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Question about deformation in force simulation

Question about deformation in force simulation

Question about deformation in force simulation

Hello all, I am currently designing a cylindrical, domed lid to an electronics case I am making. Here is the part:


My problem comes when I try to see how much force the top of that case can withstand before buckling. I apply the Solidworks' Delrin plastic (the closest to the actual plastic that the part will be made out of) and then I apply a force of 1000 pounds to the top (overkill but just for demonstration), and fix the bottom. Here is the result:


Note that the top has flattened completely with the upper sides bulging outward.

Now I change the material to carbon steel and apply a force of just 2 pounds. Here is the result:


So I am clearly doing something wrong. The deformation is the same and I feel as though none of the results are accurate. I must be missing something. I notice that the numbers on the color legend to the right change, but that doesn't change the deformation at all.

Any suggestions? Help on this would be greatly appreciated. I can't move forward on this design until I can properly strength test it.

RE: Question about deformation in force simulation

What are you expecting the results to be?

If you like the shape of the deformation but don't understand why the results look the same:

Its just the scaling of the model. If you look at the legend on each the numbers are different. Just right click the result you are looking at on the left menu (say stress1 (vonMises) ) and then click edit definition. Then choose the units you want and change the scale to true scale (1:1) or a user defined scale. Just make sure that the scales are the same for both materials and compare to see if they look different.

If you think the shape is incorrect or it not area you want deformed:

It looks like you have the base set as a fixed geometry in the fixtures setting. You should try and set it as a roller/slider. That will cause the walls to slide out at the bottom instead of it bulging at the top.
If you are trying the buckle the top of the lid you need to shrink the size of the area that the forces acts on. The only way I know how to do this is to sketch the area exactly where you want the force to act (say a .25 inch circle in the middle) and then extrude it just .001 inches. This creates a new face the force can act on and I would expect the deformation to be a bowl shape on the top.

RE: Question about deformation in force simulation

Hmm, I don't know where to start.

1. Are you interested in buckling? Then you should do a buckling analyze to see when the stiffness, due to load, reaches 0. The result is a BLF (buckling load factor) that tells how much more or less load the part can handle before buckling occurs. Use this load in a static analyze to see if the part yield from stress or buckling.
2. The result you see on the screen, as mentioned above, is a scaled deform picture, not the actual displacement. Make a displacement plot to see the values for the actual deformation on both solutions.
3. The best way to minimize a surface for loading is to make a sketch and use the split line command. Then you just split the surface without the need to add any material to get a smaller surface.
4. Roller/slider is one way to go for a more realistic boundary but a better one is to define a remote load in a point in the center, combined with a viritual wall. Roller slide prevents motion in both directions, while the remote load solution only prevents one direction (the outer edges on the bottom surface can lift when the part buckles).

RE: Question about deformation in force simulation

Just a quicky - while their suggestions for how to get your answer remain valid.... Look at your images - see the stresses listed? And see the yield strength? The steel is at 0.04% of it's yield strength, the plastic is nearly at half.

Check out "factor of safety". Good luck.

RE: Question about deformation in force simulation

I would also add that if you really are looking at any type of large deformation you really need to run this as a non-linear model. You also need to look at how you are setting up the material properties and what material model you are using. Plastics and rubbers don't behave the way metals do.

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