Fatigue initiation in C35 steel: Influence of loading and defect

• Published in: International journal of fatigue Vol. 32; no. 4; pp. 780 - 787
• Main Authors: Nasr, A., Nadot, Y., Bouraoui, Ch, Fathallah, R., Jouiad, M.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.04.2010; Elsevier
• Subjects: Applied sciences; Crack initiation; Crack propagation; Defect free material; Exact sciences and technology; Fatigue; High cycle fatigue; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Surface defective material; S– N curve; S– N curve; Defect free material; High cycle fatigue; Surface defective material; Crack initiation; Crack propagation; S-N curve; Mechanical properties; Defect; Fatigue; SN diagram
• ISSN: 0142-1123; 1879-3452
• DOI: 10.1016/j.ijfatigue.2009.09.012

The aim of this work is to study the influence of both defect and tension and torsion loading on stress number of cycles ( S– N) 25 curves for C35 steel. A spherical artificial defect has been machined at the surface of gauge length of fatigue samples. The crack initiation mechanisms have been identified based on several observations on Scanning Electron Microscope (SEM) at different stage of fatigue life. The initiation crack length definition is proposed for defect free and defective material. For defect free material, torsion loading allows relatively earlier initiation compared to tension loading. In the case of defective material, it is observed that, for the both types of loading, initiation fatigue life is not negligible by comparison to total fatigue life. It is also concluded that defects are much more deleterious to fatigue life in the range of high cycle fatigue regime. However, for the limited fatigue lives (between 10 4 and 10 5 cycles), the defect free and defective material S– N curves are relatively comparable.