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Two seminars on crack patterns

Kei Kurita (ERI, Univ. Tokyo) & Akio Nakahara (Nihon University)
When Mar 01, 2016
from 10:45 to 12:00
Where Centre Blaise Pascal
Attendees Kei Kurita & Akio Nakahara
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Bekko-Ame Cracks

Kei Kurita (Earthquake Research Inst., Univ. of Tokyo)

Bekko-Ame is a japanese traditional candy made of sugar syrup. We utilized this material in the outreach activity of our institute, special lecture for high school students. The purpose is to demonstrate essence of fracturing process and to understand earthquake phenomena. I will explain the back ground of this briefly. During the making process well-vesiculated syrup is cooled down in two kinds of metal container, a Sukiyaki nabe(thick walled container) and a thin-walled pan. When we soak these containers in a iced-water two contrasting crack morphologies are found to exist shown below. The basic mechanism for the origin is the thermal stress. In the Sukiyaki nabe small circular cracks are progressively developed with small crack sounds and finnaly they all covered the entire space. On the other hand in the thin-walled pan large linear cracks are suddenly formed with hard crack sounds. The selection of the crack morphology seems to depend on the stress field imposed by the thermal shock. Both can be used as an analogy of the earthquake phenomena.


Imprinting, rewrinting, and erasing memories in paste and their visualization as crack patterns

Akio Nakahara (Nihon University, Japan)

A densely packed colloidal suspension, called a paste, remembers the direction of external forces, such as vibration, flow and magnetic field, even after the external field is removed, and these memories in paste can be visualized as morphology of desiccation crack patterns. Therefore, by imprinting or rewriting the memory in paste, we can control the formation of crack patterns [1].

Recently we have succeeded in erasing the memory in paste by irradiating ultrasonic waves to it. Since the erasure of memory in paste increases the breaking strength of the material, it will be a useful method in the field of technology.

[1] Desiccation Cracks and their Patterns: Formation and Modelling in Science and Nature, Lucas Goehring, Akio Nakahara, Tapati Dutta, So Kitsunezaki, and Sujata Tarafdar (Wiley, 2015) .

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