How fast can you turn a motor before the magnet powderizes?

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The maximum rotational speed of a magnet before structural failure depends on its material properties and the bearing tolerances. Neodymium Iron Boron (NIB) magnets exhibit high compressive strength but lower tensile strength, leading to different failure modes at high RPMs. Typically, failure occurs due to tensile stress in the armature, which can cause components to collide with the stator and lock the motor. Additionally, when a DC motor and gearbox are allowed to free-run under load, the rated RPM can be exceeded, often resulting in damage to the armature and commutator. Understanding these dynamics is crucial for motor design and operation.
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Assuming the stator and windings won't burn out, how fast can a magnet rotate before it structurally fails?
 
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Depends on the material the magnet is made from, and also the tolerance of bearings that constrain the motion of the magnet.
 
So, NIB magnets have a way higher compressive strength (950 MPa) than tensile strength (75 MPa). As you spin it the outer edge is under greater compressive force, while the inner edge is in greater tensile force. So how does it fail at max RPM, by breaking apart or by powderizing itself? Tension or compression? And what about shear?
 
The mode of failure due to over-speed is usually a tensile failure of the armature components with the result that the armature components hit the stator poles and the motor locks.

If you allow a winch with a DC motor and gearbox to free-run under load without power applied, the rated RPM of the motor can be exceeded. What I have seen happen is the strips of copper commutator being thrown out of the armature taking the attached winding leads and brushes with them. It makes a mess.
 
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