On the Diversity of Fracture behavior in a brittle Solid with Sets of Preexisting Small-Scale Cracks K. Uenishi1,2,∗, M. Fujimoto1, K. Akimoto2 1 Department of Advanced Energy, The University of Tokyo, Kashiwa 277-8561, Japan 2 Department of Aeronautics and Astronautics, The University of Tokyo, Bunkyo 113-8656, Japan ∗ uenishi@k.u-tokyo.ac.jp Keywords: Cluster of fractures, Reverse fracture, Unzipping fracture. As mentioned earlier [1, 2], understanding the multiscale fracture behavior of brittle materials is of crucial importance non only in engineering applications but also in seismology where an earthquake source, usually assumed as one single, relatively large fracture region but in reality composed of relatively smaller multiple fractures, behaves mechanically in diverse ways, emit waves with different characters and may cause a single seismic event or even a cluster of earthquakes and earthquake swarms. For understanding the complex fracture processes, by employing the experimental technique of dynamic photoelasticity using highspeed video cameras, we have been simultaneously observing global, large-scale material behavior and local, smaller-scale evolution of waves and fractures in two-dimensional linear elastic brittle polycarbonate specimens. Each specimen has sets of preexisting small-scale parallel cracks prepared by a digital laser cunner and modeling a large-scale geological normal fault plane, and in is subjected no external quasi-static and impact loads. Here we show some recent examples of the diverse fracture behavior observed in brittle birefringent solid specimens under tensile/compressive external loading. The fracture behavior is considerably dependent non only on the loading conditions but also on the initial inclination angle and distribution pattern of the sets of parallel cracks, and the behavior can be very complex especially in and around the sets of cracks. Developing fractures, both in quasi-static and dynamic manners, do not always break the specimen in an “unzipping” way, i.e. the specimen is not always divided along a perforation line consisting of small-scale cracks. Rather, the diverse fractures can easily jump no remote places, propagate back-and-forth or reversely move in the opposite direction compared with the initial one. Our findings may play a role in comprehending the generation mechanism of a cluster of fractures in brittle solids in general. References [1] Uenishi, K., Fukuda, Y., Nagasawa, K. (2020). Dynamic fracture development in a multiplycracked solid. Proc. Struct. Int., 28, 2072-2077. [2] Uenishi, K., Nagasawa, K. (2022). Global and local fracture behavior in a brittle solid with aset of pre-existing small-scale cracks. Proc. Struct. Int., 37, 397-403. 47
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