A Theory for Fatigue Failure under Multiaxial Stress-Strain Conditions

Abstract

A new theory for multiaxial fatigue is presented that is based on a physical interpretation of the mechanisms of fatigue crack growth. It may be represented graphically by contours of constant life, which are expressed mathematically by where q, 6% and E~ are the principal strains,This equation underlines the importance of strain parameters in correlating fatigue data. I t illustrates the effect of both the shear strain and the tensile strain normal to the plane of maximum shear. The theory is compared with several classical and recent theories, which are briefly reviewed. I t is shown that classical theories of fatigue failure cannot correlate experimental data, and may be dangerous if used for design purposes.

From numerical calculations to materials testing homologation: a biaxial fatigue reliability prediction methodology for structural components

“…Therefore for the critical evaluation points, the results precision would be minor affected in 2% for a fatigue analysis considering the Brown-Miller model 3 .…”

“…In order to consider the mean stress effect on the fatigue damage, the Morrow correction 15 was adopted, as it is more indicated for steels while the Smith-Watson-Topper would be more indicated for castings and aluminum 3,16 . The final Equation 6 is to be used for the proposed method.…”

“…Fatigue cracks are mostly initiated on components surface where plane stress fatigue methods can be adopted 4 . Therefore, significant efforts on mathematical modeling development have been made considering the bi-axial damage behavior 3 . Multiaxial stress environment can be proportional or non-proportional even under uniaxial loads due to geometry constrains at notches 5 .…”

“…Multiaxial stress environment can be proportional or non-proportional even under uniaxial loads due to geometry constrains at notches 5 . Non proportional stresses require often the critical plane approach 1 and range acceptance criteria can be used to simplify the analysis scope for proportional loading 3 .…”

Notch and mean stress effect in fatigue as phenomena of elasto-plastic inherent multiaxiality

“…In particular, initially it is worth noticing here that, when plain metallic materials are subjected to multiaxial cyclic loading, micro/meso-cracks can propagate either on the component surface or inwards, the latter situation being the most damaging one [19,20] According to the above experimental outcomes, the hypothesis can be formed then that, given the assumed crack initiation location (point O in Figure 1a), fatigue damage reaches its maximum value on that material plane experiencing the maximum shear strain amplitude, γ a [1,5,6] (see Figure 1b), and it holds true independently of the complexity of the loading path damaging the material being assessed. Further, it is hypothesised that, in order to correctly take into account the mean stress effect, according to Socie [22], not only the amplitude, σ n,a , but also the mean value, σ n,m , of the stress normal to the critical plane has to be incorporated into the fatigue damage model (Fig.…”