Tim Zowada's "Bending and busting steel" demo, Ashokan 2006

[Chris Meyer]

At the 25th annual New England Bladesmiths’ Guild seminar at the Ashokan field campus of SUNY, Tim Zowada gave a demonstration entitled “Bending and busting steel.” Tim used a machine that he designed and built to show to demonstrate Young’s Modulus (aka Modulus of Elasticity) and to show the difference in breaking points between heat treated and annealed pieces of steel. The machine uses a hydraulic jack to bend pieces of steel around a fulcrum, with a strain gauge to monitor the force necessary to make the bend, and a dial test indicator to assess the amount of permanent curve (if any) the steel acquires.

Tim’s demonstration proved that it takes much more force to bend a fully hardened piece of steel until it permanently deforms, than it does to do the same to unhardened steel of the same material and size. If I recall correctly, it took over 425 ft/lbs of pressure to deform the hardened piece, but only a little over 100 ft/lbs for the annealed piece. If anyone who was there recalls the exact numbers, please post them.

For reference, Kevin Cashen has stated; Modulus of elasticity (also called "Young's modulus) is the slope of the stress/strain line at stresses less than the yield strength. (This number will be virtually identical for any steel regardless of composition or heat treatment.)

Tim Zowada

Tim’s contraption.

Applying some force.

Bending the steel.


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[Kevin R. Cashen]

Another very important part of Tim's demo to discuss is the weights suspended on the identical bars of steel. The "bender/Buster" machine was used to exceed the yeild point, but the weight demo was entirely within the proportional range. The proportional range is called such because the ammount of deformation is entirely proportional to the ammount of force applied, which is elastic in nature, and is the area of the stress strain curve that is governed by Young's handy little modulus. As soon as one reaches the yield point the deformation is no longer proportional and is plastic in nature. I have an article that I have need to finish for around a year now that included some images just like Tim's weight demo, i.e. it takes the exact same ammount of weight/force to flex a piece of completely annealed steel as it will to flex an entirely hardened piece of steel, this is why it is so misleading to confuse the terms "bending" and "flexing".

I think Tim's demo should be included in every knifemaker gathering there is until the total lack of understanding of this basic principle is finally corrected.

 

[Chris Meyer]

Yeah, what he said. Below is a picture of Tim clamping the pieces of steel to an anvil prior to hanging weights on them. Unfortunately, I apparently didn't get a picture with the weights suspended.