Study on Imaging and Strain Mapping in the Vicinity of Internal Crack Tip Using Synchrotron White X-Ray

An imaging and a strain mapping in the vicinity of a crack tip in material 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 (JIS G3128 SHY685) was used as a specimen prepared in the G-type geometry. A fatigue crack was introduced into the specimen by a cyclic loading. The imaging of the crack in the specimen was carried out by using the X-ray CCD camera that can detect the X-ray transmitted through the specimen. To measure the strain, the synchrotron white X-ray beam, which had a height of 80μm and a width of 300μm, was incident on the specimen with the Bragg angle θ of 5 degrees using the energy dispersive X-ray diffraction technique. The internal strain in the vicinity of the crack tip was mapped out by scanning the irradiated X-ray position around it. As the results, the imaging of the crack, with about 1mm length, in the specimen under the loading of crack opening was practicable by using the synchrotron white X-ray. The map of the internal strain near the crack tip of the steel of 5mm thickness could be obtained using the white X-ray with energy ranging' from 50keV to 150keV. The plastic region estimated from the distribution of the FWHM of diffracted X-ray profile almost agreed with the theoretical value calculated by fracture mechanics. it was confirmed that the synchrotron white X-ray is useful for the imaging of the internal crack and the strain mapping near it