Thread: plastic deformation

With regard to Verhoeven's 2004 paper on sharpening does anyone have a good picture of what plastic deformation is?

To me it is simply bending, however I have read some things here that sound a bit more mystical, and i have missed other observations that some experienced honer's have made regarding JV's material. So what is plastic deformation exactly?

kevint, there are two types of deformation, elastic and plastic. Elastic deformation is deformation which on relief of the deforming stress, the material gradually returns to its original shape. This type of deformation only involves the stretching of interatomic bonds. Plastic deformation is deformation beyond the elastic limit. The material never returns to its original shape. In this case, atoms and molecules actually slip past each other. In metals, if you look at a stress/strain curve, you can see the region of elastic deformation, the point where the metal reaches the elastic limit and the plastic deformation region. I've attached a stress/strain curve from Wikipedia. I hope that this helps.

Bending, as per your interpretation. This relates to bur formation (aka the wire edge) either from rounding or bending over (the plastic bit). He does mention fracture too, what everyone here would refer to as chipping, likely the result of too much bending.

Sadly, this is potentially another place where a lot of different names for the same thing are in the way of understanding. Keep it simple.

Originally Posted by blaireau

kevint, there are two types of deformation, elastic and plastic. Elastic deformation is deformation which on relief of the deforming stress, the material gradually returns to its original shape. This type of deformation only involves the stretching of interatomic bonds. Plastic deformation is deformation beyond the elastic limit. The material never returns to its original shape. In this case, atoms and molecules actually slip past each other. In metals, if you look at a stress/strain curve, you can see the region of elastic deformation, the point where the metal reaches the elastic limit and the plastic deformation region. I've attached a stress/strain curve from Wikipedia. I hope that this helps.

blaireau nailed this one on the head.
One way to look at it? Steel (or any other malleable material)is like silly putty:

-At low speeds (and with enough clearance) it stretches.
-At high speed, or with tighter tolerances, the material fractures.

With sharpening, stropping and shaving, you really have a little of both, albeit on a micro scale.

Another way to demonstrate it is to take a strip of steel - an old spoon or something will do.

Flex it gently - when you apply pressure the steel bends, when you release the pressure it goes back to it's original shape. It deformed elastically, so it sprang back when you let go.
Flex it harder - when you let go, the spoon doesn't go back to it's original shape. This is plastic deformation - you put enough pressure on it to permanently deform it.