Closure and Growth of Mode I Cracks in Biaxial Fatigue

Abstract

Abstract— —The closure behavior of mode I fatigue cracks under biaxial loading is studied with an elastic‐plastic plane stress finite element model. Biaxial stresses are shown to have a significant impact on crack closure behavior at higher maximum stresses. In general, normalized crack opening stresses are highest for equibiaxial loading and lowest for pure shear loading. The differences are apparently negligible for maximum applied stresses less than about 0.4 σ0. Experimental crack growth data are quantitatively consistent with these trends. Correlations of the experimental data with a simple ΔKeff were successful as first‐order engineering estimates. Changes in forward and reversed plastic zone sizes with biaxiality are not entirely consistent with trends in crack growth rates.

Effect of cyclic plastic strain on fatigue crack growth

“…The crack length independent factor is termed the damage parameter in conventional fatigue assessment approaches according to the local strain approach. The application-relevant crack closure effects have been taken into account by McClung [50] and Savaidis and Seeger [53,54]. In a straight forward way, Savaidis et al extended Eq.…”

“…Research began with investigations of loading cases with fixed principal axes: Biaxial and proportional loading [42][43][44][45][46][47][48][49][50][51][52][53][54][55]. The common feature of most of these modelling approaches is that the driving force parameters are composed of two factors: a function of the crack length and the hardening exponent together with the ranges of the far-field loading.…”

Recent advances in fatigue crack growth modeling

“…Several modeling efforts have focused on plane stress versus plane strain (termed out-of-plane constraint) conditions [30,35,41] and in plane constraint [48,49] where the stresses are applied both perpendicular and parallel to the crack. In general as -~/aH increases the closure levels decrease.…”

“…We will provide an account of our research on maximum stress level effects [22][23]28], notch effects [6,16,21,24], variable amplitude loading effects [7], the role of tensile stresses ahead of a crack tip [30,35,41], microstructure effects (microscopic plasticity and roughness induced closure [42][43][44][45][46][47]), in-plane and out-of-plane constraint [35,40,41,[48][49], and time dependent crack growth effects [50].…”

“…Crack growth results of Brown and Miller exhibiting higher crack growth rates for the ,k = -I case and the consolidation of results using Ah'~ee[49].Recent advances in fatigue crack growth modeling Effective stress ratio as a function of maximum stress and the prediction with the U expression (R ----0 plane stress)[50].The values for n ---0.0816 and a0 --993 MPa were chosen to represent Rene 95[50]. When ~rc/ao becomes large or when hold time th is zero, the creep deformation becomes negligible and the results asymptotically approach U0.…”