Systematic review of UIT parameters on residual stresses of sensitized AA5456 and field based residual stress measurements for predicting and mitigating stress corrosion cracking

Abstract

This thesis focuses on the use of x-ray diffraction to measure residual stresses around welds in aluminum ship structures both in the laboratory and in the field. Tensile residual stresses are often generated during welding and, in sensitized aluminum structures, can cause extensive stress corrosion cracking. Peening techniques, such as ultrasonic impact treatment (UIT), can mitigate and even reverse these tensile residual stresses. This research uses x-ray diffraction to measure residual stresses around welds in AA5456 before and after UIT. In particular, we examined the importance of UIT parameters such as peening amplitude and pin size. We found that all combinations of UIT parameters removed the tensile residual stresses and resulted in compressive stress several hundred microns below the weld surface. The exact level of compressive residual stress was sensitive to the pin size used with a smaller, but measurable, dependence upon the displacement amplitude. In an effort to extend these measurement techniques to the field, we successfully performed the first x-ray residual stress measurements on a U.S. naval combatant.