Method for fatigue life assessment of a metal structure of a bridge crane

Abstract

The application belongs to the technical field of bridge cranes, and provides a metal structure fatigue life evaluation method of a bridge crane, which comprises the following steps: according to the structure of the bridge crane, a simulation model of the bridge crane is established by using finite element software ANSYS; the dangerous stress region is determined by analyzing the stress concentration of the static working condition and the dynamic working condition respectively; the stress component in the static condition of the dangerous stress region is analyzed in the spatial distribution dimension; the uniaxial stress state in the static working condition of the dangerous stress region is monitored; and the deviation analysis is performed on the multiaxial stress damage value at the single-multiaxial change time point of the dangerous stress region. The application eliminates the error of uniaxial evaluation through multiaxial stress equivalent correction, and ensures that the fatigue life evaluation result is highly consistent with the actual stress damage law of the structure.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of bridge cranes, and in particular relates to a metal structure fatigue life evaluation method of a bridge crane. BACKGROUND

[0002] As core equipment for realizing efficient material handling in industrial production, port logistics and other fields, the metal structure (including a main beam, an end beam, a connecting joint and the like) of a bridge crane is a key component for bearing load, and needs to continuously bear alternating action of static load (such as structure dead weight, rated lifting weight, bolt pre-tightening force) and dynamic load (such as lifting impact inertia force, trolley running impact load, braking impact load) in a long-term service process, and fatigue failure has become a main inducement for causing metal structure fracture, equipment shutdown and even safety accidents, so accurate fatigue life evaluation of the metal structure is a core technical requirement for guaranteeing long-term stable operation of equipment and avoiding safety risks.

[0003] Most methods only focus on the stress state (uniaxial or multiaxial) of a dangerous stress region under a static working condition, do not further monitor the change rule of the stress state at each time point under a dynamic working condition, especially ignore the key phenomenon that the dangerous stress region under a uniaxial stress state under a static working condition may be converted into a multiaxial stress state under a dynamic impact load, and the multiaxial stress will significantly accelerate crack initiation and expansion speed through stress superposition effect, and this missing judgment of the stress state evolution directly leads to that the prior art cannot accurately identify the key inducement of fatigue damage, and further causes distortion of the judgment of the correlation degree between the stress state change and fatigue damage.

[0004] In the fatigue life calculation and safety evaluation link, the error problem of the prior art is particularly prominent: on the one hand, the existing method generally directly uses a uniaxial fatigue life evaluation model (based on a material S-N curve) to analyze the structure life under a multiaxial stress state, does not convert the multiaxial stress into equivalent uniaxial stress through a critical plane equivalent method (such as an SWT criterion) for model correction, leads to that the life evaluation result is generally high, and seriously overestimates the safety margin of the structure, so that the metal structure fails in advance in actual use.

[0005] Therefore, the application provides a metal structure fatigue life evaluation method of a bridge crane. SUMMARY

[0006] In order to make up for the deficiencies of the prior art and solve at least one technical problem proposed in the background.

[0007] The application provides a metal structure fatigue life evaluation method of a bridge crane, which comprises the following steps:

[0008] According to the bridge crane structure, a bridge crane simulation model is established by using finite element software ANSYS, stress concentration analysis is performed on the stress under static and dynamic conditions respectively, the dangerous stress region is determined, the stress component under static condition of the dangerous stress region is analyzed in the dimension of spatial distribution of stress component, and it is identified whether the dangerous stress region under static condition is in uniaxial stress state or multiaxial stress state;

[0009] Based on the uniaxial stress state of the dangerous stress region under static condition, the uniaxial stress state of the dangerous stress region under static condition is monitored, and it is judged whether the uniaxial stress state changes into multiaxial stress state at the analysis time point of running to dynamic condition;

[0010] If the uniaxial stress state changes into multiaxial stress state at the analysis time point of running to dynamic condition, deviation analysis is performed on the multiaxial stress damage value of the dangerous stress region at the uniaxial-multiaxial change time point, and the correlation between the change of the dangerous stress region from uniaxial stress state to multiaxial stress state and fatigue damage is evaluated.

[0011] If the correlation between the change of the dangerous stress region from uniaxial stress state to multiaxial stress state and fatigue damage is close, the uniaxial fatigue life evaluation method is modified by using critical plane equivalent method, and the fatigue life of the metal structure of the bridge crane is comprehensively evaluated in combination with Miner linear damage accumulation theory.

[0012] Preferably, the process of determining the dangerous stress region comprises the following steps:

[0013] The running period of the bridge crane is divided into a plurality of analysis time points at the same time interval, finite element solution of the bridge crane simulation model is completed, and stress nephogram is output at the analysis time points, including static stress nephogram under static condition and dynamic stress nephogram under dynamic condition;

[0014] The static stress concentration region and the dynamic stress concentration region are determined by the static stress nephogram and the dynamic stress nephogram.

[0015] The spatial coordinates and geometric ranges of the static stress concentration region and the dynamic stress concentration region are obtained respectively, the spatial intersection element group of the static stress concentration region and the dynamic stress concentration region is generated by using the intersect function of ANSYS software, and the region corresponding to the spatial intersection element group is recorded as the dangerous stress region.

[0016] Preferably, the process of determining the static stress concentration region comprises the following steps:

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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;

[0021] 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.

[0022] Preferably, the process of identifying whether the hazardous stress area is under uniaxial or multiaxial stress under static conditions is as follows:

[0023] The three principal stresses under static conditions within the critical stress region were extracted using the ANSYS post-processing module.

[0024] 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.

[0025] 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:

[0026] 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.

[0027] 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.

[0028] 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:

[0029] 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.

[0030] 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.

[0031] Preferably, the process of determining the multiaxial stress damage value at the single-multiaxial variation time point is as follows:

[0032] 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.

[0033] Preferably, the process of modifying the uniaxial fatigue life assessment method using the critical plane equivalent method is as follows:

[0034] 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.

[0035] 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.

[0036] 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.

[0037] The fatigue life input value under the multi-axial stress state is considered to replace the actual single-axial stress amplitude not considering the multi-axial stress state in a traditional single-axial fatigue life formula, and a modified fatigue life is calculated.

[0038] Preferably, the process for comprehensively evaluating the fatigue life of the metal structure of the bridge crane is:

[0039] Based on the Miner linear damage accumulation theory, the actual load cycle spectrum of the bridge crane is obtained, the stress cycle number under each dynamic working condition is determined, and the cumulative fatigue damage of the metal structure of the bridge crane under each dynamic working condition is calculated according to the stress cycle number under each dynamic working condition and the modified fatigue life.

[0040] 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, otherwise, it indicates that the metal structure of the bridge crane is safe and no treatment is needed.

[0041] The beneficial effects of the present application are as follows:

[0042] The present application determines the dangerous stress region of the metal structure of the bridge crane, and clearly determines the single-axial stress state and multi-axial stress state under the static working condition from the stress component dimension; subsequently, the main stress change of each analysis time point under the dynamic working condition is monitored for the dangerous stress region of the static single-axial stress state, and the single-axial change and non-change time points are accurately distinguished, which improves the accuracy and comprehensiveness of the stress analysis of the bridge crane, avoids the one-sidedness and error of the stress analysis through fine modeling and full working condition coverage, clearly masters the stress distribution law of the dangerous stress region and the evolution characteristics of the single-axial stress state and multi-axial stress state through dangerous stress region positioning and stress state dynamic monitoring, and provides a scientific and reliable technical basis for crane structure safety evaluation, fatigue life prediction and potential fault early prevention and control, effectively reduces the safety risks caused by inaccurate stress analysis or stress state change missed judgment, and effectively guarantees the long-term stable operation of the bridge crane.

[0043] The present application realizes accurate focusing of analysis resources through damage correlation degree judgment, eliminates the error of single-axial evaluation through multi-axial stress equivalent correction, ensures that the fatigue life evaluation result is highly consistent with the actual stress damage law of the structure, and based on the comparison between the cumulative fatigue damage and the threshold value, the safety state of the metal structure of the bridge crane can be intuitively and scientifically judged, timely maintenance or risk elimination is guided, and structural failure accidents caused by overestimation of life are effectively avoided, which provides accurate and reliable technical support for the whole life fatigue management and safety operation of the crane metal structure. BRIEF DESCRIPTION OF DRAWINGS

[0044] The present application will be further described below with reference to the accompanying drawings.

[0045] Figure 1 is a step flow chart of a metal structure fatigue life evaluation method of a bridge crane according to an embodiment of the present application;

[0046] Figure 2 is a system block diagram of a metal structure fatigue life evaluation system of a bridge crane according to an embodiment of the present application. DETAILED DESCRIPTION

[0047] In order to make the technical means, creative features, purposes and effects of the present application easy to understand, the present application will be further described below in combination with specific embodiments.

[0048] Embodiment 1:

[0049] Referring to Figure 1 , a metal structure fatigue life evaluation method of a bridge crane according to an embodiment of the present application includes the following steps:

[0050] Step 1: According to the structure of the bridge crane, a bridge crane simulation model is established by using the finite element software ANSYS. By analyzing the stress concentration of the static and dynamic conditions respectively, the dangerous stress area is determined. From the spatial distribution dimension of the stress component, the dominant analysis of the stress component under the static condition of the dangerous stress area is performed to identify whether the dangerous stress area under the static condition is in a uniaxial stress state or a multiaxial stress state.

[0051] It should be noted that the static condition usually includes typical conditions such as the rated load of the bridge crane, the trolley located at different positions (such as the midspan and the cantilever end), and the dynamic condition includes lifting impact, trolley running impact, braking impact, etc.

[0052] The bridge crane simulation model is established by using the finite element software ANSYS, specifically:

[0053] Based on the design drawings of the bridge crane, the three-dimensional models of each component are drawn by using CAD software according to the actual assembly relationship, and the three-dimensional models of each component of the crane are imported into the finite element software ANSYS.

[0054] According to the commonly used materials of the metal structure of the bridge crane, the material parameters are defined in the finite element software ANSYS, including: elastic modulus, Poisson's ratio, density, yield strength, and the S-N curve of the material is supplemented.

[0055] For thin-walled structures such as the main beam and the end beam, shell elements are used, and the shell element properties are defined according to the actual thickness. For complex nodes (such as the corner connecting the main beam and the end beam), local solid elements are used to avoid calculation errors of shell elements in three-dimensional stress areas.

[0056] Boundary conditions are set to simulate the actual support state of the crane; static loads and dynamic loads are applied according to the operating conditions, the static loads including: structure dead weight, rated lifting capacity, bolt pre-tightening force; the dynamic loads including: inertia force, vibration load;

[0057] The running period of the bridge crane is divided into a plurality of analysis time points according to the same time interval, the finite element solution of the bridge crane simulation model is completed, and the stress nephogram at the analysis time point is output, the stress nephogram under the static condition is recorded as a static stress nephogram, and the stress nephogram under the dynamic condition is recorded as a dynamic stress nephogram;

[0058] It should be noted that the running period of the bridge crane includes static conditions and dynamic conditions;

[0059] Based on any static stress nephogram, the area with the highest stress value (usually the area with the deepest color) is identified according to the color legend (such as from blue to green to yellow to red), and is recorded as a static high stress area, the local maximum stress value in the static high stress area of the static stress nephogram is read through the probe tool of the finite element software ANSYS, and is recorded as a stress peak value of the static high stress area, the average stress of the uniform area in the vicinity of the static high stress area is extracted, and is recorded as a static nominal stress of the uniform area;

[0060] The stress peak value of the static high stress area and the static nominal stress of the uniform area are processed by ratio, and a static stress concentration coefficient is obtained;

[0061] The static stress concentration coefficient standard value is set by a person skilled in the art according to historical experience, if the static stress concentration coefficient is greater than or equal to the static stress concentration coefficient standard value, the corresponding static high stress area is recorded as a static stress concentration area; if the static stress concentration coefficient is less than the static stress concentration coefficient standard value, the corresponding static high stress area is recorded as a non-static stress concentration area;

[0062] Based on any dynamic stress nephogram, the area with the deepest color of the dynamic stress nephogram is recorded as a dynamic high stress area, and a dynamic stress concentration coefficient is output based on the dynamic high stress area, the dynamic stress concentration coefficient is obtained in the same way as the static stress concentration coefficient, and details are not repeated here;

[0063] The dynamic stress concentration coefficient standard value is set by a person skilled in the art according to historical experience, if the dynamic stress concentration coefficient is greater than or equal to the dynamic stress concentration coefficient standard value, the corresponding dynamic high stress area is recorded as a dynamic stress concentration area; if the dynamic stress concentration coefficient is less than the dynamic stress concentration coefficient standard value, the corresponding dynamic high stress area is recorded as a non-dynamic stress concentration area;

[0064] The spatial coordinates and geometric ranges of the static stress concentration area and the dynamic stress concentration area are obtained respectively, the "Intersect area intersection" function of the ANSYS software is used to generate the spatial intersection element group of the static stress concentration area and the dynamic stress concentration area, and the area corresponding to the spatial intersection element group is recorded as a dangerous stress area;

[0065] Three principal stresses in the dangerous stress area under the static working condition are extracted by the ANSYS post-processing module;

[0066] If only one of the three principal stresses in the dangerous stress area under the static working condition is not 0, it indicates that the dangerous stress area is in a uniaxial stress state under the static working condition;

[0067] If two or three of the three principal stresses in the dangerous stress area under the static working condition are not 0, it indicates that the dangerous stress area is in a multiaxial stress state under the static working condition;

[0068] Step two: based on the uniaxial stress state of the dangerous stress area under the static working condition, the uniaxial stress state under the static working condition is monitored to determine whether the uniaxial stress state changes to a multiaxial stress state when running to a dynamic working condition analysis time point;

[0069] Based on any analysis time point under the dynamic working condition, three principal stresses in the dangerous stress area under the dynamic working condition analysis time point are extracted by the ANSYS post-processing module;

[0070] If only one of the three principal stresses in the dangerous stress area under the dynamic working condition is not 0, it indicates that the uniaxial stress state will not change to a multiaxial stress state when running to the dynamic working condition analysis time point, and the corresponding analysis time point is recorded as a non-single-multiaxial change time point;

[0071] If two or three of the three principal stresses in the dangerous stress area under the dynamic working condition are not 0, it indicates that the uniaxial stress state will change to a multiaxial stress state when running to the dynamic working condition analysis time point, and the corresponding analysis time point is recorded as a single-multiaxial change time point;

[0072] The technical scheme of the present application is: according to the structure of the bridge crane, a simulation model of the bridge crane is established by using the finite element software ANSYS, the stress concentration analysis is carried out under the static and dynamic conditions respectively, the dangerous stress area is determined, the stress component under the static condition of the dangerous stress area is analyzed in the spatial distribution dimension, and it is identified whether the dangerous stress area under the static condition is in the uniaxial stress state or the multiaxial stress state; based on the uniaxial stress state under the static condition of the dangerous stress area, the uniaxial stress state under the static condition of the dangerous stress area is monitored, and it is judged whether the uniaxial stress state changes to the multiaxial stress state when running to the dynamic condition analysis time point; the present application determines the dangerous stress area of the metal structure of the bridge crane, and clearly determines the uniaxial stress state and the multiaxial stress state under the static condition from the stress component dimension; subsequently, the principal stress change at each analysis time point under the dynamic condition is monitored for the dangerous stress area under the static uniaxial stress state, the uniaxial change and non-change time points are accurately distinguished, the accuracy and comprehensiveness of the stress analysis of the bridge crane are improved, the one-sidedness and error of the stress analysis are avoided through fine modeling and full-condition coverage, the stress distribution law of the dangerous stress area and the evolution characteristics of the uniaxial stress state and the multiaxial stress state are clearly mastered through the positioning of the dangerous stress area and the dynamic monitoring of the stress state, a scientific and reliable technical basis is provided for the safety evaluation, fatigue life prediction and potential fault early prevention and control of the crane structure, the safety risk caused by inaccurate stress analysis or missed judgment of stress state change is effectively reduced, and the long-term stable operation of the bridge crane is effectively ensured.

[0073] Example 2:

[0074] Referring to Figure 1 The metal structure fatigue life evaluation method of the bridge crane according to the embodiment of the present application further includes the following steps:

[0075] Step three: if the uniaxial stress state changes to the multiaxial stress state when running to the dynamic condition analysis time point, the deviation analysis is carried out on the multiaxial stress damage value of the dangerous stress area at the uniaxial change time point, and the correlation between the change of the dangerous stress area from the uniaxial stress state to the multiaxial stress state and the fatigue damage is evaluated;

[0076] The three principal stresses of the dangerous stress area at the uniaxial change time point are extracted, the equivalent stress of the dangerous stress area at the uniaxial change time point is calculated by using the von Mises equivalent stress criterion, and the multiaxial stress damage value at the uniaxial change time point is calculated in combination with the material S-N curve;

[0077] Summing up the multi-axial stress damage values at all single-multi-axial change time points to obtain a multi-axial stress damage cumulative value, taking the absolute value after the difference between the multi-axial stress damage cumulative value and a multi-axial stress damage cumulative standard value is processed, and then performing a ratio processing on the multi-axial stress damage cumulative standard value to obtain a multi-axial fatigue damage correlation value;

[0078] It should be noted that the multi-axial stress damage cumulative standard value is set by a person skilled in the art according to historical experience;

[0079] In some embodiments, the multi-axial fatigue damage correlation value is compared with a multi-axial fatigue damage correlation value threshold, specifically:

[0080] If the multi-axial fatigue damage correlation value is greater than the multi-axial fatigue damage correlation value threshold, it indicates that the correlation between the dangerous stress region and the fatigue damage when the dangerous stress region changes from a single-axial stress state to a multi-axial stress state is close;

[0081] If the multi-axial fatigue damage correlation value is less than or equal to the multi-axial fatigue damage correlation value threshold, it indicates that the correlation between the dangerous stress region and the fatigue damage when the dangerous stress region changes from a single-axial stress state to a multi-axial stress state is not close, and no processing is performed;

[0082] Step four: If the correlation between the dangerous stress region and the fatigue damage when the dangerous stress region changes from a single-axial stress state to a multi-axial stress state is close, the single-axial fatigue life evaluation method is modified by the critical plane equivalence method, and the fatigue life of the metal structure of the bridge crane is comprehensively evaluated in combination with the Miner linear damage accumulation theory;

[0083] It should be noted that when the correlation between the dangerous stress region and the fatigue damage when the dangerous stress region changes from a single-axial stress state to a multi-axial stress state is close, using the single-axial fatigue life evaluation method to evaluate the fatigue life of the metal structure of the bridge crane under the multi-axial stress state will result in inaccurate results, which can easily lead to overestimation of the fatigue life of the metal structure of the bridge crane, because multi-axial stress can accelerate crack propagation, and thus the single-axial fatigue life evaluation method needs to be modified by the critical plane equivalence method;

[0084] The three-dimensional principal stress time history data of the dangerous stress region at all single-multi-axial change time points are exported from the ANSYS post-processing module;

[0085] Obtain the actual load cycle spectrum of the bridge crane: based on crane design specifications (such as GB / T 3811-2008 “Crane Design Specification”) or field operation data statistics, determine the stress cycle times of each dynamic working condition (lifting impact, trolley running impact, and braking impact);

[0086] Determination of the critical plane of the dangerous stress region: from the ANSYS post-processing, for each element of the dangerous stress region, the maximum principal stress and the minimum principal stress at each single / multi-axial change time point are extracted, the maximum principal stress and the minimum principal stress of each element of the dangerous stress region are subtracted and taken one-half to obtain the maximum shear stress of each element of the dangerous stress region, the maximum shear stress of all elements of the dangerous stress region is sorted from large to small to obtain the maximum shear stress sequence of all elements of the dangerous stress region, the plane corresponding to the first maximum shear stress in the maximum shear stress sequence is extracted as the critical plane of the dangerous stress region;

[0087] The equivalent uniaxial stress under the multi-axial stress state is realized by using the SWT criterion, specifically:

[0088] Based on any single / multi-axial change time point, the maximum normal stress on the critical plane at the single / multi-axial change time point is extracted, the maximum shear stress and the minimum shear stress corresponding to the critical plane are subtracted and taken one-half to obtain the shear stress amplitude on the critical plane at the single / multi-axial change time point;

[0089] According to the maximum normal stress and the shear stress amplitude of the critical plane at the single / multi-axial change time point, the equivalent normal stress amplitude on the critical plane at the single / multi-axial change time point is calculated by the formula: , wherein, represents the maximum normal stress on the critical plane at the single / multi-axial change time point, represents the shear stress amplitude on the critical plane at the single / multi-axial change time point;

[0090] The equivalent normal stress amplitudes of all single / multi-axial change time points are sorted from large to small to obtain an equivalent normal stress amplitude sequence, and the first equivalent normal stress amplitude in the equivalent normal stress amplitude sequence is extracted as the input value of the fatigue life considering the multi-axial stress state;

[0091] 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 a key factor for determining the fatigue life;

[0092] The traditional uniaxial fatigue life is based on the S-N curve of the material, and the mathematical expression is: , wherein, represents the actual uniaxial stress amplitude without considering the multi-axial stress state, m represents the material fatigue index, which is obtained by fitting the material S-N curve, represents the uniaxial fatigue life without considering the multi-axial stress state, represents the material fatigue constant, which is obtained by fitting the material S-N curve;

[0093] ​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.

[0094] 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:

[0095] 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;

[0096] In some embodiments, cumulative fatigue damage is compared with a cumulative fatigue damage threshold, specifically:

[0097] 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.

[0098] 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.

[0099] 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.

[0100] Example 3:

[0101] Please see Figure 2As shown, the metal structure fatigue life evaluation system of the bridge crane of the embodiment of the application comprises the following modules:

[0102] The state recognition module: according to the bridge crane structure, a bridge crane simulation model is established through the finite element software ANSYS, the stress concentration analysis is carried out on the stress under the static and dynamic working conditions respectively, the dangerous stress area is determined, the stress component under the static condition of the dangerous stress area is analyzed in the spatial distribution dimension, and it is identified whether the dangerous stress area under the static working condition is in the uniaxial stress state or the multiaxial stress state.

[0103] The change analysis module: based on the uniaxial stress state of the dangerous stress area under the static working condition, the uniaxial stress state under the static working condition of the dangerous stress area is monitored, and it is judged whether the uniaxial stress state changes into the multiaxial stress state when running to the dynamic working condition analysis time point.

[0104] The correlation analysis module: if the uniaxial stress state changes into the multiaxial stress state when running to the dynamic working condition analysis time point, the deviation analysis is carried out through the multiaxial stress damage value of the dangerous stress area at the single-multiaxial change time point, and the correlation between the change of the dangerous stress area from the uniaxial stress state to the multiaxial stress state and the fatigue damage is evaluated.

[0105] The correction evaluation module: if the correlation between the change of the dangerous stress area from the uniaxial stress state to the multiaxial stress state and the fatigue damage is close, the uniaxial fatigue life evaluation method is corrected through the critical plane equivalent method, the metal structure fatigue life of the bridge crane is comprehensively evaluated in combination with the Miner linear damage accumulation theory.

[0106] The above shows and describes the basic principles, main features and advantages of the application. It should be understood by those skilled in the art that the application is not limited by the above embodiments, and the above embodiments and descriptions in the specification are only to illustrate the principles of the application, and various changes and improvements can be made without departing from the spirit and scope of the application, and these changes and improvements all fall within the scope of the claimed application. The scope of protection of the application 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. The process of 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. 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 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.

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 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.

4. The method for assessing the fatigue life of the metal structure of a bridge crane according to claim 1, 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.

5. The method for assessing the fatigue life of the metal structure of a bridge crane according to claim 1, 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.

6. The method for assessing the fatigue life of the metal structure of a bridge crane according to claim 5, 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.

7. The fatigue life assessment method for the metal structure of a bridge crane according to claim 6, 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.

8. 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 that considers multiaxial stress state instead of the actual uniaxial stress state that does not consider multiaxial stress state.

9. The method for evaluating the fatigue life of the metal structure of a bridge crane according to claim 8, 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.

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