# Shear force requirement

I am building a pneumatic shear to cut .135" C1018 round wire. We will be holding the wire in a hardened thimble and using a heat treated beveled cutting knife.

How much force do we need to be able to produce?

• Is the diameter 135 inches or 0.135 inches ? i see a dot before number one! because the force i calculated is unbelievably big, and ingot is the correct name for 135 inches not wire. Sep 26 '18 at 16:36

I use to build a very simple model first, then try to expand it. Here i try to find the minimum, force require to cut the wire, by using Tresca criterion:

Yielding starts when the maximum shear stress in the material $$\tau_{max}$$ equals the maximum shear stress at yielding in a simple tension test $$\tau_x$$. You can verify the final result with the Mohr's circle: $$\tau_{max} = \frac{\sigma_y}{2}$$

Here $$\sigma_y$$ is the yield strength of your material. A quick google search, i find the yield strength of $$370 MPa$$.

Now, the force: $$\tau_{max} = \frac{F}{A}$$

$$\tau_{max} = 185 Mpa$$ and the section area of the wires are about is about $$37 m^2$$. The require force is about $$6845 MN$$.

I worked so far conservative, by using other criteria, you may find much lower values for the force, i think, but you have to make sure if the force is enough to cut through the wires.