Consider the following stress element:
A special type of triaxial stress, called spherical stress, occurs whenever all three normal stresses are equal.
Under these stress conditions, any plane cut through the element will be subjected to the same normal stress and will be free of shear stress. Thus, we have equal normal stresses in every direction and no
shear stresses anywhere in the material [1]
[1]Mechanics of Materials 7th Ed., James Gere
This page is part of The Encyclopedia of Stresses in Solids