Hello Everyone,
I am trying to simulate a shear cyclic behavior of a spring element in ABAQUS. In the experiment performed, I am getting unsymmetrical behavior, as shown in Figure. loading is almost linear, and unloading is curved. But when simulated in ABAQUS, it is not the same. Can anyone guide me on how to define or obtain this type of behavior in ABAQUS?
Nonlinear spring behaviour with different loading and unloading characteristics can be simulated in Abaqus using a combination of material and element definitions that match the experimental data.
Firstly, you need to define your material properties. This requires a stress-strain curve from your experimental data. You can use a bilinear isotropic hardening model for the nonlinear spring to specify different hardening (or softening) behaviours in tension and compression.
However, suppose your material behaviour is not following a simple bilinear path and has a more complex hysteresis loop. In that case, you might want to use the user material subroutine (UMAT) or user-defined field variables (USDFLD). These allow you to define more complex material behaviours using a subroutine written in a programming language like Python or Fortran. You can specify the material behaviour at each integration point and each increment, effectively capturing the nonlinear, unsymmetrical behaviour you're observing in your experiment.
To define the shear cyclic behaviour, you might consider using a kinematic hardening model, which can simulate Bauschinger's effect and cyclic hardening/softening.
After defining the material properties, you should also choose an element type that can capture the large deformation behavior, if that is significant in your simulation. Elements like C3D8R or C3D20R are suitable for large deformations.
A key point to consider while defining a nonlinear spring element in Abaqus is to ensure that you use a 'Nonlinear' keyword in the spring element definition.
In summary, capturing a material's complex nonlinear, unsymmetrical behaviour requires a combination of appropriate material models and elements in Abaqus. The specific method to implement these depends on your detailed experimental results and the specifics of your simulation. You might also want to contact the Abaqus user community or technical support for more detailed guidance on your case.
Please note that Abaqus is sophisticated software, and the best practice is to always start with a simple model, validate that, and gradually add complexity.
Good luck
It would be really helpful, if you could specify what material exactly you used for the experiments, so that one can get an idea, where the hysteresis (that is, dissipation) comes from, for example, plasticity, viscosity, internal friction, etc.
The first step in choosing or building a material model should be to try to generally understand the physics of the material.
Emanuel Willert thank you for the response. I am trying to analyze rubber material using nonlinear spring elements in ABAQUS.
For rubber, there are a lot of rheological models. I don't know, however, which of these have been implemented in Abaqus.
A quick search directs to the "Parallel Rheological Framework" within Abaqus, and I guess, you can also write your own material model as well, if you are not satisfied.
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