Study On Mechanical Properties Of Compressed Particle System By Espi

Granular material system is formed by the accumulation of a large number of coarse particles,and is a complex multi-body interaction system,showing the basic characteristics of structural inhomogeneity and dynamic inhomogeneity at the particle scale.Because of the basic characteristics of granular material system,it is extremely difficult to characterize and establish the correlation between the structure and performance of particulate materials from basic theory to experimental means.The organization structure of the granular system described by the existing test and analysis means is too simplistic and lacks a real understanding of the particle structure and dynamics,which restricts the development of the study of particulate matter.Therefore,the measurement of granular system structure and dynamic properties is the basis for understanding the important physical and mechanical problems of granular materials.Compared with other granular system measurement experimental methods,as an optical measurement method,Electronic Speckle Pattern Interferometry(ESPI)has the advantages of high measurement accuracy,non-contact,full-field measurement,and the ability to obtain clear stripes on rough surfaces.It can effectively treat particulate matter to the outside world.The sensitive response of the load is accurately measured.In this paper,the particle rotation of particles under concentrated load is studied by ESPI,and displacement and strain of particles are measured based on optical methods.The main research work includes:(1)Basic theory and experimental method of ESPI.Firstly,the basic theory of ESPI measurement is described,including the basic principle of ESPI technology,phase shift technology,filtering technology,unwrapping technology,and the method flow of ESPI image processing is drawn.Then the construction of the ESPI two-dimensional platform is introduced.The platform integrates the ESPI in-plane measurement optical path in two directions,adopts a 3CCD camera for image acquisition,and adopts the time-phase shift method to separate the acquired images from the channel,and the single channel in the given direction The image is processed to obtain the direction measurement information.(2)Experimental study on the rotation of particulate matter by ESPI.First the basic theory of granular material rotation is introduced.Then the new method of ESPI is applied to measure the rotation angle,and according to this rotation measurement principle,the electric rotating platform experiment was carried out,and the calculated rotation angle was basically consistent with the rotation angle of the electric rotating platform,illustrating the accuracy of this angle measurement method.Finally,a rotation measurement experiment under the concentrated load of ESPI particulate matter was carried out.When the three sides are fixed and the upper part is free,the granular system are mainly rotated.Through this experiment,it can be seen that the ESPI method is effective and sensitive when measuring the angle of particle rotation.It provides a basis for further analysis of the contact force transmission process and energy loss between particles in the future.(3)Experimental study on measurement of displacement and strain of particulate matter.Firstly,the theoretical principle of ESPI strain measurement is proposed,then the experimental study on the sand-PMMA particle system can be found.The continuous distribution of stripes in the particle system can be found,and the stripes can also be seen in the fine sand,which reflects the ESPI method for the particle system.The deformation situation is very sensitive,and the ESPI method is widely applicable to the measurement of particle systems.Then the compression experiment of polyurethane particle system was carried out.Because the particles will couple the particle rotation and strain deformation during the loading process,and will be reflected on the phase diagram stripes,the deformation of the particles and the transmission of force can be obtained by qualitative analysis of the phase diagram.Extracting the strain and deformation information of the particles from the fringe diagram of the phase diagram needs further study.Finally,the strain of granular materials was studied by digital image correlation(DIC).First,the tensile elastic modulus measurement of polyurethane materials was conducted by DIC method and electrical measurement method respectively,the measurement results of the two methods were very similar.Then the strain measurement of polyurethane particulate material compressed was carried out by DIC,and the mechanical behavior of the particulate matter under uniform load was analyzed according to particle displacement and strain measurement information.