Do We Need Mohr's Circle?

Mohr's circle has traditionally played an important part in the presentation of stress and strain at a point to undergraduates and in analysing the output of strain-gauge rosettes. In the former role it seems to create widespread confusion among students with regard to assigning principal stresses to their associated directions. A more straightforward and fail-safe method of performing this task is described using linear transformations and eigenvalue analysis, a method which can be extended into analysis of three-dimensional stress states without introducing any new concepts. The application to examining stresses on oblique planes, in particular the octahedral stresses and the principal shear stresses, is outlined, and the response of students and colleagues to the method is reported.