Abstract
This paper proposes a new and improved way to determine the dependency of the parameter that characterizes the process zone size ∫ with fatigue life Nf. Thus, unlike the classical approach, this approach has the advantage of allowing the construction of a ∫ versus Nf relationship, which is independent of the type of test used for calibration. In order to define the new relationship, a calibration strategy is presented considering the critical plane models based on the Fatemi-Socie and Smith-Watson-Topper. The accuracy of the method is verified by using data sets taken from the literature. A study on the effect of stress ratio (R) on the behaviour of the ∫ versus Nf relationship is presented and indicates that, although such relationship seems to depend on the R value used in the calibration, the life predictions obtained by these relationships are statistically similar.
Highlights
This section briefly presents the critical distance theory [1,2,3]
The critical distance, represented by the characteristic length L varies for each method and can be calculated by Equation (1) when the point method is adopted
Castro et al [15] used the criteria of Crossland, Dang Van and the MWCM to show that the critical distance may be different from half of the El Haddad's intrinsic crack length as proposed in [1]
Summary
This section briefly presents the critical distance theory [1,2,3]. The method aims to predict the fatigue strength of components with stress concentrators, such as notches or cracks [1]. In the Theory of Critical Distances, TCD, fatigue damage is predicted when the effective stress in a process zone exceeds the fatigue resistance of the material. The idea of using such a stress parameter is quite convenient and simple, we must consider that in many situations it is not representative of the phenomenon This parameter discards the well known mean stress effect on fatigue resistance. From the phenomenological point of view, the use of σ1a does not seem to be an adequate choice In this sense, in order to solve this deficiency, some researchers have proposed critical distance models that use other parameters to represent the driving force that controls the fatigue phenomenon. Castro et al [15] used the criteria of Crossland, Dang Van and the MWCM to show that the critical distance may be different from half of the El Haddad's intrinsic crack length as proposed in [1]
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