Mesoscale Study On Localization In Granular Matter

Granular matter is of great importance in engineering with over a centuryof study. During the past decades, granular matter becomes the focus amongphysicists due to its fascinating properties. The phenomenon of localization ingranular assemblies, directly affects the macroscopic mechanical properties ofthe system. Previous study shows that the internal structure of the granularmatter significantly contributed to the bulk mechanical behavior of the system.From the perspective of particles, the study of the mesoscopic structure (suchas the force chain network), the dynamics and the relationships withmacroscopic mechanical properties serves as theoretical foundations for thosekey technologies in engineering constructions and natural disastersprevention.In this thesis, by using the two-dimensional photoelastic technique, theevolutions of force chain network in the penetration test were observed. Bytaking the advantages of graphics processing and fitting method based onfringe intensity gradient, the magnitude of inter-particle forces, as well as thechanges of force chain network, were obtained. Furthermore, the simulationresults by using PFC (Particle Flow Code) agreed well with the experimentresults. The results indicate that there exists heterogeneous force chainnetwork in granular matter, and the force chain network distribution directionswere found well aligned in the directions of the major principal stress. Theshape of force chain network changes rapidly with the change of loading.Most importantly, the concept of nonaffine strain rate based onindividual particles was presented. The nonaffine strain rate is applied toanalyze the non-uniform deformations in biaxial compression test, penetrationtest, concrete uniaxial compression test and concrete splitting tensile test.Heterogeneous distribution of particles within large nonaffine strain rate wasinvestigated by applying wavelet analysis method. Moreover, statisticalmechanics was preliminarily introduced to establish the probability distribution evolution equation of nonaffine strain rate, based on which thelocalization evolution process in biaxial test was described.To conduct statistical descriptions of both structural and mechanicalproperties of granular matter, the development of DEM parallel program wasinitiated based on the JASMIN (J Adaptive Structured Mesh applicationsInfrastructure). Isostatic compression and triaxial compression tests wereconducted and the non-homogenizing of parameters including internal forcechain network of the system, such as local volume fraction and local stress,are analyzed. The phenomena of localization in granular assemblies can beclearly shown by using a large-scale simulation and the post-processingprogram developed in this work. The incremental of wall pressure,coordination number and the mean stress of a particle scale well with theincremental packing fraction from jamming point. The standard deviationdecreases with increasing packing fraction, indicating the system is moreuniform with a more dense packing.