Discussion of: Contact between elastic bodies with an elliptic contact interface in torsion, by J. F. Cuttino, T. A. Dow, J. Appl. Mech., 1997, Vol. 64, 144-148.

by Jürgen Jäger, Blattwiesenstr. 7, D-76227 Karlsruhe, Germany,

 e-mail: j_jaeger@t-online.de

The authors present an excellent Finite Element study for torsional contact of elliptic contact areas and found the important parameters by comparison of FEM solutions for different  parameters. They presented an analytic relationship between the torque and the rotation angle, which was obtained by a curve fit of FEM results for b/a=3, where b and a denote the major and minor semi-axis of the contact  ellipse, resp. In a paper by Todd & Johnson [1987], hysteresis loops for rolling with spin have been analysed and compared with experiments. They approximated the torque Mz as a function of the angle of rotation b by: Mz=(a+bb)/(c+db), with appropriate parameters a,b,c,d. Another approximation  was proposed by Jäger (eq. 7.65 in Jäger 1992), which can directly be compared with Cuttino & Dow's theory ..... (the rest of this page is in preparation).