{"id":6008,"date":"2015-07-29T00:27:21","date_gmt":"2015-07-29T05:27:21","guid":{"rendered":"http:\/\/krisbunda.com\/blog\/?p=6008"},"modified":"2015-08-02T21:07:51","modified_gmt":"2015-08-03T02:07:51","slug":"curved-balcony-design-fea-simulation-weight-safety-check","status":"publish","type":"post","link":"https:\/\/krisbunda.com\/blog\/2015\/07\/29\/curved-balcony-design-fea-simulation-weight-safety-check\/","title":{"rendered":"Curved Balcony Design: FEA Simulation Weight Safety Check"},"content":{"rendered":"

I felt like this whole balcony extravaganza was getting a little too hysterically long, so I split it into a Design post<\/em> and an FEA post<\/em>. If you’re seeing this post first, but want to see The Origin Story of the world famous balcony series, click below:<\/p>\n

\u2666 Curved (Rolled Sheet Steel) Decorative Balcony Designs that Mimic Wrought Iron Fabrication (Go to the balcony design post)<\/a><\/span><\/h3>\n
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FEA Simulation<\/h2>\n

Here’s the meat & potatoes section. I don’t know why I said that. Actually, this is some screenshots and explanations of how I set up a simulation scenario, complete with fasteners, external fixtures, and mass loading. I wanted to safety test this thing to make sure you could park a subcompact car on it before someone’s grandchildren stand on it.<\/p>\n

Simulation Problem Setup<\/h3>\n

Models:<\/h4>\n

To set this up, at first I kept trying to use the assembly file. This means I tried to mesh all the solid parts of the assembly. Then I tried to create shells and beams and solids and super-fine mesh controls and any and every combination of mixed mesh ever conceived of. There were always problems! I couldn’t get a believable result, if I could complete a solve at all!<\/p>\n

Sometimes the road to simplicity is a complicated maze.<\/p><\/blockquote>\n

And it was all because I really wanted to get that grate deck top to mesh with all the slots in it, because I’m thinking with all that material missing, it will affect the strength, stiffness, and make it act more like a spring than a slab. But it just didn’t want to work, whatever I tried.<\/p>\n

\"Curved<\/a>
Curved Balcony SolidWorks Simulation Mixed Mesh & Mesh Controls Issues<\/figcaption><\/figure>\n

So finally, after wasting way too much time on this, I just created single-body part versions of the 4 bolt-together subassembly weldments (Deck, Front Rail, Side Rail LH, Side Rail RH – and I really didn’t need one of the sides since I cut the railing in half for symmetrical solving). This means each subassembly has a configuration where everything is suppressed except the single-body part file version of itself. And I extruded a boss through the grate on the deck to make it solid.<\/p>\n

\"Curved<\/a>
Curved Balcony SolidWorks Simulation Parts Models Setup<\/figcaption><\/figure>\n

This means there are essentially only 3 bodies in this simulation (after symmetrical cut out completely removes a side rail). I did this by saving the assembly files (*.SLDASM) out to part files (*.SLDPRT) and making sure to choose the little checkbox in the Save As dialog that saves all surfaces and bodies (“All components”). Otherwise, I was getting broken surfaces.<\/p>\n

\"Save<\/a>
Save SolidWorks .SLDASM file as .SLDPRT part file with All components radio button checked<\/figcaption><\/figure>\n

Then I had to do some massaging, adding in bosses, using the “Surface” tab to thicken and merge faces, using the “Direct Editing” tab’s “Combine Bodies” to get bodies to go together into one. This can also be a good diagnostic tool – if you can’t get bodies to combine, they must not be properly merged somewhere. So you’ll need to find a way to make a feature that connects the body to another. Of course, this is all for simplicity’s sake, so hopefully what you’re doing isn’t too complicated or time-consuming. Unfortunately, sometimes the road to simplicity is a complicated maze.<\/p>\n

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Global Contacts and Contact Sets<\/h4>\n

First, Let’s Show What Not To Do (Apparently Contact Sets don’t always override Global Contacts…)<\/h5>\n

I previously made the mistake of leaving on “Global Contact: Bonded” in this study. I didn’t think it would matter, as there are\u00a0No Penetration contact sets in the study for all the faces that should have it, and contact sets are supposed to outrank global contacts. But it was obvious when looking at the displacement plot results that this rule was not being observed.<\/p>\n

I must admit, I have had trouble getting the solver to exhibit the bonded behavior again to verify it. But it comes out with the following choices: Selected for non-touching faces, within 6mm of each other, to be bonded as incompatible mesh. Not sure why the contact sets didn’t supersede this errant global bonded contact, but you can see what the differences are below.<\/p>\n

\"DON'T<\/a>
DON’T DO THIS: SolidWorks Simulation GLOBAL BONDED contact dialog problem – Non Touching Faces, Incompatible Mesh, 6mm<\/figcaption><\/figure>\n

Here’s with the Global contact on, it makes some parts that should be just bolted together (No Penetration) act as if welded together.<\/p>\n

\"SolidWorks<\/a>
SolidWorks Simulation: Parts acting welded together when they should be no penetration, because global bonded contact not submitting to contact set hierarchy.<\/figcaption><\/figure>\n

Here’s with the Global Bonded Contact suppressed (and proper No Penetration contact sets in place):<\/p>\n

\"SolidWorks<\/a>
SolidWorks Simulation: Subweldment parts now deform independently, correctly, because global bonded contact suppressed.<\/figcaption><\/figure>\n

Here’s the Contact Visualization Plot, to show what is happening when the Global Bonded contact is on. The solver thinks, in some areas, the parts are both bonded and not bonded. No wonder it would take so long for the problem to start solving when this was happening. Also, notice all the little red spots on the scrolls \u00a0on the front rail. I think that’s the “6mm” non-touching faces option trying to weld together all these parts to themselves. This is why the Contact Visualization Plot tool can be very helpful in telling you what SW Simulation thinks the relationships are between parts.<\/p>\n

\"Confusion:<\/a>
Confusion: It’s clearer to understand why the assembly thinks some parts are welded when looking at contact visualization plot, notice that the red (bonded) areas atop the purple (no penetration) areas.<\/figcaption><\/figure>\n

Hopefully this helps as a “What Not To Do with Simulation Contacts” lesson.<\/p>\n

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No Penetration Contact Sets & Contact Visualization Plot<\/h4>\n

The relationships between the 3 weldments are explained to the simulation software by clicking the interfaces (circled in red below) and marking them as “No Penetration” contact sets. No Penetration is appropriate because they are bolt-together pieces, and they should deform as such under stress, instead of acting as if they’re glued or welded.<\/p>\n