Laboratoire Sols, Solides, Structures et Risques - 3SR

ABSTRACT Dynamic tensile tests based on the so-called spalling technique may be conducted to characterize the tensile strength and the cracking density of concretes under strain-rates in the range of 30/s to 150/s. Based on this technique, a series of experiments have been performed in LEM3 laboratory by using an instrumentation including a laser interferometer directed toward the rear face of the sample and strain-gauges on the specimen. In the present work, a series of computations of spalling tests have been conducted with the Mazars damage model. First, the loading-rate sensitivity has been identified from spalling tests to take account in the modelling of the increase of strength with strain-rate. Next, a series of numerical simulations have been performed considering various mesh sizes and by using or not the Hillerborg regularization method. Finally the ability of the Mazars model for predicting the post-peak behaviour of concrete in spalling tests has been assessed by comparing the numerous experimental measurements to numerical data.

ABSTRACT To characterize the penetration resistance of a ceramic target during impact, it is necessary to take into consideration the mechanical behaviour of the fragmented ceramic. In the present work, a series of numerical simulations have been performed to design an experimental configuration named the “normal impact test”. The aim of this configuration is to generate a strong fragmentation of the ceramic tile and to prevent any ejection of debris in order to analyse the fragmentation properties of the impacted ceramic. An anisotropic damage model has been used to perform these computations. The Weibull parameters that constitute input data of this model have been identified from four-point flexural tests performed on the so-called Hexoloy® silicon carbide. Finally, the numerical predictions are compared to the failure pattern of the fragmented ceramic.

ABSTRACT SUMMARY The aim of this study is to numerically model the fracture system at percussive drilling. Because of the complex behavior of rock materials, a continuum approach is employed relying upon a plasticity model with yield surface locus as a quadratic function of the mean pressure in the principal stress space coupled with an anisotropic damage model. In particular, Bohus granite rock is investigated, and the material parameters are defined based on previous experiments. This includes different tests such as direct tension and compression, three-point bending, and quasi-oedometric tests to investigate the material behavior at both tension and confined compression stress states. The equation of motion is discretized using a finite element approach, and the explicit time integration method is employed. Edge-on impact tests are performed, and the results are used to validate the numerical model. The percussive drilling problem is then modeled in 3D, and the bit-rock interaction is considered using contact mechanics. The fracture mechanism in the rock and the bit penetration- resisting force response are realistically captured by the numerical model. Copyright © 2013 John Wiley & Sons, Ltd.