Going back to the reference problem described in Figure 3.10, we insert cohesive nodes into the nodes through . In order to avoid cohesive failure, we set the failing stresses of the cohesive elements to be very high. Furthermore, we reduce the critical time step based on the volumetric elements by , to a value of , which ensures that any instabilities in the system are a result of the insertion algorithm and not due to the cohesive elements themselves.
The first test is a blind insertion problem where nodes are inserted without any thought to the equilibrium of system. As will be presented in the next section, blind insertion causes some nodal oscillations, which affect the accuracy of the solution. As a result, we attempt to minimize these oscillations through the use of damping. Although this has some favorable results, the implementation of damping is not very efficient, so we instead present a third method of pre- stretching cohesive nodes during insertion. This allows us to minimize the oscillations much more easily while still maintaining an accurate result. Lastly we present the results from combining dynamic insertion with multi-time step nodal subcycling to further increase our computational savings.