Papers by Author: Takahisa Shobu

Abstract: Dislocation densities of dispersion-strengthened copper with aluminum oxide, namely GlidCop were evaluated employing the X-ray line profile analysis using the modified Williamson-Hall and modified Warren-Averbach method. X-ray diffraction profiles for GldCop samples with compressive strains applied at ambient temperature were measured with synchrotron radiation. The dislocation densities of GlidCop with compressive strain ranging from 0 – 2.7 % were on the order of 1.5×10¹⁴ – 6.6×10¹⁴ m^-2.

Abstract: The dislocation density of plastically deformed oxygen free copper (OFC) was evaluated by X-ray diffraction profile analysis with synchrotron radiation. The modified Williamson-Hall and modified Warren-Averbach methods were applied to the analysis. The dislocation densities of OFC samples with compressive plastic strains of 1 % and 4 % were 5.1×10¹⁴ m^-2 and 9.2×10¹⁴ m^-2, respectively.

Abstract: Welding technologies are indispensable for fabricating various industrial structures and must be highly reliable. Since tensile residual stresses at surface after welding cause crack progress, it is important to understand how stresses built up during the welding process in order to optimize final residual stresses as reduced tensile or introduced compressive stresses. Therefore, we conducted in-situ measurements of phase transformations, stresses and temperatures during tungsten inert gas (TIG) welding to understand how stresses built up. X-ray diffraction rings were detected per 0.1 sec during TIG welding by using a large-area two-dimensional detector and the accuracy of the stress analysis was estimated to be 8 MPa using the sin2ψ technique. In this paper, we described the phase transformations of ferrite low-carbon rolled steel and the changes in stresses during TIG welding.

Abstract: A relationship between dislocation density and macro strain was investigated for GLIDCOP, dispersion-strengthened copper with ultra-fine particles of aluminum oxide. The dislocation density was estimated by applying the Warren-Averbach method to a diffraction profile measured using synchrotron radiation.

Abstract: Residual strain in oxygen-free copper, one of the materials used in high-heat-load components at SPring-8 front end, was investigated. A strain scanning method with oscillation was employed for strain measurement. The results were compared with those obtained using an elasto-plastic creep FEM analysis.

Abstract: The rotating-slit system was developed to overcome the measurement of internal stress using 2-dimensional detector. The diffraction spot trace method was proposed and examined to measure the internal stress of the material with coarse grains.

Abstract: Austenitic stainless steel (SUS316L) was used as specimen material, and the plate specimens were deformed plastically with a wide range of strain rates (6.67×10^-5~ 6.70×10²/s). The residual micro-stress for each lattice plane was measured with hard synchrotron X-rays. The residual macro-stress due to tensile deformation depended on strain rate. The residual micro-stresses varied from tension to compression, depending on the diffraction elastic constant. The soft lattice plane had tensile residual stress, and the hard lattice plane had compressive residual stress. The higher the strain rate, the smaller the difference in residual micro-stresses. The residual micro-stresses of the surfaces peened with the laser-peening or water-jet-peening were examined. Both surfaces had exhibited large compressive residual stress. The residual micro-stress on the peened surfaces showed a tendency opposite to residual micro-stress due to tensile deformation.

Abstract: For engineering components with cracks, it is very important to evaluate the reliability for fracture. The X-ray diffraction method is now widely used to measure non-destructively the loading and residual stresses in crystalline materials. Synchrotron radiation sources provide the X-rays with extremely high intensity as well as a narrow divergence. The high intensity X-rays with a narrow divergence enables stress measurements in a localized region. The strain distribution near the fatigue crack in the steel plate with ultrafine-grained surface layers, called SUF plates, was measured by the polychromatic X-ray from synchrotron radiation at SPring-8. The spatial resolution in the direction parallel to the crack propagation direction was 0.1 mm. The strain distributions at several applied stress levels were determined for six diffraction planes. The measured strain distribution was compared with the result calculated by the FE analysis. The average value of the measured strains for several diffraction planes agreed well with the calculated results.

Abstract: In-situ diffraction measurements were carried out on a tensile specimen of SUS304 stainless steel using a small autoclave at BL22XU at SPring-8. The temperature of circulating water in the autoclave was changed from room temperature to 561 K under ambient pressure and also under a pressure of 8.8 MPa. Tensile stress of 260 MPa was applied to the specimen at 561 K under 8.8 MPa, and a two dimensional strain distribution was obtained by calculation based on measured lattice spacings of the γ-Fe311 plane under various conditions. The interior region of the specimen showed higher strain compared with that on the surface region. After the tensile deformation in the autoclave, CT images of cross sections of the specimen were taken. Void-like images with about 50 μm in size were observed.

Abstract: We measured internal residual strain of GlidCopTM, a copper dispersion strengthened with aluminum oxide. The residual strains were measured by X-ray diffraction using synchrotron radiation. The purpose of this study is to verify the accuracy of an elastic-plastic analysis, which has been employed for the fatigue life prediction of GlidCop. As a result, the residual strain was estimated to be 0.11- 0.13% at any number of cycles, which is in good agreement with the analysis solutions. As to the plastic strain, we need to increase the accuracy of the calibration curve for the relationship between the FWHM of the diffraction profile and the plastic strain.