Reply To: Adhesion factor in MotorCAD Mechanical stress analysis

[James Packer]

Thanks for the question. The 'adhesion factor' is applied as a scaling factor to the magnet's Young's modulus for the magnet. If the adhesion factor is set to a low value, the magnet effectively becomes a mass loading on the rotor, without adding a stiffening effect. Because of the glue layer, this is normally a reasonable approximation, so we'd normally recommend a low value for this adhesion factor. You can also study the sensitivity of the stress to this, I'd expect a low sensitivity once you reach a reasonably low value for the adhesion factor.

One option to increase the fidelity of the calculation is to set the adhesion factor to 1.0, ensure that there is a small gap on both sides of the magnet ('Mag Gap Inner' and 'Mag Gap Outer' both non-zero), and setting the material in the rotor pocket (in the tab 'Input data->Materials', Rotor Pocket) to represent the adhesive material (for example 'Epoxy'). This allows the compliance of the glue layer to be modelled directly.

In any case, it is good to make sure that there is a gap modelled on at least one side of the magnet, as otherwise the FEA solution will represent a condition where the magnet 'glues' the two sides of the pocket together, giving an unrealistic increase in stiffness (because the Motor-CAD mechanical FEA solver is linear, gap opening effects are not included). I think from your comments, you are already doing this.