Influence of surface integrity on the fatigue strength of high-strength steels

• Influence of production process on the fatigue strength of high-strength steel
• Large-scale specimen to include the influence of realistic production environment
• Measurements of surface roughness, hardness, residual stress and fatigue strength
• Surface treatments considerably increase fatigue strength of large-scale structure.
• Sandblasting increases surface roughness but reduces fatigue strength only slightly.

This paper investigates experimentally the influence of surface integrity on the fatigue strength of high-strength steel used in large structures. The investigation utilises large-scale specimens of the balcony openings of a cruise ship. The test specimens, which have a dog-bone shape and yield strength of 355 MPa, 460 MPa, or 690 MPa, are cut by plasma. After the cutting, the specimens are treated by grinding or by grinding followed by sandblasting, i.e. using post-cutting treatments that are suitable for shipyard conditions. The resulting surface roughness, hardness profile, and residual stress are measured. Fatigue tests with a load ratio of R = 0.1 are carried out until the final failure of the specimens. The investigation shows that post-cutting treatments suitable for shipyard conditions can considerably increase the fatigue strength of high-strength steel used in opening corners of a large-scale structure. Sandblasting after grinding increases the surface roughness, but reduces the fatigue strength only slightly.