Research On Distributed Fractional Order Damping Dissipation Characteristics Of Viscoelastic Buffer System Under Dynamic Service

Construction machinery is mostly driving on harsh road surface,coupled with complex working conditions,and often bears severe vibration,leading to adverse effects such as frequent equipment failure,low operation efficiency and increase in maintenance costs.How to effectively solve the problems caused by the severe vibration of construction machinery has become an important subject for the research and development of high-horsepower and high-quality construction machinery in China.Viscoelastic buffer system can convert the vibration energy into thermal energy dissipation through the internal friction in the polymer damping material,which have the advantages of high dissipation,high reliability and low cost.Installing viscoelastic buffer system is an effective means to solve the vibration problem of construction machinery.Construction machinery mostly bear the coupling effects of temperature change,load change and impact.Viscoelastic buffer system is often under the dynamic service of multivariate mechanics,which makes it poor matching with the overall system,resulting in insufficient adaptability and unsatisfactory vibration reduction.Accurate and reliable viscoelastic constitutive model and structural dynamic analysis method are the key to the design of viscoelastic buffer system.In this thesis,the distributed fractional order model,parameter analysis and real vehicle experiment for the damping mechanism and behavior characteristics of the viscoelastic buffer system are present.The main works are as follows:(1)The general form of distributed fractional order constitutive model for viscoelastic damping materials is developed.The ability of the constitutive model to represent viscoelastic dynamic performance is studied.Based on the fractional calculus theory and the viscoelastic theory,and combining with the multidimensional evolution properties of viscoelastic damping material constituents,the distributed fractional orders model is constructed.The delay equations and dynamic mechanical property equations are derived,and the mapping relationship between model parameters and viscoelastic dynamic mechanical properties is explored.The results show that the distributed fractional order constitutive model has a wide range of characterization capabilities and can reflect the dynamic mechanical properties of viscoelastic damped materials in wide time domain and frequency domain.It can provide theoretical basis for analyzing dynamic mechanical properties of viscoelastic materials under dynamic service.(2)The impact mechanical experiment and the dynamic mechanical experiment of viscoelastic damping material are conducted,and the correctness of the distributed fractional order constitutive model for viscoelastic materials is verified.The mechanical experiments on NR and SR are carried out.The viscoelastic mechanical properties under impact and variable temperature and frequency are explained according to the damping dissipation mechanism.It is determined that viscoelastic dynamic constitutive behavior has phased characteristics,which is consistent with the scientific hypothesis of distributed fractional order.Meanwhile,the fitting accuracy of the distributed fractional order constitutive model is higher than the existing contrast models.The results show that the distributed fractional order constitutive model has a good ability to characterize the dynamic properties of viscoelastic materials at wide temperature,frequencies and strain rates,that is,high accuracy,few parameters and clear physical meanings.(3)The distributed fractional order dynamics model of viscoelastic oscillator is established,and the system damping and dissipation characteristics under harmonic excitation and impact load are studied.Combined the basic mechanical variables of viscoelastic materials with the dynamic equation of vibration system,the distributed fractional order dynamics model is established by introducing the structural geometric factor.By the numerical methods combining the Chebyshev operator matrix and fractional order calculus theory,the time-domain responses of vibration system under harmonic excitation and impact load are obtained.Based on the Laplace transform principle of the fractional order derivative,the amplitude frequency and phase frequency functions are derived.And then the system parameters characteristics and the damping dissipative properties are studied.It can provide a theoretical reference and method for the design of the viscoelastic buffer system.(4)Experimental study and damping optimization of viscoelastic buffer system are conducted,the correctness of the system dynamics model and the feasibility of the optimization proposal are verified.Aiming at the vibration problem of a loader cab,the cab theoretical vibration model is established,and the damping matching strategy of the plum-shaped damping structure is put forward through multi-objective optimization.The real vehicle tests are performed to compare the vibration characteristics of the cab before and after the optimization.The results indicate that compared to the original damping structure,the plum-shaped damping structure reduce the vibration isolation transmissibility by 3.930～8.544 d B,the driving comfort evaluation from more discomfort or uncomfortable to slight discomfort or more comfortable.It is verified the plum-shaped damping structure has good comprehensive vibration reduction performance,and better matches the vibration characteristics of the loader cab system,inhibiting the vibration of the cab significantly.This thesis focuses on dynamic properties of materials,system dynamic modeling and damping dissipation characteristics for viscoelastic materials and buffer system under dynamic service.The research results of this thesis can provide a new theoretical basis and reference for the modeling and analysis of the complex viscoelastic damping structure of high-horsepower and high-quality engineering vehicles.