Calculate Min Drum Diameter for Copper Strip 4mm Thick, max Stress 332MN/m2

[wock]

Homework Statement

3. Calculate the minimum diameter of drum on which copper strip 4mm thick may be wound if the maximum bending stress is not to exceed 332MN/m2.
Assume E = 95 GN/m2


σ /(yxE)=r

Homework Equations

The Attempt at a Solution

would this work if so i make it 1.7m aprox

 

[FredGarvin]

I believe you need to invert that answer. The form I am used to seeing is

\frac{1}{\rho}=\frac{\sigma_{max}}{E*c}

Where rho is the radius of curvature.