Issue34

L. Marsavina et alii, Frattura ed Integrità Strutturale, 34 (2015) 387-396; DOI: 10.3221/IGF-ESIS.34.43 393 R ESULTS AND DISCUSSIONS his paper is focused on the determination the crack initiation angle and the obtained crack paths under mixed mode loading of PUR foams. The obtained crack paths were digitized using a NIKON D5100 Digital Camera. Fig. 4 presents the crack paths for ASCB specimens for six loading configurations: a. mode I, b.-e. mixed modes, f. mode II. Except for the mode I case, when the crack propagates like a straight line, all other cases show curvilinear crack paths. Figure 4 : Crack paths resulted from testing ASCB specimens. In Fig. 5 the crack paths for SEC specimens are shown. More straight crack trajectories resulted on testing the SEC specimens for all loading configurations. a .  0 0 C b .  0 0 C c .  45 0 C d .  0 0 C e .  0 0 C Figure 5 : Crack paths resulted from testing SEC specimens. Figure 6 : Measurement of crack initiation angle. The crack initiation angle  c was measured on each specimen using Sigma Scan Pro software as the angle between the tangent (red line) to the crack at the initiation point and the crack initial direction (blue line) in Fig. 6. Fig. 7 presents the mean values and the range (minimum to maximum values) of the crack initiation angle  c measured on the specimens versus applied mixed mode loading Me = Arctg(K II /K I ) side by side with the predicted crack propagation angles by the four theoretical criteria. It could be observed that for predominantly mode I loadings Me < 45 0 the measured values are in good agreement with the predicted ones. For predominantly mode II loading ( Me > 45 0 ) the T