For several decades, ceramic materials have been widely used in bilayered protective configurations. However, the impact loading produces dynamic tensile stresses that spread out the ceramic tile leading to an intense fragmentation made of short oriented cracks. To improve the design of such configurations the fragmentation process needs to be better understood. The edge-on impact (EOI) testing method constitutes one of the most used experimental techniques to investigate the fragmentation process in brittle materials at high-strain-rates. A cylindrical projectile hits the edge of a target leading to a multiple fragmentation. In classical EOI experiments, an ultra-high-speed camera is used to visualize the fragmentation process on the lateral surface. However, the fragmentation pattern in the bulk of the target can only be analysed post-mortem. In the present work, in addition to this classical optical inspection method, EOI experiments have been conducted in the European Synchrotron Radiation Facility with the means of ultra-high-speed imaging, i. e., X-ray radioscopy using the 16-bunch operation mode. The target, 60 x 30 x 6 mm3, was placed in the intense X-ray beam (beam energy about 30 keV) providing an observation field of 12.8 mm in width and 8 mm in height, and impacted with a projectile velocity of 144 m/s. A Shimadzu HPV-X2 camera lens-coupled to a fast scintillator was used to visualise the fragmentation process through the thickness with an interframe time set to 1065 ns. This fragmentation pattern is compared to pictures of the lateral surface obtained with an ultra-high-speed camera or post-mortem analysis.
This paper investigates the application of CMOS-based ultra-high speed camera in characterising materials under dynamic tensile loading. A single Hopkinson bar test is used to induce an axial stress wave in the sample and a grid pattern is filmed during the test to obtain time-resolved full-field kinematic measurements. Then the acceleration fields are used to reconstruct the stress information and identify material response. Quasi-brittle materials (e.g. rocks and concrete) present a particular experimental challenge due to small deformation and low stress level at failure. The Shimadzu HPV-X2 acquisition system has been applied for such purpose and its performance was investigated by first performing a spalling test on an aluminium benchmark sample and then applied to testing ordinary concrete.
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