טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentSisso Shai
SubjectNumerical Investigation of Spherical Contact Dynamics in
Viscoelastic Materials
DepartmentDepartment of Mechanical Engineering
Supervisor Dr. Yuri Kligerman
Full Thesis textFull thesis text - English Version


Abstract

A numerical model is developed to study the contact problem between a viscoelastic sphere and a rigid flat under perfect slip contact condition. The theoretical contact model was studied numerically using a Finite Element Method, realized in the commercial software ANSYS 11.0. The effects of the static and the dynamic normal loading of the contact were considered. The Poynting -Thompson constitutive model was selected to describe the viscoelastic material properties. The numerical model was verified and validated. A validation of the model was made by comparing the results for the viscoelastic material to those of the elastic material (Hertz problem).

The plan of the present research work concentrates in four main goals:

1.      Study the effect of quasi static normal loading, P, on the contact interference (the vertical displacement of the sphere’s peak), Uy.

2.      Study of the natural vibration frequencies of the viscoelastic hemisphere, normally preloaded by the contacting rigid flat.

3.      In order to identify dynamical properties of the contacting viscoelastic hemisphere (linear or nonlinear behavior of the system), free vibrations due to the different initial conditions were studied.

4.      The last goal of the present work was to investigate the dynamic response of the viscoelastic hemisphere contacting with the rigid flat under given time varying cyclic normal load (forced vibrations).

The static analysis showed the nonlinear relation between the normal load and the contact interference. The natural frequencies of the dynamical contact system were obtained by performing a modal analysis. The free vibrations response along with the forced vibrations of the viscoelastic sphere contacting with the rigid flat were investigated. Notice that the effect of the initial conditions on the free vibration of the undamped system helps to investigate and to identify the nonlinear properties of the dynamical system and also to construct the “skeleton curve”. A sinus shaped time-varying external normal load with the different amplitudes and frequencies, was chosen for the analysis of the forced vibration. System response includes periodic solutions showed on the time series, phase-plane and fast Fourier transform (FFT) analysis. The analysis made in this research suggests a complete numerical solution of the static and dynamic viscoelastic spherical contact problem.