Thermomechanical finite element analysis to describe the engagement and wear of electromagnetic clutches

The engagement of electromagnetic clutches is modeled as transient sliding of smooth and concentric mild steel rings. The coupled thermomechanical problem is solved by finite element analysis. Calculations of transient stresses and temperatures are presented. Wear predictions, based on a local Archard model, are compared with measurements. The principal finding of the work is that smooth surface coupled thermomechanical finite element analysis fails to accurately capture thermal distortions or lack thereof as observed in tests. The asperity contacts reach high temperatures, hundreds of degrees Celsius, while the surrounding material remains much cooler and exhibits low temperature gradients. Thermal distortions are suppressed and the system operates successfully under far more severe conditions than expected. Isothermal analysis better captures the macroscopic pressure distributions in these devices than does the thermomechanical model. We also suggest a modification to local Archard model, which relates local normal pressure to wear depth. Inclusion of the macroscopic (von Mises) stress distributions, which are different on two the sliding surfaces, better captures the shapes of the observed wear tracks. Accurate modeling of such contacts will ultimately require the simultaneous analysis of microasperity contacts and the full component geometries.