Faculty Profiles - OKUMURA, Dai

Papers - OKUMURA, Dai

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Crease instability in Gent-Gent hyperelastic materials Reviewed Open Access

Seishiro Matsubara, Keijiro Kobayashi, Tatsuya Ishida, So Nagashima, Dai Okumura

International Journal of Mechanical Sciences Vol. 280 page： 109549 - 109549 2024.10

Deformation in the wrinkle–crease transformation Reviewed

Tatsuya Ishida, Seishiro Matsubara, So Nagashima, Dai Okumura

International Journal of Solids and Structures Vol. 298 page： 112876 - 112876 2024.7

Bio‐Inspired Instability‐Induced Hierarchical Patterns Having Tunable Anisotropic Wetting Properties Reviewed Open Access

So Nagashima, Ko Suzuki, Seishiro Matsubara, Dai Okumura

Advanced Materials Interfaces Vol. 10 ( 14 ) 2023.5

Mechanical nonreciprocity in a uniform composite material Reviewed

Xiang Wang, Zhihao Li, Shuxu Wang, Koki Sano, Zhifang Sun, Zhenhua Shao, Asuka Takeishi, Seishiro Matsubara, Dai Okumura, Nobuyuki Sakai, Takayoshi Sasaki, Takuzo Aida, Yasuhiro Ishida

Science Vol. 380 ( 6641 ) page： 192 - 198 2023.4

Diversity of the bifurcations and deformations on films bonded to soft substrates: Robustness of the herringbone pattern and its cognate patterns Reviewed International journal

Shotaro Kikuchi, Seishiro Matsubara, So Nagashima, Dai Okumura

Journal of the Mechanics and Physics of Solids Vol. 159 page： 104757 - 104757 2022.2

Bifurcation and deformation during the evolution of periodic patterns on a gel film bonded to a soft substrate Reviewed

Hiroaki Miyoshi, Seishiro Matsubara, Dai Okumura

JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS Vol. 148 page： 104272 - 104272 2021.3

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

In this study, we investigate the bifurcation and deformation during the evolution of periodic patterns on a gel film bonded to a soft substrate. 3D finite element analysis is performed using an inhomogeneous field theory for polymeric gels. Step-by-step eigenvalue buckling analysis is conducted to explore not only the first bifurcation, but also sequential bifurcations on bifurcated paths. When the hexagonal dimple mode occurs as the first bifurcation, the second bifurcation consists of rectangular checkerboard modes in three symmetric directions. The resulting deformation patterns are in good agreement with experiments and, surprisingly, are analogous to the in-plane buckling behavior of hexagonal honeycombs. Uniaxial, biaxial, and equibiaxial (flower-like) patterns are produced by the periodic arrangements of distorted dimples. The third and fourth bifurcations cause the coalescence of the selected dimples. This reveals the occurrence of the rectangular checkerboard modes at the second bifurcation to be the missing link in the pattern evolution from hexagonal dimples to herringbone and labyrinth patterns.

DOI： 10.1016/j.jmps.2020.104272

Web of Science

Scopus

Experiments and modeling of the viscoelastic behavior of polymeric gels Reviewed International coauthorship Open Access

Nikola Bosnjak, Siva Nadimpalli, Dai Okumura, Shawn A. Chester

JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS Vol. 137 2020.4

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

A polymeric gel is a cross-linked polymer network swollen with a solvent. Also, as is well known many polymeric materials exhibit viscoelastic behavior in their mechanical response, In this work, we report on our recent experimental observations and theoretical modeling involving the change in the viscoelastic response of the polymeric material VHB caused by equilibrium swelling in multiple solvents. To characterize this change, we have developed an experimental procedure that includes mechanical testing when virgin, free swelling, mechanical testing when swollen, and mechanical testing after drying. A model is used to help interpret the experimental results. The key finding of this work is that our results indicate that the viscoelastic behavior of initially dry VHB, reversibly, becomes essentially hyperelastic when swollen to equilibrium in multiple solvents. (C) 2019 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jmps.2019.103829

Web of Science

Scopus

Computational and physical aspects for the occurrence of crease in an elastomer under general loading conditions Reviewed International journal

Seishiro Matsubara, Atsuya Ogino, So Nagashima, Dai Okumura

International Journal of Solids and Structures Vol. 288 page： 112610 - 112610 2024.2

Inhomogeneous instability patterns in polyacrylamide hydrogel bilayers

NAGASHIMA So, UCHIYAMA Wataru, HAYASHI Shunsuke, MATSUBARA Seishiro, OKUMURA Dai

Mechanical Engineering Journal Vol. 11 ( 6 ) page： 24-00350 - 24-00350 2024

Language：English Publisher：The Japan Society of Mechanical Engineers

<p>Instability-induced patterns with spatially varying dimensions and geometric shapes, or inhomogeneous instability patterns, are ubiquitous in biological structures and have attracted much interest in both fundamental research and engineering applications. However, it remains a challenge to create such patterns using materials with stiffnesses and scales comparable to biological structures. Here, we demonstrate the creation of inhomogeneous instability patterns using film–substrate bilayers of polyacrylamide hydrogels. Swelling of thickness-gradient films on the substrates allows for the coexistence of different instability patterns, including creases and wrinkles, on the surface. The film thickness and the stiffness ratio between the film and substrate are the factors that control the characteristic length of the patterns on the millimeter scale, as well as the switching of the patterns between creases and wrinkles. Furthermore, these patterns can be generated at prescribed local areas on the surface. Our approach to creating inhomogeneous instability patterns on a single surface would help to gain insight into the morphological development of biological patterns and to fabricate bio-inspired functional surfaces.</p>

DOI： 10.1299/mej.24-00350

Web of Science

CiNii Research

ノンレシプロカルゲルの円筒押込み大変形解析 Reviewed

野々垣翔真，松原成志朗，永島壮，奥村大

計算数理工学論文集 Vol. 23 page： 123 - 128 2023.11

クリースの発達過程に対する影響因子の調査 Reviewed

石田竜也，永島壮，松原成志朗，奥村大

計算数理工学論文集 Vol. 23 page： 143 - 148 2023.11

均質化解析によるノンレシプロカルゲルの引張・圧縮非対称性評価 Reviewed

布施卓馬，松原成志朗，永島壮，奥村大

計算数理工学論文集 Vol. 23 page： 137 - 142 2023.11

LARGE DEFORMATION ANALYSIS OF A NONRECIPROCAL GEL UNDER CYLINDRICAL INDENTATION Reviewed

NONOGAKI Shoma, MATSUBARA Seishiro, Nagashima So, OKUMURA Dai

Transactions of the Japan Society for Computational Methods in Engineering Vol. 23 ( 0 ) page： 123 - 128 2023.11

Authorship：Last author Language：Japanese Publisher：Japan Society for Computational Methods in Engineering

In this study, we investigate the large deformation analysis of a nonreciprocal gel under cylindrical indentation. The nonreciprocity of the gel is modeled by extending the framework of anisotropic linear elasticity [Wang et al., 2023. Mechanical nonreciprocity in a uniform composite material. Science 380, 192–198]. Plane-strain finite-element analysis is performed by assuming the frictionless between the gel and the rigid indenter, leading to reproducing the asymmetric response of the nonreciprocal gel. It is found that severe large deformations cause non-convergence of incremental calculations, which is resolved by introducing artificial viscosity and hourglass control. The combination prevents the occurrence of hourglass deformation modes around the area directly below the indenter as well as obtains converged solutions in efficient incremental calculations. The use of larger values of the two parameters causes the increase of computational efficiency and the decrease of computational accuracy. Parametric studies elucidate the existence of the proper region of the two parameters.
Nonreciprocal gel, Tension compression asymmetry, Large deformations, FEA

DOI： 10.60443/jascome.23.0_123

CiNii Research

TENSION-COMPRESSION ASYMMETRY EVALUATION OF A NONRECIPROCAL GEL BY HOMOGENIZATION ANALYSIS Reviewed

FUSE Takuma, MATSUBARA Seishiro, NAGASHIMA So, OKUMURA Dai

Transactions of the Japan Society for Computational Methods in Engineering Vol. 23 ( 0 ) page： 137 - 142 2023.11

Authorship：Last author Language：Japanese Publisher：Japan Society for Computational Methods in Engineering

A nonreciprocal gel consisting of hydrogel and nanosheet exhibits mechanical nonreciprocity, which has potential applications in mechanical engineering. An earlier study has revealed that this mechanical nonreciprocity is triggered by the tension-compression asymmetry resulting from the microscopic buckling behavior of nanosheets during compressive deformation, but the relevant influencing factors remain unknown. In this study, we investigate the microscopic buckling behavior and the resultant tension-compression asymmetry in a nonreciprocal gel subjected to uniaxial conditions. Eigenvalue buckling and post-buckling analyses equipped with computational homogenization are performed on a unit cell modeled as an elastic bilayer for which ratios of Young’s modulus and thickness are parameterized. The results confirm that selecting a dilute microscopic buckling with the characteristic wavelength or a non-dilute microscopic buckling with the infinite wavelength hinges on the ratios of Young’s modulus and thickness, which is consistent with the theoretical solution for the buckling behavior of a layered composite. We also elucidate that the tension-compression asymmetry is more pronounced as the Young’s modulus ratio increases or the thickness ratio decreases.

DOI： 10.60443/jascome.23.0_137

CiNii Research

Time-swelling Superposition Principle for the Linear Viscoelastic Properties of Polyacrylamide Hydrogels Reviewed International journal

S. Matsubara, A. Takashima, S. Nagashima, S. Ida, H. Tanaka, M. Uchida, D. Okumura

Advanced Structured Materials: Creep in Structures VI, IUTAM Symposium Proceedings Vol. 194 page： 175 - 204 2023.8

Self-Wrinkling in Polyacrylamide Hydrogel Bilayers Reviewed

So Nagashima, Naoki Akamatsu, Xiangfu Cheng, Seishiro Matsubara, Shohei Ida, Hiro Tanaka, Makoto Uchida, Dai Okumura

Langmuir Vol. 39 ( 11 ) page： 3942 - 3950 2023.3

Self-Wrinkling in Polyacrylamide Hydrogel Bilayers Reviewed

So Nagashima, Naoki Akamatsu, Xiangfu Cheng, Seishiro Matsubara, Shohei Ida, Hiro Tanaka, Makoto Uchida, Dai Okumura

Langmuir 2023.3

クリースの発達過程に対する影響因子の調査 Reviewed

永島壮, 松原成志朗, 奥村大

計算数理工学論文集 Vol. 23 page： 143 - 148 2023

Evaluation of the Effects of Cross-Link Density and Swelling Ratio on Loading-Unloading Response in Large Strain Range of Hydrogels Reviewed

Syunpei Morita, Makoto Uchida, Yoshihisa Kaneko, Dai Okumura, Hiro Tanaka, Shohei Ida

Advanced Experimental Mechanics Vol. 7 ( 0 ) page： 90 - 96 2022.8

Language：English Publishing type：Research paper (scientific journal) Publisher：The Japanese Society for Experimental Mechanics

<p>Hydrogel contains a large amount of solvent such as water inside a three-dimensional molecular chain network structure. The content of the solvent changes during the swelling and drying processes of the hydrogel. The mechanical properties of the gel significantly change depending on the solvent content. In this study, the effects of the cross-link density and swelling ratio on the nonlinear mechanical responses of hydrogel were investigated by the cyclic tensile test. To evaluate the irreversible deformation of the hydrogel, we performed the one-time and stepwise loading-unloading tests. The stress-strain curves for the loading and unloading process obtained from the crosshead displacement were different owing to the sliding between chuck and specimen. In contrast, they were consistent for all the experimental conditions when the strain was evaluated by the digital image correlation method. Therefore, the hydrogel showed the less-rate-dependent reversible deformation from small to large strain range. Furthermore, obtained results were compared with the theoretical model based on the molecular chain network model with swelling effect. Although the model could represent the nonlinear increase in the stress during the tensile test and the decrease in the stiffness owing to the swelling, the model results were not consistent with the experimental results. Experimental and numerical results indicate that the improvement of the mechanical model is necessary based on the less-rate-dependent reversible deformation mechanisms of the hydrogel.</p>

DOI： 10.11395/aem.7.0_90

CiNii Research

Surface Instabilities of Soft Materials Invited

OKUMURA Dai

Journal of the Society of Materials Science, Japan Vol. 71 ( 6 ) page： 555 2022.6

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Papers - OKUMURA, Dai