Researches Of Experimental Modeling And System Dynamics On Frictions Concerning Extended Stribeck Effect

Friction, which belongs to the term of Tribology, is a young scientific discipline with long history. It has been proved to exist in every aspect of daily lives. In mechanical fields, friction acts as an especially important role. The full understand and control of the frictional characteristics is critical for improving machining precisions and product qualities, prolonging service lifetime.The thesis is initiated from the viewpoint of how friction acts in the mechanical engingeering, aimed to explore the experiments, theoretical modeling, identification, dynamical property of systems with friction. According to profound experiments, the static and dynamic characteristics are analysed and new friction model is provided, which is able to describe and predict those experimentally observed phenomenon as many as possible. In addition, the stick-slip effect of system with frictional parts in low velocity ranges is investigated using the newly provided friction model.Firstly, the definition and history of friction is summarized. In terms of"static and dynamic", the state-of-the-art of frictional characteristics is classified. In the light of this point, the static and dynamical friction models and their merits and drawbacks are introduced in this work. The current researching progress on nonlinear reponses of system with frictional parts such as stick-slip and limit cycling are also briefly presented.Secondly, based on the pratical research target in mechanical engineering field, the lateral/vertical friction characteristics between rail and guide shoe/pad in an elevator system are investigated macroscopically. By designing different test rigs, choosing different friction materials and performing a large amount of tests, the property of friction with respect to the variation of normal loads, relative velocities and lubricational conditions is examined. The static and dynamical properties of friction in the stage of pre-sliding and gross sliding are also studied, which results in the finding of Friction Overshoot property in the transforming stage from pre-sliding to gross sliding. The experimentally obtained Stribeck curve for different normal loads and materials are parameterized. The effects of wear on the frictional properties of surface in contact are carried out and analysed by experiments macroscopically and microscopically. Some meaningful results are visualized which provide a experimental basis for future friction modelings.Based on the linearly reciprocating friction tests, a new Bouc-Wen based single-state-variable friction model (termed as SSV) is presented. By introducing the normalized Bouc-Wen model, the new model is able to describe the behaviors of friction in the pre-sliding stage precisely. Meanwhile, a exponential function with respect to velocity and a linear function with respect to accerlation are added, which make it possible for the new model to describe the Stribeck effect and friction lag happened in gross sliding stage. According to the definition of average inflection in the bristle theory, the average effective mass of bristle is defined, which is capable to predict the experimentally found friction overshoot property smoothly during the transation from pre-sliding to gross sliding regime. The comparisons between simulation using SSV and LuGre model and the experiment results show that the proposed friction model gives better results than traditional model without losing the flexibility.Relyed on a rotational tribometer, the friction hysteresis and friction lag are further verified, and the friction lag under the uni-directional velocity excitation in gross sliding regime is also investigated. The non-local memory effect in lubricated condition is evalued as well. The tests show that the frction force varies linearly with respect to displacment in the stage of pre-sliding which is different from the cases of dry frictions. The working range of the Stribeck curve is widened by measuring Stribeck curves under different normal loads. The improved Stribeck curve becomes the function of normal load besides the relative velocity. The coupling relations between tangential and normal motions are investigated, It is the first time to observe a cross hysteretic relations between normal and tangential displacements and a hysteretic relationship between normal displacement and tangential velocity. Based on these results, a theoretical model is proposed from the physically microscopic viewpoint, and is validated by comparing the simulations with the experimental results. The measuring precision of the rotational tribometer is upgraded from the millimeter level to the micrometer level compared with the linearly reciprocating friction test rig, which gives a more profund understanding of friction characteristics and is necessary for developing high precision frition models. Grounded on the linear reciprocating and rotational friction measurements, the generalized Bouc-Wen Maxwell-Slip model (named as the GBM model) is developed.The GBM model uses a series of parallelly connected spring and friction elements to simulate properties in the pre-sliding stage; while in the gross sliding stage, the extended Stribeck curve and improved Bouc-Wen model is utilized. According to comparisons between four friction models, it is clear that the GBM model performs better on predicting friction hysteresis, friction lag, Stribeck effect, friction overshoot and normal variations than other models. At the same time, GBM model is able to describe the non-local memory and non-drifting property in the stage of pre-sliding because of the incorporation of Maxwell-Slip elements. The model equations used in pre-sliding stage is one signle-state-variable ordinary differential equation. While in the gross sliding stage, it relies on several multi-variable algebra equations which balanced the effieciency and performance of the GBM model. In addition, the GBM is able to boiled down to the Dahl, LuGre, SSV and GMS model by simplifying model parameters, making it quite suitable in the fileds where high precision and real time control abilities are extremely appreciated.Taking the single degree of freedom train model as the research object, the stick-slip effect and its mechanism in structures with frictional parts are analysed in detail. Two types of vibrations induced by stick-slip motion are dicussed. One is the cycling of stick-slip-stick motion, running in different frequencies being excited by different pulling velocities, taking the form of reciprocating motion along the relative equilibrium position of the object M, and the frequency is irrelevant with the natural frequency. The other is the high frequency vibration in the stage of stick motion. The qualitative, quantitative analyses and experimental verication show that the high frequency of the vibration is not accumulated in single value frequency but a distributed frequency range, which come from the varying stiffness between surfaces in contact. When system is in stick-slip motion, the system response can be periodic, quasi-periodic and chaos with the change of pulling velocities, system stiffness and viscous. When these parameters are increasing, system motion tends to be stabilized periodic motion from chaos. Along with this trend, the stick-slip motion will decrease and vanish, and turns out to be quais-harmonic vibration, which could disappear under extreme theoretical conditions.The results of this work may provide a scientific path through which one can obtain a better understanding on performing frictional experiments, friction characteristics, friction modeling and stick-slip effect, and then improve operational precison and service lifetime of structures.