Ansys-based method for predicting fatigue performance of cutterhead under composite stratum

Abstract

The invention relates to the technical field of engineering finite element simulation, in particular to an Ansys-based method for predicting the fatigue performance of a cutterhead under a composite stratum. According to the method, the finite element model of the shield tunneling machine cutterhead under the composite stratum is established, the dynamic stress states (such as cutting force, propulsive force and torque) of the cutterhead under alternation of soft soil and hard rock are accurately simulated, and stress amplitudes and equivalent alternating stress under different working conditions are quantified in combination with an S-N curve and a Goodman criterion. According to the method, the crack initiation position coordinates and the fatigue life distribution can be efficiently and precisely predicted, and a reliable scheme is provided for cutter head maintenance.

Description

Technical Field

[0001] The present application relates to the technical field of engineering finite element simulation, and in particular to an Ansys-based method for predicting fatigue performance of a cutterhead under a composite formation. Background Art

[0002] The cutterhead of a shield machine is one of its core components, directly impacting construction efficiency. Tunneling projects operate in a complex and ever-changing environment, and any issues with the cutterhead can slow progress or even cause serious accidents. Diagnosing the cutterhead's operating status is crucial for ensuring normal operation. Regular cutterhead diagnostics can effectively and promptly identify and resolve cutterhead issues, ensuring proper operation.

[0003] Existing cutterhead wear prediction technologies are mostly based on historical data and model analysis. However, their quality is limited by data quality and model accuracy, leading to discrepancies between the predicted results and actual tunneling conditions. Accurate prediction requires extensive field data on strata, but collecting this data in real time is challenging because vibration signals are easily affected by factors such as geology, operating conditions, and material properties. Furthermore, signal transmission is susceptible to interference and noise. Summary of the Invention

[0004] This application provides an Ansys-based method for predicting the fatigue performance of the cutterhead in composite formations. Based on the accuracy of finite element software, it can simulate the stress state, stress and deformation of the shield machine cutterhead under different working conditions, and then accurately predict the fatigue performance of the cutterhead.

[0005] The technical solution of this application is as follows: A method for predicting fatigue performance of a cutterhead in a composite formation based on Ansys includes the following steps: S1. Establish a finite element model of the cutterhead in Ansys; S2. defining external loads, cutting forces, thrust forces and torques, as well as formation parameters of various formations in the finite element model of the cutterhead; S3, with the center of the cutterhead as the center of the circle, add a circular surface imprint whose area changes dynamically according to the proportion of the stratum, so as to load the front thrust and torque caused by each type of stratum to the surface imprint; S4, set boundary conditions, divide the mesh, and perform finite element simulation according to the loading mode; S5. Extract the stress amplitude and fatigue life of the nodes at the stress concentration area and fatigue sensitive position from the finite element simulation results to obtain the SN curve of the cutterhead; S6. Calculate the equivalent alternating stress based on the average stress at the stress concentration area and fatigue sensitive position and according to the Goodman criterion; S7. According to the equivalent alternating stress, the SN curve is consulted to obtain the number of cycles as the characterization of the cutter head life. The node coordinates corresponding to the maximum equivalent alternating stress are used as the crack initiation point, and the coordinates are mapped to the actual position of the cutter head through the coordinates.

[0006] Furthermore, the strata in step S2 include soft soil strata and hard rock strata; The elastic modulus of soft soil is in the range of 20~200MPa, Poisson's ratio is 0.3~0.4, cohesion is 5~50kPa, internal friction angle is 10°~25°, and damping ratio is 5%~10%; The elastic modulus of hard rock formations ranges from 500 to 1000 MPa, the Poisson's ratio is 0.15 to 0.25, the cohesion is 100 to 500 kPa, the internal friction angle is 30° to 45°, and the damping ratio is 2% to 5%.

[0007] Furthermore, in step S3, the frontal thrust and torque are loaded onto the surface imprint in the form of dynamic loads. The dynamic load is implemented based on a time-varying load function. The frontal thrust varies in the range of 1.2 MPa to 1.8 MPa, and the torque varies in the range of 30,000 KN·m to 40,000 KN·m.

[0008] Furthermore, in step S3, the dynamic variation rule of the frontal thrust and torque applied to the circular surface imprint is determined according to the weighted ratio of the soft soil stratum and the hard rock stratum; The loading caused by the soft soil stratum covers the circular surface imprint concentrically with the center of the circular surface imprint according to the weighted proportion of the soft soil stratum, and the remaining uncovered area is covered by the loading caused by the hard rock stratum.

[0009] Furthermore, in step S4, the cutter head spoke roots, tool mounting holes, flange connection surfaces, and opening edges are meshed with encrypted meshes, while the remaining positions of the cutter head are meshed with unencrypted meshes.

[0010] Furthermore, in step S6, the stress concentration areas include the roots of the cutter disc spokes, the circumference of the cutter mounting holes, and the weld joints; Fatigue-sensitive locations include grain boundaries in high-strength steels and heat-affected zones in welds.

[0011] Furthermore, in step S6, the calculation method of the equivalent alternating stress is as follows: In step S6, the calculation method of the equivalent alternating stress is as follows: The cutterhead material is subjected to a standard fatigue test using a fatigue testing machine to obtain the number of cycles N under different stress amplitudes Δσ; Using the power function formula , fitting the experimental data; In the above formula, represents fatigue life, C represents the intercept of the SN curve, and m represents the slope of the SN curve; Correction of equivalent alternating stress based on mean stress: ; Where, Indicates the maximum bearing stress of the material tensile test, represents the mean stress.

[0012] Due to the adoption of the above technical solution, the beneficial effects of this application are as follows: 1. This application establishes a finite element model of a shield machine cutterhead in composite strata, accurately simulating the dynamic stresses (such as cutting force, thrust, and torque) experienced by the cutterhead under alternating soft soil and hard rock conditions. Combining the SN curve with the Goodman criterion, this method quantifies stress amplitudes and equivalent alternating stresses under different operating conditions. This method efficiently and accurately predicts crack initiation location coordinates and fatigue life distribution, providing a reliable solution for cutterhead maintenance.

[0013] 2. This application uses dynamic loading to map composite stratum parameters to the cutterhead surface imprint, and supports adjusting the loading area based on stratum proportions. This technical solution allows for flexible simulation of sudden stratum changes or mixed conditions during actual tunneling, resolving the inability of traditional static models to reflect dynamic load changes and ensuring simulation results are closer to real-world construction scenarios.

[0014] 3. In terms of the balance between computational accuracy and efficiency, this application adopts a differentiated meshing strategy (encrypted meshes at the spoke roots and tool mounting holes, and non-encrypted meshes in other areas) to reduce the overall number of meshes while ensuring high-precision analysis of stress concentration areas in key locations.

[0015] 4. Unlike traditional methods that rely on a large number of field parameters, this method directly obtains cutterhead stress gradient and fatigue life data based on finite element simulation, eliminating the need for complex real-time signal acquisition and processing, reducing the difficulty of data acquisition and equipment costs. It is particularly suitable for engineering scenarios with complex geological conditions or limited data acquisition.

[0016] 5. This application provides evidence to support cutterhead maintenance. The accuracy of finite element software has been accepted by various industries. Fatigue life prediction and crack initiation location analysis based on finite element models can identify and warn weak areas of the cutterhead (such as the spoke roots or high stress gradient areas) in advance, and formulate targeted prevention plans. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings described herein are used to provide further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0018] Figure 1Finite element model established for the embodiment of the present application; Figure 2 This is the loaded finite element model in the embodiment of the present application; Figure 3 This is the stress-strain cloud diagram of the finite element model in the embodiment of this application. DETAILED DESCRIPTION

[0019] Based on the background technology, this application provides a method for predicting the fatigue performance of the cutterhead under composite formation based on Ansys. Figure 1 , including the following steps: S1. Create a finite element model of the cutterhead in Ansys. Generally, when creating a finite element model, the mechanical model needs to be simplified.

[0020] S2. defining external loads, cutting forces, thrust forces and torques, as well as formation parameters of various formations in the finite element model of the cutterhead; The strata in step S2 include soft soil strata and hard rock strata; The elastic modulus of soft soil is in the range of 20~200MPa, Poisson's ratio is 0.3~0.4, cohesion is 5~50kPa, internal friction angle is 10°~25°, and damping ratio is 5%~10%; The elastic modulus of hard rock formations ranges from 500 to 1000 MPa, the Poisson's ratio is 0.15 to 0.25, the cohesion is 100 to 500 kPa, the internal friction angle is 30° to 45°, and the damping ratio is 2% to 5%.

[0021] S3. With the center of the cutterhead as the center of the circle, add a circular surface imprint whose area changes dynamically according to the proportion of the stratum, so as to load the front thrust and torque caused by each type of stratum to the surface imprint.

[0022] See attached Figure 2 In step S3, the frontal thrust and torque are applied to the surface imprint as dynamic loads. The dynamic loads are implemented based on a time-varying load function. The frontal thrust varies between 1.2 MPa and 1.8 MPa, and the torque varies between 30,000 kN·m and 40,000 kN·m. The dynamic variation rule for the frontal thrust and torque applied to the circular surface imprint is determined based on the weighted ratio of the soft soil layer to the hard rock layer. The load caused by the soft soil layer concentrically covers the circular surface imprint at the center of the circular surface imprint according to the weighted ratio of the soft soil layer, and the remaining uncovered area is covered by the load caused by the hard rock layer. For example, when the ratio of the soft soil layer to the hard rock layer is 7:3, 70% of the area outward from the center of the circular surface imprint is loaded by the soft soil layer, and the remaining outer area is loaded by the hard rock layer.

[0023] In the specific implementation, the front of the cutterhead is divided into grid areas, and each area is independently bound to the formation type (soft soil / hard rock). According to the formation weight ratio, it is set as α Activate the corresponding number of soft soil areas, and load the remaining areas with hard rock parameters. Define the formation ratio variable (α) and the time / advance distance variable (t or d). Dynamically allocate loading areas using conditional statements. Create a time-stratum ratio table in Ansys Mechanical. For example, at 0 seconds, the soft soil ratio (α) is 100%, and the hard rock ratio (1-α) is 0%; at 600 seconds, the soft soil ratio (α) is 70%, and the hard rock ratio (1-α) is 30%. Read the α value at each time point to dynamically adjust the proportion of the area covered by the surface imprint. Use Named Selections to associate faces in different areas and activate loading proportionally. The key to dynamically adjusting loading areas lies in real-time allocation of load parameters to different cutterhead areas based on formation type and ratio. Through APDL programming, Tabular Data linkage, and surface imprinting technology, high-precision simulation of complex working conditions such as alternating soft and hard formations, varying mixing ratios, and localized mutations can be achieved.

[0024] S4. Set boundary conditions, divide the mesh, and perform finite element simulation according to the loading mode.

[0025] During the specific implementation, constraints such as the cutterhead support are set, and boundary conditions are adjusted according to the specific cutterhead application and working conditions.

[0026] In step S4, the cutterhead spoke roots, tool mounting holes, flange connection surfaces, and opening edges are meshed with encrypted meshes, while the remaining cutterhead positions are meshed with unencrypted meshes.

[0027] S5. Extract the stress amplitude and fatigue life of the nodes in the stress concentration area and fatigue sensitive position from the finite element simulation results to obtain the SN curve of the cutter head. In the specific implementation, the “Stress Tool” module can be used to extract the stress amplitude of the nodes. Δσ and mean stress σ m See attached Figure 3 , and obtain the cloud map after the finite element model is loaded.

[0028] S6. Calculate the equivalent alternating stress based on the average stress at stress concentration areas and fatigue-sensitive locations using the Goodman criterion. Stress concentration areas include the cutterhead spoke roots, the circumference of the cutter mounting holes, and weld joints. Fatigue-sensitive locations include grain boundaries in high-strength steel and the heat-affected zone of welds. Fatigue-sensitive locations have lower fatigue limits.

[0029] In step S6, the calculation method of the equivalent alternating stress is as follows: The cutterhead material is subjected to a standard fatigue test using a fatigue testing machine to obtain the number of cycles N under different stress amplitudes Δσ; Using the power function formula , fitting the experimental data; In the above formula, represents fatigue life, C represents the intercept of the SN curve, and m represents the slope of the SN curve.

[0030] C reflects the theoretical life of the material under a stress of 1 MPa, and m reflects the material's sensitivity to stress amplitude. The larger the value, the faster the life decreases with stress.

[0031] Correction of equivalent alternating stress based on mean stress: ; Where, Indicates the maximum bearing stress of the material tensile test, represents the mean stress.

[0032] S7. According to the equivalent alternating stress, the SN curve is consulted to obtain the number of cycles as the characterization of the cutter head life. The node coordinates corresponding to the maximum equivalent alternating stress are used as the crack initiation point, and the coordinates are mapped to the actual position of the cutter head through the coordinates.

[0033] Cycle count is used as a lifespan indicator. To ensure safety in engineering, a lifespan corresponding to a higher reliability is often used. In this case, the cycle count is much lower than the median life, making it a conservative estimate. The median life is the number of cycles required for fatigue failure in 50% of the specimens.

[0034] Anything not described in this application can be achieved by adopting or drawing on existing technologies.

[0035] The foregoing is merely an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should all be included within the scope of the claims of the present application.

Claims

1. A method for predicting cutterhead fatigue performance in composite formations based on Ansys, characterized in that: The following steps are involved: S1. Establish a finite element model of the cutterhead in Ansys; S2. defining external loads, cutting forces, thrust forces and torques, as well as formation parameters of various formations in the finite element model of the cutterhead; S3, with the center of the cutterhead as the center of the circle, add a circular surface imprint whose area changes dynamically according to the proportion of the stratum, so as to load the front thrust and torque caused by each type of stratum to the surface imprint; S4, set boundary conditions, divide the mesh, and perform finite element simulation according to the loading mode; S5. Extract the stress amplitude and fatigue life of the nodes at the stress concentration area and fatigue sensitive position from the finite element simulation results to obtain the SN curve of the cutterhead; S6. Calculate the equivalent alternating stress based on the average stress at the stress concentration area and fatigue sensitive position and according to the Goodman criterion; S7. According to the equivalent alternating stress, the SN curve is consulted to obtain the number of cycles as the characterization of the cutter head life. The node coordinates corresponding to the maximum equivalent alternating stress are used as the crack initiation point, and the coordinates are mapped to the actual position of the cutter head through the coordinates.

2. The method for predicting fatigue performance of cutterhead in composite formation based on Ansys according to claim 1, characterized in that: The strata in step S2 include soft soil strata and hard rock strata; The elastic modulus of soft soil is in the range of 20~200MPa, Poisson's ratio is 0.3~0.4, cohesion is 5~50kPa, internal friction angle is 10°~25°, and damping ratio is 5%~10%; The elastic modulus of hard rock formations ranges from 500 to 1000 MPa, the Poisson's ratio is 0.15 to 0.25, the cohesion is 100 to 500 kPa, the internal friction angle is 30° to 45°, and the damping ratio is 2% to 5%.

3. The method for predicting fatigue performance of cutterhead in composite formation based on Ansys according to claim 2, characterized in that: In step S3, the frontal thrust and torque are loaded onto the surface imprint in the form of dynamic loads. The dynamic load is implemented based on a time-varying load function. The frontal thrust varies in the range of 1.2 MPa to 1.8 MPa, and the torque varies in the range of 30,000 KN·m to 40,000 KN·m.

4. The method for predicting fatigue performance of cutterhead in composite formation based on Ansys according to claim 3, characterized in that: In step S3, the dynamic change rule of the frontal thrust and torque applied to the circular surface imprint is determined according to the weighted ratio of the soft soil layer and the hard rock layer; The loading caused by the soft soil stratum covers the circular surface imprint concentrically with the center of the circular surface imprint according to the weighted proportion of the soft soil stratum, and the remaining uncovered area is covered by the loading caused by the hard rock stratum.

5. The method for predicting fatigue performance of cutterhead in composite formation based on Ansys according to claim 1, characterized in that: In step S4, the cutterhead spoke roots, tool mounting holes, flange connection surfaces, and opening edges are meshed with encrypted meshes, while the remaining cutterhead positions are meshed with unencrypted meshes.

6. The method for predicting fatigue performance of cutterhead in composite formation based on Ansys according to claim 1, characterized in that: In step S6, the stress concentration areas include the roots of the cutter head spokes, the circumference of the cutter mounting holes, and the weld joints; Fatigue-sensitive locations include grain boundaries in high-strength steels and heat-affected zones in welds.

7. The method for predicting fatigue performance of cutterhead in composite formation based on Ansys according to claim 1, characterized in that: In step S6, the calculation method of the equivalent alternating stress is as follows: The cutter head material is subjected to a standard fatigue test using a fatigue testing machine to obtain the number of cycles under different stress amplitudes Δσ N ; Using the power function formula , fitting the experimental data; In the above formula, represents fatigue life, C represents the intercept of SN curve, m Indicates the slope of the SN curve; Correction of equivalent alternating stress based on mean stress: ； Where, Indicates the maximum bearing stress of the material tensile test, represents the mean stress.

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