| Brittle materials are widely used in civil engineering,construction engineering and railway engineering,but deformation,fracture and crushing of such materials are poorly understood yet.Experimental studies on crushing behavior of brittle materials often suffer from expensive costs and difficulties in measuring some key data accurately although the methods are often used in understanding crushing of brittle materials.Numerical simulations can reduce experimental costs efficiently,compute some relevant data in simulation process precisely,and have better visualization of simulation process than experiments.Accordingly,a numerical method using Discrete Element Modelling(DEM)was proposed in this thesis to simulate crushing of common brittle materials — gravel particles subjected to compressive loads.All of the numerical simulations of this thesis were performed using an open-source DEM code — YADE,and main contents and conclusions of this thesis are listed as follows:1.Two modified cubic packing models were proposed by inserting each group of sub-particles with smaller radii into void space of Simple Cubic Packing(SCP)respectively,and the insertion algorithm was developed using Python programming language and implemented on YADE further.Mechanical behavior of three packing models(SCP,BCP and TCP)under both of static and dynamic loads were studied respectively.The results show that capabilities of withstanding static and dynamic loads of BCP improve significantly compared with SCP,but the capabilities of TCP were barely unchanged with compare to BCP.Besides,Fibonacci Sequence was employed to study size effects of these three packing models,and the results show peak strengths of these three packing models under uniaxial tension loads have similar trend,i.e.the peak strengths increase gradually and then converge into constants,when radii of these three packing models change with the tendency of Fibonacci Sequence.2.A new method removing a certain number of sub-particles from original regular packing models randomly was proposed to simulate defects in real gravel particles.Three-dimensional(3D)Discrete Element Modelling(DEM)was carried out to simulate crushing processes of regular gravel particles created using three different packing models(BCP,HCP and RDP)under compressive loads;two-dimensional(2D)DEM was used to study crack initiation,propagation and breakage in crushing process of regular gravel particles.Both of 2D and 3D DEM simulations can simulate crack initiation and propagation,fracture and total fragmentation in a whole process of gravel particle crushing,and the simulation results match some previous experimental studies conducted by other researchers and experimental results of this thesis well.3.Outline of an irregular gravel particle was obtained using scanning technology,and impact of stable contacts between gravel particle and platen before loading on crushing process of gravel particle was studied.The results turn out that if there exists an unstable contact between gravel particle and platen before loading,it generally leads to some minor breakage occurs at small contact areas between gravel particle and two platens when loading rate was less than 50 mm/s,but minor breakage only appears at contact area between gravel particle and upper platen when loading rate was within a range of 50 mm/s and 100 mm/s.However,if there exists at least three non-collinear contact points between gravel particle and platen before loading,the result shows that gravel particle generally breaks heavily and crushes into several fragments,and loading rates have little impact on Force-Displacement curves of the crushing process. |
