A density measurement method based on a modified cambridge model

Abstract

The application discloses a kind of based on the method for measuring the density of stockpile of modified cambridge model, the method is first measured the modified cambridge model parameter of to-be-measured stockpile using triaxial test, according to the stress-strain relationship reflected by modified cambridge model, the relationship model of internal density and stress of stockpile is established, the pressure of a point in stockpile is measured using thin film pressure sensor, the density of the point can be obtained after being substituted into pressure-density model.According to the density measurement method proposed in the application, in-situ measurement of the density of stockpile can be realized, the measurement process is simplified, the error is reduced, and the measurement accuracy is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of bulk density measurement, in particular to a bulk density measurement method based on a modified Cambridge model. BACKGROUND

[0002] Large irregular bulk material is common in the coal industry, building materials industry, large grain storage and grain processing industry, metallurgical industry, power industry, etc. The quality measurement of large irregular bulk material is of great importance, and density is a key parameter in quality measurement. The accuracy of density measurement directly affects the economic interests of both buyers and sellers. Density is the most difficult parameter to measure accurately during inventory work. The commonly used density measurement methods are simulation method and sink cylinder method. The accuracy of the simulation method depends on the degree to which the simulation pressurization experiment approximates the real situation, and the sink cylinder method causes the bulk material in the cylinder to loosen, resulting in a measured result that is often smaller than the actual value.

[0003] In view of the limitations of existing density measurement methods, a density measurement method based on a modified Cambridge model is proposed. This method directly measures the internal pressure of the bulk material to obtain the density of the bulk material to be measured, which can reduce the intermediate measurement transfer steps and improve the measurement accuracy. SUMMARY

[0004] The present application aims to provide a bulk density measurement method that can realize in-situ measurement based on the stress-strain relationship described by the modified Cambridge model. The solution adopted by the present application to solve its technical problem is:

[0005] Step 1: Consider the bulk material as a whole composed of multiple microelements. The density of a point in the bulk material can be calculated by the following formula:

[0006]

[0007] In the formula, m0 is the mass of the microelement, V0 is the initial volume of the microelement, ΔV is the volume change of the microelement after compression, and ε is the volume strain of the point.

[0008] Step 2: Place a volume V measuring cup on the balance and record the mass m1 of the empty cup. Fill the measuring cup with the sample to be measured through the funnel, scrape the surface flat with a ruler after filling, and then record the mass m2 at this time. The surface density is:

[0009]

[0010] Avoid vibration during operation. Repeat the measurement three times and take the average value as the final measurement result.

[0011] Step three: the modified Cambridge model is a constitutive model for describing stress-strain relationship by using elastic-plastic incremental theory, when the object is subjected to external force, the total volume strain increment generated by the object is equal to the sum of the elastic volume strain increment and the plastic volume strain increment, namely:

[0012]

[0013] Wherein, the elastic volume strain increment is:

[0014]

[0015] The plastic volume strain increment is:

[0016]

[0017] In the formula, p is the average principal stress, η=q / p, and M is the critical state stress ratio.

[0018] Step four: according to the volume strain increment in step three, the volume strain of the micro-element body can be calculated as:

[0019]

[0020] In the formula, C is a constant, which is determined by triaxial consolidation undrained shear test.

[0021] Step five: the modified Cambridge model parameters of the measured stockpile, Poisson's ratio v, elastic modulus E, logarithmic hardening modulus λ, isotropic swelling index κ and initial pore ratio e0 are measured by triaxial consolidation undrained shear test.

[0022] Step six: the pressure values F x , F y , F z of a point in the interior of the stockpile in x, y and z directions are measured by using a thin film pressure sensor, then:

[0023]

[0024] Step seven: according to the surface density ρ0 in step two, the volume strain ε in step four, Poisson's ratio v, elastic modulus E, logarithmic hardening modulus λ, isotropic swelling index κ and initial pore ratio e0 in step five, the density of the point in the interior of the stockpile can be calculated as:

[0025]

[0026] Compared with the existing measurement method, the present application has the following beneficial effects:

[0027] The present application can realize in-situ measurement of stockpile density, and the density value of the measuring point can be directly obtained without sampling and weighing during measurement, so that the measurement transfer step is reduced, the measurement efficiency is improved, and the error is reduced.

[0028] By measuring the modified Cambridge model parameters of the material under test, the existing database can be supplemented for future research. Attached Figure Description

[0029] Figure 1 This is a flowchart of the bulk density measurement process based on the modified Cambridge model in this measurement method. Figure 2 This is a schematic diagram of the density measurement system used in this measurement method. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the accompanying drawings.

[0031] like Figure 1 As shown, during measurement, the modified Cambridge model parameters for the material to be measured are first queried. If the parameters for the corresponding material cannot be found in the existing database, they are determined experimentally. Simultaneously, the experimental parameters for that material can be added to the database for future research. Modified Cambridge model parameters for some materials (such as soils from different regions) can be obtained by consulting relevant literature.

[0032] First, the modified Cambridge model parameters of the test stockpile were measured using triaxial experiments: Poisson's ratio ν, elastic modulus E, logarithmic hardening modulus λ, isotropic expansion index κ, and initial void ratio e0. The modified Cambridge model is a constitutive model that describes the stress-strain relationship using elastoplastic incremental theory. When subjected to external forces, the total volumetric strain increment of the object is equal to the sum of the elastic volumetric strain increment and the plastic volumetric strain increment. Based on the stress-strain relationship reflected by the modified Cambridge model, the relationship between the internal density and stress of the stockpile can be established as follows:

[0033]

[0034] In the formula, ρ0 is the surface density, with units of kg / m³. 3 C is a constant determined by a triaxial experiment; p is the average pressure exerted on the measuring point in the x, y, and z directions, in kPa.

[0035] Place a measuring cup with volume V on a balance and record the mass m1 of the empty cup. Fill the measuring cup with the sample to be tested through a funnel. After filling, level the surface with a ruler and record the mass m2 at this point. The surface density is then:

[0036]

[0037] Vibration should be avoided during operation. When measuring, repeat the measurement three times and take the average value as the final measurement result.

[0038] A schematic diagram of the density measurement system is shown below. Figure 2After the system is initialized, the pressure values Fx, Fy and Fz of a point in the stockpile in x, y and z directions are measured by using a thin film pressure sensor x y z Then:

[0039]

[0040] During the measurement, representative measuring points are taken on the upper, middle and lower layers of the stockpile. The collected pressure signals are converted into voltage signals, and after filtering and amplification, the input analog signals are converted into digital signals by an A / D conversion module, and finally sent to a single-chip microcomputer. The single-chip microcomputer program calculates the final result according to the pressure-density model and displays it. If a large amount of data operation is required after data collection, the serial communication module can be used to transmit the data to the upper computer for processing, so as to reduce the processing burden of the single-chip microcomputer system.

[0041] The above is only a preferred embodiment of the present application, and does not limit the present application. Any simple modification, change and equivalent structural change of the above embodiment according to the technical essence of the present application are still within the protection scope of the technical solution of the present application.​​

Claims

1. A method for measuring the bulk density of a pile based on the modified Cam-Clay model, characterized in that: Step 1: The pile is regarded as a whole composed of a plurality of microelements, and the density of a point in the pile can be calculated by the following formula: wherein m0 is the mass of the microelement, V0 is the initial volume of the microelement, ΔV is the volume change of the microelement after compression, and ε is the volume strain of the point; Step 2: A measuring cup with a volume of V is placed on a balance, and the mass of the empty cup m1 is recorded. The sample to be measured is loaded into the measuring cup through a funnel, and the surface is scraped flat with a ruler after filling. Then the mass m2 at this time is recorded, and the surface density is: Vibration should be avoided during operation, and the average of three repeated measurements is taken as the final measurement result; Step 3: The modified Cam-Clay model is a constitutive model that describes the stress-strain relationship using the elastic-plastic incremental theory. When subjected to external forces, the total volume strain increment of the object is equal to the sum of the elastic volume strain increment and the plastic volume strain increment, i.e.: wherein the elastic volume strain increment is: and the plastic volume strain increment is: wherein p is the average principal stress, η = q / p, and M is the critical state stress ratio; Step 4: According to the volume strain increment in Step 3, the volume strain of the microelement can be calculated as: wherein C is a constant determined by triaxial consolidation undrained shear test; Step 5: The modified Cam-Clay model parameters of the pile to be measured, Poisson's ratio v, elastic modulus E, logarithmic hardening modulus λ, isotropic swelling index κ, and initial void ratio e0, are measured by triaxial consolidation undrained shear test; Step 7: According to the surface density ρ0 in Step 2, the volume strain ε in Step 4, and the Poisson's ratio v, elastic modulus E, logarithmic hardening modulus λ, isotropic swelling index κ, and initial void ratio e0 in Step 5, the density of a point inside the pile can be calculated as: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Step six: the pressure value F of a point inside the pile in x, y, z direction is measured by using a thin film pressure sensor x , F y , F z Then: ​

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