COMPARATIVE STUDY OF INITIATION FATIGUE LIFE OF FREE DEFECT AND DEFECTIVE MATERIALS

Document Type : Original Article

Authors

1 Laboratoire de Génie Mécanique, Ecole Nationale d’Ingénieurs de Monastir, Avenue Ibn El Jazzar, 5019 Monastir, Tunisia.

2 Laboratoire de Génie Mécanique, Ecole Nationale d’Ingénieurs de Monastir, AvenueIbn El Jazzar, 5019 Monastir, Tunisia.

3 Laboratoire de Génie Mécanique, Institut supérieur de transport et de la logistique, 4000 Sousse, Tunisia.

4 Laboratoire de Mécanique et de Physique des Matériaux, UMR CNRS no. 6617, ENSMA, Téléport 2, BP 40 109, 86961 Futuroscope Cedex, France.

Abstract

ABSTRACT
This paper presents an experimental comparison of crack initiation, between free defect
and defect material, under High Cycle Fatigue (HCF) loading. Experiments are carried
out on a C35 steel. Results show that crack initiation and crack propagation
mechanisms for defective material are the same as defect free material: cracks are
initiated in the maximum shear plane then they propagate in the plane perpendicular to
the maximum principal stress direction. But the length of the stage I cracks of defect
materials is always very short in comparison with those of defect free materials. Crack
propagation regime life in defect materials is very short, contrary to defect free material
which shows an early crack initiation However, contrary to the common belief, the
fatigue life initiation is not consumed in defective material and particularly in torsion
loading where the cyclic stress tensor becomes complex around the defect.

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