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Breakage Characteristics and Crushing Mechanism of Cement Materials Using point-loading tests and the Discrete-Element Method

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JOURNAL OF MATERIALS IN CIVIL ENGINEERING 2014年第5期26卷 992-1002页

作者： Wang, Xiao-bo Xu, Wen-jie Zhang, Bing-yin Tsinghua Univ Dept Hydraul Engn State Key Lab Hydrosci & Hydraul Engn Beijing 100084 Peoples R China

A point-loading device was used to research the breakage characteristics of single particles and to study their crushing mechanism. A series of point-loading tests were completed on the basis of cement ellipsoid particles modeled in various sizes and strengths with cement pastes. A close-packing method of equal spheres with several close-packed assemblies was generated, and the corresponding numerical models for cement ellipsoid particles were established by the discrete-element method. Experimental and numerical tests show that the high-strength materials are brittle, whereas the low-strength materials are ductile, and vice versa. A comparison of the experimental and numerical results show reasonable, rational results, and indicate that the force-displacement relationship is approximately linear for this type of granular material. A measurement-sphere method was used to trace the energy and stress distribution in the particle samples. The accumulation of dilatant deformation causes the collapse of the local skeleton structures in the cement ellipsoid particles.

关键词： point-loading tests Crushing mechanism Discrete-element method Cement ellipsoid particles

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Particle crushing simulations with improved discontinuous deformation analysis

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ENGINEERING COMPUTATIONS 2014年第7期31卷 1321-1341页

作者： Wang, Xiao-Bo Xu, Wen-Jie Zhang, Bing-Yin Sun, Qi-Cheng Tsinghua Univ Dept Hydraul Engn Beijing 100084 Peoples R China

Purpose - Rock-fill dams are embankments of compacted free-draining granular earth containing an impervious zone. Earth utilized in such dams often contains a high percentage of large particles - hence the term rock-fill. Mass stability of these dams results from friction and particle interactions rather than through a cementing agent binding the particles together. However, high-stress conditions and prolonged exposure to the elements can severely damage rock-fill. Therefore, understanding and modeling rock-fill breakage is important for dam engineering. The purpose of this paper is to improve discontinuous deformation analysis (DDA) techniques for modeling rock-fill breakage, proving the new method using simulations of spherical particle crushing. Design/methodology/approach - This work models rock-fill as bonded ellipsoid particles, and develops an improved DDA method to model the breakage of particle assemblies. The paper starts by describing the principles of three-dimensional DDA for spherical particles, and then derives the submatrices for normal contact, shear contact, and frictional force. The new algorithm incorporates a bond model with a revised open-close iteration algorithm into the DDA method to simulate particle crushing. To validate the improved DDA method, calculated particle contacts and movements are validated against theoretical results. Finally, this work performs a series of point-loading experimental tests for cement ellipsoid particles of both high and low compression strengths, with the test results compared against the results from corresponding DDA simulations. Findings - In particle crushing tests, the force and displacement show an approximately linear relationship until the crushing point, at which point low compression ellipsoid particles split into several large pieces while the high-compression particles break into many small fragments. The DDA simulation results are in good agreement with the crushing tests, demonstrating the validi

关键词： point-loading tests 3D discontinuous deformation analysis Open-close iteration algorithm Particle crushing Rock-fill breakage

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