Good day, I am trying to calculate the stress along the yy-direction for a 3D object compressed in the zz direction (perpendicular to it). The width of the object (in the yy direction) is constant, and the object can only deform along the xx direction. All stresses except for sigma_zz (known) and sigma_yy (needed) are equal to 0. I am trying to write down constitutive relations for this, but I seem to be stuck. Thanks!