A fatigue life prediction method for notched welded joints

Abstract

This invention relates to the field of fatigue life prediction technology for welded structures, specifically disclosing a method for predicting the fatigue life of notched welded joints. The method includes measuring the geometry, dimensions, total area of ​​the cross-section, vertical distance from the outermost edge of the cross-section to the neutral axis, and the notch transition angle of the welded joint to be predicted; calculating the nominal stress, singular equivalent parameters, and material parameters of the welded joint; calculating the singular equivalent stress of the welded joint based on the nominal stress, singular equivalent parameters, and material parameters; and calculating the fatigue life of the welded joint based on the singular equivalent stress and the material's S&N curve. This invention introduces the concepts of singular equivalent stress and singular equivalent crack, eliminating reliance on finite element analysis and improving the prediction speed and reliability of the prediction results.

Description

Technical Field

[0001] The invention relates to the technical field of fatigue life prediction of welded structures, and in particular to a fatigue life prediction method for a notched welded joint. Background Art

[0002] When subjected to cyclic loads, stress concentration is easily generated at the sudden changes in the weld structure, which can initiate fatigue cracks and lead to fatigue fracture. Therefore, how to use parameters such as the type and size of the weld joint to quickly and accurately predict the fatigue life is of great significance for evaluating the strength of key parts of the welded structure under the main load. At present, in the prior art, for welded structures with notches, fatigue assessment is usually performed based on the simulation results of finite element models, using SN curve method, local stress-strain method, fracture mechanics method, etc., or a large number of notch fatigue feature data sets are established to use machine learning models to predict fatigue life.

[0003] The existing fatigue life prediction method for notched welded joints mainly uses the finite element analysis method. This method can obtain the stress distribution and fatigue life of notched welded joints more accurately, but its analysis process relies on finite element software. The process of establishing a finite element model is relatively cumbersome and rigorous. The refined modeling of the model will increase the simulation analysis time. It can be seen that this method is time-consuming, not suitable for scenarios without computers, and not suitable for people who do not master finite element software. In addition, finite element software has mesh sensitivity and stress calculation singularity, which makes it difficult for this method to accurately describe the stress distribution at the notch of the welded structure. On the other hand, the existing machine learning prediction method relies on data-driven, and the prediction accuracy is limited by the size and quality of the data set. The missing sensitivity of the notch characteristic parameters is strong, resulting in a lack of stability in the prediction results. Summary of the invention

[0004] The purpose of the present invention is to provide a fatigue life prediction method for a notched weld joint to solve the problem in the above-mentioned background technology that the fatigue life prediction of a notched weld joint relies on finite element analysis, it is difficult to accurately describe the stress distribution at the notch of the weld structure and the prediction result lacks stability.

[0005] In order to solve the above technical problems, the present invention provides a fatigue life prediction method for a notched weld joint, which is characterized by comprising the following steps:

[0006] S1. Measure the geometric shape, geometric dimensions, total area of ​​the cross section, vertical distance from the outermost point of the cross section to the neutral axis and notch transition angle of the weld joint to be predicted, and calculate the nominal stress, singular equivalent parameters and material parameters of the weld joint to be predicted;

[0007] S2. Calculate the singular equivalent stress of the welded joint based on the nominal stress, singular equivalent parameters and material parameters;

[0008] S3. Based on the singular equivalent stress of the welded joint and combined with the material SN curve, calculate the fatigue life of the welded joint.

[0009] Preferably, in step S1, the nominal stress of the welded joint to be predicted when subjected to tensile stress is for:

[0010] ;

[0011] in, is the tensile load, is the total area of ​​the cross section where the weld joint is located;

[0012] Nominal stress of the welded joint to be predicted when subjected to bending stress for:

[0013] ;

[0014] in, is the bending moment, is the maximum bending moment, is the vertical distance from the outermost point of the cross section to the neutral axis, is the moment of inertia, is the bending section coefficient.

[0015] Preferably, in step S1, n groups of welded joints with the same material and shape as the welded joint to be predicted are selected for fatigue testing to obtain n groups of welded joints with stress amplitudes. and fatigue life Experimental data , calculate the nominal stress of n groups of welded joints , according to the formula:

[0016] ;

[0017] Calculate the stress amplitude at the weld position Theoretical value of singular equivalent stress at ,in, , is the material constant, which is taken according to the material SN curve corresponding to n groups of welding joints. is the number of groups, ,

[0018] Singular equivalent cracks of n groups of welded joints Take any value in the range of 0-20mm and calculate the singular equivalent stress value points corresponding to n groups of welding joints :

[0019] ;

[0020] in, is a constant term based on the value of the singular equivalent crack,

[0021] Calculate the singular equivalent stress values ​​of n groups of welded joints :

[0022] ;

[0023] in, , is a constant term related to the notch transition angle of the weld joint, and ,

[0024] Adjustment The value of the singular equivalent stress theory and calculated values ​​of singular equivalent stress When the relative error value of is the smallest, the singular equivalent crack suitable for the fatigue life assessment of n groups of welded joints is obtained. , calculate the average value of n groups of singular equivalent cracks to obtain the singular equivalent crack of the welded joint to be predicted ;

[0025] Singular equivalent stress value points of welded joints to be predicted for:

[0026] ;

[0027] Singular equivalent parameters of welded joints to be predicted for:

[0028] .

[0029] Preferably, in step S1, according to the formula:

[0030] ;

[0031] Calculate the material parameters of n groups of welding joints , calculate the average value of n groups of material parameters to obtain the material parameters of the welded joint to be predicted .

[0032] Preferably, in step S2, the singular equivalent stress of the welding joint for:

[0033] .

[0034] Preferably, in step S3, the fatigue life of the welded joint for:

[0035] ;

[0036] Calculate the above formula to complete the fatigue life of the welded joint prediction.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The present invention proposes a fatigue life prediction method for a notched welded joint, which has a short prediction time and proposes the concepts of singular equivalent stress and singular equivalent crack. The singular equivalent stress is an accurate description of the fatigue assessment stress at the notch stress concentration point; different notch angles of the welded joint are accurately considered to complete parameterized value taking, which is convenient for theoretical calculation; a calculation method for material parameters is proposed, and material parameter calculation based on multiple standards is realized, ensuring speed and accuracy; it does not require a finite element theoretical foundation and no longer relies on finite element software, and is suitable for people who do not have a computer scene or have not mastered the finite element analysis technology, avoiding the mesh sensitivity and stress singularity of the finite element analysis method; the present invention improves the calculation efficiency and result reliability of fatigue strength analysis, and realizes rapid and accurate prediction of the fatigue life of a notched welded joint. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a flow chart of an embodiment of the present invention;

[0040] Figure 2 The notch in the embodiment of the present invention is equivalent to a singular equivalent crack with a transition angle of 135°. Reasonable value calculation result diagram;

[0041] Figure 3 This is a graph showing the values ​​of the parameter p related to the notch transition angle of the welded joint according to an embodiment of the present invention;

[0042] Figure 4 This is a partial schematic diagram of a notch in a welding joint according to an embodiment of the present invention;

[0043] Figure 5 This is a rendering of the effect that the notch at the weld position of the T-joint in an embodiment of the present invention is equivalent to a transition angle of 135°. DETAILED DESCRIPTION

[0044] The following embodiments of the present invention are described in further detail in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0045] A fatigue life prediction method for a notched welded joint in this embodiment is as follows: Figure 1 As shown, the following steps are included:

[0046] S1. Measure the geometric shape, geometric dimensions, total area of ​​the cross section, vertical distance from the outermost point of the cross section to the neutral axis and notch transition angle of the weld joint to be predicted, and calculate the nominal stress, singular equivalent parameters and material parameters of the weld joint to be predicted;

[0047] Nominal stress of the welded joint to be predicted when subjected to tensile stress for:

[0048] ;

[0049] in, is the tensile load, in N, is the total area of ​​the cross section where the weld joint is located, in mm;

[0050] Nominal stress of the welded joint to be predicted when subjected to bending stress for:

[0051] ;

[0052] in, is the bending moment, is the maximum bending moment, in N·mm, It is the vertical distance from the outermost point of the cross section to the neutral axis, in mm. is the moment of inertia, in mm 4 , is the bending section coefficient, in mm 3 ;

[0053] The tensile load, bending moment, maximum bending moment, moment of inertia and bending section coefficient are obtained through existing mechanical analysis methods according to the geometric shape and geometric dimensions of the welded joint to be predicted.

[0054] Select n groups of welded joints with the same material and shape as the welded joint to be predicted for fatigue test, and obtain n groups of stress amplitudes. and fatigue life Experimental data , calculate the nominal stress of n groups of welded joints , according to the formula:

[0055] ;

[0056] Calculate the stress amplitude at the weld position Theoretical value of singular equivalent stress at ,in, , is the material constant, which is taken according to the material SN curve corresponding to n groups of welding joints. is the number of groups, ,

[0057] Singular equivalent cracks of n groups of welded joints Take any value in the range of 0-20mm and calculate the singular equivalent stress value points corresponding to n groups of welding joints :

[0058] ;

[0059] in, is a constant term based on the value of the singular equivalent crack, and its specific value is shown in the following table:

[0060] ;

[0061] Calculate the singular equivalent stress values ​​of n groups of welded joints :

[0062] ;

[0063] in, , is a constant term related to the notch transition angle of the welded joint, and the parameter p is determined by different notch transition angles 2α. , the relevant common notch transition angle 2α corresponds to See the following table for the values:

[0064] ;

[0065] Schematic diagram of the structural gap and more gap transition angles Values ​​such as Figure 3 , 4 As shown in the figure, 2α represents different notch transition angle values. When the welding transition angle is 90° ; When it is a 180° straight edge, the singularity disappears , the stress is constant. When the angle at the welding transition corner is 0°, it is considered that there is a sharp crack. .

[0066] Adjustment The value of the singular equivalent stress theory and calculated values ​​of singular equivalent stress When the relative error value of is the smallest, the singular equivalent crack suitable for the fatigue life assessment of n groups of welded joints is obtained. , calculate the average value of n groups of singular equivalent cracks to obtain the singular equivalent crack of the welded joint to be predicted , unit is mm;

[0067] Singular equivalent stress value points of welded joints to be predicted for:

[0068] ;

[0069] Singular equivalent stress value point The unit is mm;

[0070] Singular equivalent parameters of welded joints to be predicted for:

[0071] .

[0072] According to the formula:

[0073] ;

[0074] Calculate the material parameters of n groups of welding joints , calculate the average value of n groups of material parameters to obtain the material parameters of the welded joint to be predicted In this embodiment, the material parameters of steels of different standards are calculated as follows:

[0075] ;

[0076] S2. Calculate the singular equivalent stress of the welded joint based on the nominal stress, singular equivalent parameters and material parameters for:

[0077] .

[0078] S3. Calculate the fatigue life of welded joints based on the singular equivalent stress of welded joints and the SN curves of corresponding standard materials such as BS7608 and IIW. for:

[0079] ;

[0080] Calculate the above formula to complete the fatigue life of the welded joint prediction.

[0081] The following is a specific example.

[0082] Taking the more common T-joint as an example, the notch position of the weld joint is equivalent to a transition angle of 135°. The equivalent effect of the notch transition angle of the T-joint is as follows: Figure 5 When the loading conditions and structural dimensions of the T-joint are given, the nominal stress If the structure is subjected to a tensile load of 1600N and the cross-sectional area is 100mm 2 , then calculate the nominal stress When the notch of the T-joint weld position is equivalent to a transition angle of 135°, , a singular equivalent crack of a welded joint with a transition angle of 135° , the value is calculated as Figure 2 As shown, the singular equivalent crack When , calculate the singular equivalent stress value point , the singular equivalent parameter can be calculated A large number of fatigue test data of T-type welded joints made of steel are selected to calculate the material parameters corresponding to the F2 joint grade of the BS7608 standard. =0.595, the calculated singular equivalent stress =9.3629, the singular equivalent stress is a stress that quickly and accurately predicts the fatigue life of the structure considering the notch effect. Select the BS7608 standard corresponding to the F2 joint grade , calculate the fatigue life of the structure .

[0083] The present invention proposes a fatigue life prediction method for a notched welded joint, which has a short prediction time and proposes the concepts of singular equivalent stress and singular equivalent crack. The singular equivalent stress is an accurate description of the fatigue assessment stress at the notch stress concentration point; different notch angles of the welded joint are accurately considered to complete parameterized value taking, which is convenient for theoretical calculation; a calculation method for material parameters is proposed, and material parameter calculation based on multiple standards is realized, ensuring speed and accuracy; it does not require a finite element theoretical foundation and no longer relies on finite element software, and is suitable for people who do not have a computer scene or have not mastered the finite element analysis technology, avoiding the mesh sensitivity and stress singularity of the finite element analysis method; the present invention improves the calculation efficiency and result reliability of fatigue strength analysis, and realizes rapid and accurate prediction of the fatigue life of a notched welded joint.

[0084] The embodiments of the present invention are given for the purpose of illustration and description, and are not intended to be exhaustive or to limit the invention to the disclosed forms. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments are selected and described in order to better illustrate the principles and practical applications of the present invention and to enable those of ordinary skill in the art to understand the present invention and thereby design various embodiments with various modifications suitable for specific uses.

Claims

1. A fatigue life prediction method for a notched weld joint, characterized in that: The following steps are involved: S1. Measure the geometric shape, geometric dimensions, total area of ​​the cross section, vertical distance from the outermost point of the cross section to the neutral axis and notch transition angle of the weld joint to be predicted, and calculate the nominal stress, singular equivalent parameters and material parameters of the weld joint to be predicted; Nominal stress σ when the welded joint is subjected to tensile stress n拉 for: Where F is the tensile load, A is the total area of ​​the cross section where the weld joint is located; Nominal stress σ when the welded joint is subjected to bending stress n弯 for: Where, M is the bending moment, M max is the maximum bending moment, y max I is the vertical distance from the outermost point of the cross section to the neutral axis. z is the moment of inertia, W z is the bending section coefficient; The nominal stress σ of the welded joint to be predicted under tensile stress n The value is σ n拉 , the nominal stress σ of the welded joint to be predicted when subjected to bending stress n The value is σ n弯 ; Select n groups of welded joints with the same material and shape as the welded joint to be predicted for fatigue test, and obtain n groups of stress amplitude S i and fatigue life N i The experimental data (S1, N1), (S2, N2), L, (S n ,N n ), calculate the nominal stress of n groups of welded joints According to the formula: The calculated stress amplitude S at the weld position is i Theoretical value of singular equivalent stress σ at y1 ,σ y2 ,Lσ yn , where m, C 材 is the material constant, which is taken according to the material SN curve corresponding to n groups of welding joints, i is the number of groups, i=1,2,L,n, Singular equivalent cracks of n groups of welded joints Take any value in the range of 0-20mm and calculate the singular equivalent stress value points corresponding to n groups of welding joints Among them, A, B, C, D, and E are constant terms based on the values ​​of singular equivalent cracks. Calculate the singular equivalent stress values ​​of n groups of welded joints Among them, p and q are constant terms related to the notch transition angle of the weld joint, and q = 3p-0.5, Adjustment The value of the singular equivalent stress theory σ y1 ,σ y2 ,Lσ yn and calculated values ​​of singular equivalent stress σ′ y2 ,L,σ′ yn When the relative error value of is the smallest, the singular equivalent crack a suitable for fatigue life assessment of n groups of welded joints is obtained. eq1 ,a eq2 ,L,a eqn , calculate the average value of n groups of singular equivalent cracks to obtain the singular equivalent crack a of the welded joint to be predicted eq ; The singular equivalent stress value point x of the welded joint to be predicted eq for: x eq =A+B·a eq +C·a eq 2 +D·a eq 3 +E·a eq 4 ; The singular equivalent parameter k of the welded joint to be predicted is: According to the formula: Calculate the material parameters of n groups of welding joints Calculate the average value of n groups of material parameters to obtain the material parameter f of the weld joint to be predicted eq； S2. Calculate the singular equivalent stress of the welded joint based on the nominal stress, singular equivalent parameters and material parameters; S3. Based on the singular equivalent stress of the welded joint and combined with the material SN curve, calculate the fatigue life of the welded joint.

2. The fatigue life prediction method of a notched weld joint according to claim 1, characterized in that: In step S2, the singular equivalent stress σ of the welded joint eq for: s eq =k·f eq ·s n 。 3. The fatigue life prediction method of a notched weld joint according to claim 2, characterized in that: In step S3, the fatigue life N of the welded joint is: Calculate the above formula to complete the prediction of the fatigue life N of the welded joint.

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