I have a beam in which there is a crack somewhere in the middle leading to two surfaces which are touching each other. The two surfaces are allowed to separate from each other. Ideally we should define contact between the surfaces, but a simple approximation is to use a spring damper system for replicating contact conditions.
This kind of behavior is modeled easily in COMSOL using a Thin Elastic layer option in which there is a predefined variable which tracks the distance between the surfaces in contact. See this for introduction to thin elastic layer in COMSOL. https://www.comsol.com/blogs/structural-analysis-with-thin-elastic-layers/
I was wondering if ABAQUS can be used to model the same kind of functionality using a subroutine. Basically I want to define an internal boundary with two surfaces and put a spring and damper between those surfaces. My approach is that I have defined this using a contact boundary condition. The surfaces are allowed to separate from each other too. In this contact condition I want to define a cohesive behavior whose stiffness is dependent on the distance between the contact surfaces.
The question is which kind of subroutine is required here? I cannot use USDFLD as it can be used only with elements that have material behavior defined with a ∗MATERIAL option. Another question is how to extract the distance between the surfaces and use it in the subroutine..
I know that I can define a UEL subroutine and define the behavior of interface myself in which I will have access to relative distance between the surfaces. But is this the only option?
Can't you just use cohesive elements or cohesive contact?
They allow for some kind of traction-separation law.
Hello Martin,
I have a nonlinear stiffness i.e. stiffness has some value when spring is in compression but in tension it becomes zero. I am vibrating the beam so that there is sudden changes and there are tension and compression cycles.
I was able to model it with cohesive elements with USDFLD subroutine. By looking at the strain variable, if strain is positive I make the stiffness zero, and when strain is negative I make the stiffness some value. But such extreme variation of stiffness lead to unreal deformations of cohesive elements i.e. penetration of surfaces into each other. So, I realized I must define cohesive contact between the surfaces to avoid this.
The problem is 1) USDFLD does not work with cohesive contact and 2) there is no variable like strain in cohesive element to determine whether there is extension or compression between the surfaces.
Thanks for the detailed explanation - instead of programming a ful UEL, it may perhaps be simpler to define the intercation with UINTER, but I've never done that, so I can't help there.
If it is just a stiffness change (no force transfered when surfaes separate, IIUC), can you not use a traction separation law (in the 6.12 manual it is in section 36.1.2, called "softened" contact relationship)? Keyword is *surface behaviour, pressure-overclosure=...
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