I have a model of a conferance table with a frame made from aluminum tubing. I'm trying to figure out if the table is pushed if it will buckle. Would I have to run a static test or buckle test? Do I have to call out all the welds? Also the bottom of the legs will not be fixed so do I have to model a floor and add some kind of friction between the floor and the table? I've done simple simulations before but this is more advanced for me.
Thanks!
good luck : ]
I would agree that the welds are the main problem to be looking at here. With that said how do I test this? Do I run this as a staic test? In my connections I enter my "edge welds". This gives me the size of weld I can use. From there I don't know where to go. I'm not an engineer so I'm not sure what exactly I'm looking for. I wish it was a simple this is going to fail or this is going to pass. I know I can use "factor of safety" but I think its more complex than that.
You would need to know the size of the weld and it's strength properties (which are a function of a lot of parameters, heat treatment, weld type, etc.). In short, I would not model this with the welds. It's really not worth it. If you have a good welder making the table, he should be able to make the weld joint near as strong as the parent metal.
Do you know the typical loads the table will see? If you don't then there is no point in modeling the table. If you do know, then do a static analysis with the load type (point load, or distributed load across the table surface, or whatever the loading condition that this table is being designed for). Run the boundary conditions I discussed previously and compare the results (my guess is that you won't see much of a difference).
We are using aluminum tubing at .125 thick. From my understanding aluminum looses some of its strength after welding. This table will be about 9 feet long with a 200lbs. top. The main concern is if it were to be dragged would the welds hold up.
Apply rollers on two adjacent legs and fixed end supports on the other two legs. apply horizonatal load at one end of the table. Iterate the load until you see yeild for aluminum at the joints. Divide that by 2 for a factor of saftey of 2. I say it's done at this point. Remember your fea simulation will capture the peak stresses with beam elements at your joints. Obviously, the peak stresses are going to happen at the joint where the surface meets the legs. The picture attached shows the setup. This is the worst case static scenario (impact will be different). It's as if you are sliding the table and it snags something at the end of the leg. Once again do a static analysis. The table I drew is stupidly simple, but it gives you the idea. I assume you guys probably have some 90's reinforcing the legs?
Another way to do it is in the picture. You exagerate the thickness of your table surface to elimnate boundary condtion effects. This will give you the same results, but the simualtion is much simpler. But then again for this simulation you would probably have to use solid elements.
the only time the weight on the table (the 200 lbs and whatever is sitting on it) matters for a collapse scenario is when there is sufficient bending in the legs which then allows a moment arm to bend the leg further. If you want a detailed analysis, maybe you could do the solid element analysis (shown in the second picture) with a high mesh concentartion around the joint and apply the load shown and also apply a load of 200lbs in-line with the leg. One thing that i do want to stress is that you not be overly concerned about modeling the weld. I think a basic stress analysis at the joint will reveal enough information. If you have reinforcements at the leg joint (like a 90 degree bracket), it'd be difficult to model the problem with beams. You would probably need to do solid elements (in which case you would only model 1 leg and a section of the table, which you would have to deem sufficiently large to keep the effects of the BCs away from the stress concentation).
Got it. I used the rollers for one side and it worked out like I thought. Thanks for the help!
Apply rollers on two adjacent legs and fixed end supports on the other two legs. apply horizonatal load at one end of the table. Iterate the load until you see yeild for aluminum at the joints. Divide that by 2 for a factor of saftey of 2. I say it's done at this point. Remember your fea simulation will capture the peak stresses with beam elements at your joints. Obviously, the peak stresses are going to happen at the joint where the surface meets the legs. The picture attached shows the setup. This is the worst case static scenario (impact will be different). It's as if you are sliding the table and it snags something at the end of the leg. Once again do a static analysis. The table I drew is stupidly simple, but it gives you the idea. I assume you guys probably have some 90's reinforcing the legs?