Issue34

Y. Sumi, Frattura ed Integrità Strutturale, 34 (2015) 43-59; DOI: 10.3221/IGF-ESIS.34.04 51 Figure 5 : Double-cantilever beam specimen [12, 24]. Figure 6 : Stability parameters for a double-cantilever beam specimen [12, 24]. Figure 7 : Crack paths observed in double-cantilever beam specimens [12, 24]. Energy Consideration of Crack Paths for Inhomogeneous Fracture Toughness Following Bilby and Cardew [20], the elastic energy release rate G due to the slightly kinked and curved crack extension can be calculated by Eq.(24) for a homogeneous material, where K I and K II , are the stress intensity factors at the extended crack tip. Substitution of Eqs. (13) and (14) into Eq. (24) leads to an expansion of G in an ascending order of h [7], and it is given by,     0 I II ; ,  O G G k k h    (48) where 0 G is obtained as   2 2 2 2 0 I II I I II II 1 ; ,  1 2 1 8 2 2 G k k k k k k                                   (49) The first and second variations of 0 G with respect to   are calculated as     2 2 0 I II I II 1  2 8 G k k k k           (50)