Abstract
Fatigue crack growth (FCG) is linked to irreversible and non-linear processes happening at the crack tip, which explains different problems observed in the use of da/dN-DK curves. The replacement of DK by non-linear crack tip parameters, namely the crack tip opening displacement (CTOD) is an interesting alternative. The objective in here is to study the effect of notches on FCG using the plastic CTOD range, dp. M(T) specimens with lateral notches of different radius (1, 2 4 and 8 mm were analysed numerically, keeping the total depth constant (8 mm). The increase of crack length increases dp and therefore FCG rate. For plane stress state, the formation of the residual plastic wake with crack propagation produces crack closure which compensates the effect of crack length and there is a stabilization of dp. The reduction of notch radius increases dp for all crack lengths, particularly for the shortest ones. For plane strain state there is almost no crack closure therefore dp is higher than for plane stress state, and the effect of crack length produces a relatively fast increase of dp
Highlights
The study of fatigue crack propagation is usually based on relations between the crack increment per load cycle, da/dN, and the stress intensity factor range, K. 1
The main objective here is to study numerically the effect of notches on fatigue crack growth rate using the plastic CTOD concept recently introduced by Antunes et al [20]
There is an exception for plane stress state, because the notch ratio of 1 mm gave slightly lower Kt than Rn=2 mm
Summary
The study of fatigue crack propagation is usually based on relations between the crack increment per load cycle, da/dN, and the stress intensity factor range, K. 1. The non-linear parameters identified in the literature review made by Antunes et al 8 were the range of cyclic plastic strain, the size of reversed plastic zone, the total plastic dissipation per cycle and the crack opening displacement Note that these non-linear crack tip parameters, and the J integral, usually replace K when the LEFM is no longer valid. Other current and important energy-based approaches are, for example, the control-volume technique introduced by Lazzarin [15] and the total strain energy density concept formulated by Ellyin [16 It should be mentioned the Theory of Critical Distances which combines a set of alternative approaches which have in common the fact that the effective stresses at the process zone is estimated on the basis of a characteristic material length, called critical distance [17,18,19]. An automatic elastic-plastic finite-element procedure was developed and the simulations were computed assuming both plane stress and plane strain conditions
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