Investigation of the Quasi-Static and Dynamic Confined Strength of Concretes by Means of Quasi-Oedometric Compression Tests

For the two last decades, the quasi-oedometric compression testing method has been widely employed to characterize the quasi-static and dynamic confined response of concrete and rock-like materials. It consists of compressing a cylindrical specimen tightly enclosed in a thick confinement vessel for determining the hydrostatic and deviatoric behaviors of these materials under pressure ranging from few tens to a thousand of MPa. Large capacity hydraulic press can be used for quasi-static loading whereas large-diameter Split-Hopkinson Pressure Bar can be employed to characterize the dynamic response of the tested samples. This chapter describes the principle of this testing technique, the processing method, validation tools provided in the literature and some key-results obtained regarding the influence of concrete composition, particles reinforcement, free water content and the loading-rates on the hydrostatic and deviatoric behaviors of concretes

A testing technique for concrete under confinement at high rates of strain

International audienceA testing device is presented for the experimental study of dynamic compaction of concrete under high strain rates. The specimen is confined in a metallic ring and loaded by means of a hard-steel Hopkinson pressure bar (80 mm diameter, 6 m long) allowing for the testing of specimens large enough regarding the aggregate size. The constitutive law for the metal of the ring being known, transverse gauges glued on its lateral surface allow for the measurement of the confining pressure. The hydrostatic and deviatoric responses of the specimen can then be computed. The proposed method is validated by several numerical simulations of tests involving a set of four different concrete-like behaviours and different friction coefficients between the cell and the specimen. Finally, three tests performed with the MB50 concrete at three different strain rates are processed with the method and are compared with literature results for the same material under quasi-static loadings

An experimental method of measuring the confined compression strength of high-performance concretes to analyse their ballistic behaviour

6 pages, 4 figures.-- Issue title: "EURODYMAT 2006 - 8th International Conference on Mehanical and Physical Behaviour of Materials under Dynamic Loading" (Dijon, France, Sep 11-15, 2006).The test known as "quasi-oedometric compression" consists of the compression of a cylindrical specimen confined in a thick vessel. In this work, an original methodology is proposed to deduce the radial stress and strain within the specimen using hoop strains measured on the external surface of the vessel, taking into account its elasto-plastic deformation. On one hand the spherical and deviatoric behaviours of two concretes are deduced. On the other hand, their ballistic behaviour is analysed using impact tests. These experiments are simulated numerically by the plasticity model of Krieg, Swenson and Taylor, and the features of the model are identified by the previous confined compression tests. The capacity of the model to describe the ballistic behaviour of such materials is shown in a comparison of the numerical simulations with the ballistic tests.The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnología (Project MAT2002-03339) for the financial support of this work and to the Délégation Générale pour I'Armement (DGA/France) for the mobility grant provided to P. Forquin.The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnología (Project MAT2002-03339) for the financial support of this work and to the Délégation Générale pour l’Armement (DGA/France) for the mobility grant provided to P. Forquin.Publicad

Probabilistic-deterministic transition involved in a fragmentation process of brittle materials: Application to a high performance concrete

International audienceDynamic loadings produce high stress waves leading to the fragmentation of brittle materials such as ceramics, concrete, glass and rocks. The transition from single fragmentation (under quasi static loading condition) to multiple fragmentation (dynamic loading) is discussed and a damage model based upon the fragmentation analysis is applied to analyze edge-on-impact of a high performnace concrete

An experimental method of measuring the confined compression strength of geomaterials

27 pages, 29 figures.Knowledge of the behaviour of geomaterials under confined compression is a pre-requisite for any analysis of their ballistic performance. This study proposes an experimental method of determining the spherical and deviatoric behaviour of these materials under high pressure. Known as the ‘quasi-oedometric compression test’ it consists of compressing a cylindrical specimen tightly enclosed in a thick confinement vessel. The principles of these quasi-oedometric tests are given first, and the steps taken for their execution, together with an examination of the steel used for the confinement vessel. An original way of analysing the data of the test is presented and validated by numerical simulations. These calculations provide valuable information about the influence of the interface product introduced between the vessel and the specimen, and that of friction. Tests are then presented with specimens of aluminium alloy to validate the experimental set-up and the method of analysis. In addition, quasi-oedometric compression tests of cement based material, with and without particles, illustrate the opportunities offered by this testing method, and show that its deviatoric strength and compaction law are significantly improved by ceramic granulates addition.The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnología (Project MAT2002-03339) for the financial support of this work and to the Délégation Générale pour l’Armement (DGA/France) for the mobility Grant provided to Dr. Forquin.Publicad

Role of porosity in controlling the mechanical and impact behaviours of cement-based materials

14 pages, 12 figures.This work deals with the influence of porosity on the tensile, the compressive and the impact behaviours of two fine cementitious mortars—one with silica fume and one without. The addition of silica fume is shown to change the pore size distribution. The mix without silica fume is characterized by porosity at the scale of the grains of fine sand (approximately 100 μm), while silica fume addition results in a more porous matrix with pore sizes of millimetre-length size. The mortar with silica fume shows a higher quasi-static compressive and flexural strength whereas the mix without silica fume is observed to be less compressible (by irreversible reduction of volume) under heavy confinement pressure (quasi-oedometric tests) and shows better ballistic performance. A numerical simulation of the impact tests employing the Krieg, Swenson and Taylor model, which accounts for both deviatoric and volumetric inelastic behaviour of the material, was undertaken using the data from quasi-oedometric tests. These calculations follow the experimental results and confirm the influence of the macroscopic porosity on the impact performance of cement-based materials.The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnología (Project MAT2002-03339) for the financial support of this work and to the Délégation Générale pour l’Armement (DGA/France) for the mobility grant provided to Dr. Forquin

Simard Denis. Éducation et herméneutique : contribution à une pédagogie de la culture

Issu d’une thèse de doctorat et publié dans le cadre d’une collection intitulée « Éducation et culture », l’ouvrage de Denis Simard, Éducation et herméneutique apporte à la réflexion pédagogique contemporaine une contribution originale, inscrite dans la problématique de la postmodernité et éclairée par les apports de la philosophie herméneutique allemande. L’ouvrage se veut essentiellement une réflexion générale sur la crise de la culture et de l’éducation mais aussi, plus profondément, sur l..

Savidan Patrick. Repenser l’égalité des chances

Au croisement de la philosophie politique et des ­sciences sociales, l’ouvrage de Patrick Savidan Repenser l’égalité des chances s’inscrit dans le vaste et multiple territoire de la réflexion contemporaine sur la question de la justice. En quoi peut consister aujourd’hui, se demande l’auteur (par ailleurs président de l’Observatoire des inégalités), une conception soutenable de la justice sociale ? Une conception « soutenable », comme le suggère l’insistance d’une mise en italique dans le cor..

Jacquet-Francillon François & Kambouchner Denis (dir.). La Crise de la culture scolaire : origines, interprétations, perspectives

Issu d’un colloque organisé à la Sorbonne en septembre 2003 sous la responsabilité conjointe du Département de philosophie de l’éducation de l’INRP, de l’École doctorale de philosophie de l’université Paris 1-Sorbonne et de l’Équipe de philosophie politique et morale de l’éducation de l’IUFM de Franche-Comté, le présent ouvrage réunit, autour du thème de la crise de la culture scolaire, un important ensemble de contributions (vingt-cinq textes d’auteurs différents et trois comptes rendus de t..

Effect of plastic deformation and boundary conditions combined with elastic wave propagation on the collapse site of a crash box

21 pages, 22 figures.Several papers have been published recently on the crashworthiness studies. The main task was to predict the energy absorption Wp and average collapse force overbar-F in time of sheet steel structures. The main objective of this contribution is to design a component that allows absorbing and dissipating a high energy Wp allowing improvements of the survivability of passengers in vehicles. However, the range of applications is larger since it includes all civil and military applications related to safety of components, or more generally of construction elements being loaded by impacts or explosions. In the present 3D case, the aim of this numerical study on dynamic loading in adiabatic conditions of deformation is to analyze the effect of elastic wave propagation combined with plastic behavior on the collapse site of a rectangular tubular structure made of steel sheet. To demonstrate the strong coupling between the effects of strain-rate sensitivity, accounted for in the constitutive relation that is used in numerical simulations, with the process of elastic wave reflection on the boundary conditions, a series of numerical simulation was performed. It is shown in this numerical study that the strain-rate sensitivity influences the position of the first collapse site. Moreover, the first collapse initiation of a structure defines the level of power absorption. Since the process of folding may be combined with bending of the structure (in particular when a local buckling appears close to the opposite side of impact), in this non-axial case the energy absorption Wp decreases and the effectiveness of the structure to the energy absorption is insufficient.The researchers of the University Carlos III of Madrid are indebted to the Spanish Ministry of Education (project DPI2005-06769), and to the Region of Madrid (project CCG06-UC3M/DPI-0796) for the financial support that allowed to perform a part of the numerical simulations.Publicad