Impact of Equivalent Young’s Modulus Ratio Values between Material Layers on Pavement Structural Fracture Performance

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Viscoroute 2.0: a tool for the simulation of moving load effects on asphalt pavement

As shown by strains measured on full scale experimental aircraft structures, traffic of slow-moving multiple loads leads to asymmetric transverse strains that can be higher than longitudinal strains at the bottom of asphalt pavement layers. To analyze this effect, a model and a software called ViscoRoute have been developed. In these tools, the structure is represented by a multilayered half-space, the thermo-viscoelastic behaviour of asphalt layers is accounted by the Huet-Sayegh rheological law and loads are assumed to move at constant speed. First, the paper presents a comparison of results obtained with ViscoRoute to results stemming from the specialized literature. For thick asphalt pavement and several configurations of moving loads, other ViscoRoute simulations confirm that it is necessary to incorporate viscoelastic effects in the modelling to well predict the pavement behaviour and to anticipate possible damages in the structure.Comment: 27 pages

A Half-analytical Elastic Solution for 2D Analysis of Cracked Pavements

International audienceThis paper presents a half-analytical elastic solution convenient for parametric studies of 2D cracked pavements. The pavement structure is reduced to three elastic and homogeneous equivalent layers resting on a soil. In a similar way than the Pasternak's modelling for concrete pavements, the soil is modelled by one layer, named shear layer, connected to Winkler's springs in order to ensure the transfer of shear stresses between the pavement structure and the springs. The whole four-layer system is modelled using a specific model developed for the analysis of delamination in composite materials. It reduces the problem by one dimension and gives access to regular interface stresses between layers at the edge of vertical cracks allowing the initial debonding analysis. In 2D plane strain conditions, a system of twelve-second order differential equations is written analytically. This system is solved numerically by the finite difference method (Newmark) computed in the free Scilab software. The calculus tool allows analysis of the impact of material characteristics changing, loads and locations of cracks in pavements on the distribution of mechanical fields. The approach with fracture mechanic concepts is well suited for practical use and for some subsequent numerical developments in 3D

Outil 2D d'analyse mécanique et paramétrique des chaussées fissurées

Ce papier présente un outil de calcul rapide et utile à l'ingénieur pour l'analyse des champs mécaniques dans les structures multicouches de chaussée fissurées. La chaussée est choisie équivalente à trois couches élastiques et homogènes reposant sur un sol. Le sol est modélisé au moyen d'une couche dite de cisaillement ajoutée à un massif de ressorts élastiques (Massif de Winkler) afin d'assurer le transfert des contraintes de cisaillement entre la chaussée et les ressorts. Le quadri-couche total (3 couches de chaussée plus 1 couche de cisaillement) est modélisé à l'aide d'un modèle simplifié (M4-5n) développé pour l'analyse du délaminage des matériaux composites. Le système de douze équations différentielles d'ordre 2 résultant, écrit complètement analytiquement, est résolu par différences finies (Newmark) dans le cas 2D des déformations planes. Sur une chaussée contenant une fissure verticale le long d'une de ses couches, les solutions semi-analytiques sont obtenues en moins d'une seconde. Cet outil autorise ainsi des études paramétriques telles que la distribution des champs mécaniques (en particulier les contraintes d'interface) en fonction de la position de la charge plus ou moins distante de la fissure verticale. Cette nouvelle modélisation montre son efficacité par rapport à l'emploi d'un code aux éléments finis classique

Apports du massif de Winkler dans la construction d'un outil de calcul de structure multicouche fissurée reposant sur un sol

Les modèles et méthodes pour décrire et prévoir les endommagements des structures multicouches consistent principalement à analyser, à l’état initial, les efforts à l’interface entre couches aux bords (ou près des fissures verticales). En ces endroits, les champs sont complexes et singuliers. Ils sont généralement calculés par des modèles assez sophistiqués. Pour l’ingénieur de bureau d’études, le besoin est de pouvoir disposer d’outils de calcul efficaces, simples et rapides à mettre en œuvre. Dans ce papier, les bases d’un outil de calcul semi-analytique dédié à l’analyse des pathologies et des solutions de renforcement des structures de chaussées sont proposées. Pour simplifier au maximum le problème final à résoudre, la chaussée est assimilée à une structure tri-couches équivalente possédant ou non une fissure verticale à travers l’épaisseur d’une couche. Elle est modélisée par le Modèle Multi-particulaire des Matériaux Multicouches (M4) à cinq champs cinématiques par couche (5n, n : nombre total de couche). L’avantage de ce modèle est de réduire d’une dimension la résolution des équations et de rendre finie les intensités des contraintes au droit des fissures à l’interface entre couches (Chabot, 1997). Cette structure repose sur un massif de sol semi-infini modélisé par un massif de Winkler (W). Les efforts de réaction du sol sont assimilés à des ressorts n’introduisant ainsi qu’une seule inconnue principale. Le modèle complet résultant est nommé le M4-5nW. L’outil numérique est présenté ici dans le cas 2D déformations planes. Les conditions aux limites de couche fissurée sont clairement introduites dans le système d’équations analytiques différentielles d’ordre 2 final à résoudre. Le problème complet 1D résultant est résolu par la méthode des différences finies utilisant le schéma de Newmark. Les solutions du logiciel, ainsi programmées dans Scilab, sont obtenues vingt fois plus rapidement que celles utilisant un massif de Boussinesq pour le sol (Tran, 2004)

Influence of sliding interfaces on the response of a layered viscoelastic medium under a moving load

This article presents a method to compute the response of a viscoelastic layered half-space to a moving load when interlayer slip is considered. The Navier equations of equilibrium are solved for each layer in the frequency domain. The solution in the spatial coordinate system is subsequently obtained by means of Fast Fourier Transform and quadrature rules applied to integrable singularities. Following the global solution technique, the developed method compiles all the interface and the boundary conditions within a global matrix and it solves a unique linear system per couple of wave numbers. This method proves to be effective and is validated in an elastic case by comparison with the ALIZE-LCPC software that implements the Burmister axisymmetric solution. The influence of the interface sliding condition on the response of a layered viscoelastic medium is studied through an application to pavement structures. In this application, the effect of the load speed on vertical and horizontal profiles of the longitudinal strain and the normal stress is analyzed. It is shown, inter alia, that the maximum extension in the medium is not systematically observed at the location of an interface and that, as expected, low speeds and interlayer slip are more damaging to the structure when either a strain or a stress criterion is considered

Mixed FE solution of the layerwise model M4-5n with emphasis on embedded discontinuities

CFRAC2017, Fifth International Conference on Computational Modeling of Fracture and Failure of Materials and Structures, NANTES, FRANCE, 14-/06/2017 - 16/06/2017A general solving method for the plate-type model called M4-5n, relying on mixed finite elements is presented hereafter. In particular, we explain how embedded discontinuities in a multilayer pavement structure can be easily taken into account using the numerical approach developed... As an illustration, the approach developed is used to simulate the mechanical response of a pavement structure with cracks on which a full-scale accelerated fatigue test was performed

Analyses mécaniques d'une structure bi-couches délaminante par flexion 4 points

Pour l'étude de propagations de fissures à l'interface entre couches de chaussée composite, un essai de flexion 4 points spécifique sur structure bi-couches est proposé. Le dimensionnement initial des éprouvettes est effectué par des simulations numériques élastiques pour maximiser l'intensité des contraintes « M4-5n » à l'interface entre couches. Les ruptures d'interface sont attendues en mode mixte (mode I et II). Les résultats sont comparés à ceux obtenus par calculs éléments finis et par de premiers essais en statique sur structure alu/PVC et béton de ciment/enrobé bitumineux

eRoads Group (from a pavement point of view)

International audienc

Characterization of Debonding at the Interface between Layers of Heterogeneous Materials coming from Roads

Road structures are made by a superposition of different layers of heterogeneous materials (bituminous materials, cement concrete, composite grids, etc). The durability of such composite structures depends on severe climate conditions that occur during their lifetimes and multiple heavy loads that move on them. Various damages are identified such as delamination mechanisms at the interface between surface pavement layers. Studying debonding phenomenon is a necessity in order to propose innovative solutions to maintain an old efficient transport road network. This also helps to develop new concepts for turning road infrastructure with new added functionalities such as those that integrates into the road surfaces a dynamic charging box for electric vehicles. Nowadays, this type of cracking in pavement structures is still not well understood. As for edge delamination in composite field, edge effect of existing joints or vertical cracks in a pavement layer create such a high concentration of both normal and shear interface stresses that the crack could propagate along the interface between the two different layers before penetrating through one of materials or even debonding elsewhere far from them (Chabot et al., 2013). Appropriate fracture opening pure mode I or II and mixed mode laboratory tests under several static and fatigue load conditions and various environmental conditions (mainly temperature and moisture) need to be adapted or developed for the specific bending study of such multilayered structures. The main objective of this paper is to compare the results from different techniques in the aim to characterize experimentally the interface crack initiation and propagation by way of interfacial fracture energies obtained on composite specimens coming from road construction. Shear fracture mode tests in the pavement field are not so easy to modify and it is not so simple to compare their ""pure"" mode test results to a part of those coming from fracture mixed mode tests. In the present work and following many previous works, the Wedge Splitting Test (WST) developed by Tschegg (1986) is chosen. This test is a quite convenient test method to study the fracture behaviour at the interface of heterogeneous materials in mode I. The WST test has been adapted for specimens extracted from full scale pavement sections (Gharbi et al., 2017). Cubical shape specimens of important size (compared to the granular maximum size of the materials) are prepared with a cylindrical groove instead of a traditional rectangular groove. A slim wedge of 14° is used to ensure principally the studying of the interface debonding phenomenon in a quasi-pure opening Mode I. A notch of 5 mm thick is sawed at the interface between the two material layers to guarantee the initiation of the crack at the interface. A finite element study is conducted to analyze the effect of variation of the specimen dimensions. Static tests controlled with a constant displacement speed rate (0.7mm/mn or 2 mm/min) and constant temperatures (~20°C) are performed in order to determine the specific fracture energy (GF) of interface between bi-layered specimens. Different techniques are used to evaluate initiation and propagation of the fracture with the modified WST test. The tensile strength and the fracture energy are firstly estimated from the splitting force (FS) - Crack Mouth Opening Displacement (CMOD) curve. To obtain the displacement field at points between the two crack lips, the Digital Image Correlation (DIC) technics are used. Then these displacement fields are introduced in the elastic model proposed by Dunder (1969) to calculate, under 2D conditions (plane stress and deformation), the strain energy release rate evolution. This energy depends on the interface crack length estimated also by DIC measurements. Results found from the two methods are finally discussed