Papers by Author: Koji Kiriyama

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.

Abstract: Duplex stainless steels (DSSs) have microstructures of α and γ-phases of iron and exhibit changing of their mechanical properties by aging above 300°C, so that strain behavior is expected to be complicated under stress loading. In order to estimate lattice strains and to determine their behavior, lattice strain measurements of aged DSSs have been performed using synchrotron radiation white X-rays. As a result, it was found that the lattice strain was not always correspond with applied macro strain, and the lattice strains of γ-phase showed no elongation in comparison with those of α-phase in the aged specimen. These results mean that complex strain distributions between (hkl) planes already exist in the early stage of elastic deformation, and suggest that fracturing of aged DSSs under tensile loading occurs preferentially on γ-phase rather than α-phase.

Abstract: A transmission imaging and a strain mapping in the vicinity of a crack tip in steel were investigated using a high energy white X-ray obtained from BL28B2 beam line at SPring-8 in Japan. Low-alloy and high-tensile steel was used as a specimen prepared in the G-type geometry with a rectangular sectional part of 5mm thickness for a four-point bending. A fatigue crack was introduced into the notch root on the tension side of the specimen by a pulsating bending load. The imaging of the crack in the specimen under the bending load was carried out by using the CCD camera that can detect indirectly the X-ray transmitted through the specimen. To measure the internal strain in the vicinity of the crack tip, the synchrotron white X-ray beam, which had a height of 80m and a width of 300m, was incident on the specimen with the Bragg angle  of 5 degrees using the energy dispersive X-ray diffraction technique. As the results, the transmitted image of the crack showed that the crack in the specimen was propagated deeper than that on the surface. The map of the internal strain near the crack tip could be obtained using the white X-ray with energy ranging from 50keV to 150keV. It became clear by the numerical simulation that the FWHM of diffracted X-ray profile measured near the crack tip was increased due to the steep change in the strain distribution. It was confirmed that the synchrotron white X-ray was useful for the imaging of the internal crack and the strain mapping near it.

Abstract: This paper presents a basic research on a measurement of strain in the bulk of materials by using high energy white X-ray from a synchrotron radiation source of SPring-8 in Japan. A high-tensile strength steel (JIS-SHY685) was used as a specimen loaded with bending. Strain distribution in it was evaluated by the energy dispersive method using diffracted X-ray transmitted through the specimen. As a result, the internal strain of high-tensile steel of 5, 10 and 15 mm thickness could be evaluated using white X-ray which range of energy from 50 keV to 150 keV. The measurement with a high degree of accuracy was accomplished using α-Fe321 diffraction in this material. The results showed that the internal strain measurement in the depth of the order of millimeter using the high energy white X-ray is practicable at SPring-8.