Research On Variable-order Constitutive Model And Damping Characteristics Of Viscoelastic Material

Engineering vehicle is often working on off-road and facing the severe operating conditions such as complex road excitation and variable temperatures.Violent vibration of vehicle is generated in the working process that would exert a negative impact on the vehicle,drivers and surroundings.Therefore,vibration control of the engineering vehicle has become an important issue to be solved urgently in designing and manufacturing of high-end engineering equipment in domestic.Viscoelastic buffer system has the strong ability of vibration dissipation and has been widely used in the field of vibration and noise control of engineering equipment.Viscoelastic damping material is an important part of viscoelastic buffer system.The mechanical behavior of viscoelastic damping material presents strong nonlinearity in variable operating conditions.Therefore,the accurate modeling of viscoelastic damping material is an important part in designing,analyzing and developing of viscoelastic buffer systems.It is also an effective way to guarantee the efficient service of engineering vehicle.In resent years,the theory of variable-order calculus has become one of the hotspots in mathematics.Some useful conclusions are obtained,which provide a powerful method for analyzing of nonlinear systems.The viscoelastic damping material is the research object in this thesis.Based on the viscoelastic theory and variable-order calculus theory,the variable-order constitutive model and damping characteristics of viscoelastic damping material are studied.The main researches are displayed as follows.(1)Based on the viscoelastic theory and variable-order calculus theory,the variable-order fractional viscoelastic comprehensive(VOVC)constitutive model is established.The functional relationships between the viscoelastic coefficient,the material coefficient and strain are researched.The physical meanings and the identification methods of those coefficients are determined.Quantitative description of the constitutive mechanical behavior of the material in tensile and resilient processes under large deformation condition is realized.Based on the Laplace transform principle and the VOVC constitutive model,the VOVC dynamic mechanical model is deduced.The coefficients identification methods of the dynamic model are defined.That model can be used to predict the dynamic behavior of the material in variable temperatures and frequencies accurately.The establishment of the above two models provide a theoretical method and basis for researching and designing of the viscoelastic damping material.(2)The quasi-static and dynamic mechanical tests on viscoelastic damping material are carried out,respectively.The coefficients of VOVC constitutive model and dynamic mechanical model are identified.The relationship between viscoelastic coefficient,strain and frequency is determined,which conforms to the scientific hypothesis of variable-order calculus.The results show that the models established in this thesis have high prediction accuracy.The models can described the quasi-static constitutive mechanical behavior and variable temperatures and frequencies dynamic mechanical properties of viscoelastic damping material quantitatively and accurately.The correctness of the models are verified.Meanwhile,the VOVC constitutive model and dynamic mechanical model have the advantages of simple structure,few parameters and clear identification process,clear physical meaning of parameters and low calculation cost.(3)Based on the time-temperature superposition principle and viscosity equation,the relationship between the material dynamic mechanical propertie and the reduction frequency is investigated,and the time-temperature superposition model with vertical factor(VFTTS)model is established.The calculation methods of the horizontal factor and vertical factor are determined.The drawing method of main curves and nomograph are developed.Based on this,combined with the model-view-controller framework,the special software for calculating and analyzing the dynamic mechanical behavior of viscoelastic damping material is researched and developed.The researches show that the master curves constructed by VFTTS model have better coherence and consistency.It can precisely predict the dynamic behavior of viscoelastic damping material in the wide/ultra-wide frequency domain.Meanwhile,the special software greatly improves the calculation efficiency and accuracy,shortens the product development cycle,and has a good engineering application prospect.(4)The dynamic model of cab system is established and analyzed.The optimal solution sets of the equivalent stiffness and equivalent damping of the absorber are obtained by multi-objective optimization.Based on this,the viscoelastic material of the original absorber is upgraded.Combined the constitutive parameters calculated by the VOVC constitutive model and the elasticity modulus determined by the material nomograph,the FEM of the new absorber is analyzed.The compressive test and dynamic property test are done to verify the rationality and feasibility of the prioritization scheme.Meanwhile,real vehicle validation test are carried out.The results show that the transfer ratio of the new viscoelastic absorber has reduced 3.811～8.031 d B.The parameters of the new viscoelastic absorber matches better with the cab system.In this thesis,the variable-order constitutive model of the viscoelastic material is researched.The evolution of order function and damping characteristics of material are determined.The precise prediction of dynamic mechanical properties of material in wide/ultra-wide frequency domain is realized.The special software is developed.The works in this thesis provide theoretical reference and technical support for researching and designing of the viscoelastic buffer system for high-end engineering vehicles in China.