Studies On Thermal Expansion And Mechanical Properties Of Resin Mineral Composite For Machine Tool

With the rapid development of modern industry,the machining of high-precision parts has put forward higher requirements for the traditional machining industry.The vibration generated during ultra-precision machining can affect the machining accuracy of the workpiece seriously.In order to effectively absorb the vibration generated during machining process,the mostly used methods are optimizing the structure and material of machining tool bed.In now days,the machine tool bed and other basic components are mainly made of cast iron and welding steel.The damping performances of those materials are poor,making the machine tool can not effectively absorb the vibration generated during machining process.The research and development of new material with excellent damping performance for ultra-precision machining tool bed is now of great significance.Resin mineral composite(RMC)is composed of natural stone aggregates with excellent strength,organic resin with great damping performance,and reinforced by other components of great performances.The excellent damping property,good corrosion resistance and good forming ability make RMC become the ideal material for ultra-precision machine tool bed.However,due to the high coefficient of thermal expansion and low mechanical strength of RMC,its application in manufacturing ultra-precision machine tool bed has been limited.The aggregate material,resin,curing agent,deformable agent,strengthening component are selected based on their properties and roles of RMC.The formula of epoxy resin and curing agent is calculated.Based on Eshelby equivalent inclusion theory,the mixed inclusion model of RMC is established.The effective modulus of the equivalent matrix model and mixed inclusion model are calculated using the Mori-Tanaka method.The calculation results of the effective modulus are in good agreement with the experimental results.The influence factors of elastic modulus of RMC are analyzed theoretically.The average coefficient of thermal expansion(CTE)is used as the characterization parameter of thermal expansion property of RMC.Based on the theory of free volume,the changing increasing rate of thermal expansion curve in glass-trasition zone is explained reasonably.Based on the curing characteristics of epoxy resin,the thermal expansion properties and mechanical properties of RMC are improved by using post-cure process.The theoretical CTEs of RMC are calculated by using different models.The results show that the Levin-Hashin lower bound model and Levin-Mori-Tanaka model can be used to set bounds on CTEs of RMC,The Levin-Mori-Tanaka model can describes the changing trend of CTEs of RMC well.Based on the equivalent inclusion theory,the prediction model of effective CTE of three-phase composite material is established.The influence factors of CTE of RMC are analyzed by the established model.The concept of net resin content of RMC is introduced.The influences of fly ash and mineral filler on the properties of RMC and the working performance of concrete premix are taken into account.The ranges of the base addition content of fly ash and mineral filler are determined.Based on fractal theory,the continuous grading schemes of RMC are calculated.Based on the maximum density curve theory,the continuous grading schemes are evaluated and the fractal dimension is divided between F=2.3?2.6.The coarse aggregate gradation schemes of composite materials are designed.Based on the fractal theory,the average volume and surface area of single particle size aggregate are studied.The relationship between the total surface area of single size aggregate and the size of mesh is derived.The quantitative relationship between the total surface area of different aggregate gradation schemes are established.The effects of aggregate size,aggregate gradation,grading method,maximum aggregate size,resin content,vibration time and defoaming agent dosage on machenical and thermal expansion properties of RMC are studied systemerically.The stress transfer model of fiber-matrix is established based on the shear lag theory.The distribution of fiber axial tensile stress and fiber-matrix interfacial shear stress is analyzed.The influences of fiber length on fiber axial tensile stress and fiber-matrix interfacial shear stress are analyzed.The influence of fiber content on the maximum fiber axial tensile stress and the maximum shear stress of the fiber-matrix interface are analyzed.RMC is reinforced by aramid fiber.The optimum fiber content and fiber length are decided by experimental tests.The surface of aramid fiber is treated with ultrasonic and phosphoric acid.The surface treatment mechanisms are studied systematically.The effects of surface treatments on enhancement effect of aramid fiber are studied systematically.The thermal expansion constraint model of aramid fiber is established.The influence of fiber content on CTEs of RMC is studied.