Crane girder fatigue analysis method

Abstract

The invention discloses a crane main beam fatigue analysis method which comprises the following steps: establishing a crane main beam three-dimensional model, and establishing a grid model of a crane main beam; statics analysis is carried out on the main beam, and a stress-strain distribution cloud picture of the main beam under the full-load working condition is obtained; searching an area with relatively large stress, determining a dangerous point position, and extracting dangerous point stress-strain data; calculating the strain energy density on any plane by using a coordinate transformation principle; solving a strain energy stagnation point function to determine the position of a critical plane; estimating the fatigue life by using an approximate S-N curve; according to the actual situation, stress correction is conducted on the stress; and finally, the reasonable fatigue life of the crane girder is obtained. According to the method, the fatigue life of the crane girder is pre-estimated by adopting a critical plane method, so that the more accurate fatigue life is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of crane fatigue data processing, and particularly relates to a crane girder fatigue analysis method. BACKGROUND

[0002] With the rapid development of China, cranes are widely used in the fields of port transportation, railway transportation, mining and metallurgy. The crane has a large working load, and once the crane is damaged, a major safety accident will occur. However, sometimes even if the stress value does not exceed the strength limit of the material, the crane may still have a damage phenomenon, i.e. fatigue damage. Fatigue damage is one of the most common failure modes of the crane girder, so when the crane is detected, the fatigue life of the girder needs to be calculated through fatigue analysis to ensure the normal working time.

[0003] The commonly used method in engineering is the traditional Miner rule. The Miner rule simplifies the damage curve into a straight line, considers that the relationship between fatigue damage and cycles can be represented by a linear relationship, and is linearly superimposed. The Miner rule assumes that the stresses are independent of each other, and the cumulative damage gradually increases, and when the critical fatigue damage value is reached, the material will have fatigue failure.

[0004] Since the Miner rule greatly simplifies the identification of the fatigue damage mechanism, the influence of low load is ignored, and fatigue failure is considered to occur only when the load exceeds the fatigue limit. The accuracy of the calculation results of the Miner rule is low due to the contradiction between some assumptions and the actual engineering situation. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the background art, and to provide a crane girder fatigue analysis method which can quickly and accurately complete stress analysis and fatigue analysis of the girder to obtain the fatigue analysis results of the girder.

[0006] The technical scheme of the present application is: a crane girder fatigue analysis method, comprising the following steps:

[0007] (1) a three-dimensional model is established according to the actual shape and size of the crane girder, a network model of the girder is established by the finite element method, and the girder parameters including material, span, upper and lower flange width, upper and lower flange thickness, web thickness and height, web distance are set, and after the setting is completed, the model is meshed;

[0008] (2) statics simulation of the crane girder under full load and empty load conditions is performed, and the statics deformation, stress and strain analysis nephogram corresponding to the actual working condition are obtained;

[0009] (3) Based on the deformation, stress, and strain cloud diagrams from step (2), locate the dangerous locations of the crane during operation, extract the stress and strain state of the dangerous point section, and obtain the stress curve in that area.

[0010] (4) Conduct an experiment on the main beam of the crane under standard working conditions, observe and compare whether the information on the dangerous position of the main beam is similar to the stress analysis cloud diagram described in step (2), and then compare the stress curve obtained in step (3) with the stress curve obtained by actual measurement; if there is a significant deviation between the two, return to step (2) and reset the constraints and basic conditions in step (2) until the calculated stress curve is close to the stress curve obtained by the actual working condition experiment.

[0011] (5) Based on the stress and strain of the critical point in step (4), use the coordinate transformation formula And the strain energy density energy function, to determine the location of the critical surface, where M is the rotation angle θ around the original coordinate system X and Y axes and The obtained continuous transformation matrix; coordinate transformation: the stress σ in the original coordinate system is strain ε is Using coordinate transformation matrix We obtain the stress tensor σ′ and strain tensor ε′ on any plane passing through the critical point, i.e., σ′=M T σM, ε′=M T εM; Determining the location of the critical surface: Under triaxial stress, the formula for calculating strain energy density is as follows: σ1, σ2, and σ3 represent the first, second, and third principal stresses, respectively; ε1, ε2, and ε3 represent the first, second, and third principal strains, respectively; the formula for calculating the strain energy density within the linear elastic range is: E is the elastic modulus of the material, μ is the Poisson's ratio, and G is the shear modulus. Using this formula, the energy function with strain energy density as the damage parameter after coordinate transformation is obtained. right By taking the partial derivative with θ, we obtain information about stationary points and the maximum and minimum values ​​of the function, determine the location of the critical surface, and obtain the stress matrix of the critical surface. And according to the formula Obtain equivalent stress

[0012] (6) Based on the critical surface obtained in step (5), determine the stress condition at that location, and use the approximate SN curve S m ·N=C and Goodman's stress correction equation Fatigue calculations were performed on the main beam.

[0013] The main beam parameters include material properties, density, and elastic modulus.

[0014] If, in step (4), the constraints and solution factors have been reset but the error between the measured data and the actual situation still cannot be reduced, then the shape, size parameters and mesh parameters of the three-dimensional model in step (1) are adjusted, and step (2) is returned to repeat.

[0015] Compared with existing technologies, this invention employs a relatively mature static analysis method, and it is easier to obtain accurate stress results under the uniform speed condition of the main beam. This invention is more applicable to high-cycle fatigue in applications such as cranes, and the selection of strain energy density as a damage parameter helps to improve the accuracy of the analysis and calculation results. Attached Figure Description

[0016] Figure 1 This is a flowchart of the fatigue analysis method for the main beam of a crane according to the present invention. Detailed Implementation

[0017] This embodiment describes a fatigue analysis method for a crane main beam. See also... Figure 1 The fatigue analysis method for the main beam of the crane in this embodiment includes the following steps:

[0018] (1) Establish a three-dimensional model based on the actual shape and size of the crane main beam, establish a network model of the main beam using the finite element method, and set the main beam parameters including material, span, upper and lower flange width, upper and lower flange thickness, web thickness and height, and web distance. After setting, mesh the model.

[0019] An initial state model is established based on the main beam drawings, and the material properties of the main beam are set accordingly. In this embodiment, the material is Q235B, and the material properties are shown in Table 1.

[0020] Table 1

[0021]

[0022] Mesh model: Based on the shape characteristics of the model and the possible large stress areas, the mesh is optimized in a targeted manner. The mesh size is selected as 20mm, and the number of meshes is controlled to not exceed 200,000 as much as possible to ensure the accuracy of finite element analysis while also having a fast calculation speed.

[0023] (2) Perform static simulation of the main beam of the crane under full load to obtain the deformation, stress and strain analysis cloud diagrams corresponding to the actual working conditions.

[0024] Static simulation of the main beam was performed using ANSYS software or SOLIDWORKSSimulation. Under full load conditions, the deformation, stress, and strain analysis contour plots of the main beam were obtained.

[0025] (3) Based on the deformation, stress, and strain cloud diagrams from step (2), locate the dangerous locations of the crane during operation, extract the stress and strain state of the dangerous point section, and obtain the stress curve in that area.

[0026] (4) Conduct an experiment on the main beam of the crane under standard working conditions, observe and compare whether the information on the dangerous position of the main beam is similar to the stress analysis cloud diagram described in step (2), and then compare the stress curve obtained in step (3) with the stress curve obtained by actual measurement; if there is a significant deviation between the two, return to step (2) and reset the constraints and basic conditions in step (2) until the calculated stress curve is close to the stress curve obtained by the actual working condition experiment.

[0027] (5) Based on the stress and strain of the critical point in step (4), use the coordinate transformation formula And the strain energy density energy function, to determine the location of the critical surface, where M is the rotation angle θ around the original coordinate system X and Y axes and The resulting continuous transformation matrix;

[0028] Coordinate transformation: The stress σ in the original coordinate system is strain ε is Using coordinate transformation matrix We obtain the stress tensor σ′ and strain tensor ε′ on any plane passing through the critical point, i.e., σ′=MTσM, ε′=M T εM;

[0029] Determining the location of the critical surface: Under triaxial stress, the formula for calculating strain energy density is as follows: σ1, σ2, and σ3 represent the first, second, and third principal stresses, respectively, and ε1, ε2, and ε3 represent the first, second, and third principal strains, respectively. The formula for calculating the strain energy density within the linear elastic range is as follows:

[0030] E is the elastic modulus of the material, μ is the Poisson's ratio, and G is the shear modulus. Using this formula, the energy function with strain energy density as the damage parameter after coordinate transformation is obtained. right By taking the partial derivative with θ, we obtain information about stationary points and the maximum and minimum values ​​of the function, determine the location of the critical surface, and obtain the stress matrix of the critical surface. And according to the formula Obtain equivalent stress

[0031] (6) Based on the critical surface obtained in step (5), determine the stress condition at that location, and use the approximate SN curve S m ·N=C and Goodman's stress correction equation Fatigue calculations were performed on the main beam.

[0032] Fatigue analysis: using the approximate SN curve formula S m The relationship between the number of cycles and stress is obtained by N = C, and the Goodman stress correction equation is applied. S in the formula can be obtained from the stress level in actual work. a(R＝-1) Combining these two factors allows us to obtain the fatigue life of the crane's main beam and prove whether the crane meets fatigue design requirements. (In the approximate SN curve formula, S represents the stress level, and m and C are parameters related to material, stress ratio, loading method, etc.) u For tensile strength; S in the stress correction equation a =(S max -S min ) / 2, S m =(S max +S min ) / 2, S max and S min These represent the maximum and minimum equivalent stresses at the critical point of the critical surface.

Claims

1. A fatigue analysis method for a crane main beam, characterized in that, Includes the following steps: (1) Establish a three-dimensional model based on the actual shape and size of the crane main beam, establish a network model of the main beam using the finite element method, and set the main beam parameters including material, span, upper and lower flange width, upper and lower flange thickness, web thickness and height, and web distance. After setting, mesh the model. (2) Static simulation of the main beam of the crane under full load and no load conditions was carried out to obtain the deformation, stress and strain analysis cloud diagrams corresponding to the actual working conditions. (3) Based on the deformation, stress, and strain cloud diagrams of step (2), find the dangerous location of the crane during the working process, extract the stress and strain state of the dangerous point section, and obtain the stress curve in the area. (4) Conduct an experiment on the main beam of the crane under standard working conditions, observe and compare whether the information on the dangerous position of the main beam is similar to the stress analysis cloud diagram described in step (2), and then compare the stress curve obtained in step (3) with the stress curve obtained by actual measurement; if there is a significant deviation between the two, return to step (2) and reset the constraints and basic conditions in step (2) until the calculated stress curve is close to the stress curve obtained by the actual working condition experiment. (5) Based on the stress and strain of the critical point in step (4), use the coordinate transformation formula And the strain energy density energy function, to determine the location of the critical surface, where M is the rotation angle θ around the original coordinate system X and Y axes and The obtained continuous transformation matrix; coordinate transformation: the stress σ in the original coordinate system is strain ε is Using coordinate transformation matrix We obtain the stress tensor σ′ and strain tensor ε′ on any plane passing through the critical point, i.e., σ′=M T σM, ε′=M T εM; Determining the location of the critical surface: Under triaxial stress, the formula for calculating strain energy density is as follows: σ1, σ2, and σ3 represent the first, second, and third principal stresses, respectively; ε1, ε2, and ε3 represent the first, second, and third principal strains, respectively; the formula for calculating the strain energy density within the linear elastic range is: E is the elastic modulus of the material, μ is the Poisson's ratio of the material, and G is the shear modulus of the material; This formula is used to obtain the energy function after coordinate transformation, with strain energy density as the damage parameter. right By taking the partial derivative with θ, we obtain information about stationary points and the maximum and minimum values ​​of the function, determine the location of the critical surface, and obtain the stress matrix of the critical surface. And according to the formula Obtain equivalent stress (6) Based on the critical surface obtained in step (5), determine the stress condition at that location, and use the approximate SN curve S m • N = C and Goodman's stress correction equation Fatigue calculations were performed on the main beam.

2. The fatigue analysis method for a crane main beam according to claim 1, characterized in that, The main beam parameters mentioned in step (1) include material properties, density, and elastic modulus.

3. The fatigue analysis method for a crane main beam according to claim 1, characterized in that, If, in step (4), the constraints and solution factors have been reset but the error between the measured data and the actual situation still cannot be reduced, then the shape, size parameters and mesh parameters of the three-dimensional model in step (1) are adjusted, and step (2) is returned to repeat.

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