mechanics of materials Mohr

I want to know what is the meaning of dσ/du in this solution?

• That is a very poorly worked up solution. They introduce a bunch of extraneous symbols without explanation. The derivative is actually with respect to sigma_y and they expect you to recognize that u depends only on sigma_y. Note the gobbledygook before that line is such a mess I'm not convinced its correct. Nov 9 '17 at 14:38

For same shearing stress if absolute value of $$\sigma_x$$-$$\sigma_y$$ is larger, points on Mohr circle are wider apart and $$R$$ is larger thus maximum shear stress is larger. Variable $$u$$ is introduced to represent this connection and derivative was tried to obtain solution but it failed and solution was obtained using geometric properties of Mohr's circle. You should try to draw circle for better understanding.