Issue 38

M. Leitner et alii, Frattura ed Integrità Strutturale, 38 (2016) 47-53; DOI: 10.3221/IGF-ESIS.38.06 50 R R 2 2 1                   (2) Multiaxial fatigue tests under proportional rotating bending and torsion loading are carried out in order to assess the fatigue behavior under multiaxial loading for the investigated steel 50CrMo4. The tests are performed in the unnotched specimen condition at a loading stress ratio of R=-1 and a shear to normal stress ratio of  T /   =0.5 . Fig. 4 summarizes the uniaxial results under pure normal and pure shear stress, and the combined proportional loading mode. The application of the model according to Gough and Pollard illustrates a good accordance to the test results. Moreover, the method demonstrates its applicability for numerous test results incorporating steel, cast iron and aluminium specimens in [6]. Figure 4. Multiaxial fatigue behaviour under proportional loading (50CrMo4). C RITICAL PLANE APPROACH mong stress, strain and energy based multiaxial fatigue criteria, the critical plane approach is one widespread method due to its effectiveness and broad application range. The general procedure of the approach is a reduction of the multiaxial stress condition to an equivalent uniaxial stress, firstly introduced by [7]. Definition of the cutting plane angle  and calculation of the associated normal and shear stress is shown in Fig. 5. Figure 5. Evaluation of normal and shear stress in critical plane. A review of critical plane orientations in multiaxial fatigue failure criteria for metallic materials is provided in [8]. One basic equivalent stress concept is introduced by Huber-Mises-Hencky assuming a ratio of normal to shear stress fatigue strength of √3, see Eq. 3 in case of plain stress condition. Another approach by Lamé takes only the portion of the (maximum) normal stress into account, see Eq. 4. v n n 2 2 1 3       (3) A