| In recent years, the development of highway and railway has accelerated the process of high speed and loading of transport machines, which deserves higher properties of the friction material in the brake system. Higher speed of vehicles needs stable properties of the friction material in a comparatively larger scale of speed and temperature. Due to its good heat resistant performance, abundance of output, fine mechanical property and favorable matching with resin matrix, asbestos is widely applied in early formulations of friction materials. But because of the harm it has to man's health and the environmental pollution it may cause, many studies have been conducted on asbestos-free friction materials. There are mainly cast iron, semi-metal and ceramic friction materials. The formulations of ceramic friction materials are metal-free raw materials which can well solve the problems of corrosion and friction noise of semi-metal and cast iron materials. So, ceramic materials have been given much attention in the friction material study in many countries. The development of new friction materials tends to rely much on experience and the assessment of the formulations of friction materials involve many factors such as mechanical properties, friction properties, cost, etc, causing some difficulties in the study and application of new friction materials. This dissertation, based on the study and application of friction materials in the world, is a study on new friction materials from the aspects of development, optimization, assessment of integrated properties of friction materials, friction wear mechanism and coupling of thermal and strength, etc. Ceramic friction materials are prepared by pre-modeling, hot-press and post-cure. The mechanical properties of the friction materials such as density, strength, hardness, are tested. Friction tester with constant speed is used to test tribological properties of friction coefficient, wear rate, etc. Formulations of optimized friction materials are obtained according to golden section method, fuzzy theory and grey system theory. The physiognomy of wear face is observed with scan electron microscopy (SEM). The wear mechanism of ceramic friction materials is discussed. The coupling of thermal and strength of ceramic friction materials is simulated with finite element method (FEM). And the temperature change of the friction face is tested on friction tester with constant speed. The comparison between the simulation result and the friction experiment with constant speed shows the consistency between the two. This proves the feasibility of finite element method in the analysis of coupling of thermal and strength, which provides theoretical and experimental foundation for the development of new friction materials and the study of wear mechanism of friction materials.Being the most important constituent of friction materials, fiber is closely related to the friction property and the mechanical strength of the material. Its major function is to create certain strength and toughness in the material so as to make the material endure mechanical processes of instantaneous impacting, shearing, tensile of brake and avoid mechanical damage of crack, failure, collapsing, etc. The frequently used fibers in ceramic friction materials include ceramic fiber, glass fiber, carbon fiber, potassium titanate whisker, Aramid pulp, etc. They have the required properties of sufficient strength, toughness, good performance against friction and wear, better heat resistant performance, reasonable hardness, etc. In this dissertation, alumina silicate fiber, carbon fiber, potassium titanate whisker are used as main materials. Alumina silicate fiber has high melting point, fine mechanical properties at high temperature and low density. It is widely used in high temperature field, but comparatively much less used in friction material field. More than ten or even tens of raw materials are involved in the formulations of friction materials, each of which having its role to play. And the properties considered in friction materials include mechanical property, friction property, cost, etc. So the development of new friction materials relies much on experience. The dissertation provides a quantitative calculating method of the development of new friction materials and successfully develops the formulations of a new type of friction materials. The specific steps are as follows. First, choose the fiber. Hybrid fiber reinforced composite is made by adding alumina silicate fiber to semi-metal friction material. New friction material is prepared by adding adequate modifier to the blended matrix of PF resin modified with cashew oil and nitrile-butadiene rubber (NBR). The friction properties are tested. The effect of alumina silicate fiber content on the friction properties is analyzed. The result shows alumina silicate fiber can be used as the fiber of friction materials and a small quantity of ceramic fiber can obviously improve the friction properties of semi-metal friction material. Ceramic fiber can be applied to the production of high-property ceramic friction materials because of its ability to improve the stability of friction coefficient, especially at high temperature. When the content of ceramic fiber is above 5wt.%, there is no obvious connection between the increase of content and the stability and variability coefficient of the material. But the recovery coefficient decreases and the wear rate increases with the increase of the content of ceramic fiber. This indicates that with the content of alumina silicate ceramic fiber going beyond a certain degree, the recovery coefficient of the friction material becomes worse, which increases in turn the wear rate of the material. This is attributed to the fact that ceramic fibers rupture into short ceramic fibers under the influence of friction and form abrasive grains on the friction interface, which adds to the grain-abrasion of the friction material. Therefore, adequate amount of raw materials with low friction coefficient should be added when ceramic fiber is used as friction reinforcement.Carbon fiber is a new kind of polycrystalline inorganic material. The imperfect graphite crystal grows along the direction of fiber axis. And the fiber has the structure of"disordered layer graphite". The structure can work as reinforcement and solid lubricant. Carbon fiber has the properties of low density, high strength, high modulus, heat and chemical corrosion resistant, etc. Potassium titanate whisker has the properties of high mechanical property, corrosion resistant, stable chemical property, which are suitable for reinforcement, manufacturing exactitude assembly. The high performance ceramic friction material is prepared using ceramic fiber, carbon fiber and potassium titanate whisker as reinforcement, cashew oil modified PF resins and NBR as matrix in the paper.Then, golden section method is employed to design 9 original ceramic friction material formulations. Orthogonal experiments are arranged to show the effects of ceramic fiber, carbon fiber and potassium titanate whisker content on the integrated properties of friction material. The fuzzy theory is used to calculate the fuzzy overall merits of formulations including mechanical, tribological properties and cost. The grey system theory is employed to analyze the sensitivities of the contents of there `reinforcements. According to the sequence of sensitivities, the best formulation selected in the 9 original ones is modified based on the method of golden section. Four new formulations of composites are obtained. The grey system theory and fuzzy overall merits are employed again to optimize the formulations, And the best formulation ofThe temperature of friction interface increases rapidly in the process of brake. The increase of temperature induces the change of stress state on the surface of friction material. Excess temperature can cause the degradation of matrix PF which leads to the decrease of friction coefficient. It is important to predict the change of temperature field and stress field of friction material because the state of temperature and stress field can affect the fatigue wear of friction material. On the basis of irreversible thermodynamics, differential equations of thermal conduction are dispersed by FEM. And the distributions of temperature and stress on the surface of friction are simulated. Simulated conclusions are then validated by friction tests with constant speed. It can be conclude that the temperature of the leading edge of friction material is much higher then the other edge in the process of brake. The highest temperature on the friction interface rises with the increase of brake pressure. The results of friction tests with constant speed show that the temperature of brake lining material surface rises with the passage of time. The higher the pressure is, the faster the temperature rises. It can be found that the temperature of friction interface calculated by FEM is higher the temperature measured in friction test. Ignoring the heat dissipation by means of cross-ventilation, radiation and temperature rising of abrasive particles induces the difference between the results of simulation and test. In order to obtain more exact results by means of simulation, wear and chemical reaction of friction material should be taken into account.Keywords: ceramic fiber, friction material, friction, wear, finite element method...
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