How is this multiaxial relationship derived in this paper?
How did one arrive at the red-underlined part in the equation (2) from differentiating equation (1)? Please see the picture:
The paper referred here:
Chen, Y., Zhuang, W., Wang, S., Lin, J., Balint, D., & Shan, D. (2012). Investigation of FE model size definition for surface coating application. Chinese Journal of Mechanical Engineering, 25(5), 860-867.
