Fatigue resistance of stainless steel bolts under tension

Bolted connections made of stainless steel are increasingly used in cyclic loading applications. The design rules according to the current version of the first generation of EN 1993-1-9 were historically developed for carbon steel bolts and apply equally to stainless steel bolts, although the material properties of carbon and stainless steel bolts differ significantly. Furthermore, the fatigue resistance of stainless steel bolts is almost unknown. In the draft of the second generation of EN 1993-1-9, FprEN 1993-1-9, design rules for stainless steel bolts are not specified anymore. For this reason, fatigue tests under constant amplitude loading under tension were conducted with bolts M16, M20, M24 and M36 according to EN ISO 4014/4017 made of austenitic stainless steel (A2 and A4) and austenitic-ferritic (duplex) stainless steel (D4, D6 and D8) with property classes 70, 80 and 100. In total, 175 fatigue tests under constant amplitude loading under tension were performed in accordance with DIN 969. The fatigue tests showed that the investigated stainless steel bolts achieve higher fatigue resistances than specified by the detail category according to EN 1993-1-9, so that the specified fatigue resistance is conservative. Based on the results, modifications of the detail categories for stainless steel bolts and rods are proposed, which allow a more economical design. The results of this investigation have already been proposed for an early amendment to FprEN 1993-1-9. This paper provides background information of the proposed modifications.