Issue 35

R. Sepe et alii, Frattura ed Integrità Strutturale, 35 (2015) 534-550; DOI: 10.3221/IGF-ESIS.35.59 540 Figure 9 : FE model of the panel. Sines criterion Experimental investigations in last years have provided numerous hypotheses on the Multiaxial High-Cycle Fatigue criteria. In literature, many proposals of such criteria can be found [20-28]. From a numerical point of view, the criteria which may be conveniently applied are of two types: criteria based on stress state invariants and criteria using average stresses or deformations in an elementary volume. In 1959, Sines [29] reviewed the results of experiments on the effect of different combinations of tensile, compressive, and torsional mean and alternating stresses on fatigue life. He reported that alternating shear stresses appeared to cause fatigue failure. On this basis, he formulated a criterion including the amplitude of octahedral shear stresses and the first linear stress invariant. The stress components of these criteria are easy to obtain from FEA’s. The invariant formulae usually consist of quantities related to hydrostatic and octahedral stresses. The use of these hypotheses allows to determine the initiation point of fatigue cracks provided that structural load conditions respect two main assumptions:  the structure is subject to alternating proportional loads;  the directions of the principal stresses are fixed during the application of the loads. However, the orientation of potential cracks with these criteria cannot be defined. The Sines criterion has the following form:      , oct H m k (1)