| It is a common problem that the granular material will break under the external impact,such as the piling process,the dynamic compaction in the geotechnical engineering,the impact of the missile in the military field,etc.Because the impact load will cause a high strain rate,it put the material in a high stress state.As the most widely distributed material in nature,the particle breakage of rock has already attracted the attention of many researchers in the world,and a lot of related research work has been carried out.In recent years,with the rise of large-scale civil and industrial construction in China,a large number of stones,such as coarse aggregates and sandstones,have been widely used in infrastructure construction such as transportation and water conservancy.The fragmentation of rock particles will seriously affect the practicability and security of these facilities,so it is receiving more and more attention.SHPB test technology is a widely used standard method for testing the dynamic mechanical properties of materials.In this paper,a Separate Hopkinson Pressure Bar(SHPB)device is used to perform impact crushing tests on two different kind of Nishan Stone and Shoushan Stone.The stress-strain curves of rock particle under different strain rates are measured and analyzed.The effect of strain rate on the dynamic constitutive of rock particle is analyzed,and the strain rate-dependent constitutive theory of two types of stone is constructed by two independent variables: strain rate enhancement factor and damage softening factor.The broken pieces of the stone are screened and counted,and the particle gradation curve of the broken pieces is used as a measure to quantify the degree of fracture of the rock particle.Using the fractal geometry theory,the fractal dimension is calculated,meanwhile,the relationship between impact velocity,rock dynamic compressive strength and fractal dimension is analyzed.In this paper,two kinds of stone are subjected to impact crushing test and simulated by Discrete Element Method.By comparing the difference of mechanical response between two types of rock under impact load,the influence of impact velocity on rock particle fragmentation is studied.The paper is divided into three parts:First,the research background of rock particle fragmentation under impact and the research status at home and abroad,including the factors affecting rock particle fragmentation and numerical simulation research methods,systematically summarize the research progress of rock particle fragmentation in PFC.Second,the SHPB test is carried out on the rock particle,and the stress-strain curves of the rock particle under different strain rates are measured.The influence of strain rate on the rock constitutive relations during the impact process is analyzed,and the constitutive equation correlated with strain rate for the two types of stone is established.Quantifying the degree of the sample fragmentation based on the particle grading curve of the fragment and the fractal geometry theory.Third,the discrete element simulation program PFC is used to simulate the rock particle impact crushing process.Compared with the test,the numerical simulation can directly display the variables that are difficult to be measured in the actual test,such as crack propagation,energy conversion,etc.These variables help us to understand the impact crushing process more deeply,and the influence of the cross-sectional shape of the sample on the strength of the rock particle was studied.In addition,the calibration of the bond strength between particles in numerical simulation is also a difficult and important point.This paper establishes the strength criterion related to the bond strength and impact velocity,and hopes to provide some references for scholars in this field. |
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