Shuhai Zhang presented his research at EMI 2015 Conference
The title of the Shuhai’s presentation is: “Variational Multiscale Enrichment with Mixed Boundary Conditions for Elasto-Viscoplastic Problems”.
Presentation Abstract:
We present the formulation and implementation of the variational multiscale enrichment (VME) method for the analysis of elasto-viscoplastic problems. VME is a global-local approach that allows accurate fine scale representation at small subdomains, where important physical phenomena are likely to occur. The response within far-fields is idealized using a coarse scale representation. The fine scale representation not only approximates the coarse grid residual, but also accounts for the material heterogeneity. The inelastic material behavior is modeled using Perzyna type viscoplasticity coupled with flow stress evolution idealized by the Johnson-Cook model. To investigate accuracy based on the effect of the choice of the boundary conditions at the fine scale, a one-parameter family of mixed boundary conditions that range from Dirichlet to Neumann is employed. The key contributions of the work are: (1) extending the VME method to account for the presence of material nonlinearity which previous work on VME does not include; and (2) employing mixed boundary conditions for inelastic problems to reduce the overconstraint imposed by the homogeneous Dirichlet boundary conditions (residual-free bubbles), which is a typical choice in the variational multiscale literature. This nonlinear VME system is linearized and evaluated using the Newton-Raphson iterative scheme. Two sets of numerical simulations will be presented to verify the implementation of the VME method against direct finite element simulations. The first set of simulations tests a 2-D square panel under uniform tensile load and pure shear load to study the effect of boundary conditions. The second set of simulations is performed on a notched specimen under uniform tensile load. The results of the numerical verifications reveal high accuracy of the VME computational methodology, especially when optimal mixed boundary conditions are employed.