A multi-axial fatigue life calculation method for quayside crane metal structures

Abstract

The present invention relates to the technical field of metal life calculation for quayside bridges, and discloses a multi-axis fatigue life calculation method for metal structures of quayside bridges, comprising the following steps: S1: according to the structure of the quayside bridge, a three-dimensional model of the quayside bridge is established, and the strength analysis is performed on it through finite element software to obtain the stress-time history of the dangerous point on the dangerous section; S2: the monitoring data of the metal structure of the quayside bridge by the sensor is collected, and the stress-time history is obtained by sorting and analyzing; S3: the finite element model is corrected according to the measured data combined with the simulated stress-time history; S4: the location of the dangerous section of the quayside bridge under different working conditions is solved; S5: according to the finite element analysis results, combined with the location of the dangerous section, the maximum shear strain amplitude section is searched. The multi-axis fatigue life calculation method for metal structures of quayside bridges can solve the problem that the fatigue life is calculated with the converted equivalent stress under non-proportional loading, and the error is large.

Description

Technical Field

[0001] The invention relates to the technical field of quay crane metal life calculation, and in particular to a multi-axis fatigue life calculation method for a quay crane metal structure. Background Art

[0002] Many mechanical components are in a multiaxial cyclic stress-strain state during their service life, and multiaxial fatigue failure is the main failure mode. The loading process will cause the principal stress and strain directions to change, resulting in additional hardening. Compared with uniaxial fatigue, multiaxial fatigue involves more complex loading conditions, component geometry, and material response, so there is currently no universally accepted failure criterion.

[0003] In uniaxial fatigue, crack initiation and propagation are all along a fixed plane. However, in multiaxial fatigue loading, the direction and length of the crack depend on many factors, such as the loading path and material properties. Findley, Reis], Yang and Zhang studied the crack behavior of 76ST61 aluminum alloy, three different steels, S45 carbon steel, 2A12 T4 aluminum alloy and 30CrMnSiA steel respectively. They found that the crack initiation and propagation behavior of the specimen was affected by the loading path. Compared with uniaxial fatigue cracks, the initiation and propagation behavior of cracks under multiaxial fatigue paths is more complicated.

[0004] Under non-proportional cyclic loading, its strain principal axis rotates continuously, and the cyclic stress-strain relationship based on the effective stress-strain relationship is not unique, and will depend on the shape of the loading path. Studies on the cyclic constitutive behavior of some materials under non-proportional cyclic loading have shown that non-proportional cyclic loading will produce significant additional strengthening and significantly affect fatigue life. The results of Socie's study on low-cycle fatigue of 304 stainless steel showed that under a circular path, the additional strengthening doubled and the life was reduced by 90%. For Inconel718 alloy, the additional strengthening increased by 10-15% and the fatigue life was reduced by 50%. Similarly, Chen's study on 42CrMo steel also reached the same conclusion. Therefore, when studying high-cycle fatigue under non-proportional cyclic loading, the effect of additional strengthening on life must be considered.

[0005] In response to these problems, scholars at home and abroad have done a lot of work. According to the different macro and micro phenomena in the multi-axial high-cycle fatigue failure process, they have proposed methods that can solve some problems. They can be roughly divided into three categories: equivalent stress method, energy method, and critical surface method.

[0006] Early damage parameters were mostly established based on static strength criteria. They can be used well for proportional loading conditions, but they cannot be used for non-proportional life prediction because they cannot consider the life reduction phenomenon under non-proportional loading. To make up for this deficiency, many models have been proposed in recent decades. According to the properties of the damage parameters used, multi-axial fatigue life prediction models can be divided into three categories: equivalent stress method, energy method, and critical surface method. Among them, the critical surface method was developed based on the experimental observation of crack nucleation and propagation during loading. It has good multi-axial fatigue life assessment capabilities and clear physical meanings, so it has been widely used.

[0007] With the development of complex equipment, the cost of its design, construction, testing, operation, maintenance and other life cycle has increased significantly. At the same time, the complexity of equipment has greatly increased the probability of failure, performance degradation and functional failure. Therefore, how to use existing technology to predict the fatigue life of components, achieve the purpose of condition-based maintenance, and reduce unnecessary losses is one of the biggest problems currently faced. Therefore, it is particularly important to adopt a reasonable and more accurate multi-axis fatigue life calculation model.

[0008] The working stress value of the crane's metal structure is less than the yield stress of the material, and the stress-strain relationship is linear, which belongs to high-cycle fatigue. The nominal stress estimation method based on the pSN curve and Miner's linear cumulative damage principle is usually used to estimate the fatigue life of its metal structural parts. The basic idea of ​​the nominal stress method is: starting from the SN curve of the material, considering various influencing factors, deriving the SN curve of the component, combining the measured stress-time history, using Miner's cumulative damage theory and the derived life estimation formula for estimation, and then combining the structural status of the crane for a comprehensive analysis to estimate the safe service life of the crane. The specific steps are as follows:

[0009] 1) Data collection: The life estimation of the structure is based on the collection of stress data. The sampled data in the field test should be able to reflect the actual working condition of the crane being tested, simulate the daily working condition of the crane, and test the stress-time history curve of the typical working cycle;

[0010] 2) "Rainflow counting method" for statistical analysis: For random loads, "rainflow counting" is often used in fatigue design to statistically analyze the number and regularity of stress cycles in the stress-time history, and the Goodman isolife curve is used to correct the actual stress spectrum to make it an equivalent load spectrum with a mean value of 0;

[0011] 3) Divide all stress cycles into K levels, and count the number of stress cycles at each level to obtain its equivalent load spectrum, and use the pSN curve of the component:

[0012] lgN=lgC+mlgΔσ

[0013] 4) According to Miner's cumulative damage theory, calculate the cumulative damage degree under the test working cycle:

[0014]

[0015] 5) Lifespan estimation

[0016]

[0017] The fatigue life of the component is calculated based on the damage degree of each measuring point, that is, the effective number of cycles of the component at each measuring point under cyclic load. The fatigue life calculation method commonly used in this method is: Miner criterion or relative Miner criterion. The criterion assumes that the accumulation of fatigue damage is linear and does not consider the mutual effect between loads. The use of this criterion (Miner criterion) requires the conversion of multi-axial stress into equivalent stress through the Von Mises criterion, but experiments have shown that under non-proportional loading, the error of calculating fatigue life using the converted equivalent stress is large. Summary of the invention

[0018] 1. Technical issues to be solved

[0019] In view of the shortcomings of the prior art, the present invention provides a multi-axis fatigue life calculation method for quay crane metal structures, which has the advantage of improving prediction accuracy and solves the problem of large errors in fatigue life calculation using converted equivalent stress under non-proportional loading.

[0020] (II) Technical solution

[0021] In order to achieve the purpose of improving the prediction accuracy, the present invention provides the following technical solution: a multi-axial fatigue life calculation method for a quay crane metal structure, comprising the following steps:

[0022] S1: According to the quay crane structure, a three-dimensional model of the quay crane is established, and its strength is analyzed by finite element software to obtain the stress-time history of the dangerous points on the dangerous section;

[0023] S2: Collect the monitoring data of the metal structure of the quay bridge from the sensor, and sort and analyze it to obtain the stress-time history;

[0024] S3: Modify the finite element model based on measured data combined with simulated stress-time history;

[0025] S4: Solve the location of the dangerous section of the quay crane under different working conditions;

[0026] S5: Based on the finite element analysis results and the location of the dangerous section, search for the section with the maximum shear strain amplitude and use this section as the critical surface. The specific method for determining the critical surface is as follows:

[0027] The normal strain and shear strain on the plane at an angle θ to the axis can be expressed as:

[0028]

[0029]

[0030] Where: ε y =-υε x (2)

[0031] Substituting (2) into (1) yields:

[0032]

[0033]

[0034] The strain state under multiaxial loading is expressed by the following formula:

[0035]

[0036] For sinusoidal loading, the shear strain amplitude and normal strain amplitude on the plane at an angle θ to the axis of the specimen can be expressed as follows:

[0037]

[0038]

[0039]

[0040] Where:

[0041]

[0042]

[0043] From (3) and (4) we know that Δγ / 2 and Δε n / 2 is (ζ+η), and its range is (-π / 2,π / 2). When sin(ωt+η)=1, Δγ(θ) / 2 can reach its maximum value, which is:

[0044]

[0045] The above equation is differentiated with respect to θ to obtain the location of the maximum shear strain amplitude, that is:

[0046]

[0047] The phase angle θ at which the maximum shear strain amplitude occurs c for:

[0048]

[0049] The maximum shear strain amplitude is expressed as:

[0050]

[0051] The known eq , Substituting λ into the above formula, we can get θ c From the calculation results, we can know that in the range of (-π / 2,π / 2) Δγ max (θ) / 2 takes the extreme value of θ c There are 4, two of which are extreme values ​​(θ 1 ,θ 2 ) makes Δγ max (θ) / 2 takes the same maximum value, at this time:

[0052]

[0053] θ 1 ,θ 2 Substituting into the above formula, we can get the normal strain amplitude of each The critical surface is defined as the shear plane with the largest normal strain amplitude, so the normal strain amplitude on the critical surface takes the larger value of the two:

[0054]

[0055] S6: According to the load spectrum and the position of the critical surface, the normal strain, shear strain, normal stress and shear stress on the surface are calculated, and the change history of the normal strain, shear strain, normal stress and shear stress with time is recorded;

[0056] S7: Count the cycles of normal strain, shear strain, normal stress and shear stress to obtain a stress spectrum including mean value and amplitude, eliminate the influence of mean stress by the mean square method, and convert the variable amplitude into equal amplitude;

[0057] S8: Substitute the constant-amplitude stress amplitude and strain amplitude obtained in step S7 into the new multiaxial fatigue life model to perform life prediction.

[0058] The new multiaxial fatigue life prediction model is as follows:

[0059]

[0060] Preferably, the stress-time history acquisition method in S1 and S2 is the same, and the acquisition method comprises the following steps:

[0061] A1: Install the sensor at the point to be monitored, start the crane, and lift the goods to zero;

[0062] A2: The mobile trolley realizes the lifting-unloading process;

[0063] A3: Record the lifting weight, lifting position and unloading position;

[0064] A4: The data collected by the sensor is transmitted to the computer for signal processing and analysis, and converted into stress-time history.

[0065] Preferably, the correction in S3 is specifically: correcting the finite element model by a model correction method so that the stress-time history acquired by the finite element model is similar to the stress-time history acquired by the sensor, and the error is within an allowable range.

[0066] Preferably, in the step S4, the stress-time history needs to be obtained through the modified finite element model during the solution process to prepare for the subsequent process, and the obtaining method includes the following steps:

[0067] B1: Determine the fatigue calculation point;

[0068] B2: Prepare a working condition table, and record the lifting amount, lifting position, and unloading position according to the actual working conditions;

[0069] B3: Conduct finite element analysis;

[0070] B4: Obtain stress-time history in different directions;

[0071] B5: Organize the data.

[0072] Preferably, in step S6, the normal strain, shear strain, normal stress and shear stress on the surface are stress strains in different directions.

[0073] Preferably, in the step S7, the variable amplitude is converted into a constant amplitude, and what is converted is the stress spectra of different amplitudes described above.

[0074] Preferably, in B4, Von Mises stress is not obtained, but stresses in different directions, X direction and Y direction, are actually obtained.

[0075] (III) Beneficial effects

[0076] Compared with the prior art, the present invention provides a multi-axial fatigue life calculation method for quay crane metal structures, which has the following beneficial effects:

[0077] 1. The multi-axis fatigue life calculation method for the quay crane metal structure adopts a multi-axis fatigue life calculation model, which has higher prediction accuracy than the uniaxial fatigue life calculation model.

[0078] 2. This multi-axial fatigue life calculation method for the quay crane metal structure uses a modified finite element model to extract the stress-time history of the dangerous point. DETAILED DESCRIPTION

[0079] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0080] A multi-axial fatigue life calculation method for a quay crane metal structure comprises the following steps:

[0081] S1: According to the quay crane structure, a three-dimensional model of the quay crane is established, and its strength is analyzed by finite element software to obtain the stress-time history of the dangerous points on the dangerous section;

[0082] S2: Collect the monitoring data of the metal structure of the quay bridge from the sensor, and sort and analyze it to obtain the stress-time history;

[0083] S3: Modify the finite element model based on measured data combined with simulated stress-time history;

[0084] S4: Solve the location of the dangerous section of the quay crane under different working conditions;

[0085] S5: Based on the finite element analysis results and the location of the dangerous section, search for the section with the maximum shear strain amplitude and use this section as the critical surface. The specific method for determining the critical surface is as follows:

[0086] The normal strain and shear strain on the plane at an angle θ to the axis can be expressed as:

[0087]

[0088]

[0089] Where: ε y =-υε x (2)

[0090] Substituting (2) into (1) yields:

[0091]

[0092]

[0093] The strain state under multiaxial loading is expressed as follows:

[0094]

[0095] For sinusoidal loading, the shear strain amplitude and normal strain amplitude on the plane at an angle θ to the axis of the specimen can be expressed as follows:

[0096]

[0097]

[0098] Where:

[0099]

[0100]

[0101] From (3) and (4) we know that Δγ / 2 and Δε n / 2 is (ζ+η), and its range is (-π / 2,π / 2). When sin(ωt+η)=1, Δγ(θ) / 2 can reach its maximum value, which is:

[0102]

[0103] The above equation is differentiated with respect to θ to obtain the location of the maximum shear strain amplitude, that is:

[0104]

[0105] The phase angle θ at which the maximum shear strain amplitude occurs c for:

[0106]

[0107] The maximum shear strain amplitude is expressed as:

[0108]

[0109] The known eq , Substituting λ into the above formula, we can get θ c From the calculation results, we can know that in the range of (-π / 2,π / 2) Δγ max (θ) / 2 takes the extreme value of θ c There are 4, two of which are extreme values ​​(θ 1 ,θ 2 ) makes Δγ max (θ) / 2 takes the same maximum value, at this time:

[0110]

[0111] θ 1 ,θ 2 Substituting into the above formula, we can get the normal strain amplitude of each The critical surface is defined as the shear plane with the largest normal strain amplitude, so the normal strain amplitude on the critical surface takes the larger value of the two:

[0112]

[0113] S6: According to the load spectrum and the position of the critical surface, the normal strain, shear strain, normal stress and shear stress on the surface are calculated (the stress and strain described here are stresses and strains in different directions), and the changes of the normal strain, shear strain, normal stress and shear stress over time are recorded;

[0114] S7: Count the cycles of normal strain, shear strain, normal stress and shear stress to obtain a stress spectrum including mean value and amplitude, eliminate the influence of average stress by the mean square method, and convert the variable amplitude into equal amplitude (the converted stress spectrum here is the stress spectrum of different amplitudes described above);

[0115] S8: Substitute the constant-amplitude stress amplitude and strain amplitude obtained in step S7 into the new multiaxial fatigue life model to perform life prediction.

[0116] The new multiaxial fatigue life prediction model is as follows:

[0117]

[0118] The stress-time history acquisition method in S1 and S2 is the same, and the acquisition method includes the following steps:

[0119] A1: Install the sensor at the point to be monitored, start the crane, and lift the goods to zero;

[0120] A2: Mobile trolley realizes the lifting-unloading process;

[0121] A3: Record the lifting weight, lifting position and unloading position;

[0122] A4: The data collected by the sensor is transmitted to the computer for signal processing and analysis, and converted into stress-time history.

[0123] The correction in S3 is specifically: correcting the finite element model by a model correction method so that the stress-time history acquired by the finite element model is similar to the stress-time history acquired by the sensor, and the error is within the allowable range.

[0124] In the step S4, the stress-time history needs to be obtained through the modified finite element model during the solution process to prepare for the subsequent process. The obtaining method includes the following steps:

[0125] B1: Determine the fatigue calculation point;

[0126] B2: Prepare a working condition table, and record the lifting amount, lifting position, and unloading position according to the actual working conditions;

[0127] B3: Conduct finite element analysis;

[0128] B4: Obtain stress-time history in different directions (Von Mises stress is not obtained here, but stress in different directions, such as X direction and Y direction);

[0129] B5: Organize the data.

[0130] In summary, the multi-axial fatigue life calculation method for the metal structure of the quay crane sets the correction of the finite element model, and corrects the finite element model according to the actual monitoring data, so that the analysis result and the actual monitoring result are within a reasonable allowable error range; the acquisition of the stress-time history of the dangerous point is set: the dangerous point is obtained according to the force analysis, and the stress spectrum of the dangerous point is extracted based on the corrected finite element model; a new multi-axial fatigue life prediction model is set, and on the basis of retaining the physical meaning and advantages of the parameters, no additional material constants or empirical parameters are introduced. Combined with the Manson-Coffin-Basquin equation, a new multi-axial fatigue life calculation model is constructed, which is suitable for shear failure forms; the shear stress amplitude and normal stress amplitude obtained by the cycle count are converted into equivalent stress by the improved mean square heel method, and the number of cycles and the degree of damage of a single cycle are obtained by substituting them into the multi-axial fatigue life. According to the Miner formula, each damage is linearly accumulated and converted into time, that is, the fatigue life of the metal structure of the quay crane is obtained.

[0131] It should be noted that the term "comprises" or any other variation thereof is intended to cover non-exclusive inclusion, so that a process, method, article, or device that includes a series of elements includes not only those elements, but also includes other elements that are not explicitly listed, or also includes elements inherent to such process, method, article, or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the presence of other identical elements in the process, method, article, or device that includes the element.

[0132] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A multi-axial fatigue life calculation method for quayside crane metal structures. It is characterized in that The following steps are involved: S1: According to the quay crane structure, a three-dimensional model of the quay crane is established, and its strength is analyzed by finite element software to obtain the stress-time history of the dangerous points on the dangerous section; S2: Collect the monitoring data of the metal structure of the quay bridge from the sensor, and sort and analyze it to obtain the stress-time history; S3: Modify the finite element model based on measured data combined with simulated stress-time history; S4: Solve the location of the dangerous section of the quay crane under different working conditions; S5: Based on the finite element analysis results and the location of the dangerous section, search for the section with the maximum shear strain amplitude and use this section as the critical surface. The specific method for determining the critical surface is as follows: The normal strain and shear strain on the plane at an angle θ to the axis are expressed as: where: ε y = -υε x (2) Substituting (2) into (1) we obtain: The strain state under multiaxial loading is expressed as follows: For sinusoidal loading, the shear strain amplitude and normal strain amplitude on the plane at an angle θ to the axis of the specimen are expressed as follows: Where: From (3) and (4) we know that Δγ / 2 and Δε n / 2 is (ζ+η), and its range is (-π / 2,π / 2), and when sin(ωt+η)=1, Δγ(θ) / 2 reaches its maximum value, and its value is: The above equation is differentiated with respect to θ to obtain the location of the maximum shear strain amplitude, that is: The phase angle θ at which the maximum shear strain amplitude occurs c for: The maximum shear strain amplitude is expressed as: The known υ eq , Substituting λ into the above formula, we can get θ c , from the calculation results, we know that in the range of (-π / 2,π / 2) Δγ max (θ) / 2 takes the extreme value of θ c There are 4, two of which are extreme values ​​(θ 1 ,θ 2 ) makes Δγ max (θ) / 2 takes the same maximum value, at this time: θ 1 ,θ 2 Substituting into the above formula, we can get the normal strain amplitude of each The critical surface is defined as the shear plane with the largest normal strain amplitude, so the normal strain amplitude on the critical surface takes the larger value of the two: S6: According to the load spectrum and the position of the critical surface, the normal strain, shear strain, normal stress and shear stress on the surface are calculated, and the change history of the normal strain, shear strain, normal stress and shear stress with time is recorded; S7: Count the cycles of normal strain, shear strain, normal stress and shear stress to obtain a stress spectrum including mean value and amplitude, eliminate the influence of mean stress by the mean square method, and convert the variable amplitude into equal amplitude; S8: Substitute the constant-amplitude stress amplitude and strain amplitude obtained in step S7 into the new multiaxial fatigue life model to perform life prediction. The new multiaxial fatigue life prediction model is as follows:

2. A multi-axial fatigue life calculation method for a quayside crane metal structure according to claim 1, Features: The stress-time history acquisition method in S1 and S2 is the same, and the acquisition method includes the following steps: A1: Install the sensor at the point to be monitored, start the crane, and lift the goods to zero; A2: Mobile trolley realizes the lifting-unloading process; A3: Record the lifting weight, lifting position and unloading position; A4: The data collected by the sensor is transmitted to the computer for signal processing and analysis, and converted into stress-time history.

3. The multi-axial fatigue life calculation method for the metal structure of the quay crane according to claim 1, Features: The correction in S3 is specifically: correcting the finite element model by a model correction method so that the stress-time history acquired by the finite element model is similar to the stress-time history acquired by the sensor, and the error is within the allowable range.

4. The multi-axial fatigue life calculation method for the metal structure of the quay crane according to claim 1, Features: In the step S4, the stress-time history needs to be obtained through the modified finite element model during the solution process to prepare for the subsequent process. The obtaining method includes the following steps: B1: Determine the fatigue calculation point; B2: Prepare a working condition table, and record the lifting amount, lifting position, and unloading position according to the actual working conditions; B3: Conduct finite element analysis; B4: Obtain stress-time history in different directions; B5: Organize the data.

5. The multi-axial fatigue life calculation method for the metal structure of the quay crane according to claim 1, Features: In the step S6, the normal strain, shear strain, normal stress and shear stress on the surface are stress strains in different directions.

6. A multi-axial fatigue life calculation method for a quayside crane metal structure according to claim 1, Features: In the step S7, the variable amplitude is converted into a constant amplitude, and the converted stress spectrum with different amplitudes is the stress spectrum with different amplitudes described above.

7. A multi-axial fatigue life calculation method for a quayside crane metal structure according to claim 4, Features: In B4, Von Mises stress is not obtained, but stress in different directions, X direction and Y direction, is actually obtained.

Images