PSI - Issue 61

Koji Uenishi et al. / Procedia Structural Integrity 61 (2024) 108–114 Uenishi et al. / Structural Integrity Procedia 00 (2024) 000 – 000

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between real three-dimensional propagation of fractures / waves and less complex one- or two-dimensional ones (e.g. Graff, 1975; Rinehart, 1975; Uenishi, 2021) should be more cautiously taken into account. Of course, the above observations are only for the polycarbonate specimens where multiple small-scale cracks can be precisely set by a digital laser cutter in a controlled fashion. There exist many other brittle materials where small-scale cracks cannot be set exactly as desired, and it is not certain whether the phenomena observed in polycarbonate plates can be found in other brittle materials. However, as described in the beginning, in the nature, there exist groups of smaller-scale cracks like “damage zones” in brittle rocks near geological fault planes that can induce a cluster of earthquakes also under quasi-static tensile “normal faulting” loading conditions. Also, fracture once propagating upwards from the hypocenter and then moving downwards from the top free surface back to the hypocenter has been recognized from the seismological observations (Ide et al., 2011) on the occasion of the 2011 off the Pacific coast of Tohoku, Japan, earthquake (Uenishi and Nagasawa, 2023). Thus, the experimentally identified phenomena, especially those found in the unique case 2 (Fig. 2), may offer a deeper insight into the understanding of the fundamental mechanisms of initiation, continuation and arrest of such earthquake clusters and swarms. Although our idea of studying the mechanical behavior of preset multiple small-scale cracks, briefly described above, derives mainly from the field observations of a cluster of earthquakes and earthquake swarms, multiple or perforated crack behavior in solid materials has been investigated in a variety of fundamental and applied fields of engineering and science, ranging from e.g. fracture propagation in a perforated plate under thermal fatigue (Tokiyoshi et al., 2001), dynamic fracture in thin plates with parallel single edge cracks (Yao et al., 2002), in a material containing pores (Carlsson and Isaksson, 2019) or in perforated plates (Peng et al., 2023) and non destructive testing (NDT) for fracture in perforated sheet metals (Dastjerdi et al. 2011) to fracture propagation in a perforated gear system (Ma et al., 2015) as well as to geophysical and geotechnical issues such as fracture around a single central hole in granite due to impact after high temperature-water cycle (Wang et al., 2023) and liquid water flow in perforated cracks of microporous layer (Lin et al., 2023, 2024). However, instead of straight cracks, perforated materials have usually circular holes and those holes are often aligned in a single or two straight line(s), and more general and comprehensive fracture behavior of truly multiple small-scale cracks has not been thoroughly understood yet. Thus, we believe that our current observations will assist in understanding more deeply the mechanisms of generation of a cluster of fractures or swarms of fractures in brittle solids in a more general framework and the results obtained through this series of experiments are of practical importance and worth further analytical and numerical investigations. Now we are examining the mechanical effect of impact-induced (generalized) Rayleigh waves propagating along the free outer surfaces and along the aligned small-scale cracks on the generation of the abovementioned rather peculiar fracture behavior. Acknowledgements The research has been financially supported by the Japan Society for the Promotion of Science (JSPS) through the “KAKENHI: Grant -in- Aid for Scientific Research (C)” Program under grant number 23K04021. References Carlsson, J., Isaksson, P., 2019. Crack Dynamics and Crack Tip Shielding in a Material Containing Pores Analysed by a Phase Field Method. Engineering Fracture Mechanics 206, 526 – 540. Dastjerdi, M. H., Rübesam, M., Rüter, D., Himmel, J., Kanoun, O., 2011. Non Destructive Testing for Cracks in Perforated Sheet Metals. IEEE 8th International Multi-Conference on Systems, Signals & Devices, 5 pages. Gomez, Q., Uenishi, K., Ionescu, I. R., 2020. Quasi-Static versus Dynamic Stability Associated with Local Damage Models. Engineering Failure Analysis 111, 104476. Graff, K.F.: Wave Motion in Elastic Solids, Clarendon Press, Oxford, 1975. Ide, S., Baltay, A., Beroza, G. C., 2011. Shallow Dynamic Overshoot and Energetic Deep Rupture in the 2011 Mw 9.0 Tohoku-Oki Earthquake. Science 332, 1426 – 1429. Lin, R., Dong, M., Lan, S., Lou, M., 2023. Numerical Simulation of Liquid Water Transport in Perforated Cracks of Microporous Layer. Energy 262, 125372.