Multiaxial Fatigue Strength to Notched specimens made of 40CrMoV13.9

Abstract

Fatigue is a process (succession of mechanisms) which under the action of time-varying strains or deformations modifies the local properties of a material. These can lead to the formation of cracks and eventual rupture of the structure. Fatigue is in particular characterized by an extent of variation in stress which may be well below the yield strength of the material. The main stages of fatigue failure of an assembly are the initiation of cracks (if defects are not already present in the material), the propagation of cracks and the final rupture. The parameters often used to predict the fatigue behavior and thus the number of cycles at break of a structure is: The amplitude of the stress (loading or imposed strain), its average value, the surface state and the medium In which the structure will be used. Even if the study of fatigue is based on theoretical considerations (in particular the mechanics of the rupture), it is essentially an experimental field. The characterization of a material, a part, an assembly, a structure, requires numerous tests and measurements. The work deals with multiaxial fatigue power of specimens which are notched and all made of 40CrMoV13.9. Circumferentially V-notched specimens and semicircular notched were tested under combined tension and torsion loading, both, in phase or out of phase. Geometry of symmetric axis of V notched issues has been characterized of a notch radius constant from (1 mm) and V-notch opening angle of 90°. The semicircular specimens were characterized by a constant notch tip radius. For both situations the net diameter sectional area was 12 mm. The results from multi-axial tests are discussed together with those obtained being all under loading pure torsion and tension by the issues notched having the same geometry. Altogether more than 120 new fatigue data are summarized in the present work. All presented fatigue data are first in terms of nominal amplitudes stress and then reanalyzed in terms of the mean value of the strain energy density evaluated over a finite size semicircular sector surrounding the tip of the notch.