OXFORD-UMAT: An efficient and versatile crystal plasticity framework
The crystal plasticity-based finite element method is widely used as it allows complex microstruc8 tures to be simulated and for direct comparison with experiments. In this paper, we introduce
and demonstrate a new crystal plasticity code (OXFORD-UMAT for Abaqus® 9 ), which we have
10 made freely available online to encourage other researchers to use crystal plasticity. The model
11 is able to simulate a wide range of materials and incorporates two different solvers based on the
12 solution of slip increments and Cauchy stress with variants of state update procedures including
13 explicit, semi-implicit, and fully-implicit for computational efficiency that can be set by the user
14 based on the application. The constitutive laws are available for a range of materials with mul15 tiple phases, including widely used constitutive laws for slip, creep, strain hardening, and back
16 stress. The model includes geometrically necessary dislocations that can be computed using the
17 finite element interpolation functions by four alternative methods including: the total form with
18 and without a correction for the dislocation flux, a rate form, and a slip-gradient formulation all of
19 which are available in various 2D (plane stress and plane strain) and 3D including the linear and
20 quadratic elements. In addition, the initial strengthening and subsequent softening seen in irradi21 ated materials can also be simulated with the model in either a simplified way or more rigorous
22 way. Here we include full derivations of the key equations used in the code and then demonstrate
23 the capability of the code by modeling single-crystal and large-scale polycrystal cases. Compar24 ison of the OXFORD-UMAT with the other available crystal plasticity codes for Abaqus reveals
25 the efficiency of the proposed approach with its multimodal structure offering greater flexibility to
26 handle convergence issues commonly found in practical applications.
27 Keywords: crystal plasticity, finite element method, Abaqus UMAT, time integration methods,
28 explicit – semi-implicit – fully-implicit state update, forward-gradient method