A mechanistic model for the influence of stress ratio on the LEFM fatigue crack growth behavior of metals and alloys—I. Crack-ductile materials

Transitional behavior of fatigue crack growth in welded joint of 25Cr2Ni2MoV steel

“…9a, c and e are 28%, 30.6% and 28.6%, respectively. Similar behavior of the facet distribution have been reported by Lal [10], Liaw et al [31] and us [32]. This means that facet feature of fracture surface morphology is related to the changes of transition point in BM.…”

“…However, for the da/dN at the corresponding transition point, Schijve [24] argued it was a constant over a wide range of stress ratios for the aluminum alloys. On the contrary, the da/dN at the transition point was found decreased with the decrease of stress ratio R according to Lal [10]. Radhakrishnan [9] concluded that both the da/dN and DK t decrease with the increase of R. These indicate the influence of R on the transition point is still an open issue.…”

“…In contrast, in the Paris regime a linear relationship is generally reported. Therefore, a transition point is inevitable between the near-threshold and Paris regimes of a da/dN À DK curve [9,10]. According to Liu and Liu [11] and Yoder et al [12], FCG data below such a kind of transition point denote the onset of real threshold regime, while those above the transition point belong to the Paris regime by considering the similarity of fracture morphology [13].…”

“…As such, the transitional behavior of FCG curve is generally recognized as a symbol of the fracture mode change during the crack propagation [10,[14][15][16]. According to McDowell and Dunne [17], crack growth in the Paris regime is driven by multi-slip deformation.…”

“…Effects of load ratio R on the transition point have been investigated extensively [1,11,15,23]. It has been recognized that the value of DK at the transition point decreases with R increasing [9,10,14,24]. However, for the da/dN at the corresponding transition point, Schijve [24] argued it was a constant over a wide range of stress ratios for the aluminum alloys.…”