Is leather stronger when laminated with an additional layer of leather?

[JLSleather]

Well, yah--- that's what I said.  The speed and circumference of the pulley is the same at all times, so the "tension" on the belt is constant (after start-up).  In teh "straightaway" ... there is tension, and in the bends, there is both tension and compression.  And regardless of the direction (grain in or grain out) of the leather, the bend radius -- the part actually doing the "curve", is not the middle of the leather.

BUT, the "tension" on teh belt is constant -- not increasing. Once it reaches full speed, the tension is not increased.  Still, the belt will fail over time, even though the tension is not increased.

But the question -- to get back to the original -- was concerning leather of the SAME thickness, either 1 layer or 2 adding up to the same thickness. Personally, I think :

1.)  Big Souix makes a great point above about putting holes in leather (or anything really).

2.)  This entire thing will go the way of that thing about Photoshop "brushes" for stamping tools.. lots of words, no action.

 

[TonyRV2]

Thats exaclty it TT.  The tensile forces are much, much greater on the belt in a pulley system.  The only reason the grain side is put toward the pulley is not because of strength, but because of the higher density of the cell structure (that which makes the grain side flat). The flatness of the grain side which is what gives it better properties to engage the pulley.  Frictional forces are much higher with grain to pulley rather than flesh to pulley, so there is less slippage.  Also, when the grain is toward the outside it tends to crack.  This is also something that tends to be better with the grain facing the pulley....what compression forces there are tend to keep the grain more compact.

I'll see if I can find that link again and post it.

[TonyRV2]

53 minutes ago, TinkerTailor said:

Do you have a link for that reference? i would like to add it to my library./

I looked ain a bunch of books for the section i remembered reading on drive belting, but I could not find it. I have read that they shaved/sanded/buffed the grain off when they layered skived hides to make thicker heavy duty drive belting. They would arrange  them like a deck of spread out playing cards, with the hides half overlapped to get more thickness. The glue joint was not as strong grain to flesh as it was flesh to flesh, hence the removal of the grain.

Also, as to the original question, Leather belting was never stitched only glued. The sections of belt were joined with stitching or clips, but the pieces are way longer than a hide is. The individual hides were glued together. I am sure if glue worked good enough here, it will hold up the that dirty hairy gun on yer belt

I also have a few scientific journals that talk about leather tensile strength from the early 1900s but they are way too dry to read right now......

Here's the link to the google book.  The explanation basically starts on page 182, section 26.
 

https://books.google.com/books?id=QV8IAAAAQAAJ&pg=PA183&lpg=PA183&dq=which+is+a+stronger+material+the+grain+side+or+the+flesh+side+of+leather?&source=bl&ots=H_oOqbEpfM&sig=oOIV8XoJqE_IGMlnreVk_-wOKlI&hl=en&sa=X&ved=0ahUKEwiYjffGlYjRAhUpqlQKHR91BdUQ6AEIRzAI#v=onepage&q=which is a stronger material the grain side or the flesh side of leather%3F&f=false

[thekid77]

When I originally posted this question, I should have been more specific...the context of the question are two plies stronger than one (assuming same thickness), was in reference to reinforcing the buckle ends on a leather belt.....my apologies for lack of clarity....the topic has gone six ways from Sunday....

Thank you everyone for your input and for sharing your experience....personally, I feel that two layers laminated together are stronger than one.....not saying this is the truth, but I'm relating it to comparison the strength of single plies of wood vs wood laminates...i don't see why the same theory would not be true for leather

[RockyAussie]

4 hours ago, thekid77 said:

When I originally posted this question, I should have been more specific...the context of the question are two plies stronger than one (assuming same thickness), was in reference to reinforcing the buckle ends on a leather belt.....my apologies for lack of clarity....the topic has gone six ways from Sunday....

Thank you everyone for your input and for sharing your experience....personally, I feel that two layers laminated together are stronger than one.....not saying this is the truth, but I'm relating it to comparison the strength of single plies of wood vs wood laminates...i don't see why the same theory would not be true for leather

If 2 top grains are used the answer is defiantly yes and I would guess by about 50% or more. The type of glue used if any would also add a further factor. If used against where the bar of the buckle comes in contact I would use the top grain to make contact. Making sure the stretch in the hide is cut in the correct way, will have a large bearing on the durability as well.

[Northmount]

19 hours ago, nstarleather said:

Plywood and OSB orient the grain of the wood to cross and create the strength.   If you were to create a laminate using the grain parallel as opposed to perpendicular, you wouldn't get the same strength.   Leather grain isn't the same thing.

It would be interesting to see if there are any bow makers here and what their comment and experience would be.  Their laminations are all oriented along the length of the bow.  Maybe it has more to do with how much spring.  Off topic, but interesting.

Tom

[TinkerTailor]

32 minutes ago, northmount said:

It would be interesting to see if there are any bow makers here and what their comment and experience would be.  Their laminations are all oriented along the length of the bow.  Maybe it has more to do with how much spring.  Off topic, but interesting.

Tom

Wood is unidirectional. It needs to be in the direction the tree grows. If you take a sheet of plywood that is 5 layers thick, it will be much stiffer and stronger parallel to the grain in the direction that has 3 layers going the same way. Any laminations with the grain direction the wrong way will crack. In addition, as moisture content changes wood only expands and contracts widthwide and not lengthwise. Having the expansion and contraction of the layers opposing each other can lead to glue joint failure. This is one of the reasons plywood left outside delaminates. Bowyers laminate in other omnidirectional materials like rawhide, sinew or fiberglass to counteract woods nature to split along the grain.

 

The long and short of the leather  laminate question is this:

• Full thickness, unsplit leather is stronger than split of equal weight, as listed in several textbooks. removing 1/3 of the thickness from the backside reduces the strength by half.
• Leather fibers are omnidirecional and do not run parallel like wood, meaning comparisons are not that accurate.
• Glue does not increase tensile strength. It maintains a cohesive bond so the 2 layers act as one layer. (there is engineering data for this.) Wood laminates are stronger because wood is unidirectional and 2 pieces with slightly differing angles to grain structure will triangulate each other when bonded. The omnidirectional nature of leather fibers intertwining means they do not have this property.
• The data supports that the surface grain does not add to strength. It does add to durability and resistance to contamination(which are a different topic), but not strength.
• The data also supports that the grain is harder to bond to, meaning face to grain glue joints are weaker and as such, a laminate of this type is likely weaker once the glue bond lets go,  than a cohesive laminate that acts as a single layer would be.

With that said, and assuming we are talking about unflawed leather, a belt made with 2 unsplit strips of 5 oz glued together back to back should be just as strong as a belt made from unsplit 10 oz. If it is stitched as well as glued, the stitching will add a small amount of strength but also pierce the leather as mentioned so to be a fair comparison the 10 oz would be need be stitched as well. In this case they should also be the same.

A belt made with 2 layers of hide split to 5 oz will be weaker than a belt made from unsplit 10 oz. but likely are the same strength as leather split to 10 oz.

As to the existence of the grain protecting the leather, longevity is a different question to strength.

Edited December 23, 2016 by TinkerTailor

[TonyRV2]

On 12/22/2016 at 10:07 AM, TinkerTailor said:

Do you have a link for that reference? i would like to add it to my library./

I looked ain a bunch of books for the section i remembered reading on drive belting, but I could not find it. I have read that they shaved/sanded/buffed the grain off when they layered skived hides to make thicker heavy duty drive belting. They would arrange  them like a deck of spread out playing cards, with the hides half overlapped to get more thickness. The glue joint was not as strong grain to flesh as it was flesh to flesh, hence the removal of the grain.

Also, as to the original question, Leather belting was never stitched only glued. The sections of belt were joined with stitching or clips, but the pieces are way longer than a hide is. The individual hides were glued together. I am sure if glue worked good enough here, it will hold up the that dirty hairy gun on yer belt

I also have a few scientific journals that talk about leather tensile strength from the early 1900s but they are way too dry to read right now......

Here's the link to the google book.  The explanation basically starts on page 182, section 26.
 

https://books.google.com/books?id=QV8IAAAAQAAJ&pg=PA183&lpg=PA183&dq=which+is+a+stronger+material+the+grain+side+or+the+flesh+side+of+leather?&source=bl&ots=H_oOqbEpfM&sig=oOIV8XoJqE_IGMlnreVk_-wOKlI&hl=en&sa=X&ved=0ahUKEwiYjffGlYjRAhUpqlQKHR91BdUQ6AEIRzAI#v=onepage&q=which is a stronger material the grain side or the flesh side of leather%3F&f=false

 

I consider myself a student of one of the renown sheath makers of our time, Paul Long, having purchased and studied all of his DVD's time and time again.  Now according to Paul, when gluing two pieces of leather together PROPERLY, flesh side to flesh side, the bond will be so strong that any attempt to tear it apart will result in the leather fibers ripping before the glue bond gives way.  This would lend credence to the idea that laminating two pieces of leather together would likely increase the tensile strength.  I say likely only because I haven't seen or heard of tests of this sort actually being performed.  Paul's idea of 'properly', to which I have personally subscribed, is to put two coats of Barge on each surface when doing flesh to flesh.  The first coat is allowed to tack up and soaks into the fibers, the second coat then lays atop the first.  So I believe that the glue bond does not diminish the overall strength of the leather although this does not really speak to the quality of finishing the edges of the leather in order to prevent affects of weathering on the material.  To summarize, the tensile strength (the degree by which the leather could be stretched before breaking is likely increased as it would be no different than using two straps connecting two point as opposed to one.  The shear strength, that is ripping one layer from the other, would remain unchanged as compared to a single strap subjected to shear forces.  Thats my story and I'm stickin' to it, at least until someone else changes my mind.

[Chief31794]

Boy, this got into detail, I ain't got all that science, but what I've observed over the years is that a belt with two layers will hold a 1911 weight pistol with less "sag" than a single layer belt of the same thickness, that's what I based my comment on. I don't make belts for use on machinery so that may be different, but when someone wants a belt for carry, I highly recommend a double layer belt as they last longer and sag less under the same use and weight carry.

Chief

[bikermutt07]

In my experience a single layer of uncut non stitched leather will last a cow a lifetime.