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

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

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

Relationship between static bending and compressive behaviour of particle-reinforced cement composites

11 pages, 9 figures.Innovative particle-reinforced materials made of alumina particles and cement-based matrix were designed, manufactured and tested to evaluate the potential use of ceramic aggregates in concretes. These particle-reinforced composites were tested in three-point bending and uniaxial compression conditions to determine the influence of the shape and size of the ceramic inclusions, and the addition of silica fume on the mechanical properties. A specific methodology combining post-mortem observations with a statistical analysis of tensile failure stresses (average strength and Weibull modulus) was conducted to deduce the origin of failure for each cement-based composite (porosity or ceramic particles/matrix decohesion). A remarkable correlation is observed between bending failure stress level and the average strength measured under uniaxial compression loading. As main conclusion, addition of alumina particles in a mortar appears to strengthen or to weaken the composite depending on whether silica fume is used in the cementitious matrix.The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnología (Project MAT2002-03339) and to the Comunidad Autónoma de Madrid (CCG06-UC3M/DPI-0796) 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

An experimental method of measuring the quasi-static and dynamic confined behaviour of PMMA

A testing device is presented for the experimental study of the confined behaviour of PMMA in compression under quasi-static loading or at high strain-rates. The constitutive relation of the material ring (allowing to confine the PMMA) being known, transverse gauges glued on its lateral surface allow for the measurement of the lateral confining pressure. The hydrostatic pressure and the Mises stress may be computed. Quasi-static and dynamic tests performed in a strain-rate range of 1e-3/s 1e3/s are processed with the method and compared to results of unconfined compression tests. It is found that the compressive behaviour of PMMA is weakly influenced by the level of pressure and much more sensitive to strain-rate: an elastic brittle behaviour is observed at high strain-rates in unconfined or confined conditions whereas elastoplastic behaviour is noted under quasi-static loading

Relationship between mesostructure, mechanical behaviour and damage of cement composites under high-pressure confinement

13 pages, 11 figures.This work seeks to determine how the mesostructure of seven types of cement composites containing alumina particles or not controls their deviatoric strength, compaction law, and damage under high-pressure of confinement. First, the method of analysis of quasi-oedometric compression tests is presented. Accuracy of the method for concrete is discussed by means of numerical simulations. The confined compression tests performed show the effects of adding ceramic aggregates. Furthermore, an application of post-mortem analysis by infiltration technique of each specimen is presented, revealing a highly micro-cracked pattern depending of the mesostructure of these materials. From these observations, a discussion is presented on the influence that the addition of ceramic aggregates exerts on the confined behaviour of these composites. The tests showed a highly beneficial effect of the presence of particles, on both the deviatoric strength and the compaction law of the concretes considered.The authors are indebted to the Spanish Comisión Interministerial de Ciencia y Tecnología (Project MAT2002 03339), to the Comunidad Autónoma de Madrid and the University Carlos III of Madrid (CCG06 UC3M/DPI 0796 and CCG07 UC3M/DPI 3395) for the financial support of this work. To the Délégation Générale pour l’Armement (DGA/France) for the mobility grant provided to Dr. Forquin.Publicad