PolyUMod Abaqus Hint: When to Set the ORIENT Flag for Anisotropic Materials

Introduction - PolyUMod Abaqus Hints

Did you know that the first 16 material parameters for all PolyUMod Abaqus material models are control variables that can be used to set various behaviors of the material models? Most of the time you do not need to worry about any of those parameters, but there are situations when they are important. One such case is when you are using an Abaqus FE simulation with an anisotropic PolyUMod material model. In this case you need to set the ORIENT flag properly.

The PolyUMod User’s Manual specifies that the ORIENT flag is global parameter 10:

Abaqus/Standard

When using Abaqus/Standard, use the ORIENT value specified in the following table:

Here is an example anisotropic PolyUMod TNV material model (in inp-file format) with the ORIENT flag set to 4.

				
					*User Material, constants=55
**..:....1....:....2....:....3....:....4....:....5....:....6....:....7....:....8
**     MM,      ODE,      JAC,     ERRM,   TWOD_S,     verb,    VTIME,    VELEM,
       29,        0,        3,        0,        0,        1,        0,        0,
**   VINT,   ORIENT,    NPROP,    NHIST,      GMU,   GKAPPA,    FAILT,    FAILV,
        0,        4,       55,       43,        1,      500,        0,        0,
** NType1,   NType2,   NType3,   NType4,      C10,      C20,      C30,   kappa1,
        2,        7,        0,        0,        1,    -0.05,    0.001,      200,
** kappa2,   kappa3,   tauHat,       mm,       bb,       p0,      fff,     epsF,
        0,        0,       10,        8,        0,        0,        1,      0.1,
**   ceps,      fss,      C10,      C20,      C30,   kappa1,   kappa2,   kappa3,
      0.1,        1,        1,    -0.05,    0.001,      200,        0,        0,
**    k11,      k12,      k13,       k2,     disp,      a1x,      a1y,      a1z,
      100,        0,        0,        0,      0.1,        1,        0,        0,
**    a2x,      a2y,      a2z,      a3x,      a3y,      a3z,    alpha
        0,        1,        0,        0,        0,        1,        1

Abaqus/Explicit

When using a PolyUMod Abaqus material model, if the ORIENT flag is set to zero (0) then the right stretch tensor (U) will be used instead of the deformation gradient. If this flag is set to one (1) then the total deformation gradient will be used and the final calculated stress will be rotated to the intermediate coordinate system that is used by Abaqus/Explicit. It is recommended to set ORIENT=0 if the material is isotropic hyperelastic or if the applied rigid body rotations are small. In all other cases it is recommended to set ORIENT=1.

MCalibration

All PolyUMod global parameters can also be set from MCalibration. Just switch to the “PolyUMod Variables” tab in the Material Model Dialog. See image the following image.