous. At the scale of their constituents, these materials require a measurement technique featuring simultaneously both a good spatial resolution and a good strain resolution. To date, there are only few experimental studies available in the literature that describe the thermal and mechanical behavior of bituminous mixes at the scale of the constituent. The aim of this work is, on the one hand, to evaluate the possibilities of using the grid method (GM) for the analysis of the thermo-mechanical properties of asphalt mixtures and, on the other hand, to characterize the effect of the recycled asphalt pavement (RAP) inclusion on the local behavior of these materials. Full-field measurements provided by GM allow to study the response of these materials at scales ranging from the component to the mixture itself. These results enable us to validate an innovative experimental approach for the analysis of asphalts. It gives access to reliable and rich information at the scale of the microstructure. Some aspects related to the impact of RAP on the local behavior of asphalt were also provided.Les enrobés bitumineux sont des matériaux composites complexes constitués de plusieurs phases : granulats, liants bitumineux et vides. L'assemblage de ces phases définit une microstructure très complexe qui pilote la réponse macroscopique des enrobés. Classiquement, les réponses mécanique et thermique des enrobés sont caractérisées par des essais à l'échelle macroscopique en supposant que le matériau est homogène et isotrope. À l’échelle des constituants, la caractérisation de ces matériaux nécessite d’utiliser une technique de mesure disposant simultanément d’une bonne résolution spatiale et d’une bonne résolution de mesure. L’enjeu de ce travail est d’une part d’évaluer les possibilités d’utilisation de la méthode de la grille (MG) pour l’analyse des propriétés thermo-mécaniques des enrobés bitumineux, et d’autre part de caractériser, grâce à l’apport de cette méthode, l’effet de l’introduction d’agrégats d’enrobés (AE). L’étude expérimentale comprend des essais de compression et de traction ainsi que des essais de gel-dégel. Les champs cinématiques issus de la MG ont permis d'étudier la réponse de ces matériaux à des échelles allant de l’échelle du constituant jusqu’à celle de l’éprouvette. Les résultats obtenus ont également permis de valider une approche expérimentale innovante pour l’analyse des enrobés en permettant d’accéder à des informations fiables et riches à l’échelle de la microstructure. Certains aspects liés à l'impact du recyclage sur le comportement local de l’enrobé sont également fournis

Local behavior of recycled asphalt pavement : contribution of full-field measurements

Les enrobés bitumineux sont des matériaux composites complexes constitués de plusieurs phases : granulats, liants bitumineux et vides. L'assemblage de ces phases définit une microstructure très complexe qui pilote la réponse macroscopique des enrobés. Classiquement, les réponses mécanique et thermique des enrobés sont caractérisées par des essais à l'échelle macroscopique en supposant que le matériau est homogène et isotrope. À l’échelle des constituants, la caractérisation de ces matériaux nécessite d’utiliser une technique de mesure disposant simultanément d’une bonne résolution spatiale et d’une bonne résolution de mesure. L’enjeu de ce travail est d’une part d’évaluer les possibilités d’utilisation de la méthode de la grille (MG) pour l’analyse des propriétés thermo-mécaniques des enrobés bitumineux, et d’autre part de caractériser, grâce à l’apport de cette méthode, l’effet de l’introduction d’agrégats d’enrobés (AE). L’étude expérimentale comprend des essais de compression et de traction ainsi que des essais de gel-dégel. Les champs cinématiques issus de la MG ont permis d'étudier la réponse de ces matériaux à des échelles allant de l’échelle du constituant jusqu’à celle de l’éprouvette. Les résultats obtenus ont également permis de valider une approche expérimentale innovante pour l’analyse des enrobés en permettant d’accéder à des informations fiables et riches à l’échelle de la microstructure. Certains aspects liés à l'impact du recyclage sur le comportement local de l’enrobé sont également fournis.Asphalt mixtures are complex composite materials constituted of several phases, namely aggregates, bituminous binder and voids. The assembly of these phases defines a highly complex microstructure, which drives the macroscopic response of asphalt mixtures. Classically, both the mechanical and the thermal responses of asphalt materials are characterized by using experiments at the scale of the mixture assuming that the material is homogeneous. At the scale of their constituents, these materials require a measurement technique featuring simultaneously both a good spatial resolution and a good strain resolution. To date, there are only few experimental studies available in the literature that describe the thermal and mechanical behavior of bituminous mixes at the scale of the constituent. The aim of this work is, on the one hand, to evaluate the possibilities of using the grid method (GM) for the analysis of the thermo-mechanical properties of asphalt mixtures and, on the other hand, to characterize the effect of the recycled asphalt pavement (RAP) inclusion on the local behavior of these materials. Full-field measurements provided by GM allow to study the response of these materials at scales ranging from the component to the mixture itself. These results enable us to validate an innovative experimental approach for the analysis of asphalts. It gives access to reliable and rich information at the scale of the microstructure. Some aspects related to the impact of RAP on the local behavior of asphalt were also provided

STUDYING WITH A FULL-FIELD MEASUREMENT TECHNIQUE THE LOCAL RESPONSE OF ASPHALT SPECIMENS SUBJECTED TO FREEZE- THAW CYCLES

International audienceIn cold regions, pavements suffer from the thermal cracking caused by the contraction and expansion of asphalt under temperature changes. The thermal behavior of asphalt at the macroscopic scale has been widely studied using testing devices such as the Asphalt Thermal Cracking Analyzer (ATCA) [1] and the Asphalt Concrete Cracking Device (ACCD) [2]. However, since low temperature damages are initiated in the internal structure of asphalt mixtures, understanding the thermal response of asphalt components (bitumen and aggregates) is of great practical importance to have a better understanding of the overall thermal response of pavements. The major problem is however to measure the local thermal response of these materials. Full-field measurement techniques, which have now widely spread in experimental mechanics, are useful to have a better understanding of the asphalt behavior under thermal loadings. In recent years, these methods have become major tools to inspect and characterize the mechanical response of such materials. The main full-field measurement methods that are used by the pavement community are the digital image correlation (DIC) [3–5] and more recently the grid method (GM) [6,7]. This last technique was used here because it exhibits a good compromise between spatial resolution and measurement resolution [8], which is crucial here, the material under investigation being highly heterogeneous. Till now, the application of such measurement techniques for the characterization of asphalt was limited to their mechanical response, and few emphasis has been placed on the investigation of their thermal response. In this study, four Hot Mixtures Asphalt (HMA) specimens with 0%, 20%, 40% and 100% of RAP (Recycled Asphalt Pavement) content were considered. These materials were used in a previous study, which was devoted to the characterization of the effect of RAP on the local mechanical behavior of recycled asphalt pavements [6]. These RAP materials are composed of granite, basalt and gneiss. The virgin materials are constituted from limestone aggregates and a virgin bituminous binder. Freeze-thaw tests were carried out on these materials. They were performed in a climate chamber at a temperature range of [-10°C 20°C]. At the global scale, the specimens exhibited an anisotropic behavior along both the vertical and horizontal directions. The comparison of the global strain-temperature curves showed that the inclusion of 100% RAP resulted in an increase of the Coefficient of Thermal Contraction (CTC) of the specimen. Typical examples of the displacement fields obtained for the 100% RAP specimen at T=-10°C are shown in Figure 1

Investigation of tropical wood modification under hydro-mechanical loadings with digital image correlation and X-ray microtomography

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Sur la durabilité des essences tropicales par couplage corrélation d'image et microtomographie à rayons X

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Towards the local expansion and contraction measurement of asphalt exposed to freeze-thaw cycles

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Applying a full-field measurement technique for studying the local deformation in reclaimed asphalt pavements

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