Evaluating Elastic Modulus Of Materials At Special Environments Based On The Split Ring Method And The Relative Method

With the rapid development of various advanced materials, it is necessary to assemble different functional materials together or to design high-performance elements at micro scales, for the purposes of serving safely and functioning well at many outer and inner special conditions. Among them, elastic modulus is one of key mechanical properties and structural parameters for many materials, which plays an important role in material design and safe service. In this dissertation, the relative method and the split ring method proposed by my group previously were respectively applied or combined organically to start the research work on the elastic modulus of materials at high and ultra-high temperature, the elastic modulus of coatings on tubes and other evaluation work with related theoretical analysis and experimental study.First, the relative method was used to solve the problem of deformation measurement at ultra-high temperature. The real deformation of split ring specimen was obtained via comparing the difference of cross beam between split ring specimen and rigid disk, as a result of calculating the elastic modulus over 1500 °C. This novel method is used to solve the international problem of deformation measurement at high and ultra-high temperature, without any other advanded and complicated instruments, which could be applied to estimate and characterize the elastic modulus of materials at such harsh environment rapidly, efficiently, accurately and conveniently.Second, based on the problem to evatuate the elastic modulus of coatings on tubes, the relative method was combined with the split ring method to deduce the calculating formulas of elastic modulus for three patterns of tube coatings, with the tests of CVD-SiC coatings on graphite tubes. Mathematical equivalence relationships were established between the coated and the uncoated split ring specimens so that their ratios of the elastic modulus and the compressive displacement could be used to calculate the elastic modulus of coatings on tubes.Besides the above two combinations of the relative method and the split ring method to estimate the mechanical properties of materials at special environments, the single relative method and split ring method were also developed further, respectively.1) The relative method that could measure high-temperature deformation was introduced into 3-point bending test to assess the elastic modulus of low-stiffness materials at ultra- high temperature, such as graphite. Based on this novel approach, the effects of porosity on the elastic modulus of graphite from 1500 °C to 2000 °C were also discussed. The results show that porosity takes both pros and cons on the elastic modulus of graphite at ultra-high temperature, so there must be an optimized porosity for graphite which possesses higher corresponding inflection point temperature and elastic modulus over 2000 °C than other grahite.2) The calculating formulas of the closed ring method were deduced to evaluate the elastic modulus and bending strength of low-stiffness tube materials, especially for fiber reinforced composite tubes. As an important supplement of the split ring method, these two methods complement the insufficiency of each other so as to be suitable to evaluate the mechanical properties of most tube materials.3) On the basis of orginal relative method to evaluate coating modulus in the perpendicular direction, the calculating formula was derived to evaluate the elastic modulus of coatings in the horizontal direction. This novel idea will be used to establishe and improve the evaluation system of mechanical properties of coatings in different directons.