Implementation of Constitutive Model in FEA for Nonlinear Behavior of Plastics

The main elements of implementation into a finite-element analysis (FEA) package of the earlier developed model for nonlinear viscoelastic behavior of plastics are described. The Henriksen scheme of discretization of the hereditary integral has been chosen for implementation. This scheme enables development of a fast procedure for modeling of viscoelastic behavior. As a result, the time necessary for calculation of problems of viscoelasticity is not much larger than the calculation time required for simulation of elasto-plastic behavior. Several discretization schemes have been analyzed, implemented in FEA software MARC and verified. The numerical algorithm, which is chosen as a result of comparison, allows us to reach a total deviation of less than 8% to 10% for the modeling of creep and recovery of PMMA and HDPE for the broad range of loading levels. The case study of a thick plate under distributed transversal loading is examined to compare the results achieved using the Schapery model with the newly proposed approach.