Issue 41

V.M. Machado et alii, Frattura ed Integrità Strutturale, 41 (2017) 236-244; DOI: 10.3221/IGF-ESIS.41.32 240 fact, cracks (short or long) should not be modeled as 1D unless their fronts uniformly cut the whole piece thickness and can be described by just 1 coordinate. Moreover, these estimates are only valid for mechanically short cracks, those with both a and a 0 larger than the grain size of the material gr . The FCG behavior of microcracks with sizes a and a 0 < gr is sensitive to microstructural features, but since grains (let alone dislocations) cannot be mapped in practical applications yet, their use for structural engineering purposes may be questionable. Figure 2 : Larger stress ranges  tolerable by the studied component under many R –ratios as a function of the size a of an edge crack, for w = 3.4mm , h = 1.12 ,  K th0  6MPa  m , a 0  59mm ,  6 , and  F  1.6 . Figure 3 : Influence of the typical ranges of FCG threshold 6 <  K th0 < 12MPa  m and of Bazant’s data-fitting exponent 1.5 <  < 8 on the largest stress ranges  0 tolerated by the studied piece. T HE BEHAVIOR OF SHORT CRACKS UNDER EP CONDITIONS nder contained elastoplastic conditions around crack tips, which invalidate the use of SIFs to quantify the local crack driving forces, the non-propagating crack problem can be modeled using the J -integral approach [16-17], as originally proposed in [11]. However, since like in the LE case short fatigue cracks present higher FCG rates than long cracks in the EP case as well, it is operationally convenient to modify their J th ( a ) propagation threshold to consider the effects of the short crack characteristic size a 0 when accounting for their peculiar behavior near EP notch tips. In the LE case, the size-dependent threshold J th (a) must of course be given by K th (a) 2 /E' , where E'  E or E'  E /( 1   2 ) for plane stress or plane strain limit conditions. In this way, J th (a) can then be easily compared with the crack driving force quantified by J when modeling the EP short crack behavior. If the stresses controlled by J grow proportionally to the load U