Tensile tests using plate specimens with a surface flaw were conducted in order to study the large deformation behavior of steels with a flaw. Steels prepared for examination had tensile strengths of 470–490MPa with different stress-strain relationships. The strain distribution during loading and the maximum strain at fracture were measured in order to investigate the influence of stress-strain properties on ductile fracture. The crack shape changes during ductile crack growth were also examined and compared with empirical formulae for estimating fatigue crack shape change. In order to assess test results, three dimensional elastoplastic finite element analyses were carried out which included detailed analysis of the influence of stress-strain properties on deformation behavior. In addition, a simplified analytical model to estimate fracture strain and critical flaw size was proposed using the stress-strain relationship of Swift’s equation. The results from the model show fairly good agreement with experimental results.

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