The Influence of Mismatch Effect on the High Cycle Fatigue Resistance of High Strength Steel Welded Joints

Abstract

The objective of this article is to present the newest results of our research work related to the high cycle fatigue resistance of advanced high strength steels. In order to determine and compare the fatigue resistance, high cycle fatigue (HCF) tests were performed on two strength categories (S690 and S960) of high strength steels including quenched and tempered (Q+T) and thermomechanical (TM) types. During the HCF tests base materials and their welded joints were investigated at different mismatch conditions (matching, undermatching, overmatching). Measured and analysed data about base materials and welded joints were compared and discussed. Statistical approach was applied during the preparation and the evaluation of the investigations, which increased their reliability. The parameters of the HCF design curves were calculated based on the Japanese testing method (JSME S 002-1981) which uses 14 specimens. During the evaluation the results were compared with each other and with literary data. According to the presented examinations the HCF resistance of the base materials is more advantageous than the welded joints. The TM steel indicated better fatigue resistance than the quenched and tempered one of the same category. The matching problem had influence on the HCF resistance of high strength steels, depending on the strength category and the steel type.