In the analysis section above, we have found that blind insertion of cohesive elements introduces oscillations of the local nodes. And, although damping was able to minimize these oscillations, it was not the optimal method because of its cumbersome implementation requiring trial and error to find the damping coefficients. Instead we have developed a method where the cohesive elements are pre-stretched during their dynamic insertion. This method is able to completely minimize the oscillations while maintaining the accuracy of the solution.
We now apply this dynamic insertion method to several problems by using two different cohesive element selection criteria. These criteria are used to determine the optimal location and time for insertion of cohesive elements. The first is based on a bounding box approach where all edges within a growing bounding box are made cohesive. The second uses a stress criteria, based on the average volumetric stresses, to determine if a particular edge should have a cohesive element inserted. We present both of these methods below, as well as the results of their application to various problems.