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STUDY ON COMPUTERIZED TOMOGRAPHY AND STRAIN MAPPING NEAR THE INTERNAL CRACK TIP OF STEEL BAR USING SYNCHROTRON WHITE X-RAY

A computerized tomography (CT) and a strain mapping near a crack tip in material were investigated using a white X-ray obtained from BL28B2 beam line at SPring-8 in Japan. A low-alloy and high-tensile steel was used as a specimen prepared in the tensile bar with a parallel part of 5mm diameter. A fatigue crack was introduced into the specimen under the pulsating tension load. The computerized tomography of the crack in the specimen was carried out by using the CCD camera that can detect indirectly the X-ray transmitted through the specimen. To measure the strain using the energy dispersive X-ray diffraction technique, 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. As the results, the computerized tomography of the crack in the specimen under the tensile loading was practicable by using the white X-ray. The map of the internal strain near the crack tip of the specimen could be obtained using the high energy white X-ray. It was confirmed that the maximum tensile strain was distributed circularly along the crack tip estimated by CT.