Issue 36

V. Petrova et alii, Frattura ed Integrità Strutturale, 36 (2016) 8-26; DOI: 10.3221/IGF-ESIS.36.02 23 (a) (b) (c) (d) Figure 21 : Schematic representation of the fracture angles: (a) and (b) for three equal cracks with inclined angles β= 90° and 60° correspondingly; (c) and (d) for three crack of sizes a 1 =1 and a 2 = a 3 =0.5 and with inclined angles β= 90° and 60°. Crack interaction effect The shielding – amplification effects are observed in crack interaction problems, i.e. some geometries of the interacting cracks can enhance or suppress the propagation of each other. This problem has long history of discussion especially for macro-microcrack interaction problems [21]. In a recent paper by Wang et al [22] the authors return to this problem. The shielding and amplification effects of transverse array of microcracks on a main crack were investigated using extended FEM with respect to SIFs. The SIFs at the main crack tip include not only the interaction between the main crack and each of small cracks, but also include mutual interaction of microcracks. It was pointed out that the interaction between microcracks can weaken their amplification-shielding effect on the main crack and this effect was demonstrated in [22]. In the present problem for edge cracks we can check whether this interaction effect presents or not. Consider the case of two edge cracks with sizes ( a 1 , a 2 )=(1.0, 0.5) and three edge cracks with sizes ( a 1 , a 2 , a 3 )=(1.0, 0.5, 0.5), in both cases the cracks have same inclination angle β to the surface β n = β . Introduce the a notation Δ 1 = k I (1) – k 0 for two cracks with distance between the cracks d =2 and for distance d =4 Δ 2 = k I (2) – k 0 and Δ 3 = k I (3) – k 0 for 3 cracks with equal distances between the cracks d =2, where k I (n) is the SIF at the tip of large crack, k 0 is the SIF for a single edge crack. These values of Δ determine interaction effects between the cracks, i.e. the influence of small cracks on the large crack 1. The value Δ 1 + Δ 2 – Δ 3 will give the magnitude of mutual interaction of small cracks (crack 2 and 3) and %100 ] /) [( 0 3 2 1   k f