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

Abstract

The test known as 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. Compression tests known as were developed on geomaterials (their name refers to the very weak radial displacement during the test). A cylindrical concrete specimen is placed in a confinement vessel. Subjected to axial compression, the specimen expands radialy and exerts pressure on the confinement vessel. The test produces a greater axial stress and a greater radial stress on the specimen, so the hydrostatic confinement pressure varies considerably during the test and the resistance to these different confinement pressures can be measured. Several experimental devices for quasi- oedometric compression were set up (3, 4). Burlion (3) performed those tests assuming an elastic deformation of the vessel so the radial strain and stress of the specimen were deduced from the micro- deformation of the vessel (a few hundredths %) measured by gauges on its outer surface. A quasi- oedometric compression device was also developed with smaller vessels (4). This device was adapted to Hopkinson Bars to measure the dynamic strength of the MB50 microconcrete. The analysis in axial stress showed a very limited influence of the rate of loading on the stress level, even at a strain rate that reached 400s −1 . In this paper, a quasi-oedometric device and a new methodology of analysis are presented and used with two concretes. After that, their ballistic performances are discussed in relation with their properties measured under confined compression. Finally a model is used to simulate numerically the ballistic tests, and the results in terms of depth of penetration are compared with the experimental results.