Acceptance Criteria for Welds Retrofitted by Ultrasonic Impact Treatment (UIT)

A study was recently undertaken to examine the fatigue performance of structural steel welds subjected to Ultrasonic Impact Treatment (UIT) at various levels, and to relate this performance to geometric and metallurgical properties measured to control the treatment quality. Fatigue tests of non-load carrying fillet welded attachments were conducted. During the tests, crack growth was monitored using the alternating current potential drop (ACPD) method. Following the tests, local geometric and metallurgical properties were measured and a statistical analysis of the fatigue life data was performed. UIT was found to significantly improve the fatigue lives of weld details, regardless of the treatment level. The treatment level had little impact on the mean stress-life (S-N) curves. However, it was seen to impact the design (95% survival probability) S-N curves. Near-surface micro hardness and compressive residual stress measurements were greatest for the over-treated welds, followed by the properly treated and then the under-treated welds. Increasing the treatment speed resulted in greater reductions in the micro hardness and residual stress levels than under-treating by decreasing the treatment intensity. In the proposed paper, this study will be briefly summarized. Based on the results of this experimental research and statistical analysis, recommendations will be made regarding the development of quality control procedures and acceptance criteria for welds retrofitted by UIT.