**5. Conclusions**

This paper presented new experimental results on the nonlinear response of large size TPJBs related to the dynamic/static load ratio, showing that nonlinear effects, usually neglected in conventional experimental identification procedures of the bearing dynamic coefficients, should be considered. A quasi-static procedure devised for a preliminary estimate of the bearing stiffness and of the linear displacement range was used to investigate, in a novel way, the nonlinear response of TPJBs. It consists of applying a slowly rotating force to the floating stator. Orbits with particular shapes, different from elliptical, were observed for increasing dynamic to static load ratio.

Numerical simulation using simple bearing models and assuming quadratic stiffness terms and coefficient load dependence generated orbits with shapes similar to the experimental ones for high load ratios where linear models fail, proving the presence of nonlinearities in the bearing reaction to excitation as also indicated by the presence of 2X and 3X harmonic components in the FFT of stator displacements but absent in the FFT of the dynamic load.

These results are the first step for a further study on nonlinear identification of first and higher order coefficients by optimization techniques.

**Author Contributions:** Conceptualization, E.C. and P.F.; Data curation, E.C. and P.F.; Methodology, E.C. and P.F.; Writing – original draft, E.C. and P.F.; Writing – review & editing, E.C. and P.F.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors thank Francesco Maestrale and Matteo Nuti of AM Testing s.r.l. for performing the experimental tests.

**Conflicts of Interest:** The authors declare no conflict of interest.
