Issue 12

M. Angelillo et alii, Frattura ed Integrità Strutturale, 12 (2010) 63-78; DOI: 10.3221/IGF-ESIS.12.07 74 Photoelastic images of a strip, of the type o f Fig. 14, with a preexisting straight crack at  =40°, are shown in Fig. 15, where the interferometric fringes before and after crack propagation are reported. (a) (b) Figure 15 : Photoelastic images for a straight crack in mixed Mode I&II. Fringe pattern before cracking (a) and after kinking (b) . From Al Bin Mousa [13] . With the MTS-criterion the angle of kinking, in terms of the Stress Intensity Factor (SIF) ratio  =K 2 /K 1 , is given by               4 81 1 tan 2 Arc (7) With the GMax-criterion the angle of kinking, in terms of the SIF ratio  =K 2 /K 1 , is given by         2 1 2 tan    Arc (8) A plot of the kink angle as a function of the SIF ratio is reported in Fig. 16, where also a comparison with some experimental results, taken from the literature and collected by Al Bin Mousa in [13], is shown. (a) (b) (c) Figure 16 : Plots of the kinking angles versus the SIF ratio (a) , lower curve: GMax-criterion, upper curve: MTS-criterion. Comparisons of the theoretical curves with experimental results (b) . The graph (b) is taken from Al Bib Mousa [13] and “present work” in the legend (c) refers to [13]. The case represented in Fig. 1, with H=B=L, S H =(1)  and V H =(1)  , is then solved with our computer model.