| Being a sort of new principle micro-motors in the frontier of science,standing wave ultrasonic motor(SWUM)has the advantages of compact structure,flexible design,effective driving and low cost.However,small contact area,high stress gradient,strong impact effect,and severe wear are prone to restrain friction stability and wear resistance,bringing in strait challenges to the various and reliable applications.For this purpose,this paper makes a systematic and thorough study on the friction and wear behavior of stator and slider to provide guidance and support for theoretical design,material selection,operation and maintenance of SWUMs.The main content of this thesis includes the following parts:The dynamic mechanism of SWUM friction interface is studied based on the elastic contact theory,and the nonlinear effects(such as the intermittent and impact contact)are revealed.After study of contact characteristics,the fundamental reasons for the instability of the contact state are discussed.The contact process of the stator and slider is illustrated,i.e.sequentially expanded contact and reduced contact.Finite element method(FEM)is used to analyze and verify the contact characteristics of the stator and slider of SWUM.According to the elliptical motion of the stator tip,the geometric condition of dynamic contact is obtained by comparing the vibration displacement and the indentation deformation.Considering the inertial effect of piezoelectric vibration and the bristlestiffness of surface asperities,a general friction model of the stator and slider is established.Then the power transmission mechanism of SWUM is analyzed.The timevariation characteristics of dynamic friction between the driving tip and slider are revealed.According to the heat balance of friction work and strain energy,temperature rises induced by sliding friction and ultrasonic impact are conducted.The results are prone to illustrate brittle fracture,plastic deformation,oxidation,and/or chemical wear of the contact surfaces of the stator and slider.The experimental apparatus for friction and wear of SWUM is developed and the operation characteristic is investigated.Taking the circle numbers of stable running as a gauge,the service lifespan of SWUM with different friction materials are comparatively analyzed.Wear resistance of ceramic materials is higher than that of metallic materials.Clear differences in service performances are revealed for the concrete friction materials.The counterparts of AlSiCp/SiC highlight the durable lifespan and reliable operation of SWUM.The contact interface of the oxide ceramic material is directly driven by the mechanical action,which shows the characteristics of abnormal wear and friction.After microscopic morphology analysis of wear surfaces by using scanning electron microscopy and X-ray diffraction analysis,wear and failure mechanisms of driving tips and sliders are revealed.Material loss and failure of oxide ceramics are accounted for the defective accumulation by the multilevel plastic deformation and the cleavage fracture under the alternating thermal-mechanical stresses.Differently,wear behavior of nonoxide ceramics is accounted for the sliding friction and impact contact,resulting in surface oxidation.Consequently,oxide film and/or solid solution of low shear strength is generated on contact surfaces.Based on the contact characteristics,friction and wear behaviors of stator and slider of SWUM,a time-weighted average prediction model of multimode wear mechanisms was proposed.Cases of several driving tips mated with alumina sliders are investigated by the improved model,which is also verified by using the fatigue wear of elastic contact theory.Considering the single-factor analysis hardly to the material properties,wear lifespans of different materials are predicted by using artificial neural network(ANN).For small samples and multi factors,the influence of material properties on wear life of the stator and slider are studied to provide supporting for evaluation of the running life of SWUM. |
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