Brittle materials are subjected to high-strain-rates tensile loadings in various conditions such as in protective structures subjected to impact or blast, in the mining industry or in various industrial processes. Under very high strain-rate loadings, brittle materials experience a multiple-fragmentation process made of numerous oriented cracks triggered on critical defects. However due to a lack of data regarding the activated defects at very small scale the fragmentation process remains difficult to model. The Brittle's CODEX chair aims to gain insight into the link between the microstructural parameters of brittle materials and their response under very high-strain-rate loading. In the present contribution, a closed form solution of the fragmentation process is developed considering any populations of critical defects. Secondly, the microstructure of three brittle materials is being analysed by using x-ray micro-tomography. Based on these experimental data the dynamic fragmentation properties of one of these materials are predicted as function of the applied loading rate.