Elastomer materials

I have difficutly to determine the allowable shear stress and allowable compressive stress for urethane circular plate. I am applying compressive force on the assembly on wich urethane is sandwiched between aluminum plate

Material properties are belows:

URETHANE PROPERTIES
Shore Hardness..............................................................................68-73A
Tensile, psi ........................................................................................ 5500
100% Modulus, psi………………………………………………………….425
300% Modulus, psi .............................................................................. 620
Elongation, % ...................................................................................... 670
Die C Tear, pli...................................................................................... 290
Split Tear, pli........................................................................................ 120
Compression Set, %.............................................................................. 22
Rebound, %........................................................................................... 47
Cured Density………………………………………………………………..tbd