Method for evaluating fatigue life of metal structure of bridge crane

Abstract

The invention belongs to the technical field of bridge cranes, and provides a bridge crane metal structure fatigue life evaluation method, which comprises the following steps: establishing a bridge crane simulation model through finite element software ANSYS according to a bridge crane structure, and respectively carrying out concentrated analysis on stress under a static working condition and a dynamic working condition to obtain the fatigue life of a bridge crane metal structure. The method comprises the following steps: determining a dangerous stress area, carrying out dominant analysis on stress components of the dangerous stress area under a static condition from a spatial distribution dimension of the stress components, and monitoring a uniaxial stress state of the dangerous stress area under the static condition. Deviation analysis is carried out through the multi-axis stress damage value of the dangerous stress area at the single-multi-axis change time point, the single-axis evaluation error is eliminated through multi-axis stress equivalent correction, and it is ensured that the fatigue life evaluation result is highly consistent with the actual stress damage rule of the structure.

Description

Technical Field

[0001] This invention belongs to the technical field of bridge cranes, specifically a method for assessing the fatigue life of the metal structure of a bridge crane. Background Technology

[0002] As a core piece of equipment for efficient material handling in industrial production and port logistics, bridge cranes rely on their metal structures (including main beams, end beams, and connecting nodes) as key load-bearing components. During long-term service, they must continuously withstand the alternating effects of static loads (such as structural self-weight, rated lifting capacity, and bolt preload) and dynamic loads (such as lifting impact inertia, trolley travel impact load, and braking impact load). Fatigue failure has become a major cause of metal structure fractures, equipment downtime, and even safety accidents. Therefore, accurate fatigue life assessment of their metal structures is a core technical requirement for ensuring long-term stable operation of equipment and mitigating safety risks.

[0003] Most methods only focus on the stress state (uniaxial or multiaxial) of the dangerous stress area under static conditions, without further monitoring the change law of stress state at each time point under dynamic conditions. In particular, they ignore the key phenomenon that dangerous stress areas under static conditions that are in a uniaxial stress state may transform into a multiaxial stress state under dynamic impact loads. Multiaxial stress can significantly accelerate crack initiation and propagation through stress superposition effect. This omission of stress state evolution directly leads to the inability of existing technology to accurately identify the key causes of fatigue damage, thus causing a distortion in the judgment of the "degree of correlation between stress state change and fatigue damage".

[0004] In the fatigue life calculation and safety assessment process, the error problem of existing technologies is particularly prominent: On the one hand, existing methods generally directly use uniaxial fatigue life assessment models (based on material SN curves) to analyze the structural life under multiaxial stress states, without using the critical plane equivalent method (such as the SWT criterion) to convert multiaxial stress into equivalent uniaxial stress for model correction, resulting in generally high life assessment results, seriously overestimating the safety margin of the structure, causing metal structures to fail prematurely in actual use.

[0005] Therefore, the present invention provides a method for evaluating the fatigue life of the metal structure of a bridge crane. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, at least one technical problem raised in the background art is solved.

[0007] This invention provides a method for assessing the fatigue life of the metal structure of a bridge crane, comprising: Based on the structure of the bridge crane, a simulation model of the bridge crane was established using the finite element software ANSYS. By conducting stress concentration analysis under static and dynamic conditions respectively, the critical stress area was identified. From the spatial distribution dimension of stress components, the stress components under static conditions of the critical stress area were analyzed to identify whether the critical stress area was under uniaxial stress or multiaxial stress under static conditions. Based on the uniaxial stress state under static conditions in the dangerous stress region, the uniaxial stress state under static conditions in the dangerous stress region is monitored to determine whether the uniaxial stress state changes to a multiaxial stress state when the dynamic condition analysis time point is reached. If the uniaxial stress state changes to a multiaxial stress state when the dynamic working condition analysis time point is reached, the deviation analysis is performed by the multiaxial stress damage value of the critical stress area at the time point of uniaxial-multiaxial change, and the correlation between the critical stress area changing from a uniaxial stress state to a multiaxial stress state and fatigue damage is evaluated. If the correlation between the change of the critical stress region from a uniaxial stress state to a multiaxial stress state and fatigue damage is close, the uniaxial fatigue life assessment method is modified by the critical plane equivalent method. Combined with Miner's linear damage accumulation theory, the fatigue life of the metal structure of the bridge crane is comprehensively assessed.

[0008] Preferably, the process of determining the hazardous stress area is as follows: The operating period of the bridge crane is divided into several analysis time points according to the same time interval. The finite element solution of the bridge crane simulation model is completed, and stress cloud diagrams are output at the analysis time points, including static stress cloud diagrams under static conditions and dynamic stress cloud diagrams under dynamic conditions. Static stress concentration regions and dynamic stress concentration regions are determined by static stress cloud diagrams and dynamic stress cloud diagrams. The spatial coordinates and geometric ranges of the static stress concentration region and the dynamic stress concentration region are obtained respectively. The Intersect function of ANSYS software is used to generate spatial intersection element groups of the static stress concentration region and the dynamic stress concentration region. The region corresponding to the spatial intersection element group is recorded as the critical stress region.

[0009] Preferably, the process of determining the static stress concentration region is as follows: Based on any static stress cloud map, the region with the highest stress value is identified by color legend and recorded as the static high stress region. In the static high stress region of the static stress cloud map, the local maximum stress value is read by the probe tool of the finite element software ANSYS and recorded as the stress peak value of the static high stress region. In the uniform region of characteristic size near the static high stress region, the average stress of the uniform region is extracted and recorded as the static nominal stress of the uniform region. The static stress concentration factor is obtained by comparing the peak stress in the static high-stress region with the static nominal stress in the uniform region. If the static stress concentration factor is greater than or equal to the standard value of the static stress concentration factor, then the corresponding static high stress region is recorded as the static stress concentration region. Preferably, the process of determining the dynamic stress concentration region is as follows: the dynamic stress concentration factor is obtained in the same way as the static stress concentration factor; If the dynamic stress concentration factor is greater than or equal to the standard value of the dynamic stress concentration factor, then the corresponding dynamic high stress region is recorded as the dynamic stress concentration region.

[0010] Preferably, the process of identifying whether the hazardous stress area is under uniaxial or multiaxial stress under static conditions is as follows: The three principal stresses under static conditions within the critical stress region were extracted using the ANSYS post-processing module. If only one of the three principal stresses in the static condition of the critical stress region is not zero, it indicates that the critical stress region is under uniaxial stress; otherwise, it indicates that the critical stress region is under multiaxial stress.

[0011] Preferably, the process of determining whether the stress state has changed to a multiaxial stress state at the time point of dynamic working condition analysis is as follows: Based on any analysis time point under dynamic conditions, the three principal stresses in the critical stress area under dynamic conditions are extracted by the ANSYS post-processing module. If the critical stress region is under dynamic working conditions and only one of the three principal stresses is not zero, it indicates that the stress state has not changed to a multiaxial stress state when the dynamic working condition analysis time point is reached, and the corresponding analysis time point is recorded as a non-single-multiaxial change time point; otherwise, it indicates that the stress state has changed to a multiaxial stress state when the dynamic working condition analysis time point is reached, and the corresponding analysis time point is recorded as a single-multiaxial change time point.

[0012] Preferably, the process of assessing the correlation between fatigue damage and the change of the critical stress region from a uniaxial stress state to a multiaxial stress state is as follows: Extract the three principal stresses of the critical stress region at the time points of uniaxial and multiaxial variation, and determine the multiaxial stress damage value at the time points of uniaxial and multiaxial variation. The multiaxial stress damage values ​​at all uniaxial and multiaxial change time points are summed, and the difference is taken from the cumulative standard value of multiaxial stress damage. The absolute value is then compared with the cumulative standard value of multiaxial stress damage to obtain the multiaxial fatigue damage correlation value. If it is greater than the multiaxial fatigue damage correlation value threshold, it indicates that the correlation between the critical stress area changing from a uniaxial stress state to a multiaxial stress state and fatigue damage is close; otherwise, it indicates that the correlation between the critical stress area changing from a uniaxial stress state to a multiaxial stress state and fatigue damage is not close.

[0013] Preferably, the process of determining the multiaxial stress damage value at the single-multiaxial variation time point is as follows: Based on the three principal stresses of the critical stress region at the time points of uniaxial and multiaxial variation, the equivalent stress of the critical stress region at the time points of uniaxial and multiaxial variation is calculated using the von Mises equivalent stress criterion. Combined with the material SN curve, the multiaxial stress damage value at the time points of uniaxial and multiaxial variation is calculated.

[0014] Preferably, the process of modifying the uniaxial fatigue life assessment method using the critical plane equivalent method is as follows: Export the three-dimensional principal stress time history data of the critical stress region at all uniaxial and multiaxial variation time points from the ANSYS post-processing module, determine the critical plane of the critical stress region, and realize the equivalent uniaxial stress under multiaxial stress state using the SWT criterion. Based on any uniaxial and multiaxial variation time point, extract the maximum normal stress on the critical plane at the uniaxial and multiaxial variation time point. Subtract the maximum shear stress and minimum shear stress corresponding to the critical plane and take half to obtain the shear stress amplitude on the critical plane at the uniaxial and multiaxial variation time point. The equivalent normal stress amplitude on the critical plane at the single- or multi-axis change time point is calculated based on the maximum normal stress and shear stress amplitude. Sort the equivalent normal stress amplitudes at all single-axis and multi-axis variation time points from largest to smallest to obtain the equivalent normal stress amplitude sequence. Extract the first equivalent normal stress amplitude in the equivalent normal stress amplitude sequence as the fatigue life input value considering multi-axis stress state. The corrected fatigue life is calculated by replacing the actual uniaxial stress amplitude in the traditional uniaxial fatigue life formula with the fatigue life input value considering multiaxial stress state instead of the actual uniaxial stress state that does not consider multiaxial stress state.

[0015] Preferably, the process of comprehensively evaluating the fatigue life of the metal structure of the bridge crane is as follows: Based on Miner's linear damage accumulation theory, the actual load cycle spectrum of the bridge crane is obtained, the stress cycle number under each dynamic condition is determined, and the cumulative fatigue damage of the bridge crane metal structure under each dynamic condition is calculated based on the stress cycle number under each dynamic condition and the corrected fatigue life. If the cumulative fatigue damage is greater than or equal to the cumulative fatigue damage threshold, it indicates that the metal structure of the bridge crane is unsafe and needs to be inspected and repaired in time; otherwise, it indicates that the metal structure of the bridge crane is safe and no action needs to be taken.

[0016] The beneficial effects of this invention are as follows: This invention identifies the critical stress areas of the metal structure of a bridge crane and clarifies its uniaxial and multiaxial stress states under static conditions from the perspective of stress components. Furthermore, for the critical stress areas under static uniaxial stress states, it monitors the principal stress changes at various analysis time points under dynamic conditions, accurately distinguishing between uniaxial and multiaxial changing time points and non-changing time points. This improves the accuracy and comprehensiveness of stress analysis for bridge cranes. It avoids the one-sidedness and errors of stress analysis through refined modeling and full-condition coverage, and clearly understands the stress distribution patterns and evolution characteristics of uniaxial and multiaxial stress states by locating critical stress areas and dynamically monitoring stress states. This provides a scientific and reliable technical basis for crane structural safety assessment, fatigue life prediction, and early prevention of potential faults, effectively reducing safety risks caused by inaccurate stress analysis or missed stress state changes, and strongly ensuring the long-term stable operation of bridge cranes.

[0017] This invention achieves precise focus of analytical resources through damage correlation judgment, eliminates the error of uniaxial assessment through multiaxial stress equivalent correction, and ensures that the fatigue life assessment results are highly consistent with the actual stress damage law of the structure. Based on the comparison of cumulative fatigue damage and threshold, it can intuitively and scientifically determine the safety status of bridge crane metal structure, guide maintenance or eliminate risks in a timely manner, and effectively avoid structural failure accidents caused by overestimation of life. It provides accurate and reliable technical support for fatigue management and safe operation and maintenance of crane metal structure throughout its entire life cycle. Attached Figure Description

[0018] The invention will now be further described with reference to the accompanying drawings.

[0019] Figure 1 This is a flowchart illustrating the steps of a method for assessing the fatigue life of a bridge crane's metal structure according to an embodiment of the present invention. Figure 2 This is a system block diagram of a fatigue life assessment system for the metal structure of a bridge crane according to an embodiment of the present invention. Detailed Implementation

[0020] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0021] Example 1:

[0022] Please see Figure 1As shown in the figure, a method for assessing the fatigue life of the metal structure of a bridge crane according to an embodiment of the present invention includes the following steps: Step 1: Based on the structure of the bridge crane, a simulation model of the bridge crane is established using the finite element software ANSYS. By performing stress concentration analysis under static and dynamic conditions respectively, the critical stress area is determined. From the spatial distribution dimension of stress components, the stress components under static conditions in the critical stress area are analyzed to identify whether the critical stress area is in a uniaxial stress state or a multiaxial stress state under static conditions. It should be noted that static working conditions typically include the rated lifting capacity of the bridge crane and the trolley being in different positions (such as mid-span or cantilever end), while dynamic working conditions include hoisting impact, trolley running impact, braking impact, etc. A simulation model of the bridge crane was established using the finite element software ANSYS. Specifically: Based on the design drawings of the bridge crane, the components are assembled according to the actual assembly relationship. The three-dimensional models of each component are drawn using CAD software and then imported into the finite element software ANSYS. Based on the commonly used materials for the metal structure of bridge cranes, material parameters are defined in the finite element software ANSYS, including: elastic modulus, Poisson's ratio, density, yield strength, and the SN curve of the material is supplemented. For thin-walled structures such as main beams and end beams: use shell elements and define the shell element properties according to the actual thickness; for complex nodes (such as the corner where the main beam connects to the end beam): locally switch to solid elements to avoid the calculation error of shell elements in the three-dimensional stress zone. Set boundary conditions to simulate the actual support state of the crane; apply static and dynamic loads according to the operating conditions. Static loads include: structural self-weight, rated lifting capacity, and bolt preload; dynamic loads include: inertial force and vibration load. The running period of the bridge crane is divided into several analysis time points according to the same time interval. The finite element solution of the bridge crane simulation model is completed. Stress cloud diagrams are output at the analysis time points. The stress cloud diagram under static working conditions is recorded as the static stress cloud diagram, and the stress cloud diagram under dynamic working conditions is recorded as the dynamic stress cloud diagram. It should be noted that the operating periods of a bridge crane include both static and dynamic conditions. Based on any static stress cloud map, the region with the highest stress value (usually the darkest region) is identified by color legend (e.g., from blue → green → yellow → red), and is recorded as the static high stress region. In the static high stress region of the static stress cloud map, the local maximum stress value is read by the probe tool of the finite element software ANSYS, and is recorded as the stress peak value of the static high stress region. In the uniform region with a feature size (e.g., 10 times the diameter of the opening) near the static high stress region, the average stress of the uniform region is extracted and recorded as the static nominal stress of the uniform region. The static stress concentration factor is obtained by comparing the peak stress in the static high-stress region with the static nominal stress in the uniform region. The standard value of the static stress concentration factor is set by those skilled in the art based on historical experience. If the static stress concentration factor is greater than or equal to the standard value, the corresponding static high stress area is recorded as a static stress concentration area; if the static stress concentration factor is less than the standard value, the corresponding static high stress area is recorded as a non-static stress concentration area. Based on any dynamic stress cloud map, the region with the darkest color in the dynamic stress cloud map is recorded as the dynamic high stress region. Based on the dynamic high stress region, the dynamic stress concentration factor is output. The method of obtaining the dynamic stress concentration factor is the same as that of obtaining the static stress concentration factor, and will not be described in detail here. The standard value of the dynamic stress concentration factor is set by those skilled in the art based on historical experience. If the dynamic stress concentration factor is greater than or equal to the standard value, the corresponding dynamic high stress area is recorded as the dynamic stress concentration area; if the dynamic stress concentration factor is less than the standard value, the corresponding dynamic high stress area is recorded as the non-dynamic stress concentration area. The spatial coordinates and geometric ranges of the static stress concentration region and the dynamic stress concentration region are obtained respectively. The "Intersect Region Intersection" function of ANSYS software is used to generate spatial intersection element groups of the static stress concentration region and the dynamic stress concentration region. The region corresponding to the spatial intersection element group is recorded as the critical stress region. The three principal stresses under static conditions within the critical stress region were extracted using the ANSYS post-processing module. If only one of the three principal stresses in the static condition of the critical stress region is not zero, it indicates that the critical stress region is under uniaxial stress under the static condition. If two or three of the three principal stresses in the static working condition of the dangerous stress region are not zero, it indicates that the dangerous stress region is in a multiaxial stress state under the static working condition. Step 2: Based on the uniaxial stress state under static conditions in the critical stress area, monitor the uniaxial stress state under static conditions in the critical stress area and determine whether the uniaxial stress state has changed to a multiaxial stress state when the dynamic condition analysis time point is reached. Based on any analysis time point under dynamic conditions, the three principal stresses in the critical stress area under dynamic conditions are extracted by the ANSYS post-processing module. If the critical stress region is under dynamic working conditions and only one of the three principal stresses is not 0, it means that the uniaxial stress state will not change to the multiaxial stress state when running to the dynamic working condition analysis time point. The corresponding analysis time point is recorded as the non-uniaxial / multiaxial change time point. If two or three of the three principal stresses in the dangerous stress region under dynamic conditions are not zero, it means that the uniaxial stress state will change to a multiaxial stress state when running to the dynamic condition analysis time point. The corresponding analysis time point is recorded as the uniaxial-multiaxial change time point. The technical solution of this invention is as follows: Based on the structure of the bridge crane, a simulation model of the bridge crane is established using the finite element software ANSYS. By performing stress concentration analysis under static and dynamic conditions respectively, the critical stress area is determined. From the spatial distribution dimension of stress components, a dominant analysis is performed on the stress components under static conditions in the critical stress area to identify whether the critical stress area is in a uniaxial stress state or a multiaxial stress state under static conditions. Based on the uniaxial stress state under static conditions in the critical stress area, the uniaxial stress state under static conditions in the critical stress area is monitored to determine whether the uniaxial stress state changes to a multiaxial stress state when the dynamic condition analysis time point is reached. This invention determines the critical stress area of ​​the bridge crane's metal structure and clarifies its uniaxial stress state under static conditions from the perspective of stress components. The analysis covers both axial and multiaxial stress states. Further, focusing on the critical stress areas under static uniaxial stress states, the analysis monitors the principal stress changes at various analysis time points under dynamic conditions, accurately distinguishing between uniaxial and multiaxial changing time points and non-changing time points. This improves the accuracy and comprehensiveness of stress analysis for bridge cranes. Through refined modeling and full-condition coverage, it avoids the one-sidedness and errors of stress analysis. Furthermore, by locating critical stress areas and dynamically monitoring stress states, it clearly understands the stress distribution patterns in critical stress areas and the evolution characteristics of uniaxial and multiaxial stress states. This provides a scientific and reliable technical basis for crane structural safety assessment, fatigue life prediction, and early prevention of potential faults. It effectively reduces safety risks caused by inaccurate stress analysis or missed stress state changes, strongly ensuring the long-term stable operation of bridge cranes.

[0023] Example 2:

[0024] Please see Figure 1As shown in the figure, a method for assessing the fatigue life of the metal structure of a bridge crane according to an embodiment of the present invention further includes the following steps: Step 3: If the uniaxial stress state changes to a multiaxial stress state when the dynamic working condition analysis time point is reached, the deviation analysis is performed by the multiaxial stress damage value of the critical stress area at the time point of the uniaxial-multiaxial change to assess the correlation between the critical stress area changing from a uniaxial stress state to a multiaxial stress state and fatigue damage. The three principal stresses of the critical stress region at the single- and multi-axis variation time points are extracted. The equivalent stress of the critical stress region at the single- and multi-axis variation time points is calculated using the von Mises equivalent stress criterion. Combined with the material SN curve, the multiaxial stress damage value at the single- and multi-axis variation time points is calculated. The multiaxial stress damage values ​​at all single and multiaxial variation time points are summed to obtain the cumulative multiaxial stress damage value. The difference between the cumulative multiaxial stress damage value and the cumulative standard value of multiaxial stress damage is taken and the absolute value is then compared with the cumulative standard value of multiaxial stress damage to obtain the multiaxial fatigue damage correlation value. It should be noted that the cumulative standard value of multiaxial stress damage was set by those skilled in the art based on historical experience; In some embodiments, the multiaxial fatigue damage correlation value is compared with a multiaxial fatigue damage correlation value threshold, specifically: If the multiaxial fatigue damage correlation value is greater than the multiaxial fatigue damage correlation value threshold, it indicates that the correlation between the critical stress area changing from a uniaxial stress state to a multiaxial stress state and fatigue damage is close. If the multiaxial fatigue damage correlation value is less than or equal to the multiaxial fatigue damage correlation value threshold, it indicates that the correlation between the critical stress area changing from a uniaxial stress state to a multiaxial stress state and fatigue damage is not strong, and no action is taken. Step 4: If the correlation between the change of the critical stress region from a uniaxial stress state to a multiaxial stress state and fatigue damage is close, the uniaxial fatigue life assessment method is modified by the critical plane equivalent method. Combined with Miner's linear damage accumulation theory, the fatigue life of the metal structure of the bridge crane is comprehensively assessed. It should be noted that when the critical stress area changes from a uniaxial stress state to a multiaxial stress state, it is closely related to fatigue damage. Using the uniaxial fatigue life assessment method to assess the fatigue life of the metal structure of the bridge crane under multiaxial stress state will lead to inaccurate results and may easily cause the fatigue life of the metal structure of the bridge crane to be overestimated, because multiaxial stress will accelerate crack propagation. Therefore, it is necessary to correct the uniaxial fatigue life assessment method by using the critical plane equivalent method. Export the three-dimensional principal stress time history data of the critical stress region at all uniaxial and multiaxial variation time points from the ANSYS post-processing module; Obtain the actual load cycle spectrum of the bridge crane: Based on the crane design specifications (such as GB / T 3811-2008 "Crane Design Specification") or on-site operation data statistics, determine the stress cycle number of each dynamic working condition (lifting impact, trolley travel impact, braking impact); Determine the critical plane of the critical stress region: From the ANSYS post-processor, for each element in the critical stress region, extract the maximum principal stress and minimum principal stress at the single-axis and multi-axis variation time points. Subtract the maximum principal stress and minimum principal stress of each element in the critical stress region and take half to obtain the maximum shear stress of each element in the critical stress region. Sort the maximum shear stress of all elements in the critical stress region from largest to smallest to obtain the maximum shear stress sequence of all elements in the critical stress region. Extract the plane corresponding to the first maximum shear stress in the sequence as the critical plane of the critical stress region. The SWT criterion is used to realize the equivalent uniaxial stress under multiaxial stress state, specifically: Based on any single- or multi-axis variation time point, the maximum normal stress on the critical plane of the single- or multi-axis variation time point is extracted. The difference between the maximum and minimum shear stresses corresponding to the critical plane is processed and then halved to obtain the shear stress amplitude on the critical plane of the single- or multi-axis variation time point. Based on the maximum normal stress and shear stress amplitude at the critical plane of uniaxial / multiaxial variation time points, using the formula: The equivalent normal stress amplitude on the critical plane at the single-axis / multi-axis variation time point was calculated. In the formula, This represents the maximum normal stress on the critical plane at the time point of uniaxial / multiaxial variation. This represents the shear stress amplitude on the critical plane at the time point of uniaxial or multiaxial variation. Sort the equivalent normal stress amplitudes at all single-axis and multi-axis variation time points from largest to smallest to obtain the equivalent normal stress amplitude sequence. Extract the first equivalent normal stress amplitude in the equivalent normal stress amplitude sequence as the fatigue life input value considering multi-axis stress state. It should be noted that the reason for extracting the first equivalent normal stress amplitude in the equivalent normal stress amplitude sequence is that the first equivalent normal stress amplitude is the key factor that determines fatigue life. Traditional uniaxial fatigue life is based on the material's SN curve, and its mathematical expression is: In the formula, This represents the actual uniaxial stress amplitude without considering multiaxial stress states, and m represents the material fatigue index, obtained by fitting the material's SN curve. This indicates the uniaxial fatigue life without considering multiaxial stress conditions. This represents the material fatigue constant, obtained by fitting the material's SN curve. The corrected fatigue life is calculated by replacing the actual uniaxial stress amplitude in the traditional uniaxial fatigue life formula with the fatigue life input value that considers multiaxial stress state, which does not consider multiaxial stress state. Based on Miner's linear damage accumulation theory, the cumulative fatigue damage of the bridge crane's metal structure under various dynamic working conditions is calculated. Specifically: Based on the number of stress cycles under each dynamic working condition (lifting impact, trolley running impact, braking impact), the formula is used: The cumulative fatigue damage of the bridge crane's metal structure under various dynamic working conditions was calculated. In the formula, Let i be the number of stress cycles under the i-th type of dynamic working condition. The corrected fatigue life under the i-th type of dynamic working condition; In some embodiments, cumulative fatigue damage is compared with a cumulative fatigue damage threshold, specifically: If the cumulative fatigue damage is greater than or equal to the cumulative fatigue damage threshold, it indicates that the metal structure of the bridge crane is unsafe and needs to be repaired in time. If the cumulative fatigue damage is less than the cumulative fatigue damage threshold, it means that the metal structure of the bridge crane is safe and no treatment is required. The technical solution of this embodiment is as follows: If the uniaxial stress state changes to a multiaxial stress state when the dynamic working condition analysis time point is reached, the deviation analysis is performed on the multiaxial stress damage value of the dangerous stress area at the time point of the uniaxial-multiaxial change to assess the correlation between the dangerous stress area changing from a uniaxial stress state to a multiaxial stress state and fatigue damage; if the correlation between the dangerous stress area changing from a uniaxial stress state to a multiaxial stress state and fatigue damage is close, the uniaxial fatigue life assessment method is corrected by the critical plane equivalent method, and combined with Miner's linear damage accumulation theory, the fatigue life of the metal structure of the bridge crane is comprehensively assessed; this invention achieves precise focus of analysis resources through damage correlation judgment, eliminates the error of uniaxial assessment through multiaxial stress equivalent correction, and ensures that the fatigue life assessment results are highly consistent with the actual stress damage law of the structure; by determining the safety status of the metal structure of the bridge crane, timely guidance is provided for maintenance or risk elimination, effectively avoiding structural failure accidents caused by overestimation of life, and providing accurate and reliable technical support for the full life cycle fatigue management and safe operation and maintenance of the crane metal structure.

[0025] Example 3:

[0026] Please see Figure 2 As shown in the figure, a fatigue life assessment system for the metal structure of a bridge crane according to an embodiment of the present invention includes the following modules: State identification module: Based on the structure of the bridge crane, a simulation model of the bridge crane is established using the finite element software ANSYS. By performing stress concentration analysis under static and dynamic working conditions respectively, the dangerous stress area is identified. From the spatial distribution dimension of stress components, the stress components under static conditions of the dangerous stress area are analyzed to identify whether the dangerous stress area is in a uniaxial stress state or a multiaxial stress state under static working conditions. Change Analysis Module: Based on the uniaxial stress state under static conditions in the critical stress area, it monitors the uniaxial stress state under static conditions in the critical stress area and determines whether the uniaxial stress state has changed to a multiaxial stress state when the dynamic condition analysis time point is reached. Correlation Analysis Module: If the uniaxial stress state changes to a multiaxial stress state when running to the dynamic working condition analysis time point, the deviation analysis is performed by the multiaxial stress damage value of the dangerous stress area at the time point of uniaxial-multiaxial change, and the correlation between the dangerous stress area changing from a uniaxial stress state to a multiaxial stress state and fatigue damage is evaluated. Correction Assessment Module: If the correlation between the change of the critical stress region from a uniaxial stress state to a multiaxial stress state and fatigue damage is close, the uniaxial fatigue life assessment method is corrected by the critical plane equivalent method. Combined with Miner's linear damage accumulation theory, the fatigue life of the metal structure of the bridge crane is comprehensively assessed.

[0027] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for assessing the fatigue life of the metal structure of a bridge crane, characterized in that: include: Based on the structure of the bridge crane, a simulation model of the bridge crane was established using the finite element software ANSYS. By conducting stress concentration analysis under static and dynamic conditions respectively, the critical stress area was identified. From the spatial distribution dimension of stress components, the stress components under static conditions of the critical stress area were analyzed to identify whether the critical stress area was under uniaxial stress or multiaxial stress under static conditions. Based on the uniaxial stress state under static conditions in the dangerous stress region, the uniaxial stress state under static conditions in the dangerous stress region is monitored to determine whether the uniaxial stress state changes to a multiaxial stress state when the dynamic condition analysis time point is reached. If the uniaxial stress state changes to a multiaxial stress state when the dynamic working condition analysis time point is reached, the deviation analysis is performed by the multiaxial stress damage value of the critical stress area at the time point of uniaxial-multiaxial change, and the correlation between the critical stress area changing from a uniaxial stress state to a multiaxial stress state and fatigue damage is evaluated. If the correlation between the change of the critical stress region from a uniaxial stress state to a multiaxial stress state and fatigue damage is close, the uniaxial fatigue life assessment method is modified by the critical plane equivalent method. Combined with Miner's linear damage accumulation theory, the fatigue life of the metal structure of the bridge crane is comprehensively assessed.

2. The method for assessing the fatigue life of the metal structure of a bridge crane according to claim 1, characterized in that: The process for determining the critical stress area is as follows: The operating period of the bridge crane is divided into several analysis time points according to the same time interval. The finite element solution of the bridge crane simulation model is completed, and stress cloud diagrams are output at the analysis time points, including static stress cloud diagrams under static conditions and dynamic stress cloud diagrams under dynamic conditions. Static stress concentration regions and dynamic stress concentration regions are determined by static stress cloud diagrams and dynamic stress cloud diagrams. The spatial coordinates and geometric ranges of the static stress concentration region and the dynamic stress concentration region are obtained respectively. The Intersect function of ANSYS software is used to generate spatial intersection element groups of the static stress concentration region and the dynamic stress concentration region. The region corresponding to the spatial intersection element group is recorded as the critical stress region.

3. The method for assessing the fatigue life of the metal structure of a bridge crane according to claim 2, characterized in that: The process of determining the static stress concentration region is as follows: Based on any static stress cloud map, the region with the highest stress value is identified by color legend and recorded as the static high stress region. In the static high stress region of the static stress cloud map, the local maximum stress value is read by the probe tool of the finite element software ANSYS and recorded as the stress peak value of the static high stress region. In the uniform region of characteristic size near the static high stress region, the average stress of the uniform region is extracted and recorded as the static nominal stress of the uniform region. The static stress concentration factor is obtained by comparing the peak stress in the static high-stress region with the static nominal stress in the uniform region. If the static stress concentration factor is greater than or equal to the standard value of the static stress concentration factor, then the corresponding static high stress region is recorded as the static stress concentration region.

4. The method for assessing the fatigue life of the metal structure of a bridge crane according to claim 3, characterized in that: The process of determining the dynamic stress concentration region is as follows: The dynamic stress concentration factor is obtained in the same way as the static stress concentration factor; If the dynamic stress concentration factor is greater than or equal to the standard value of the dynamic stress concentration factor, then the corresponding dynamic high stress region is recorded as the dynamic stress concentration region.

5. The method for assessing the fatigue life of the metal structure of a bridge crane according to claim 2, characterized in that: The process of identifying whether a critical stress region is under uniaxial or multiaxial stress under static conditions is as follows: The three principal stresses under static conditions within the critical stress region were extracted using the ANSYS post-processing module. If only one of the three principal stresses in the static condition of the critical stress region is not zero, it indicates that the critical stress region is under uniaxial stress; otherwise, it indicates that the critical stress region is under multiaxial stress.

6. The method for assessing the fatigue life of the metal structure of a bridge crane according to claim 2, characterized in that: The process of determining whether the stress state has changed to a multiaxial stress state at the time point of dynamic working condition analysis is as follows: Based on any analysis time point under dynamic conditions, the three principal stresses in the critical stress area under dynamic conditions are extracted by the ANSYS post-processing module. If the critical stress region is under dynamic working conditions and only one of the three principal stresses is not zero, it indicates that the stress state has not changed to a multiaxial stress state when the dynamic working condition analysis time point is reached, and the corresponding analysis time point is recorded as a non-single-multiaxial change time point; otherwise, it indicates that the stress state has changed to a multiaxial stress state when the dynamic working condition analysis time point is reached, and the corresponding analysis time point is recorded as a single-multiaxial change time point.

7. The fatigue life assessment method for the metal structure of a bridge crane according to claim 6, characterized in that: The process of assessing the correlation between fatigue damage and the change of the critical stress region from a uniaxial stress state to a multiaxial stress state is as follows: Extract the three principal stresses of the critical stress region at the time points of uniaxial and multiaxial variation, and determine the multiaxial stress damage value at the time points of uniaxial and multiaxial variation. The multiaxial stress damage values ​​at all uniaxial and multiaxial change time points are summed, and the difference is taken from the cumulative standard value of multiaxial stress damage. The absolute value is then compared with the cumulative standard value of multiaxial stress damage to obtain the multiaxial fatigue damage correlation value. If it is greater than the multiaxial fatigue damage correlation value threshold, it indicates that the correlation between the critical stress area changing from a uniaxial stress state to a multiaxial stress state and fatigue damage is close; otherwise, it indicates that the correlation between the critical stress area changing from a uniaxial stress state to a multiaxial stress state and fatigue damage is not close.

8. The method for assessing the fatigue life of the metal structure of a bridge crane according to claim 7, characterized in that: The process of determining the multiaxial stress damage value at the time point of uniaxial-multiaxial variation is as follows: Based on the three principal stresses of the critical stress region at the time points of uniaxial and multiaxial variation, the equivalent stress of the critical stress region at the time points of uniaxial and multiaxial variation is calculated using the von Mises equivalent stress criterion. Combined with the material SN curve, the multiaxial stress damage value at the time points of uniaxial and multiaxial variation is calculated.

9. The method for assessing the fatigue life of the metal structure of a bridge crane according to claim 6, characterized in that: The process of modifying the uniaxial fatigue life assessment method using the critical plane equivalent method is as follows: Export the three-dimensional principal stress time history data of the critical stress region at all uniaxial and multiaxial variation time points from the ANSYS post-processing module, determine the critical plane of the critical stress region, and realize the equivalent uniaxial stress under multiaxial stress state using the SWT criterion. Based on any uniaxial and multiaxial variation time point, extract the maximum normal stress on the critical plane at the uniaxial and multiaxial variation time point. Subtract the maximum shear stress and minimum shear stress corresponding to the critical plane and take half to obtain the shear stress amplitude on the critical plane at the uniaxial and multiaxial variation time point. The equivalent normal stress amplitude on the critical plane at the single- or multi-axis change time point is calculated based on the maximum normal stress and shear stress amplitude. Sort the equivalent normal stress amplitudes at all single-axis and multi-axis variation time points from largest to smallest to obtain the equivalent normal stress amplitude sequence. Extract the first equivalent normal stress amplitude in the equivalent normal stress amplitude sequence as the fatigue life input value considering multi-axis stress state. The corrected fatigue life is calculated by replacing the actual uniaxial stress amplitude in the traditional uniaxial fatigue life formula with the fatigue life input value considering multiaxial stress state instead of the actual uniaxial stress state that does not consider multiaxial stress state.

10. The method for assessing the fatigue life of the metal structure of a bridge crane according to claim 9, characterized in that: The process of comprehensively evaluating the fatigue life of the metal structure of the bridge crane is as follows: Based on Miner's linear damage accumulation theory, the actual load cycle spectrum of the bridge crane is obtained, the stress cycle number under each dynamic condition is determined, and the cumulative fatigue damage of the bridge crane metal structure under each dynamic condition is calculated based on the stress cycle number under each dynamic condition and the corrected fatigue life. If the cumulative fatigue damage is greater than or equal to the cumulative fatigue damage threshold, it indicates that the metal structure of the bridge crane is unsafe and needs to be inspected and repaired in time; otherwise, it indicates that the metal structure of the bridge crane is safe and no action needs to be taken.

Images