Panel Bond Testing
Lead Driver
Joined: Aug 2006
Posts: 8,094
Likes: 654
From: Brentwood, TN
Something is wrong with that adhesive, either that or there is just not enough of it in the joint. Whatever the case, testing should reflect the actual conditions under which the part is being used. Does this "peeling back" of the joined metal mimic the stresses that the part would be subjected to under normal use? The metals that I use are not so thin as to peel away. When a thin strip bends then all the force applied is concentrated at a single point/edge of adhesion instead of being distributed across a broad surface area. That is the beauty of panel adhesive over weld...more structural integrity is achieved due to a broader area of adhesion.
Laughing Gas
Joined: Aug 2014
Posts: 806
Likes: 95
From: Madera Ranchos
Do a test with a pc 1x2x6 x same gauge as being used in the application. Do the pull test from the center for a more even pull. This should give you a closer strength test of the actual application.
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Laughing Gas
Joined: Sep 2011
Posts: 1,001
Likes: 20
From: West Virginia
Something is wrong with that adhesive, either that or there is just not enough of it in the joint. Whatever the case, testing should reflect the actual conditions under which the part is being used. Does this "peeling back" of the joined metal mimic the stresses that the part would be subjected to under normal use? The metals that I use are not so thin as to peel away. When a thin strip bends then all the force applied is concentrated at a single point/edge of adhesion instead of being distributed across a broad surface area. That is the beauty of panel adhesive over weld...more structural integrity is achieved due to a broader area of adhesion.
Both pieces were squirted with a bead, and then brushed out. Look at the squeeze out on the edges. There was plenty of material. This is 3M 08115 purchases on a couple different dates. I really don't think there is anything wrong with it. If there was it would fail the sheer test.
I used 3/8" because that is the common overlap using a flange tool.
I do think the T-peel test is a pretty good representative of real world conditions. If a patch is hit in the middle it would put sheer force on the edges and be fine. HOWEVER, if one edge were to get hit or come loose the panel could be peeled off relatively easily.
Fleet Mechanic
Joined: Jun 2015
Posts: 1,879
Likes: 295
From: Central Michigan
This is very interesting to me though I have never used panel adhesive yet. I think the test you are using would make any adhesive fail. Because you are bending the sheet metal as you pull it. This wouldn't happen in a real world situation, unless a collision, say another car trying to rip off your fender..? It seems if the load was all along the piece then it would hold. What I an saying is you are destroying the piece of sheet metal as you are bending it/ making it come apart- right? Say you had 2 flat pieces of steel you bonded together and some huge force came along and started to pull and bend one of the Pieces at the end. As it pulled it ruined the piece ( made it not flat) and separated the bond. So is it a moot point that the bond eventually failed as the piece was already bent and probably destroyed anyway? If you took 2 pieces of 2" square tubing and bonded them together and them tried to pull them apart evenly, I think that would be a more accurate test as you wouldn't have the bending first.
Lead Driver
Joined: Aug 2006
Posts: 8,094
Likes: 654
From: Brentwood, TN
It's your call...personally if I was looking to perform a meaningful test I would set up the test conditions to mirror my application. In your case, a section of hood metal and a section of louver panel and bond them together just the way they would be on your "production" hood. Apply forces to the test panel that you would expect to see on your "production" hood and see how the bond holds. An egg will support a lot more weight than any portion of it's shell alone.
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