(231) |

where is a vector of tractions and is a vector of strains obtained from displacement jumps smeared over the element length. Furthermore, is the damage variable varying from 0 (undamaged) to 1 (fully damaged). Also, is the elastic stiffness matrix which is based on the elastic modulus of the lattice material , and a parameter which is the ratio of the modulus of the shear and normal direction. The strength envelope is elliptic (Figure 12) and determined by three parameters, , and . The evolution of the damage variable is controlled by normal stress-normal crack opening law. The three possible laws are linear, bilinear and exponential (Figure 13).

The model parameters are summarised in Tab. 50.

2018-01-02