ABSTRACT

Investigations on high strength steel S690QL butt welds with different mechanical post weld surface treatments have been carried in order to show how different treatment intensities are interacting with the near surface residual stress condition and at least with the resulting fatigue strength. Experiments with high frequency hammer peening techniques in comparison to shot peening processes reveal, that the penetration depth of the induced compressive residual stresses is higher after the application of the hammer peening processes. However this does not necessarily lead to the best residual stress distribution because high intensities may also produce detrimental tensile residual stresses in deeper surface layers. Finally the results show, that the combination of different measurement techniques enables a reliable characterization of such treatments.

INTRODUCTION

Many efforts have been realized in the last three decades to develop methods for a fatigue strength improvement of welded constructions [Heeschen 1986, Müsgen 1982, Maddox 2004]. This is due to the well known effect that the fatigue strength of welded steel and aluminium joints usually is very low after welding in comparison to the base material. Thus the usage of modern materials like fine grained high strength steels does not lead to remarkable improvement of the fatigue strength under alternating or partially tensional loading conditions if the same welding procedures are used. As many investigations have shown a post weld treatment with help of thermal or mechanical treatment methods can be very helpful regarding to the final fatigue strength. Target of the REFRESH-project, which is supported by the German Federal Ministry for Education and Research (BMBF), where the presented investigations are related to, is to develop strategies which allow a significant extension of the fatigue endurance of welded steel constructions like bridges or the supporting structures of wind energy plants.

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