Issue 41

J.A.O. González et alii, Frattura ed Integrità Strutturale, 41 (2017) 227-235; DOI: 10.3221/IGF-ESIS.41.31 231 Figure 5 : (a) Vertical displacement and (b) strain field maps obtained from VIC-3D DIC analysis. Figure 6 : Typical P op measurements made using redundant and independent back-face and near-field strain gage readings, as well as the signal obtained from the DIC analyses performed in the new thin DC(T) specimen with t  2mm , while the crack was propagating under nominally plane stress conditions. Figure 7 : Typical P op measurements made using redundant and independent back-face and near-field strain gage readings, as well as the signal obtained from the DIC analyses in the new thick DC(T) specimen with t  30mm , while the crack was propagating under nominally plane strain conditions. The FCG rates measured in all thin and thick specimens remained essentially fixed (and independent of their thickness) during the entire FCG process. This result confirms the classic ASTM view that da/dN  K curves measured under fixed R -ratios can properly characterize the FCG of structural materials independent of the specimen geometry, at least when applied to the tested steel. Moreover, it also confirms, or at least cannot deny, that {  K , K max } can be considered as the FCG driving forces, so that  K can be used as a similitude parameter in FCG predictions. On the other hand, this data can also be used to question the alternative view that FCG is driven by  K eff . Those unambiguous tests clearly show that the crack opening ratio K op /K max significantly and steadily decreased as the crack size increased in both the thin and the thick specimens, decreasing the size of the predominantly elastic residual ligament that forces their closure. So, it can be