Issue 51

F. Frabbrocino et alii, Frattura ed Integrità Strutturale, 51 (2020) 410-422; DOI: 10.3221/IGF-ESIS.51.30 418  characteristic length equal to / 1/ 3 D R   in the tip region and transition mesh in the remaining part of the plate with maximum length equal to / 20 /1 D R   (M1);  characteristic length equal to / 1/ 4 D R   in the tip region and transition mesh in the remaining part of the plate with maximum length equal to / 15/1 D R   (M2);  characteristic length equal to / 1/ 4 D R   in the tip region and transition mesh in the remaining part of the plate with maximum length equal to / 3/1 D R   (M3). Fig. 8 shows the mesh discretization around the crack tip region for M1 M2 and M3 configurations. In this case the numerical simulations are employed by considering the loading condition with 0 5 1 33  . . MPa m I K . Figure 8 : Mesh discretizations detail around the crack tip for M1, M2 and M3 configurations. Figure 9 : Comparisons in term CPU time and number of degrees of freedom for the numerical simulation performed by using different mesh discretizations (M1, M2 and M3). In Fig. 10a, comparisons in terms of crack tip speed as a function of the crack tip position in terms of mesh configuration, are reported. The results show how the proposed model is able to describe dynamic crack propagation phenomena by using a coarse mesh discretization. The results, reported in Fig. 10b, present a good agreement in the prediction of the dynamic SIF time history. Moreover, the solution is quite independent from the mesh utilized in the numeric model, since also using a coarse discretization (i.e. M1) no instability phenomena are observed in the prediction of the fracture variables. Fig. 11 shows a synoptic representation of the mesh motion during the crack propagation for the M1 configuration. The mesh movements of the crack tip region are enforced rigidly, ensuring accuracy in the prediction of the fracture variables. In the remaining parts in which a lower accuracy is required the mesh is affected by distortion phenomena produced by the mesh motion. However, once the distortion tolerance is reached, a re-meshing procedure with an update of the ALE and structural variables is achieved.