Nonlinear Vibration Mechanisms And Energy Dissipation Of Contact Interfaces

The vibration characteristics and energy dissipation mechanism at contactinterfaces not only significantly affect the dynamic performance of mechanical system,but also greatly affect the amplitude, frequency and phase responses of measuredcharacteristic signal, and thus further influence the accuracy and reliability of machinerycondition mointering. Due to the complexity and diversity of contact interfacesassociated with mechanical system, the mechanism of some very importantphenomenons are unclear, especially the critical problems as stiffness and dampingcharacteristics at contact interfaces, model characterization for interface with complexattribution, nonlinear dynamic process, contact vibration at multiple interfaces and itseffect on system. The interface properties have become the basic key problem inmechanical area. Therefore, it is of great significance to explore the contact dynamics atinterfaces.This thesis foucuses on the nonlinear vibration characteristics and energydissipation mechanism of several basic contact interfaces, including sphere contactinterface considered the effect of gravity, rough contact interface, sliding contactinterface and layered multiple transmitting interfaces. The dynamic models areestablished and the contact stiffness and damping characteristics of two type interfaces,i.e., the sphere and the rough contact interface are studied. The contact vibration andenergy dissipation characteristics at these interfaces and the transmission performance atmultiple interfaces are presented. The accuracy of the established critical models andthe results are validated through experiments. The main works done in this paper are asfollows:①The model of an elastic sphere in contact with a rigid flat surface is establishedon the static equilibrium position considering the effect of gravity. The Hertziansphere-plane contact model exhibited liner viscous damping is difficult to accuratelydescribe the contact force-displacement relationship due to the interface properties,damping capacity and other effects. The effect of nonlinear damping on the freevibration responses are studied by employing a general viscous damping functionrelated to the displacement raised to an arbitrary rational positive power law. It is shownthat the feature response parameters are almost identical for different damping modelsand it is thus difficult to identify the damping model. A damping model identification method is therefore proposed based on the restoring force and is validated usingexperimental results. The damping models for spheres with different materials as steeland Low Density Polyethylene (LDPE) are obtained.②The “single metal block-rigid plane” rough interface model and the “multiplerough surface metal blocks-rigid plane” multiple interfaces model are established tostudy the plastic deformation and energy dissipation for contact interaction normal tothe rough interface. The fractal geometry of rough surface, the continuity hardeningcriterion for plastic material and the amount of plastic energy dissipation equaling to thearea of the loading and unloading curves are coupled to avoid the discontinuity of theelastic-plastic transition. Effects of surface topography, plastic hardening behavior ofmaterial and interface friction on the force-deformation relationship are presented. Theenergy dissipation characteristics due to plasticity hardening and the energy dissipationratio at different interfaces are studied. The plastic contact deformation and the energydissipation meachnism are presented.③The dynamic model for an elastic block with rough surface in contact with arigid flat surface is established. The rough surface is characterized by self-affine andscale-indenpent fractal geometry and the force-deformation relationship for roughsurface with different topographies are calculated to overcome the scale-denpent defectof current models based on statistical rough surface description. The contact stiffnessexpressions for the rough elastic body and the asperities are further established. Effectof surface topography on the contact stiffness is presented. The natural frequency andthe free vibration energy dissipation for rough solid with different surface topographiesare evaluated. The experimental results on energy dissipation observed for verticalcontact vibration are supported.④The force-displacement expressions at the connecting end of the slip interfaceare derived for different interface slipping states, including no slip, micro-slip andmacro-slip and the dynamic model for the slipping interface system are furtherestablished. The current models are on the assumption of uniform pressure distributionalong the interface and limit to only studying the effect of micro-slip on the systemvibratiory responses. The established model considered the ununiform pressuredistribution along the interface, and the natural frequency, the amplitude responsesunder harmonic excitation and the energy dissipation per cycle are further calculated fordifferent interface slipping states. The dynamic responses and energy dissipationcharacteristics of the slipping interface system are presented. ⑤The single slipping interface model is extended and the multiple transmittinginterfaces model “Sphere-Joint Assembled Multi-layered Plates”(SJAMP) isestablished to consider the coupling between the frictional interfacial motion alonginterfaces and the normal contact motion. The dynamic responses at the multipleinterfaces under shock excitation are calculated. Expression relates the accelerationamplitude at different interfaces and the shock amplitude is established. Thetransmission of vibration and energy through the multiple interfaces are characterizedby the defined vibration transmission ratio and energy transmission ratio. The inputenergy transmission ratio of the impact energy at the input interface is studied and thevibration and energy transmission characteristics at the multiple interfaces of layeredand jointed plates associated with friction are presented. Experimental validation isperformed and shows good agreement with numerical results.