研究者詳細 - 奥村　大

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

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

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

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

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

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

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

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

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

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

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

クリースの発達過程に対する影響因子の調査査読有り

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

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

Advanced Experimental Mechanics 7 巻 ( 0 ) 頁： 90 - 96 2022年8月

ソフトマテリアルの表面不安定招待有り

奥村大

材料 71 巻 ( 6 ) 頁： 555 2022年6月

弾性体に誘起するクリースの発生と伝播の有限要素解析

松原成志朗, 星亮吾, 永島壮, 奥村大

理論応用力学講演会講演論文集 66 巻 ( 0 ) 頁： 5 2022年

記述言語：日本語出版者・発行元：日本学術会議「機械工学委員会・土木工学・建築学委員会合同IUTAM分科会」

クリースは圧縮負荷が作用する弾性体の自由表面上で鋭い溝のような変形として発生する．クリースは弾性体の自由表面上で伝播して脳のしわなどに見られる特徴的なパターンを形成する．クリースの伝播は，直前のクリースが形成する不均質な変位場がトリガーとなると予想されるが，詳細なメカニズムはわかっていない．また，各々のクリースには固有間隔が存在し得るものの，これを決める要因についてもわかっていない．本研究では，V字型欠陥を有するに対して二つの異なるアプローチでクリースの発生と伝播の有限要素解析を実施し，逐次的なクリースの発生機構と固有間隔を規定する要因を明らかにする．

DOI： 10.11345/japannctam.66.0_5

リッジパターン変態のプレストレッチ依存性と分岐座屈特性査読有り

松原成志朗, 永島壮, 奥村大

計算数理工学論文集 22 巻頁： 117 - 121 2022年

Modeling of cyclic hardening and evaluation of plastic strain range in the presence of pre-loading and ratcheting 査読有り

Ohno, N; Nakamoto, H; Morimatsu, Y; Okumura, D

INTERNATIONAL JOURNAL OF PLASTICITY 145 巻 2021年10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 Plasticity

An extended evolution equation of cyclic hardening is proposed to include the effect of maximum plastic strain due to pre-loading and ratcheting. A set of extended evolution equations is also proposed for a plastic strain surface to properly evaluate the cyclic plastic strain range in the presence of pre-loading and ratcheting. These extensions are verified by performing uniaxial cyclic experiments of 316 stainless steel at 600°C. The experiments are accurately simulated using a constitutive model with the extensions in addition to the resetting scheme of the plastic strain surface recently proposed by the authors. The extension for the plastic strain surface allows fairly good simulation of the experiments without recourse to the resetting scheme if the strain range does not markedly decrease with the number of cycles. The extended equations are further used to discuss the effect of maximum plastic strain considering previous experiments.

DOI： 10.1016/j.ijplas.2021.103074

Implicit rule on the elastic function of a swollen polyacrylamide hydrogel 査読有り

Kawai, R; Tanaka, H; Matsubara, S; Ida, S; Uchida, M; Okumura, D

SOFT MATTER 17 巻 ( 19 ) 頁： 4979 - 4988 2021年5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：Soft Matter

A full understanding of the elastic properties of hydrogels under swelling is required for their practical application in the chemical and biomedical engineering fields. This is because hydrogels are expected to retain water during mechanical use in moist atmospheres. In the present study, we investigated the relationship between the elastic modulus and the swelling ratio in a specific type of hydrogel (a polyacrylamide gel). The elasticity and swelling data revealed that these two parameters are proportionally related in hydrogels comprising adequate amounts of monomers and crosslinkers. We also demonstrated that this proportional relationship inherently conforms to the linear elastic behaviour predicted by the Flory-Rehner free energy function (the F-R model). The implicit rule is established by the extended F-R model with two scaling exponents. The extended model is capable of representing the irregular elasticity of swollen gels formed from low- or high-molecular-weight polymers.

DOI： 10.1039/d1sm00346a

PubMed

リンクル・クリース解析における初期不整と要素分割の影響査読有り

星亮吾, 三好宏明, 松原成志朗, 奥村大

日本機械学会論文集 87 巻 ( 898 ) 頁： 21 - 00045-21-00045 2021年5月

担当区分：最終著者記述言語：日本語出版者・発行元：一般社団法人日本機械学会

This study investigates the effects of initial imperfection and mesh resolution on the wrinkling and creasing. Finite element analyses are conducted to simulate compression behaviors of an incompressible Neo-Hookean elastic plane with a V-shaped notch as initial imperfection, so that the occurrences and evolutions of wrinkle and crease are evaluated quantitatively. As a result, it is demonstrated that the origins of wrinkle and crease can be determined by the overall and local strains even for the introduction of a V-shaped notch. Further, we illustrate that the converged specific local strain with respect to the increase of mesh resolution almost coincides with the condition of the occurrence of wrinkle (i.e., εw = 0.456) when the depth of a V-shaped notch is sufficiently small. We also show that the sizes of wrinkle and crease do not converge due to strain localization around a V-shaped notch. In the investigation of pattern evolutions about initial imperfection, we illustrate that two kinds of pattern evolution can be comprehensively discussed by varying the depth of a V-shaped notch, so that the condition of the occurrence of crease can be organized by the sharpness of a V-shaped notch.

DOI： 10.1299/transjsme.21-00045

ヘリンボン及びトリプルジャンクションパターンの発達に対する影響因子解析査読有り

奥村大

計算数理工学論文集 21 巻頁： 51 - 56 2021年

A general expression for linearized properties of swollen elastomers undergoing large deformations 査読有り国際共著 Open Access

Okumura, D; Kawabata, H; Chester, SA

JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 135 巻 2020年2月

担当区分：筆頭著者,　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 develop a general expression for the linearized properties of swollen elastomers undergoing large deformations. The free energy function of swollen elastomers is assumed to obey the Frenkel–Flory–Rehner hypothesis, i.e., the elastic and mixing contributions are additive. The elastic strain energy is not assumed to have a particular form but is assumed only to be a function of a set of strain-invariants. A linearization procedure is used to obtain the general expression for the Young's modulus and Poisson's ratio under an arbitrary base state. The derived expression includes a characteristic term, which has the ability to describe a transient state between the extreme states prescribed by two distinct conditions. The verification is performed by estimating the shear modulus and considering the original Flory–Rehner framework. In addition, to show the usefulness, an extended Gent model is examined to elucidate the interactions between limiting chain extensibility and the second strain-invariant.

DOI： 10.1016/j.jmps.2019.103805

アクリルアミドハイドロゲルの粘弾性特性に及ぼす含水量の影響

高島晃, 松原成志朗, 伊田翔平, 田中展, 内田真, 奥村大

年次大会 2020 巻 ( 0 ) 頁： J03127 2020年

ゲル膜の立体化に関する形態形成機構解析

星亮吾, 三好宏明, 奥村大

東海支部総会講演会講演論文集 2020.69 巻 ( 0 ) 頁： 121 2020年

ガラス基盤上のアニオン性アクリルアミドゲル膜の立体構造構築における影響因子解析

河合遼太, 松原成志朗, 伊田翔平, 田中展, 内田真, 奥村大

年次大会 2020 巻 ( 0 ) 頁： J02102 2020年

ゲル膜立体化の有限要素影響因子解析

星亮吾, 三好宏明, 松原成志朗, 奥村大

年次大会 2020 巻 ( 0 ) 頁： J03140 2020年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

We perform a finite element analysis of gel membrane constrained on a grass substrate to investigate influence factors in a three dimensional structure assembled from a gel film. In-plane compressive stresses cause a three dimensional deformation due to swelling of a gel film. Such a deformation is influenced by attractive force, friction, imperfection and so on. In this study, we, particular, investigate the influence of attractive force by conducting finite element analysis for the Neo-Hookean body. The obtained results are shown to discuss deformation patterns caused in response to different attractive forces.

DOI： 10.1299/jsmemecj.2020.j03140

膨潤エラストマー解析のためのGent-Gent超弾性モデルの有限要素実装

菊池正太郎, 三好宏明, 松原成志朗, 奥村大

年次大会 2020 巻 ( 0 ) 頁： J03139 2020年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

In this study, we conduct finite element implementation of a Gent-Gent hyperelastic model for swollen elastomers. To this end, an inhomogeneous field theory for swollen elastomers is extended using the Gent-Gent model, which includes the effects of limiting chain extensibility and the second strain-invariant. The extended theory is implemented into a commercial finite element package using a user-defined material subroutine. The inflation of a spherical balloon made of swollen elastomers is computed and the results are verified with an analytical prediction.

DOI： 10.1299/jsmemecj.2020.j03139

膨潤エラストマーのためのGent-Gent超弾性モデルの有限要素実装

菊池正太郎, 三好宏明, 川端宏典, 奥村大

東海支部総会講演会講演論文集 2020.69 巻 ( 0 ) 頁： 120 2020年

膨潤エラストマーに対するGent-Gent超弾性モデルの有限要素実装査読有り

菊池正太郎, 三好宏明, 松原成志朗, 奥村大

日本機械学会論文集 86 巻 ( 890 ) 頁： 20 - 00233-20-00233 2020年

担当区分：最終著者記述言語：日本語出版者・発行元：一般社団法人日本機械学会

In this study, we conduct finite element implementation of a Gent-Gent hyperelastic model for swollen elastomers. To this end, an inhomogeneous field theory for swollen elastomers is extended using the Gent-Gent model, which includes the effects of limiting chain extensibility and the second strain-invariant. The extended theory is implemented into a commercial finite element package using a user-defined material subroutine. The accuracy of the implementation is verified by analyzing Young's modulus and Poisson's ratio of swollen elastomers undergoing large deformations. Further, the inflation of a spherical balloon made of swollen elastomers is computed as an example. The results are verified with an analytical prediction and demonstrate the inflation behavior of swollen elastomers.

DOI： 10.1299/transjsme.20-00233

硬質ゲル膜のパターン発展分岐座屈解析

三好宏明, 松原成志朗, 奥村大

年次大会 2020 巻 ( 0 ) 頁： J02103 2020年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

In this study, we perform buckling and postbuckling analysis to invesigate the pattern evolution in a sttiff gel film bonded on a soft substrate. The film and substrate are modeled as the Neo-Hookean solid model. Further, the film is assumed to obey the Flory–Rehner framework for polymeric gels. Since the film swells, the in-plane compressive stresses increases in the film, which causes buckling, i.e., patterns transformation occurs. Finite element analysis is conducted by introducing the Flory–Rehner framework into a user-defined material subroutine (Hong et al., 2009). The step-by-step eigenvalue buckling analysis, which was developed by Okumura et al. (2018), is employed to investigate the onset points and modes of bifurcations. The employment allows us to sequentially trace the first, second and further bifurcations on the bifurcated paths. The obtained results are shown and discussed.

DOI： 10.1299/jsmemecj.2020.j02103

Resetting scheme for plastic strain range evaluation in cyclic plasticity: Experimental verification 査読有り

Ohno, N; Nakamoto, H; Morimatsu, Y; Hamada, T; Okumura, D

INTERNATIONAL JOURNAL OF PLASTICITY 123 巻頁： 56 - 69 2019年12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 Plasticity

It has been proposed that a plastic strain surface is reset to a point and re-evolves every cycle to correctly evaluate the plastic strain range under cyclic loading (Ohno et al., 2018b). This resetting scheme has the advantage of providing a definite value for the evolution parameter irrespective of the amounts of cyclic hardening, pre-straining, and ratcheting. In the present study, the resetting scheme was experimentally verified by performing the following three types of uniaxial cyclic tests of 316 stainless steel at 600 °C: constant strain range, gradual decrease, and step decrease tests. The gradual decrease tests, a new type of cyclic tests, had gradual strain range reduction with increasing number of cycles in the absence and presence of ratcheting such as found at notch roots. Thus, the effect of the strain range history on cyclic hardening was observed to be weaker than that due to stepwise decreasing the strain range. Using a constitutive model with the resetting scheme enabled good simulation of the cyclic hardening behavior in the gradual decrease tests. Cyclic softening after stepwise decreasing the strain range was also simulated well by extending the evolution equation of cyclic hardening.

DOI： 10.1016/j.ijplas.2019.07.008

Evaluation of the effects of cross-linking and swelling on the mechanical behaviors of hydrogels using the digital image correlation method 査読有り Open Access

Uchida, M; Sengoku, T; Kaneko, Y; Okumura, D; Tanaka, H; Ida, S

SOFT MATTER 15 巻 ( 16 ) 頁： 3389 - 3396 2019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：Soft Matter

Experimental evaluation and modeling are important steps in the investigation of the mechanical behaviors of hydrogels in the small- to large-strain range. In this study, the effects of cross-linking and swelling on the true stress-strain response of a specific type of hydrogel (polyacrylamide) were evaluated using a uniaxial tensile test. The development of true strain on the surface of the hydrogel was measured using the digital image correlation method. The specimens with higher cross-link density exhibited a higher initial elastic modulus and earlier orientation hardening. The initial elastic modulus was reduced by the swelling, whereas the orientation hardening occurred in an earlier strain range in the swollen hydrogel. The mechanical responses of the as-prepared and swollen hydrogels with different cross-linker contents were fitted using a non-Gaussian statistical model. The conventional model underestimated the decrease in the elasticity owing to the swelling effect and overestimated the increase in the stress in the large-strain range. The mechanical model was suitably modified to yield an accurate reproduction of the mechanical responses. The proposed model, which was characterized by five material parameters, was found to reproduce the characteristics of the mechanical responses of the as-prepared and swollen hydrogels with different cross-linker contents.

DOI： 10.1039/c9sm00049f

Measurements and FEM Analyses of Strain Distribution in Small Sn Specimens with Few Crystal Grains 査読有り国際誌 Open Access

Sasaki, T; Yanase, A; Okumura, D; Kariya, Y; Koganemaru, M; Ikeda, T

MATERIALS TRANSACTIONS 60 巻 ( 6 ) 頁： 868 - 875 2019年

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

Soldering is used to bond a semiconductor chip to a print circuit board (PCB). It is known that Sn, which is the base metal of Pb-free solder, shows remarkable crystal anisotropy. Clarifying the effect of Sn anisotropy on strain distribution is important for lifetime evaluation. The strain distribution in a micro specimen was measured under a tensile test by a digital image correlation method (DICM) with a microscope. Strain distributions were also analyzed by the finite element method with Hill's anisotropic yield criterion and the crystal plasticity finite element analysis (CPFEA) with considering the critical resolves shear stress (CRSS) of each slip system. The deformation of the crystal structure of ¢-Sn depends on the size, number, and orientation of crystal grains. The CRSS was noticeably different for each slip system, and the yield stress varied with the orientation of crystal grains. Although the CPFEA without considering strain hardening was effective for predicting deformation within crystal grains, it is necessary to consider the strain hardening of crystals to predict the stress-strain curve of a micro specimen.

DOI： 10.2320/matertrans.MH201808

Flory-Rehner モデルの高度化と凸凹パターン変態解析への適用

三好宏明, 川端宏典, 奥村大

東海支部総会講演会講演論文集 2019.68 巻 ( 0 ) 頁： 616 2019年

ゲル膜の表面不安定から誘起される立体構造構築における影響因子解析

菱田湧士, 河合遼太, 奥村大, 伊田翔平, 田中展, 内田真

計算力学講演会講演論文集 2019.32 巻 ( 0 ) 頁： 230 2019年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

In this study, we observe three-dimensional (3D) structure formation induced by the surface instability of gel films generated on petri dishes. As the volume swelling ratio of the films increases, surface instability induces wrinkling and creasing, which result in causing the development of the unique 3D structure. The effective factors are discussed.

DOI： 10.1299/jsmecmd.2019.32.230

ガラス基盤上のゲル膜に生じる膨潤誘起形態形成の基礎的観察

河合遼太, 菱田湧士, 奥村大, 伊田翔平, 田中展, 内田真

M&M材料力学カンファレンス 2019 巻 ( 0 ) 頁： OS1104 2019年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

In this study, we conducted the fundamental observation of swelling-induced morphological formation in gel films on a glass substrate. As the swelling ratio increases, pattern transformation occurs in incremental steps. It was found that surface creasing caused a unique pattern transformation, which generated a 3D structure from a 2D gel film.

DOI： 10.1299/jsmemm.2019.os1104

ハイドロゲルの引張応答に及ぼす架橋濃度および膨潤時間の影響の評価

仙石達也, 内田真, 兼子佳久, 奥村大, 田中展, 伊田翔平

関西支部講演会講演論文集 2019.94 巻 ( 0 ) 頁： P004 2019年

膨潤エラストマーの線形弾性特性に及ぼす負荷条件の影響

川端宏典, 奥村大

計算力学講演会講演論文集 2019.32 巻 ( 0 ) 頁： 237 2019年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

This study investigates the effect of loading conditions on the linear elastic properties of swollen elastomers. We employ the Flory-Rehner theory with the extended Gent model as the elastic strain energy. The interactions of limiting chain extensibility, the second strain-invariant, solvent migration and the loading conditions are analyzed via the Young's modulus and Poisson's ratio.

DOI： 10.1299/jsmecmd.2019.32.237

膨潤エラストマーの線形弾性特性に及ぼすひずみの第二不変量の影響

川端宏典, 奥村大

東海支部総会講演会講演論文集 2019.68 巻 ( 0 ) 頁： 127 2019年

硬質ゲル膜の六方ディンプルパターンから派生する形態

三好宏明, 奥村大

M&M材料力学カンファレンス 2019 巻 ( 0 ) 頁： OS0234 2019年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

In this study, buckling and postbuckling analysis is performed to investigate the evolution of dimple patterns in a stiff gel membrane constrained on a soft substrate. The film and substrate are modeled as the Neo-Hookean solid model. The film is also assumed to obey the Flory–Rehner framework for polymeric gels. Since the film swells, the in-plane compressive stresses increase in the film, which causes buckling, i.e., pattern transformation occurs. In finite element analysis, a step-by-step eigenvalue buckling analysis is employed to analyze the onset points and modes of buckling. The employment allows us to sequentially trace the first, second and further bifurcations on the bifurcated paths. The obtained results show the pattern transformation process from hexagonal dimples to labyrinths.

DOI： 10.1299/jsmemm.2019.os0234

硬質ゲル膜に生じるディンプルパターンの発生と発達の分岐座屈解析

奥村大, 三好宏明

計算力学講演会講演論文集 2019.32 巻 ( 0 ) 頁： 232 2019年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

In this study, we perform the bifurcation analysis of the generation and evolution of of dimple patterns in a stiff gel membrane constrained on a soft substrate. The film and substrate are modeled as the Neo-Hookean solid model. Further, the film is assumed to obey the Flory–Rehner framework for polymeric gels. Since the film swells, the in-plane compressive stresses increase in the film, which causes buckling, i.e., pattern transformation occurs. Finite element analysis is conducted by introducing the Flory–Rehner framework into a user-defined material subroutine (Hong et al., 2009). The step-by-step eigenvalue buckling analysis, which was developed by Okumura et al. (2018), is employed to investigate the onset points and modes of bifurcation. The employment allows us to sequentially trace the first, second and further bifurcations under the bifurcated paths. The obtained results are shown and discussed.

DOI： 10.1299/jsmecmd.2019.32.232

微小スズ試験片の結晶粒中のひずみ計測と結晶塑性理論による解析

池田徹, 佐々木拓海, 小金丸正明, 柳瀬篤志, 奥村大, 苅谷義治

年次大会 2019 巻 ( 0 ) 頁： J01102 2019年

基盤に拘束されたゲル膜の線形弾性特性解析

川端宏典, 奥村大, 大野信忠

M&M材料力学カンファレンス 2019 巻 ( 0 ) 頁： OS1904 2019年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

In this study, we investigate the linear elastic properties of gel membranes constrained on a rigid substrate. To this end, the Flory–Rehner framework for polymeric gels is considered, which is extended by introducing an extended Gent model. The linear perturbation analysis demonstrates the dependence of limiting chain extensibility and the second strain invariant on the in-plane stiffness of gel membranes constrained on a rigid substrate.

DOI： 10.1299/jsmemm.2019.os1904

圧縮環境下で膨潤させたハイドロゲルの膨潤量および引張挙動

仙石達也, 森田隼平, 内田真, 兼子佳久, 奥村大, 田中展, 伊田翔平

M&M材料力学カンファレンス 2019 巻 ( 0 ) 頁： OS1103 2019年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

The effect of swelling on the true stress-strain response of a hydrogel was evaluated using a uniaxial tensile test, and the response was represented by the constitutive equation based on the molecular chain network theory. The experimental results clarified that the initial elastic modulus was reduced by an increase in the degree of swelling. Two different constitutive equations, where the swelling stretch was introduced in different forms, were proposed to predict the effect of swelling. The obtained results of two equations underestimated and overestimated the effect of the swelling on the true stress-strain curve. This result indicates that the mechanical response of the swollen hydrogel can accurately be predicted using the parameter related to the swelling stretch.

DOI： 10.1299/jsmemm.2019.os1103

ハイドロゲルを用いた成長誘起形態形成の基礎的観察

鷹見岳杜, 菱田湧士, 奥村大, 伊田翔平, 田中展, 内田真

東海支部総会講演会講演論文集 2019.68 巻 ( 0 ) 頁： 617 2019年

ハイドロゲルの膨潤に関する速度形構成式の定式化

内田真, 仙石達也, 森田隼平, 兼子佳久, 奥村大, 田中展, 伊田翔平

計算力学講演会講演論文集 2019.32 巻 ( 0 ) 頁： 226 2019年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

Mechanical and chemical coupling behavior of hydrogel was modeled by formulating the rate-form constitutive equation in which the elastic part of the deformation was introduced into the molecular chain network theory. The time-dependent development of the swelling was represented by the simple power-law with osmotic pressure between the polymer and solvent. The material parameters employed in the proposed model were given by comparing the decrease in the tensile load applied to the hydrogel specimen in the solvent. Finally, the FEM simulation of the buckling behavior owing to the swelling of the hydrogel in the container was performed.

DOI： 10.1299/jsmecmd.2019.32.226

ゲル膜のリンクル解析に及ぼす軟質基盤厚さの影響査読有り

奥村大

計算数理工学論文集 19 巻頁： 31 - 36 2019年

Effects of two scaling exponents on biaxial deformation and mass transport of swollen elastomers 招待有り査読有り国際誌

Okumura, D; Mizutani, M; Tanaka, H; Uchida, M

INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES 146 巻頁： 507 - 516 2018年10月

担当区分：筆頭著者,　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：International Journal of Mechanical Sciences

In this study, we investigate the effects of two scaling exponents on the biaxial deformation and mass transport of swollen elastomers. Two scaling exponents are included in an extended version of the Flory–Rehner model (Okumura et al., J. Mech. Phys. Solids, 2016); two scaling exponents are used to adjust the swelling effects on the Young's modulus and osmotic pressure of swollen elastomers, resulting in the ability to predict swelling-induced strain softening under uniaxial tensile loading. It is found that when biaxial tensile loading is given under stress control, strain softening is accelerated by increasing the biaxial stress ratio, while under strain control, the responses become more complicated, which can be interpreted by considering that Poisson's ratio at equilibrium free swelling can take negative values depending on the two scaling exponents. Further, the effect of the two scaling exponents on mass transport is discussed by analyzing the swelling kinetics of a gel layer constrained on a rigid substrate.

DOI： 10.1016/j.ijmecsci.2017.08.042

Thermo-mechanical cyclic hardening behavior of 304 stainless steel at large temperature ranges: Experiments and simulations 招待有り査読有り

Ohno, N; Yamamoto, R; Okumura, D

INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES 146 巻頁： 517 - 526 2018年10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 Mechanical Sciences

Thermo-mechanical cyclic experiments on 304 stainless steel were performed at several temperature ranges with Tmin (minimum temperature) of 150 °C and Tmax (maximum temperature) ranging from 350 °C to 1000 °C. Corresponding isothermal cyclic experiments were also performed at several temperatures. Temperature-history dependent cyclic hardening was thus observed to significantly occur under thermo-mechanical cyclic loading when Tmax was around 600 °C. In contrast, almost no cyclic hardening occurred when Tmax was 1000 °C. The observed, thermo-mechanical cyclic hardening behavior was then simulated using a cyclic viscoplastic constitutive model with a cyclic hardening parameter. The simulation focused on the saturated state of cyclic hardening, leading to the following findings. The saturated thermo-mechanical cyclic hysteresis loops were not predicted well by simply taking into account temperature dependence in the cyclic hardening parameter. Then, by assuming the cyclic hardening parameter to be dependent on Tmax, the saturated thermo-mechanical hysteresis loops were simulated well. These mean that the cyclic hardening parameter of 304 stainless steel should not change with temperature but depend on Tmax in the saturated state of cyclic hardening under thermo-mechanical cyclic loading.

DOI： 10.1016/j.ijmecsci.2017.06.018

Macroscopic out-of-plane auxetic features of a laminated open-cell structure with in-plane negative Poisson's ratios induced by bridging beam components 査読有り

Suga, K; Tanaka, H; Okumura, D; Shibutani, Y

SMART MATERIALS AND STRUCTURES 27 巻 ( 8 ) 2018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：Smart Materials and Structures

This paper presents the out-of-plane mechanism of a laminated open-cell structure that is exerted by a simple control of the geometric configuration. We propose two types of structural units that are assembled with beam and column members in a tetragonal system, and with the geometric difference between them being the presence of a reinforced beam. For the two unit cells, we develop finite element models according to a homogenization method and analyze the macroscopic linear and nonlinear elastic properties. The numerical results show that the cellular structure, which is bridged by additional beams, exhibits strong auxeticity with high negative values of Poisson's ratio in the lamination direction, while retaining the in-plane negative Poisson's ratios. We assess the sensitivity of the linear and nonlinear out-of-plane response to changes in the component geometry. Finally, we discuss the large deformation behaviors of the out-of-plane mechanisms to quantify the amounts of three-dimensional rotations of the internal components.

DOI： 10.1088/1361-665X/aacd31

Ultimate swelling described by limiting chain extensibility of swollen elastomers 査読有り国際共著 Open Access

Okumura, D; Chester, SA

INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES 144 巻頁： 531 - 539 2018年8月

担当区分：筆頭著者,　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：International Journal of Mechanical Sciences

In this study, we study ultimate swelling characterized by limiting chain extensibility of swollen elastomers. Limiting chain extensibility is introduced into the Flory–Rehner theory using the Arruda–Boyce eight chain model and the Gent phenomenological model. The difference between these models is unified by defining a single scalar function. The inequality derived from this function allows for analysis to provide an ultimate value of swelling ratio. This ultimate value is not exceeded at equilibrium swelling regardless of the set of material constants. Under uniaxial loading at equilibrium swelling, deswelling can occur even in tension. Further, the very large swelling behavior of pH sensitive hydrogels is found to originate from the resistance generated by approaching the ultimate value of swelling ratio.

DOI： 10.1016/j.ijmecsci.2018.06.011

Buckling and postbuckling of etching-induced wiggling in a bilayer structure with intrinsic compressive stress 査読有り

Okumura, D; Sugiura, J; Tanaka, H; Shibutani, Y

INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES 141 巻頁： 78 - 88 2018年6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：International Journal of Mechanical Sciences

In this study, we investigate buckling and postbuckling of etching-induced wiggling in a bilayer structure consisting of mask and masked layers. To show effects of explicit modeling of etching process, two mask–masked ridge models with and without etching (Models w/E and w/oE) are analyzed using finite element analysis. The etching process is explicitly introduced via step-by-step eigenvalue buckling analysis. Although Model w/oE predicts a constant value of the critical wavelength of wiggling regardless of the change in ridge width, Model w/E predicts a shorter wavelength depending on the decrease in ridge width and the increase in intrinsic compressive stress in the mask layer. In postbuckling analysis, Model w/oE predicts a monotonic increase in the wiggling amplitude with the constant wavelength, whereas Model w/E predicts saturation of the wiggling amplitude owing to the decreasing wavelength. In the explicit modeling of etching process, the wiggling behavior shows completely opposite tendencies. Dimensional analysis is performed to obtain empirical equations, which are compared with an experiment.

DOI： 10.1016/j.ijmecsci.2018.03.032

EFFECT OF CYCLIC HARDENING ON STRESS RELAXATION IN SUS316HTP UNDER CREEP-FATIGUE LOADING AT 700°C: EXPERIMENTS AND SIMULATIONS 招待有り査読有り国際誌 Open Access

Ohno, N; Sasaki, T; Shimada, T; Tokuda, K; Yoshida, K; Okumura, D

JOURNAL OF THEORETICAL AND APPLIED MECHANICS 56 巻 ( 2 ) 頁： 497 - 510 2018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 Theoretical and Applied Mechanics (Poland)

Cyclic hardening and stress relaxation experiments of SUS316HTP were performed under creep-fatigue loading with tensile strain holding at 700◦C. Experiments revealed that under strain holding, the slow stress-relaxation stage satisfying Norton’s law with slight cyclic hardening followed a rapid stress-relaxation stage that was noticeably affected by cyclic hardening. This suggests that in the slow stress-relaxation stage, inelastic deformation mechanisms different from that of viscoplasticity occurred. Experiments were simulated using a cyclic viscoplastic-creep model in which the inelastic strain-rate was decomposed into viscoplastic and creep components that were affected differently by cyclic hardening. The simulation accurately reproduced the experiments.

DOI： 10.15632/jtam-pl.56.2.497

Resetting scheme for plastic strain surface in constitutive modeling of cyclic plasticity 査読有り Open Access

Ohno, N; Yamamoto, R; Sasaki, T; Okumura, D

ZAMM-ZEITSCHRIFT FUR ANGEWANDTE MATHEMATIK UND MECHANIK 98 巻 ( 4 ) 頁： 518 - 531 2018年4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：ZAMM Zeitschrift fur Angewandte Mathematik und Mechanik

A resetting scheme is proposed for correctly evaluating the plastic strain range to analyze structural components subjected to regular cyclic loading following pre-loading. In this scheme, a plastic strain surface, referred to as the plastic-strain-range surface in the present paper, is reset to a point and re-evolves every cycle, with its size at the end of the last cycle considered to be the plastic strain range of the current cycle. This resetting scheme provides a definite value for the evolution parameter of the plastic-strain-range surface irrespective of the amounts of cyclic hardening, pre-straining, and ratcheting. The resetting scheme is implemented in a cyclic viscoplastic model in finite element methods, and is applied to analyze a notched bar subjected to cyclic loading at its ends. Furthermore, the validity of the resetting scheme for non-proportional cyclic loading is examined by analyzing the cyclic behavior along elliptic and rhombic strain paths. It is shown that the resetting scheme allows the use of a definite value for the evolution parameter of the plastic-strain-range surface in the presence of any cyclic hardening and/or ratcheting. Moreover, it is shown that the resetting scheme can be valid for cyclic loading with a certain degree of non-proportionality.

DOI： 10.1002/zamm.201700298

Mechanism of plastic deformation in a magnesium nanotwinned structure by molecular dynamics simulations 査読有り

Dai Okumura, Masanari Otsuka, Yoji Shibutani

Zairyo/Journal of the Society of Materials Science, Japan 67 巻 ( 2 ) 頁： 215 - 221 2018年2月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Society of Materials Science Japan

In this study, we perform molecular dynamics simulations to investigate plastic deformation modes of a magnesium (Mg) nanotwinned structure. Periodic units including (10 11) twin boundaries (TBs) are analyzed using an embedded atom method potential. Equal spaces between the TBs are assumed at the initial state and the space is parametrized in the range between about 5 nm and 30 nm. It is found that plastic deformation is triggered by the slip along a (10 11) twinning plane near a TB, and that this event induces two different deformation modes depending on the space, i.e., the migration of the TBs and the evolution of double twinning, which leads to void nucleation and polycrystallization. The plastic deformation provided by the two different modes is quantitatively verified from geometric analysis. As the space decreases, the migration of the TBs is superior to the evolution of double twinning.

DOI： 10.2472/jsms.67.215

SUS316 の 700°C でのクリープ疲労における繰返し硬化の応力緩和挙動への影響

佐々木達也, 大野信忠, 島田健弘, 徳田憲二, 吉田公亮, 奥村大

東海支部総会講演会講演論文集 2018.67 巻 ( 0 ) 頁： 511 2018年

線形摂動法を用いた拡張 Flory-Rehner モデルの膨潤度依存性解析

真野貴文, 奥村大

東海支部総会講演会講演論文集 2018.67 巻 ( 0 ) 頁： 202 2018年

真性圧縮応力を有する二層構造のエッチング誘起うねり座屈解析

杉浦順哉, 奥村大, 田中展

東海支部総会講演会講演論文集 2018.67 巻 ( 0 ) 頁： 509 2018年

円孔ゲル膜に生じる長波長変形の座屈固有値解析

春日井彰志, 奥村大

東海支部総会講演会講演論文集 2018.67 巻 ( 0 ) 頁： 508 2018年

ポリアクリルアミドハイドロゲルの単軸引張試験とその評価

清水章司, 奥村大, 伊田翔平, 田中展, 内田真

東海支部総会講演会講演論文集 2018.67 巻 ( 0 ) 頁： 212 2018年

Validation of Crush Energy Calculation Methods for Use in Accident Reconstructions by Finite Element Analysis

Numata S., Mizuno K., Ito D., Okumura D., Kinoshita H.

SAE International Journal of Transportation Safety 6 巻 ( 2 ) 頁： 133 - 145 2018年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SAE International Journal of Transportation Safety

The crush energy is a key parameter to determine the delta-V in accident reconstructions. Since an accurate car crush profile can be obtained from 3D scanners, this research aims at validating the methods currently used in calculating crush energy from a crush profile. For this validation, a finite element (FE) car model was analyzed using various types of impact conditions to investigate the theory of energy-based accident reconstruction. Two methods exist to calculate the crush energy: the work based on the barrier force and the work based on force calculated by the vehicle acceleration times the vehicle mass. We show that the crush energy calculated from the barrier force was substantially larger than the internal energy calculated from the FE model. Whereas the crush energy calculated from the vehicle acceleration was comparable to the internal energy of the FE model. In full frontal impact simulations, the energy of approach factor (EAF) has a linear relation with the residual crush, which had been validated in previous experimental studies. In our study using FE analysis, we found that the slope of EAF versus the residual crush was comparable with that of the dynamic crush energy versus the dynamic crush for crashes at 55 km/h. Using this slope and the residual crush from a 55 km/h impact test, the slope and the intercept of the EAF vs. residual crush can be determined using only one crash test. A database of the slopes and the intercepts was made using Japan New Car Assessment Program (JNCAP) tests. In offset impact simulations, the crush energy calculated from the crush profile agreed with the internal energy of the car FE model when at least one front rail was involved. In oblique impacts, the correction factor for crush energy is not necessary within 20 degrees of principal direction of force of the car's longitudinal axis.

DOI： 10.4271/09-06-02-0009

エラストマーの膨潤限界に及ぼす二軸変形の影響国際共著

奥村大, ショーン A. チェスター

計算力学講演会講演論文集 2018.31 巻 ( 0 ) 頁： 217 2018年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

In this study, ie investigate the effect of biaxial deformation on ultimate sielling characterized by limiting chain extensibility of elastomers. Limiting chain extensibility is introduced into the Flory–Rehner theory. To obtain a single unified inequality, stretches are normalized using the material constant that accounts for limiting chain extensibility. Using the derived inequality, systematic analysis provides the ultimate values of sielling ratio under biaxial loading.

DOI： 10.1299/jsmecmd.2018.31.217

ハイドロゲルの膨潤-弾性相互作用の実験的評価

菱田湧士, 奥村大, 伊田翔平, 内田真, 田中展

M&M材料力学カンファレンス 2018 巻 ( 0 ) 頁： OS0715 2018年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

In this study, we performed the equilibrium free swelling and subsequent uniaxial tensile tests of polyacrylamide hydrogels to investigate the interactions between swelling and elasticity. The experimental data were reproduced by adjusting two scaling exponents of the extended Frory-Rehner model. We discussed the tendency of a set of the obtained material parameters.

DOI： 10.1299/jsmemm.2018.os0715

膨潤エラストマーの線形弾性特性に関する閉形解の導出

川端宏典, 奥村大, 大野信忠

M&M材料力学カンファレンス 2018 巻 ( 0 ) 頁： OS0305 2018年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

In this study, we derive a closed-form solution for linear elastic properties of swollen elastomers. To this end, linear perturbation analysis is applied to the Flory-Rehner theory. Instead of the Neo-Hookean solid model in the theory, the strain energy function is assumed to consist of three invariants to obtain the most general expression.

DOI： 10.1299/jsmemm.2018.os0305

膨潤エラストマーの分子鎖伸び切り限界と膨潤限界の関係

奥村大, ショーン A. チェスター

M&M材料力学カンファレンス 2018 巻 ( 0 ) 頁： OS0609 2018年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

In this study, we study ultimate swelling characterized by limiting chain extensibility of swollen elastomers. Limiting chain extensibility is introduced into the Flory-Rehner theory. The derived inequality allows for analysis to provide an ultimate value of swelling ratio. This ultimate value is not exceeded at equilibrium swelling regardless of the set of material constants. Under uniaxial loading at equilibrium swelling, deswelling can occur even in tension.

DOI： 10.1299/jsmemm.2018.os0609

数結晶粒よりなる微細すず試験片のひずみ測定と有限要素法を用いた結晶塑性解析

佐々木拓海, 奥村大, 苅谷義治, 小金丸正明, 池田徹

計算力学講演会講演論文集 2018.31 巻 ( 0 ) 頁： 084 2018年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

Soldering is used for bonding a print circuit board (PCB) and a semiconductor chip. It is known that Sn, which is the base metal of Pb-free solder, shows remarkable crystal anisotropy. To clarify the effect of anisotropy of Sn on strain distribution is important for lifetime evaluation. The strain distribution in a micro specimen under a tensile test was measured by a digital image correlation method (DICM) with a microscope. The strain distribution was also analyzed by the crystal plasticity finite element analysis (CPFEA) considering the critical resolves shear stress (CRSS) of each slip system. The deformation of the crystal structure of β-Sn depends on the size, number and orientation of crystal grains. The CRSS was noticeably different for each slip system, and the yield stress varied with the orientations of crystal grains. Although the CPFEA without considering strain hardening was effective for predicting deformation within crystal grains, it is necessary to consider the strain hardening of crystals to predict the stress-strain curve of a micro-specimen.

DOI： 10.1299/jsmecmd.2018.31.084

弾性ひずみエネルギー依存性を考慮した膨潤エラストマーの線形弾性特性解析

川端宏典, 奥村大

計算力学講演会講演論文集 2018.31 巻 ( 0 ) 頁： 314 2018年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

In this study, we perform analysis of linear elastic properties considering the influence of elastic strain energies of swollen elastomers. A closed form solution derived in the most general expression is used to introduce the Gent model in the Flory-Rehner theory. The effects of limiting chain extensibility are discussed.

DOI： 10.1299/jsmecmd.2018.31.314

単軸引張変形下において負のポアソン比を示す積層セル構造体の面外力学応答のモデル化

田中展, 須賀海斗, 奥村大, 渋谷陽二

計算力学講演会講演論文集 2018.31 巻 ( 0 ) 頁： 250 2018年

記述言語：日本語出版者・発行元：一般社団法人日本機械学会

In this study, we analyze the mechanical responses of the two types of laminated cellular structures using finite element models based on a homogenization method. In the numerical simulations, we obtain the homogenized elastic modulus tensors for the two structural units and show that the cellular structure, which is bridged by additional beams, exhibits strong auxeticity with high negative values of Poisson's ratio in the lamination direction, while retaining the in-plane negative Poisson's ratios. We then assess the sensitivity of the linear and nonlinear out-of-plane response to changes in the component geometry. According to the analytical results, we propose a simple periodic framework consisting polyhedron blocks and spherical joints, which can represent the similar auxetic behavior the cellular structure exhibits in the in-plane and out-of-plane directions.

DOI： 10.1299/jsmecmd.2018.31.250

拡張 Flory-Rehner モデルの実装と増分安定性の検討

エラストマーの極限膨潤に及ぼす分子鎖伸び切り限界の二軸変形依存性査読有り国際共著

奥村大

計算数理工学論文集 18 巻頁： 7 - 18 2018年

アクリルアミドハイドロゲルを用いた拡張Flory-Rehnerモデルの基礎的検証査読有り

奥村大, 清水章司, 伊田翔平, 内田真, 田中展

計算数理工学論文集 17 巻頁： 53 - 58 2017年12月

アクリルアミドハイドロゲルを用いた拡張Flory-Rehnerモデルの基礎的検証査読有り

奥村大, 清水章司, 伊田翔平, 内田真, 田中展

計算数理工学論文集 17 巻頁： 53 - 58 2017年12月

Evaluation of Deformation Behavior of Hydrogel on Uniaxial Tensile Test using Digital Image Correlation 査読有り

Keita Suzuki, Makoto Uchida, Yoshihisa Kaneko, Dai Okumura, Hiro Tanaka, Shohei Ida

Proceedings of the 12th International Symposium on Advanced Science and Technology in Experimental Mechanics 頁： 035 2017年11月

ゲル膜に生じる膨潤誘起パターン変態の有限要素解析

寺井喜彦, 奥村大

東海支部総会講演会講演論文集 2017.66 巻 ( 0 ) 頁： 521 2017年

清水章司, 奥村大

東海支部総会講演会講演論文集 2017.66 巻 ( 0 ) 頁： 522 2017年

微細パターン構造の面外うねり座屈解析における板厚の影響

杉浦順哉, 奥村大, 田中展

東海支部総会講演会講演論文集 2017.66 巻 ( 0 ) 頁： 518 2017年

微細パターン構造のうねり座屈に及ぼす板厚と真性応力の影響

杉浦順哉, 奥村大, 田中展

計算力学講演会講演論文集 2017.30 巻 ( 0 ) 頁： 205 2017年

分子動力学法による β-Sn の微視的塑性変形解析

松野夏輝, 木下佑介, 奥村大

東海支部総会講演会講演論文集 2017.66 巻 ( 0 ) 頁： 523 2017年

予ひずみを受ける膨潤エラストマーの弾性特性解析

奥村大, 真野貴文

計算力学講演会講演論文集 2017.30 巻 ( 0 ) 頁： 212 2017年

ポーラスゲル膜の膨潤誘起パターン変態におけるドメインウォール形成機構の解析

奥村大, 春日井彰志

東海支部総会講演会講演論文集 2017.66 巻 ( 0 ) 頁： 520 2017年

ポーラスゲル膜に生じる膨潤誘起不安定変形の座屈固有値解析

磯村泰爾, 奥村大

東海支部総会講演会講演論文集 2017.66 巻 ( 0 ) 頁： 519 2017年

ポーラスゲル膜に生じる膨潤誘起不安定の要素分割依存性

春日井彰志, 磯村泰爾, 奥村大

計算力学講演会講演論文集 2017.30 巻 ( 0 ) 頁： 204 2017年

ポーラスゲル膜に生じるドメインウォール欠陥の座屈固有値解析

春日井彰志, 奥村大, 大野信忠

M&M材料力学カンファレンス 2017 巻 ( 0 ) 頁： OS1604 2017年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人日本機械学会

In this paper, we perform eigenvalue buckling analysis to investigate a defect of domain walls (DWs) in a diamond plate pattern (DPP), which is caused by swelling-induced pattern transformation in porous gel films. It is found that DWs in a DPP can be captured as long wavelength buckling. The critical stress of DWs in a DPP is higher than that of a uniform DDP, but as periodic units increase, both are identical. This means that this defect, i.e., DW, is hardly eliminated in DPPs. Further, the pattern of DWs consists of 4 basic buckling modes, which are obtained from extending the buckling mode of the DPP using the Bloch wave.

DOI： 10.1299/jsmemm.2017.os1604

ポリアクリルアミドハイドロゲルを用いた拡張Flory-Rehnerモデルの実験的検証

清水章司, 奥村大, 伊田翔平, 田中展, 内田真

M&M材料力学カンファレンス 2017 巻 ( 0 ) 頁： OS0306 2017年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人日本機械学会

An extended F-R model is experimentally verified using polyacrylamide hydrogels. Stress-stretch responses of the extended F-R model are compared with those of the original F-R model and the Ogden model. As a result, the extended F-R model is superior to the original F-R model because the extended F-R model can adjust swelling dependence of Young's modulus. Further, the extended F-R model is comparable to the Ogden model for small deformations because the extended F-R model does not include the effect of limiting chain extensibility. The results of the extended F-R model imply that polyacrylamide hydrogels can cause swelling-induced strain softening.

DOI： 10.1299/jsmemm.2017.os0306

ポリアクリルアミドハイドロゲルの単軸引張試験に基づく拡張 Flory-Rehner モデルと Ogden モデルの比較解析

清水章司, 奥村大, 伊田翔平, 田中展, 内田真

計算力学講演会講演論文集 2017.30 巻 ( 0 ) 頁： 241 2017年

Effects of two scaling exponents on swelling-induced softening of elastomers under equibiaxial and planar extensions

Okumura D., Mizutani M.

Key Engineering Materials 725 KEM 巻頁： 427 - 432 2017年

記述言語：日本語出版者・発行元：Key Engineering Materials

We study the effects of two scaling exponents on the mechanical properties of swollen elastomers under equibiaxial and planar extensions. Two scaling exponents are introduced to extend the Flory-Rehner free energy function, and are adjusted based on the previous study. Results show that swelling-induced strain softening is apt to occur under equibiaxial extension compared to uniaxial extension. The additional tensile stress in a lateral direction enables it to occur in relatively poor solvents, and accelerates the onset point. Planar extension shows more complicated responses because the stress in the constrained direction changes dramatically depending on the combination of two scaling exponents and the Flory-Huggins interaction parameter.

DOI： 10.4028/www.scientific.net/KEM.725.427

Thermo-mechanical cyclic plastic behavior of 304 stainless steel at large temperature ranges

Ohno N., Yamamoto R., Okumura D.

Key Engineering Materials 725 KEM 巻頁： 275 - 280 2017年

記述言語：日本語出版者・発行元：Key Engineering Materials

Thermo-mechanical cyclic experiments on 304 stainless steel were performed at several temperature ranges which had maximum temperatures ranging from 350°C to 1000°C and a minimum temperature of 150°C. Related isothermal cyclic experiments were also performed. Temperature-history dependent cyclic hardening significantly occurred under thermo-mechanical cyclic loading with maximum temperatures around 600°C, whereas almost no cyclic hardening was observed when the maximum temperature was 1000°C. The observed thermo-mechanical cyclic plastic behavior in the saturated state of cyclic hardening was then simulated using a cyclic viscoplastic constitutive model, leading to the following findings. It was difficult to predict the saturated thermo-mechanical cyclic behavior using only the isothermal cyclic experimental data. The saturated thermo-mechanical cyclic behavior was simulated well by introducing a cyclic hardening parameter depending on the maximum temperature. This means that the cyclic hardening parameter should not change with temperature but depend on the maximum temperature in the saturated state of cyclic hardening under thermo-mechanical cyclic loading.

DOI： 10.4028/www.scientific.net/KEM.725.275