A method for predicting the fatigue life of a tunnel boring machine cutterhead

Abstract

The invention discloses a method for predicting the fatigue life of a shield machine cutterhead, which belongs to the technical field of fatigue life prediction of shield mechanical equipment. The method comprises the following steps: step 1, using Solidworks to perform three-dimensional modeling according to a cutterhead structure, including a cutterhead body and a roller cutter system; step 2, performing static analysis on the cutterhead structure, the static analysis including force F analysis, torque force T analysis and thrust Z analysis; step 3, using finite element analysis software Ansys workbench to perform finite element static analysis on the cutterhead; step 4, performing compression processing on an initial load, using a MATLAB software programming method to compress data, then using MATLAB software to perform programming, using a rain flow counting method on the compressed data, obtaining a relationship between a mean value, an amplitude and a number of cycles, and obtaining data through Weibull distribution; step 5, correcting the obtained data and then bringing them into a fatigue tool in Ansys workbench for calculation, and obtaining a minimum fatigue life of the cutterhead through a Miner criterion.

Description

Technical Field

[0001] The invention belongs to the technical field of fatigue life prediction of shield mechanical equipment, and in particular relates to a method for predicting the fatigue life of a shield machine cutter head. Background Art

[0002] Currently, methods for predicting the fatigue life of shield cutterheads primarily include empirical models and damage accumulation models. The advantage of empirical models is their simplicity, ease of implementation, and the lack of computational and analytical requirements, making them suitable for simple engineering problems. The damage accumulation model considers factors such as the material's stress-strain response, the effects of cyclic loading, and stress concentration, using mathematical models to describe the material's damage accumulation and fatigue life consumption. However, shield machines operating underground are subject to complex and ever-changing conditions, including geological conditions, groundwater, and rock formation variations. Existing fatigue life prediction techniques struggle to fully account for the impact of these factors on the cutterhead's fatigue life. As a key component of a shield machine, the cutterhead's materials and structure are often complex, and it is subject to high-intensity, high-frequency cyclic loading. This presents challenges for fatigue life prediction techniques. Furthermore, the shield machine cutterhead's operating environment is complex, and its location is difficult to directly observe and monitor. This makes it difficult to obtain cutterhead operating data and monitor its fatigue status in real time. Therefore, a shield machine cutterhead fatigue life prediction method is urgently needed to quickly, economically, and accurately determine the fatigue life of critical points on the cutterhead. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for predicting the fatigue life of a shield machine cutterhead, so as to solve the problems in the prior art of insufficient prediction capability for complex working conditions and difficulty in obtaining cutterhead operation data.

[0004] To achieve the above object, the present invention provides a method for predicting the fatigue life of a shield machine cutter head, comprising the following steps:

[0005] Step 1: Use SolidWorks to perform 3D modeling based on the cutterhead structure, including the cutterhead body and the cutter system. The cutterhead body and the cutter system are both arranged at the head of the shield machine, and the cutter system includes a double-edged cutter and a single-edged cutter.

[0006] Step 2: Perform static analysis on the cutterhead structure. The static analysis includes force F analysis, torque T analysis, and thrust Z analysis.

[0007] Step 3: Use the finite element analysis software Ansys workbench to perform finite element static analysis on the cutterhead;

[0008] Step 4: compress the initial load and compress the data using the MATLAB software programming method. Then, use the MATLAB software to program the compressed data using the rain flow counting method to obtain the relationship between the mean, amplitude and number of cycles, and obtain the data through Weibull distribution.

[0009] Step 5: The corrected data is then brought into the fatigue tool in Ansys Workbench for calculation. The minimum fatigue life of the cutterhead is obtained using the Miner criterion. The specific expression of the Miner criterion is as follows:

[0010]

[0011] where N i Table 1 shows the actual number of cycles of the i-th load cycle, Indicates the theoretical fatigue life of the material under the same load cycle.

[0012] Preferably, the force F is the force that the cutter system on the cutter head exerts on the tunnel face when the shield machine is tunneling, performing cutting rotation and also supporting the tunnel face. The cutter system is subjected to the force exerted by the rock on itself, specifically including the positive thrust F in the same direction as the tunneling direction. v , rolling force F perpendicular to the excavation direction r , lateral force F generated by cutterhead vibration s , the specific expression is as follows:

[0013] F=F v +F r +F s .

[0014] Preferably, the torque force T is caused by the friction resistance of the cutterhead and the resistance of the cutter system when cutting the soil, specifically including the friction resistance torque T1 between the front of the cutterhead and the soil layer; the friction resistance torque T2 between the back of the cutterhead and the soil in the soil bin; the friction resistance torque T3 between the side of the cutterhead and the soil layer; and the resistance torque T4 of the soil layer when the tool is cutting. The specific expression of the torque force T is as follows:

[0015] T=T1+T2+T3+T4.

[0016] Preferably, the friction resistance torque T1 between the front face of the cutterhead and the soil layer is generated when the cutterhead cuts the soil layer. The cutting action of the tool generates soil resistance, and at the same time, the contact surface between the cutterhead and the excavated soil generates friction, thereby generating friction resistance torque. The specific expression is as follows:

[0017]

[0018] Where k is the lateral pressure coefficient of the soil layer; f is the friction coefficient of the soil layer; γ is the gravity density of the soil, in kN / m3 H is the depth from the shield machine axis to the ground, in meters; D is the cutterhead diameter, in meters; in the actual calculation of friction resistance torque, the contact area between the cutterhead and the ground is taken into account, and the opening ratio ζ is introduced. The friction resistance torque T1 between the front of the cutterhead and the soil layer is expressed as:

[0019]

[0020] Preferably, the friction resistance torque T2 between the back of the cutterhead and the soil in the soil bin is that during the forward excavation of the shield machine, the slag enters the soil bin from the opening of the cutterhead and is not completely filled; in addition, under the action of the stirring rod, the fluidity of the slag is enhanced, and the friction coefficient between the soil in the soil bin and the back of the cutterhead is smaller than the friction coefficient between the soil layer and the front of the cutterhead. Therefore, the specific calculation expression of the friction resistance torque T2 between the back of the cutterhead and the soil in the soil bin is as follows:

[0021]

[0022] Among them, k1 is the adjustment coefficient.

[0023] Preferably, the friction resistance torque T3 between the cutterhead side and the soil layer is that the cutterhead diameter is set larger than the front shield diameter. During the excavation process, the cutterhead side is subjected to the friction resistance torque from the soil layer. When calculating, the vertical soil pressure and lateral soil pressure on the cutterhead side are decomposed and converted into the positive pressure acting on the cutterhead side surface. The specific calculation expression is as follows:

[0024]

[0025] Where W is the width of the cutter head side, in m.

[0026] Preferably, the soil resistance torque T4 during tool cutting is generated by overcoming the soil shear force when the cutterhead rotates and excavates, and the specific expression is as follows:

[0027]

[0028] Where q u is the uniaxial compressive strength of the soil layer, in kN / m 2 ;μ max is the maximum excavation speed of the shield machine, in m / min; ω is the cutterhead speed, in r / min; the uniaxial compressive strength of the soil layer refers to the ultimate bearing capacity of the soil sample when it fails under compressive stress in one direction, expressed as the maximum bearing capacity per unit area.

[0029] Preferably, the thrust Z is the resistance to overcome the cutterhead rotation process, including the front propulsion resistance of the cutterhead, the friction resistance between the outer side of the shield machine and the soil layer, and the tool cutting resistance. The specific expression is as follows:

[0030]

[0031] Where P is the empirical thrust per unit excavation surface.

[0032] Preferably, the specific process of step 3 is as follows:

[0033] S31. Establish a finite element model: Convert the actual engineering structure into a finite element model, import the cutterhead 3D model from SolidWorks into ANSYS Workbench software and establish a model that can be recognized by the finite element analysis software;

[0034] S32. Material selection: Describe the materials and mechanical properties in the model, including elastic modulus, Poisson's ratio, and thermal expansion coefficient;

[0035] S33. Meshing: Divide the finite element model into many small units (such as triangles, quadrilaterals, hexahedrons, etc.). Appropriate mesh sizes should be selected for different engineering structures to avoid distortion in simulation experiments.

[0036] S34, Apply boundary conditions: Set constraints and loads on the model, including fixed boundary conditions, moments, and contact stresses;

[0037] S35. Result calculation and analysis: Run the software to perform finite element analysis to obtain strain and stress.

[0038] Preferably, the correction in step 5 includes straight line correction and curve correction, and the specific expression is as follows:

[0039] Straight line correction:

[0040]

[0041] Curve correction:

[0042]

[0043] Among them, S a is the stress amplitude; S m is the mean stress; S -1 is the stress value when the stress ratio is –1; S u is the yield stress.

[0044] Therefore, the present invention adopts the above-mentioned method for predicting the fatigue life of the cutterhead of a shield machine. Through finite element analysis and Matlab algorithm, the fatigue life of the dangerous points of the cutterhead is quickly and accurately predicted, which solves the problem that the empirical model method is difficult to fully consider the impact of repeated working conditions on the fatigue life of the cutterhead; using the finite element analysis method, the stress and strain distribution of the shield cutterhead under various working conditions is accurately obtained, which solves the problem of difficulty in obtaining cutterhead operation data and real-time monitoring of cutterhead fatigue status. It reduces the cost of monitoring data, improves economic benefits, and quickly and accurately predicts the fatigue life of the shield cutterhead. It is of great significance to ensure the safe and stable operation of the shield machine, reduce maintenance costs, optimize engineering design, save resources and protect the environment. It provides reliable technical support for the operation management and engineering design of the shield machine and promotes the sustainable development and application of shield technology.

[0045] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a flow chart of a method for predicting the fatigue life of a shield machine cutterhead according to the present invention;

[0047] Figure 2 A three-dimensional model diagram of a cutterhead according to an embodiment of the present invention;

[0048] Figure 3 A three-dimensional model diagram of a single-edge hob according to an embodiment of the present invention;

[0049] Figure 4 A three-dimensional model diagram of a double-edged hob according to an embodiment of the present invention;

[0050] Figure 5 A diagram showing a force model of a hob according to an embodiment of the present invention;

[0051] Figure 6 A finite element model diagram of a cutterhead according to an embodiment of the present invention;

[0052] Figure 7 The finite element analysis results of the cutterhead of the embodiment of the present invention are shown in Figure 1, where (a) is the total deformation distribution diagram of the cutterhead; (b) is the strain distribution diagram of the cutterhead; (c) is the stress distribution diagram of the cutterhead; and (d) is the load distribution diagram of the cutterhead.

[0053] Figure 8 This is a time history diagram of the load after compression according to an embodiment of the present invention;

[0054] Figure 9 This is a diagram showing the results of the rain flow counting method according to an embodiment of the present invention;

[0055] Figure 10 This is a Weibull distribution test diagram according to an embodiment of the present invention;

[0056] Figure 11 This is a fatigue life cloud diagram of an embodiment of the present invention. DETAILED DESCRIPTION

[0057] The following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0058] See also Figure 1 A method for predicting the fatigue life of a shield machine cutterhead comprises the following steps:

[0059] Step 1: Use SolidWorks to perform 3D modeling based on the cutterhead structure. Since the cutterhead structure is too complex and has many assembly relationships, when performing 3D modeling in SolidWorks, appropriate simplification is performed based on the cutterhead simplification principle without affecting the actual operation. The simplified model is as follows: Figure 2 As shown, it includes a cutter head and a cutter system. Both the cutter head and the cutter system are arranged at the head of the shield machine. The cutter system includes double-edged cutters and single-edged cutters. Figure 3 and Figure 4 As shown;

[0060] Step 2: Perform static analysis on the cutterhead structure. The static analysis includes force F analysis, torque T analysis, and thrust Z analysis.

[0061] The force F is the force exerted by the cutter system on the cutter head and the tunnel face when the shield machine is tunneling. The cutter system is subjected to the force exerted by the rock on itself, including the positive thrust F in the same direction as the tunneling direction. v , rolling force F perpendicular to the excavation direction r , lateral force F generated by cutterhead vibration s ,like Figure 5 The specific expression is as follows:

[0062] F=F v +F r +F s .

[0063] The torque force T is caused by the friction resistance of the cutterhead and the resistance of the cutter system when cutting the soil. Specifically, it includes the friction resistance torque T1 between the front of the cutterhead and the soil layer; the friction resistance torque T2 between the back of the cutterhead and the soil in the soil bin; the friction resistance torque T3 between the side of the cutterhead and the soil layer; and the resistance torque T4 of the soil layer during cutting. The specific expression of the torque force T is as follows:

[0064] T=T1+T2+T3+T4.

[0065] The friction resistance torque T1 between the front of the cutterhead and the soil layer is generated when the cutterhead cuts the soil layer. The cutting action of the tool will generate soil resistance. At the same time, the contact surface between the cutterhead and the excavated soil will generate friction, thereby generating friction resistance torque. The specific expression is as follows:

[0066]

[0067] Where k is the lateral pressure coefficient of the soil layer; f is the friction coefficient of the soil layer; γ is the gravity density of the soil, in kN / m 3 H is the depth from the shield machine axis to the ground, in meters; D is the cutterhead diameter, in meters; in the actual calculation of friction resistance torque, the contact area between the cutterhead and the ground is taken into account, and the opening ratio ζ is introduced. The friction resistance torque T1 between the front of the cutterhead and the soil layer is expressed as:

[0068]

[0069] The front area of ​​the cutterhead is 12.6m 2 The opening ratio is 35%. The specific values ​​of its parameters are shown in Table 1:

[0070] Table 1 Parameter values ​​used to calculate torque T1

[0071] f γ k H ζ D 0.4 <![CDATA[23kN / m 3 ]]> 0.42 2.8m 0.35 6m

[0072] The friction resistance torque T2 between the back of the cutterhead and the soil in the soil bin is generated when the shield machine advances forward. The soil enters the soil bin from the opening of the cutterhead and is not completely filled. In addition, the fluidity of the soil is enhanced by the action of the stirring rod. The friction coefficient between the soil in the soil bin and the back of the cutterhead is smaller than the friction coefficient between the soil layer and the front of the cutterhead. Therefore, the specific calculation expression of the friction resistance torque T2 between the back of the cutterhead and the soil in the soil bin is as follows:

[0073]

[0074] Among them, k1 is the adjustment coefficient. The specific values ​​of its parameters are shown in Table 2:

[0075] Table 2 Parameter values ​​used to calculate torque T2

[0076] f γ k H D <![CDATA[k1]]> 0.4 <![CDATA[23kN / m 3 ]]> 0.42 2.8m 6m 0.8

[0077] The friction resistance torque T3 between the cutterhead side and the soil layer is when the cutterhead diameter is set larger than the front shield diameter. During the excavation process, the cutterhead side is subjected to the friction resistance torque from the soil layer. When calculating, the vertical soil pressure and lateral soil pressure on the cutterhead side are decomposed and converted into the positive pressure acting on the cutterhead side surface. The specific calculation expression is as follows:

[0078]

[0079] Where W is the width of the cutter head side, in meters. The specific values ​​of its parameters are shown in Table 3:

[0080] Table 3 Parameter values ​​used to calculate torque T3

[0081] f γ k H D W 0.4 <![CDATA[23kN / m 3 ]]> 0.42 2.8m 6m 0.7m

[0082] The soil resistance torque T4 during tool cutting is generated when the cutterhead rotates to overcome the soil shear force. The specific expression is as follows:

[0083]

[0084] Where q u is the uniaxial compressive strength of the soil layer, in kN / m 2 ;μ max is the maximum tunneling speed of the shield machine, in m / min; ω is the cutterhead speed, in r / min; the uniaxial compressive strength of the soil layer refers to the ultimate bearing capacity of the soil sample when it fails under uniaxial force, expressed as the maximum bearing capacity per unit area. The specific parameters are shown in Table 4:

[0085] Table 4 Parameter values ​​used to calculate torque T4

[0086] D <![CDATA[μ max ]]> <![CDATA[q u ]]> ω 6m 0.08m / min <![CDATA[4600kN / m 2 ]]> 0.7r / min

[0087] In actual engineering practice, these four torques account for 95% of the total torque of the cutter head. According to a lot of engineering experience, the remaining torques can be ignored.

[0088] The thrust Z is the resistance to overcome the cutterhead rotation process, including the front thrust resistance of the cutterhead, the friction resistance between the outer side of the shield machine and the soil layer, and the cutting resistance of the tool. The specific expression is as follows:

[0089]

[0090] Where P is the empirical thrust per unit excavation surface, generally 1000~1300kN / m 2According to an empirical formula, the cutterhead thrust of a 6m diameter shield machine is at least 28,274kN. However, based on the selected cutter specifications and a maximum rock-breaking load of 300 MPa per cutter, the maximum thrust the cutterhead can withstand is 12,000 kN, far less than the thrust calculated by the empirical formula. However, exceeding this maximum thrust will cause the actual rock-breaking load borne by the cutter during operation to exceed the maximum rock-breaking load of 300 MPa. If the actual rock-breaking load borne by the cutter exceeds the maximum rock-breaking load, it may damage or destroy the cutter, and may even cause the cutterhead to malfunction or shut down. Therefore, when designing and operating a shield machine, it is necessary to strictly adhere to the maximum rock-breaking load limit of the cutter and avoid overloading to ensure normal operation and extend the equipment life. Therefore, in this experiment, the cutterhead thrust was set based on the maximum rock-breaking load that the cutter can withstand.

[0091] Step 3: Use the finite element analysis software Ansys workbench to perform finite element static analysis on the cutterhead; the specific process is as follows:

[0092] S31. Establish a finite element model: Convert the actual engineering structure into a finite element model, import the cutterhead 3D model from SolidWorks into ANSYS Workbench software and establish a model that can be recognized by the finite element analysis software;

[0093] S32. Material selection: Describe the materials and mechanical properties in the model, including elastic modulus, Poisson's ratio, and thermal expansion coefficient;

[0094] S33. Meshing: Divide the finite element model into many small units (such as triangles, quadrilaterals, hexahedrons, etc.). Appropriate mesh sizes should be selected for different engineering structures to avoid distortion in simulation experiments.

[0095] S34, Apply boundary conditions: Set constraints and loads on the model, including fixed boundary conditions, moments, and contact stresses;

[0096] S35. Result calculation and analysis: Run the software to perform finite element analysis to obtain strain and stress.

[0097] Finite element analysis software was used to perform finite element static calculations on the cutterhead, determining the load distribution and the location of the cutterhead's critical points. The 3D cutterhead model was imported from SolidWorks into ANSYS Workbench software for finite element static calculations. The physical parameters of the TBM cutterhead material, Q345D, are: yield strength 345 MPa, density ρ = 7850 kg / m 3, Poisson's ratio ν = 0.3, elastic modulus = 210GPa. Where D means that the V-notch impact test energy of the material at -20℃ is greater than 27J. The cutterhead finite element model panel has a diameter of 6.6m, 4 double-edged center hobs, 23 single-edged hobs, and the model is divided into tetrahedral elements. The total number of nodes is 2512975 and the total number of elements is 1587130. Figure 6 As shown in the figure, the meshing accuracy is very high and the model is relatively complex. Then solve the problem and get the total deformation, elastic strain and stress, and load result diagram, as shown in the figure. Figure 7 As shown in the figure, the maximum stress of the cutterhead structure is 5.73Mpa, located at the maximum deformation of the cutterhead block. The maximum deformation of the cutterhead is 0.082673mm, located on the side of the cutterhead. The maximum deformation along the axis is 3% of the cutterhead thickness. In summary, it can be considered that the design of the shield machine cutterhead meets the requirements.

[0098] Step 4: Compress the initial load. The compressed data is as follows: Figure 8 As shown. Using MATLAB software to program, the rain flow counting method is used on the compressed data to obtain the relationship between the mean, amplitude and number of cycles as shown below. Figure 9 In order to verify that the load amplitude-frequency relationship in each direction conforms to the two-parameter Weibull distribution, MATLAB software is used to write a Weibull distribution program to test the rationality of the amplitude sample, and also to verify the rationality of the load obtained by simulation. The results are shown in Figure 10 As shown. Analyzing the test graph, the data points are distributed along the Weibull distribution fitting curve, proving the rationality of the data. The Weibull distribution expression is as follows:

[0099]

[0100] Where x is a random variable representing the life or failure time of a product; λ is a scale parameter, which usually represents the mean life of the distribution; k is a shape parameter, which is used to describe the shape of the distribution.

[0101] Step 5: Correct the obtained data, which includes straight line correction and curve correction. The specific expression is as follows:

[0102] Straight line correction:

[0103]

[0104] Curve correction:

[0105]

[0106] Among them, S a is the stress amplitude; S m is the mean stress; S -1 is the stress value when the stress ratio is –1; Su is the yield stress;

[0107] Then, the fatigue tool in Ansys Workbench is used for calculation, and the minimum fatigue life of the cutterhead is obtained using the Miner criterion. The specific expression of the Miner criterion is as follows:

[0108]

[0109] where N i Table 1 shows the actual number of cycles of the i-th load cycle, It represents the theoretical fatigue life of the material under the same load cycle. According to the Miner criterion, the minimum fatigue life of the cutter head is 401580 times, that is, the fatigue life of the cutter head danger point is 401580 times. The cutter head fatigue life cloud diagram is as follows: Figure 11 shown.

[0110] Therefore, the present invention adopts the aforementioned shield machine cutterhead fatigue life prediction method. A three-dimensional model of the shield cutterhead is created using SolWorks software. Finite element analysis is then performed on the cutterhead using Ansys Workbench software. By setting material parameters, meshing, adding loads, and setting boundary conditions, the total deformation, elastic strain, and stress, as well as load results, are obtained for the cutterhead under specific operating conditions. Finally, rainflow counting is performed using MATLAB software, and data is obtained using a Weibull distribution. A modified SN curve is generated in Ansys, and the cutterhead fatigue life is calculated using the Miner criterion.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for predicting the fatigue life of a shield machine cutterhead, characterized in that: The following steps are involved: Step 1: Use Solid Works to perform three-dimensional modeling according to the cutterhead structure, including a cutterhead body and a roller cutter system, wherein the cutterhead body and the roller cutter system are both arranged at the head of the shield machine, and the roller cutter system includes a double-edged roller cutter and a single-edged roller cutter; Step 2: Perform static analysis on the cutter head structure, including force F analysis, torque T analysis and thrust Z analysis; Step 3: Use finite element analysis software Ansys workbench to perform finite element static analysis on the cutterhead; Step 4: compress the initial load, compress the data using the MATLAB software programming method, and then use the MATLAB software to program the compressed data using the rain flow counting method to obtain the relationship between the mean, amplitude and number of cycles, and obtain the data through Weibull distribution; Step 5: The corrected data is then brought into the fatigue tool in Ansys workbench for calculation. The minimum fatigue life of the cutterhead is obtained by the Miner criterion. The specific expression of the Miner criterion is as follows: Where N i Table 1 shows the actual number of cycles of the i-th load cycle, It represents the theoretical fatigue life of the material under the same load cycle; The correction in step 5 includes straight line correction and curve correction. The specific expression is as follows: Straight Line Correction: Curve correction: Among them, S a is the stress amplitude; S m is the stress mean; S -1 is the stress value when the stress ratio is –1; S u is the yield stress.

2. A method for predicting the fatigue life of a shield machine cutterhead according to claim 1, characterized in that: The force F is the force of the rock on the cutter system when the shield machine is excavating. The cutter system on the cutter head interacts with the tunnel face to cut and rotate, and also supports the tunnel face. The cutter system is subjected to the force of the rock on itself, including the positive thrust F in the same direction as the excavation direction. v , rolling force F perpendicular to the excavation direction r , the lateral force F generated by the vibration of the cutter head s， The specific expression is as follows: F=F v +F r +F s 。 3. A method for predicting the fatigue life of a shield machine cutterhead according to claim 2, characterized in that: The torque force T is caused by the friction resistance of the cutter disc and the resistance of the roller cutter system when cutting the soil, including the friction resistance torque T1 between the front of the cutter disc and the soil layer; the friction resistance torque T2 between the back of the cutter disc and the soil in the soil bin; the friction resistance torque T3 between the side of the cutter disc and the soil layer; and the resistance torque T4 of the soil layer when the tool is cutting. The specific expression of the torque force T is as follows: T=T1+T2+T3+T4.

4. A method for predicting the fatigue life of a shield machine cutterhead according to claim 3, characterized in that: The friction resistance torque T1 between the front of the cutterhead and the soil layer is that when the cutterhead cuts the soil layer, the cutting action of the tool will generate soil resistance. At the same time, the contact surface between the cutterhead and the excavated soil will generate friction, thereby generating friction resistance torque. The specific expression is as follows: Where k is the lateral pressure coefficient of the soil layer; f is the friction coefficient of the soil layer; γ is the gravity density of the soil, in kN / m 3 ; H is the depth from the axis of the shield machine to the ground, in m; D is the cutterhead diameter, in m; In the actual calculation of friction resistance torque, the contact area between the cutterhead and the ground is taken into account, and the opening ratio ζ is introduced. Then the friction resistance torque T1 between the front of the cutterhead and the soil layer is expressed as:

5. A method for predicting the fatigue life of a shield machine cutterhead according to claim 4, characterized in that: The friction resistance torque T2 between the back of the cutter disc and the soil in the soil bin is that when the shield machine is moving forward, the slag enters the soil bin from the opening of the cutter disc and is not completely filled; in addition, under the action of the stirring rod, the fluidity of the slag is enhanced, and the friction coefficient between the soil in the soil bin and the back of the cutter disc is smaller than the friction coefficient between the soil layer and the front of the cutter disc. Therefore, the specific calculation expression of the friction resistance torque T2 between the back of the cutter disc and the soil in the soil bin is as follows: Among them, k1 is the adjustment coefficient.

6. A method for predicting the fatigue life of a shield machine cutterhead according to claim 5, characterized in that: The friction torque T3 between the cutter head side and the soil layer is that the cutter head diameter is set larger than the front shield diameter. During the excavation process, the cutter head side is subjected to the friction torque from the soil layer. When calculating, the vertical soil pressure and lateral soil pressure on the cutter head side are decomposed and converted into the positive pressure acting on the cutter head side surface. The specific calculation expression is as follows: Where W is the width of the cutter disc side, in m.

7. A method for predicting the fatigue life of a shield machine cutterhead according to claim 6, characterized in that: The soil resistance torque T4 during tool cutting is generated when the cutterhead rotates to overcome the soil shear force. The specific expression is as follows: In the formula, q u is the uniaxial compressive strength of the soil layer, in kN / m 2 ; μ max is the maximum excavation speed of the shield machine, in m / min; ω is the cutterhead speed, in r / min.

8. A method for predicting the fatigue life of a shield machine cutterhead according to claim 7, characterized in that: The thrust Z is the resistance to overcome the cutterhead rotation process, including the front thrust resistance of the cutterhead, the friction resistance between the outer side of the shield machine and the soil layer, and the tool cutting resistance. The specific expression is as follows: Where P is the empirical thrust per unit excavation surface.

9. A method for predicting the fatigue life of a shield machine cutterhead according to claim 8, characterized in that: The specific process of step 3 is as follows: S31. Establish finite element model: convert the actual engineering structure into a finite element model, import the cutter head 3D model from Solidworks into ANSYS Workbench software and establish a model recognized by finite element analysis software; S32. Material selection: Describe the materials and mechanical properties in the model, including elastic modulus, Poisson's ratio, and thermal expansion coefficient; S33, Meshing: Divide the finite element model into many small units; S34, Apply boundary conditions: Constrain and set loads for the model, including fixed boundary conditions, moments, and contact stresses; S35. Result calculation and analysis: Run the software to perform finite element analysis to obtain strain and stress.

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