Catherine Froustey

Multiaxial fatigue endurance of 30NCD16 steel

Abstract Various criteria used to choose specimen dimensions under multiaxial fatigue have been proposed but their validity is not proven because not enough tests have been carried out in this field. A machine for carrying out fatigue tests under simple, radial and complex loads has therefore been designed. This prototype enables a specimen to be subjected to the loadings experienced by a propeller shaft: a combination of asymmetrical bending (plane or rotative bending) and torsion with various values. The results obtained for an aeronautical steel (30NCD16 steel) enable examination of the validity of the three accepted criteria for this study and the proposal of two methods of sizing (the former theoretical, the latter empirical) which better reflect the experimental results.

Multiaxial fatigue of steel―testing out of phase and in blocks : validity and applicability of some criteria

Abstract The criteria used to calculate the dimensions of specimens under multiaxial fatigue are compared with some particularly unusual or discriminating test results. Tests carried out with combined loadings and in blocks of different loadings, and some tests on data in published work enable us to define the area of application and the validity of criteria. The most widely used approach, with two stresses applied to one specific facet, is shown to be inaccurate in a number of test configurations. An energy-based approach would seem to be more appropriate.