Details of a Researcher - Omiya, Masaki

This study investigated the effects of micro- and nanostructures on the adhesion strength between copper and an encapsulating mold compound (EMC). The shape of the microgrooves was designed based on fracture mechanics theory, and the effect of laser-induced periodic structure surface (LIPSS) formation on the microgroove was investigated using numerical simulations. The designed surface profiles were fabricated using femtosecond laser treatments, and the adhesion strength between copper and the EMC was evaluated. The results show that deep microgrooves improved the adhesion strength owing to the anchor effect. However, the aspect ratio between the pitch and depth of the microgroove had a limitation in enhancing the adhesion strength. The formation of LIPSSs on the mountaintop of the microgroove was very effective; however, an LIPSS on the valley of the microgroove was ineffective. Numerical analyses revealed that LIPSSs suppressed the shear deformation of the EMC and worked as resistance to interface delamination. Based on the findings obtained in this study, combining micro- and nano-scale surface structure formation with femtosecond laser treatments is an effective and eco-friendly method for improving adhesion strength.

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Effect of rubber modification on fracture toughness of epoxy adhesives under mode I and mode II loading

Makoto Imanaka, Masaki Omiya, Keisuke Hara, Hayato Nakatani

Theoretical and Applied Fracture Mechanics (Elsevier) 122 103604 2022.09

Research paper (scientific journal), Joint Work, Corresponding author, Accepted, ISSN 01678442

In the present study, the effects of rubber modification on the joint strength and fracture toughness of epoxy adhesives under mode I and II loading were investigated using Arcan-type adhesively bonded joints. The results of the fracture tests under mode I loading revealed the occurrence of stress whitening owing to triaxial tensile stresses near the crack tip. The joint strength and fracture toughness were calculated using the J-integral value, where the adhesive layer was considered as an elastic–plastic material. The crack-growth energy was also calculated using the J-integral value, where the adhesive layer was considered as an elastic material. The results revealed that rubber modification under mode I loading induced an increase in the joint strength, fracture toughness, and crack-growth energy. Rubber modification under mode II loading did not induce stress whitening near the crack tip owing to low triaxial tensile stresses. However, macroscopic void growth and significant plastic deformation were observed in the adhesive layer. Rubber modification induced a slight decrease in the joint strength; however, it induced a significant increase in the fracture toughness owing to the growth of the plastic zone in the adhesive layer. The calculated crack-growth energy decreased slightly, in accordance with the joint strength. It was concluded that rubber modification contributed to an increase in the crack-growth resistance under mode I loading and not under mode II loading. Furthermore, a correlation was observed between the joint strength and crack-growth energy.

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Influence of strength and notch shape on crack initiation and propagation behavior of advanced high strength steel sheets

Masaki Omiya, Seiya Arakawa, Zhenduo Yao, Mayu Muramatsu, Shinnosuke Nishi, Kenji Takada, Masanobu Murata, Kazuaki Okato, Kensuke Ogawa, Kai Oide, Takaya Kobayashi, Jike Han, Kenjiro Terada

Engineering Fracture Mechanics (Elsevier) 271 108573 2022.06

Research paper (scientific journal), Joint Work, Lead author, Corresponding author, Accepted, ISSN 00137944

Advanced high-strength steels (AHSSs) are widely adopted in car body structures to achieve weight reduction for energy efficiency and crash safety. This study investigates the effects of material strength and notch shapes on crack initiation and propagation behaviors in AHSS sheets used in car body structures. Tensile tests were conducted for three types of Japanese grade AHSS (JSC590, JSC980, and JSC1180) specimens and two notch root radii (R0.5 and R5). The crack initiation and propagation behaviors were found to strongly depend on the material strength and notch root radius. The crack generated from the notch root for the R0.5 specimens, whereas it generated from 1 to 2 mm inside the notch root for the R5 specimens. Unstable crack propagation occurred beyond the maximum load for the R5 and JSC1180 specimens, whereas only stable crack propagation occurred for the R0.5 specimens. From the digital image correlation analyses, we found that the specimen notch radius affects the stress triaxiality and equivalent plastic strain around the notch root. The JSC980 material had the highest crack initiation energy, which correlates with the plastic dissipation energy utilized for thickness reduction. The JSC590 material exhibited the highest crack propagation energy, which correlates with the true fracture strain.

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圧延方向が及ぼす薄板 Cu-Sn-P 銅合金条材の疲労き裂進展特性への影響

土屋朱美果，三田夏大，大宮正毅

日本材料学会第71期学術講演会講演論文集 (日本材料学会) 405 1 - 2 2022.05

Research paper (conference, symposium, etc.), Joint Work, Last author, Corresponding author

Evaluation of thermal fatigue crack propagation in underfill resin materials for electronic packages

Watanabe Y., Yamaguchi H., Enomoto T., Ogawa K., Kobayashi T., Omiya M.

Fatigue and Fracture of Engineering Materials and Structures (Wiley) 45 ( 5 ) 1349 - 1360 2022.05

Research paper (scientific journal), Last author, Corresponding author, Accepted, ISSN 8756758X

To improve the fatigue life of electronic packages, it is necessary to clarify thermal fatigue characteristics of underfill resin materials. In this study, a new setup for measuring thermal fatigue crack growth was developed, and the effects of thermal cycle conditions and silica filler contents on fatigue crack propagation were investigated. The results show that the likelihood of crack initiation increased with the filler content and the temperature of the thermal cycles. Comparing the results with those from mechanical fatigue tests, crack initiation and propagation occurred at lower ΔK and the crack growth rates were higher for thermal fatigue. Observations of the fracture surface revealed that the cracks propagated inside the underfill resin, which resulted in smaller crack growth resistance than that in mechanical fatigue. The addition of fillers introduced a crack propagation path at the interface between fillers and resins and enhanced the crack propagation resistance in thermal fatigue.

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Crack growth simulation in thin plate using simplified strain based damage model

Seo J.M., Kim Y.J., Omiya M.

Engineering Fracture Mechanics (Elsevier) 260 2022.02

Research paper (scientific journal), Joint Work, Accepted, ISSN 00137944

In this study, a simple strain based damage model is applied to simulate the ductile crack growth in thin 590 MPa class steel plates with notch and hole. The model depends only on the stress triaxiality and has two parameters. Determination of two parameters is straightforward by analyzing the tensile test results of flat plate specimen and plate specimen with sharp notches. The determined damage model is then applied to simulate the crack growth in other two types of test specimens containing plates with hole and notch, and a good agreement between the simulated and experimental results is obtained. It is found that the simulation results are primarily affected by the in-plane element size in the crack growth direction. On the other hand, the out-of-plane element size does not affect simulation results. It is found that the use of an in-plane element size of 0.1 mm or less is appropriate.

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Generation of micro/nano hybrid surface structures on copper by femtosecond pulsed laser irradiation

Nakajima A., Omiya M., Yan J.

Nanomanufacturing and Metrology (Nanomanufacturing and Metrology) 5 ( 3 ) 274 - 282 2022

Research paper (scientific journal), Joint Work, Accepted, ISSN 2520811X

The delamination of copper lead frames from epoxy molding compounds (EMC) is a severe problem for microelectronic devices, as it leads to reduced heat dissipation or circuit breakage. The micro/nanoscale surface structuring of copper is a promising method to improve the copper–EMC interfacial adhesion. In this study, the generation of micro/nano hybrid structures on copper surfaces through femtosecond pulsed laser irradiation is proposed to improve interfacial adhesion. The micro/nano hybrid structures were realized by generating nanoscale laser-induced periodic surface structures (LIPSS) on microscale parallel grooves. Several types of hybrid surface structures were generated by changing the laser polarization direction, fluence, and scanning speed. At a specific aspect ratio of microgrooves, a latticed structure was generated on the sides of microgrooves by combining LIPSS formation and direct laser interference patterning. This study provides an efficient method for the micro/nanoscale hybrid surface structure formation for interfacial adhesion improvement between copper and EMC.

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Gradient damage model for ductile fracture introducing degradation of damage hardening modulus: implementation and experimental investigations

Han J., Matsubara S., Nishi S., Takada K., Muramatsu M., Omiya M., Ogawa K., Oide K., Kobayashi T., Murata M., Moriguchi S., Terada K.

International Journal of Fracture (International Journal of Fracture) 2022

ISSN 03769429

This study presents a gradient damage model for ductile fracture, in which the damage hardening modulus is degraded by the accumulation of plastic deformation and the volume expansion caused by negative hydrostatic pressure. The proposed model fulfills the thermodynamic requirements, and the governing equations are derived from energy minimization principles. Two parameter studies are carried out to confirm the basic performance of the proposed model, in which some typical ductile fracture responses are demonstrated by changing parameters for degrading the damage hardening modulus. Also, a series of numerical experiments are presented to reveal the ability of the proposed model to successfully simulate the fracture tests of advanced high strength steel sheets with different tensile strengths. It is indeed confirmed by the close agreement with experimental results that the proposed model is capable of realizing the breaking elongation, the transitional behavior from unstable to stable crack propagations, and the corresponding load–displacement curves. Also, the model successfully reproduces and predicts the crack initiation positions in notched specimens with different notch radii.

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薄板Cu-Sn-P銅合金条材における疲労き裂進展特性

三田夏大，大宮正毅，土屋朱美果

第20回破壊力学シンポジウム講演論文集 (日本材料学会) 17 - 22 2021.11

Research paper (conference, symposium, etc.), Corresponding author

水の電気分解を利用したパラジウム薄膜ソフトアクチュエータ

大宮正毅，黒川正人，出口早織

日本機械学会2021年度年次大会講演論文集 (日本機械学会) S041-10 1 - 3 2021.09

Research paper (conference, symposium, etc.), Joint Work, Lead author, Last author, Corresponding author

超高張力鋼板のスポット溶接部におけるき裂発生・進展挙動解析

幺振鐸，大宮正毅

日本機械学会2021年度年次大会講演論文集 (日本機械学会) J043-11 1 - 4 2021.09

Research paper (conference, symposium, etc.), Joint Work, Last author, Corresponding author

Improvement of experimental device for high cycle fatigue tests of copper alloy strips and characterizing fatigue properties

Natsuhiro MITA, Masaki OMIYA, Shingo WATANABE

日本機械学会論文集 (日本機械学会) 87 ( 900 ) 1 - 16 2021.07

Research paper (scientific journal), Joint Work, Accepted

自動車用高強度薄板鋼板におけるき裂進展挙動に及ぼす切欠きの影響

大宮正毅，荒川誠弥，村松眞由，西紳之介，高田賢治，小川賢介，生出佳，小林卓哉，村田真伸，岡東寿明，韓霽珂，寺田賢二郎

日本材料学会第70期学術講演会講演論文集 302 1 - 2 2021.05

Research paper (conference, symposium, etc.), Joint Work, Lead author, Corresponding author

Load transfer Ubistar(U**) calculation in structures under dynamic loading

Masaki Omiya, Kunihiro Takahashi

日本機械学会論文集 (日本機械学会) 87 ( 896 ) 1 - 12 2021.04

Research paper (scientific journal), Joint Work, Lead author, Corresponding author, Accepted

銅合金条材のための高サイクル疲労試験機の改良と疲労特性の把握

三田夏大，渡邊慎吾，大宮正毅

日本機械学会関東支部第 27 期総会・講演会講演論文集 (日本機械学会) 10B05 1 - 5 2021.03

Research paper (conference, symposium, etc.), Joint Work, Last author, Corresponding author

Influence of rubber content on failure mode and resistance characteristics of pc/abs blends and their abs constituents under impact

Machmud M.N.I.Z.A.R., Masaki O., Hirotsugu I., Kikuo K.

Key Engineering Materials (Key Engineering Materials) 892 KEM 67 - 73 2021

ISSN 10139826

This present study has been re-established to investigate failure mode and resistance characteristics of the PC/ABS blends and their ABS constituents under impact for a range of rubber contents. This present study has still been experimentally performed under an instrumented-drop weight impact test (DWIT) at a room temperature. It has been finally revealed that with a particular size of rubber particle, content of rubber significantly influenced impact failure modes and impact resistances of the PC/ABS blends and their ABS constituents as well. The test results showed that impact strength of the blends was improved about 23.22% and 155.33% due to increase in content of rubber up to 15 wt% and 20 wt%, respectively. There was also found that an increase in impact toughness of the blends for 57.48% and 239.23% was due to increase in content of rubber up to 15 wt% and 20 wt%, respectively. Whilst, impact strength of the ABS was improved about 392.98% and 190.12% due to increase in content of rubber up to 15 wt% and 20 wt%, respectively. An increase in impact toughness of the ABS for 308.20% and 172.56% was due to increase in content of rubber up to 15 wt% and 20 wt%, respectively.

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Deformation mechanism of hydrogen-assisted ionic polymer metal composite actuator

Omiya M., Kurokawa M.

Mechanics of Advanced Materials and Structures (Mechanics of Advanced Materials and Structures) 2021

ISSN 15376494

Hydrogen power sources are expected to be the main power source for a sustainable society in the future. Therefore, the development of mechanical parts or systems to adapt to the usage of hydrogen is a key issue. Ionic polymer metal composite (IPMC) actuators are composed of an electrolyte polymer membrane coated with electrodes. Owing to their light weight, flexibility, and ease of miniaturization, IPMC actuators are promising candidates for use as micro-actuators in small robots, microvalves, or artificial muscles. In this study, a hydrogen-assisted IPMC actuator is developed, and its deformation mechanism is investigated. The hydrogen absorption produced by water splitting and the hydrated cation movement in the electrolyte are the driving forces involved in this actuator. The effects of applied voltage, thickness of palladium electrodes, and length of the actuators are studied. Moreover, the contributions of bending moments by a hydrated cation movement and those by hydrogen absorption to the bending deformation are separately clarified. The results indicate that the deformation mechanism of the hydrogen-assisted IPMC actuator depends on the applied voltage, palladium-electrode thickness, and actuator length. The contribution of the hydrogen assistance decreases with the applied voltage, while that of the hydrated cation movement increases. In addition, the specimen with a shorter length exhibits a larger hydrogen-induced moment ratio. These results suggest that the hydrogen assistance to the bending deformation is more effective in IPMC actuators with a shorter and thinner palladium electrode.

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