Matching effect on fatigue crack growth behaviour of high-strength steels GMA welded joints

The objective of the paper is to study the influence of the mismatch effect on high-strength steels and to determine fatigue crack propagation design curves. In order for determination and comparison of the fatigue resistance, fatigue crack growth tests were performed on S690QL, S960QL quenched and tempered, and S960M thermomechanically rolled high-strength steels. Fifteen-millimeter- and 30-mm-thick base materials were used for our investigations. Welded joints were made from these base materials, using gas metal arc welding with matching, overmatching, and undermatching filler metals. In the paper, the performance of the welding experiments will be presented, especially with the difficulties of the filler material selection; along with the results of the fatigue crack growth examinations executed on the base materials and its welded joints. Statistical aspects were applied both for the presenting of the possible locations of the cracks in the base materials and the welded joints and for the processing of the measured data. Furthermore, the results will be compared with each other, and the possibility of derivation of fatigue crack propagation design or limit curves will be referred.