Issue 21

A. De Iorio et alii, Frattura ed Integrità Strutturale, 21 (2012) 21-29; DOI: 10.3221/IGF-ESIS.21.03 28 Further relations seem to be detectable between the loading ratio R and the parameters β and γ, on the one end, and between the parameter γ and the constant C, on the other end, as it can be seen in Fig. 17 and 18. Figure 17 : Correlation between β, γ values with the loading ratio. Figure 18 : Correlation between β, γ values with the constant C. Obviously, about these latter relations, further experimental investigations on other materials and with a greater number of loading conditions are needed. C ONCLUSIONS n analytical model to interpolate the experimental crack growth curves (actual crack length as function of the number of cycles), that is alternative to the methods proposed by the ASTM 647-95a Standard, has been derived analysing the data of 180 fatigue crack propagation tests carried out by Ghonem and Dore. By a cross-check performed by means of the normality test of the residuals and the coefficient of determination R 2 , it has been highlighted that it is possible to identify those data groups, if present, which move in an anomalous and non influential manner away from the trend of the other data points, so as to be able to take in count of them in the analysis of the results. Furthermore, the model parameters have been evaluated and some interesting correlations have been found between them, which, after further validation by means of an extended experimentation, could be useful to build up a new phenomenological model, that is robust and well-rounded at the same time, to compute the fatigue crack growth rates. A