Yes and no. All my sources are listed in the Bibliography, but I don’t give sources for each individual species/data point in the book.

It is indeed amazing that this should be so – truly a correct use of the word, rather than the ‘Amaaaazing’ that vocabulary-poor Americans (and now, and aping them, Europeans too) use to describe every observation they make that is on the positive side of neutral.

And it’s also amazing that Stradivarius and Guarnerius must have, without instruments, been able to appreciate the subtleties of this variation when selecting trees from which to make their violins.

That makes all the difference according to my knowledge in engineering. The instantaneous blow in force probably makes the MOR slightly more relevant. A lot of axe shafts rupture mainly due to grain run out in the shafts. So that is by definition a rupture that occurs. Which evidently has a much lower resistance to force when grains are not aligned as straight as possible from the bottom of the handle to the top of the axe head (eye). According to the science on Britannica https://www.britannica.com/science/wood-plant-tissue/Hygroscopicity the best measure of a woods strength is the density, but as you Eric point out in your book, it doesn’t correlate perfectly. Another site says best hammers and also best flexible hammers are those with low MOE and high MOR.
I think I will go for a madagascar rosewood (dalbergia baronii) for my 2-bladed wood splitter with about 40% more janka hardness than the strongest hickory and approx 15% higher resistance to rupture. Last but not least, it´ll look epic! :)

Just note that in testing MOE, the load is applied gradually, so it doesn’t directly equate to something like a hammer blow or a swing from an axe. There are other, more specialized tests that are used to measure a wood’s impact resistance, which don’t always correlate strongly to its MOE.

If there are any structural engineers on this thread, please chime in but, as I understand it, MOE is a good measure of a wood’s strength *relative* to other woods and would be a good place to narrow down woods choices for active applications like a hammer or axe handle. MOR is an *absolute* measure of a wood’s maximum load before failure and therefore would be a useful data point for wood to be used in building applications when used in conjunction with the MOE. Yellow pine would not be a suitable axe handle but it’s high strength combined with a high degree of plasticity makes it an excellent building material able to handle wind and snow loads while still returning to its original shape.

yes, I think I udnerstand it now. I had to discuss this with my mechanical engineer colleague. So basically the MOR starts counting once the material has gone from elastic to plastic. The MoE is the force measured just until plasticity, which as you say takes a higher force than the force to rupture the plasticity in the material.
So the question then is. Which one is the best measure for a woods true strength? For instance, if you want the strongest axe shaft to your large firewood splitter, should you go with a wood with higher MOE vs MOR or the other way around?

I was also confused by this. The MOE is a measure of the amount a material changes shape is some dimension (be that stretching, compressing, or bending) under a stress that does not exceed the material’s elastic range (i.e. the point where the material won’t spring back to is original shape).

This produces a ratio (unlike the MOR which is a direct measure of the force necessary to produce failure) but the ratio is “hidden” because the units measuring the deformation are cancelled out in the equation.

To address your specific question, the MOE can be (and often is) bigger than the MOR if, for instance, the ratio of the deformation of a material to its original length is very small like 1/100 under a stress load of 10,000 ft-lb/in^2. This would give a MOE of 1,000,000 while it’s entirely imaginable that the material could have a MOR of 15,000.

What I find interesting is how the MOR can be lower than the MOE. How can you measure the elasticity of a wood if it will break before you see a bending? Look at the https://www.wood-database.com/rhodesian-teak/ for instance. The MOR occurs at a much much lower force than the MOE.
I will assume that I am misunderstanding something here.

In either case you’d want to stay well within your outer limits. Module of rupture is useful to know as well. That’s the point at which you’d get fracturing in the grain. With a canoe working within the modulus of rupture would be fine since it will remain in the same shape. Module of rupture doesn’t account for fatigue though. Bend a board to much and it may not break but it won’t necessarily spring back to its original shape. So with a bow modulus of elasticity is what you’re looking for since that’s the limit you can bend it and have it return to form. Laminations can increase this obviously. Ash or hickory is good for a bow. Yew if you can find it.

Finally, it’s important to note that E is a constant, so it’s only a way of comparing woods relative to each other or other materials. The most important contributor to a piece of lumber’s actual stiffness is its dimensions. It’s intiutive, but here the physics gets tricky. Thicker and shorter make for stiffer stock.

Carroll It doesn’t look like anything unfortunately. It is only after you combine this value “E” with geometric dimensional properties of the element being loaded or designed that you can compute a relationship between load and deflection (movement). For example, a simple expression of the shortening of a column under load would be delta = P*L / (E*A). This is saying the column gets shorter by an amount delta equal to the product of the load (P) and the length (L) of the column divided by the product of the modulus (E) and the area (A). So in this example the actual stiffness (the ratio of load to deflection) is (E*A)/L where the geometry terms I mentioned to you are the A and L of the column which are combined with E before E really givens you anything useful.

The nice thing about knowing E though is that, with a little engineering background, you can compare different materials to each other in useful ways that permits you get better ideas about how loads work in the structure or item being considered.

2. From your diagram, it appears you are actually talking about the flexural modulus, which may or may not be equivalent to the tensile modulus or the compressive modulus, depending on the material. For wood, I don’t know if they are the same or different. Perhaps you do?

https://en.wikipedia.org/wiki/Flexural_modulus

I think the flexural modulus also depends on the orientation of the grain, radial or tangential, to the force. For example, a quater-sawn guitar neck is much stiffer then one made from plain-sawn wood. Perhaps you could specify which orientation your numbers are referring to?

3. It would be really useful if you could also include Poissan’s ratio. With that, I can calculate plate rigidity, as in a guitar top. I have found values for some woods here:

https://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/ch04.pdf

Thank you for all your hard work on the wood database. You might be interested in the data and calculations I have created for wood used in musical instruments:

https://en.wikipedia.org/wiki/Tonewood#Mechanical_properties_of_tonewoods

Greg

“1.76 and 1.82 is not a discrepancy.”

Actually, it is a discrepancy. Perhaps you meant to say it is not a large difference. If so, I would agree with that. But it is most definitely a discrepancy in the database. Even 1.80 and 1.81 would be a discrepancy. A reference should not give different values for the same thing. Now, if the reference had quoted a range (the same range both times), that would be fine. But giving two different numbers for the same thing is a discrepancy.

1.76 and 1.82 is not a discrepancy. Those are good values to use.

Woods actually vary a lot more than that. It is not like you are testing a mill run of SAE 1035 steel, or something. Wood varies in the same species by geographical location. It also varies by altitude in the same location. Scots pines at sea level to 500 feet are soft and weak. If you go a mile on up that same hill to 2,500 to 3,000 feet, it is 50% more dense than the sea level wood, whether green or oven dried to the same MC. The modulus can also be twice as high, so that would be like having a 1.82 and a 0.91 in the same species from an identical location in the cut in each tree.

What is even more amazing, is if you keep going up to about 4,000 feet, the wood is about back to being as soft and weak as the sea level wood.