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The importance offracture surface analysis, by which the mechanism and mechanical condition can be found through the marks left on the fracture surface of the materials such as dimple, cleavage, and striation, has been accepted to clarifY the causes offailure of engineering structures and as a guide to future design. At present, the optical microscope (OM) and scanning electron microscope (SEM) are widely used for the fracture surface analysis. The fracture surfaces of the structural components, however, are often damaged by contact between the conjugate fracture surfaces and also by the environmental corrosion during and after the fracture, which makes the examination of the fracture surface by OM and SEM difficult. In order to solve this problem, a new fractographic technique by an X-ray method, which is called X-ray fractography, has been established as a useful method for fracture surface analysis, especially when OM and SEM fractography are difficult to apply. In the new method, the X-ray diffraction technique is used together with OM and SEM. The X-ray parameters such as the residual stress and peak profile, which can be obtained not only from the fracture surface but also from the subsurface of the fractured sample, are examined in correlation with the applied stress intensity factor, K, at which fracture occurs. Many examples of the application of the X-ray fractographic technique have been reported on the fracture surfaces of fatigue, impact, and stress corrosion cracking. These results indicate that it is possible to estimate the maximum applied stress intensity factor, Kmax , quantitatively by measuring the thickness of the plastically deformed region that was built up after the fracture, using the knowledge of fracture mechanics. The residual stress and full-width at half maximum (FWHM), which are measured from the fracture surface, can be used to determine the mechanical conditions such as Kmax and stress intensity factor range, 11K.