Kyushu University · Engineering
Professor Masaki Tanaka's research lab specializes in the fundamental mechanics and microstructural behavior of advanced metallic materials, with a focus on fracture toughness, ductile-to-brittle transition, and plastic deformation mechanisms. The lab investigates how microstructure—such as grain refinement, dislocation mobility, and phase distribution—affects mechanical properties in steels and other alloys under various conditions. Using advanced characterization techniques like electron microscopy, nanoindentation, and molecular dynamics simulations, the lab explores the relationship between material structure and performance at the micro- and nanoscale. Their work also extends to understanding surface plasmon effects in nanostructured metal arrays, particularly in the terahertz frequency range.
Figures are computed from collected data and may differ slightly.
We studied the role of surface-plasmon polaritons (SPPs) in a bandpass transmission property of two-dimensional metal hole arrays (2D-MHAs) by investigating the effect of thin dielectric layers on the 2D-MHA surfaces. We measured zero-order transmission spectra of the 2D-MHAs by changing the thickness of the dielectric layer and found that the bandpass transmission peak shifted to the lower-frequency side with increasing layer thickness, owing to the change of the resonant frequency of the SPP.
In order to elucidate the mechanism behind the decrease in the brittle-to-ductile transition (BDT) temperature with the addition of Ni, impact tests and tensile tests were performed at various test temperatures from 130K to 320K with Ni added ultra-low carbon steels. The dependence of absorbed impact energy on temperature and the Ni content indicates that the BDT temperature was decreased with the increasing Ni content, which suggests that the dislocation mobility at low temperatures was increas
Brittle-ductile transition (BDT) behaviour was investigated in low carbon steel deformed by an accumulative roll-bonding (ARB) process. The temperature dependence of its fracture toughness was measured by conducting four-point bending tests at various temperatures and strain rates. The fracture toughness increased while the BDT temperature decreased in the specimens deformed by the ARB process. Arrhenius plots between the BDT temperatures and the strain rates indicated that the activation energy
Wire-drawn fully pearlitic steel was twisted at room temperature. As a result, a delamination crack propagated along the longitudinal direction of the wire. Backscattered electron and transmission electron microscopy images indicated that the cementite lamellae beneath the delamination crack had vanished. In addition, a fine-grained structure was observed. This indicated that the delamination fracture was not a brittle one but a shear one associated with local severe plastic deformation.
Nanoindentation testing using a Berkovich indenter was conducted to explore the relationships among indentation hardness (<i>H</i>), elastic work energy (<i>W</i><sub>e</sub>), plastic work energy (<i>W</i><sub>p</sub>), and total energy (<i>W</i><sub>t</sub> = <i>W</i><sub>e</sub> + <i>W</i><sub>p</sub>) for deformation among a wide range of pure metal and alloy samples with different hardness, including iron, steel, austenitic stainless steel (<i>H</i> ≈ 2600-9000 MPa), high purity copper, sin
Fracture toughness of silicon crystals has been investigated by indentation methods, and their surface energy has been calculated using molecular dynamics (MD). When a conical indenter was forced into a (001) silicon wafer at room temperature, {110} cracks were mainly introduced from the indent, indicating that fracture occurs most easily along the {110} plane among the crystallographic planes of the 〈001〉 zone. To confirm this orientation dependence, surface energies for those planes were compu
The enhancement of toughness at low temperatures in fine grained low carbon steel was studied, basing on a shielding theory due to dislocations and grain boundaries. Fully annealed low carbon steel was subjected to an accumulative roll bonding (ARB) process for grain refining. The grain size perpendicular to the normal direction was found to be approximately 200 nm after the ARB process. The fracture toughness of low carbon steel ARB applied was measured at 77 K by four-point bending, comparing
Dislocations in a silicon single crystal introduced by three point-bending at a high temperature were observed by electron tomography in annular dark field-scanning transmission electron microscopy (ADF-STEM). Commercially available P type (001) single crystal wafers were employed. An ADF STEM tilt series was acquired from −60° to +60° in tilt range with 2° in tilt step. The diffraction vector was maintained close to g(hkl)=220 during the acquisition by adjusting the [110] direction of the sampl
The temperature dependence of the yield stress, effective stress and activation volume on the Cu content in steel was assessed using polycrystalline ultra-low carbon steels with 0.5, 1 and 2 mass% Cu added. A small hump was seen in the effective stress–temperature curve for ultra-low carbon steel, which has also been reported for high-purity single-crystal iron. The effective stress was found to decrease with increasing the Cu content. The activation volume was found to be linearly related to th
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