2020年06月, 日本材料学会, 令和元年度学術奨励賞　　　　　　　　　　　　　　　
藤村奈央

2017年03月, 日本材料学会 疲労部門委員会, 第33回疲労シンポジウム・第1回生体・医療材料シンポジウム 優秀研究発表賞　　　　　　　　　　　　　　　
藤村奈央, 国内学会・会議・シンポジウム等の賞

2013年07月, 21st Rudy Scavuzzo Student Paper Symposium Competition at the 2013 ASME Pressure Vessels Piping Conference, Honorable Mention (Ph. D. Category)　　　　　　　　　　　　　　　
藤村奈央, 国際学会・会議・シンポジウム等の賞

2011年07月, Student Paper Competition 2011 ASME Pressure Vessels and Piping Conference, The First Runner-Up Student Paper, Student Paper Competition　　　　　　　　　　　　　　　
藤村奈央, 国際学会・会議・シンポジウム等の賞

Nondestructive Observation of Small Internal Cracks in Gigacycle Fatigue of Titanium Alloys
Takashi Nakamura, Fumiyoshi Yoshinaka, Gaoge Xue, Nao Fujimura, Kosuke Takahashi
Materia Japan, 63, 11, 770, 775, Japan Institute of Metals, 2024年11月01日
研究論文（学術雑誌）

Toughened single-lap joints by composite bondline of adhesive and double-sided tape
Kosuke Takahashi, Zhantong Sun, Takuma Kikuzawa, Kounosuke Shimamura, Sourabh Jagrat, Nao Fujimura, Takashi Nakamura
Advanced Composite Materials, 1, 17, Informa UK Limited, 2023年11月20日
研究論文（学術雑誌）

Experimental Approach for Clarifying Initiation and Growth Behaviors of Internal Fatigue Cracks Using Synchrotron Radiation Multiscale X-ray Computed Tomography
Takashi Nakamura, Gaoge Xue, Yuma Kon, Nao Fujimura, Takuya Yamazaki, Nobuyuki Tonozaki, Akihisa Takeuchi, Masayuki Uesugi, Kentaro Uesugi
Materials Performance and Characterization, 12, 2, 107, 128, ASTM International, 2023年11月10日
研究論文（学術雑誌）, Abstract

The very high cycle fatigue (VHCF) phenomenon has been recognized and extensively studied in the past quarter century. One of the most peculiar and noticeable characteristics of VHCF is the transition of the origin site from the surface to the interior of the material in long-life regimes over 107 cycles. In particular, in high-strength metals, a tiny site can become an origin of internal fatigue cracks, such as nonmetallic inclusions of several micrometers to several tens of micrometers in high-strength steels and crystal grains of several tens of micrometers in titanium alloys. However, such small cracks are difficult to detect using conventional nondestructive approaches, such as industrial X-ray computed tomography (CT) or ultrasonic CT. Given this background, we have attempted to use a synchrotron radiation multiscale X-ray CT provided by SPring-8 in Japan. This system comprises a projection CT (micro-CT) with a spatial resolution of approximately 1 μm and a phase-contrast imaging CT (nano-CT) with a spatial resolution of approximately 200 nm or higher. The present study introduces our experimental approach to clarify internal fatigue crack behaviors using the multiscale X-ray CT with in situ fatigue testing. First, the principle of material selection focusing on the VHCF study is explained with the details of the materials used: (α+β) type Ti-6Al-4V, β type Ti-22V-4Al, and 17-4 precipitation-hardened martensite stainless steel. Afterward, the outline and primary performance of the multiscale X-ray CT are described. Subsequently, important points in conducting accurate in situ fatigue tests are discussed from the viewpoints of the development policies of the testing system and preparation of the special thin specimen for CT imaging. Finally, the multiscale X-ray CT is conducted for the above materials, and the initiation and growth behaviors of the internal fatigue cracks are compared and discussed for an in-depth understanding of the VHCF phenomenon.

Room-Temperature-Nitriding of Pure Titanium Using Scanning Cyclic Press in a Nitrogen Environment
Yuta Funaki, Nao Fujimura, Takashi Nakamura, Kosuke Takahashi, Tatsuki Wajima
Journal of the Japan Institute of Metals and Materials, 87, 11, 305, 308, Japan Institute of Metals, 2023年11月01日
研究論文（学術雑誌）

Full-life growth behavior of a naturally initiated internal fatigue crack in beta titanium alloy via in situ synchrotron radiation multiscale tomography
Gaoge Xue, Takashi Nakamura, Nao Fujimura, Kosuke Takahashi, Hiroyuki Oguma, Akihisa Takeuchi, Masayuki Uesugi, Kentaro Uesugi
International Journal of Fatigue, 170, 107571, 107571, Elsevier BV, 2023年05月
研究論文（学術雑誌）

Characterization of internal fatigue crack initiation in Ti‐6Al‐4V alloy via synchrotron radiation X‐ray computed tomography
Fumiyoshi Yoshinaka, Takashi Nakamura, Hiroyuki Oguma, Nao Fujimura, Akihisa Takeuchi, Masayuki Uesugi, Kentaro Uesugi
Fatigue & Fracture of Engineering Materials & Structures, Wiley, 2023年02月03日
研究論文（学術雑誌）

Fatigue Life Distribution Analysis of α+β Titanium Alloy Based on the Initiation and Propagation Behaviors of Small Internal Cracks
Hironori MORISHITA, Takashi NAKAMURA, Nao FUJIMURA, Kosuke TAKAHASHI
Journal of the Society of Materials Science, Japan, 71, 12, 997, 1004, Society of Materials Science, Japan, 2022年12月15日
研究論文（学術雑誌）

Generalized characteristics of peel tests independent of peel angle and tape thickness
Masako Yamada, Kosuke Takahashi, Nao Fujimura, Takashi Nakamura
Engineering Fracture Mechanics, 271, 2022年08月
研究論文（学術雑誌）, The peel tests of pressure-sensitive adhesive (PSA) tapes were conducted to clarify the effect of the peel velocity, peel angle, and tape thickness. We focused on the viscoelastic deformation of the PSA layer and its relationship with the adhesion energy. It was found that, at a sufficiently low strain rate of the PSA layer, the adhesion energy has a threshold value of debonding. In addition, the increase of adhesion energy from the threshold value is proportional to the maximum stretch of the PSA layer and follows a power law relationship with the strain rate. The general relationship between the adhesion energy and the strain of PSA layer, independent from the peel angle and tape thickness, was established.

Initiation and propagation of small fatigue crack in beta titanium alloy observed through synchrotron radiation multiscale computed tomography
Gaoge Xue, Takashi Nakamura, Nao Fujimura, Kosuke Takahashi, Hiroyuki Oguma, Akihisa Takeuchi, Masayuki Uesugi, Kentaro Uesugi
Engineering Fracture Mechanics, 263, 108308, 108308, Elsevier BV, 2022年03月
研究論文（学術雑誌）

Three-dimensional Observation of Small Fatigue Cracks Growth Process in a Beta Titanium Alloy Ti-22V-4Al using Multiscale Synchrotron Radiation Computed Tomography
中村 孝, 藤村 奈央, 小熊 博幸, 竹内 晃久, 上椙 真之, 上杉 健太朗
Proceedings of the 7th International Conference on Advanced Steels, ICAS 2022, -, 132, 135, 2022年, ［査読有り］
研究論文（学術雑誌）

The Formation Process of Multiple Facets in Internal Fatigue Fractures of (α+β) Ti-6Al-4V
中村 孝, 藤村 奈央
Proceedings of the 7th International Conference on Advanced Steels, ICAS 2022, -, 136, 139, 2022年, ［査読有り］
研究論文（学術雑誌）

Estimation of Fatigue life for internal cracks using crack growth rates measured in a vacuum environment
中村 孝, 藤村 奈央
Proceedings of the 7th International Conference on Advanced Steels, ICAS 2022, -, 140, 143, 2022年, ［査読有り］
研究論文（学術雑誌）

Detection of small internal fatigue cracks in Ti-6Al-4V via synchrotron radiation nanocomputed tomography
Gaoge Xue, Yuta Tomoda, Takashi Nakamura, Nao Fujimura, Kosuke Takahashi, Fumiyoshi Yoshinaka, Akihisa Takeuchi, Masayuki Uesugi, Kentaro Uesugi
Fatigue and Fracture of Engineering Materials and Structures, 2022年
研究論文（学術雑誌）, Two types of synchrotron radiation computed tomography (SR-CT)—projection CT (micro-CT) and phase-contrast imaging CT (nano-CT)—were used to observe internal fatigue cracks in (α + β) Ti-6Al-4V alloy. Micro-CT detected cracks in the specimen at ~1 μm spatial resolution, and the nano-CT provided magnified images at ~200 nm spatial resolution. The crack initiation sites were clarified as the α-phase for both the surface and internal cracks; however, their opening behaviors differed. A sharp crack tip was observed in the surface crack, and the crack tip opening displacement (CTOD) increased with an increase in the applied load. By contrast, a blunted crack tip, similar to that of a crack in a vacuum, was observed for the internal crack, and its CTOD remained almost constant regardless of the applied load. These phenomena are likely to explain the different behaviors of surface and internal cracks, particularly the slower growth rate of internal cracks, which leads to a longer fatigue life in the very high cycle fatigue regime.

放射光X線ナノCTを用いたその場引張・疲労試験による炭素繊維–エポキシ樹脂の界面はく離検出
勝谷 亮介, 松尾 拓磨, 髙橋 航圭, 藤村 奈央, 中村 孝
日本複合材料学会誌, 47, 5, 186, 193, The Japan Society for Composite Materials, 2021年09月15日
研究論文（学術雑誌）

Initiation and propagation processes of internal fatigue cracks in β titanium alloy based on fractographic analysis
Gaoge Xue, Takashi Nakamura, Nao Fujimura, Kosuke Takahashi, Hiroyuki Oguma
Applied Sciences (Special Issue: Advances in Very-High-Cycle Fatigue), 11, 1, MDPI, 2021年, ［査読有り］
英語, 研究論文（学術雑誌）, Uniaxial fatigue tests were conducted for a beta titanium alloy Ti-22V-4Al up to a very high cycle fatigue (VHCF) regime. The initiation and propagation processes of the internal fatigue cracks were investigated using 3D fractographic analysis. Multiple facets were observed at the crack initiation site. Three facet initiation models were proposed based on the surface appearances and the 3D facet bonding patterns of the multiple facets, and the major facet was determined to be the true crack initiation site. Using the size of the major facet, a Tanaka-Akiniwa model, which can determine the material constants for the Paris law using only conventional fatigue tests, was applied to reveal the propagation process of the internal cracks. A reverse fatigue life prediction was also conducted to evaluate the accuracy of the material constants obtained using the Tanaka-Akiniwa model. When the facet initiation models were applied, the predictions showed less deviation and better agreement than when the facet initiation process was not considered. The findings of this study indicate that the formation of multiple facets in beta titanium alloys is sequential rather than simultaneous.

Effect of vacuum pressure on small crack propagation in Ti-6Al-4V
Fumiyoshi Yoshinaka, Gaoge Xue, Nao Fujimura, Takashi Nakamura
International Journal of Fatigue, 142, ELSEVIER SCI LTD, 2021年, ［査読有り］
英語, 研究論文（学術雑誌）, In this study, small crack propagation tests are conducted on artificially defected specimens of Ti-6Al-4V under air and vacuum pressures of 100 Pa, 10(-2) Pa, 10(-4) Pa, and 10(-6) Pa. Fracture surfaces between these environments are compared, and the effect of vacuum pressure on the crack propagation process is investigated. The similarities between surface cracks in vacuum and internal cracks in the very high cycle regime are also discussed from the perspectives of crack propagation rate and fractographic characteristics. From the results, it was observed that there was a tendency for the crack initiation life to increase and the crack propagation rate to decrease with a decrease in the vacuum pressure, although no notable distinction was observed in air and under 10(0) Pa. The fractography exhibited an angular surface with sharp edges in air and under 10(0) Pa. However, a granular feature with rounded edges was observed below 10(-2) Pa and became more pronounced as the vacuum pressure decreased. The window periods, which formed an oxidized surface coverage, were believed to account for the vacuum effect on crack propagation rate and fracture surface features. Both the crack propagation rate and fractographic features of surface cracks under 10(-4)-10(-6) Pa resembled those of internal cracks; therefore, the presumably working vacuum environment around internal cracks was considered to be at a high vacuum level.

Scanning Cyclic Pressを用いたマグネシウム合金の表面改質に及ぼす負荷繰返し数の影響
阿部 すずか, 藤村 奈央, 大賀 向陽, 髙橋 航圭, 中村 孝, 和島 達希
年次大会, 2020, J13107, 一般社団法人 日本機械学会, 2020年
日本語, A new surface modification technique, scanning cyclic press (SCP), was developed. SCP scans a metal surface with a vibrating indenter and refines the surface layer using cyclic compressive loading. This study applied SCP to the surface of magnesium alloy AZ31 under number of cyclic loading of 3.2×10⁵ and 8.0×10⁶ cycles to investigate the effect on surface structure. After applying SCP, the cross sections of specimens were observed by electron back scattering diffraction (EBSD) using SEM. As a result, a fine structure around 1－10 μm in grain size and a twin were formed in the surface layer of both specimens. The depth of these structures from the surface remained unchanged regardless of the number of cyclic loading. However, the surface structure under 8.0×10⁶ cycles was finer than that under 3.2×10⁵ cycles. This is likely caused by the increase of accumulated plastic strain during SCP process.

雰囲気制御scanning cyclic pressによる純チタンの常温窒化プロセスに関する検討
福田 哲也, 上遠野 寛, 藤村 奈央, 髙橋 航圭, 中村 孝, 和島 達希
年次大会, 2020, J13108, 一般社団法人 日本機械学会, 2020年
日本語, A new surface modification technique, scanning cyclic press (SCP), was applied to commercially pure titanium (CP-Ti) in a nitrogen atmosphere at room temperature. During the SCP process, a vibrating indenter reciprocally scanned the specimen’s surface to apply cyclic low compressive load. In this study, a possibility of a room-temperature-nitriding technique using SCP was investigated. Before and after SCP, the surface and the cross-section of the specimens were observed using a laser microscope and scanning ion microscope (SIM), respectively. Then, elemental and composition analyses were conducted by using EPMA and XRD. As a result, a pale golden color, which is known as a characteristic of titanium nitride coating, appeared at the surface of SCP-treated specimen. The SIM observation of the cross-section showed that a nanocrystalline structure was created in the surface layer, and the nitrogen element was detected in the same layer. The XRD analysis showed a strong possibility to form titanium nitride at the surface of SCP-treated specimen. These results suggested that nitrogen element surrounding the specimen diffused into the microstructure beneath the surface and likely created titanium nitride during SCP even at room temperature.

マルチスケール解析によるモルタル材料の損傷シミュレーション
大山 航汰, 高橋 航圭, 藤村 奈央, 中村 孝
年次大会, 2020, J03323, 一般社団法人 日本機械学会, 2020年
日本語, In this study, multi-scale analysis was carried out by designing a porous cement paste model, and a mortar model using glass spheres as fine aggregates. The tensile simulation of porous cement paste model was conducted by RVE model that reflects the distribution of pore size in a cement specimen. It was shown that the elastic modulus and strength of cement have a linear relationship with porosity. The finite element model of cylindrical samples was then created to simulate the splitting tensile test. For the cylindrical mortar model, spatial variation of the physical properties due to the porosity distribution in cement was reflected. When cement had a distribution of physical properties, the strength of the cement model was similar to that of mortar model as it was observed from the experiment, whereas the strength of the cement model was higher by 20 % if uniform physical properties were used for cement matrix. It was confirmed that our simulation well corresponded to the experimental result of at the ages of 28 days. In addition, the decrease in the strength, which would be expected for further aging mortar, can be also modeled by the porous layer at glass-cement interface, representing the Interfacial Transition Zone.

Surface modification of machine-finished magnesium alloy AZ31 using a scanning cyclic press
Nao Fujimura, Koyo Ooga, Kosuke Takahashi, Takashi Nakamura, Tatsuki Wajima
Mechanical Engineering Journal, 7, 4, JAPAN SOC MECHANICAL ENGINEERS, 2020年, ［査読有り］, ［筆頭著者, 責任著者］
英語, 研究論文（学術雑誌）, A machined material has a work-hardened layer at its surface. In this study, a surface modification technique, the scanning cyclic press (SCP), was applied to machined specimens of magnesium alloy, AZ31, to investigate whether SCP can improve its fatigue properties regardless of the surface finish. During the SCP process, a vibrating indenter reciprocally scanned the specimen's surface, and it applied cyclical low-compressive loadings to the surface for 8 x 10(6) cycles. After applying SCP, the surfaces of the specimens were observed using a laser scanning microscope, and the surface roughness was measured. The surface observation and surface roughness measurement showed that the changes in the surface state after applying SCP were relatively small and the surface roughness after applying SCP was more homogenous than before applying SCP. Uniaxial push-pull fatigue tests were conducted for SCP-treated specimens and untreated specimens. The test results showed that the fatigue life of SCP-treated specimens was longer than that of untreated specimens. To clarify the reason for the improvement effect, the fracture surfaces were observed using a scanning electron microscope (SEM). The SEM observation showed that the fracture morphology was different between the SCP-treated specimen and the untreated specimen. In the SCP-treated specimen, fatigue fracture origins were sub-surface, while the untreated specimen fractured at the surface. These results suggest that SCP could improve the fatigue properties of AZ31 regardless of the surface finish of the specimen before SCP.

放射光顕微CTによる高強度金属内部の高分解能非破壊観察
今 佑宇真, 中村 孝, 藤村 奈央, 吉中 奎貴, 髙橋 航圭, 竹内 晃久, 上椙 真之, 上杉 健太朗
M&M材料力学カンファレンス, 2019, PS22, 一般社団法人 日本機械学会, 2019年
日本語, To investigate the initiation and propagation processes of internal fatigue crack in high strength metallic materials, high resolution and non-destructive observation technique was proposed. The opening and closing behaviors of fatigue cracks in Ti-6Al-4V, and the non-metallic inclusions in SNCM439, which are regarded as a potential crack initiation site, were observed by synchrotron radiation CT (SR-CT) at SPring-8. To ensure a sufficient X ray transmission, fatigue specimens with a small diameter were designed, and a tensile loading jig was newly developed to measure the CTOD during SR-CT. In Ti-6Al-4V, micro CT and nano CT with a resolution around 1 μm and 200 nm, respectively, were used to observe internal cracks. As a result, it was clarified that surface cracks and internal cracks showed different behaviors. The crack tip of surface cracks had a sharp shape and the CTOD was changed by the tensile load. On the other hand, the shape of crack tips of internal cracks was blunted, and the tensile load did not affect CTOD. This crack blunting was explained by the vacuum-like environment around the internal crack. In SNCM439, small non-metallic inclusions with the size around 8 μm in diameter were clearly observed. Accordingly, it is expected that we can observe the initiation and propagation of internal cracks in high strength steel by repeating fatigue tests and SR-CT alternately.

真空環境下におけるき裂進展速度に基づく内部き裂の疲労寿命推定
ソラブ クマール モディ, メヘンディラッタ パラス, 塚越 拓摩, 中村 孝, 藤村 奈央, 髙橋 航圭
M&M材料力学カンファレンス, 2019, PS23, 一般社団法人 日本機械学会, 2019年
日本語, In recent years, it has been revealed that in high strength steel, fracture occurs from non-metallic inclusions inside of the material in the very high cycle region. However, because of the difficulty in directly observing the internal fatigue process, its mechanism is still unknown. Subsequently efforts are being made for better understanding of fatigue crack initiation and propagation. In this study, we have tried to estimate life in this subsurface fatigue region using crack growth rates measured in a vacuum environment and compare it with actual life found out in subsurface fractures in fatigue test to better understand fatigue crack properties.

表面改質技術Scanning Cyclic Pressによる低炭素鋼S25Cの疲労特性改善効果
丹野 椋子, 藤村 奈央, 中村 孝, 髙橋 航圭
M&M材料力学カンファレンス, 2019, PS01, 一般社団法人 日本機械学会, 2019年
日本語, In this study, we applied a new surface modification technique, scanning cyclic press (SCP) to machined specimens of low carbon steel S25C. In the SCP process, a vibrating indenter scans the metal surface and cyclically applies a variable low compressive load to modify the microstructure at the surface. During applying the SCP, the processing parameters, such as the scanning speed, the amount of compressive load and the number of cyclic loading, were changed to investigate the effects on the microstructure and the fatigue property. After applying the SCP, the surface roughness of specimens became smaller than that before. To clarify the changes in the microstructure beneath the surface of the SCP-treated specimens, the cross-section was created using focused ion beam technique. Scanning ion microscopic observations showed the microstructure refinement at the surface layer. The microstructure refinement was promoted with increasing the scanning speed, and the surface hardness also increased. Additionally, at the higher compressive load and the larger number of cyclic loading, finer microstructure was observed at the surface layer above the modified microstructure. This result suggested that the microstructure refinement is promoted by increasing the amount and the number of compressive loading. Fatigue test results showed that the fatigue lives of the SCP-treated specimens were 2 to 50 times longer than that of non-treated specimens.

Nano-structural refinement of metallic surfaces by using low-compression cyclical loading
N. Fujimura, T. Nakamura, M. Ueno
Mechanical Engineering Letters, 4, 2018年12月, ［査読有り］, ［筆頭著者, 責任著者］
英語, 研究論文（学術雑誌）

オーステナイト系ステンレス鋼の低サイクル疲労における表面性状の変化機構
藤村奈央, 西塚祐斗, 髙橋航圭, 中村孝
日本機械学会論文集, 84, 864, 2018年08月, ［査読有り］, ［筆頭著者, 責任著者］
日本語, 研究論文（学術雑誌）

Changing Mechanisms of Surface Relief and the Damage Evaluation of Low Cycle Fatigued Austenitic Stainless Steel
Nao Fujimura, Takashi Nakamura, Kosuke Takahashi
MATEC Web of Conferences, 165, EDP Sciences, 2018年05月25日, ［査読有り］, ［筆頭著者, 責任著者］
英語, 研究論文（国際会議プロシーディングス）, To quantitatively investigate the cause of the changes in arithmetic mean roughness Ra and arithmetic mean waviness Wa of austenitic stainless steel under low-cycle fatigue loading, precise observation focusing on persistent slip bands (PSBs) and crystal grain deformations was conducted on SUS316NG. During the fatigue tests, the specimen's surface topography was regularly measured using a laser microscope. The surface topographies were analysed by frequency analysis to separate the surface relief due to PSBs from that due to grain deformation. The height caused by PSBs and that by grain deformation were measured respectively. As a result, both of the heights rose with the increase of usage factor (UF). The amount of increase in the heights with respect to UF increased with strain range. The trend of development of both heights was similar with the trend of Ra and Wa. A comparison between Ra and the height caused by PSBs showed that these values strongly correlated with each other. A comparison between Wa and the height caused by grain deformation also showed that these values strongly correlated with each other. Consequently, the surface texture parameters Ra and Wa represent the changes in the heights of surface reliefs due to PSBs and grain deformation.

高強度鋼の疲労き裂進展特性に及ぼす真空環境の影響―ΔK漸増試験による微小き裂の挙動―
石原 梨沙, メヘンディラッタ パラス, 中村 孝, 藤村 奈央, 髙橋 航圭
M&M材料力学カンファレンス, 2018, OS0802, 一般社団法人 日本機械学会, 2018年
日本語, In recent years, it has been revealed that in high strength steel, fracture occurs from non-metallic inclusions inside of the material in the very high cycle region. However, because of the difficulty in directly observing the internal fatigue process, its mechanism is largely unknown. In this study, we try to clarify the internal fatigue process on the basis that the environment around an internal crack is like a vacuum environment. Also, it has been reported that the effect of vacuum environment is more prominent in the initial stages of crack propagation. This suggests that targeting the crack propagation process of small cracks, like that with the same size as a small defect, would shed light on the controlling factors in the internal fatigue process. Thus, we conducted ΔK-increasing tests in air and in vacuum using specimens with a small artificial defect on its surface. As a result, fatigue crack propagation rates in vacuum were lower than that in air. Also, when compared with the results of long cracks, the crack propagation rates in both environments were much higher. However, after eliminating the effect of crack closure for the results of long crack, the crack propagation rates in both environments matched.

高強度鋼の疲労き裂進展特性に及ぼす真空環境の影響-ΔK 漸減試験による長いき裂の挙動-
メヘンディラッタ パラス, 石原 梨沙, 中村 孝, 藤村 奈央, 高橋 航圭
M&M材料力学カンファレンス, 2018, OS0801, 一般社団法人 日本機械学会, 2018年
日本語, Sub-surface fractures are known as a characteristic fatigue mode of high strength steel in the very high cycle region. To reveal the mechanism of sub-surface fractures, ΔK-decreasing tests were conducted in high vacuum and air environments based on the idea that sub-surface cracks are exposed to a vacuum-like environment. As a result, fatigue crack growth rates in high vacuum were slower than those in air. In high vacuum, fatigue crack growth still took place at a considerably low rate around 10^-13 m/cycle, and the effective threshold stress intensity factor rage (ΔK_eff) in high vacuum lower to that in air. Unlike in air environment, negligible effects of oxide-induced crack closure in vacuum was considered as the reason for the results. The behavior of fatigue crack growth properties in high vacuum well explained the characteristics of sub-surface crack growths in very high cycle regime.

有限要素解析による樹脂材料の修復特性評価
長谷川 諒, 高橋 航圭, 藤村 奈央, 中村 孝
機械材料・材料加工技術講演会講演論文集, 2018.26, 910, 一般社団法人 日本機械学会, 2018年
日本語

両面粘着テープの併用による接着継手の強度向上
菊澤 卓馬, 高橋 航圭, 藤村 奈央, 中村 孝
機械材料・材料加工技術講演会講演論文集, 2018.26, 909, 一般社団法人 日本機械学会, 2018年
日本語

Scanning Cyclic Pressによるマグネシウム合金AZ31の表面改質と疲労特性改善効果
藤村 奈央, 中村 孝, 髙橋 航圭, 和島 達希
材料, 66, 12, 906, 912, 公益社団法人 日本材料学会, 2017年12月01日, ［査読有り］, ［筆頭著者, 責任著者］
日本語, 研究論文（学術雑誌）, A new surface modification technique, scanning cyclic press (SCP), was developed. SCP scans a metal surface with a vibrating indenter under precise loading control based on servo fatigue testing machine and can apply a variable cyclically compressive load. This study applied SCP to magnesium alloy AZ31 to investigate the effect on fatigue properties. After applying SCP, the surfaces of specimens were observed by using a laser scanning microscope and uniaxial push-pull fatigue tests were conducted. As a result, surface roughness of SCP-treated specimens slightly increased; however, the fatigue life became longer than that of untreated specimens. To clarify the reason for the improvement effect, fracture surfaces of the specimens were investigated in detail on the basis of SEM observation. SEM observation showed differences between the fracture surfaces of the untreated and SCP-treated specimens. The origin of fracture was at the surface in the untreated specimen. In the SCP-treated specimen, however, the fracture origins were sub-surface and a band-like layer just beneath the surface was observed on fracture surface, whereas the layer did not exist on that of untreated specimen. The surface hardness of SCP-treated specimen increased to almost twice as much after applying SCP. The result suggests that SCP modified surface layer of specimen and this layer suppressed crack initiation from surface.

Ti-22V-4Alにおける疲労き裂発生過程の観察
鹿島 彰太, 髙梨 圭, 吉中 奎貴, 中村 孝, 藤村 奈央, 髙橋 航圭
M&M材料力学カンファレンス, 2017, PS32, 一般社団法人 日本機械学会, 2017年
日本語, It is generally reported on titanium alloys that crack initiation occurs from a small flat plane called the “facet”. Thus, it is important to investigate facet formation processes in revealing the fatigue characteristics of titanium alloy. In the present work, β type titanium alloy Ti-22V-4Al was investigated in order to elucidate the fatigue crack initiation process. An axial load fatigue test was carried out with an etched specimen in order to examine the positional relationship between the microstructure and crack initiation site (in the grain or at the grain boundary). After the fatigue test, the fracture surface and the specimen surface were observed by using a scanning electron microscope. From the fracture surface observation, four crack propagation traces were observed on the fracture surface. When focusing on the crack initiation site, it was revealed that each crack initiated from a facet. Then, the facet angle was measured as the angle between the loading direction and the normal to the facet plane, which revealed that the shear stress largely contributed to crack initiation. The result of the specimen surface observation demonstrated that crack initiation occurred in β phase without α precipitate rather than at the β grain boundary. Therefore, in this sample material, crack initiated in β phase mainly by the shear stress.

Ti-22V-4Alにおける疲労き裂発生・進展特性
髙梨 圭, 鹿島 彰太, 吉中 奎貴, 中村 孝, 藤村 奈央, 髙橋 航圭
M&M材料力学カンファレンス, 2017, PS29, 一般社団法人 日本機械学会, 2017年
日本語, To investigate the fatigue crack initiation and propagation properties of Ti-22V-4Al, uniaxial fatigue tests and surface observation were carried out. As a result of surface observation, the crack initiation life of each crack was clarified. The cracks initiated at N = 2000 to 8000 cycles. Based on the crack initiation life of each crack, the tendency of crack initiation was investigated using probability paper. As a result, it was shown that the crack initiation life follows the lognormal distribution. Based on the crack propagation observation results, the relationship between the crack growth rate da/dN and the stress intensity factor range ΔK was investigated. As a result, in the small ΔK region, the dispersions of each crack was large. However, with the increase in ΔK, the dispersions became smaller and showed a certain width. Comparing with the same material with different heat treatment samples, da/dN-ΔK relations in large ΔK regions show similar value. So it suggests that crack propagation resistance may not be affected by the precipitation amount of α phase in this material.

AZ31の疲労特性に及ぼすScanning Cyclic Pressの影響
大賀 向陽, 藤村 奈央, 中村 孝, 髙橋 航圭, 和島 達希
M&M材料力学カンファレンス, 2017, PS27, 一般社団法人 日本機械学会, 2017年
日本語, Magnesium alloy is the lightest metal among all practical metals and recognized as a promising material; however, it has a limited use because of the poor fatigue properties. In this study, a new surface modification technique, scanning cyclic press (SCP), was applied to magnesium alloy AZ31 to improve its fatigue properties. SCP scans a metal surface with a vibrating indenter under precise loading control based on a servo testing machine and can apply a variable cyclically compressive load. The surface observation on AZ31 specimens showed an increase in surface roughness of SCP-treated specimens. However, the fatigue life of SCP-treated specimens clearly increased. Microstructure of a cross section of SCP-treated specimen was observed using an optical microscope. A fine mesh-patterned region was formed beneath the surface to a depth of 50 μm. The fracture surface observation showed that the fracture origin of SCP-treated specimens located in subsurface site whereas that of untreated specimens was at the surface of the specimen. The observation also showed a band-like layer just beneath surface in SCP-treated specimen which did not exist in the untreated specimen. The layer corresponded to the mesh-patterned region. The results suggested that SCP changed the surface microstructure of magnesium alloy and suppressed crack initiation from the specimen's surface.

低サイクル疲労を受けたSUS316NGの表面性状変化機構と損傷評価
藤村 奈央, 西塚 祐斗, 中村 孝, 髙橋 航圭
M&M材料力学カンファレンス, 2017, OS0527, 一般社団法人 日本機械学会, 2017年
日本語, To quantitatively investigate the cause of the changes in arithmetic mean roughness R_a and arithmetic mean waviness W_a of austenitic stainless steel under low-cycle fatigue loading, precise observation focusing on slip bands and grain deformations was conducted on SUS316NG. During the fatigue tests, the specimen's surface topography was regularly measured using a laser microscope. The surface topographies obtained were analyzed by frequency analysis to separate the surface relief due to persistent slip bands (PSBs) from that due to crystal grain deformation. The height caused by PSBs and that by crystal grain deformation were measured respectively. As a result, the both heights developed with the increase of usage factor (UF). The amount of increase in the heights with respect to UF increased with strain range. The trend of development of both heights was similar with the trend of R_a and W_a. A comparison between R_a and the height caused by PSBs showed that these values strongly correlated with each other. A comparison between W_a and the height caused by crystal grain deformation also showed that these values strongly correlated with each other. Consequently, the surface texture parameters R_a and W_a represent the changes in the heights of surface reliefs due to PSBs and crystal grain deformation.

Scanning cyclic pressを用いた金属表層の組織制御
中村 孝, 藤村 奈央, 水谷 一皓, 髙栁 伊吹, 和島 達希
年次大会, 2017, J1310106, 一般社団法人 日本機械学会, 2017年
日本語

ポリイミドフィルムにおける膜厚方向破壊靭性の計測と評価
南雲 慶憲, 坂本 悠介, 中村 孝, 藤村 奈央, 髙橋 航圭
M&M材料力学カンファレンス, 2016, OS05-10, 一般社団法人 日本機械学会, 2016年
日本語, Polyimide (PI) film with a surface small defect subjected to tensile load is fractured by the crack propagation from the defect in the film thickness direction. However, the evaluation method of fracture toughness in this type of fracture hasn’t yet been established. In this paper, SENT tests were carried out using 125 μm-thick PI films with a surface pre-crack having different depths from 10 μm to 60 μm, and fracture processes focusing on crack opening and crack extension were observed with a color 3D laser scanning microscope. Based on the results, fracture toughnesses J_in in the direction of film thickness were calculated by using two different equations for SENT specimen. As a result, J_in values were clarified to have a slight dependency on pre-crack depth. The differences between J_in values calculated by the two equations were considered small, and fracture toughness was in the range from 0.4 to 1 kJ/m².

Cyclic Pressによる低炭素鋼のナノ微細化表面改質
中村 孝, 中谷 建太朗, 宮崎 数則, 藤村 奈央, 柴山 環樹, 和島 達希
年次大会, 2016, J1610202, 一般社団法人 日本機械学会, 2016年
日本語

SUS316NGの低サイクル疲労における表面性状変化とその機構
西塚 祐斗, 藤村 奈央, 中田 康敬, 上遠野 寛, 中村 孝
年次大会, 2016, J0310101, 一般社団法人 日本機械学会, 2016年
日本語, To investigate the cause of the change of arithmetic mean roughness R_a and arithmetic mean waviness W_a of austenitic stainless steel under low-cycle fatigue loading, precise observation focusing on slip bands and grain deformations was conducted on SUS316NG. During the fatigue tests, the specimen's surface topography was regularly measured using a laser microscope. The surface topographies obtained were analyzed by frequency analysis to separate the surface relief due to persistent slip bands from that due to crystal grain deformation. The height caused by persistent slip bands and that by crystal grain deformation were measured respectively. As a result, the both heights in initial stage of usage factor (UF) more developed compared with those in later stage of UF. The amount of increase in the heights with respect to UF increased with strain range. The trend of development of both heights was similar with the trend of R_a and W_a.

ナノ微細化表面改質を目的とするScanning Cyclic Pressの開発と低炭素鋼への適用
宮崎 数則, 中村 孝, 藤村 奈央, 柴山 環樹, 和島 達希
年次大会, 2016, J1610203, 一般社団法人 日本機械学会, 2016年
日本語, A surface modification technique named as scanning cyclic press (SCP) was newly developed, which refines the surface layer of metallic materials by scanning metal surface with a vibrating indenter. This study applied SCP to the surface of low carbon steel S25C and conducted surface observation, cross-sectional observation, and push-pull fatigue tests followed by fracture surface observation. As a result, SCP modification improved surface roughness and generated gradient structure consisting of nanocrystalline and refined layers. This technique also improved fatigue life compared with that of untreated specimens. Fracture surface observation indicated that nano-structural layer formed in the outermost surface of the specimen suppressed initiation of fatigue crack and improved fatigue properties of refined material.

Quantitative characterization of the changes in surface topography of austenitic stainless steel under low cycle fatigue loading
Tomoki Shinko, Takashi Nakamura, Nao Fujimura, Yasutaka Nakata
Zairyo/Journal of the Society of Materials Science, Japan, 64, 11, 910, 917, Society of Materials Science Japan, 2015年, ［査読有り］
英語, 研究論文（学術雑誌）, Low-cycle fatigue tests of SUS316NG austenitic stainless steel were conducted for several strain ranges (0.76, 1.26, 2.1, 4.1, and 8.1%) in which the specimen’s surface topography was regularly measured using a laser scanning microscope. The surface topographies obtained were analyzed by frequency analysis to separate the surface relief due to persistent slip bands (PSBs) from that due to crystal grain deformation. The PSBs-induced surface relief evolution and the grain-deformation-induced one were quantitatively evaluated by using arithmetic mean roughness Ra and arithmetic mean waviness Wa, respectively. The Î"Ra and Î"Wa, the increments in Ra and Wa from the initial values, increased with the usage factor (UF) for each strain range. Moreover, the rates of increase in Î"Ra and Î"Wa with respect to UF increased with the strain range. Î"Wa/Î"Ra was larger for higher strain ranges. This tendency of Î"Wa/Î"Ra indicates that the surface relief due to grain deformation develops more prominently than that due to PSBs for larger strain ranges. The results for Ra and Wa agree with the results of surface topography observation. On the basis of these results, a method was developed for estimating the UF of fatigued material and the applied strain range by using only the measured Ra and Wa.

APPLICATION OF SURFACE ROUGHNESS PARAMETERS TO THE EVALUATION OF LOW CYCLE FATIGUE DAMAGE IN AUSTENITIC STAINLESS STEEL
Nao Fujimura, Takashi Nakamura, Hiroyuki Oguma
PROCEEDINGS OF THE ASME PRESSURE VESSELS AND PIPING CONFERENCE - 2013, VOL 5, AMER SOC MECHANICAL ENGINEERS, 2014年, ［査読有り］, ［筆頭著者］
英語, 研究論文（国際会議プロシーディングス）, Changes in the surface roughness of SUS316NG during cyclic loadings were investigated, and the relations between those changes and the crack initiation and propagation processes are discussed on the basis of microscopic observations and cellulose acetate replica observations. Strain-controlled fatigue tests were conducted at three constant strain ranges. Surface roughness was measured periodically during the tests, and three roughness parameters were calculated: arithmetic mean roughness R-a, surface profile maximum height R-max, and maximum valley depth R-v. Until the middle of fatigue life, all three increased linearly with the number of cycles regardless of the strain range, and their rates of increase became smaller with decreasing strain range. Surface observation revealed that small cracks initiated very early in fatigue life, propagated slowly until the middle of fatigue life, and then grew rapidly. Changes in surface roughness are therefore sensitive to fatigue loading even when cracks are very small and crack detection is difficult. The results suggest that surface roughness can probably be used to assess fatigue damage because until the middle of fatigue life it increases linearly with the number of cycles. The definition of each roughness parameter and the changes show that R-max and R-v are suitable for damage assessment.

表面粗さ測定に基づくSUS316NGの疲労損傷評価と適用範囲
藤村奈央, 中村孝, 小熊博幸, 中島智広, 信耕友樹
材料, 62, 12, 750, 755, The Society of Materials Science, Japan, 2013年12月, ［査読有り］, ［筆頭著者］
日本語, 研究論文（学術雑誌）, Changes in the surface roughness of SUS316NG during cyclic loadings were investigated, and the relationship between those changes and the fatigue damage processes, including evolution of surface relief due to active slip systems, were discussed on the basis of microscopic observations. Strain-controlled fatigue tests were conducted at three constant strain ranges Δε = 8, 4, and 1%. During the tests, surface roughness was measured periodically at cycles determined with respect to the usage factor UF, and then the surface was observed directly to clarify the surface morphology. As a result, until the middle of fatigue life, the arithmetic mean roughness R<font size="-1">a</font> increased linearly with the number of cycles regardless of the strain range conditions. Clear changes in surface roughness were obtained even at a strain range as small as 1%. The results suggest that the surface roughness measurement can probably be used to assess fatigue damage because it increases linearly with the number of cycles until the middle of fatigue life. The rate at which surface roughness increased with UF became smaller with decreasing applied strain range. In the damage process, the surface became uneven because of active slip systems and the asperity became larger when the number of cycles increased. Surface observations revealed that the number of slip bands decreased and the development of the asperity became more difficult with decreasing applied strain range. The change tendencies of surface roughness were similar to those of the density of slip bands at each strain range. This shows that the rate at which surface roughness increased with UF is affected by the number of slip bands at each strain range condition.

Changes in Surface Roughness during Low Cycle Fatigue Process of Austenitic Stainless Steel
Nao FUJIMURA, Takashi NAKAMURA, Hiroyuki OGUMA
Journal of Solid Mechanics and Materials Engineering, 7, 3, 372, 380, The Japan Society of Mechanical Engineers, 2013年, ［査読有り］, ［筆頭著者］
英語, Changes in surface roughness during low cycle fatigue loading were investigated on austenitic stainless steel, SUS316NG, commonly used in the piping systems of nuclear power plants. The fatigue damage process, including crack initiation and propagation, was observed using cellulose acetate replicas, and the relationship between the process and changes in surface roughness was discussed. Strain-controlled fatigue tests were conducted on mirror polished specimens at constant strain range conditions Δε = 8, 4, and 1%. During the cyclic loadings, the surface roughness was measured at cycles determined with respect to the usage factor UF_pre. As a result, the surface roughness was found to increase roughly linearly until approximately UF_pre = 0.4 regardless of the strain range conditions. The rate at which surface roughness increased with UF_pre became smaller with decreasing applied strain range. In the damage process, small cracks were observed to initiate very early in fatigue life. The cracks propagated slowly until about the middle of fatigue life, however it grew rapidly after around UF_pre = 0.6. These results showed that the change in surface roughness is sensitive to fatigue loading even when cracks are very small and crack detection is difficult. The obtained results suggest that surface roughness can probably be used to assess fatigue damage until the middle of fatigue life because of its linear increase with respect to the number of cycles.

DAMAGE ASSESSMENT ON LOW CYCLE FATIGUE PROPERTIES OF CYCLIC PRE-STRAINED AUSTENITIC STAINLESS STEEL
Nao Fujimura, Hiroyuki Oguma, Takashi Nakamura
PROCEEDINGS OF THE ASME PRESSURE VESSELS AND PIPING CONFERENCE VOL 1, 1061, 1067, AMER SOC MECHANICAL ENGINEERS, 2012年, ［査読有り］, ［筆頭著者］
英語, 研究論文（国際会議プロシーディングス）, The effects of cyclic pre-strain on low cycle fatigue properties of austenitic stainless steel were investigated, and the fatigue damage was assessed based on several parameters such as the full width at half maximum (FWHM) of diffracted X-ray profile and surface roughness of specimens. The strain-controlled tests were conducted under strain ratio R epsilon = -1 and various constant total strain ranges. Also the change in remnant fatigue lives were investigated when the cyclic pre-strain were applied to the specimens under the different number of cycles which were determined with reference to the usage factor UFpre ranged from 0.2 to 0.8. As a result, the remnant fatigue life of the pre-strained samples became shorter than that of the sample without pre-strain as the UFpre increased. The relationship between the pre-strain damage expressed in UFpre and the remnant fatigue damage in UFpost was roughly described by the cumulative linear damage law: UTpre + UFpost = 1. Namely, the cyclic pre-strain affected the remnant fatigue lives. In order to evaluate the effects of cyclic pre-strain on fatigue lives more precisely, the damage in the cyclic pre-straining processes was estimated by using FWHM and surface roughness. The FWHM of the specimens with pre-strain once decreased with increase in UFpre, and then increased after showing a minimum value. The surface roughness of specimens increased linearly with an increase of the number of pre-straining cycles. These results suggested that the damage due to pre-strain can be assessed by means of FWHM and surface roughness of specimens.

Scanning cyclic pressによる表面改質を施したマグネシウム合金の疲労特性
藤村奈央, 高橋航圭, 中村孝, 和島達希, 疲労シンポジウム講演論文集, 36th, 2024年

βチタン合金における内部疲労き裂進展特性
XUE Gaoge, 藤村奈央, 高橋航圭, 中村孝, 疲労シンポジウム講演論文集, 36th, 2024年

(α+β)Ti-6Al-4Vにおける内部疲労き裂の繰返し圧縮負荷による凝着挙動
舩木優大, 増谷幸香, XUE Gaoge, 高橋航圭, 藤村奈央, 中村孝, 疲労シンポジウム講演論文集, 36th, 2024年

析出硬化ステンレス鋼SUS630の表面および内部起点型微小疲労き裂進展特性
上野竜史, XUE Gaoge, 舩木優大, 高橋航圭, 藤村奈央, 中村孝, 疲労シンポジウム講演論文集, 36th, 2024年

析出硬化ステンレス鋼SUS630における内部微小疲労き裂の発生・進展挙動
中村孝, 五十嵐元, 藤村奈央, 高橋航圭, 日本材料学会学術講演会講演論文集(CD-ROM), 73rd, 2024年

破面解析に基づくTi-22V-4Al合金における内部疲労き裂の発生・進展過程
薛 高格, 藤村 奈央, 中村 孝, 小熊 博幸, 髙橋 航圭, M&M材料力学カンファレンス, 2019, 0, OS0908, 2019年

Uniaxial fatigue tests of Ti-22V-4Al alloy were carried out up to very high cycle regime at various stress ratios. In case of internal crack, so-called facets regarded as a crack initiation site were found from the fracture surface. To figure out the internal crack initiation and propagation process, fractographic analysis using 3D SEM was conducted. Material constants "C" and "m" in the Paris law were obtained by comparing the characteristics of facets around the fracture origins to estimate fatigue life caused by internal crack, and a new model of facet initiation process was proposed. As a result, the internal crack fatigue life estimation using the proposed model was clarified to be effective to evaluate experimental results.

, 一般社団法人 日本機械学会, 日本語

放射光顕微CTによるTi-6Al-4Vの内部疲労き裂発生過程
中村 孝, 友田 悠太, 藤村 奈央, 吉中 奎貴, 小熊 博幸, 竹内 晃久, 上椙 真之, 上杉 健太朗, M&M材料力学カンファレンス, 2019, 0, OS0909, 2019年

The initiation process of internal fatigue cracks in Ti-6Al-4V in very high cycle regime was investigated via synchrotron radiation X-ray CT. A projection-type CT with a resolution of one micrometer or below and a phase contrast imaging-type CT with a resolution of sub-micrometer were used. The projection-type CT revealed that 1) more than twenty cracks initiated in one specimen, 2) fatigue life varied widely from 20% to 70% of the average fatigue life, and 3) whether the initiated crack can smoothly propagate or not was determined by the nonuniformity of surrounding microstructure. The imaging-type CT clarified that the crack initiation was caused by slip deformation in α phase and that the shape of internal crack tip was blunter than that of surface crack tip.

, 一般社団法人 日本機械学会, 日本語

OS0913-454 低サイクル疲労損傷を受けたSU5316NGにおける表面粗さの分布特性
藤村 奈央, 中村 孝, 信耕 友樹, M&M材料力学カンファレンス, 2015, "OS0913, 454-1"-"OS0913-454-3", 2015年11月21日
To statistically investigate the changes and the distributions in surface roughness, strain controlled low cycle fatigue tests of austenitic stainless steel were conducted under strain range Δε=8, 4%. During the tests, the specimen's surface topography was regularly measured using a laser scanning microscope. The surface topographies obtained were analyzed by frequency analysis to separate the surface relief due to persistent slip bands. The persistent-slip-bands-induced surface relief evolution was quantitatively evaluated by using arithmetic mean roughness R_a. As a result, R_a at Δε=8, 4% increased with the increase of UF (Usage Factor). The R_a data were plotted roughly linearly on a log-normal probability paper. It suggests that R_a likely follows a log-normal distribution. On the probability papers, the slope of R_a plots and the average value at Δε=8, 4% were clearly different. It shows that the distribution form of R_a varies between different Δε. The slopes of R_a plots at each UF were similar on the paper. It showed that the dispersion of R_a data didnot change even if UF increases., 一般社団法人日本機械学会, 日本語

G0301502 二段二重低サイクル疲労におけるSUS316NGの表面性状評価
中田 康敬, 西塚 祐斗, 信耕 友樹, 藤村 奈央, 中村 孝, 年次大会 : Mechanical Engineering Congress, Japan, 2015, "G0301502, 1"-"G0301502-5", 2015年09月13日
To investigate the effects of change in loading amplitude on surface topography, two-step loaded low-cycle fatigue tests of SUS316NG austenitic stainless steel were conducted. During the tests, the specimen's surface topography was regularly measured using a laser scanning microscope. The surface topographies obtained were analyzed by frequency analysis to separate the surface relief due to persistent slip bands from that due to crystal grain deformation. The persistent-slip-bands-induced surface relief evolution and the grain-deformation-induced one were quantitatively evaluated by using arithmetic mean roughness R_a and arithmetic mean waviness W_a, respectively. As a result, the rates of increase in R_a and W_a changed obviously after changing loading amplitude. The results for R_a and W_a agree with the results of surface observation, the increases in the numbers of slip bands and deformed crystal grains changed after changing loading amplitude., 一般社団法人日本機械学会, 日本語

142 低サイクル疲労過程におけるSUS316NGの表面性状評価(材料力学・機械材料)
中田 康敬, 信耕 友樹, 藤村 奈央, 中村 孝, 北海道支部講演会講演概要集, 2014, 53, 27, 28, 2014年09月27日
一般社団法人日本機械学会, 日本語

OS2126 オーステナイトステンレス鋼の渦電流信号に及ぼす表面粗さの影響
堀川 紀孝, 濱口 萌愛, 藤村 奈央, 中村 孝, M&M材料力学カンファレンス, 2014, "OS2126, 1"-"OS2126-3", 2014年07月19日
Austenite stainless steel is widely used in power plants and nondestructive damage estimation method is required to determine the damage on the structure due to fatigue or earthquake. Eddy current method is one of the nondestructive inspection technique, and it reflects the surface condition of the metal. Surface roughness of the specimen increased by the deformation and the roughness change is used to estimate the damage by the low cycle fatigue. This report deals with the eddy current signal change due to the surface roughness. Test pieces of SUS316 with 6mm in diameter were prepared, and the surface was ground with emery paper. Eddy current testing was carried out with two types of the probe and testing frequency of 200kHz and 1MHz. Eddy current signal, which is output of the eddy current instrument, were measured. Eddy current signal was changed by surface grinding. Grinding on the surface showed significant effect on the eddy current signal. It is caused by removal of residual stress near the surface of the test piece that induced by the drawing process. Difference in the eddy current signal by the surface roughness within 1μm in Ra is quite small and higher testing frequency is required to distinguish the difference., 一般社団法人日本機械学会, 日本語

OS0820 SUS316NGの二段二重低サイクル疲労における表面粗さの変化
藤村 奈央, 中村 孝, 小熊 博幸, 新沼 賢基, M&M材料力学カンファレンス, 2014, "OS0820, 1"-"OS0820-3", 2014年07月19日
Changes in surface roughness of SUS316NG during cyclic variable loadings were investigated. Strain controlled two-step fatigue tests were conducted under two different strain ranges. In the tests, strain range was switched from Δε_H=4% to Δε_L=2% or from Δε_L=2% to Δε_H=4% at the usage factor UF=0.2. The specimen's surface was observed by a laser scanning microscope to clarify the surface profile and surface roughness R_a. As a result, R_a increased with UF during the first and second steps in the two-step tests. The increasing rate of R_a at the second step became smaller after strain range was changed from 4% to 2%, whereas it became larger after strain range was changed from 2% to 4%. The increasing tendencies of Ra at each step were similar to those in fatigue test under constant strain ranges Δε=4% and 2%, respectively. The results suggest that changes in surface roughness under two-step variable loadings can be described by superimposing R_a values in order of loading, which were obtained under constant strain range tests. Surface observation revealed that the height change in surface profile during each loading step varied depending on the strain range. This shows that the history of strain range affected the changes in surface profile, and it is the reason that the increasing rate of R_a changed in the two-step tests., 一般社団法人日本機械学会, 日本語

OS0819 低サイクル疲労損傷を受けたオーステナイト系ステンレス鋼における表面性状の定量的評価
信耕 友樹, 藤村 奈央, 中田 康敬, 小熊 博幸, 中村 孝, M&M材料力学カンファレンス, 2014, "OS0819, 1"-"OS0819-3", 2014年07月19日
Low-cycle fatigue tests of SUS316NG were conducted under conditions of strain range Δε=2, 4 and 8%. During the fatigue tests, changes in surface relief of specimen were measured by a laser scanning microscope. The surface roughening due to slip bands and deformation of grains was quantitatively evaluated by using arithmetic average roughness R_a and arithmetic average waviness W_a respectively. As a result, R_a and W_a increased with the increase of UF (Usage Factor), and the increasing rates of R_a and W_a with respect to UF became larger in larger strain ranges. The ratio of increasing rate of W_a to R_a also became larger in larger strain ranges. This result indicates that the surface roughening due to deformation of grains is caused more significantly than that due to slip bands is in larger strain ranges. Based on the different tendencies of R_a and W_a, we suggested a new damage evaluation method which can estimate UF and applied strain range of fatigued material., 一般社団法人日本機械学会, 日本語

PS15 SUS316NGの低サイクル疲労における表面性状の変化
新沼 賢基, 藤村 奈央, 信耕 友樹, 中村 孝, 小熊 博幸, M&M材料力学カンファレンス, 2013, "PS15, 1"-"PS15-3", 2013年10月12日
A strain controlled two step test was conducted to investigate changes in the surface features of SUS316NG during cyclic variable loading. In the two step test, strain range was switched from Δ_<εH> = 4% to Δ_<εL> = 2% at the usage factor UF= 0.2. The specimen surface was observed by a laser microscope to clarify the surface morphology and surface roughness R=a. Initiation and propagation of the main crack was also observed by using cellulose acetate replica The results in the two step test were compared with those obtained in fatigue tests under constant strain ranges. As a result changes in surface features such as slip bands and surface asperities clearly depended on the value of strain ranges even under the same UF value. Small cracks initiated very early in the fatigue life, however, they hardly propagated until the middle of fatigue life. In contrast, Ra clearly increased from the beginning to the middle of fatigue life. These results suggest that surface roughness can be an effective parameter for fatigue damage assessment. In addition, the increasing rates of Ra during the first and second steps in two step test were similar to those in fatigue tests under constant strain ranges Δ_ε = 4% and Δ_ε = 2%, respectively. Therefore, the history of strain range under cyclic variable loadings can probably be described from the value of R_a and the increasing rate of R_a in the fatigue tests under constant strain ranges., 一般社団法人日本機械学会, 日本語

108 表面粗さに基づいたSUS316NGの低サイクル疲労損傷評価(材料力学III)
信耕 友樹, 藤村 奈央, 新沼 賢基, 小熊 博幸, 中村 孝, 北海道支部講演会講演概要集, 2013, 52, 15, 16, 2013年09月28日
一般社団法人日本機械学会, 日本語

214 オーステナイト系ステンレス鋼の低サイクル疲労特性と損傷評価(材料力学V)
中島 智広, 藤村 奈央, 新沼 賢基, 小熊 博幸, 中村 孝, 北海道支部講演会講演概要集, 2012, 51, 65, 66, 2012年10月20日
一般社団法人日本機械学会, 日本語

OS2109 オーステナイト系ステンレス鋼の低サイクル疲労における表面粗さの影響
藤村 奈央, 中村 孝, 小熊 博幸, M&M材料力学カンファレンス, 2012, "OS2109, 1"-"OS2109-3", 2012年09月22日
The effects of surface roughness on low cycle fatigue properties were investigated by strain-controlled fatigue tests using specimens of austenitic stainless steel finished by two different methods: machining and mirror polishing. During fatigue tests, the surface roughness of each specimen was measured, and crack initiation and propagation were observed using cellulose acetate replicas. As a result, the fatigue life of mirror polished specimen was longer than that of machined one. It was shown that the surface roughness affected the fatigue life. The change of surface roughness of each specimen showed the same increasing tendency with respect to the number of cycles. However, around the end of fatigue life, the surface roughness of mirror polished specimen became larger than that of machined one. In the damage process, the crack initiated at the very early stage of fatigue life. The crack growth rate was small until the middle of fatigue life; however, it increased rapidly after that. The surface roughness affected the crack initiation, and that is the reason why the fatigue life and the change of surface roughness were different between each specimen., 一般社団法人日本機械学会, 日本語

704 オーステナイト系ステンレス鋼の低サイクル疲労特性に及ぼす繰返し予ひずみの影響と損傷評価(変動応力・予ひずみ効果,疲労損傷観察ならびに強度評価,オーガナイスドセッション1)
藤村 奈央, 小熊 博幸, 中村 孝, 学術講演会講演論文集, 61, 181, 182, 2012年
日本材料学会, 日本語

220 繰返し予ひずみを受けたSUS316NGの低サイクル疲労特性(材料力学VII)
中島 智広, 藤村 奈央, 小熊 博幸, 中村 孝, 北海道支部講演会講演概要集, 2011, 50, 77, 78, 2011年10月01日
一般社団法人日本機械学会, 日本語

604 原子力構造用材料の低サイクル疲労特性に及ぼす繰返し予ひずみの影響(計算力学・材料力学I)
藤村 奈央, 小熊 博幸, 中村 孝, 北海道支部講演会講演概要集, 2010, 49, 145, 146, 2010年11月07日
一般社団法人日本機械学会, 日本語

534 オーステナイト系ステンレス鋼の低サイクル疲労特性に及ぼす平均ひずみの影響(予ひずみ・平均ひずみ・平均応力の影響,疲労研究の課題と展望,オーガナイスドセッション1)
藤村 奈央, 水門 恵理, 中村 孝, 小熊 博幸, 学術講演会講演論文集, 59, 405, 406, 2010年
日本材料学会, 日本語

Ti-22V-4Alの内部疲労破壊に及ぼす寸法効果の影響　　　　　　　　　　　　　　　
陳 柏育, 薛 高格, 中村 孝, 藤村 奈央, 髙橋 航圭
日本機械学会 M&M2021材料力学カンファレンス, 2021年09月15日, 英語, 口頭発表（一般）
2021年09月15日 - 2021年09月16日

(α+β) Ti-6Al-4Vの内部疲労破壊におけるマルチファセット形成過程　　　　　　　　　　　　　　　
山崎 拓也, 森下 弘法, 友田 悠太, 中村 孝, 藤村 奈央, 髙橋 航圭
日本機械学会 M&M2021材料力学カンファレンス, 2021年09月15日, 日本語, 口頭発表（一般）
2021年09月15日 - 2021年09月16日

Analysis of fatigue life distribution of Ti-6Al-4V based on the initiation and propagation behaviors of small internal cracks　　　　　　　　　　　　　　　
Hironori Morishita, Takashi Nakamura, Nao Fujimura, Kosuke Takahashi
Eighth International Conference on Very High Cycle Fatigue (VHCF8), 2021年07月09日, 英語, 口頭発表（一般）
2021年07月05日 - 2021年07月09日

Classification of internal fatigue crack growth stages of (α+β) Ti-6Al-4V by fractographic analysis focusing on multiple facet formation　　　　　　　　　　　　　　　
Takuya Yamazaki, Hironori Morishita, Yuta Tomoda, Takashi Nakamura, Nao Fujimura, Kosuke Takahashi
Eighth International Conference on Very High Cycle Fatigue (VHCF8), 2021年07月09日, 英語, 口頭発表（一般）
2021年07月05日 - 2021年07月09日

Improvement of the fatigue property of magnesium alloy AZ31 through a new surface modification technique: scanning cyclic press　　　　　　　　　　　　　　　
Nao Fujimura, Suzuka Abe, Koyo Ooga, Takashi Nakamura, Kosuke Takahashi, Tatsuki Wajima
Eighth International Conference on Very High Cycle Fatigue (VHCF8), 2021年07月09日, 英語, 口頭発表（一般）
2021年07月05日 - 2021年07月09日

Initiation and propagation process of small fatigue crack in beta titanium alloy via multiscale synchrotron radiation computed tomography　　　　　　　　　　　　　　　
Gaoge Xue, Takashi Nakamura, Nao Fujimura, Hiroyuki Oguma, Akihisa Takeuchi, Masayuki Uesugi, Kentaro Uesugi
Eighth International Conference on Very High Cycle Fatigue (VHCF8), 2021年07月06日, 英語, 口頭発表（一般）
2021年07月05日 - 2021年07月09日

Nondestructive observation of internal fatigue crack initiation in Ti-6Al-4V via synchrotron radiation X-ray CT　　　　　　　　　　　　　　　
Fumiyoshi Yoshinaka, Takashi Nakamura, Hiroyuki Oguma, Nao Fujimura, Akihisa Takeuchi, Masayuki Uesugi, Kentaro Uesugi
Eighth International Conference on Very High Cycle Fatigue (VHCF8), 2021年07月06日, 英語, 口頭発表（一般）
2021年07月05日 - 2021年07月09日

Sanning Cyclic Pressを用いたマグネシウム合金の表面改質に及ぼす負荷繰返し数の影響　　　　　　　　　　　　　　　
阿部すずか, 藤村奈央, 大賀向陽, 髙橋航圭, 中村孝, 和島達希
日本機械学会 2020年度年次大会, 2020年09月

微小内部き裂の発生・進展挙動に基づくα+β型チタン合金の疲労寿命分布解析　　　　　　　　　　　　　　　
森下弘法, 中村孝, 藤村奈央, 髙橋航圭
日本材料学会第69期学術講演会, 2020年05月

表面改質技術Scanning Cyclic Pressを施した低炭素鋼S25Cの疲労特性　　　　　　　　　　　　　　　
藤村奈央, 丹野椋子, 宮﨑数則, 中村孝
日本材料学会 第69期学術講演会, 2020年05月

Scanning Cyclic Pressを施したマグネシウム合金の疲労特性と表層組織観察　　　　　　　　　　　　　　　
藤村奈央, 大賀向陽, 大久保賢二, 中村孝, 髙橋航圭, 和島達希
日本材料学会第68期学術講演会, 2019年05月24日, 日本語, 口頭発表（一般）
［国内会議］

Ti-6Al-4Vにおける表面および内部微小疲労き裂の開閉口挙動　　　　　　　　　　　　　　　
友田悠太, 中村孝, 藤村奈央, 吉中奎貴, 小熊博幸, 竹内晃久, 上椙真之, 上杉健太朗
日本材料学会第68期学術講演会, 2019年05月, 口頭発表（一般）
2019年05月 - 2019年05月

接着継手強度に及ぼす両面テープ併用の効果　　　　　　　　　　　　　　　
髙橋航圭, 菊澤卓馬, 藤村奈央, 中村孝
日本材料学会第68期学術講演会, 2019年05月, 口頭発表（一般）

大気および真空環境における微小疲労き裂の進展・停留挙動　　　　　　　　　　　　　　　
塚越拓摩, 石原梨沙, Paras MEHENDIRATTA, 中村孝, 藤村奈央, 髙橋航圭
日本材料学会第68期学術講演会, 2019年05月, 口頭発表（一般）

放射光顕微CTによるTi-6Al-4Vの内部疲労き裂発生過程
中村 孝, 友田 悠太, 藤村 奈央, 吉中 奎貴, 小熊 博幸, 竹内 晃久, 上椙 真之, 上杉 健太朗
M&M材料力学カンファレンス, 2019年, 一般社団法人 日本機械学会, 日本語
2019年 - 2019年,

The initiation process of internal fatigue cracks in Ti-6Al-4V in very high cycle regime was investigated via synchrotron radiation X-ray CT. A projection-type CT with a resolution of one micrometer or below and a phase contrast imaging-type CT with a resolution of sub-micrometer were used. The projection-type CT revealed that 1) more than twenty cracks initiated in one specimen, 2) fatigue life varied widely from 20% to 70% of the average fatigue life, and 3) whether the initiated crack can smoothly propagate or not was determined by the nonuniformity of surrounding microstructure. The imaging-type CT clarified that the crack initiation was caused by slip deformation in α phase and that the shape of internal crack tip was blunter than that of surface crack tip.

破面解析に基づくTi-22V-4Al合金における内部疲労き裂の発生・進展過程　　　　　　　　　　　　　　　
薛 高格, 藤村 奈央, 中村 孝, 小熊 博幸, 髙橋 航圭
M&M材料力学カンファレンス, 2019年, 一般社団法人 日本機械学会, 日本語
2019年 - 2019年,

Uniaxial fatigue tests of Ti-22V-4Al alloy were carried out up to very high cycle regime at various stress ratios. In case of internal crack, so-called facets regarded as a crack initiation site were found from the fracture surface. To figure out the internal crack initiation and propagation process, fractographic analysis using 3D SEM was conducted. Material constants "C" and "m" in the Paris law were obtained by comparing the characteristics of facets around the fracture origins to estimate fatigue life caused by internal crack, and a new model of facet initiation process was proposed. As a result, the internal crack fatigue life estimation using the proposed model was clarified to be effective to evaluate experimental results.

Changing mechanisms of surface relief and the damage evaluation of low cycle fatigued austenitic stainless steel　　　　　　　　　　　　　　　
N. Fujimura, T. Nakamura, K. Takahashi
12th international fatigue congress Fatigue 2018, 2018年05月, 英語, 口頭発表（一般）
［国際会議］

加熱修復機能を有する樹脂材料の硬化成形温度の検討　　　　　　　　　　　　　　　
岸本繁人, 高橋航圭, 中村孝, 藤村奈央
日本材料学会 第3回材料WEEK 若手学生研究発表会, 2017年10月11日, 日本語, ポスター発表
［国内会議］

Scanning Cyclic Pressによるアルミニウム合金のナノ微細化表面改質　　　　　　　　　　　　　　　
髙栁伊吹, 中村孝, 藤村奈央, 高橋航圭, 和島達希
2017年10月11日, 日本語, ポスター発表
［国内会議］

走査型 Cyclic Press “SCP”の開発と低炭素鋼の表面改質　　　　　　　　　　　　　　　
水谷一皓, 中村孝, 藤村奈央, 高橋航圭, 和島達希
日本材料学会 第3回材料WEEK 若手学生研究発表会, 2017年10月11日, 日本語, ポスター発表
［国内会議］

振動圧縮荷重を用いた表面改質技術“Cyclic Press”の提案とチタン合金への適用　　　　　　　　　　　　　　　
上遠野寛, 中村孝, 吉中奎貴, 藤村奈央, 高橋航圭, 和島達希
日本材料学会 第3回材料WEEK 若手学生研究発表会, 2017年10月11日, 日本語, ポスター発表
［国内会議］

OS0527 低サイクル疲労を受けたSUS316NGの表面性状変化機構と損傷評価　　　　　　　　　　　　　　　
藤村奈央, 西塚祐斗, 中村孝, 髙橋航圭
M&M2017材料力学カンファレンス, 2017年10月08日, 日本語, 口頭発表（一般）
［国内会議］

PS32 Ti-22V-4Al における疲労き裂発生過程の観察　　　　　　　　　　　　　　　
鹿島彰太, 髙梨圭, 吉中奎貴, 中村孝, 藤村奈央, 髙橋航圭
M&M2017材料力学カンファレンス, 2017年10月07日, 日本語, ポスター発表
［国内会議］

PS29 Ti-22V-4Alにおける疲労き裂発生・進展特性　　　　　　　　　　　　　　　
髙梨圭, 鹿島彰太, 吉中奎貴, 中村孝, 藤村奈央, 髙橋航圭
M&M2017材料力学カンファレンス, 2017年10月07日, 日本語, ポスター発表
［国内会議］

PS27 AZ31の疲労特性に及ぼすScanning cyclic pressの影響　　　　　　　　　　　　　　　
大賀向陽, 藤村奈央, 中村孝, 髙橋航圭, 和島達希
M&M2017材料力学カンファレンス, 2017年10月07日, 日本語, ポスター発表
［国内会議］

J1310106 Scanning cyclic pressを用いた金属表層の組織制御　　　　　　　　　　　　　　　
中村孝, 藤村奈央, 水谷一皓, 髙栁伊吹, 和島達希
日本機械学会年次大会, 2017年09月04日, 日本語, 口頭発表（一般）
［国内会議］

155 Development of a new surface modification technique: scanning cyclic press and its application for the improvement of fatigue life of magnesium alloy　　　　　　　　　　　　　　　
Nao FUJIMURA, Takashi NAKAMURA, Tatsuki WAJIMA
Seventh International Conference on Very High Cycle Fatigue, 2017年07月05日, 英語, 口頭発表（一般）
［国際会議］

Scanning Cyclic Pressを用いたマグネシウム合金AZ31の表面改質と疲労特性改善効果　　　　　　　　　　　　　　　
藤村奈央, 中村孝, 上遠野寛, 宮崎数則, 柴山環樹, 和島達希
第33回疲労シンポジウム・第1回生体・医療材料シンポジウム, 2016年11月12日, 日本語, 口頭発表（一般）
［国内会議］

OS0510 ポリイミドフィルムにおける膜厚方向破壊靱性の計測と評価　　　　　　　　　　　　　　　
南雲慶憲, 坂本悠介, 中村孝, 藤村奈央, 髙橋航圭
M&M2016材料力学カンファレンス, 2016年10月08日, 日本語, 口頭発表（一般）
［国内会議］

J1610203 ナノ微細化表面改質を目的とするScanning Cyclic Pressの開発と低炭素鋼への適用　　　　　　　　　　　　　　　
宮崎数則, 中村孝, 藤村奈央, 柴山環樹, 和島達希
日本機械学会年次大会, 2016年09月14日, 日本語, 口頭発表（一般）
［国内会議］

J1610202 Cyclic Press による低炭素鋼のナノ微細化表面改質　　　　　　　　　　　　　　　
中村孝, 中谷建太朗, 宮崎数則, 藤村奈央, 柴山環樹, 和島達希
日本機械学会年次大会, 2016年09月14日, 日本語, 口頭発表（一般）
［国内会議］

J0310101 SUS316NGの低サイクル疲労における表面性状変化とその機構　　　　　　　　　　　　　　　
西塚祐斗, 藤村奈央, 中田康敬, 上遠野寛, 中村孝
日本機械学会年次大会, 2016年09月14日, 日本語, 口頭発表（一般）
［国内会議］

OS0913-454 低サイクル疲労損傷を受けたSU5316NGにおける表面粗さの分布特性
藤村 奈央, 中村 孝, 信耕 友樹
M&M材料力学カンファレンス, 2015年11月21日, 日本語
To statistically investigate the changes and the distributions in surface roughness, strain controlled low cycle fatigue tests of austenitic stainless steel were conducted under strain range Δε=8, 4%. During the tests, the specimen's surface topography was regularly measured using a laser scanning microscope. The surface topographies obtained were analyzed by frequency analysis to separate the surface relief due to persistent slip bands. The persistent-slip-bands-induced surface relief evolution was quantitatively evaluated by using arithmetic mean roughness R_a. As a result, R_a at Δε=8, 4% increased with the increase of UF (Usage Factor). The R_a data were plotted roughly linearly on a log-normal probability paper. It suggests that R_a likely follows a log-normal distribution. On the probability papers, the slope of R_a plots and the average value at Δε=8, 4% were clearly different. It shows that the distribution form of R_a varies between different Δε. The slopes of R_a plots at each UF were similar on the paper. It showed that the dispersion of R_a data didnot change even if UF increases.

G0301502 二段二重低サイクル疲労におけるSUS316NGの表面性状評価
中田 康敬, 西塚 祐斗, 信耕 友樹, 藤村 奈央, 中村 孝
年次大会 : Mechanical Engineering Congress, Japan, 2015年09月13日, 日本語
To investigate the effects of change in loading amplitude on surface topography, two-step loaded low-cycle fatigue tests of SUS316NG austenitic stainless steel were conducted. During the tests, the specimen's surface topography was regularly measured using a laser scanning microscope. The surface topographies obtained were analyzed by frequency analysis to separate the surface relief due to persistent slip bands from that due to crystal grain deformation. The persistent-slip-bands-induced surface relief evolution and the grain-deformation-induced one were quantitatively evaluated by using arithmetic mean roughness R_a and arithmetic mean waviness W_a, respectively. As a result, the rates of increase in R_a and W_a changed obviously after changing loading amplitude. The results for R_a and W_a agree with the results of surface observation, the increases in the numbers of slip bands and deformed crystal grains changed after changing loading amplitude.

142 低サイクル疲労過程におけるSUS316NGの表面性状評価(材料力学・機械材料)
中田 康敬, 信耕 友樹, 藤村 奈央, 中村 孝
北海道支部講演会講演概要集, 2014年09月27日, 日本語

OS2126 オーステナイトステンレス鋼の渦電流信号に及ぼす表面粗さの影響
堀川 紀孝, 濱口 萌愛, 藤村 奈央, 中村 孝
M&M材料力学カンファレンス, 2014年07月19日, 日本語
Austenite stainless steel is widely used in power plants and nondestructive damage estimation method is required to determine the damage on the structure due to fatigue or earthquake. Eddy current method is one of the nondestructive inspection technique, and it reflects the surface condition of the metal. Surface roughness of the specimen increased by the deformation and the roughness change is used to estimate the damage by the low cycle fatigue. This report deals with the eddy current signal change due to the surface roughness. Test pieces of SUS316 with 6mm in diameter were prepared, and the surface was ground with emery paper. Eddy current testing was carried out with two types of the probe and testing frequency of 200kHz and 1MHz. Eddy current signal, which is output of the eddy current instrument, were measured. Eddy current signal was changed by surface grinding. Grinding on the surface showed significant effect on the eddy current signal. It is caused by removal of residual stress near the surface of the test piece that induced by the drawing process. Difference in the eddy current signal by the surface roughness within 1μm in Ra is quite small and higher testing frequency is required to distinguish the difference.

OS0820 SUS316NGの二段二重低サイクル疲労における表面粗さの変化
藤村 奈央, 中村 孝, 小熊 博幸, 新沼 賢基
M&M材料力学カンファレンス, 2014年07月19日, 日本語
Changes in surface roughness of SUS316NG during cyclic variable loadings were investigated. Strain controlled two-step fatigue tests were conducted under two different strain ranges. In the tests, strain range was switched from Δε_H=4% to Δε_L=2% or from Δε_L=2% to Δε_H=4% at the usage factor UF=0.2. The specimen's surface was observed by a laser scanning microscope to clarify the surface profile and surface roughness R_a. As a result, R_a increased with UF during the first and second steps in the two-step tests. The increasing rate of R_a at the second step became smaller after strain range was changed from 4% to 2%, whereas it became larger after strain range was changed from 2% to 4%. The increasing tendencies of Ra at each step were similar to those in fatigue test under constant strain ranges Δε=4% and 2%, respectively. The results suggest that changes in surface roughness under two-step variable loadings can be described by superimposing R_a values in order of loading, which were obtained under constant strain range tests. Surface observation revealed that the height change in surface profile during each loading step varied depending on the strain range. This shows that the history of strain range affected the changes in surface profile, and it is the reason that the increasing rate of R_a changed in the two-step tests.

OS0819 低サイクル疲労損傷を受けたオーステナイト系ステンレス鋼における表面性状の定量的評価
信耕 友樹, 藤村 奈央, 中田 康敬, 小熊 博幸, 中村 孝
M&M材料力学カンファレンス, 2014年07月19日, 日本語
Low-cycle fatigue tests of SUS316NG were conducted under conditions of strain range Δε=2, 4 and 8%. During the fatigue tests, changes in surface relief of specimen were measured by a laser scanning microscope. The surface roughening due to slip bands and deformation of grains was quantitatively evaluated by using arithmetic average roughness R_a and arithmetic average waviness W_a respectively. As a result, R_a and W_a increased with the increase of UF (Usage Factor), and the increasing rates of R_a and W_a with respect to UF became larger in larger strain ranges. The ratio of increasing rate of W_a to R_a also became larger in larger strain ranges. This result indicates that the surface roughening due to deformation of grains is caused more significantly than that due to slip bands is in larger strain ranges. Based on the different tendencies of R_a and W_a, we suggested a new damage evaluation method which can estimate UF and applied strain range of fatigued material.

繰返し負荷を受けたSUS316NGの表面粗さ測定に基づく損傷評価
藤村奈央, 信耕友樹, 中村孝
疲労シンポジウム講演論文集, 2014年, 日本語

Application of surface roughness parameters to the evaluation of low cycle fatigue damage in austenitic stainless steel
Nao Fujimura, Takashi Nakamura, Hiroyuki Oguma
American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP, 2013年12月01日
Changes in the surface roughness of SUS316NG during cyclic loadings were investigated, and the relations between those changes and the crack initiation and propagation processes are discussed on the basis of microscopic observations and cellulose acetate replica observations. Strain-controlled fatigue tests were conducted at three constant strain ranges. Surface roughness was measured periodically during the tests, and three roughness parameters were calculated: arithmetic mean roughness Ra, surface profile maximum height R max, and maximum valley depth Rv. Until the middle of fatigue life, all three increased linearly with the number of cycles regardless of the strain range, and their rates of increase became smaller with decreasing strain range. Surface observation revealed that small cracks initiated very early in fatigue life, propagated slowly until the middle of fatigue life, and then grew rapidly. Changes in surface roughness are therefore sensitive to fatigue loading even when cracks are very small and crack detection is difficult. The results suggest that surface roughness can probably be used to assess fatigue damage because until the middle of fatigue life it increases linearly with the number of cycles. The definition of each roughness parameter and the changes show that Rmax and Rv are suitable for damage assessment. Copyright © 2013 by ASME.

PS15 SUS316NGの低サイクル疲労における表面性状の変化
新沼 賢基, 藤村 奈央, 信耕 友樹, 中村 孝, 小熊 博幸
M&M材料力学カンファレンス, 2013年10月12日, 日本語
A strain controlled two step test was conducted to investigate changes in the surface features of SUS316NG during cyclic variable loading. In the two step test, strain range was switched from Δ_<εH> = 4% to Δ_<εL> = 2% at the usage factor UF= 0.2. The specimen surface was observed by a laser microscope to clarify the surface morphology and surface roughness R=a. Initiation and propagation of the main crack was also observed by using cellulose acetate replica The results in the two step test were compared with those obtained in fatigue tests under constant strain ranges. As a result changes in surface features such as slip bands and surface asperities clearly depended on the value of strain ranges even under the same UF value. Small cracks initiated very early in the fatigue life, however, they hardly propagated until the middle of fatigue life. In contrast, Ra clearly increased from the beginning to the middle of fatigue life. These results suggest that surface roughness can be an effective parameter for fatigue damage assessment. In addition, the increasing rates of Ra during the first and second steps in two step test were similar to those in fatigue tests under constant strain ranges Δ_ε = 4% and Δ_ε = 2%, respectively. Therefore, the history of strain range under cyclic variable loadings can probably be described from the value of R_a and the increasing rate of R_a in the fatigue tests under constant strain ranges.

SUS316NGの低サイクル疲労における表面性状の変化
新沼賢基, 藤村奈央, 信耕友樹, 中村孝, 小熊博幸
日本機械学会M&M2013材料力学カンファレンス(CD-ROM), 2013年10月10日, 日本語

108 表面粗さに基づいたSUS316NGの低サイクル疲労損傷評価(材料力学III)
信耕 友樹, 藤村 奈央, 新沼 賢基, 小熊 博幸, 中村 孝
北海道支部講演会講演概要集, 2013年09月28日, 日本語

表面粗さに基づいたSUS316NGの低サイクル疲労損傷評価
信耕友樹, 藤村奈央, 新沼賢基, 小熊博幸, 中村孝
日本機械学会北海道支部講演会講演概要集, 2013年09月28日, 日本語

表面粗さ計測に基づくSUS316NGの疲労損傷評価と適用範囲
藤村奈央, 中村孝, 小熊博幸, 中島智広, 信耕友樹
日本材料学会学術講演会講演論文集, 2013年05月17日, 日本語

214 オーステナイト系ステンレス鋼の低サイクル疲労特性と損傷評価(材料力学V)
中島 智広, 藤村 奈央, 新沼 賢基, 小熊 博幸, 中村 孝
北海道支部講演会講演概要集, 2012年10月20日, 日本語

オーステナイト系ステンレス鋼の低サイクル疲労特性と損傷評価
中島智広, 藤村奈央, 新沼賢基, 小熊博幸, 中村孝
日本機械学会北海道支部講演会講演概要集, 2012年10月20日, 日本語

OS2109 オーステナイト系ステンレス鋼の低サイクル疲労における表面粗さの影響
藤村 奈央, 中村 孝, 小熊 博幸
M&M材料力学カンファレンス, 2012年09月22日, 日本語
The effects of surface roughness on low cycle fatigue properties were investigated by strain-controlled fatigue tests using specimens of austenitic stainless steel finished by two different methods: machining and mirror polishing. During fatigue tests, the surface roughness of each specimen was measured, and crack initiation and propagation were observed using cellulose acetate replicas. As a result, the fatigue life of mirror polished specimen was longer than that of machined one. It was shown that the surface roughness affected the fatigue life. The change of surface roughness of each specimen showed the same increasing tendency with respect to the number of cycles. However, around the end of fatigue life, the surface roughness of mirror polished specimen became larger than that of machined one. In the damage process, the crack initiated at the very early stage of fatigue life. The crack growth rate was small until the middle of fatigue life; however, it increased rapidly after that. The surface roughness affected the crack initiation, and that is the reason why the fatigue life and the change of surface roughness were different between each specimen.

オーステナイト系ステンレス鋼の低サイクル疲労特性に及ぼす繰返し予ひずみの影響と損傷評価
藤村奈央, 小熊博幸, 中村孝
日本材料学会学術講演会講演論文集, 2012年05月25日, 日本語

704 オーステナイト系ステンレス鋼の低サイクル疲労特性に及ぼす繰返し予ひずみの影響と損傷評価(変動応力・予ひずみ効果,疲労損傷観察ならびに強度評価,オーガナイスドセッション1)
藤村 奈央, 小熊 博幸, 中村 孝
学術講演会講演論文集, 2012年05月25日, 日本語

オーステナイト系ステンレス鋼の低サイクル疲労における表面粗さの影響
藤村奈央, 中村孝, 小熊博幸
日本機械学会M&M2012材料力学カンファレンス(CD-ROM), 2012年, 日本語

Damage assessment on low cycle fatigue properties of cyclic pre-strained austenitic stainless steel
Nao Fujimura, Hiroyuki Oguma, Takashi Nakamura
American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP, 2011年12月01日
The effects of cyclic pre-strain on low cycle fatigue properties of austenitic stainless steel were investigated, and the fatigue damage was assessed based on several parameters such as the full width at half maximum (FWHM) of diffracted X-ray profile and surface roughness of specimens. The straincontrolled tests were conducted under strain ratio Rε = -1 and various constant total strain ranges. Also the change in remnant fatigue lives were investigated when the cyclic pre-strain were applied to the specimens under the different number of cycles which were determined with reference to the usage factor UFpre ranged from 0.2 to 0.8. As a result, the remnant fatigue life of the pre-strained samples became shorter than that of the sample without pre-strain as the UFpre increased. The relationship between the pre-strain damage expressed in UFpre and the remnant fatigue damage in UFpost was roughly described by the cumulative linear damage law: UFpre + UFpost = 1. Namely, the cyclic pre-strain affected the remnant fatigue lives. In order to evaluate the effects of cyclic pre-strain on fatigue lives more precisely, the damage in the cyclic pre-straining processes was estimated by using FWHM and surface roughness. The FWHM of the specimens with pre-strain once decreased with increase in UF pre, and then increased after showing a minimum value. The surface roughness of specimens increased linearly with an increase of the number of pre-straining cycles. These results suggested that the damage due to pre-strain can be assessed by means of FWHM and surface roughness of specimens. © 2011 by ASME.

繰返し予ひずみを受けたSUS316NGの低サイクル疲労特性
中島智広, 藤村奈央, 小熊博幸, 中村孝
日本機械学会北海道支部講演会講演概要集, 2011年10月01日, 日本語

220 繰返し予ひずみを受けたSUS316NGの低サイクル疲労特性(材料力学VII)
中島 智広, 藤村 奈央, 小熊 博幸, 中村 孝
北海道支部講演会講演概要集, 2011年10月01日, 日本語

604 原子力構造用材料の低サイクル疲労特性に及ぼす繰返し予ひずみの影響(計算力学・材料力学I)
藤村 奈央, 小熊 博幸, 中村 孝
北海道支部講演会講演概要集, 2010年11月07日, 日本語

オーステナイト系ステンレス鋼の低サイクル疲労特性に及ぼす平均ひずみの影響
藤村奈央, 水門恵理, 中村孝, 小熊博幸
日本材料学会学術講演会講演論文集, 2010年05月21日, 日本語

534 オーステナイト系ステンレス鋼の低サイクル疲労特性に及ぼす平均ひずみの影響(予ひずみ・平均ひずみ・平均応力の影響,疲労研究の課題と展望,オーガナイスドセッション1)
藤村 奈央, 水門 恵理, 中村 孝, 小熊 博幸
学術講演会講演論文集, 2010年05月21日, 日本語

ラボラトリーセミナー　　　　　　　　　　　　　　　
北海道大学
2014年04月 - 現在

自然科学実験　　　　　　　　　　　　　　　
北海道大学
2018年 - 2020年