Issue 48

F. V. Antunes et alii, Frattura ed Integrità Strutturale, 48 (2019) 666-675; DOI: 10.3221/IGF-ESIS.48.63 673 The variation of crack length is the cause of the global trend for the increase of  p with crack growth. For plane stress state, the increase of crack length is accomplished by an increase of crack closure which stabilizes the values of  p . In other words, the effect of crack length is compensated by the increase of crack closure. The decrease of notch radius produces a faster increase of crack closure and therefore a faster stabilization of  p . For plane strain state, there is almost no crack closure, therefore  p is bigger than for plane stress state. The absence of crack closure produces a faster growth of  p with crack propagation, explained by the increase of crack length and by the progressive separation from the notch. Ding et al.  28  studied the 1070 steel in the form of round bars and concluded that for positive stress ratios FCG is mainly influence by notch plasticity, while for negative stress ratios crack closure plays a significant role. Hammouda et al.  29  attributed the observed short crack growth phenomenon to the combined effect of the notch plasticity and the crack- tip plasticity. Li  30  suggested that the fatigue crack growth from a notch was dominated by notch plasticity within the notch plasticity zone and the notch plasticity induced crack closure out of the notch plasticity zone. Figure 7 : Variation of crack closure with crack length. C ONCLUSIONS numerical study was developed to study the effect of notches on fatigue crack growth rate. As the crack propagates, there is an increase of  p and therefore of fatigue crack growth rate. For plane stress state, the reduction of notch radius increases  p for all crack lengths, particularly for the shorter ones. The crack closure level increases with the decrease of notch radius, and this explains the convergence of  p for different notch radius as the crack propagates. For plane strain state there is almost no crack closure, therefore the crack length has a greater impact on plastic CTOD range. A CKNOWLEDGEMENTS his research is sponsored by FEDER funds through the program COMPETE (under project T449508144- 00019113) and by national funds through FCT – Portuguese Foundation for Science and Technology, under the project PTDC/EMS-PRO/1356/2014. One of the authors, P.A. Prates, was supported by a grant for scientific research also from the Portuguese Foundation for Science and Technology (SFRH/BPD/101465/2014). All supports are 0 10 20 30 40 50 0 0.5 1 1.5 2 U clos [%] x n [mm] Rn=1 mm Rn=2 mm Rn=4 mm Rn=8 mm plane  stress plane  strain A T R n x n