I'm not sure if it's friction or vibration (stump grinder).Maybe the question is, why is there so much friction that it tears away?
No, I have both chains and the cone is "snapped" into the U-joint.there are usually plastic pins that push in to hold the round cone end that covers the U joint onto the tube. usually the chains are hooked to the cone and both sections of shield should have chains that keep them from rotating. are you missing a chain so that one tube is fixed and the other rotating?
Thank youThe PTO shield should be free spinning from the shaft, many will have chains and clips to prevent the shield from rotating, some do not and will tend to spin with the PTO shaft. It is just a guard, it can be done away with and as long as the proper respect is shown to the pto shaft there will be no ill effects.