Papers by Author: Zhen Chen

Abstract: To predict a complete process of failure evolution, discontinuous bifurcation analysis has been performed to link elastoplasticity and damage models with decohesion models. To simulate multi-phase interactions involving failure evolution, the Material Point Method (MPM) has been developed to discretize localized large deformations and the transition from continuous to discontinuous failure modes. In a recent study for the Sandia National Laboratories (SNL) challenge, the decohesion modeling is improved by making the failure mode adjustable and by replacing the critical normal and tangential decohesion strengths with the tensile and shear peak strengths, in order to predict the cracking path in a complex configuration with the least computational cost,. It is found that there is a transition between different failure modes along the cracking path, which depends on the stress distribution around the path due to the nonlocal nature of failure evolution. Representative examples will be used to demonstrate the recent advances in simulating failure evolution with the MPM.

Abstract: Nanocomposite coating films have been increasingly used in industrial applications because of their unique mechanical and physical properties. Residual stresses generated during the growth of sputter-deposited thin films due to a strain mismatch between the film and the substrate may lead to significant failure problems. Large residual stresses may generate buckling, delamination and film fracture. Although buckles with cracks in thin films have been experimentally observed, their origins are still not well understood.

Abstract: To better understand the responses of ultrananocrystalline diamond (UNCD) under extreme working conditions, a numerical study is performed to investigate the size, loading rate and thermal effects on the material properties of UNCD films. A combined kinetic Monte Carlo (KMC) and molecular dynamics (MD) method is first applied to simulate the growth of polycrystalline UNCD films. The responses of the resulting UNCD films with various grain sizes are then investigated by applying displacement–controlled tensile loading with different rates and temperatures in the MD simulations. The preliminary results presented in this paper provide a better understanding of the combined size, rate and thermal effects on the material properties of UNCD.