**5. Conclusions**

A series of Brazilian tests of TATB-PBX at different temperatures were conducted, while the evolution of micro-structure inside the specimens was obtained through in-situ μCT observation. Through the digital imaging process, CT slice images were analyzed. Fracture degree and complexity were defined and were used to quantitatively describe the fracture characteristics at different temperatures. The fractal characteristic of cracks was also analyzed by using box-counting method. The interior displacement fields of particles were also studied and all of the above results were also proved by SEM detection.

The 3D crack morphology was obtained, and it could be seen clearly and directly at lower temperatures that the cracks were straighter while at higher temperatures, especially above the glass transition temperature of binders, the cracks were more tortuous. The fracture degree was used to characterize the level of the fractures; while the fracture complexity was used to characterize the tortuosity character of the fractures. It could be seen that the fracture complexity tended to increase as the temperature rose, which implied a more tortuous crack. The fractal dimension of cracks showed a grea<sup>t</sup> minus linear relation with the temperature, which meant that as the temperature rose, the fracture fractal dimension decreased and the fracture surface was smoother. The interior displacement fields of particles showed the micro-structure evolution inside the specimens, which agreed with the macro-mechanical behavior at different temperatures. In SEM images, the typical morphology of fractures at different temperatures was obtained and proved the above conclusions. It was found that at lower temperatures, especially lower than the glass transition temperature of binders, there was slipping and shear among particles, and particles tended to displace and disperse; while at higher temperatures, especially above the glass transition temperature of binders, there was reorganization of particles and particles tended to merge, disperse, and reduce sizes, rather than displacing.

**Author Contributions:** J.-M.L. conceived the whole research; H.C. and Z.-N.Y. designed the experiments in detail; Z.-N.Y. and H.C. performed the experiments and analyzed the data; B.D. gave some advice in experiments and W.-B.Z. gave some advice in analysis. Z.-N.Y. and H.C. wrote the paper.

**Acknowledgments:** This work was founded by NSAF (U1330202), National Natural Science Foundation of China (11572294), and National Key Scientific Instrument and Equipment Development Project (2013YQ03062907).

**Conflicts of Interest:** The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.
