Here is a question regarding “preload” or maybe “pre-displacement”. How do I apply a force at A and then also a displacement/force between two points B? the displacement or force between the two forks B, should be independent from the frame where a force is applied at A, such the the deformation due to B sort of rides on the deformation due to A. It may be a dumb question that is obvious, but I haven’t used FEA in a few months and I can’t think of a way.
Don’t you actually mean “dependent” (at least in terms of the second solution using the first one as a base state) ? It’s easy to have independent solutions if you use two steps with no plasticity or contact. If you do include those effects, the deformation in the second step will be based on the deformation from the first step.
OK, so you would separate the application of force A from the one at B. And how do I apply the load/displacement at B? it goes from one fork to the other rather than from ground to one of the forks.
You can try with a single step too (amplitudes can be utilized to control the BC/load variation if needed) but such sequential loadings are usually simulated in multiple steps.
You may apply it in opposite directions to both forks like in your drawing.
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I think you can use force at A, and it will be independent of the load/deformation due to B.
But if you apply displacements at A, it will not work. The displacements are always given in absolute coordinates in regard to the undeformed mesh.
Oh okay I see! yeah this helps a bunch. Well, let’s say the opposing forces at B are applied at the same step as A say Fy=10N and -10N. then as A rotates the part, the forces at B would still be pointing vertically in Y. How can we make them ride on the surface to the new rotation angle? even if I applied the force at step 2, I would have to know the angle at which force A rotated parts B so I can align the force at B to that angle and act as if a preload was applied at B between the forks. It would be so very cool if we could create two surfaces or node sets and let them be the locating features for the force B.
I love this! LOL. Its a theoretical part come true!
you’ll notice how the forks B do not meet each other as expected but there is a little X direction displacement because the forces remain aligned vertically the entire time and not with respect to each other.
Oh that’s weird. I made two opposing boundary layers and I applied pretension at B, but it doesn’t behave as I expected. I thought it was going to bring the two forks together. I applied first 10N, then 20, then 200N and didn’t see the part deform correctly:
I even suppressed the force at A.
fork_example.pmx (66.6 KB) Here’s the model if anyone wants to play with it.
Hi Matej,
I was taking a look at this and I found that deactivating a second step do not deactivate all the loads contained on it. In particular the preload definition.
Picture Shows Step 2 is deactivated but preload defined in Step 2 is still active. Not sure if this could affect the analisys in some way.
Hi Matej, I also noticed that when a new part is created from a set of elements, the new part doesn’t respect the element type. Let’s say the original was C3D8I, the new is now C3D8. I think it should preserve the type of element.
Regards
The pre-tension section keyword is active since you use it in step 1. And it is a model keyword and not a step keyword, so it needs to be defined before the steps are defined. And I think it should not affect the result.
Yes, the behaviour you describe is by design. Sometimes element sets containing multiple element types can be created and converted to parts. Then, the base element types can-not be taken into account. So the element type resets.