Effect of residual stresses on fatigue strength of high strength steel sheets with punched holes

• Tensile and compressive residual stresses were induced around punched hole edges.
• Heat treatment at 823 K for 1 h improved the fatigue strength of punched steels.
• The tensile residual stresses around the hole edges reduced the fatigue strength.
• Fatigue limits were evaluated by the residual stresses and hardness change.

The effect of residual stresses on the reverse bending fatigue strength of steel sheets with punched holes was studied for steels with tensile strength grades of 540 MPa and 780 MPa. Tensile and compressive residual stresses were induced around the punched holes. Heat treatment of the specimens with punched holes at 873 K for 1 h decreased the residual stresses around the holes and improved the fatigue strength of the sheets. This result means that the tensile residual stresses induced in the sidewalls of the holes and near the hole edges by punching reduced fatigue strength. The effect of the residual stresses on the fatigue limits of the edges was estimated by the modified Goodman relation using the residual stresses after cyclic loading and the ultimate tensile strength at the fatigue crack initiation sites.