Do Tresca or von Mises really fit anything well? I've only ever seen data that looks like this [1] which is all over the place. Can we even control shear stress

Do Tresca or von Mises really fit anything well? I've only ever seen data that looks like this [1] which is all over the place. Can we even control shear stress accurately in a lab? Tensile and compression tests are easy but shear stress tends to be non-uniform through a sample. Then there's the mystery (afaik) world of uniform tri-axial tension which seems to be impossible to measure. I wasn't talking about fatigue, but damping too for sure. Analysts often use Rayleigh damping even though it makes no sense physically, uses parameters that aren't material properties, and just happens to be a convenient formula that works with some solution techniques. [1] http://www.w.continuummechanics.org/images/vonmises/Experimental_Yield_Data.png http://www.w.continuummechanics.org/images/vonmises/Experime...