Guide to using material model No. 11 in NIKE2D: An internal variable, viscoplasticity model

摘要

The need to accurately model the superplastic forming process which is highly rate and temperature dependent motivated the evaluation of Bammann's internal variable, viscoplasticity material model. The model is based upon the concepts of unified creep plasticity, but employs a yield surface for efficient implementation into large-scale numerical computer codes. It has proven elsewhere to be quite successful in describing large strain, thermal-mechanical behavior of crystalline materials. Features of the model enable it to simulate the apparent strain-rate behavior exhibited by many metals above one half the melt temperature. It is the efficient incorporation of features that make the model attractive for use in finite element modeling of metal deformation processes. Although this model was implemented into the Lawrence Livermore National Laboratory's NIKE2D finite element program in 1986, there have been no known reports of successful use by NIKE2D users. The purpose of this report is to provide the user the proper format to input model parameters, a procedure for determining appropriate values for material constants from experimental data, and supplemental information on the model relevant to the implementation in the NIKE2D finite element program. Detailed accounts of the theoretical aspects of the model can be found in the cited references. 4 refs., 8 figs.