Different results of Simulation from Solid Mechanics and shell

Hello, I have a problem when doing a simulation with a bend pipe meshed by shell element. The results of principal strains are one time larger than meshed by solid mechanics. But the results of principal stresses from both shell and solid models are the same.

The parameter of the bend pipe, Position for analysis and line graphs for principal strains are uploaded as Attachment. In my Simulation, the pipe is loaded by 300N downwards on cross section A (see photos), cross section B is fixed. The material is structural steel. The position for plotting graph is an outside circle on bend pipe (position C in photo). There are two photos show the principal strains from shell element and solid mechanics. That's obvious to observe the big difference between two graphs.The results of principal strains by shell element are one time larger than meshed by solid mechanics.

And I have also simulated with the shell and solid models in software Autodesk Simulation, the results of stains and stresses are the same as the one from solid model in Comsol . So it means the result of solid model in Comsol is correct，the problem now is just the inaccuracy of principal strain by shell model in Comsol. Is it a mistake from setting and operation by shell element, or maybe a bug in Comsol?

So I ask for your help here and look forward to a suggestion from some of you!

Thank you,
Alick