Wood hardness help please

[davidwyby]

I deal with tamarix aphylla a bit down here. It's similar to cottonwood. The only indication of hardness I can find is this " The Janka hardness was estimated at ca. 33.7 N/mm2 in the transverse direction ..."

Link : Microsoft Word - Tamarix-paper _SDU-submitted_.doc

I can't figure out how to convert that spec to some standard numbers so that I can compare to other woods.

Here is cottonwood and sample of "normal" hardness specs.

Eastern Cottonwood | The Wood Database (Hardwood)

Thanks

 

[lxskllr]

I don't understand tamarix numbers. Janka is how much force it takes to shove a ball into a piece of wood. I'm not sure it's a trivial calculation to covert from mm² because you have to calculate the area of a sphere with a constantly changing radius. I don't think the force is going to be linear.

 

[Nutball]

Simple math with Google doing it for you. Convert Newtons to whatever, and convert square mm to whatever. Just know that if you change the surface area units, you need to proportionally change the number such that it still matches the same pressure at the original surface area.

Don't over think the sphere, it doesnt matter unless you plot force vs depth. Otherwise it's just like PSI.

 

[flushcut]

I don’t really consider cottonwood a “hard” wood but it is certainly a tough wood. Lots of heavy equipment haulers like cottonwood for trailer decks in my neck of the woods.

 

[lxskllr]

It's not simple math, and I don't know that the author of the tamarix paper knows what he's talking about. A mm² isn't a sphere which must be used to be a janka test.

edit:
Just running straight math, the janka test has a final surface area of 100mm², so that would be 33.7*100=3370. That's way past the cottonwood estimate.

edit2:
I found the full study, and they have a chart that compares it to ash. Might give you some idea of what you're dealing with.

https://www.wfdt.teilar.gr/web/papers/conference/2010_physical_mechanical_properties_Tamarix_wood.pdf

edit3:
and here's the wiki on janka hardness. White ash shows up, so you can run the percentages and see what it falls near for something familiar.

Janka hardness test - Wikipedia

en.wikipedia.org

If I did the math right, you're in this general area(3363)



edit4:
LoL! I'm looking at it, and that hits close to the straight math. Your cottonwood estimate off? If straight math works with the study, I think they may be misusing the numbers. I don't think it's appropriate to change the janka readings to mm². It could very well be that 1mm² is easier to push into the wood than a 100mm ball due to side pressure on the curved surface. I'd like to hear from a material scientist on that.

 

[davidwyby]

Thanks @lxskllr

I’m getting about 750 lbf janka using the percentages