CN111444651A - Intermittent welding seam strength evaluation method - Google Patents
Intermittent welding seam strength evaluation method Download PDFInfo
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- CN111444651A CN111444651A CN202010242395.1A CN202010242395A CN111444651A CN 111444651 A CN111444651 A CN 111444651A CN 202010242395 A CN202010242395 A CN 202010242395A CN 111444651 A CN111444651 A CN 111444651A
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Abstract
The invention provides an intermittent welding seam strength evaluation method, aiming at the structural form that the size of a discontinuous welding seam is greatly different from the integral structure, the continuous welding seam is simplified into a weld connection unit, an integral finite element model is established, the position strength of the welding seam is analyzed, repeated modeling is avoided, the calculated amount is reduced, and the evaluation efficiency is improved; meanwhile, the weld parameter distribution condition is collected through test piece testing, the weld equivalent stress distribution condition is calculated by combining the established integral finite element model according to the weld length and width divergence distribution condition, the weld strength is evaluated by comparing with the material strength, and the batch evaluation of the structural weld strength and the control of the weld quality consistency are realized. The method has the advantages of being more consistent with a real structural state, realizing batch weld evaluation once, avoiding repeated iteration of finite element modeling in modeling, and having the characteristics of high precision and high efficiency.
Description
Technical Field
The invention belongs to the technical field of structural strength analysis and calculation, and particularly relates to an intermittent welding seam strength evaluation method.
Background
The efficiency and the solving precision of evaluating the structural performance can be greatly improved by continuously developing a finite element theory and combining with continuously improving the computing capability of a computer, but for structures with greatly different scales, the general method is to firstly solve the overall strength and the rigidity, and for parts with more local details or more concerned, a substructure algorithm is adopted, and more precise finite element modeling is further developed for the local structures, so that the problems can be solved. The method has the problems that finite element modeling needs to be carried out repeatedly, the integral model is solved firstly, the boundary condition of a local important welding seam area is obtained from the integral solving result, then the finite element model of the encryption grid is established again in the important welding seam area, different models need to be established in different areas, the solving efficiency is not high, modeling needs to be carried out again and repeatedly to evaluate the divergence of welding seam parameters in the actual welding process, the calculated amount is large, the number of iteration times is large, and the efficiency is not high.
Disclosure of Invention
In order to solve the problems, the invention provides an intermittent welding seam strength evaluation method, which comprehensively uses finite element analysis results and theoretical analysis calculation, considers the divergence distribution condition of welding seam parameters of an actual welding structure, realizes high-quality, high-efficiency and high-precision evaluation of batch welding seam strength, and finally realizes accurate prediction of the bearing performance of the whole structure.
The technical scheme adopted by the invention for solving the technical problems is as follows:
an intermittent welding seam strength evaluation method comprises the following steps:
s1, selecting a group of welding seam parameters, establishing an integral finite element model of the target structure, and simplifying each continuous welding seam position into a weld connecting unit;
s2, carrying out overall structural strength calculation through a finite element model, and extracting forces and moments in three orthogonal directions at each weld connecting unit position;
s3, calculating the stress corresponding to each continuous welding seam position, obtaining the full stress tensor of the welding seam position, calculating the characteristic value of the full stress tensor of each welding seam position, and obtaining the main stress of the welding seam position in three directions;
s4, calculating equivalent stress of the welding seam position by adopting a fourth strength criterion, comparing the equivalent stress with the tensile strength of the material, entering a step S5 if the requirement of safety margin is met, and returning to the step S1 to increase the width and the length of the welding seam if the requirement of safety margin is not met;
s5, performing test piece welding test, and determining the ranges of the width and the length of the welding seam according to the scattering range of the welding seam parameters, wherein the ranges are marked as [ B1 ], B2] and [ L1, L2 ] respectively;
s6, calculating the stress corresponding to each continuous welding seam position under the condition of the combination of the width and the length of four welding seams of B1L 1, B1L 2, B2L 1 and B2L 2, obtaining a group of full stress tensors of each welding seam position, and solving the characteristic value of the full stress tensors to obtain the principal stress at the welding seam position under four conditions;
s7, calculating the equivalent stress of the welding seam position by adopting a fourth strength criterion, and obtaining the stress dispersion range [ sigma ] of each welding seam positionMin,σMax]Comparing the maximum stress values of all the welding positions with the tensile strength performance of the welding position material, and if the safety margin requirement is met, the stress spread range sigma of all the welding positionsMaxAnd σMinIf the ratio is not greater than the threshold, the evaluation is completed; if not, the process returns to step S5Small weld spread. .
Further, the weld parameters in the step S1 include a weld length, a weld width, a welding position, and a form of the weld.
Further, the welding seam is in the form of a double staggered intermittent welding seam.
Further, the width and length of the welding seam are selected within the following ranges: the width of the welding line is 0.9-1.4 times of the thickness of the skin, and the length of the welding line is 14-20 times of the width of the welding line.
Further, the stress calculation formula in the steps S3 and S6 is:
wherein B is the weld width, L is the weld length, F1、F2、F3Respectively, three directional forces, M1、M2、M3Three directional moments are respectively;
the full stress tensor is
Further, the fourth intensity criterion in the steps S4 and S7 is to calculate the equivalent stress formula of the weld position as follows:
wherein σ1、σ2、σ3The main stress in three directions corresponding to the welding seam position.
Further, the safety margin calculation method in steps S4 and S7 is:
wherein σbAnd sigma is the calculated equivalent stress of the welding seam position for welding the tensile strength of the base material.
Further, the safety margin in step S4 is not less than 0.5, and the safety margin in step S7 is not less than 0.2.
Further, the threshold value in step S7 is 2.
The invention has the beneficial effects that:
aiming at the structural form with larger difference between the dimension of a discontinuous welding seam and the overall structure, the invention simplifies the continuous welding seam into a weld connecting unit, establishes an overall finite element model, analyzes the position strength of the welding seam, avoids repeated modeling, reduces the calculated amount and improves the evaluation efficiency; meanwhile, the weld parameter distribution condition is collected through test piece testing, the weld equivalent stress distribution condition is calculated by combining the established integral finite element model according to the weld length and width divergence distribution condition, the weld strength is evaluated by comparing with the material strength, and the batch evaluation of the structural weld strength and the control of the weld quality consistency are realized. The method has the advantages of being more consistent with a real structural state, realizing batch weld evaluation once, avoiding repeated iteration of finite element modeling in modeling, and having the characteristics of high precision and high efficiency.
Drawings
The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. It is obvious that the drawings in the following description are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort.
FIG. 1 is a top view of a discontinuous weld structure in an embodiment of the present invention;
FIG. 2 is a cross-sectional view of a portion A-A of the interrupted reflow structure of FIG. 1;
FIG. 3 is a top view of the intermittently welded structure of FIG. 1 without the skin structure;
FIG. 4 is an enlarged view of a single weld and coordinate definition according to an embodiment of the present invention;
FIG. 5 is a flow chart of a weld strength assessment method according to an embodiment of the present invention;
wherein, 1 is a skin structure, 2 is a frame structure, and 3 is a welding line.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
Taking a cabin structure containing internal pressure as an example, a typical unit welding structure of a local skin and a skeleton is shown in fig. 1-3, a skin structure 1 is coated on a frame structure 2, and laser intermittent welding is adopted between the skin structure 1 and the frame structure 2 to control overall deformation. In the embodiment, the dimension of the cabin body is in a meter-scale dimension, the dimension difference is 1000 times, if the weld joint position strength is evaluated by direct finite element modeling, the weld joint position strength needs to be obtained by repeated calculation of a finite element substructure, the calculation amount is large, the stress concentration and local stress distortion caused by structural discontinuity cannot be avoided, an ideal analysis result is difficult to obtain, the welding parameter divergence distribution condition in an actual structure is ignored, and the evaluation precision is reduced. The invention provides an intermittent welding seam strength evaluation method, a flow chart is shown in figure 5, and the method comprises the following steps:
the method comprises the following steps: and selecting a group of welding seam parameters, establishing a target structure integral finite element model, and simplifying each continuous welding seam position into a weld connecting unit.
The weld parameters include weld length, weld width, weld location, and weld form. According to the material of the component and the thickness of the skin, laser penetration welding is selected and adopted, and the form is double-strip staggered intermittent welding lines; the welding position can be designed according to the actual working condition; the width and the length of the welding line can be set according to experience, and in order to better meet the requirements of welding quality and deformation control, the width and the length of the welding line can be selected according to the rule that the width of the welding line is 0.9-1.4 times of the thickness of the skin, and the length of the welding line is 14-20 times of the width of the welding line.
In this embodiment, the skin thickness is 2.5mm, the selected weld width B0 is 2.5mm, the weld length L0 is 40mm, and the distance between the center lines of the two welds is 6 mm.
The method comprises the steps of simulating a real state as much as possible by adopting universal finite element analysis software Abaqus, determining material properties, loads, boundary conditions, grids and units, and establishing a target integral structure finite element model comprising a skin structure 1, a connected frame structure 2 and a welding seam 3 position structure, wherein each continuous welding seam position is simplified into a weld connecting unit which comprises three moving degrees of freedom and three rotating degrees of freedom and is used for outputting force and moment transmitted between two connecting areas.
Step two: and carrying out overall structural strength calculation, and extracting forces and moments in three orthogonal directions at each weld connecting unit position.
For convenience of description, given local coordinate definition of a single weld, which is also the coordinate of the weld connecting unit, as shown in fig. 4, the origin of the coordinate is the centroid of the weld, the length direction of the weld is the X axis, the normal direction of the weld is the Y axis, the side pointing to the skin is positive, and the width direction is the Z axis.
Calculating the integral bearing performance of the structure of the cabin containing the internal pressure by using a finite element model, taking a weld unit as an example, extracting the forces and moments in three orthogonal directions of the position of the weld connecting unit and the forces F in three directions of an X axis, a Y axis and a Z axis1、F2、F33.3kN, -3.6kN, -4.0kN and three-direction moment M1、M2、M3Are respectively-7.65 N.m, -5.70N.m and-4.88 N.m.
Step three: according to the width and the length of the welding seam selected in the step one, calculating the stress corresponding to each continuous welding seam position, namely the weld connecting unit, and obtaining the full stress tensor of the welding seam position
Calculating the characteristic value of the full stress tensor of each welding seam position
Namely the main stress in three directions corresponding to the position of the welding seam.
The stress calculation formula is respectively as follows:
wherein B is the weld width, L is the weld length, F1、F2、F3Respectively, three directional forces, M1、M2、M3Three directional moments are respectively.
Calculating to obtain sigma11、σ22、σ33、τ23、τ13、τ12Respectively at 33MPa, -36MPa, -40MPa,-183.6MPa、-68.4MPa、-58.56MPa。
Using Matlab software or Python/Numpy software to solve the built full stress tensor eigenvalue to obtain the principal stress
Namely the main stress in three directions corresponding to the position of the welding seam.
Step four: calculating equivalent stress of welding seam position by adopting fourth strength criterion
And (4) comparing the equivalent stress with the tensile strength of the material, entering the next step if the requirement of the safety margin is met, returning to the step one to increase the width and the length of the welding line if the requirement of the safety margin is not met, and entering the next step until the requirement of the safety margin is met.
The equivalent stress level of the weld joint position is obtained by calculation to be 361.25 MPa. Compared with the tensile strength of the material, the material meets the safety margin of at least more than 0.5 and meets the requirement.
The safety margin calculation method comprises the following steps:
wherein σbSigma is the welding seam stress obtained by welding base material tensile strength and evaluation, and sigma in the invention is the welding seam position equivalent stress sigma obtained by calculationMises。
And step five, performing test piece level welding test according to the requirements of the length and width of the welding seam, and determining the spread range of the width and length of the welding seam according to the spread range of the parameters of the welding seam, wherein the spread range is marked as [ B1, B2] and [ L1, L2 ].
Step six: determining the width range of the welding seam according to the step five [ B1, B2]]And weld length range [ L1, L2]Respectively calculating the stress corresponding to each continuous welding seam position under the condition of four combinations of B1L 1, B1L 2, B2L 1 and B2L 2, and obtaining the full stress tensor of the welding seam position under the condition of the four combinations
Three eigenvalues of the built full stress tensor are solved respectively,
obtaining the three-direction main stress sigma corresponding to the welding seam position under four conditions1、σ2、σ3。
And (3) by adopting a stress calculation formula in the third step, performing combined calculation according to B1L 1, B1L 2, B2L 1 and B2L 2 to obtain four groups of stress tensors under the condition of considering the divergence distribution of welding parameters, wherein the unit of the stress is MPa:
the Matlab software or Python/Numpy software is adopted to solve the built full stress tensor eigenvalue to obtain the principal stress under the condition of four groups of combinations
The main stresses in three directions corresponding to the positions of the welding seams under the four combinations are respectively
Step seven: respectively calculating equivalent stress of weld joint positions under four conditions by adopting a fourth strength criterion
Obtaining the stress dispersion range [ sigma ] of the welding seam positionMin,σMax]Taking σMaxAnd comparing the tensile strength performance of the material at the welding seam position, and evaluating to obtain the safety margin of the welding seam position strength. And calculating the stress dispersion range of all welding seam positions, and comparing the maximum value of the stress of all welding seam positions with the tensile strength performance of the material at the welding seam position. If the requirement of safety margin is met and the quality consistency of the welding seam is ensured, sigma in the stress dispersion range of all welding seam positionsMaxAnd σMinAnd if the ratio is not greater than the threshold value, finishing the evaluation, and if the ratio is not greater than the threshold value, returning to the step five to narrow the weld spreading range.
In the embodiment, the four groups of results are calculated to obtain equivalent Mises stresses of 375.83MPa, 334.03MPa, 243.22MPa and 216.16MPa respectively, so that the influence of actual welding seam parameter divergence on actual strength is obvious, compared with the condition that the skin and the frame structure parent metal are titanium alloy, the safety margin of at least 0.2 is met, and the sigma is higher than the safety margin of the skin and the frame structure parent metalMaxAnd σMinThe ratio is less than the threshold value 2, and the requirement is met. Under the condition that the requirements are not met, the welding process needs to be optimized, and particularly, measures such as better equipment control by adopting laser energy, auxiliary welding tools and the like for reducing the divergence distribution of welding seams are added, and the dispersion range of the sizes of the welding seams is controlled, so that the welding strength and the welding seam consistency of the whole structure are ensured.
The welded cabin structure containing internal pressure is subjected to test testing, and the obtained high stress of the welding seam position is consistent with the evaluation result, so that the evaluation method is reasonable and effective and can be matched with the component test result.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
The invention has not been described in detail and is in part known to those of skill in the art.
Claims (9)
1. The method for evaluating the strength of the intermittent welding seam is characterized by comprising the following steps of:
s1, selecting a group of welding seam parameters, establishing an integral finite element model of the target structure, and simplifying each continuous welding seam position into a weld connecting unit;
s2, carrying out overall structural strength calculation through a finite element model, and extracting forces and moments in three orthogonal directions at each weld connecting unit position;
s3, calculating the stress corresponding to each continuous welding seam position, obtaining the full stress tensor of the welding seam position, calculating the characteristic value of the full stress tensor of each welding seam position, and obtaining the main stress of the welding seam position in three directions;
s4, calculating equivalent stress of the welding seam position by adopting a fourth strength criterion, comparing the equivalent stress with the tensile strength of the material, entering a step S5 if the requirement of safety margin is met, and returning to the step S1 to increase the width and the length of the welding seam if the requirement of safety margin is not met;
s5, performing test piece welding test, and determining the ranges of the width and the length of the welding seam according to the scattering range of the welding seam parameters, wherein the ranges are marked as [ B1 ], B2] and [ L1, L2 ] respectively;
s6, calculating the stress corresponding to each continuous welding seam position under the condition of the combination of the width and the length of four welding seams of B1L 1, B1L 2, B2L 1 and B2L 2, obtaining a group of full stress tensors of each welding seam position, and solving the characteristic value of the full stress tensors to obtain the principal stress at the welding seam position under four conditions;
s7, calculating the equivalent stress of the welding seam position by adopting a fourth strength criterion, and obtaining the stress dispersion range [ sigma ] of each welding seam positionMin,σMax]Comparing the maximum stress values of all the welding positions with the tensile strength performance of the welding position material, and if the safety margin requirement is met, the stress spread range sigma of all the welding positionsMaxAnd σMinIf the ratio is not greater than the threshold, the evaluation is completed; if not, the process returns to step S5 to narrow the bead distribution range.
2. The weld strength evaluation method according to claim 1, wherein the weld parameters in the step S1 include a weld length, a weld width, a welding position, and a form of the weld.
3. The weld strength evaluation method according to claim 2, wherein the weld is in the form of a double staggered intermittent weld.
4. The weld joint strength evaluation method according to claim 2, wherein the width and length of the weld joint are selected from the range of: the width of the welding line is 0.9-1.4 times of the thickness of the skin, and the length of the welding line is 14-20 times of the width of the welding line.
5. The weld strength evaluation method according to claim 1, wherein the stress calculation formula in the steps S3, S6 is:
wherein B is the weld width, L is the weld length, F1、F2、F3Respectively, three directional forces, M1、M2、M3Three directional moments are respectively;
the full stress tensor is
6. The weld strength evaluation method according to claim 5, wherein the fourth strength criterion in the steps S4 and S7 is to calculate the equivalent stress formula of the weld position as follows:
wherein σ1、σ2、σ3The main stress in three directions corresponding to the welding seam position.
7. The weld strength evaluation method according to claim 6, wherein the safety margin calculation methods in the steps S4 and S7 are as follows:
wherein σbFor welding the tensile strength of the base material, sigma is the calculated equivalent stress sigma of the welding seam positionMises。
8. The weld strength evaluation method according to claim 1, wherein the safety margin in step S4 is not less than 0.5, and the safety margin in step S7 is not less than 0.2.
9. The weld strength evaluation method according to claim 1, wherein the threshold value in step S7 is 2.
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