You state that your results seem right after applying your bending load, but the results go wrong after applying the thermal load. So I would recommend you check the value of the coefficient of thermal expansion for the material you are using-both for unit consistency and order of magnitude. I roughly calculated that for steel you would have a stress build up due to the thermal expansion of about 97 ksi. So you would have a maximum stress of roughly 120 ksi (23 ksi from bending + 97 ksi) assuming linear superposition and shaft is constrained fully in longitudinal direction. So I agree, your results for stress do seem high at 6 million psi. You may also want to check for stress concentrations at the clamps. You may want to check the vm stress results at the midpoint of the beam on the compression side to see if they are closer to what you expect.
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