A 3D Single Crystal Hyper elastic-viscoplastic material model, applied to metallic HCP granular structures
Jonathan Gordon  1@  , Eudardo De Souza Neto  1@  , Matthew Thomas  2@  
1 : Collage of Engineering, Swansea University
Swansea University, Bay Campus, Engineering Central, Fabian way, Crymlyn Burrows, Swansea, Wales, UK, SA1 8EN -  United Kingdom
2 : Timet UK Ltd.
PO Box 704, Witton, Birmingham, B6 7UR, UK -  United Kingdom

A material model is created to further understanding of micro-mechanical effects at high strain rates for HCP metals such as Titanium. This model is of interest to the aviation industry where the deformation of Titanium alloys, exhibiting high strength to weight ratios, at high strain rates is very important.

A compressible Neo-Hookean model is used to describe the elastic behaviour and is coupled with a visco plastic model to provide a hyper elastic- viscoplastic explicit stress update routine. The model is rate dependant with the rates of plastic deformation of each slip system governed appropriate hardening yield law.

This current model is applied to the use of HCP metallic structure, and allows for plastic deformation to occur on any or all of the thirty slip systems present. Each of the five families of slip systems is independently defined, therefore allowing for the Critical Resolved Shear Stress (CRSS) of each family to be set. Having the ability define the CRSS of each family allows for more accurate representation of the HCP crystal as the CRSS values from literature show a substantial difference between the families of slip systems. The material parameters that feed into the yield law are also defined for each family of slip systems.

The material model is then benchmarked through comparing a single element fully defined at all nodes to provide a plane strain scenario. The results of this test are compared with the results from the same boundary conditions run as a two dimensional plain strain model that has previously been benchmarked. A three element dog bone test is also conducted.

Three dimensional polycrystalline Representative Volume Elements (RVE's) are created through the use of NEPER and Gmsh. The physical grain geometry is created from statistical data which is provided form EBSD analysis. This data is used to provide NEPER a platform to create the Grain structure. Once the grain structure is created it is passed to Gmsh for meshing. 

Online user: 1