Authors: D. Carvalho, A. L. L. Silva, A. M. P. Jesus, A. A. Fernandes

The fatigue behaviours of S235, S355 and S690 structural steel grades have been investigated by means of smooth and compact tension (CT) specimens. Strain-life, cyclic elastoplastic and fatigue crack propagation behaviours are compared for the proposed steels aiming the investigation of the influence of the materials static strength on fatigue. The paper also addresses the mean stress effects on fatigue crack propagation rates, through tests performed for distinct stress ratios. Besides the materials comparison based on pure mode I fatigue crack propagation tests, mixed I/II mode fatigue crack propagation test results are also presented and discussed specifically for the S235 steel grade, using a modified CT specimen. The experimentally observed crack paths on modified CT specimens were simulated by means of the FEM, to assess the history of the mode I and mode II stress intensity factors. The Virtual Crack Closure Technique was applied. The validity of existing models for fatigue crack propagation under mixed-mode conditions were assessed for the S235 steel grade.

D. Carvalho¹ | A. L. L. Silva^2,3 | A. M. P. Jesus^1,3 | A. A. Fernandes^2,3
1 Universidade de Trás-os-Montes e Alto Douro, UTAD, Vila Real, Portugal
2 Faculdade de Engenharia da Universidade do Porto, Porto, Portugal
3 IDMEC, Porto, Portugal