ABAQUS user subroutines for the simulation of viscoplastic - loicz

5. User material routines and their applications
The material models mentioned above are implemented into the commercial FE code ABAQUS
as user-defined material model by writing the corresponding user subroutines, UMAT, see Table 1.
With help of these UMATs one can apply the models in an FE analysis of viscoplastic damage
behaviour of engineering components and structures. All the routines are written in the computer
language FORTRAN using the forward integration algorithm for numerical integration. Only isothermal
loading conditions have been considered and the damage deactivation has not been included in any of
the routines. Viscoplastic FE calculations are very time consuming. In the routines however, no
automatic time step control is used, so that there is a necessity to improve the respective algorithms. All
examples presented below are conducted using ABAQUS/Standard 5.8.
model UMAT
CHABOCHE model coupled with damage d-chaboche.f
BODNER-PARTOM model coupled with damage d-bodner.f
anisotropic creep and damage model of BERTRAM,
OLSCHEWSKI & QI
d-scsrr99.f
Table 1: Constitutive models and names of the respecitve UMATs
5.1 Circumferentially notched bar — CHABOCHE model coupled with damage
The material parameters of the CHABOCHE model of IN 738 LC have been determined by
OLSCHEWSKI et al. [1990] and their values at 850 °C are shown in Table 2. The material parameters of
the damage model were estimated by using numerical optimization methods to fit the creep data of the
three creep tests presented in the work of OLSCHEWSKI et al. [1990]. During this process the above
values of the parameters of the CHABOCHE model were kept constant. Table 3 shows a set of damage
parameters for IN 738 LC at 850 °C. Note that just three uniaxial tests are not sufficient for parameter
identification, so that the values given in Table 3 are only first estimates. For lack of biaxial test data, the
anisotropy parameter β can not be determined. Comparison of the experiments and the predictions by
the CHABOCHE model and by the coupled model with damage, respectively, using the material
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