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Prevost XLII Skin Delamination Repair
04-30-2017, 18:25 (This post was last modified: 05-01-2017 11:21 by travelite.)
Post: #31
RE: XLII Panel Repair Alternative
I'm sure it's fixed. It'd be lunacy for Prevost to offer a bus with glued on stainless panels otherwise. I know if I had loose panels I'd have Prevost re-attach them with the latest adhesive and process. No way would I let them drill holes for the rivet fix. Last thing I need is a new trainie with 10 hours of experience drilling into the side of my coach. I know that a properly adhesive attached panel provides sufficient strength and toughness, and I know it can last. I prefer glue!

Here's an alternative to stainless steel acid etching, or grinding, or sandblasting for panel prep: the sol-gel process.

david brady,
'02 Wanderlodge LXi 'Smokey' (Sold),
'04 Prevost H3 Vantare 'SpongeBob'

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05-01-2017, 15:07 (This post was last modified: 05-01-2017 15:07 by cmillsap.)
Post: #32
RE: XLII Panel Repair Alternative
(04-30-2017 18:25)davidbrady Wrote:  I'm sure it's fixed. It'd be lunacy for Prevost to offer a bus with glued on stainless panels otherwise. I know if I had loose panels I'd have Prevost re-attach them with the latest adhesive and process. No way would I let them drill holes for the rivet fix. Last thing I need is a new trainie with 10 hours of experience drilling into the side of my coach. I know that a properly adhesive attached panel provides sufficient strength and toughness, and I know it can last. I prefer glue!

Here's an alternative to stainless steel acid etching, or grinding, or sandblasting for panel prep: the sol-gel process.

David,

It may be fixed but only time will tell.

I find it hard to argue that glue is a better fastener than rivets. But I do understand why Prevost does it. There are several reasons but mainly because it is more economical and it improves the bus’s appearance.

I’m very happy with my XL2 with glued panels but I was dang sure to have the glued panels inspected before I bought it. I accept the fact that a panel may become loose sometime in the future and I will just get it re-glued if it ever happens.

It would be prudent to add a panel inspection to any P.D.I when purchasing any coach with glued panels including an H3 as there have been a few loose panels found on them as you well know.


Chuck & Tela Millsap
Arizona
2003 Marathon XLII S/S
2000 Wanderlodge LXi S/S
2004 Wanderlodge M380 D/S
2000 Wanderlodge LXi N
/S
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05-01-2017, 17:26 (This post was last modified: 05-01-2017 21:59 by travelite.)
Post: #33
RE: XLII Panel Repair Alternative
(05-01-2017 15:07)cmillsap Wrote:  David,

It may be fixed but only time will tell.

I find it hard to argue that glue is a better fastener than rivets. But I do understand why Prevost does it. There are several reasons but mainly because it is more economical and it improves the bus’s appearance.

Hi Chuck,

Mostly because rivets aren't very good, especially blind rivets. They're terrible in tension and in shear they're only as strong as the thinnest material being joined. Prevost uses a 3/16" blind rivet which has an allowable shear strength of a few hundred pounds but the loads are always a combination of shear and tension so the strength is actually something less. I haven't measured a Prevost lately but I'm guessing there's a rivet every 3" or so. This gives a linear strength of 100lbs/in. A properly adhered panel using urethane, epoxy, or MMA can achieve better than 2000 psi, so if the bead is one inch wide that's 2000 pounds per inch. This leaves lots of safety factor for heat aging, shrinkage, and variations in application. Plus, glues allow expansion of the panel. How many of us have listened to rivets popping and movement as the sun shines over the coach. Each time this happens there's fretting of the rivet hole. Rivets require holes that are imperfectly filled by the rivet and which allow water in. They make prepping and painting difficult, they allow little expansion of the panel, they create point loads and stress raisers, and they don't dampen movement as well as adhesives. There's also a list of disadvantages to adhesives, but it's the future.


(05-01-2017 15:07)cmillsap Wrote:  It would be prudent to add a panel inspection to any P.D.I when purchasing any coach with glued panels including an H3 as there have been a few loose panels found on them as you well know.

I did have Donny Myers of DMRV remove a leaking panel and re-bond it. It was the upper panel between the slides, originally put on by Vantare, and leaking since the bus was new. I have documentation from the first owner, dated months after taking delivery, complaining about clothing getting wet in basement bay 4 on the driver's side. He took it back to Vantare and they tried to squeeze in additional adhesive but they never permanently fixed it. Donny said, "Vantare barely had any adhesive at the top of the panel". It wasn't a hard fix. If you have a leak, remove the panel and reattach it! No big deal. BTW, Donny's shop is the only shop in town for Vantare owners!

Here's an interesting paper by Loctite on bonding various metals.

david brady,
'02 Wanderlodge LXi 'Smokey' (Sold),
'04 Prevost H3 Vantare 'SpongeBob'

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05-02-2017, 22:01 (This post was last modified: 05-02-2017 22:01 by davidbrady.)
Post: #34
RE: XLII Panel Repair Alternative
Some good stuff on designing with adhesives over here.

david brady,
'02 Wanderlodge LXi 'Smokey' (Sold),
'04 Prevost H3 Vantare 'SpongeBob'

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05-03-2017, 13:39 (This post was last modified: 05-03-2017 13:40 by Hisham Amaral.)
Post: #35
RE: XLII Panel Repair Alternative
There are Cherry max used in aircraft that have the same strength as the upset rivet joint, used mostly in wing panels repair where fritting have occurred which leaves a smoked rivet joint, and any where that a structural joint is required. I think Prevost uses the stainless rivet on the panel fixes.
Info on Cherry Max rivets:
RIVET
The CherryMAX® Rivet is available in both nominal and 1⁄64" oversize
shank diameters and is available in four material combinations:
• 5056 Aluminum Sleeve/Alloy Steel Stem (50KSI Shear)
• 5056 Aluminum Sleeve/Cres Stem (50KSI Shear)
• Monel Sleeve/Cres Stem (75KSI Shear)
• INCO 600 Sleeve/INCO X-750 Stem (75KSI Shear)
Also a PDF from the web site on Cherry Max Rivets:
http://www.cherryaerospace.com/docs/cata...A-1011.pdf
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05-03-2017, 17:38 (This post was last modified: 05-03-2017 17:57 by davidbrady.)
Post: #36
RE: XLII Panel Repair Alternative
Hi Hish,

Thanks for the info on the CherryMAX. It is indeed a very good blind rivet. You know this stuff Hish, but for the benefit of others who find this stuff interesting, we now need to consider the bearing shear strength of the hole in the stainless side panel. The strength of the bearing area is given by BearingYieldStrength*D*t. Where:

BearingYieldStrength = 1.5 TensileYieldStrength = 1.5*30000 = 45000 psi
D = diameter of the hole = 3/16 = 0.1875"
t = thickness of the thinnest sheet = 0.060"

Which gives a bear shear strength of (45000*0.1875*0.060) = 506 pounds, so using CherryMAX rivets has made the hole in the skin the limiting factor. Given a 3" rivet pitch we're limited to 506/3 = 169 lb/in of linear strength on the panel edge. Frankly, I'd rather have a rivet break than a panel break.

I'm still puzzled over why the H3 doesn't see the same issues as the XLII. After all the H3 is also bonding stainless steel. The H3 has a stainless space frame superstructure to which Prevost has bonded a fiberglass-reinforced polymer (FRP) side panel. Apparently the stainless bonding issues aren't a problem in the H3. Why?

I have a theory, It may have to do with exterior side panel buckling strength. I know on my H3 the FRP panels are only attached to the stainless space frame along the edges. The XLII attaches panels around the panel perimeter and also in the center of the panel. I wonder how the buckling strength compares between a Prevost FRP panel and a stainless steel panel. Of course, Prevost has complete control of the buckling stiffness of the stainless panel. They do this by adding stiffening ribs. I'm thinking the H3 FRP panels may have less buckling resistance and because they're not attached in the center they're allowed to buckle, however slight the buckle may be, it may be just enough to keep the glue stresses within its elastic region and down so low that stainless adhesive failure doesn't occur. I know... speculation, but still interesting. Thoughts?

david brady,
'02 Wanderlodge LXi 'Smokey' (Sold),
'04 Prevost H3 Vantare 'SpongeBob'

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05-03-2017, 18:46
Post: #37
RE: XLII Panel Repair Alternative
David
If you constrain a sheet panel on all four side you can introduce the XL2 failure that we see with delaminating conditions of the bonded surface. With a flat sheet of "FRP" that failure may be taken out by the flexibility of the material.
Been a long time since I did any engineering 12 years down and counting.
You may want to start playing with the FEA program that you have, that may shade some on the issue.
Pervost have changed the structure from 2007 on they may have learned something from the XL2. my opinion they should forget bonding and go back to rivet process. The XL is a good looking vehicle, I can understand cost but the price Prevost is charging for the shell they reconsider going back to rivet.
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05-03-2017, 19:49 (This post was last modified: 05-03-2017 23:44 by travelite.)
Post: #38
RE: XLII Panel Repair Alternative
Hi Hish,

I thought about Lisa (FEA) but I don't know enough about the XLII panel geometry to model it. It'd have to be a solid model, simply supported and elastically restrained to model the adhesive. As usual, getting the constraints right is the hardest part and it may be beyond the capabilities of Lisa, for instance I'd have to use a spring to model the glue and that may be too much of a simplification. The idea is that the side panel, when compressed longitudinally parallel to the ribs, needs to be able to pinch in or out at the top or the bottom to allow buckling. Pretty complex for Lisa. Prevost can easily adjust the buckling strength by a factor of 10 over a flat piece of steel by adjusting the rib count and the dimensions of the ribs. A flat piece of steel has very little buckling resistance. This is what we see on the sides of Wanderlodge PT's, Wide Bodies, and LXi's. You can sight down the side and see the skin buckle on a hot day. The same with the XL, the skin can get very wavy. Folks like the flat looking non-wavy sides of the XLII. The rivet fix Prevost is now using on the XLII only uses fasteners on the four sides, nothing in the center; maybe they know something they're not telling?

Remember this thread: http://www.prevostgurus.com/showthread.php?tid=71. Gives us a good look at the rib count and dimensions.

david brady,
'02 Wanderlodge LXi 'Smokey' (Sold),
'04 Prevost H3 Vantare 'SpongeBob'

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travelite (05-03-2017)
05-03-2017, 23:48
Post: #39
RE: Prevost XLII Skin Delamination Repair
David yes do, the simplest way to model the flat plate is constrain the panel at the four corners and run a model analysis. Try that and see the results.
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05-04-2017, 10:51
Post: #40
RE: Prevost XLII Skin Delamination Repair
(05-03-2017 23:48)Hisham Amaral Wrote:  David yes do, the simplest way to model the flat plate is constrain the panel at the four corners and run a model analysis. Try that and see the results.

Thanks Hish, I checked Lisa (FEA) and it is able to model thin skin panel buckling. Stand by! Smile

david brady,
'02 Wanderlodge LXi 'Smokey' (Sold),
'04 Prevost H3 Vantare 'SpongeBob'

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