[S-CG69] Rheology, fracture and friction in Earth and planetary sciences

[SCG69-07] Memory of magnetic paste and its effect on crack formation

*Akio Nakahara¹, Kyosuke Uchida¹, Sho Sasagawa¹, Yousuke Matsuo¹, So Kitsunezaki², Ferenc Kun³, Lucas Goehring⁴, Tsuyoshi Mizuguchi⁵ (1.College of Science and Technology, Nihon University, 2.Research Group of Physics, Division of Natural Sciences, Faculty of Nara Women’s University, 3.Department of Theoretical Physics, University of Debrecen, 4.School of Science and Technology, Nottingham Trent University, 5.Department of Physics, Osaka Prefecture University)

Keywords:desiccation crack, clay paste, memory effect, plastic deformation

Clay paste, i.e., a densely packed colloidal suspension, remembers the direction of its motion under applied forces and, when it is dried, the morphology of desiccation crack patterns depends on the memory of such motion. For example, when a clay paste remembers the direction of vibrational motion such as earthquake, all primary desiccation cracks propagate in the direction perpendicular to the direction of the vibrational motion that the paste has experienced. On the other hand, when a paste remembers the direction of its shear flow motion such as debris flow, all primary cracks propagate along the direction of its shear flow motion. Here we find that, when clay paste includes magnetic particles, it remembers the direction of applied magnetic field not only in the form of magnetization but also in the form of plastic deformation, and, when it is dried, all primary cracks propagate along the direction of applied magnetic field. By performing X-ray CT scan of the sample at Spring-8, we find that the chain formation and orientation of colloidal particles play important roles in memory effect. As the application of memory effect of paste, we can control the morphology of crack patterns by imprinting, rewriting and erasing memories in paste and produce various types of crack patterns, such as striped, radial, ring, spiral, lattice and random structures. We can also observe crack patterns and microstructure of clay to read the information on what happened to the clay paste in the past.