Titebond Properties - Help me understand

[Jacob Reverb]

OK, I was looking at the Titebond website and found this:

Titebond Original
Bond Strength 3,600 psi
77% Wood Failure in hard maple (under ASTM D-905)

Titebond III
Bond Strength 4,000 psi
57% Wood Failure in hard maple (under ASTM D-905)

If Titebond III has 11% higher bond strength than Titebond Original, shouldn't the percentage of wood failure (under the same testing protocol) be HIGHER with Titebond III than Titebond Original?

:confused::confused::confused:

[Justin Leiwig]

OK, I was looking at the Titebond website and found this:

Titebond Original
Bond Strength 3,600 psi
77% Wood Failure in hard maple (under ASTM D-905)

Titebond III
Bond Strength 4,000 psi
57% Wood Failure in hard maple (under ASTM D-905)

If Titebond III has 11% higher bond strength than Titebond Original, shouldn't the percentage of wood failure (under the same testing protocol) be HIGHER with Titebond III than Titebond Original?

:confused::confused::confused:

Not necessarily. If it works like epoxy the stronger the bond, the more brittle the cured epoxy. Less bond strength means the joint can flex instead of just crack. Just my experience with golf clubs and epoxy though..never needed more than titebond II

[Julian Wong]

If Titebond III has 11% higher bond strength than Titebond Original, shouldn't the percentage of wood failure (under the same testing protocol) be HIGHER with Titebond III than Titebond Original?

:confused::confused::confused:

Higher bond strength = holds wood better = less failures.

[Justin Leiwig]

Higher bond strength = holds wood better = less failures.

I think your misunderstanding. As I read it to be that the actual wood failed, not the joint in their testing. Hence his question

Just like testing screws vesus dowels versus mortise & tenon The wood always fails before the joint gives way.

[ken gibbs]

So if the wood fails before the joint, you only need to use a bonding agent with enough strength to be slightly stronger than the wood itself.

[Jacob Reverb]

Correctimundo.

But why does the wood fail MORE with the WEAKER glue and LESS with the STRONGER glue?

Edit: And another thing: If the WOOD fails at 3,600 or 4,000 psi, that just tells us the strength of the WOOD, not the GLUE joint. So why do they even bother telling us how often the wood failed before the glue joint? Now I'm really confused.

Edit #2: Google amazes me. A search for the ASTM testing protocol turned up this interesting reading:

http://www.fpl.fs.fed.us/documnts/pdf2005/fpl_2005_frihart002.pdf

[Eddie Darby]

Epoxy is in the area of 15,000 psi or thereabouts, and there is no wood that will allow that to be tested, so they use metal plates.
So epoxy tested on wood would give you a result like this; 4,300 psi 100% wood failure.

The 4,300 is the highest average reading that the tests with wood, would give using epoxy glue, and so is not an 'absolute', nor is it a measure of the epoxy's total strength, just an indication of the fact that it is stronger than the wood.

Wood in these tests can fail due to numerous various reasons such as grain orientation in the test samples, drying cracks, moisture content, porousity, surface contamination and oxidation etc. etc.

If Titebond could bond metal, then you would have a more consistant test sampling and a better idea of the total strength of the glue.

Glues/adhesives themselves can fail for a number of reasons also, so all these factors must take into account to give a 'real world experience' that the end user can expect.

These are all numbers generated in a lab, but glues are used mostly outside of labs and can fail due to enviromental reasons, such as moisture, so these tend to be more important, than the actual total strength. Take these into consideration when choosing an adhesive.