Hybrid measurement of CT and strain distribution of fatigue crack in steel bars using high energy synchrotron radiation monochromatic X-rays

Shobu, Takahisa  ; Tanaka, Keisuke*; Hashimoto, Atsushi*; Narita, Junichi*

Fracture mechanics have been successfully applied for damage tolerant design of engineering structures against fatigue and stress corrosion cracking. The stress intensity factor is a key parameter to predict the progress of cracking behavior, and is computed from the shape of cracks and the loading stress distribution. In the present study, using high energy monochromatic X-rays of energy 66.4 keV from the synchrotron radiation source, SPring-8, we have developed a system to perform the hybrid measurement of imaging of cracks and strain distribution around cracks. High tensile strain ahead of the crack was measured at the maximum stress, while the strain on the crack face was low because of crack opening. The full width at half maximum (FWHM) increased near the crack tip under loading, and then decreased after unloading. This recoverable part of FWHM by unloading was caused by the steep distribution of the applied stress in the vicinity of the crack tip.