A thin sheet consists of material that follows the von Mises yield criterion with yield stress s Y =

A thin sheet consists of material that follows the von Mises
yield criterion with yield stress _Y = 270 MPa. The
sheet is subjected to plane stress. If _x = 100 MPa and _y
= -100 MPa, determine the value of the shear stress _xy
required to cause yielding of the material.