Issue 36

L. C. H. Ricardo et alii, Frattura ed Integrità Strutturale, 36 (2016) 201-215; DOI: 10.3221/IGF-ESIS.36.20 204 Figure 2 : Three-dimensional plastic zone [11]. a) b) Figure 3 : Dugdale Plastic Zone Strip Model under plane stress conditions. a) Dugdale crack; b) wedge crack . In the original Paris crack propagation equation [6] the driving parameters are C,  K and m, as shown in Fig. 1. Among other limitations, this equation is valid only in the region (b). So, it does not cover the near threshold region (a) nor the unstable region (c). Some researchers have proposed similar equations that cover one or both extremes of the curve in Fig. 1. In Tab. 1 it is possible to see some other crack propagation equations for constant amplitude loading, which are modifications of the Paris equation, relating the mentioned parameters and Kc, the critical stress intensity factor.   min max ( ) 1 m c C K da dN K K K K          max ( ) m c C K da dN K K    1 max ( ) ( ) m m da C K K dN    Table 1 : Some Empirical Crack Growth Equations for Constant Amplitude Loading [6]. Murthy et al. [13] discuss crack growth models for variable amplitude loading and the mechanisms and contribution to overload retardation. There are many authors which have been developing fatigue crack growth models for variable amplitude loading. Tab. 2 presents some authors and the application of their models.