Enhancing fatigue strength of welded joints made of SBHS700 by hammer peening with ICR apparatus and HFMI treatment
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RESEARCH PAPER
Enhancing fatigue strength of welded joints made of SBHS700 by hammer peening with ICR apparatus and HFMI treatment Yuki Ono 1 & Koji Kinoshita 1 Received: 26 May 2020 / Accepted: 14 October 2020 # International Institute of Welding 2020
Abstract This paper investigates the fatigue strength enhancement of two types of peening techniques: hammer peening with impact crackclosure retrofit apparatus and high-frequency mechanical impact (HFMI) treatment on out-of-plane gusset-welded joints made of SBHS700. In this work, fatigue tests were continuously carried out using plate specimens that were removed from a previously tested girder specimen. The results showed that the fatigue strength enhancement of these peening techniques on the welded joints was expected to be at least three classes higher compared with as-welded details with similar dimensions. Unexpectedly, the improvement effect of the hammer peening on one specimen was slightly lower than that of the other specimens. According to SEM observation, the cause of the slight reduction was that due to its weld shape, the distance between the crack initiation point and the treatment edge became greater than 2 mm. Finally, evaluations were performed on available data, including the test results from this study, based on an extended Modified Goodman model to estimate the fatigue limits of HFMI-treated joints. Consequently, the estimation results by the model indicated a good agreement with the fatigue strength enhancement of HFMI treatment and a possibility to be able to assess the enhancement of the hammer peening. Keywords High frequency mechanical impact treatment . Hammer peening . Impact crack-closer retrofit . Welded joint . Fatigue strength improvement . Steels for bridge high-performance structures . Fatigue life extension
1 Introduction For steel bridges, an application of high-strength steels has been an effective approach to weight reduction and has resulted in cost savings for construction and transportation [1–3]. According to the requirements, steels for bridge highperformance structures (SBHS), which were newly developed in Japan, have recently been applied due to their higher strength and beneficial weld ability and work ability. However, it has been known that the fatigue strength of welded joints may be independent of the steel tensile strength of the base metal [4], which results in difficulty using highRecommended for publication by Commission XIII - Fatigue of Welded Components and Structures * Yuki Ono [email protected] Koji Kinoshita [email protected] 1
Gifu University, Gifu, Japan
strength steels to steel bridges efficiently. Therefore, the fatigue strength of welded joints made of high-strength steels must be enhanced. To enhance the fatigue strength of welded joints, the use of post-weld treatment techniques has been widely investigated. One of the treatments includes finishing methods, such as grinding [5, 6] and TIG dressing [7], which decrease the stress concentration at weld toes of potential fatigue cracks
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