DETERMINATION OF PREFRACTURE DAMAGE IN FATIGUED AND STRESS-CORRODED MATERIALS BY X-RAY DOUBLE CRYSTAL DIFFRACTOMETRY.

The lattice defects induced in fatigued aluminum alloys and in austenitic stainless steel and titanium-aluminum alloys subjected to stress corrosion were investigated by a method based on X-ray double crystal diffractometry combined with X-ray topography. X-ray rocking curves of the grain reflections from the surface layer and bulk material of the specimens were obtained. Investigation of the induced excess dislocations in depth by incremental surface removal showed that there exists a dynamical interplay between the buildup of excess dislocations in the surface and bulk. By measuring the progressive buildup of excess dislocations in depth as a function of the number of cycles for fatigue, or the elapsed exposure time for stress corrosion, the induced damage to the material could be assessed. Consequently, the remaining lifetime of the materials could be predicted by the nondestructive X-ray method at various stages of their lives.