I've been trying to have simulation replicate a physical test I did on a drive shaft. The FEA stresses seem realistic, as it failed around 43,000 in-lb. But the deformation does not, as seen in the comparison of the FEA and physical torque vs. twist graph. I'm using a true stress and true strain curve obtained through lab testing. I can't figure out why these graphs differ so much. Any help would be greately appreciated.