研究者詳細 - 奥村　大

論文 - 奥村　大

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Crease instability in Gent-Gent hyperelastic materials 査読有り Open Access

Matsubara, S; Kobayashi, K; Ishida, T; Nagashima, S; Okumura, D

INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES 280 巻頁： 109549 - 109549 2024年10月

担当区分：最終著者掲載種別：研究論文（学術雑誌）出版者・発行元：International Journal of Mechanical Sciences

We study the crease instability of an incompressible Gent-Gent elastomer under general loading conditions. The Gent-Gent model has two distinct characteristics: the logarithmic nonlinearity triggered by I2 energy term and the strain hardening due to limiting chain extensibility. By performing finite element analysis combined with an evaluation of surface tension, we investigate the effects of the two characteristics on the critical creasing onset and the creasing onset delayed by surface tension. The results show that uniaxial compression induces logarithmic nonlinearity that accelerates the critical creasing onset, whereas equibiaxial compression hastens the initiation of strain hardening that delays the critical creasing onset. In addition, logarithmic nonlinearity mitigates the delay in creasing onset caused by surface tension under the uniaxial condition, and strain hardening suppresses creasing in cooperation with surface tension under the equibiaxial condition. Conversely, under the plane strain condition, two characteristics have little effect on the creasing onset delayed by surface tension.

DOI： 10.1016/j.ijmecsci.2024.109549

Open Access

Web of Science

Scopus

Deformation in the wrinkle-crease transformation 査読有り

Ishida, T; Matsubara, S; Nagashima, S; Okumura, D

INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES 298 巻頁： 112876 - 112876 2024年7月

担当区分：最終著者,　責任著者掲載種別：研究論文（学術雑誌）出版者・発行元：International Journal of Solids and Structures

We investigate deformation in the wrinkle–crease transformation to reveal the missing link between the wrinkling and creasing instabilities, which occur on the surface of elastomers under compression. Plane-strain finite element (FE) analysis is performed by combining a nonlinear perturbation approach to find two bifurcated solutions for the flat surface in a metastable state. The first solution is the stable deformation path for crease evolution, and the second solution is the previously unknown unstable deformation path from wrinkling to creasing. The two deformation paths are not independent, and they are connected at the critical strain for creasing εC. The resulting deformation at εC acts as a precursive deformation to cause creasing. Although the unstable path is initiated by the wrinkling instability as a bifurcation, the creasing instability (i.e., εC) is interpreted as the singular point at which the unstable path switches to the stable path. A chain reaction model is developed to describe the mechanism and deformation of the wrinkle–crease transformation, and it shows good agreement with the FE prediction within an inevitable limitation of FEs.

DOI： 10.1016/j.ijsolstr.2024.112876

Web of Science

Scopus

Bio-Inspired Instability-Induced Hierarchical Patterns Having Tunable Anisotropic Wetting Properties 査読有り Open Access

Nagashima, S; Suzuki, K; Matsubara, S; Okumura, D

ADVANCED MATERIALS INTERFACES 10 巻 ( 14 ) 2023年5月

担当区分：最終著者掲載種別：研究論文（学術雑誌）出版者・発行元：Advanced Materials Interfaces

This paper introduces a method for the bottom-up fabrication of bio-inspired hierarchical patterns having tunable anisotropic wetting properties. The method exploits the surface instability of bilayers comprising a gold nanofilm attached to a substantially prestretched elastomer substrate. Upon film formation, highly aligned wrinkles spontaneously form on the surface owing to the surface instability driven by the compressive residual stress in the film. Thereafter, uniaxial compressive strain is applied to the film by prestretch relaxation of the substrate, which generates an array of high-aspect-ratio ridges on the surface. Consequently, hierarchical patterns comprising unidirectionally aligned ridges covered with wrinkles are obtained. Water droplets placed on surfaces having the aforementioned hierarchical patterns show direction-dependent contact angles, resulting in elongated shapes, which indicates the presence of anisotropic wetting properties. The magnitude of wetting anisotropy can be tuned by simple control of the applied compressive strain and film thickness.

DOI： 10.1002/admi.202300039

Open Access

Web of Science

Scopus

Mechanical nonreciprocity in a uniform composite material 査読有り

Wang, X; Li, ZH; Wang, SX; Sano, K; Sun, ZF; Shao, ZH; Takeishi, A; Matsubara, S; Okumura, D; Sakai, N; Sasaki, T; Aida, T; Ishida, Y

SCIENCE 380 巻 ( 6641 ) 頁： 192 - 198 2023年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Science

Mechanical nonreciprocity, or the asymmetric transmission of mechanical quantities between two points in space, is crucial for developing systems that can guide, damp, and control mechanical energy. We report a uniform composite hydrogel that displays substantial mechanical nonreciprocity, owing to direction-dependent buckling of embedded nanofillers. This material exhibits an elastic modulus more than 60 times higher when sheared in one direction compared with the opposite direction. Consequently, it can transform symmetric vibrations into asymmetric ones that are applicable for mass transport and energy harvest. Furthermore, it exhibits an asymmetric deformation when subjected to local interactions, which can induce directional motion of various objects, including macroscopic objects and even small living creatures. This material could promote the development of nonreciprocal systems for practical applications such as energy conversion and biological manipulation.

DOI： 10.1126/science.adf1206

Web of Science

Scopus

PubMed

Diversity of the bifurcations and deformations on films bonded to soft substrates: Robustness of the herringbone pattern and its cognate patterns 査読有り国際誌

Kikuchi, S; Matsubara, S; Nagashima, S; Okumura, D

JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 159 巻頁： 104757 - 104757 2022年2月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Mechanics and Physics of Solids

In this study, we investigate the diversity of the bifurcations and deformations during evolution of periodic patterns on compressed films bonded to compliant substrates. Three-dimensional finite element analysis is performed assuming that the first bifurcation has either the hexagonal or square (i.e., checkerboard) dimple mode. Step-by-step eigenvalue buckling analysis is performed to explore sequential bifurcations on the bifurcated paths. It is found that at the second bifurcation, a rectangular checkerboard or stripe mode occurs depending not only on the Young's modulus ratio of the film and substrate, but also on the magnitude of the imperfection prescribed by the first bifurcation mode. Different bifurcation modes give a family of herringbone deformation patterns with different dimensions, i.e., the evolutional process is multiple and robust. Further, superposition of the identical modes in symmetric directions elucidates the existence of distinctive patterns cognate with the herringbone pattern, including a variety of experimentally observed patterns.

DOI： 10.1016/j.jmps.2021.104757

Web of Science

Scopus

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

Miyoshi, H; Matsubara, S; Okumura, D

JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 148 巻頁： 104272 - 104272 2021年3月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Mechanics and Physics of Solids

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 査読有り国際共著 Open Access

Bosnjak, N; Nadimpalli, S; Okumura, D; Chester, SA

JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 137 巻 2020年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Mechanics and Physics of Solids

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.

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 査読有り国際誌

Matsubara, S; Ogino, A; Nagashima, S; Okumura, D

INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES 288 巻頁： 112610 - 112610 2024年2月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：International Journal of Solids and Structures

We study the occurrence of crease in an elastomer under three loading conditions from both computational and physical points of view. A two-dimensional finite element analysis, including a perturbation force-based approach, is performed to detect the stable creased state, where the crease formation is completed. A mesh convergence study for the energy release and crease depth in the creased state provides a guideline for the finite element mesh requisite for predicting the occurrence of crease. We also visualize the mesh convergence for the critical creasing onset by plotting the set of compressive strain and mesh resolution at the point where the energy release is zero. In addition, the present evaluation method of the surface tension using the energy release and surface area change for an elastomer with a traction-free surface yields a good prediction for the creasing onset delayed by surface tension without additional numerical implementations or adjustment parameters. This facilitates the comprehensive study of the creasing onset delayed by the surface tension under general loading conditions. The results reveal that tensile deformation in the out-of-plane direction encourages the retardation of the creasing onset via the extension of the width and the energy emission. We further demonstrate that energetically preferential crease interval can be used to evaluate the spacing between creases delayed by moderate surface tension.

DOI： 10.1016/j.ijsolstr.2023.112610

Web of Science

Scopus

Inhomogeneous instability patterns in polyacrylamide hydrogel bilayers

Nagashima, S; Uchiyama, W; Hayashi, S; Matsubara, S; Okumura, D

MECHANICAL ENGINEERING JOURNAL 11 巻 ( 6 ) 頁： 24-00350 - 24-00350 2024年

ノンレシプロカルゲルの円筒押込み大変形解析査読有り

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 23 巻頁： 123 - 128 2023年11月

クリースの発達過程に対する影響因子の調査査読有り

石田竜也，永島壮，松原成志朗，奥村大

計算数理工学論文集 23 巻頁： 143 - 148 2023年11月

均質化解析によるノンレシプロカルゲルの引張・圧縮非対称性評価査読有り

布施卓馬，松原成志朗，永島壮，奥村大

計算数理工学論文集 23 巻頁： 137 - 142 2023年11月

ノンレシプロカルゲルの円筒押込み大変形解析査読有り

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 23 巻 ( 0 ) 頁： 123 - 128 2023年11月

均質化解析によるノンレシプロカルゲルの引張・圧縮非対称性評価査読有り

布施卓馬, 松原成志朗, 永島壮, 奥村大

計算数理工学論文集 23 巻 ( 0 ) 頁： 137 - 142 2023年11月

Time-swelling Superposition Principle for the Linear Viscoelastic Properties of Polyacrylamide Hydrogels 査読有り国際誌

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

Advanced Structured Materials: Creep in Structures VI, IUTAM Symposium Proceedings 194 巻頁： 175 - 204 2023年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Advanced Structured Materials

We study the linear viscoelastic properties of polyacrylamide hydrogels over a wide range of swelling and deswelling states. The experimental data of dynamic moduli demonstrate that deswollen hydrogels exhibit the linear viscoelastic behaviors while swollen hydrogels behave as a purely elastic material. To capture the linear viscoelastic nature of deswollen hydrogels, we advocate the time-swelling superposition principle inspired by the swelling-dependent linear viscoelasticity model. In this principle, the Williams-Landel-Ferry type equation and the scaling law prescribe the horizontal and vertical shift factors as a function of the volume swelling ratio, making it possible to organize the dynamic moduli in the deswelling state. The resulting master curves elucidate that the dynamic moduli have a positive power-law correlation with the angular frequency. In addition, two shift factors reveal that deswelling enhances both frequency sensitivity and elastic property in dynamic moduli. The scaling exponents of the elastic moduli in the deswelling state are, in particular, larger than those in the swelling state, regardless of the contents of monomer and cross-linker. The generalized Maxwell model equipped with identified material parameters quantifies the linear viscoelastic behaviors that depend on frequency and water content.

DOI： 10.1007/978-3-031-39070-8_12

Scopus

Self-Wrinkling in Polyacrylamide Hydrogel Bilayers 査読有り

Nagashima, S; Akamatsu, N; Cheng, XF; Matsubara, S; Ida, S; Tanaka, H; Uchida, M; Okumura, D

LANGMUIR 39 巻 ( 11 ) 頁： 3942 - 3950 2023年3月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Langmuir

Swelling of a gel film attached to a soft substrate can induce surface instability, which results in the formation of highly ordered patterns such as wrinkles and folds. This phenomenon has been exploited to fabricate functional devices and rationalize morphogenesis. However, obtaining centimeter-scale patterns without immersing the film in a solvent remains challenging. Here, we show that wrinkles with wavelengths of up to a few centimeters can be spontaneously created during the open-air fabrication of film-substrate bilayers of polyacrylamide (PAAm) hydrogels. When the film of an aqueous pregel solution of acrylamide prepared on the PAAm hydrogel substrate undergoes open-air gelation, hexagonally packed dimples initially emerge on the surface, which later evolve into randomly oriented wrinkles. The formation of such self-organized patterns can be attributed to the surface instability resulting from autonomous water transport in the bilayer system during open-air fabrication. The temporal evolution of the patterns can be ascribed to an increase in overstress in the hydrogel film due to continued water uptake. The wrinkle wavelength can be controlled in the centimeter-scale range by adjusting the film thickness of the aqueous pregel solution. Our self-wrinkling method provides a simple mechanism for the generation of swelling-induced centimeter-scale wrinkles without requiring an external solvent, which is unachievable with conventional approaches.

DOI： 10.1021/acs.langmuir.2c03264

Web of Science

Scopus

PubMed

Self-Wrinkling in Polyacrylamide Hydrogel Bilayers 査読有り

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

Langmuir 2023年3月