Question

Explain what is special about principal planes, principal directions and principal stresses. What is the special characteristic of the principal stress tensor?

Answer 1

Principle planes are the planes on which only normal stresses act and no shear stresses occur on such planes.

Principal directions are the set of axes along which normal stresses are maximised. These are eigen vectors corresponding to principal stresses.

Principal stresses are the maximum normal stresses that act on the planes and where no normal stresses happens to be present. It is the eigen values of stress tensor.

Principal stress tensor is the set of eigen valuea of the stress tensor.