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Stress Levels in an edge....
#1
Photo 
    Just bored this morning....so for fun, I ran some simple FEA on a knife blade section.

Standard width kitchen knife
Material: 1045 steel.....just because I had full properties
20 deg bevel
0.00005 in apex radius

Load over 1 inch......5lbf total

File attached.....
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#2
Sam, thanks for posting the results of your modelling. Smile 

Please can you repeat your calculations for an apex width of 100 nanometers, which is the expected apex width of DE razor blade? The included bevel angle is circa 15 degrees.
 
Jan


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#3
(02-20-2019, 01:50 PM)Jan Wrote: Sam, thanks for posting the results of your modelling. Smile 

Please can you repeat your calculations for an apex width of 100 nanometers, which is the expected apex width of DE razor blade? The included bevel angle is circa 15 degrees.
 
Jan

Jan,

if we are going to do this.....give me some more real world info......how think is a DE blade?....and its flat ( parallel surfaces) except for the bevel?....

15 degrees total included angle?

Also.....I am using a "fixture" in my model as the spine of the knife......in a DE razor, how far back from the apex would it be "fixtured" or held....

finally....how much force shall we apply over the std 25mm edge length?



Happy to do this and give something back....
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#4
Very interesting Jan and Sam. Would you be willing to share a little more, Sam, with the Exchange about how your modeling program works? To put it more succinctly, we're asking for a little "schooling" here so that we can better understand what you're teaching here.
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#5
(02-20-2019, 05:45 PM)EOU Wrote: Very interesting Jan and Sam. Would you be willing to share a little more, Sam, with the Exchange about how your modeling program works? To put it more succinctly, we're asking for a little "schooling" here so that we can better understand what you're teaching here.

Hi All,

I am a Mechanical Engineer by day. I stumbled upon knives, because I am also a home chef, and wanted to "understand" sharp more.....2 yrs later...

a tormek,
a PT50B
a 2 stage paperwheel honing station
a 60x lighted loop

you guys have cost me all my vacation money.....and maybe next years as well.....

But Honestly, I thank all of you on here, as well as a trove of other guys who have posted super interesting tech stuff, or answered my stupid questions...

FEA ( Finite Element Analysis) is something that I do.....but it is always on a macroscopic scale.....I have never played with it at microscopic scale......so I decided this would further my understanding.

Low forces on very small areas lead to high force per unit area numbers.....this in turn can create both tensive and compressive stresses in the material under load.....I was simply curious as to what those values might be when chopping a carrot or potato.....

Most steel ( in my experience in industry) has a yeild of 50-100 ksi ( 1000psi) in tension....and all steel has a youngs modulus about the same regardless of the steel....so......I applied it to a blade made from something I had numbers on.

This was a static/elastic simulation.....in reality this is well beyond looking at plastic deformation of burrs and the likes....but at a base level it tells me things.....that stresses might actually be beyond yield at the nodal level.

For 5 lbs of force, I find that kinda cool!

I will do the DE Blade, once I have the constraints......lets see!

Sam
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#6
Rainbow 
(02-20-2019, 02:47 PM)Sam Sloane Wrote:
(02-20-2019, 01:50 PM)Jan Wrote: Sam, thanks for posting the results of your modelling. Smile 

Please can you repeat your calculations for an apex width of 100 nanometers, which is the expected apex width of DE razor blade? The included bevel angle is circa 15 degrees.
 
Jan

Jan,

if we are going to do this.....give me some more real world info......how think is a DE blade?....and its flat ( parallel surfaces) except for the bevel?....

15 degrees total included angle?

Also.....I am using a "fixture" in my model as the spine of the knife......in a DE razor, how far back from the apex would it be "fixtured" or held....

finally....how much force shall we apply over the std 25mm edge length?

Happy to do this and give something back....


Sam, thanks for your readiness to model the DE razor blade for us. The thickness of the DE razor blade is some 0.2 mm and bevel length is some 36 mm. 15 degrees is the total included angle. When we fix the blade in the middle, it will be 11 mm back from the apex. I think we are able to apply circa 100 gram-force over 25 mm edge length.

 
Jan


P.S.: My max. stress estimate based on merchant numbers is  circa 75 kpsi.


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#7
    Its about half of what you expected Jan! 35 ksi. !
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#8
Sam, thank you for your stress calculations! Smile
I am surprised how small the max stress is. Please have you considered 100 nanometers apex width which means 50 nanometers apex radius?
 
Jan


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#9
Checked and found 1 mistake.....I was running it over 36mm in length.....not 25mm

so at 100g, 25mm 50nan apex radius..... 51 KSI
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#10
OK, thanks!

Jan


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