Issue 41

A. Mardaliazad et alii, Frattura ed Integrità Strutturale, 41 (2017) 504-523; DOI: 10.3221/IGF-ESIS.41.62 509 Fig. 5). Because the connectivity between these particles is considered as a part of the computation procedure, a straightforward handling of problems with large deformations is allowed by using the SPH method [33]. Figure 5 : SPH particles in a 2D problem domain. A numerical technique, namely FEM-coupled to-SPH, was developed, inspired by [25], to take advantage of both the FEM and the SPH methods. The Lagrangian meshed elements were eroded after reaching a certain criterion by using this technique, and they were adaptively transformed to SPH particles that inherit identical mechanical properties with the failed elements. The implementation of this technique in LS-DYNA was carried out by calling the keyword called ADAPTIVE_SOLID_TO_SPH. However, since many of the material keywords available in the LS-DYNA material library, i.e. the ones used in this study (KCC), do not have any internal eroding algorithm, an external eroding algorithm is required to be implemented in conjunction with this keyword. The element erosion of the models of this article was obtained by using MAT_ADD_EROSION and specifying a certain value for the maximum shear strain (EPSSH). Therefore, each hexahedral solid element who meets this criterion will be eroded, and then by defining the two input parameters of ADAPTIVE_SOLID_TO_SPH keyword as ICPL=1 and IOPT=1, the software automatically replaces those eroded elements with a certain number of SPH particles. The number of particles can be controlled by the users, i.e. it can be 1, 8 or 27 in case of hexahedral elements (see Fig. 6). Within this study, the failed solid elements were converted into one SPH particle to keep the time consumption cost low. Figure 6 : Transformed SPH particles from a hexahedral 3D solid element. This method can be implemented in ABAQUS by choosing the option “conversion to particles” from “element type” panel at the mesh module. Unlike the LS-DYNA, an external eroding algorithm in never required since the elements which meet a user-specified criterion are automatically transformed to a certain number (from 1 up to 343) of SPH particles. The maximum principle strain is considered as the conversion criterion for all the models developed by ABAQUS in this study. Karagozian and Case Concrete (KCC) model The studies on the nonlinear concrete material models that were implemented by the Lagrangian finite element code DYNA3D at 1992 (reported in [34]), showed that the material model 16 (concrete/geological material) presented appropriate and attractive features. To overcome the shortcomings of this material model, Malvar et al. developed another (a) (b) (c)