Issue 33

J.T.P. Castro et alii, Frattura ed Integrità Strutturale, 33 (2015) 97-104; DOI: 10.3221/IGF-ESIS.33.13 103 the crack path in the thicker than in the thinner test specimens, or under plane strain instead of plane stress conditions, contrary to what could be expected beforehand. Finally, it should be mentioned that other limitations of the hypothesis “  K eff is the actual FCG driving force” are explored in [1] . Figure 8 : FCG rates da/dN and crack opening ratios K op /K max measured along the crack path in the thin DC(T) specimens ( t  2mm ), supposedly under pl-  conditions. Figure 9 : FCG rates da/dN and crack opening ratios K op /K max measured along the crack path in the thick DC(T) specimens ( t  30mm ), supposedly under pl-  conditions. C ONCLUSIONS long standing discussion about the actual fatigue crack growth driving force, which for many is the {  K , K max } pair whereas for many others is  K eff , remains more relevant than ever because it is a necessary condition to decide which model is the most appropriate to make FCG predictions under variable amplitude loading in practical applications. This study certainly does not settle this point, but it does present some easily reproducible results that clearly cannot be explained by the  K eff hypothesis. R EFERENCES [1] Castro, J.T.P., Meggiolaro, M.A., Miranda, A.C.O., Singular and non-singular approaches for predicting fatigue crack growth behavior, Int J Fatigue, 27 (2005) 1366-1388. A