Simulate load on fabric

[1502211]

Hi there,

I am trying to run this really simple simulation of a load applied to a thin leather cloth hanging from two horizontal bars.

As I am trying to perform a nonlinear simulation using the leather material but it seems not to be working and this error always pops up. I also tried other fabric-like materials like fabric, carpet, linen but I always get the same error. 

Why is that? If I pick a hard material such as ABS or Aluminum it all works perfectly but I need to see how the material deforms!

[John_Holtz]

Hi @1502211 

I would have never guessed from your description that you were receiving a "NON-ZERO LOAD VECTOR REQUIRED FOR NONLINEAR ANALYSIS" error!

Since the analysis works with different materials, my guess is that one of the other warnings is leading to the error. Have you checked the material properties to confirm that the properties necessary for a stress analysis are in the library? (You can search the output file to review all of the warnings. "Results > Solver Data > Solver Output".)

A more important question is this: are you sure you are going to get the answers you want? I think that solid elements used in the simulation will not give correct answers for a "thin cloth". You need to use different software that has membrane elements (or software that has shell elements where you can change the bending stiffness and membrane stiffness to simulate a fabric. Nastran In-CAD or Inventor Nastran has this capability).

[1502211]

Hi,

Many thanks for your reply. I will now check if I can find the source of the error. And yes you are right, I believe I need to use another software. I will check that out too.

However, I think that for the type analysis I want to run I could just apply a force on a linear material and see how the horizontal bars react to the load. I guess the type for the material used where the load is applied doesn't really matter as far as it has a similar weight and stiffness as leather, right?

Thanks, Andrea

[John_Holtz]

Hi Andrea,

I agree that using a material (any material) that has the same stiffness as the leather will be reasonable for seeing the behavior of the horizontal bars.

When I re-read your post, I saw that you are performing a nonlinear analysis. Now that I think about it, a nonlinear might do a fair job of simulating the behavior of a cloth. In the real world, the force is resisted by the membrane stress (stretching) of the cloth. In the simulation, the load is initially resisted by the bending stress in the cloth. As the cloth deforms more, the force develops more membrane stress like it does in real life.

Let us know how it works out.

[1502211]

Hi John, 

Thank you for your reply. Yes, I agree, I believe that a non-linear simulation will do the job. Now that I've been running ore simulations what I think it is most important for me is the displacement of the fabric related to its initial position. I wouldn't want the fabric to deform excessively, that's another thing I have to keep in mind.

I'll keep you updated,

Thanks again!. 

Andrea

[Anonymous]

Hi, I have a similar application where I need to simulate loads on material. I would be interested to know how you got your material to interact with the 2 poles? 

[John_Holtz]

Hi @Anonymous 

What is your material? If it is thin, then you will not get accurate results from Fusion. Thin parts (especially thin parts that have no bending resistance like materials) cannot be simulated with a solid. Solids are the only option in Fusion. (Looking back at Andrea's images, the leather is rather thick, at least for a material. Andrea will need to comment whether modeling the "thick" leather using solids gave reasonable results or not.)

If the goal of the analysis is to determine what happens in the poles (as in Andrea's example), it would be better to do a hand calculation of what force is transmitted from the fabric to the pole, and apply that load directly to the poles. In this situation, the fabric does not need to be modeled.

If the fabric is important in the simulation, or the geometry is too complex to calculate the load transferred to the poles by hand, then you need to use Inventor Nastran so that the fabric can be more accurately modeled.

[Anonymous]

Hi,

I’m no CAD expert so am struggling - I’m trying to model what’s called a silt curtain. An example would be a vertical sheet of strong woven nylon canvas ( like they use in aggregate bags). At the top of the canvas 8cm square floats are slid into a welded pocket. At the bottom of the sheet is a galvanised steel chain in a similar pocket. The curtain is anchored in a lake/,river and it prevents silt escaping from building sites/ flooding etc.

The whole structure is a single sheet with the top and bottom pockets made from the edges bent over and heat welded.

I have no idea how to model the interaction between the canvas and the floats/ chain. I thought your model might be a good place to start as it’s identical in principal.

Peter

[John_Holtz]

Hi Peter,

When you write "I have no idea how to model the interaction between the canvas and the floats/ chain", are you asking about how to create the 3D CAD model? If this is your question, I suggest that you create a new post to the forum so that the modeling experts can provide some assistance. A sketch or something to show what you are trying to draw, and specific questions about what you need help with would be good.

Or are you asking how to perform a stress analysis in the simulation workspace? Presumably the chain is on the bottom of the lake and the floats cause the sheet to be stretched by some combination of buoyancy and/or current flow. Or maybe the sheet does not reach the bottom but just hangs down X meters due to the weight of the chain. In this case, an "engineering sketch" of what the simulation would look like would be helpful. However, the sheet sounds way too thin to be simulated in Fusion.