Issue 48

F. V. Antunes et alii, Frattura ed Integrità Strutturale, 48 (2019) 666-675; DOI: 10.3221/IGF-ESIS.48.63 670 Figure 3 : Distribution of von Mises equivalent stress ahead of the notch (uncracked geometry; elastic behavior). (a) Plane stress state. (b) Plane strain state. Plastic CTOD range Figs. 4a and 4b present typical results of CTOD versus load, measured for crack increments of 40 and 800  m, respectively. The first node behind crack tip is closed at minimum load and only opens when the load reaches point A (Fig. 4b), which is the crack opening load. After opening the CTOD increases linearly with load, but after point B there is some deviation from linearity which indicates the occurrence of plastic deformation. The maximum CTOD occurs at point C, which corresponds to the maximum applied load. After the maximum load there is also a linear variation of CTOD with load decrease. With subsequent load decrease, reversed plastic deformation starts and the crack closes again. The plastic deformation increases progressively for loads above point B, up the maximum load. The plastic CTOD was obtained subtracting the elastic CTOD from the total CTOD. The comparison of both figures indicates that the crack increment increases the crack closure level, which is logical because the plastic wake increases. The slope of linear regime increases because the rigidity of the specimen reduces with crack growth. Although the increase of crack closure, the crack growth increases the plastic CTOD range, which results from the effect of crack length on crack tip stresses. Figure 4 : Crack tip opening displacement (plane stress, R n = 4 mm). (a)  a=40  m. (b)  a=800  m. 0 0.2 0.4 0.6 0.8 1 0 100 200 300 400 CTOD [  m] Force [N] Total CTOD Plastic CTOD A B C 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0 100 200 300 400 CTOD [  m] Force [N] Total CTOD Plastic CTOD A B C  p 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0  vM /  nom x n [mm] Rn= 1 mm Rn=2 mm Rn=4 mm Rn=8 mm 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 0 1 2 3  vM /  n om x n [mm] Rn=1 mm Rn=2 mm Rn=4 mm Rn=8 mm (b) R n x n (a)