CN111523183A - Simulation modeling method for mechanical property and fracture failure of welding joint - Google Patents
Simulation modeling method for mechanical property and fracture failure of welding joint Download PDFInfo
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Abstract
The invention discloses a simulation modeling method for mechanical property and fracture failure of a welding joint, which comprises the steps of slicing a welding sample plate according to the temperature change conditions of different areas in the welding process before finite element modeling, then testing to obtain the material constitutive parameters of each tensile sample, and applying the material constitutive parameters of each tensile sample to each micro-area during finite element modeling, so that different micro-areas have different mechanical property parameters, the precise description of the mechanical property of the micro-area of the welding joint is realized, the modeling precision and the modeling accuracy are greatly improved, and the problem of inaccurate model caused by the fact that the same material constitutive parameter is adopted by the whole welding joint is avoided.
Description
Technical Field
The invention belongs to the technical field of metal material connection performance analysis, and particularly relates to a metal material welding joint mechanical property and fracture failure simulation modeling method.
Background
Soldering is a very efficient joining process that allows permanent joining of materials to be joined, typically by applying heat or pressure, or both, to form a solder joint. However, after welding the materials, the properties of each part of the joint are not uniform, and there may be the following reasons: 1) the material composition, the performance and the like of the filled welding wire are inconsistent with those of the connecting material; 2) the welded heat affected zone is heated to different degrees, and heat treatment is carried out to different degrees, so that the welded microstructure is changed and uneven; 3) the welding of dissimilar materials, there are differences in the original material composition and structure of both sides of the weld. It is therefore important to have a fine description of the mechanical properties of the welded joint, in particular the properties of the individual micro-areas.
For example, it has been widely used for aluminum alloy members for vehicles such as automobiles, rail transportation, ships, aerospace, and the like. Compared with steel welding, the aluminum alloy has high heat capacity coefficient, large heat conductivity coefficient and large linear expansion coefficient, and the heat input amount of the welded aluminum alloy is 2-4 times that of the welded steel at the same welding speed. The continuous input of heat in the welding process can cause local microstructure evolution of the welded joint to cause strength softening. However, the aluminum alloy welded structural part is a key part in a vehicle body and plays a role in bearing, and the welding softening causes the strength reduction to cause the aluminum alloy welded structural part to break and fail in an accident. Therefore, the failure position of the welding joint and the mechanical property characteristic of the joint are accurately predicted, and the method has great significance for evaluating the welding seam arrangement and service safety in structural design.
Finite element modeling analysis is a computer-aided way which is very important for describing the deformation behavior and the fracture behavior of the metal material under the action of external force. For a homogeneous bulk material, the computer simulation modeling analysis steps are as follows: 1) performing a tensile experiment on an ideal material to obtain a stress-strain curve of the ideal material, and solving parameters such as yield strength, tensile strength, elongation, strain hardening index, strain softening index and the like on the curve to be used as a mechanical constitutive equation of the material; 2) the block material is considered to be completely uniform, then grid division is carried out through a finite element method, and the uniform block is divided into a limited number of independent units; 3) inputting the material parameters obtained in the step 1 into a finite element in the model established in the step 2; 4) setting working condition parameters of the model, including stress magnitude, stress position, direction, distribution rule and the like, and establishing a stress calculation model; 5) setting a calculation step length by adopting a specific iterative algorithm, deforming and superposing all the finite elements in a specific deformation mode, setting a corresponding convergence value, and realizing the coordination and consistency of the deformation among all the finite elements by adopting iterative calculation to reach the set convergence value; 6) and after the calculation is finished, outputting cloud pictures of deformation, stress and the like of the limited units, and analyzing the stress condition of the part. In the process, the step 1) is a material parameter obtaining process; steps 2) and 3) are finite element modeling processes; steps 4) and 5) are calculation processes; step 6) is an analysis process. For any finite element mechanical simulation analysis case, the acquisition and modeling process of the material performance is the most important, and the accuracy of the model fineness and the material characteristics determines the accuracy of the final calculation result.
For welded structures (welded joints), conventional finite element modeling analysis methods are not suitable, mainly because the welded joints are not homogeneous materials, the mechanical properties of both sides of the welded joints and the weld zones thereof are not uniform, and the material parameters of adjacent micro-regions (micro-regions) are not uniform. Therefore, a more refined model needs to be established for simulation analysis, the structure should be divided into fine units or layers with uniform mechanical properties as much as possible, the material parameters of the small units are obtained, and a more refined finite element model is established again, and then simulation calculation and result analysis are performed.
However, at present, no mature finite element modeling method for the welding joint exists, and the method applied in the industry at present is rough, and the process is as follows: taking out the welded joint, preparing a tensile sample, carrying out tensile experiment test, obtaining the integral mechanical property data and the fracture position of the welded joint, obtaining the tensile constitutive equation of the joint, taking the parameters contained in a stress-strain curve and the like of the fracture position (generally, the position with the worst mechanical property) as the material parameters of the whole joint, and calculating by using a conventional uniform material finite element model. The simulation analysis result obtained by the method has low precision, and particularly the deformation difference of the whole joint is large; in addition, the above method cannot truly describe the true stress and deformation conditions of each point (area) on the joint, which is not beneficial to making clear and accurate simulation prediction.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a simulation modeling method for the mechanical property and the fracture failure of a welding joint, and aims to solve the problems of low modeling precision and poor accuracy in the traditional method.
The invention solves the technical problems through the following technical scheme: a simulation modeling method for mechanical property and fracture failure of a welding joint comprises the following steps:
step 1: preparing a welding sample plate, and acquiring the temperature change ranges of different areas on the welding sample plate in the welding process, wherein the different areas are areas which are perpendicular to the length direction of a surface to be welded and are parallel to the surface to be welded;
step 2: cutting the welding sample plate along the direction vertical to the length direction of the surface to be welded according to the temperature variation range of different areas in the step 1 to obtain a plurality of tensile samples;
and step 3: performing mechanical property test on each tensile sample to obtain a stress-strain curve of each tensile sample, and simulating the stress-strain curve of each tensile sample by using a constitutive model to obtain material constitutive parameters of each tensile sample; and obtaining the strain energy at break of each tensile sample;
and 4, step 4: establishing a finite element model according to the welding sample plate, and then carrying out micro-area division and grid division on the finite element model according to the actual size of each tensile sample;
and 5: and (3) applying the material constitutive parameters and the fracture strain energy of each tensile sample in the step (3) to the micro-area corresponding to each tensile sample to obtain the accurate finite element model of the welding sample plate.
According to the method, different areas in the actual welding process are correspondingly provided with different thermal shocks (different mechanical properties under different thermal shocks) to slice the welding sample plate in a layered mode, material constitutive parameters of each tensile sample are obtained, the material constitutive parameters of each tensile sample are applied to each micro area in a finite element model, the different micro areas of the welding sample plate are correspondingly provided with different material constitutive parameters (namely the mechanical property parameters), accurate description of the mechanical properties of the micro areas of the welding joint is achieved, modeling precision and modeling accuracy are greatly improved, the problem that the model is inaccurate due to the fact that the same material constitutive parameters are adopted for the whole welding joint is solved, calculation and analysis are conducted on the basis, and accurate simulation prediction can be obtained.
Further, in step 1, the method for acquiring the temperature variation ranges of different areas includes:
step 1.1: sequentially dividing the base material into n regions on the base material along the length direction vertical to the surface to be welded of the base material, wherein the width of each region is not more than 2 mm;
step 1.2: and monitoring the temperature change condition of each area in the welding process to obtain the temperature change range of different areas on the welding sample plate.
Further, in step 1.2, a type K thermocouple is used to monitor the temperature change of each zone.
Further, in the step 1, simulact software is used to obtain the temperature variation ranges of different areas.
Further, in step 1, the welding joint type of the welding template is a butt joint, a T-joint, an angle joint, or a lap joint.
Further, in the step 2, the cutting processing mode is a linear cutting mode.
Further, in the step 3, a Johnson-Cook model is adopted to simulate the stress-strain curve of each tensile sample, and the expression of the Johnson-Cook model is as follows:
wherein, sigma is the equivalent stress,eq、
and
equivalent plastic strain, strain rate in the test and reference strain rate, respectively; t, TrAnd TmThe instantaneous temperature at strain, the reference temperature and the melting temperature of the material, respectively; A. b, C, n and m are the initial yield stress, strain hardening coefficient, strain rate coefficient, strain hardening index and heat softening index, respectively, at a reference temperature.
Further, in step 3, the fracture strain energy of each tensile specimen is obtained using the Cockcroft-Latham ductile fracture rule.
Further, in the step 4, for the finite element model of the butt joint, the mesh division size in the range of 3.8mm to 19mm from the center of the weld is 0.5mm × 0.5mm × 1mm, and the mesh division size in other ranges is 1mm × 1mm × 1 mm.
Advantageous effects
Compared with the prior art, the simulation modeling method for the mechanical property and the fracture failure of the welding joint, provided by the invention, comprises the steps of slicing a welding sample plate according to the temperature change conditions of different areas in the welding process before finite element modeling, then testing to obtain the material constitutive parameters of each tensile sample, and applying the material constitutive parameters of each tensile sample to each micro-area during finite element modeling, so that different micro-areas have different mechanical property parameters, the accurate description of the mechanical property of the micro-area of the welding joint is realized, the modeling precision and the modeling accuracy are greatly improved, and the problem of inaccurate model caused by the fact that the whole welding joint adopts the same material constitutive parameter is avoided.
Drawings
In order to more clearly illustrate the technical solution of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only one embodiment of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
FIG. 1 is a schematic diagram of a butt joint and zone division according to an embodiment of the present invention;
FIG. 2 is a perspective view of a butt joint and a zone division according to an embodiment of the present invention;
FIG. 3 is a cloud of temperature profiles for a butt joint in an embodiment of the invention;
FIG. 4 is a dimensional view of a tensile specimen of a butt joint in an embodiment of the present invention;
FIG. 5 is a graph of engineering stress-strain for a tensile specimen of a butt joint in an embodiment of the present invention;
FIG. 6 is a diagram of a finite element network model of a butt joint in an embodiment of the present invention;
FIG. 7 is a force-displacement simulation result of a butt joint model in an embodiment of the present invention;
FIG. 8 is a schematic diagram of a T-joint and zone division in an embodiment of the invention;
FIG. 9 is a graph of engineering stress versus strain for a T-joint tensile specimen in an example of the present invention;
FIG. 10 shows the force-displacement simulation results of the T-joint model in the embodiment of the present invention.
Wherein, 1-welding seam, 2-aluminum plate, 3-fixed end, 4-loading end, A-length direction of the surface to be welded and B-cutting direction.
Detailed Description
The technical solutions in the present invention are clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
Taking 6061-T6 aluminum plates for butt welding as an example, the simulation modeling method for mechanical property and fracture failure of the welding joint provided by the invention comprises the following steps:
1. preparing a welding sample plate, and acquiring the temperature change ranges of different areas on the welding sample plate in the welding process, wherein the different areas are areas which are perpendicular to the length direction of the surface to be welded and parallel to the surface to be welded.
Because the welding heat influence states of the aluminum plates on the two sides of the butt joint welding seam are the same, only the temperature change ranges of different areas on the aluminum plate on one side in the welding process need to be acquired, and one welding seam is applied or welded on the side surface (namely the surface to be welded) of the aluminum plate to simulate the thermal shock in the actual welding process, and the application of the welding seam on the side surface of the aluminum plate can be equivalent to the welding heat influence state of the single side of the welding joint, as shown in fig. 1 and 2. The specific parameters of the raw material aluminum plate are as follows: thickness T is 10mm, length is 300mm, width is l, heat treatment state is T6, tensile strength is 342MPa, yield strength is 323MPa, and elongation after fracture is 9%. The welding wire adopted in the welding process is an ER5356 aluminum alloy welding wire with the diameter of 1.2 mm. The welding equipment adopts an OTC double-pulse MIG welding machine (the model is DP400), the welding current is 150A, the welding speed is 60cm/min, the dry elongation of the welding wire is 15mm, the protective gas is argon with the concentration of 99.999 percent, and the gas flow is 20L/min. In order to prevent the aluminum plate from shaking during welding, the two ends of the aluminum plate are tightly pressed by the tool.
In order to obtain the thermal shock effect of different areas of the aluminum plate in the welding process, the aluminum plate is divided into areas L along the direction vertical to the length direction of the surface to be welded1Region L2Regions L3, … …, and region LnWherein n is a positive integer, the thickness of the individual regions does not exceed 2mm, L1In the region close to the weld joint, LnIs the area away from the weld; while applying a welding seam on the side surface of the aluminum plate, monitoring the temperature change condition of each area by using a K-type thermocouple, obtaining the temperature change range of each area (the temperature distribution difference of the same area is very small) as shown in the following table 1, and obtaining the tensile stress, the yield strength and the elongation after fracture of the tensile sample corresponding to different areas by combining the mechanical property test result of the step 3. The fusion zone is a narrow area between the welding seam and the base metal, the metal is in a partial melting state, the crystal grains are large, the plasticity and the toughness of the metal are reduced, and the fusion zone is a weak area in the welding joint and is also an area where the welding seam and the heat affected zone are mutually transited. The heat affected zone is a base material zone which is changed because the base material of the near-welding-seam zone is also subjected to the action of arc heat in the welding process, and the structure and the performance of the base material are changed.
The method of the invention is equally applicable to other welded joints, such as T-joints, angle joints or lap joints.
TABLE 1 temperature variation Range of n different zones
In this embodiment, the welding analysis platform of the simulact software may be used to obtain the temperature variation ranges of different regions, and a three-dimensional finite element model is established and gridded according to the actual sizes of the aluminum plate and the weld joint. The model grid adopts three-dimensional 8-node units, the minimum size of the aluminum plate and the welding seam grid is divided into 1mm multiplied by 2mm for taking account of calculation efficiency and simulation precision, the total number of nodes is 125612, the total number of units is 105735, a temperature field distribution cloud chart of a welding sample plate section in the welding process obtained through simulation of simulfact software is shown in figure 3, as can also be seen from figure 3, the temperature on the section is in a horizontal state (in a contour line distribution rule), the highest temperature close to the welding seam position reaches 633 ℃, and the highest temperature is the intermediate temperature of a fusion welding seam area; the temperature is gradually reduced along the direction far away from the welding seam fusion area (namely the direction vertical to the surface to be welded), and the temperature distribution difference of the same area on the cross section is extremely small, so that the equivalent sample of the heat affected zone can be obtained by slicing and sampling (stretching the sample) vertical to the surface to be welded, and the feasibility of the cutting partition mode is effectively proved.
2. And (3) cutting the welding sample plate along the direction vertical to the length direction of the surface to be welded according to the temperature change range of different areas in the step (1) to prepare a plurality of tensile samples.
The temperature distribution difference of the same area is extremely small, so that the mechanical property difference of the same area is also extremely small, the welding sample plate is cut into a plurality of slices along the direction perpendicular to the length direction of a surface to be welded, the slices are processed to obtain a tensile sample, the size of the tensile sample is designed according to the standard ASTM E8M-09, the detailed size is shown in figure 4, the total length of the tensile sample is 100mm, the width of a clamping part is 10mm, the width is 6mm, the gauge length is 30mm, the fillet radius R is 6mm, and the thickness T is 1 mm.
The aluminum plate is sliced according to the temperature change range of different areas on the aluminum plate, the number of the tensile samples can be the same as the number of the areas, or can be different from the number of the areas, when the temperature change of two adjacent areas is extremely small, the two areas can be combined to form one tensile sample, and when the temperature change of the same area is large, the area can be divided into two or more tensile samples. In this embodiment, the number of tensile specimens corresponds to the number of areas one by one, i.e., the tensile specimens 1 to 17 correspond to the area L1～L17. However, in the finite element modeling, the number of micro-regions and the number of tensile samples must be one-to-one, so that the material constitutive parameters of the tensile samples can be ensured to be applied to each corresponding micro-region.
3. Performing mechanical property test on each tensile sample to obtain a stress-strain curve of each tensile sample, and simulating the stress-strain curve of each tensile sample by using a constitutive model to obtain material constitutive parameters of each tensile sample; and the strain energy at break of each tensile specimen was obtained.
The mechanical properties of the tensile specimens were measured on an Instron 3369 universal tester at a tensile speed of 2mm/min, and the results of the quasi-static tensile tests of each tensile specimen are shown in FIG. 5. As can be seen from fig. 5 and table 1, the tensile strength of each sample in the direction away from the weld (or the direction of the surface to be welded) shows a tendency of decreasing first and then increasing, wherein the elongation after fracture of sample 2 and sample 3 in the heat affected zone tensile sample is 23.35% and 23.49%, respectively, which are significantly higher than those of the other heat affected zone samples, and it can be seen that there is a better plastic deformability at the positions of sample 2 and sample 3; the tensile strength of sample 5 was the lowest of 201MPa, the strength coefficient thereof was about 58.6% of that of the base material, the tensile strengths of sample 16 and sample 17 were 340MPa and 343MPa, respectively, and the elongation after fracture was 9.29% and 9.06%, respectively, and it was estimated that the mechanical properties of the material were not affected by the heat of welding from the position of sample 16 (divided into the base material region from sample 16). From this, it can be seen that the heat affected zone is a sample range included in samples 1 to 15, has a width of about 17mm, and is also a region in which fine mechanical parameters need to be input in the simulation modeling analysis process of the present invention.
The selection of a proper constitutive equation (or called a constitutive model) to describe the deformation behavior of the material is an important premise for the numerical simulation of the toughness fracture of the aluminum alloy welding joint. The Johnson-Cook model is an empirical viscoplasticity constitutive equation and can well describe the work hardening, strain rate and temperature rise softening effect of a metal material. The constitutive equation has clear physical meaning, simple form and convenient parameter solution, and is the most extensive constitutive model in the current engineering application. Thus, the present example uses the Johnson-Cook model to numerically simulate an aluminum alloy weld joint, as follows:
in the formula (1), σ represents an equivalent stress,eq、
and
equivalent plastic strain, strain rate in the test and reference strain rate, respectively; t, TrAnd TmThe instantaneous temperature at strain, the reference temperature and the melting temperature of the material, respectively; A. b, C, n and m are the initial yield stress, strain hardening coefficient, strain rate coefficient, strain hardening index and heat softening index, respectively, at a reference temperature. In the present example, the strain rate at room temperature is based on
Is 1 × 10-3s-1The quasi-static tensile test of (2), determining parameter A, B, n. When the strain rate is less than 1s-1In the process, the material tissue distortion energy and dislocation caused by deformation are relatively low, and the deformation heat has sufficient time to diffuse outwards (refer to the welding deformation of a 6061-T651 aluminum alloy sheet joint proposed by leaf flood and the like, Chinese non-ferrous metals academic report 2014(10):2435-The strain rate and the quasi-static reference strain rate in the examples are both 1 × 10-3s-1Neglecting deformation temperature rise in quasi-static state, i.e. T ═ T at the momentrAt room temperature, formula (1) can be simplified as:
σ＝(A+Bn) (2)
the stress-strain curves of the substrate (i.e., the mechanical properties of the material are no longer affected by the heat of welding), the heat affected zone, and the weld were fit by MATLAB programming to obtain parameters A, B and n values, respectively, and thus A, B and n values for each tensile specimen.
According to the theory of ductile fracture, fracture failure of a material during plastic strain is caused by material damage. Cockcroft et al consider that the maximum tensile stress is the main factor causing material failure, and when the plastic work per unit volume reaches a certain limit value, the material is damaged, i.e. the fracture strain energy of the material unit should be equal to the integral of the maximum tensile stress in the sample unit along the plastic strain path, and the basis for determining material failure is obtained, and when the fracture strain energy reaches a critical value WcWhen this happens, the material breaks. The Cockcroft-Latham ductile fracture criterion is more accurate in predicting aluminum alloy fracture failure (refer to Terreost M, Feuerhak A, Traut D, et al. extension of the normalized Cockcroft and Lathamm with a detailed description of the normalized ductile data values for the compressed crack in molten extrusion [ J]International Journal of material formation 2015,9(4):1-8 and N.le
Thuillier S,Manach P Y.Aluminumalloy damage evolution for different strain paths–Application to hemmingprocess[J]Engineering framework Mechanics,2009,76(9): 1202-:
in formula (3), σ1Is the biggest principalStress, WcIs a critical value of the integrated fracture strain energy W.
4. And establishing a finite element model according to the welding sample plate, and then carrying out micro-area division and grid division on the finite element model according to the actual size of each tensile sample.
And (3) introducing the 3D model of the welding sample plate into Hypermesh finite element software, carrying out micro-area division according to the actual size of each tensile sample, and then dividing the grid. The simulation model adopts 8-node grid units, the total number of nodes of the whole model is 19374, and the total number of grids is 14668. The material in the simulation is MAT24 material card, considering the simulation precision and the calculation efficiency, the grid size near the welding seam (within the range of 3.8 mm-19 mm from the welding seam center) is divided into 0.5mm multiplied by 1mm, the grid size at the position far away from the welding seam is divided into 1mm multiplied by 1mm, as shown in FIG. 6, L1-L15 near the welding seam are heat affected zones, two end parts are parent metal, L1-L15 correspond to 15 tensile samples, and each tensile sample corresponds to a micro zone.
5. And (3) applying the material constitutive parameters and the fracture strain energy of each tensile sample in the step (3) to the micro-area corresponding to each tensile sample to obtain the finite element model of the accurate welding sample plate.
Each tensile sample corresponds to a micro-area of a finite element model (other areas of the finite element model are base materials or base materials and are not affected by heat), the tensile samples correspond to the micro-areas one by one, and material constitutive parameters and fracture strain energy of each tensile sample are input into the corresponding micro-areas, so that each micro-area of the finite element model corresponds to different material constitutive parameters and fracture strain energy, the mechanical properties of the micro-area of the welded joint are accurately described, and the modeling precision and the modeling accuracy are greatly improved.
After modeling is completed, all degrees of freedom of the fixed end are constrained, a speed load of 2mm/min is applied to the loading end, and a grid unit is subjected to simulation in a full-integration unit mode.
In order to characterize the work hardening state of the material in the plastic stage, the present embodiment employs a Hollomon power index hardening model, and the expression is as follows:
σT＝K(T)n(4)
wherein:Ttrue strain, K is the strengthening coefficient, n is the hardening index, σTIs true stress. The hardening section curve mainly represents the relationship between stress and strain under large deformation, and the experimental result shows that the position with larger strain is mainly in the heat affected zone, so that the real stress-strain curve of the samples 2-6 (corresponding to the grids of the L2-L6 regions) is mainly fitted in the simulation, and the material characteristic parameters of each region, such as the hardening index n and the strengthening index K, are shown in Table 2.
TABLE 2 mechanical Properties of microcell Material
Simulating the simulation fracture failure by adopting a GISSMO model, setting a failure criterion card of the GISSMO by using MAT _ ADD _ EROSION in the LS-DYNA simulation, and adding related parameters of the GISSMO failure.
FIG. 7 is a force-displacement curve of the tensile finite element model simulation results and test results for a butt joint. In the initial stage, the tensile sample is in the elastic deformation stage, the force changes linearly along with the displacement, the plastic deformation of the tensile sample begins to dominate along with the increase of the displacement, the change of the force and the displacement gradually increases in a nonlinear manner, and finally fracture failure occurs. The peak force of simulation and experiment is 7182N and 7172N respectively, the simulation error is 0.1%, the displacement of the simulation and experiment when the fracture fails is 3.3mm and 3.5m m respectively, and the simulation error is 5.7%. The variation trend of force along with displacement, the magnitude of peak force and the displacement corresponding to fracture failure in the simulation and experiment results of the butt joint are shown, the consistency of the simulation and experiment results is good, the method for performing finite element simulation prediction on a plurality of tensile samples by equivalence of the welding joint is feasible, the prediction precision can meet engineering requirements, and the method also has a certain reference value for strength simulation prediction of other joint forms.
Example 2
Taking the example that the welding material is 6063-T6 aluminum alloy extrusion plate for T-shaped welding, the invention provides a simulation modeling method for mechanical property and fracture failure of a welding joint, which comprises the following steps:
1. preparing a welding sample plate (the welding joint is a T-shaped joint), and acquiring the temperature variation range of different areas on the welding sample plate in the welding process, wherein the different areas are areas which are perpendicular to the length direction of the welding seam (or the length direction of a surface to be welded) and parallel to the welding seam (or the surface to be welded).
The welding wire is an ER5356 aluminum alloy welding wire with the diameter of 1.2mm, the welding current is 130A, the arc voltage is 20V, and the welding speed is 60 cm-min-1The welding template with the gas flow rate of 17 L.min.T consists of a rectangular wall plate with the thickness of 300mm × 150 and a rectangular rib plate with the thickness of 300mm × 90mm, and the welding direction of the welding template is perpendicular to the extrusion direction of the plate (the welding line is distributed perpendicular to the extrusion direction), as shown in figure 8.
Dividing the T-shaped welded joint into a Weld (WZ), a heat-affected zone 4(HAZ4), a heat-affected zone 3(HAZ3), a heat-affected zone 2(HAZ2), a heat-affected zone 1(HAZ1) and a Base Metal (BM) according to the temperature variation range of different areas; the panel is also subdivided into heat affected zone 5(HAZ5), heat affected zone 6(HAZ6), heat affected zone 7(HAZ7) and BM on both sides.
2. And (3) cutting the welding sample plate along the direction vertical to the length direction of the welding line according to the temperature change range of different areas in the step (1) to obtain a plurality of tensile samples.
The cutting treatment was performed according to the area division in step 1, and tensile specimens BM, WZ, HAZ1, HAZ2, HAZ3, HAZ4, HAZ5, HAZ6, and HAZ7 were obtained (the tensile specimens correspond to the area division in step 1 one by one). The dimensions of the tensile specimens were prepared according to the national standard GT/B2651-2008.
3. Performing mechanical property test on each tensile sample to obtain a stress-strain curve of each tensile sample, and simulating the stress-strain curve of each tensile sample by using a constitutive model to obtain material constitutive parameters of each tensile sample; and the strain energy at break of each tensile specimen was obtained.
Mechanical testing of tensile specimens was performed on an Instron 3369 Universal testing machine at a tensile speed of 5mm/min, and the results of the quasi-static tensile test for each tensile specimen are shown in FIG. 9. Tensile properties of the tensile specimens are shown in Table 3 below, RmAs is apparent from table 3, in the T-shaped welded joint: the mechanical property of the base material is higher than that of the heat affected zone, and the elongation of the heat affected zone close to the welding seam is larger than that of the base material; the tensile strength of a heat affected zone (HAZ2) of the rib plate is lowest (158.04MPa), the mechanical properties of the rest heat affected zones in the rib plate are gradually enhanced along with the distance from a welding seam, the tensile strength of the welding seam is 183.55MPa, and the welding seam and the HAZ2 have fracture risks in the stretching process by considering the structure of the T-shaped joint and the mechanical properties of the HAZ 2.
TABLE 3 tensile Property parameters of the tensile specimens
A Johnson-Cook model is adopted to carry out numerical simulation on the T-shaped welding joint, and MATLAB programming is adopted to fit stress-strain curves of a parent material or a base material (namely the mechanical property of the material is not affected by the heat of welding any more), a heat affected zone and a welding seam, so as to respectively obtain parameters A, B and n values, and further obtain A, B and n values of each tensile sample. Obtaining fracture strain energy W using Cockcroft-Latham criterioncW in this embodimentc73.1MPa, equivalent plastic strain 0.266.
4. And establishing a finite element model according to the welding sample plate, and then carrying out micro-area division and grid division on the finite element model according to the actual size of each tensile sample.
And (3) introducing a 3D model of the T-shaped welding joint into Hypermesh finite element software, dividing micro-areas according to each tensile sample, dividing grids, and selecting hexahedral units, wherein the size of the unit grid is 1 mm.
5. And (3) applying the material constitutive parameters and the fracture strain energy of each tensile sample in the step (3) to the micro-area corresponding to each tensile sample to obtain the finite element model of the accurate welding sample plate.
The base material (i.e., parent material) was fitted using the MAT-107 material model to obtain the values of Johnson-Cook model parameters A, B, n as listed in Table 4. One end of the simulation sample is a rigid body with fixed constraint, and the other end of the simulation sample is stretched at a constant speed of 5mm/min along the axial direction. And (5) carrying out solving calculation by adopting an LS-DYNA display platform. Fig. 10 is a comparison result of a force-displacement curve obtained by simulation and test, the simulation and test results are basically consistent before the necking stage, and in the simulation, the parallel length is continuously reduced without breaking due to lack of a material failure criterion, so that the force-displacement curve is slowly reduced at a displacement of 1.75mm without sudden change, and the model parameters can be proved to effectively predict the deformation behavior and load change before the sample breaks.
TABLE 4 failure parameters at substrate, heat affected zone and weld
According to the modeling method, the equivalent welding joint is prepared, the welding joint is sliced in layers according to the temperature change range of different areas of the welding joint, the fine representation of the local mechanical property of the heat affected zone of the welding joint is obtained, the finite element model is divided into micro-areas according to the actual size of the tensile sample obtained after slicing in layers, and the material constitutive parameters or the mechanical property parameters of each tensile sample are applied to the corresponding micro-areas, so that each micro-area of the finite element model corresponds to different material constitutive parameters, the mechanical property of the welding joint is represented more accurately, and the modeling precision and the modeling accuracy are greatly improved; according to the simulation structure of force-displacement, the simulation prediction performed by the model has good consistency of simulation and experimental results and high prediction precision, and the prediction precision can meet the engineering requirements.
The above disclosure is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of changes or modifications within the technical scope of the present invention, and shall be covered by the scope of the present invention.
Claims (9)
1. A simulation modeling method for mechanical property and fracture failure of a welding joint is characterized by comprising the following steps:
step 1: preparing a welding sample plate, and acquiring the temperature change ranges of different areas on the welding sample plate in the welding process, wherein the different areas are areas which are perpendicular to the length direction of a surface to be welded and are parallel to the surface to be welded;
step 2: cutting the welding sample plate along the direction vertical to the length direction of the surface to be welded according to the temperature variation range of different areas in the step 1 to obtain a plurality of tensile samples;
and step 3: performing mechanical property test on each tensile sample to obtain a stress-strain curve of each tensile sample, and simulating the stress-strain curve of each tensile sample by using a constitutive model to obtain material constitutive parameters of each tensile sample; and obtaining the strain energy at break of each tensile sample;
and 4, step 4: establishing a finite element model according to the welding sample plate, and then carrying out micro-area division and grid division on the finite element model according to the actual size of each tensile sample;
and 5: and (3) applying the material constitutive parameters and the fracture strain energy of each tensile sample in the step (3) to the micro-area corresponding to each tensile sample to obtain the accurate finite element model of the welding sample plate.
2. A modeling method in accordance with claim 1, wherein: in the step 1, the method for acquiring the temperature variation ranges of different areas comprises the following steps:
step 1.1: sequentially dividing the base material into n regions on the base material along the length direction vertical to the surface to be welded of the base material, wherein the width of each region is not more than 2 mm;
step 1.2: and monitoring the temperature change condition of each area in the welding process to obtain the temperature change range of different areas on the welding sample plate.
3. A modeling method in accordance with claim 2, wherein: in the step 1.2, a K-type thermocouple is adopted to monitor the temperature change condition of each area.
4. A modeling method in accordance with claim 1, wherein: in the step 1, the temperature variation ranges of different areas are obtained by using simulact software.
5. A modeling method in accordance with claim 1, wherein: in the step 1, the welding joint type of the welding sample plate is a butt joint, a T-shaped joint, an angle joint or an overlap joint.
6. A modeling method in accordance with claim 1, wherein: in the step 2, the cutting processing mode is a linear cutting mode.
7. A modeling method in accordance with claim 1, wherein: in the step 3, a Johnson-Cook model is adopted to simulate the stress-strain curve of each tensile sample, and the expression of the Johnson-Cook model is as follows:
wherein, sigma is the equivalent stress,eq、
and
equivalent plastic strain, strain rate in the test and reference strain rate, respectively; t, TrAnd TmThe instantaneous temperature at strain, the reference temperature and the melting temperature of the material, respectively; A. b, C, n and m are the initial yield stress, strain hardening coefficient, strain rate coefficient, strain hardening index and heat softening index, respectively, at a reference temperature.
8. A modeling method in accordance with claim 1, wherein: in step 3, the fracture strain energy of each tensile specimen was obtained using the Cockcroft-Latham ductile fracture rule.
9. A modeling method in accordance with claim 1, wherein: in the step 4, for the finite element model of the butt joint, the grid division size in the range of 3.8 mm-19 mm from the center of the weld is 0.5mm × 0.5mm × 1mm, and the grid division size in other ranges is 1mm × 1mm × 1 mm.
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