Validation of the fatigue strength assessment of HFMI-treated steel joints under variable amplitude loading
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RESEARCH PAPER
Validation of the fatigue strength assessment of HFMI-treated steel joints under variable amplitude loading M. Leitner 1
&
M. Stoschka 1 & Z. Barsoum 2 & M. Farajian 3
Received: 6 September 2019 / Accepted: 15 June 2020 # The Author(s) 2020
Abstract A recommendation for the application and fatigue assessment of the HFMI post-treatment was published by the IIW in 2016. Recently, the therein recommended HFMI design curves in case of constant amplitude loading (CAL) were validated involving test data with different base material yield strengths, increased plate thicknesses, and elevated load ratios. Continuative to this previous work, this paper focuses on the fatigue assessment of HFMI-treated steel joints under variable amplitude loading (VAL). Four test data sets including randomly distributed VAL and a sufficient amount of tested specimens to ensure a statistically verified assessment are investigated. It is shown that an application of the recommended equivalent stress range approach and a further comparison of the test results to the design curves under CAL lead to a conservative fatigue assessment if the recommended value of the specified damage sum of D = 0.5 is used. Furthermore, an increased value of D = 1.0 still maintains a conservative design as presented in the study. Based on this work involving the analysed data sets, it can be concluded that the recommended procedure is well applicable and a conservative fatigue design is facilitated. Keywords Fatigue strength . Welded joint . Steel . HFMI treatment . Variable amplitude loading . Equivalent stress range . Specified damage sum
1 Introduction The fatigue strength of welded steel joints is generally independent of the base material’s yield strength, see IIW recommendation [1]. The application of post-weld-treatment techniques, like the HFMI treatment, is well applicable in order to utilize the lightweight potential of high-strength steel materials [2]. Guidelines for the fatigue assessment [3] under both constant (CAL) [4] and variable amplitude loading (VAL) [5],
Recommended for publication by Commission XIII - Fatigue of Welded Components and Structures * M. Leitner [email protected] 1
Department Product Engineering, Chair of Mechanical Engineering, Montanuniversität Leoben, Leoben, Austria
2
Department of Engineering Mechanics, KTH Royal Institute of Technology, Stockholm, Sweden
3
Fraunhofer Institute for Mechanics of Materials IWM, Freiburg, Germany
as well as for quality assurance [6], are developed and published as IIW recommendation for the HFMI treatment [7]. Recently, the applicability of this guideline for the fatigue strength assessment of HFMI-treated steel joints under CAL incorporating increased yield strengths, R-ratios, and plate thicknesses is validated by numerous fatigue tests data sets, see [8, 9]. In case of VAL, Palmgren [10] and Miner [11] proposed a linear damage accumulation, whereas a damage sum D of D = 0.5 is conservatively recommended in [1, 7]. In [12], a study including medium- and
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