I am modeling a human spine. I am applying displacement from top side and fixing the bottom and the model is working properly but when I change the displacement to concentrated force it is dying because of max penetration error and element distortion. I tried to apply very very minute amount of force which again caused my model to die. I wanted to know why the effect of force and displacement should not be the same in a model while both are at the same direction?!
I can't say for sure since I didn't see how you defined your model, but for exemple in undeformable solid statics, it is easier to determine the forces acting on multi-part body in a certain configuration (angles, positions of parts respectively to one another) than doing it the other way around. I suppose it is the same for Abaqus regarding deformable solids.
Apart from that, if your geometry is not 1D, a force in a certain direction won't necessarily produce a displacement only in the same direction, especially if it's concentrated.
Till elastic limit the effect should be same but if it exceed the elastic limit then it's behavior generally changed. Check it properly.
Check the force in system in case of defined displacement case, and compare to your input.
Penetration error suggests you are having geometrical interference, try using general contact it should solve penetration issue, are you making dynamic analysis?
you need to provide more information to get idea of what you want to do.
Etienne Lebard, Dhaval P. Shah and Pankaj Biswas thanks for your replies. Just FYI I am doing static study and have hypoelastic and elastic materials in my model. I had applied the force in z direction and the boundary condition In U3. I solved the issue for the force with changing the iteration to 0.001. However, for the displacement the model was solved by the min iteration of 0.1. I exactly don't know why these two behaviors require different iterations but I solved the issue, although it is taking more time for the force to be solved.
Ardalan
Hi Ardalan Seyed Vosoughi,
With your question you try the human to describe with a mathematical function.
F – Force; D – Verschiebung F =ȸ f(D) und D = ȹ f(F).
ȸ - characteristics of human spine when effect of force
ȹ - characteristics of human spine when effect of displacement
First note: You wonder that the behavior of the spine is apparently not as a function.
Definition Function:
“In order to avoid the use of the informally defined concepts of "rules" and "associates", the above intuitive explanation of functions is completed with a formal definition. This definition relies on the notion of the Cartesian product. The Cartesian product of two sets X and Y is the set of all ordered pairs, written (x, y), where x is an element of X and y is an element of Y. The x and the y are called the components of the ordered pair. The Cartesian product of X and Y is denoted by X × Y.”
Second note: The mechanical model of "Your spine", it seems look. See below.
Quite apart from that I can not imagine, that one so simple must reflect a human spine, a) represents: the unloaded spine. With 24 vertebrae, intervertebral discs, etc . When the force is applied b) (possibly. also in load steps), then each vertebra bears and the sum of the single deformations results in the total deformation of the spine. It is quite so, that the individual vertebrae take up different loads thereby and these have, different loading and displacement limits. The vertebrae react differently, dependent to types of loading.
Shifts one now the upper plate (the whole spine) by the amount Δl, see c), then the upper vertebrae will more deformed than the lower. Practically you break the patient's neck. The "attempt was successful". Q.e.d., individual vertebrae have exceeded the limit of their mechanical load capacity. Their loss leads to total loss of the system Human. The "inverse function" was deadly!
3. Note: You should a expert of biomechanics consult for model development.
I hope I have helped a little.
Good luck, especially for the patients!!!
Thanks Michael Lersow for your clarification. I did not know that Abaqus is applying BC like that. However, I am seeing the displacement in my discs not in the bone. But if that is true the issue is goin to happen in the upper discs.
- Badges
- Science topic