Finite Analysis of fabrics

[MohdAc1412]

Hello everyone, I'm trying to build a finite element model for my MSc dissertation on abaqus... the process is quite tricky, and there are so many unknowns in terms of material properties and element sizes... to cut a long story short, what i'm supposed to build is a simplified model to study the mechanism of pulling-out of fabrics in a piece of garment... i'm not an expert in abaqus, so what i was able to do is two plates surrounding a rod, and a force is applied on the end of the rod, the interaction between the rod and the inside of the plates is a simple tangential friction, of course i had to fix all other ends...
I'm currently trying to verify the tension transmitted along the rod, if the rod has infinite stiffness, then there will be no tension transmitted and the force will be transmitted as bending moment, is there a way to do check on the tension transmitted along the rod if the rod has a lower stiffness?
Thanks

 

[IRstuff]

> student posting is generally not allowed so your thread may get deleted
> is the rod a real thing or your representation of a thread?
> your plates are supposed to be the fabric?
> perhaps a less point-solution based description might be a better problem description
> there is an Abaqus forum here, so you may want to red flag this post anyway, and post in the Abaqus forum instead.

TTFN
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[btrueblood]

What IRstuff said. But, also, could you please re-phrase this so it makes sense:

"I'm currently trying to verify the tension transmitted along the rod, if the rod has infinite stiffness, then there will be no tension transmitted and the force will be transmitted as bending moment, is there a way to do check on the tension transmitted along the rod if the rod has a lower stiffness?"

There is, can, and will be tension transmitted along a rod of infinite stiffness. Do you mean the inverse (an infinitely "soft" rod)? Or compression along a fiber/yarn that can't transmit compressive loads? Or are you saying the infinitely stiff rod interacts poorly with a finite stiffness shear connection - if this latter, consider that the problem is in the formulation using infinite stiffness which are not practical.

 

[MohdAc1412]

Thanks for your reply and my apologies, i had no intentions of breaking the forum rules... I'm just seeking others' opinions as I've minimum knowledge of textile engineering and/or modelling anything other than concrete beams...
I didn't describe the problem very well because I'm a bit confused myself, and I thought, tbh no one would reply... to answer your questions...
the rod is a representation of a thread, it's made of the same material as the two plates (fabrics), the two extreme cases are when the rod has infinite Modulus of elasticity (let's say that the rod has 200Gpa of steel while the two plates have 10Gpa), in this case when applying a 50 N load on the far end of the rod that's spanning out of the two surrounding plates (cantilever), the rod deformation will be minimum and a low value of bending moment will be balanced by a reaction at the clamp... the other case, which i cannot model because i keep getting an error saying displacement increment for contact is too big , is when the rod is so soft with a very low modulus, which will cause the rod to deform and follow the force direction on the end (if the force is vertical, the rod will be straight and vertical) till the rod contacts the entry point between the two plates and follow the curvature (shape) of that plate... i'm not sure about the following points:
- is it possible to model the second case? or abaqus will keep exiting the analysis with the same error if displacements are too high?
- when meshing parts, they are displayed on my screen in yellow, while usually in other models, they show in green, does that mean i'm missing something important?
- no matter what, i keep getting warnings about increments, is it a concern? noting that i'm trying build the model keeping the real sizes of threads instead of scaling.
- i left a very small gap between the rod and the plates, this gives an error.
thanks!

 

[IRstuff]

> a thread is not infinitely stiff, so that's fundamentally an issue.
> I would imagine that the thread behaves as if it were elastic, as would your "sheets"

TTFN
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[MartinShane]

If I were in your situation I might start by looking at scholarly articles discussing micromechanics FEA of composites and fabrics. There's a lot to find if you search for "micromechanical fabric model" or similar terms. Many (most?) will focus on developing models for Fiber reinforced composites, but the fabric models and assumptions are likely to be similar to what you would need.

 

[MohdAc1412]

I appreciate your help... I'm progressing and I think I've figured most of the problems that i was facing... but the final result is quite strange and it's not exactly what I was expecting... so if you can enlighten me with some of ur suggestions i will be grateful...
Now, what I've done is a rod running through two sheets, let's say that the length of the rod is 1 mm and the sheets are covering half that distance... then the cantilevered part of that rod has a load of 100 N in y and x directions... and there's a tangential friction (penalty) with a coefficient of 0.2 between the plates and the rod, there's no gap between the plates and the rod so i'm assuming that elements are in contact, i even applied some pressure on the sheets to ensure elements are in proper contact, the plates are fixed on all sides and the rod is fixed on the other end between the plates... What i expected is that friction will cause a decrease in the reaction force on the fixed end of the rod, and some of the transmitted load will transfer through friction to the plates then to the fixed ends of the plates... that's true for the y direction force,and i almost get the entire force transmitted to the fixed ends of the sheets, however, for x direction force, instead of getting a value lower than 100, i get 200 + ....
What seems to be the problem? it's pretty weird
Thanks

 

[MartinShane]

A picture or sketch of your model / loading might make it easier for people to help.

 

[IceBreakerSours]

Do you have to model discrete fibers? If not, try reading about the fabric material available in Abaqus?

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