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Seminar on Mechanical Science and Bioengineering
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208th
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March 11th, 2025 11:00-12:00 Seminar Room J404 |
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| An Expedition in Potential Energy Landscape to Decipher Disordered Solids | |
| Glasses, as a disordered and non-equilibrium metastable material system, do not have well-defined topological defects such as dislocations and grain boundaries. For this reason glasses exhibit many promising physical and mechanical performance and endow the system with wide-range and continuous tunability, as opposed to their crystalline counterparts. However, also due to the lack of order and disappearance of lattice periodicity, building a valid structures-properties relationship in glasses has been a longstanding challenge. In this talk I will show that there exists a hidden order in disordered glassy materials, and such order can be revealed from the potential energy landscape (PEL) of the system. It is demonstrated that macroscopic deformation mechanisms (localized vs cascade) depend on the density of local minima of the materials underlying PEL: higher density would enable more efficient energy dissipation and yield better ductility. I will also show that the competitions between the elementary activations and relaxations on PEL determine many critical phenomena in disordered materials, such as aging/rejuvenating crossover, thermo-mechanical hysteresis, etc. The PEL perspective allows us to develop a self-consistent equation to describe the time evolution of the disorder materials under complex surrounding environments. The implications of these examples, as well as the broad impacts on other important problems such as metastable grain boundaries under extreme processing, will also be discussed. | |
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Dr. Yue Fan
University of Michigan |
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207th
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January 16th, 2025 15:30-16:30 B102 |
| In Japanese | |
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206th
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December 23, 2024 16:50-17:50 G508 |
| In Japanese | |
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205th
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November 12, 2024 13:30-14:30 Seminar Room C (C419) |
| In Japanese | |
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204th
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November 1, 2024 10:30-11:30 A442 |
| In Japanese | |
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203rd
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December 3, 2024 11:00-12:00 Seminar Room C |
| In Japanese | |
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202nd
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October 25, 2024 14:00-15:00 Seminar Room J114 |
| Electron-Beam Induced Athermal Deformation: A Novel Understanding for Viscoplastic Deformation and Mechanical Amorphization of Amorphous and Crystalline Silica | |
| Amorphous silica, typically brittle, can undergo viscoplastic deformation at elevated temperatures. In this study, we highlight the possibility of achieving precise nanoscale mechanical shaping of amorphous silica through electron-matter interactions, without the need for heating. We found that ductile plastic deformation and densification can be induced athermally by focused scanning electron beams at low acceleration voltages. Our simulations indicate that the extent of deformation is governed by the interaction volume, where inelastic scattering occurs. Moreover, we demonstrated that electron beam irradiation can dramatically facilitate solid-state mechanical amorphization of crystalline α-quartz at room temperature, a process that usually demands high pressure. Microstructural examinations and atomic-scale simulations suggest that this is attributed to the uniformly distributed delocalized electrons, introduced by the electron beam excitation, collectively moving like anions situated between the positively charged silicon ions, effectively mitigating the repulsive forces within the distorted atomic structures. This research not only deepens our comprehension of electron-matter interactions but also unveils a new pathway for mechanical forming and processing of glass and ceramic materials.anisms of MPEAs. | |
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Dr. In-Suk Choi
Department of Materials Science and Engineering, Seoul National University |
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201st
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October 11, 2024 13:30-14:30 Room B401 |
| In Japanese |
