A specific energy-based rock cutting critical depth determination method

Abstract

The application provides a rock cutting critical depth determination method based on specific energy, and the specific energy of rock cutting is calculated by the rock cutting force and the trench cross-sectional area during the rock cutting process. The specific energy of the process changes from sharp decline to gradual flatness or stability with the change of the cutting depth, and the depth is related to the basic properties of the rock and the rock cutting parameters. The application determines the critical cutting depth by the obvious dividing point in the relationship between the specific energy and the cutting depth, can obviously identify the transition process from plastic failure to brittle failure in the rock cutting process, has guiding significance for the design of the rock entering angle of the cutting tool, the angle and the width of the cutting tooth, and helps to improve the quality of the rock strength data selection of the core sample estimated based on the plastic cutting mode only, gives the determination value of the critical transition depth, and has the ability to predict the critical depth without involving the rock property measurement.

Description

Technical Field

[0001] This invention relates to the field of rock cutting technology, and in particular to a method for determining the critical depth of rock cutting based on specific energy. Background Technology

[0002] Rock cutting utilizes rigid cutting tools to create a certain depth of cut on the rock surface. Two distinct failure modes have been identified during rock cutting: ductile failure and brittle failure. When the cutting depth is shallow, ductile failure is predominant. As the cutting depth increases, the failure mode gradually shifts to brittle failure as the dominant mode. The threshold depth, or critical depth, for the transition from ductile to brittle failure in rock cutting depends not only on the properties of the rock but also on the cutting operation parameters. Understanding this critical depth is crucial for optimizing tool design and operating parameters.

[0003] Currently, there are only qualitative and empirical methods for determining the critical depth of rock cutting, and no quantitative method exists. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for determining the critical depth of rock cutting based on specific energy, based on the cutting depth that transitions from plastic failure to brittle failure as mentioned in the background art above. The method can more clearly and effectively identify the critical depth, and the determination of the critical depth is of great significance for the design of cutting tools and the setting of cutting parameters.

[0005] The critical depth for rock cutting described in this invention refers to the energy dissipated within the material in the form of plastic flow, with plastic failure being the primary mode, when the cutting depth is small. When the cutting depth is large, rock failure is mainly brittle, and energy dissipation occurs at the macroscopic discontinuous crack surface at the cutting edge. During this process, the specific energy changes from a sharp decrease with the cutting depth to a gradual leveling off or stabilizing. Therefore, there exists a critical depth that describes the turning point from plastic failure to brittle failure in rock cutting, and this depth is related to the basic properties of the rock and the rock cutting parameters. The specific energy described in this invention refers to the energy required to cut and break a unit volume of rock, which can be equivalent to the ratio of cutting force to the cross-sectional area of ​​the cut groove, directly reflecting the efficiency of rock cutting.

[0006] The technical solution can be summarized as follows:

[0007] A method for determining the critical depth of rock cutting based on specific energy: by measuring and calculating various cutting depths H i SPE at the specific energy iA scatter plot of the "cutting specific energy - cutting depth" relationship was plotted, and the inflection point with a significant change was found from the scatter plot based on the characteristic that the relationship between the two changes from a sharp decrease to a gradual flattening or stabilization. Specifically, this invention reveals for the first time that fitting the scatter points before and after the inflection point yields two different functional relationships: a power function and a linear function. Through mathematical solution methods, this dividing point can be accurately determined, that is, the specific critical depth at which the rock cutting failure mode changes from plastic failure to brittle failure.

[0008] The application value of this invention lies in its method for determining the critical depth of rock cutting based on rock cutting specific energy. This method determines the transition of cutting failure modes from the perspective of energy dissipation during the cutting process, using the change in specific energy and cutting depth obtained from experiments to determine the critical depth. This method can clearly and effectively identify the transformation process between plastic and brittle failure modes of rock. In other words, this method can clearly and effectively identify and determine the critical depth through the change in the functional relationship between specific energy and cutting depth, which is of great significance for optimizing the design and setting of cutting parameters during the construction of cutting tools.

[0009] Further specific implementation technical solutions are provided:

[0010] A method for determining the critical depth of rock cutting based on specific energy is characterized in that: during the rock cutting process, when the cutting depth reaches a certain depth, the failure mode of rock cutting changes from plastic failure to brittle failure. The specific energy of cutting is obtained by calculating the rock cutting force and the cross-sectional area of ​​the groove. During the process, the specific energy of cutting will change from a sharp decrease to a gradual or stable change with the cutting depth, and this depth is related to the basic properties of the rock and the rock cutting parameters.

[0011] The failure mode of rock cutting is characterized by the following: When the cutting depth is small during rock cutting, energy is dissipated within the material in the form of plastic flow, with plastic failure taking precedence. This manifests as the rock near the tooth tip being crushed into fine powder under compression when the cutting teeth penetrate the rock. When the cutting depth is large, rock failure is mainly characterized by brittle failure, and energy dissipation occurs at the macroscopic discontinuous crack surface at the tip of the cutting teeth. This manifests as rock fragments falling from the rock surface near the tooth tip.

[0012] Furthermore, the specific steps include the following:

[0013] Step 1: Conduct the rock cutting process using a rock cutting test platform;

[0014] Step 2: Determine the rock cutting force and the cross-sectional area of ​​the groove, and calculate the specific cutting energy;

[0015] Step 3: Determine the relationship between cutting specific energy and cutting depth through experiments, and then determine the critical cutting depth by calculating the intersection of the function curves.

[0016] Furthermore, in step 1, an existing rock cutting test platform is utilized, including cutting teeth 2, tooth holders 3, force sensors 5, angle adjustment hydraulic systems 8, rake arms 9, height adjustment hydraulic systems 10, a trolley 11, and a traction power and control system 14. The cutting teeth used in the test are rock dredging sharp teeth used in rock dredging engineering. To ensure that the tooth tips do not become dull during the test, the tooth tips are replaced after every three sets of tests to maintain their sharpness. A force sensor is installed at the tooth holder to monitor the change of cutting force over time in real time. The traction trolley moves at a certain speed. The trolley and cutting teeth are connected through the rake arms. The trolley allows adjustment of the rake arms' lifting, lowering, left and right movement, as well as the extension and retraction of the hydraulic cylinder at the front end of the rake arms, thereby adjusting the cutting depth and position of the cutting teeth.

[0017] Furthermore, in step 1, during the test, the sample is cut by the cutting teeth driven by the translational movement of the trolley, and the change of cutting force is monitored by the force sensor.

[0018] Furthermore, in step 2, the determination of the rock cutting force is characterized by the fact that the cutting force is an important cutting parameter reflecting the ease of rock breaking, the minimum strength required for the cutting teeth, and the power required by the cutting tool. During the cutting process, the forces acting on the cutting teeth include a horizontal force along the tangent at the tooth tip and a vertical force perpendicular to the cutting force. By decomposing the forces acting on the cutting teeth along the cutting direction and the vertical direction, the cutting force-time history curves of the cutting teeth under different working conditions are obtained. Combined with the empirical relationship that the peak cutting force is basically twice the average cutting force, the average cutting force F required to calculate the specific energy is derived. In addition, the cutting force is also affected by the cutting angle and the cutting depth. When the cutting angle is determined, the cutting force and the cutting depth are basically linearly related.

[0019] Furthermore, in step 2, the determination of the cross-sectional area of ​​the groove is characterized by: measuring the cutting depth h of each segment of the rock groove in n segments. i and cutting width d i And combined with formula Perform cross-sectional area calculations or collect rock chips after cutting, determine the chip volume V and the groove length l, and combine them with the formula. Perform cross-sectional area calculation.

[0020] Furthermore, in step 2, the cutting specific energy (SPE) is characterized in that: the cutting specific energy (SPE) refers to the energy required to cut and break a unit volume of rock, obtained by measuring the average cutting force. and the cross-sectional area of ​​the groove The ratio is calculated, and its value directly reflects the cutting efficiency during rock cutting.

[0021] Furthermore, in step 3, the critical depth determination method is characterized by: measuring and calculating each cutting depth H. i SPE at the specific energy i A scatter plot of the relationship between cutting energy and cutting depth was plotted. Based on the characteristic that the relationship changes from a sharp decrease to a gradual flattening or stabilization, an inflection point with a significant change was identified in the scatter plot. Fitting the scatter points before and after the inflection point yielded two different functional relationships: a power function and a linear function. Combining this with the failure modes of rock cutting, this boundary point was determined to be the critical depth at which the rock cutting failure mode transitions from plastic failure to brittle failure.

[0022] Compared with existing methods, the present invention has the following advantages:

[0023] (1) This invention determines the critical cutting depth by identifying the clear dividing point in the relationship between specific energy and cutting depth, which can clearly identify the transformation process from plastic failure to brittle failure during rock cutting. Before and after the dividing point, the plastic failure and brittle failure processes of rock cutting can be simulated by the fitted piecewise function relationship, and the specific energy or energy changes with cutting depth during the failure process can be further understood.

[0024] (2) The method for identifying and determining the critical depth provides guidance for the design of the cutting tool's rock entry angle, tooth angle, and tooth width. It also helps improve the quality of data selection for estimating rock strength in core samples based solely on plastic cutting modes.

[0025] (3) Furthermore, using cutting specific energy to determine the critical transition depth has two advantages. First, the method of this invention can provide a definite value for the critical transition depth, while general conceptual models can only predict them qualitatively. Second, the method of this invention has the ability to predict the critical depth without involving rock property measurements, while conceptual models require prior knowledge of uniaxial compressive strength and fracture toughness.

[0026] The method of this invention is applicable to the calculation and determination of the critical cutting depth of different types of rocks in the field of rock excavation and rock breaking engineering and rock cutting. Attached Figure Description

[0027] Figure 1 Schematic diagram of rock cutting failure process;

[0028] Figure 2 Schematic diagram of the cutting tool teeth used in the embodiments;

[0029] Figure 3 Schematic diagram of rock cutting test platform;

[0030] Figure 4 Installation diagram of the knife-tooth force sensor;

[0031] Figure 5Figures from rock cutting plasticity and brittle fracture tests in the examples;

[0032] Figure 6 Example 1: Relationship between the amount of chips and cutting force after cutting fine sandstone and time;

[0033] Figure 7 Example 1: Relationship between cutting specific energy and cutting depth in fine sandstone and determination of critical depth;

[0034] Figure 8 Example 2: Relationship between specific energy of limestone cutting and cutting depth and determination of critical depth.

[0035] Figure 3 middle:

[0036] 1-Test bench, 2-Test blade, 3-Gear seat, 4-Flange, 5-Three-dimensional force sensor, 6-Connecting plate, 7-Connecting frame, 8-Angle adjustment hydraulic device, 9-Rake arm, 10-Height adjustment hydraulic device, 11-Trolley, 12-Rail, 13-Steel cable, 14-Traction power and control system, 15-Sample fixing plate, 16-Fixing part height adjustment bolt, 17-Sample fixing platform base plate, 18-High-speed camera, 19-Infrared thermal imager. Detailed Implementation

[0037] The technical solutions provided in this application will be further described below with reference to specific embodiments and accompanying drawings. The advantages and features of this application will become clearer from the following description.

[0038] It should be noted that the embodiments of this application are preferred for implementation and are not intended to limit the application in any way. The technical features or combinations of technical features described in the embodiments of this application should not be considered isolated; they can be combined with each other to achieve better technical effects. The scope of the preferred embodiments of this application may also include other implementations, and this should be understood by those skilled in the art to which the embodiments of this application pertain.

[0039] Techniques, methods, and apparatus known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and apparatus should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limiting. Therefore, other examples of exemplary embodiments may have different values.

[0040] The accompanying drawings in this application are all in a very simplified form and use non-precise proportions, intended only to facilitate and clarify the illustration of the embodiments of this application, and are not intended to limit the implementation of this application. Any modifications to the structure, changes in the proportional relationships, or adjustments to the size, without affecting the effects and purposes achieved by this application, should fall within the scope of the technical content disclosed in this application. Furthermore, the same reference numerals appearing in the various drawings of this application represent the same features or components, and can be applied to different embodiments.

[0041] This invention fits the scattered points before and after the inflection point of change to have two different functional relationships: power function and linear function. Then, it calculates that the dividing point is the specific and precise critical depth at which the rock cutting failure mode changes from plastic failure to brittle failure.

[0042] The rock cutting test platform and its functions can be found in Chinese invention application "Multifunctional device for studying the cutting mechanism of rock and soil and optimizing cutting teeth" (publication number CN110487663A), i.e. Figure 3 As shown.

[0043] The following two embodiments are provided to verify the conclusions of the technical solution of the present invention.

[0044] Example 1

[0045] In this example, the test rock sample was a fine sandstone, yellowish-brown in color. The basic physical properties and strength indices of the rock sample are shown in Table 1. Before the test, the rock sample was processed into a smooth, flat cuboid to ensure a stable cutting depth during the cutting process. The cutting teeth used in the test were tapered pointed teeth, with the shape and parameters as shown in Table 1. Figure 2 As shown. To ensure the tooth tip does not become dull during the experiment, it is replaced after every three sets of tests to maintain its sharpness. Furthermore, a force sensor 5 is installed at the end of the tooth holder 3, connected to the tooth holder 3 via a circular flange 4, allowing for real-time monitoring and plotting of the cutting force's time-history curve. During the experiment, the tooth uses a constant cutting speed v = 0.6 m / s. By changing the cutting depth (0.2 cm to 4 cm) and cutting angle (42° to 57°), the sensor acquisition device obtains the time-history changes of the cutting force under different experimental conditions. During the experiment, a rock cutting test platform is used to control the cutting angle, depth, speed, and other factors to cut the rock sample. The traction trolley moves at a constant speed. The trolley 11 is connected to the tooth via a height-adjusting hydraulic system 10. The trolley allows adjustment of the height-adjusting hydraulic system 10's lifting, lowering, left, and right movements, as well as the extension and retraction of the hydraulic cylinder at the front end of the height-adjusting hydraulic system 10, thereby adjusting the cutting depth and position of the tooth. During the test, the cutting teeth were driven to cut the sample by the translation of the trolley, and the cutting force was monitored by the force sensor 5.

[0046] Table 1. Basic physical properties and strength index values ​​of the tested fine sandstone

[0047]

[0048] After the experiment was completed and the data was processed, the cutting force values ​​and corresponding cutting depth values ​​were obtained as shown in Table 2.

[0049] Table 2. Changes in experimental cutting force and corresponding depth of cut.

[0050] Cutting depth / cm Cutting force / kN Cutting depth / cm Cutting force / kN Cutting depth / cm Cutting force / kN Cutting depth / cm Cutting force / kN 0.24 3.0225 0.71 2.0145 0.98 2.0125 1.30 1.2266 0.25 4.1293 0.73 1.5562 1.06 2.0182 1.49 1.3678 0.40 1.9482 0.81 1.746 1.06 1.8434 1.62 1.4899 0.41 2.5231 0.83 2.108 1.06 2.0381 1.7 1.4103 0.46 2.1779 0.84 1.2781 1.08 1.803 2.07 1.7102 0.46 2.3859 0.85 2.3048 1.09 1.3916 2.31 1.9164 0.54 2.4538 0.90 1.7626 1.17 1.9413 2.83 2.0014 0.59 1.5707 0.92 1.5202 1.20 1.1506 3.11 1.7606 0.67 1.8532 0.96 1.6189 1.21 1.4584 3.36 1.9078 0.69 2.2228 0.98 1.3445 1.21 1.4543 3.78 1.4459

[0051] The rock cutting energy is calculated by using cutting force monitored in real time by a force sensor and the cross-sectional area of ​​the groove at different cutting depths. The calculation results are shown in Table 3.

[0052] Table 3. Experimental specific energy changes and corresponding cutting depth changes

[0053]

[0054] By plotting the relationship curve between cutting energy and cutting depth, as shown in... Figure 6 It can be clearly identified that the curve has a distinct dividing point at a certain location. Curve fitting reveals that the data before the cutting depth reaches 1.38 cm exhibits a power function shape. After fitting, the power function is: y = 0.9751x -1.441 (correlation coefficient R) 2 =0.9422);

[0055] The subsequent data exhibited a linear function shape, which, after fitting, became: y = -0.1553x + 0.8322 (correlation coefficient R0). 2 =0.9507).

[0056] The correlation coefficient R between the two is 2 Both are around 94%, indicating a strong correlation.

[0057] Based on the principle that rock cutting failure gradually transitions from ductile to brittle failure, the sandstone in this experiment underwent a ductile failure process before 1.38 cm, with the specific energy exhibiting a power-law relationship with the cutting depth. After 1.38 cm, the rock underwent a brittle failure process, with the specific energy exhibiting a linear relationship with the cutting depth. Therefore, the critical cutting depth for the sandstone sample in this embodiment is 1.38 cm, which is the x-coordinate of the intersection of the two fitted functions.

[0058] Fitting the scattered points before and after the inflection point of change yields two different functional relationships: power function and linear function. The boundary point can also be accurately determined through mathematical solution methods. That is, the specific critical depth at which the rock cutting failure mode changes from plastic failure to brittle failure is 1.38 cm.

[0059] Example 2

[0060] Unlike the rock properties in Example 1, limestone was used as the cutting rock sample. Following the same experimental method as in Example 1, the cutting specific energy and cutting depth were calculated by testing, and the critical cutting depth was determined by fitting data points to identify the dividing point. The basic physical properties and strength indicators of the rock sample are shown in Table 4. After the experiment was completed and the data was processed, the cutting force values ​​and corresponding cutting depth values ​​were obtained as shown in Table 5.

[0061] Table 4. Basic physical properties and strength index values ​​of the tested limestone

[0062]

[0063] Table 5. Changes in experimental cutting force and corresponding depth of cut.

[0064] Cutting depth / cm Cutting force / kN Cutting depth / cm Cutting force / kN Cutting depth / cm Cutting force / kN Cutting depth / cm Cutting force / kN 0.44 4.5404 1.35 3.0753 2.26 5.0714 3.58 4.7775 0.56 3.8461 1.47 5.123 2.32 4.8906 3.63 4.7208 0.63 5.2640 1.67 4.4146 2.48 5.7548 3.73 5.6118 0.69 4.7389 1.96 4.6815 2.73 5.1283 3.88 5.6396 0.94 4.0989 2.02 5.1338 2.86 5.6156 1.00 3.5700 2.18 5.3366 3.51 4.8929

[0065] The rock cutting energy is calculated by using cutting force monitored in real time by a force sensor and the cross-sectional area of ​​the groove at different cutting depths. The calculation results are shown in Table 6. The relationship between cutting energy and depth of cut is plotted as follows: Figure 7 It can be clearly identified that the curve has a distinct dividing point at a certain location. Curve fitting reveals that the data before the cutting depth reaches 1.65cm exhibits a power function shape. After fitting, the power function is: y = 2.5599x -0.981 (correlation coefficient R) 2 =0.9054); and the subsequent data exhibited a linear function shape, which, after fitting, became: y = -0.3655x + 2.1685 (correlation coefficient R). 2 =0.9053), the correlation coefficient R of the fit 2 Both are around 90%, indicating a strong correlation.

[0066] Table 6. Experimental specific energy changes and corresponding cutting depth changes

[0067]

[0068] The above description is merely a description of preferred embodiments of this application and is not intended to limit the scope of this application in any way. Any changes or modifications made by those skilled in the art based on the above-disclosed technical content should be considered as equivalent and valid embodiments and fall within the scope of protection of the technical solution of this application.

Claims

1. A method for determining the critical depth of rock cutting based on specific energy, characterized in that: During the rock cutting process, as the cutting depth increases, the failure mode of rock cutting changes from plastic failure to brittle failure. The cutting specific energy, calculated by the rock cutting force and the cross-sectional area of ​​the groove, changes from a sharp decrease to a gradual or stable change with the cutting depth. This depth is related to the basic properties of the rock and the rock cutting parameters. The failure modes of rock cutting are as follows: When the cutting depth is small during rock cutting, energy is dissipated in the damaged material in the form of plastic flow and plastic failure takes precedence. This is manifested in the fact that when the cutting teeth cut into the rock, the rock near the tooth tip is crushed into fine powder under the compression. When the cutting depth is large, the rock failure is mainly in a brittle failure state and energy dissipation occurs at the macroscopic discontinuous crack surface at the tip of the cutting teeth. This is manifested in the rock surface near the tooth tip where rock fragments fall off. Specifically, the steps include the following: Step 1: Conduct the rock cutting process using a rock cutting test platform; Step 2: Determine the rock cutting force and the cross-sectional area of ​​the groove, and calculate the specific cutting energy; Step 3: Determine the relationship between cutting specific energy and cutting depth through experiments, and then determine the critical cutting depth by calculating the intersection of the function curves.

2. The method as described in claim 1, characterized in that, Step 1 utilizes an existing rock cutting test platform, including cutting teeth (2), tooth holder (3), force sensor (5), angle adjustment hydraulic system (8), rake arm (9), height adjustment hydraulic system (10), trolley (11), and traction power and control system (14). The cutting teeth used in the test are rock dredging sharp teeth used in rock dredging projects. To ensure that the tooth tips do not become dull as the test progresses, the tooth tips are replaced after every three sets of tests to keep them sharp. A force sensor is installed at the tooth holder to monitor the change of cutting force over time in real time. The trolley is moved to traction. The trolley and the cutting teeth are connected through the rake arm. The trolley can be used to adjust the lifting and lowering of the rake arm and its left and right movement, as well as the extension and retraction of the hydraulic cylinder at the front end of the rake arm, thereby adjusting the cutting depth and position of the cutting teeth.

3. The method as described in claim 2, characterized in that, In step 1, during the test, the test specimen is cut by the cutting teeth driven by the translational movement of the trolley, and the change of cutting force is monitored by the force sensor.

4. The method as described in claim 1, characterized in that, Step 2, the determination of rock cutting force: Cutting force is an important cutting parameter reflecting the ease of rock breaking, the minimum strength required of the cutting teeth, and the power required by the cutting tool. During the cutting process, the cutting teeth are subjected to horizontal forces along the tangent at the tooth tip and vertical forces perpendicular to the cutting force. By decomposing the forces on the cutting teeth along the cutting direction and the vertical direction, the cutting force-time history curves of the cutting teeth under different working conditions are obtained. Combined with the empirical relationship that the peak cutting force is basically twice the average cutting force, the average cutting force required to calculate the specific energy is derived. In addition, the cutting force is also affected by the cutting angle and the cutting depth. When the cutting angle is determined, the cutting force and the cutting depth are basically linearly related.

5. The method as described in claim 1, characterized in that, Step 2, the determination of the cross-sectional area of ​​the trench: by dividing... Sectional measurement of the cutting depth of each segment of the rock cutting groove and cutting width And combined with formula Perform cross-sectional area calculations or collect rock chips after cutting, determine the chip volume V and the groove length l, and combine them with the formula. Perform cross-sectional area calculation.

6. The method as described in claim 1, characterized in that, In step 2, the cutting specific energy This refers to the energy required to cut and break a unit volume of rock, measured as the average cutting force. and the cross-sectional area of ​​the groove The ratio is calculated, and its value directly reflects the cutting efficiency during rock cutting.

7. The method as described in claim 1, characterized in that, In step 3, the critical depth determination method is characterized by: measuring and calculating each cutting depth. Specific energy at the location A scatter plot of the relationship between cutting energy and cutting depth was plotted. Based on the characteristic that the relationship between the two changes from a sharp decrease to a gradual flattening or stabilization, an inflection point with obvious change was found in the scatter plot. The scatter points before and after the inflection point were fitted with two different functional relationships, namely power function and linear function. Combined with the failure mode of rock cutting, the dividing point can be identified as the critical depth at which the failure mode of rock cutting changes from plastic failure to brittle failure.

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