Splitting Force of Wood 4

[smith16]

Im trying to get a splitting force required for wood with as Strength in Shear at 2660 psi. The Log i'm calculating for is 16" Diam. and 20" long. Im ending up with like 851000 lbs required to split which seems really high.... Does anyone know if this is right...I dont think it is

 

[tomwalz]

If you are trying to split a 16" diameter log sideways (against the grain) in a single blow it sounds about right.

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

 

[hydtools]

Here is some wood properties information.

What you are interested in is the tensile strength perpendicular to the grain. For Douglas fir it is 2 MPa.

http://www.worldwideflood.com/ark/design_calculations/wood_strength.htm

Ted

 

[GregLocock]

or 300 psi

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[hydtools]

Here is another source:

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

Ted

 

[smith16]

thanks alot for your help guys...The application i'm calculating for is splitting wood across the length of the log.... ive tried the calculations with the values i obtained with your help. The value for shear parallel to grain ends up around 2300 psi, and i'm still getting a similar value (approximately 750000 lbs to split). I'm using a design stress formula (Sus=F/A)So using 2300 as the Ultimate strength in shear and using 16" X 20" cross section, i get around 750000.. Any help would be greatly appreciated.

 

[CorBlimeyLimey]

This might be easier ... and cheaper.

http://www.thestickler.com/article.asp?id=5833

 

[MintJulep]

Splitting wood is NOT a shearing action.

As pointed out by hydtools, you are interested in the tensile strength perpendicular to the grain.

As you drive a wedge in parallel to the grain you are developing tensile forces perpendicular to the grain.

 

[Compositepro]

It is a tensile force but the failure mode is peel which is where most materials are weakest and why splitting wood is such a commonly used process.

 

[unclesyd]

Take a look at this article using fracture mechanics inestigating the splitting of wood.

http://www.atypon-link.com/WDG/doi/pdf/10.1515/HF.2007.056?cookieSet=1

Lots of information on the fracture of wood.

http://www.google.com/search?q=frac...afe=off&rlz=1T4GGIH_enUS245US245&start=0&sa=N

 

[btrueblood]

I think the OP is mis-stating what he's looking for, he wants to shear a log not split it. He says he wants to "split.. wood across the length of the log", i.e. shear the log in two across the skinny direction. More like what a log shear does (or a chainsaw), not what a log splitter does. For a log shear, 750 kips for a 16" log does not sound unreasonable, that's about what the force generated by a logging harvester ought to be given the size of the hydraulics.

see:

http://www.forestryequipmentsales.com/categories/9/16.html

for some examples.

 

[hydtools]

smith16, it sounds like we need to have a better description of what you want to do in order for us to give you more help.

Ted

 

[smith16]

Sorry to create any confusion. What im looking to calculate is the splitting force required to split the wood as shown in the attached link (first video).

 

[berkshire]

smith16
I think this is the Patent description for the machine you showed.

http://www.patentstorm.us/patents/4875514-fulltext.html

If this is what you are doing, you are splitting on 3 planes across the end face of the log simultaneously.
If this is, in fact, what you are trying to do, you are going to have a hard time getting an exact figure, because of the interactions of several splits occuring at the same time.
B.E.

 

[smith16]

Yeah I assumed that would be the case. My design uses only two splitting blades perpendicular from each other, so the logs would just be split into 4. I thought that if i just analyzed the cutting with one splitting knife (cutting the log in half), my design would be safe.

 

[berkshire]

smith16
Hyd Tools and Mint Julep have pretty much called what you need.
Do you have a bursting cone on the front of the blades?
Maybe you should analyze the force for the cone using the tensile strength perpendicular to the grain for the wood you are using.
If you do not have a cone, then doubling the force you got with one knife should give you enough to start the split then the forces should reduce.
B.E.

 

[unclesyd]

Just a little empirical information concerning log processors based on observations of one in operation.

The one I observed had a 56 hp diesel engine with a stacked pump(2). I don't think the pump was two stage. The pressure gauge was not working on this unit due a leak.
The ram was rated at 33 tons. I have a single wedge 26 ton splitter with a 8.5 hp gas engine that struggles with a large diameter log. The log processor had no problems with large logs, max was 28"dia x 24" long. It was capable of using 4,6,or 8 blades.
The flow rate of the pump was quite high as the forward stroke while cutting was quite high. It seem to keep the same speed despite the number of blades. The blades on the cutter head are not in the same plain as each is set back from a 1/8" to 1/4" from each other. The key to fast operation was that the splitter head had to be centered on the log. The cylinder appeared to be 4" cylinder with a oversize piston rod.
The higher hp and large pump really increase the speed of each stroke as compared to my single. The owner of this log processor stated that he was going to upgrade to a 66 hp engine to speed up processing.

 

[tomwalz]

What you are doing is generally considered splitting wood with the length of the log or with the grain and not across the length of the log.

Some of the rental units advertise between 5 tons and 22 tons of force.


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

 

[btrueblood]

Rats...I really wanted to discuss snipping off a 16" log with a pair of really big scissors.

As for splitting, where's the fun in a hydraulic splitter? You aren't a real man unless you've spent a summer splitting 36" cottonwood boles with a maul and wedge + sledge. Wussies.

 

[Compositepro]

I have done in-depth studies on the forces required to split wood. I have an 1890's farm house that we heat with wood and cut and split several cords a year. (Its better than a gym membership). You will encounter a very wide range of forces required. Green wood is much easier to saw than dry. But dry wood is much easier to split. Unsplit wood dries very slowly. A wedge or maul in green wood will tend to deform or crush the wood rather than start a split. Then friction between the wood and wedge becomes a major factor. Frozen green wood will split much easier. Straightness of the woodgrain is a big factor as well as species of wood. Elm is a ***** to split.

While a hydraulic cylinder must be able to generate sufficient force to start a split, the work required will determine the engine size. A maul or sledge is an energy storage device and the force it generates is determined by the wood itself. You have no idea how much force it hits with without measuring instruments but it real easy to tell how much work you are doing!