PSI - Issue 68

ScienceDirect Structural Integrity Procedia 00 (2025) 000–000 Structural Integrity Procedia 00 (2025) 000–000 Available online at www.sciencedirect.com Available online at www.sciencedirect.com ScienceDirect Available online at www.sciencedirect.com ScienceDirect

www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia

Procedia Structural Integrity 68 (2025) 554–558

European Conference on Fracture 2024 Acceleration and deceleration of unzipping supershear fracture propagating along a straight perforation line consisting of small scale cracks Koji Uenishi a,b, *, Kaichi Akimoto b , Masanao Sekine b a Department of Advanced Energy, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, 277-8561 Chiba, Japan b Department of Aeronautics and Astronautics, The University of Tokyo, 7-3-1 Hongo, Bunkyo, 113-8656 Tokyo, Japan Abstract We experimentally investigate two-dimensional dynamic fracture propagation along a straight perforation line containing multiple small-scale cracks. If there exists only one single perforation line in a brittle polycarbonate specimen, dynamic fracture due to application of external quasi-static loading seems propagating unidirectionally in an “unzipping” way along the perforation line, simply linking the edges of the cracks without diverting and branching. However, a closer look into the photographs experimentally obtained by a high-speed video camera shows that fracture propagation is not always unidirectional and its speed also fluctuates back-and-forth between subsonic and supershear levels, i.e. the speed can be lower or higher than the relevant shear wave speed of the specimen during propagation. Generally, the propagation speed becomes maximum just before the fracture leaves the edge of a preexisting small-scale crack and it is low just before the fracture approaches the edge of the next crack in the perforation line. Furthermore, the fluctuation of fracture propagation speed at supershear levels may generate multiple Mach (shock) wavefronts with different Mach angles. © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ECF24 organizers Keywords: Unzipping fracture; Supershear fracture; Multiple Mach wavefronts European Conference on Fracture 2024 Acceleration and deceleration of unzipping supershear fracture propagating along a straight perforation line consisting of small scale cracks Koji Uenishi a,b, *, Kaichi Akimoto b , Masanao Sekine b a Department of Advanced Energy, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, 277-8561 Chiba, Japan b Department of Aeronautics and Astronautics, The University of Tokyo, 7-3-1 Hongo, Bunkyo, 113-8656 Tokyo, Japan Abstract We experimentally investigate two-dimensional dynamic fracture propagation along a straight perforation line containing multiple small-scale cracks. If there exists only one single perforation line in a brittle polycarbonate specimen, dynamic fracture due to application of external quasi-static loading seems propagating unidirectionally in an “unzipping” way along the perforation line, simply linking the edges of the cracks without diverting and branching. However, a closer look into the photographs experimentally obtained by a high-speed video camera shows that fracture propagation is not always unidirectional and its speed also fluctuates back-and-forth between subsonic and supershear levels, i.e. the speed can be lower or higher than the relevant shear wave speed of the specimen during propagation. Generally, the propagation speed becomes maximum just before the fracture leaves the edge of a preexisting small-scale crack and it is low just before the fracture approaches the edge of the next crack in the perforation line. Furthermore, the fluctuation of fracture propagation speed at supershear levels may generate multiple Mach (shock) wavefronts with different Mach angles. © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ECF24 organizers Keywords: Unzipping fracture; Supershear fracture; Multiple Mach wavefronts © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ECF24 organizers

* Corresponding author. Tel.: +81-4-7136-3824; fax: +81-4-7136-3824. E-mail address: uenishi@k.u-tokyo.ac.jp * Corresponding author. Tel.: +81-4-7136-3824; fax: +81-4-7136-3824. E-mail address: uenishi@k.u-tokyo.ac.jp

2452-3216 © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ECF24 organizers 2452-3216 © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ECF24 organizers

2452-3216 © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ECF24 organizers 10.1016/j.prostr.2025.06.096