# Knife edge thickness/surface area

1. Nov 19, 2008

### droc22

I'm having a hard time finding some documentation on the thickness of a knife edge. I need to calculate the force to slice an apple. I found the skin bursting strength to be 1.1 MPa. That means that assuming the thickness blade to be 10.0 micro-meters and the max length of contact with the blade and apple is about 10 cm, the force I get is 1.1 N.

Does that sound about right. I would rather not assume, if someone knows of a source of knife edge specification.

Thanks.

2. Nov 19, 2008

### FredGarvin

I don't know of a reference, but you may want to look at that strength number for skin. That may not take into account the shear forces that are present in a cutting motion. The failure of skin due to a knife would not be failure due to normal stresses. That would be like tearing the skin apart.

I'll look to see if I can find anything for surgical scalpels.

3. Nov 19, 2008

### Danger

We had a thread about the sharpest knife in the world last year, but I can't remember what forum it was in. Obsidian blades can get down to a thickness of one molecule. I seem to recall that the best steel ones were somewhere around 50 times thicker.

4. Nov 20, 2008

### redargon

are you just trying to find an approximate, becasue so far with your assumptions, you're working with a square apple and a straight blade and finding the force required to split the skin. With a round apple your point of contact intially will be very small and then enlarge as you slice through.

to cut a slice you'll probably have to take friction of the knife passing through the apple into account.

5. Jan 27, 2009

### mooktank

I am also having trouble finding any documentation on minimum edge thickness except my knife is CPM-S90V with a thickness of .150" and an included angle of 40 degrees. I just want to see how much strain I can put on a block of delrin with my blade without destroying it for 10 cycles or so.