Characterising materials under dynamic loading events : From images to analysis

Start Date
09-12-2019 15:00
End Date
09-12-2019 16:30
Room 337, Central Building
Speaker's name
Brastislav Lukic
Speaker's institute
Université Grenoble Alpes - CNRS
Contact name
Eva Jahn
Host name
Alexander Rack
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There are many loading scenarios in which quasi-brittle geomaterials, such as rocks and concrete, get exposed to dynamic loads. In such load cases, generated stress waves propagate within the material. During their propagation, compressive waves can reflect from material discontinuities and free edges causing tensile stresses to emerge that lead the material to break and fragment. In certain situations, this can lead to immediate devastating outcomes, such as the collapse of concrete buildings exposed to blast loading. In other situations, such as sudden pressure rises in nuclear power plants, the concrete confinement vessel can sustain a certain amount of micro-cracking through which aggressive agents slowly leak out of the container. On the other hand, in engineering applications related to rock blasting in mining industry, material destruction with an optimal amount of effort is desirable. In all these situations the dynamic response of the material needs to be well understood and characterized. This will then allow the development of adequate material models that can be used within numerical simulation tools that could aid in mitigating risks and also allow advancing the developments in the engineering industry. In recent years, standard high-strain rate testing techniques, such as Split Hopkinson Bar systems and gas gun rigs have been coupled with ultra-high speed imaging methods. Thanks to microscopic temporal resolution, the high speed imaging diagnostics has led to a better understanding of many dynamic processes involved. Novel photomechanical processing methods have been developed that allow extracting material response directly from imaging data obtained on the sample surface. The use of digital image correlation methods also proved to be a powerful tool for studying dynamically propagating surface cracks induced by stress waves. On the other hand, high spatial resolution tomography methods such as neutron and x-ray imaging allow revelling fine spatial details in the material volume and allow visualising phenomena of fluid flow through the pre-existing crack network. Recent developments in synchrotron X-ray sources are now enabling through volume observation of multiple fracturing of material under dynamic loading with a high temporal resolution, giving new insights into phenomena involved. The seminar will focus on some of these experimental methods with a perspective of working towards using both the high spatial resolution of microtomography methods and high temporal resolution of Mhz radiography methods to potentially extend their use in the domain of dynamic characterisation of building materials.

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