Issue 35

X.C. Arnoult et alii, Frattura ed Integrità Strutturale, 35 (2016) 509-522; DOI: 10.3221/IGF-ESIS.35.57 520 1/2 L c a Pmf W K BW        (2) Where m is the number of ligaments, P the load on each ligament, W and B are full specimen width and thickness, and a f W       the function of the crack length-to-width ratio. When the subunit toughness is estimated, the global fracture toughness can be computed using the following equation [33]: 0 1 24 L c Ic f ys K K E B B            (3) where ys  is the yield strength, E the elastic modulus, f  the true fracture strain for plain stress condition, B the full thickness of specimen, and 0 B the maximum thickness in which the plane-stress fracture can fully develop. Rao et al [13] used these two equations to estimate the fracture toughness of aluminum-lithium alloys and the agreement between the experimental results and estimation was excellent according to them. C ONCLUSION s seen above, numerical simulation by finite-element-analysis [15] may be used to provide the stress distribution close to the back and the head of delamination crack. Nevertheless, this type of simulation accounts only for one delamination crack and therefore, cannot provide information on the impact of multi-delamination cracks on c K and c J . Furthermore, no explanation can be provided about the influence of delamination cracks on the crack growth rate of the macrocrack. Neither is it clear if the delamination cracks appear before or during the propagation of the macrocrack. Thus to clarify these two questions it is necessary to develop a simulation methodology that could foresee if there are some reciprocal influences between the macrocrack and the delamination cracks. The use of multi-scale modeling to estimate the stress and strain distribution inside grains and at grain boundaries could help to progress in this field and define a delamination cracks criterion.  Heat treatment, test temperature, thickness of specimen and stress distribution significantly influence the number, width and length of delamination cracks.  For Charpy impact test, the upper shelf energy decreases, the DBTT shifts to lower temperatures and the lower shelf energy increases in the presence of delamination cracks.  Large number of delamination cracks yields to inferior toughness.  The presence of ferrite together with a harder phase combined with high intensity of {100} orientation plane favors the occurrence of delamination cracks.  The delamination cracks occur in brittle manner at weak interfaces.  The delamination cracks change the stress distribution from plane-strain to plane-stress condition. The presented work was financially supported by the SUSEN Project CZ.1.05/2.1.00/03.0108 realized in the framework of the European Regional Development Fund (ERDF). R EFERENCE [1] Guo,W., Dong, H., Lu, M., Zhao, X., The coupled effects of thickness and delamination on cracking resistance of X70 pipeline steel, Int. J. Pressure Vessels Pip., 79 (2002) 403-412. [2] Yang, Z., Huo, C.Y., Guo, W., The Charpy Notch Impact Test of X70 Pipeline Steel with Delamination Cracks. Key Eng. Mater., 297-300 (2005) 2391-2396. A