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Two-Parameter Approach for Short Cracks at Notches
Seitl, Stanislav ; Hutař, Pavel ; Knésl, Zdeněk
A two parameter constraint-based fracture mechanics method is applied to the behavior of microstructurally and mechanically short fatigue cracks. A short crack in the vicinity of a grain boundary and a crack which is engulfed by the plastic strain field of a notch are studied as examples. The different levels of stress constraint are quantified by using the T-stress and the Q parameter. The corresponding calculations are performed by using a finite element method (ANSYS system). The influence of the T values on the propagation of short fatigue cracks is analyzed. The size of the plastic zone and the crack closure are significantly affected by the level of constraint. The influence of constraint on small fatigue crack growth kinetic is studied under the assumption that the controlling variable for the rate of propagation of the fatigue crack is the size of the plastic zone.
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Evalution of Q-parameter in the case of microstructurally short fatigue cracks
Seitl, Stanislav
The paper presents evaluation of the elastic-plastic Q-parameter in the case of microstructurally short fatigue cracks, i.e. for cracks for which the crack size is comparable to the scale of the characteristic microstructural dimension such as the grain size. The microstructurally short crack is modelled as a crack with its tip in the vicinity of an interface between two different materials (elastic one and steel 12060), see Fig.1. Q-parameter is calculated by means of direct use of finite element results, namely the difference from the T = 0 reference solution, see Eq.5. Q-parameter is determined as a function of the crack orientation with respect to the interface, the crack length and the ratio of Young's modulus of both materials, see. Fig.1.
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