Peel tests for carbon/epoxy.

[RPstress]

Does anyone have thoughts on what peel tests can be used for testing adhesive between two monolithic carbon/epoxy laminates?

The usual sort of monolithic substrate peel that our lab does is typically T-peel and they don't have any suggestions for an 'equivalent' for non-yielding low strain to failure substrates like carbon.

It looks as if it's not really possible to measure much about adhesive peel for monolithic carbon/epoxy.

 

[berkshire]

RP,
Can you use climbing drum ASTM1781 or are your laminates too thick for that?
B.E.

 

[Compositepro]

That kind of joint is usually designed to avoid peel loading because peel will not be good. The peel failure will move into the laminate because matrix resins are stiffer than adhesive resins. The test then would be similar to the G1c toughness test.

There was a good article recently by Don Adams in High Performance Composites magazine about composite toughness test methods. You could contact him directly at Wyoming Test Fixtures.

 

[RPstress]

Thank you both.

 

[PanelGuy]

Agree 100% with CP...Call Dr. Adams.

Doing a true T-peel would be best, but you need to mold your substrates that way which may be a problem. But if you are needing it frequently the fixtures would not be so bad.

Also you could look at Lap shear. This gets interesting because if you perhaps thin out your substrates a little and overlap far enough (or cut them narrow), There is a potential to cause enough strain to make it "peel".

HOWEVER...my guess is that due to the stiffness of the laminates you would never need peel...seriously, are they going to curl? Best off to work some other cleavage test and call it good. My technicians love debating whether the peel is zero or infinite when the panel wraps itself around the drum.

 

[berkshire]

"My technicians love debating whether the peel is zero or infinite when the panel wraps itself around the drum."

Good one Panel Guy.

B.E.

 

[allcomposites]

Another solution is to adapt the wedge test (ASTM D3762) for your composite application.

This a quite simple test and economical (you can machine the wedge in your shop). But you have to be careful when comparing results (this is a qualitative analysis).

 

[SWComposites]

RP-
many questions to ask before you go charging off running tests:
- what test result(s) do you want to get from the tests? stress values? fracture toughness?
- what are you going to do with the test data?
- what analysis method are you going to use it with?
- what is the specific configuration of your bonded joints?

There is no generic "peel" material property. Most "peel" tests are quasi-point-design, so they can be linked to a specific application. Or consider conducted mode I type fracture coupon tests with a bonded laminate.

 

[RPstress]

This was desire for 'peel' as a characteristic to aid ranking of adhesives for material selection.

This was because some adhesives with a high GIc have low metallic peel, and the feeling was that a lower peel would be less desirable.

The final application involves impact.

 

[allcomposites]

RP, we have used the Wedge Test to compare adhesion performance between carbon/epoxy laminates (Hex8552) of various adhesives (3M-FM300 and similar). Results were confirmed by drum peel test, which took few weeks.

The advantage of this test is that you only need two composites strips (instead of a full panel). The limitation is that you don’t get peel values but moreover a qualitative debonding energy (which is useful for comparing between adhesives).

If you don’t need these data for numerical calculations, it may be simple solution.

 

[PanelGuy]

You know, it may be useful to set your own internal standard. Perhaps pick a metallic substrate with appropriate surface tretments that you make your standard and then make it thin enough to allow a T-peel. You will have to go back through your "catalog" and redo some testing, but it would give you a point of reference.

I do suggest the if you use a surface treament like a priming or anodizing the it be colored and colored different from you system (just for testing) so that when you test you can determine whether the coating bond or the surface bond has failed.

We frequently bond to an anodized coating that is very thin and clear so end up using an ohmeter to check if we failed to bond to the surface or peeled the coating off.