ISSN: 1546-962X
Page Count: 11

Fatigue Strength in Presence of Inhomogeneities: Influence of Constraint
Beretta, S
Professor, Researcher, and Ph.D. Student, Politecnico di Milano,

Carboni, M
Professor, Researcher, and Ph.D. Student, Politecnico di Milano,

Madia, M
Professor, Researcher, and Ph.D. Student, Politecnico di Milano,

(Received 13 April 2005; accepted 26 January 2006)

Abstract

The effect of defects on the entity of the fatigue limit is nowadays well known and is demonstrated to be equivalent to the nonpropagating condition of short cracks. The influence of constraint at the defect tip has been addressed in the present paper considering a mild steel whose mechanical behavior has been experimentally determined together with the propagation threshold values for long cracks. The activity has first dealt with the determination of the Kitagawa diagram by means of fatigue limit tests using specimens containing micro-notches with different shapes (drilled holes and narrow slits). Experimental results showed a significant influence of the defect shape on the fatigue limit and thresholds. In order to understand the reasons, defects have then been analyzed by elasto-plastic FEM analyses. Computational results have confirmed a significant difference in the global constraint factor at the crack tip between round and narrow defects.

Keywords:
fatigue, constraint factor, defect shape, fatigue thresholds

Paper ID: JAI13199
DOI: 10.1520/JAI13199
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