Research Topics
At the end of the sixties, Professor P.V. Danckwerts, Shell Professor at Cambridge University used to say that "a good experimental research on crushing and grinding is lacking". This remark is still sound today as the processes of matter division have often been let aside in academia. As for solid fragmentation, important progresses have been achieved in the analytic description of an isolated propagating fracture, and classical studies have, on the other opposite, documented the overall statistics of the fragment sizes of, for instance, a broken object due to an impact. However, the bridge between these two levels of description is still unclear.
Gallery
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| Fragments of a sugar cube after multiple impacts. At each impact, fragments of different sizes are produced. Only fragments whose size is in a specific range are kept. Smaller are removed, bigger ones are impacted once more. The procedure is repeated until no large fragments remain. |
| A rod made of a brittle material (actually a dry spaghetto) is impacted axially. When the impacting object hits the rod, a compressive front propagates and triggers a buckling instability. The rod bends with a charcteristic wavelength and breaks into fragments. |
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| Recoil of a rubber band. A rubber band is stretched and suddenly released at one end. A front propagates towards the clamped end at the speed of sound. When the front reaches the clamped end, it rebounds and triggers a buckling instability. This dynamic buckling instability is a key element to understand the rod fragmentation. |
| Front propagation in a rubberband. A rubber band is initially stretched (stretching < 100 %) and then suddenly released. A front propagates from the free end towards the clamped end and rebounds. The front separates a stretched area and a stress free area. The front speed is about c = 50 m/s, the celerity of sound in rubber. |