Allowable stresses in high-frequency mechanical impact (HFMI)-treated joints subjected to variable amplitude loading

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• 作者：Eeva Mikkola ; Heikki Remes
• 关键词：(IIW Thesaurus)Peening ; Fatigue improvement ; Variable loading ; Residual stresses ; Notch effect ; Computation
• 刊名：Welding in the World
• 出版年：2017
• 出版时间：January 2017
• 年：2017
• 卷：61
• 期：1
• 页码：125-138
• 全文大小：
• 刊物主题：Metallic Materials; Continuum Mechanics and Mechanics of Materials; Theoretical and Applied Mechanics;
• 出版者：Springer Berlin Heidelberg
• ISSN：1878-6669
• 卷排序：61

文摘

The effectiveness of high-frequency mechanical impact (HFMI) is considered to rely on the existence of compressive residual stresses. To determine when residual stress relaxation occurs, and what the resulting influence on fatigue improvement is, local stress-strain response in as-welded and HFMI-treated weld toes was modelled under different peak stress conditions. Then, effective notch stress analysis was used to correlate these results with available experimental observations. The simulations showed that high stress ratios and compressive peak stresses were critical with respect to residual stress relaxation, as expected. A compressive peak stress of 0.6f_y (nominal yield strength) resulted in full residual stress relaxation. The relative fatigue damage calculations and the notch stress analysis indicated, however, that fatigue improvement could be expected even after significant residual stress relaxation. Based on this and previously observed benefit for high stress ratios, an increase in maximum allowable stresses for HFMI-treated welded steel joints is suggested. The maximum stress ratio is proposed to be increased from R = 0.52 to R = 0.7, and the maximum stress range to limit compressive stresses is proposed to be increased from ΔS_max = 0.9f_y to ΔS_max = 1.2f_y, which corresponds to S_min = −0.6f_y for stress ratio R = −1.