Thank you for the shared knowledge. Where can I find this testing app? Thank in advance

at around 4:40, apparently the opposite is true in real test. More thickness dissipates stresses, however real world test generally show the opposite.

@stevenabbott3685

Жыл бұрын

Interesting point - and I don't know the answer. However, I can speculate that a thicker adhesive has a chance to fail cohesively, which is not a mode covered by the app. Because "adhesion is a property of the system" we have to think carefully about the overall effect of any one variable such as thickness, while here I'm only looking at stress concentrations, not the same thing as "adhesion".

for the welded pieces of distinct material can we also talk of bonding strength? Is the developed adhesive theory also relevant?

@stevenabbott3685

Жыл бұрын

If the weld is perfect then by definition we have a single piece of material and then "adhesion" is just the yield strength of the material - though I've never needed to know the fracture mechanics of how concentrated stresses get along the weld line. And if the weld is imperfect, say with a Griffith crack, then it's all about crack propagation. All way outside anything I know. Sorry!

Thank you for this video. So all the values we find in the literature about bonding strength measuring shear load at fracture by lap joint norm astm D1002 are highly inaccurate? if so perhaps this could be fixed if a factor between the measured value ( the sum of shear and peel value) and the only shear stress would exist?

@stevenabbott3685

Жыл бұрын

They are a (hopefully) accurate measure of what the test provides, but they are otherwise highly misleading. And if they quote numbers such as X N/m2 then they are wrong because although the N are correct, the m2 are wrong because only a small part of the joint has experienced the stresses. In the book I talk of a few attempts to work out the "real" adhesion of the same joint measured using different techniques by experts ... and they simply can't be compared. A double lap joint does a better job at measuring shear failure adhesion, but it's a lot of work and it still tells you surprisingly little about what's going on - because Adhesion is a Property of the System. It's always better to do a test that relates to the specific failure modes experienced in your real application. Such tests won't be ASTM, but they will be much more useful.

Good evening.Very interesting video. I am not sure to have understood the peel strength. Considering a lap joint where the adhesive forms a plan xz and we apply a load along z direction. Is this CORRECT that the shear strength corresponds to the tensor Tyz? and the peel strength to the stress tensor Tyy? Or how do you quantify numerically the peel vs shear strength? I am currently studying on project to assess the bonding strenght in between a multi-material Additve manufactured piece. I am now making a Comsol modelisation so as to provide hopefully the purest shear strength possible for a lap-joint test. What do you think about it?

@stevenabbott3685

Жыл бұрын

If you have the luxury of doing real calculations with, say, Comsol then you don't need these simple apps. As I say many times, "Adhesion is a property of the system" so knowing the system is the first requirement. In my simple apps I merely choose systems that have tractable formulae because I'm not smart enough to write anything that involves Finite Element stuff. Additive manufacturing is often hugely disappointing because interlayer adhesion can be catastrophic ... often because there's insufficient time/temperature to get polymer entanglement across the boundary. Certainly fused filament objects are often hopeless: temperatures high enough to guarantee entanglement make the whole part sag. Go to a lower temperature and the part stays the right shape, but entanglement is insufficient - I had to read a bunch of papers on the topic. So I don't think my apps help you directly, but if they help emphasise "system" thinking then they'll have achieved something!

Hello, is the software you are using here publically available?

@wiltherdelacuesta8175

2 жыл бұрын

Hi, did you find it?