stored in the broken beams represents the energy needed to create these new crack surfaces inside the solid.

In order to simulate the break-up of the disc due to impact with a hard plate, a repulsive force is introduced between the plate and those polygons of the disc which have overlap with the plate. This repulsive force is proportional to the overlap area, similarly to the polygon-polygon contacts but with a higher stiffness value. The contact force of the disc and the plate has vertical direction, tangential component like friction is excluded in the present study.

The time evolution of the system is obtained by numerically solving Newton’s equations of motion of the individual polygons (Molecular Dynamics). For the solution of the equations we use a Gear Predictor-Corrector scheme of fifth order, which means that we have to keep track of the coordinates and all their derivatives up to fifth order. The breaking criterion of beams is evaluated in each iteration time step and those beams which fulfill the condition are removed from the calculations. The simulation stops after no beams break during a certain number of time steps. Previously this model has been applied to study fragmentation of solids 