User modified abaqus CDP material model development in impact

One of the most difficult tasks in VTT IMPACT project has proven to be the simulation of hard missile (or projectile) impact benchmark tests, especially if one considers accurate prediction of the residual velocity as the most important measure of success. The difficulty comes inherently from the shortages of classical FEM in describing macroscopic cracking and fragmentation of solid bodies. Hence the accuracy of hard missile impact simulations depends on how accurately not only the material constitutive relations are chosen, but also how well multibody dynamics can be implemented, including contact algorithms, timely tearing and breaking of ductile materials and physically plausible fracture and fragmentation of quasi-brittle materials. The concrete model under consideration is the Concrete Damaged Plasticity (CDP) model available in the Abaqus Finite Element (FE) software with appropriate modifications applied via a VUSDFLD user subroutine. The IRIS 2010 punching tests is considered as the validation benchmark for this study. The main aim is not yet to simulate the test as accurately as possible, but to find out the effect of all the possible model and analysis parameters. The model is found to be relatively stable and insensitive to many of those parameters, but great care should be taken in defining the material parameters and time incrementation for the simulation.