Shear stress acting on an element

[chetzread]

Homework Statement

When an element of material is subjected to pure shear stress , equlibrium requires that equal shear stress must be developed on four faces of an element .

Homework Equations

The Attempt at a Solution

I can't understand the statement . I assume the 'element ' is cubic ... When the element is subjected to pure shear stress , equal shear stress must be developed on all six surfaces of element , right ? [/B]

 

[chetzread]

is there anything wrong with the notes ?

 

[Mapes]

Pure shear stress involves only four planes; e.g., a shear stress $\tau_{xy}$ implies that there is traction on the planes with positive- and negative-facing normal vectors in the $x$ and $y$ directions. There's no normal or shear force applied to the remaining two planes (in this case, the planes with positive- and negative-facing normal vectors in the $z$ direction).