PhD DEFENSE BY BRATISLAV LUKIC

This PhD project was supervised by Pascal Forquin and Dominique Saletti (3SR).

The defense will take place in the Wilfried Killian amphitheatre at 9 am.

Abstract

In this thesis a photomechanical spalling testing technique has been used in light of identifying concrete failure properties under dynamic tension. The experimental technique uses ultra-high speed imaging, the grid method and the virtual fields method. First, in order to investigate the accuracy and validate the data processing, a method of using simulated experiments has been developed by numerically recreating the entire identification process. In this way, several potential sources of errors have been investigated allowing to place guidelines on how to perform the experiment in a more reliable manner. Second, several ultra-high speed acquisition systems have been used in order to investigate their contribution to a possible measurement refinement. In this case, the trial experiments have been conducted on a material of known characteristics which allowed investigating metrological performance of the cameras on the entire identification chain. Finally, the experimental methodology has been applied to testing several grades of concrete in light of identifying the material constitutive response as well as their fracturing characteristics under dynamic tension. The identified tensile strengths in this work were found to be consistently lower than those obtained from the standard processing of the rear-face velocity profile. Moreover, the values of the identified specific fracture energy were also found to be markedly lower than the ones reported in the literature.
Keywords: Ultra-high-speed imaging, The Grid method, The Virtual Fields Method, high strain rate, tensile strength, concrete, simulated photomechanical experiments.