Issue 51

F. Fabbrocino et alii, Frattura ed Integrità Strutturale, 51 (2020) 410-422; DOI: 10.3221/IGF-ESIS.51.30 415 where   x y J , J is the tangential or normal components of the dynamic J integral. Figure 3 : Schematic representation of the path independent J integral developed by Nishioka (1997). The computation of the SIFs is developed by using the component separation method, where I K and II K expressions are related to the dynamic J integral, crack velocity parameters and evolution functions [24]. In order to compute the crack propagation direction a proper crack kinking criterion has to be considered. The proposed model incorporates Maximum Energy release rate criterion which is simply defined as follows: 1 0 Y X J tan J          (15) in which 0  is measured with respect the horizontal global axis (Fig. 3). R ESULTS n this section, results are developed with the purpose to verify the consistency and the reliability proposed methodology, by means of comparisons with numerical and experimental data. Moreover, a sensitivity analysis is carried out to verify the consistency of the proposed model in term mesh dependence and accuracy of crack tip motion. In particular, the computational performance of the proposed model is verified by means the investigation of two loading configurations based on a rectangular sample made of Araldite-B. At first, the simulations are conducted on the loading configurations experimentally tested in [25], which involve a pure mode I loading condition. The loading scheme, boundary conditions and geometric configuration are represented in Fig. 4, whereas the mechanical parameters are summarized in Table. 1. Fig. 4b reports the mesh discretization adopted in the numerical simulations, in which a relatively refined mesh is considered only around the crack tip region, whereas the remaining part of the structure presents a transition mesh with a lower element size. The mesh discretization is featured by a ratio between the characteristic length element and the moving region radius equal to in the tip region and transition mesh in the remaining part of the plate with maximum length equal to (M2), involving in a total number of DOFs equal to 7516 . Numerical and experimental data are collected by means of a two-step analysis. The first one is needed to load the structure by means a static analysis, in which a vertical displacement at the pin is applied until the mode I SIF reaches its critical value [25]. Once the SIF reaches    D   R   / 1/ 4 D R   / 15/1 D R