Laboratory of Mechanical and Functional MaterialsHokkaido University

In situ analysis of three-dimensional microcrack propagation in CFRP

Damage in CFRP has traditionally been examined through surface observations. However, damage propagates not only along the surface but also into the material, making it essential to capture three-dimensional crack propagation to understand the underlying mechanisms. Our laboratory has developed a dedicated system that uses X-ray computed tomography (CT) at the SPring-8 synchrotron radiation facility to nondestructively track internal microcracks in three dimensions under cyclic loading. This approach allows us to investigate the fundamental processes of fatigue damage.

Crack propagation at the interface between epoxy resin and carbon fibers

Interfacial cracks between carbon fibers and epoxy resin have been regarded as the origins of fatigue failure in CFRP. However, detecting interfacial debonding that occurs randomly among countless carbon fibers is extremely challenging. By preparing specimens containing a single carbon fiber embedded in epoxy resin, our laboratory achieved the first visualization of interfacial cracks originating from an individual carbon fiber. We further observed three-dimensional interfacial crack propagation under cyclic loading at high resolution using synchrotron radiation X-ray nano-CT and quantitatively related the extent of crack growth to the fracture toughness of the resin.

Research Publications

• Xuan Ngoc Chau Ho, Kosuke Takahashi, Noelle Billon, Jean-Luc Bouvard. Understanding the antiplasticization effect in epoxy resin: Interpretation using a physics-based constitutive model. Mechanics of Materials 2026;223:105864. https://doi.org/10.1016/j.mechmat.2026.105864
• Ryoma Nishiguchi, Naoya Matsuda, Kaede Yada, Kosuke Takahashi. Carbon-Fiber Interface Crack Extraction Using Machine-Learning Denoising of Low-dose X-ray CT. Journal of the Japan Society for Composite Materials 2026;52(1):22–29. https://doi.org/10.6089/jscm.52.22
• Naoya Matsuda, Kosuke Takahashi. Quantitative analysis of interface crack propagation along a single carbon fiber under off-axis cyclic loading using nanoscopic three-dimensional imaging. Composites Science and Technology 2026;276:111522. https://doi.org/10.1016/j.compscitech.2026.111522
• Kosuke Takahashi, Takuma Matsuo, Katsuma Wakabayashi, Akihisa Takeuchi, Masayuki Uesugi, Kentaro Uesugi, Takashi Nakamura. Influence of irradiation with synchrotron radiation X-ray on Nano-Scale CT for carbon fibers and epoxy matrix. Composites Part A: Applied Science and Manufacturing 2025;198:109060. https://doi.org/10.1016/j.compositesa.2025.109060
• Kosuke Takahashi, Ryuto Higashiyama, Gaoge Xue, Takashi Nakamura. In situ analysis of three-dimensional microcrack propagation in cross-ply laminates using synchrotron radiation X-ray computed tomography. Composites Science and Technology 2024;258:110918. https://doi.org/10.1016/j.compscitech.2024.110918
• Kosuke Takahashi, Takuma Matsuo, Wataru Sato, Takashi Nakamura. Decreasing propagation rate of interfacial debonding between a single carbon fiber and epoxy matrix under cyclic loading. Composites Science and Technology 2024;258:110900. https://doi.org/10.1016/j.compscitech.2024.110900
• Kosuke Takahashi, Ryosuke Shoya, Takuma Matsuo, Wataru Sato, Takashi Nakamura, Akihisa Takeuchi, Masayuki Uesugi, Kentaro Uesugi. X-ray nanoimaging of a transversely embedded carbon fiber in epoxy matrix under static and cyclic loads. Scientific Reports 2022;12(1):8843. https://doi.org/10.1038/s41598-022-12724-1
• 勝谷亮介, 松尾拓磨, 髙橋航圭, 藤村奈央, 中村孝. 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. 日本複合材料学会誌 2021;47(5):186–193. https://doi.org/10.6089/jscm.47.186

Development of strength prediction methods based on the mechanisms of pressure-sensitive adhesive peeling

Pressure-sensitive adhesives are widely used for joining components in electronic devices, sealing, and medical tapes. Accurate prediction of peel strength is essential for developing reliable products. However, unstable fracture and large deformation within the adhesive during peeling make such predictions challenging. Our laboratory aims to establish a general method for evaluating peel strength based on the mechanical properties of adhesive tapes. By investigating evaluation methods that are independent of measurement conditions and clarifying how adhesive microstructure affects deformation, we have identified key factors needed to predict strength. We are now developing strength prediction models that incorporate appropriate measurements of the adhesive mechanical properties governing peeling behavior.

Enhancing bond strength with a composite bondline of adhesive and double-sided tape

Adhesive bonding plays an important role, particularly in aerospace applications, as a lightweight method for joining dissimilar materials. In a typical joint, overlapping components are bonded with an adhesive, but stress concentrations at the ends of the bonded region can initiate damage. Although thinner adhesive layers can improve strength, controlling their thickness becomes more difficult. Our laboratory has investigated the combined use of adhesive and double-sided tape to reduce stress concentrations at the ends of the joint while simplifying control of bondline thickness. We have demonstrated improvements in static strength and fatigue life, as well as easy control of bondlines as thin as 30 µm. We are now applying this technology to the adhesive bonding of composite materials.

Quantitative evaluation of food stickiness using adhesion testing

As the population ages, more people experience difficulty swallowing. Our laboratory has applied techniques for evaluating soft materials, developed through research on pressure-sensitive adhesives, to investigate quantitative methods for assessing ease of swallowing. By measuring the detachment of thickened foods from the throat using an approach analogous to adhesive tape peeling, we seek to understand swallowing from a mechanical perspective. Quantifying food adhesion and ease of detachment will help establish objective indicators that complement practical experience when adjusting foods for people with swallowing difficulties.

Research Publications

• Ashwani Kumar Devisharan, Xuan Ngoc Chau Ho, Kounosuke Shimamura, Kosuke Takahashi. Enhancement of strength and durability in single-lap joints using thin double-sided tape. International Journal of Solids and Structures 2026;338:114082. https://doi.org/10.1016/j.ijsolstr.2026.114082
• Kosuke Takahashi, Masako Yamada, Tatsuya Sasaki, Takashi Nakamura. Viscous dissipative energy density as a general adhesion characteristic of adhesive tape. Soft Matter 2025;21(30):6078–6087. https://doi.org/10.1039/d5sm00347d
• Kosuke Takahashi, Ryo Yoshida, Kohei Ohie, Satomi Kumagai, Yuji Tasaka. Adhesion testing of dysphagia diets for the quantitative evaluation of swallowing. Food Hydrocolloids 2026;171:111816. https://doi.org/10.1016/j.foodhyd.2025.111816
• Kosuke Takahashi, Zhantong Sun, Takuma Kikuzawa, Kounosuke Shimamura, Sourabh Jagrat, Nao Fujimura, Takashi Nakamura. Toughened single-lap joints by composite bondline of adhesive and double-sided tape. Advanced Composite Materials 2024;33(4):640–656. https://doi.org/10.1080/09243046.2023.2284057
• Masako Yamada, Kosuke Takahashi, Nao Fujimura, Takashi Nakamura. Generalized characteristics of peel tests independent of peel angle and tape thickness. Engineering Fracture Mechanics 2022;271:108653. https://doi.org/10.1016/j.engfracmech.2022.108653
• Kosuke Takahashi, Futoshi Yanai, Kazuaki Inaba, Kikuo Kishimoto, Yuichi Kozone, Toshio Sugizaki. Sticking Effect of a Tackifier on the Fibrillation of Acrylic Pressure-Sensitive Adhesives. Langmuir 2021;37(39):11457–11464. https://doi.org/10.1021/acs.langmuir.1c01381
• Kosuke Takahashi, Ryuto Oda, Kazuaki Inaba, Kikuo Kishimoto. Scaling effect on the detachment of pressure-sensitive adhesives through fibrillation characterized by a probe-tack test. Soft Matter 2020;16(28):6493–6500. https://doi.org/10.1039/d0sm00680g

Effects of vacuum pressure on very high cycle fatigue

To clarify the differences between conventional fatigue damage originating at the material surface and very high cycle fatigue originating inside the material, our laboratory focuses on the vacuum pressure surrounding cracks. Surface cracks are exposed to air, causing their surfaces to oxidize. Internal cracks, in contrast, are enclosed by the surrounding material and are thought to experience a near-vacuum environment. By investigating surface crack propagation at different vacuum pressures, we aim to elucidate the damage mechanisms of very high cycle fatigue.

Surface microstructure refinement using the Scanning Cyclic Press method

Because conventional fatigue damage originates at the material surface, improving surface mechanical properties can enhance durability. Our laboratory is developing the Scanning Cyclic Press (SCP) method, a new surface modification technique that repeatedly applies a precisely controlled, low compressive load to the material surface. This method can form amorphous and nanostructured layers near the surface. We aim to develop it into a technology for improving the fatigue properties and corrosion resistance of metallic materials.

Research Publications

• Yuta Funaki, Kosuke Takahashi, Tatsuki Wajima, Takashi Nakamura. Mechanism of room-temperature nitriding in pure titanium by the scanning cyclic press. Materialia 2026;46:102720. https://doi.org/10.1016/j.mtla.2026.102720
• 舩木優大, 藤村奈央, 中村孝, 髙橋航圭, 和島達希. 窒素環境におけるScanning Cyclic Pressを用いた純チタンの常温窒化. 日本金属学会誌 2023;87(11):305–308. https://doi.org/10.2320/jinstmet.j2023015
• Gaoge Xue, Takashi Nakamura, Nao Fujimura, Kosuke Takahashi, Hiroyuki Oguma, Akihisa Takeuchi, Masayuki Uesugi, Kentaro Uesugi. Full-life growth behavior of a naturally initiated internal fatigue crack in beta titanium alloy via in situ synchrotron radiation multiscale tomography. International Journal of Fatigue 2023;170:107571. https://doi.org/10.1016/j.ijfatigue.2023.107571
• Takashi Nakamura, Gaoge Xue, Yuma Kon, Nao Fujimura, Takuya Yamazaki, Nobuyuki Tonozaki, Akihisa Takeuchi, Masayuki Uesugi, Kentaro Uesugi. Experimental Approach for Clarifying Initiation and Growth Behaviors of Internal Fatigue Cracks Using Synchrotron Radiation Multiscale X-ray Computed Tomography. Materials Performance and Characterization 2023;12(2):107–128. https://doi.org/10.1520/mpc20230023
• Gaoge Xue, Yuta Tomoda, Takashi Nakamura, Nao Fujimura, Kosuke Takahashi, Fumiyoshi Yoshinaka, Akihisa Takeuchi, Masayuki Uesugi, Kentaro Uesugi. Detection of small internal fatigue cracks in Ti-6Al-4V via synchrotron radiation nanocomputed tomography. Fatigue & Fracture of Engineering Materials & Structures 2022;45(9):2693–2702. https://doi.org/10.1111/ffe.13765
• Gaoge Xue, Takashi Nakamura, Nao Fujimura, Kosuke Takahashi, Hiroyuki Oguma, Akihisa Takeuchi, Masayuki Uesugi, Kentaro Uesugi. Initiation and propagation of small fatigue crack in beta titanium alloy observed through synchrotron radiation multiscale computed tomography. Engineering Fracture Mechanics 2022;263:108308. https://doi.org/10.1016/j.engfracmech.2022.108308
• 森下弘法, 中村孝, 藤村奈央, 髙橋航圭. 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. 材料 2022;71(12):997–1004. https://doi.org/10.2472/jsms.71.997
• Gaoge Xue, Takashi Nakamura, Nao Fujimura, Kosuke Takahashi, Hiroyuki Oguma. Initiation and Propagation Processes of Internal Fatigue Cracks in β Titanium Alloy Based on Fractographic Analysis. Applied Sciences 2021;11(1):131. https://doi.org/10.3390/app11010131
• Fumiyoshi Yoshinaka, Gaoge Xue, Nao Fujimura, Takashi Nakamura. Effect of vacuum pressure on small crack propagation in Ti-6Al-4V. International Journal of Fatigue 2021;142:105961. https://doi.org/10.1016/j.ijfatigue.2020.105961
• Gaoge Xue, Nao Fujimura, Takashi Nakamura, Hiroyuki Oguma, Kosuke Takahashi. Initiation and propagation process of the internal fatigue crack in Ti-22V-4Al alloy based on fractographic analysis. The Proceedings of the Materials and Mechanics Conference 2019;2019:OS0908. https://doi.org/10.1299/jsmemm.2019.os0908

Detection of internal fracture in cementitious materials through three-dimensional strain analysis

Damage in concrete is thought to originate from microcracks at internal air voids and in the transition zones formed at cement-aggregate interfaces. Observing damage processes inside dense concrete materials, however, has been challenging. Our laboratory developed a dedicated testing apparatus for in situ experiments at SPring-8, enabling nondestructive observation of the internal structure. By combining digital volume correlation, which visualizes strain, with image processing techniques such as denoising, we relate crack propagation that cannot be discerned by visual inspection to the internal structure of the material.

Design of steel fiber based on damage mechanisms in steel fiber reinforced concrete

Steel fiber geometry in SFRC has traditionally been investigated through experimental trial and error. Achieving substantial improvements in strength, however, requires fiber designs based on an understanding of damage mechanisms in concrete. To quantitatively evaluate bonding at the steel fiber-cement interface, mechanical interlocking, and matrix damage, our laboratory uses synchrotron radiation X-ray CT for in situ internal observations. This approach has enabled us to visualize crack initiation and interfacial debonding near the interface. By combining these images with three-dimensional strain analysis and numerical simulations, we investigate steel fiber geometries based on the underlying damage mechanisms.

Research Publications

• 長尾莉希, 高橋航圭, 大山航汰, 辻埜真人. セメントの空隙率空間分布が骨材混入による割裂引張強度の変化に及ぼす影響. 日本複合材料学会誌 2024;50(5):163–170. https://doi.org/10.6089/jscm.50.163