Fatigue strength of thermal cut edges—influence of ISO 9013 quality groups

Abstract

The use of high strength steels has gained importance due to the interest in effective light steel constructions. Besides the well-designed weld seams, free cutting edges gain technical and economic relevance as locations for potential fatigue cracks. In this investigation, fatigue tests were carried out on 8-mm- and 20-mm-thick samples with a minimum yield strength ranging from 355 to 960 MPa at a stress ratio of R = 0.1. The cutting methods used were oxygen, plasma, and laser cutting. The surface roughness, hardness profile, and residual stresses were measured to classify the specimens into quality groups according to ISO 9013. Most of the specimens are classified in the quality groups 2 and 3. A slight tendency can be seen that the fatigue strength decreases with an increasing roughness value. Increasing local hardness values at the cut edges also have a minor negative influence on the fatigue strength. No positive impact was observed for increasing tensile strength on the fatigue strength. With higher surface roughness values, larger notches exist, the crack initiation starts early, and the fatigue strength decreases.