Hi
I want to write a UINTER for contact in metal forming. Where can I find a constitutive model for contact in metal forming. Does anybody have an example of implementing a UINTER subroutine? I tried to study the verification example of abaqus (which is attached) but I couldn't understand it, since the documentation did not give the constitutive model and it's just the Fortran code.
Thanks
Problem description
uinternx.inp
This test verifies that user subroutine UINTER properly models hard contact between a deformable and a rigid surface. A single CPE4 element is brought into contact with an analytical rigid surface using displacement boundary conditions. User subroutine UINTER models the contact using a penalty approach. The results are compared against those obtained using the default hard contact model in Abaqus/Standard, which uses a Lagrange multiplier-based approach to enforce the contact constraints. It is observed that the penalty approach results in a small penetration of the slave nodes into the master surface. As a result, there is a difference (about 7.5%) in the contact pressure between the model using UINTER and the model using the default hard contact model.
The lOpenClose flag is also tested in this problem.
uinternf.inp
This test verifies that user subroutine UINTER properly models softened contact along with frictional sliding between a deformable and a rigid surface. The softened contact is modeled using an exponential pressure-clearance relationship, while the shear behavior is modeled using standard Coulomb friction. Both normal and shear behaviors are modeled in user subroutine UINTER using a penalty approach. The problem is carried out in two steps. In the first step the deformable body is brought into contact with the rigid surface using boundary conditions. In the second step the deformable body is made to slide on the rigid surface using boundary conditions. The results are compared with a similar problem using the corresponding built-in models in Abaqus/Standard, invoked using the *SURFACE BEHAVIOR and the *FRICTIONsuboptions of the *SURFACE INTERACTION option. The results using the two different approaches (user subroutine UINTER versus built-in models) are found to be in good agreement.
uinterht.inp
This test models heat transfer between two surfaces through gap conduction. The model consists of two DC2D4 elements separated by a distance. The two elements are at different initial temperatures. The thermal interaction is modeled using user subroutine UINTER by defining the heat flux at the two surfaces as a result of gap conduction. The variations of the heat fluxes with respect to the surface temperatures, which contribute to the Jacobian, are also specified. The analysis is continued till steady-state conditions are reached. The results are compared with a similar model that uses the built-in capability in Abaqus/Standard to model gap conductance (invoked using the *GAP CONDUCTANCEoption). The results using the two approaches are identical.
uintertd.inp
This test is identical to the verification problem ufricxxy.inp (“FRIC,” Section 4.1.4) that uses user subroutine FRIC to define the shear interaction between the surfaces, except that both the mechanical and thermal interactions are modeled using user subroutine UINTER. It provides verification for using the user subroutine UINTER in a *COUPLED TEMPERATURE-DISPLACEMENT procedure. As a result of modeling the normal mechanical interaction through UINTER, a penalty approach is used in uintertd.inp, as opposed to the Lagrange-multiplier-based approach of the built-in hard contact model that is used in ufricxxy.inp. The results using the two approaches are in good agreement.
uinterny.inp and uinterim.inp
The test uinterny.inp is similar to the test uinternx.inp. It includes an extra dummy step in the beginning which is used by uinterim.inp to test import of the original model definition. The results of the imported analysis are identical to the results of the original problem. In addition,uinterny.inp also includes basic verification for user-defined state variables that are used to store the two local surface directions and the coordinates of the contact point.
Results and discussion
The results in all cases were compared to built-in surface interaction models in Abaqus/Standard and were found to be in good agreement.
Input files
uinternx.inpTest for surface interaction in the normal direction in a static procedure.
uinternx.fUser subroutine UINTER used in uinternx.inp.
uinternf.inpTest for surface interaction in both the normal and the shear directions in a static procedure.
uinternf.fUser subroutine UINTER used in uinternf.inp.
uinterht.inpTest for thermal surface interaction in a heat transfer procedure.
uinterht.fUser subroutine UINTER used in uinterht.inp.
uintertd.inpTest for both mechanical and thermal surface interactions in a coupled temperature-displacement procedure.
uintertd_surf.inpTest for both mechanical and thermal surface interactions in a coupled temperature-displacement procedure using the surface-to-surface contact formulation.
uintertd.fUser subroutine UINTER used in uintertd.inp and uintertd_surf.inp.
uinterny.inpThis test is similar to uinternx.inp. It includes a dummy step in the beginning which is used by uinterim.inp to test import of the original model definition. This problem also includes basic verification for user-defined state variables in user subroutine UINTER.
uinterim.inpImport analysis from uinterny.inp.
uinterny.fUser subroutine UINTER used in uinterny.inp and uinterim.inp.
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