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Re: Bonded Connections with Shell Elements
Sounds to me like you are on the right path here Bruce. I've also struggled with this a lot. In fact I've wasted hours trying to find where bonds are not working. The problem is the same as with most aspects of Simulation - it is just too unpredictable. There needs to be more explicit guidelines on how to get this kind of thing working properly. I put it down to cheap skate software development.
Having got that off my chest, some suggestions that you might find helpful. Try splitting the terminating surface where two shells intersect. Sometimes I will extend a surface to intersect the adjacent surface and in that way get rid of the gap. If you do this and get a compatible bond you should not need to define a contact at the intersection.
I guess you worked out that you find where the shell bonds failed by checking the dsplacement plot. I've heard it said failed bonds can also be checked usng the buckling plots but have never worked out how. Sometimes I will add a fixed restraint to the shells and release the restrainsts one by one to find the ne that is not bonded and creates instability in the model.
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Re: Bonded Connections with Shell Elements
try 2010 it appears to be substantially more robust and works without much model prep on surfaces/shells - I have not done exhaustive work but I ran a couple of models and no splitting, no manual connections and a pretty decent analysis against the fully split all edge lenght match version. Oh and the split tool is so improved as to not be believable - split multile bodies of the intersection variety the way it would work if the developer where an FEA guy - well almost that would be split all no picking or anything. Anyway, much improved, hassel and tedium much lowered - to maybe the point where it doens't bug me - I would need a big model to confirm that though and I have done really big ones with the old stuff - worlds bigest vacuum chamber roughly 40' x 40' x 26' and prismatic - not round.
In prior versions I would recommend the fully split approach where all connections have the same edge length. I would not use any "bonded connections" accept to different element types like beams and solids to shells. This aproach mostly works unless higher order geometry is involved and there are workarounds for that as well.
Also in 2010 no manual conteact definitions are required for beam to shell or shell to shell - well at least for the few I tried and I am pretty good at breaking the stuff without a lot of effort. It is the most encouraged I have been in many a release so far - but the jury is still out on the over all state of things.
You can still break it but it doesn't take much to get an acceptable workaround, at least for what I have tested so far.
If you are using earlier version that 2009, bonded connections on shells won't work if the gap is bigger than about the shell thickness definition.
Derek - all is not lost....it looks alot better.
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Re: Bonded Connections with Shell Elements
Hello Bill. I spent a lot of time on Beta testing this year. I'm happy to agree that there are some good things that have been introduced in 2010 including the features that reduce the need to define contacts in studies. But I reported a lot of bugs. Around 90 SR's were sent through. Many of the SPR's are still outstanding. This is where SolidWorks falls down. For me the norm on a project is to spend as much time discovering bugs and convincing my local VAR ad SW that they exist as I do getting the job done. I'll start to smile when that ratio changes.
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Re: Bonded Connections with Shell Elements
Thanks for the replies. I am using 2009 64 bit right now, and have been scratching my head this am about trying 2010 version.
I am simulating welds for the most part as these are 19' to 45' frame weldments mostly comprised of sheet metal parts welded together ranging in parts numbers from 25 to 150 of various thicknesses. Also note that I am prepping in Solid Edge and sending a parasolid or step file over to SW and completing missed stuff or changes in SW - so they are not actually SW sheet metal files. Not sure if that matters.
I think I will try 2010 version to see what it does - if I understand you correctly Bill then the global contact of bonded should work, even with edges of different lengths? When they failed in the past I have been spliting the surface and also placing a manual bonded connection, maybe that was not required...
If I can prep the geometry to get a proper mesh and not required to be manually bonded, I am all for that so I'll give it a whirl with 2010.
Thanks again for the tips - much appreciated. These groups are great.
Bruce
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Re: Bonded Connections with Shell Elements
http://www.cosmosm.com/pages/news/COSMOSCompanion-TipsTricks.html
There's some really good info about modelling welds at the COSMOS Companion site. I just got a copy last week of issues #116 & 122, which are about techniques for analyzing welds and weld fatigue. Wading through the registration may take a couple attempts!
One of the recommendations is to model welds as line contact and use analytical methods to size welds from there.
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Re: Bonded Connections with Shell Elements
Gaaa! Still no luck getting through to the COSMOS Companion content. Maybe you'll have better luck. I actually got my copies from someone who downloaded them previously. -
Re: Bonded Connections with Shell Elements
I'm not really trying to size welds with these studies, more just get an understanding of stresses/deflections through the frame in the big picture. I believe I have already seen the cosmos companion on welds about a year ago, unless a new one is out...
On a side note I did some training with FE-Safe with Verity which is aimed at fatigue of welds and is a more of an analyst tool but should be more accurate - unfortunately it is not compatible with SW Simulation and is expensive.
Bruce
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Re: Bonded Connections with Shell Elements
You might try using Split Line to divide bonding faces so that they are identical shape. This will help make compatible mesh.-
Re: Bonded Connections with Shell Elements
Sorry - yes, I am using that as my primary fix right now for failed bonds as it does work. Perfectly mated and identical lengths seem to make bonds happiest, which I guess is understandable and produces the nicest mesh.
Thanks
Bruce
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Re: Bonded Connections with Shell Elements
As I said earlier when I do an analysis all the edge lengths are made to be the same and coincident. I just use surfaces - no solids in the model so any reference to sheet metal is of no relevance what so ever.
In 2010 there is an edge weld connector that is new. I would not go relying on it unless you have tested it to verify its accuracy and under what conditions it provides reliable results. It would have been better if they had just provided the nodal loads (forces) for axial and shear. Then you could design the weld using conventional methods if you know the loads you need to withstand. Of course, you can always make the joint stronger than the parent material, however that may not be practical. Alternatively, you could do the whole thing in solid with a minimum of elements and get the transmission loads at the weld interfaces and use those. They should be reasonable but don't rely on it for stresses.
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Re: Bonded Connections with Shell Elements
Bill, et al:
the "Edge Weld" connector in 2010 works really well as a connector - it spans gaps very nicely and is very easy to use. However, I have conducted some simple bend, shear, and normal load testing to try and understand the output and was not able to obtain agreement with hand calculations (i.e, the output appears non-sensical altogether). I turned in the test model and got an SPR: 525838, as posted by Himanshu (technician at SW Corp) as he verified the issue. The way I understand it, the connector algorithm is fashioned identically to the methods outlined in Vince Adams' COSMOSCompanion series. The upshot: for now, I would not recommend using the outputs of the connector until the SPR is addressed. - Tony
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Re: Bonded Connections with Shell Elements
Hi Anthony,
How is this new weld connector different than an edge to surface bonded connection in shells? Is it correct to say it tranfers the loads okay, but do not interrogate it to determine the forces through it?
Thanks
Bruce
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Re: Bonded Connections with Shell Elements
Bill, one more question;
Are you using different thicknesses? Or is the primary structure mostly the same thickness and done with one surface body, or is it many individual surfaces bonded together using automatic global bonded contacts? Sorry - just trying fully understand your approach.
New constraints or connections always scare me, and that is one thing I don't like about cosmos is the never ending string of changes on the interface, which means I am not always 100% sure of what it is doing without a lot of tests. Improvements are good and bad sometimes.
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Re: Bonded Connections with Shell Elements
Hi Bruce,
In 2009 making things different thicknesses is an issue - more work not impossible. You just can't split a suface and add a doubler by, say, doubling the thickness of that patch, like a pipe penetration as an example. In 2009 this short coming is addressed. It worked fine in 2008 but when they moved to surface bodies as the specification item they forgot about accomodating doublers - they were thinking, apparently, of only the sheet metal constant thickness type of components. In 2009 you can specify by patch or by surface body. You can have different components as surface and do the analysis in an assembly - this had issues in previous releases as hiding a surface only component would not hide it from the stress plot. I think this works in 2010 - haven't checked in 2009 but it probably does.
When I do shell meshing I pay almost zero attention to the global bonded contact condition since it is set by default. I just checked and if it isn't set to bonded the shell edges don't bond if it is say set to free, even withthe same edge lengths. So it has to be set to bonded but that is all I rely on when building a model. So my approach is use surfaces, whether they are in the same part or as parts in an assembly, ensure all edge lengths are the same and use only global bonded contact. Thsi provides a decent analysis. On occaision if two cylindrical surfaces have the same edge lengths they don't bond properly. When that happens I cut away the edges and build an incontext surface to span the gap by whatever means is appropriate (extrude/loft sweep or whatever). That fixes most problems when surfaces edges fail to bond properly.
On your last comment, it is very sad in my view, that they just chuck this stuff out there with no papers outlining what the approach does and how it performs compared to conventional methods be they FEA or hand calcs. They treat it like CAD where no one cares how, say the surface got there as long as it shows up, where in FEA it matter a great deal to understand this level of detail or you just might kill somebody or wreck some expensive piece of kit. The executive level just doesn't appear get ithat distinction. Some of the rank and file guys get it but they are unable to convince their bosses or so it appears as the approach hasen't changed much. It does get frustrating from time to time. On the up side the innovation rate is pretty astounding but I would trade a low innovation rate for well documented code where I get it done with confidence.
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Re: Bonded Connections with Shell Elements
http://www.cosmosm.com/files/COMPANION/116_Welds.pdf
Finally found a working link to the COSMOS Companion weld analysis issue.
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Re: Bonded Connections with Shell Elements
Joe Galliera
Nov 16, 2009 11:13 AM
Try this link: http://bit.ly/1igwe7 (63.3 MB)
It has the videos and PDFs for the weld sizing and weld fatigue. But if you can log onto the SW forums, is there a problem finding the Companion series via the Customer Portal. Here's how: Under the References group, click on Webinars... it takes you right to it.
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