CN102435514A - Detecting method for identifying dynamic mechanical property parameters of materials in different zones of welding spot - Google Patents

Abstract

The invention discloses a detecting method for identifying dynamic mechanical property parameters of materials in different zones of a welding spot, comprising the following steps: (1) preparing a welding spot specimen for hardness test; (2) selecting a plurality of spots for hardness test in the entire welding spot zone in the diameter direction of welding spot test, and dividing zones according to hardness values; (3) carrying out dynamic indentation test in the divided zones to obtain a load depth curve of different test points; (4) establishing a finite element model of the indentation test and verifying; (5) constructing optimized mathematical models at different zones of the welding spot according to a simulated result of the finite element model of the indentation test and a corresponding test result; and (6) solving the optimized mathematical models in the step (5) by adopting an overall optimization algorithm to obtain dynamic mechanical property parameters of different zones of the welding spot. The detecting method is simple in principle, convenient to operate and is capable of measuring the local dynamic mechanical property parameters of materials within the range of millimeter and even micrometer sizes. In addition, the application range of the indentation test is widened.

Description

A kind of detection method of discerning solder joint zones of different material dynamic mechanical performance parameter

Technical field

The present invention is mainly concerned with material tests field in the mechanical engineering manufacturing, refers in particular to a kind of detection method of spot area material mechanical parameters.

Background technology

Sheet metal is being carried out in the welding process; Because the influence of resistance heat; The material behavior of welding region can change, and this just makes this regional performance also be different from mother metal, can welding region be divided into three sub regions according to the characteristic of hardness: mother metal district, heat-affected zone, solder joint district.Because the size of general mother metal is compared enough big with the heat-affected zone; So in the past to research in this respect, all ignored the material behavior of heat-affected zone; Promptly adopt conode connected mode or the mode that is rigidly connected directly to link to each other often welding region being carried out the finite element numerical modeling with mother metal; Can not consider the material behavior at solder joint place obviously in this case, this modeling method is not enough to the true mechanical response of simulating solder joint material; On the other hand, considering the mechanical response at solder joint place, promptly adopt the body unit butt welding point to carry out modeling, but the material parameter of welding material is very doubt, usually is rule of thumb to set, and is that each regional material behavior of supposition solder joint is uniform.Yet, learn the mechanical property parameters and the non-uniform Distribution of solder joint through mixcrohardness test, thereby can not simply each regional mechanical property material of solder joint be designed to a fixed value.In sum, the disposal route of present butt welding point can not satisfy the demand of actual engineering.It is the main connected mode of vehicle body parts that solder joint connects; Butt welding point connects accurately simulates the accuracy and confidence that directly has influence on whole finite element model; Concerning the success or failure that whole simulation is analyzed, accurately obtaining of the precision of solder joint model and the material parameter of welding material is closely bound up.

Because the solder joint welding process is equivalent to a heat treatment process; Directly cause the heterogeneous microstructure at spot area place to lead normal complicacy and the zones of different place has different microstructures; For the iron and steel metal, the metallographic structure of solder joint middle comprises martensite and bainite, and there is the mixing metallographic structure heat-affected zone; Existing martensite, bainite; Ferrite and pearlite are arranged again, and these different metallographic structures have caused solder joint place material different characteristic, discover that further the mechanics parameter here can present the heterogeneity distribution; It is the parameter attribute that can there be graded at solder joint, place, heat-affected zone; So only stretch or compression test is difficult to confirm the concrete mechanics parameter at solder joint zones of different place through simple, and the stress-strain relation at this place is very difficult obtains through conventional method, so can not carry out inverse problem of parameter to it according to the thinking of curve fitting.

In addition; The mechanical property parameters of solder joint can change along with the variation of rate of strain under dynamic condition; Thereby from the mechanics parameter that static hardness obtains can't reflect the collision this welding material under high rate of strain dynamic behaviour; Based on this problem, the material dynamic mechanical characterisitic parameter that how accurately to obtain the solder joint zones of different just seems particularly important.

Hardness is the ability of material opposing local plastic deformation, and the microhardness indentation test provides the strength of materials characteristic of measuring and estimate micron order even nano level sign size for us.In the research work in the past; No matter be to traditional metal materials or new material as the foam metal; All be based upon on the equally distributed basis of these material parameters, and mostly concentrate in the identification of material static parameter, seldom measure the dynamic parameter of material through dynamic indentation test; Littler sign size or even nano level strength of materials characteristic are measured and estimated to the dynamic stiffness indentation test for we provide; Be the especially method of the mechanical property of metal or material point circumferential surface of a kind of evaluating material, utilize on the rigid pressure head that stress pulse acts on sample contacts, make specimen surface form dynamic impression; And then recording the dynamic indentation hardness and the dynamic state material characteristic curve of material, the rate of strain during the dynamic stiffness test can reach 10 ³-10 ⁴/ s reflected that conscientiously material opposing pressure head dynamically is pressed into deformation ability, and this test is efficient and convenient, sample does not have destruction, can embody the important parameter characteristic of material high strain rate effect under complicated three-dimensional stress state.On the other hand, be reflected signal ε through dynamic Hopkinson pressure bar test fundamental equation _i(t), transmission signal ε _r(t), elastic modulus E, wave velocity C ₀, test specimen the long-pending A of initial cross sectional ₀With original depth L ₀Just can derive the mean stress of test specimen

And mean strain

Between relation, so just can simulate the mechanics parameter of homogeneous material.Yet when having the material dynamic performance parameter of unevenness characteristics for the identification detection as this each regional material behavior of solder joint, each regional initial cross sectional to be measured is amassed A ₀Be difficult to confirm, therefore, can not directly obtain stress-strain relation through dynamic indentation test, and then can not directly simulate this regional dynamic mechanical parameter according to the fundamental equation of appeal.

Summary of the invention

The technical matters that the present invention will solve just is: to the technical matters that prior art exists, the present invention provides the detection method that a kind of principle is simple, easy to operate, can measure the material dynamic mechanical performance parameter of solder joint zones of different in millimeter even the micron-scale scope.

For solving the problems of the technologies described above, the present invention adopts following technical scheme:

A kind of detection method of discerning solder joint zones of different material dynamic mechanical performance parameter is characterized in that step is:

(1) preparation is used for the solder joint sample that hardness test is used, and the solder joint surface of carrying out the hardness test side is polished, polished;

(2) choose some spots in the whole spot area on solder joint specimen finish direction and carry out hardness test, carry out subregion according to the hardness number that records;

(3) the butt welding point zones of different is carried out dynamic indentation test, obtains the load depth curve at each place, testing site in the zones of different;

(4) set up the indentation test finite element numerical model: in order to reduce the calculating scale, whole indentation test finite element numerical model and load all are axisymmetric about center line, in addition; In order not make model too huge, adopt here to physical size suitable carry out scaling, length is reduced to 1000mm by original 3040mm; Increasing diameter is added to 25mm; The length of test specimen and diameter also are changed to 22mm and 18mm respectively, and such advantage is to optimize the quality of grid, reduce the model scale; On the other hand, because the effect that drop bar only is used to produce stress pulse, so in the indentation test finite element numerical model, need not consider drop bar, substituted method is that direct input end at incident bar applies the stress pulse that is uniformly distributed with.

(5) on the basis of step (3), (4); Draw the target response function at zones of different place according to dynamic indentation test finite element numerical model and corresponding test findings, according to the analog result of indentation test finite element numerical model and corresponding experimental result to obtain the optimization mathematical model at solder joint zones of different place;

(6) combine optimized Genetic Algorithm, set this algorithm initial value, initial parameter to the solving result of genetic algorithm with find the solution efficient certain influence all arranged, the parameter that needs to set in advance has: population size M, promptly the quantity of contained individuality in the population generally gets 20～100; The termination of iterations number of times T of heredity computing generally gets 100～500; Crossover probability P _c, generally get 0.4～0.99; The variation probability P _m, generally get 0.0001～0.1.According to the trial curve of continuous each selected point of iterative approach of the selected target response function of step (5), if reach certain convergence criterion, then iteration stops in the process of iteration, and the mechanics parameter under this iteration step promptly is the optimum solution under certain suitable interval.

As further improvement of the present invention:

In the said step (3), carry out at least three indentation tests in the institute subregion.

Said optimization mathematical model is shown in the following formula:

$\left\{\begin{array}{c}\mathrm{Minmize}:\mathrm{\Δf}(x_1,x_2,\·\·\·,x_n)=\sqrt{\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{\left(\frac{F_i^{\exp }(x_1,x_2,\·\·\·,x_n)-F_i^{\mathrm{sim}}(x_1,x_2,\·\·\·,x_n)}{F_i^{\exp }(x_1,x_2,\·\·\·,x_n)}\right)}^2}\\ \mathrm{Subject\; to}:\left\{\begin{array}{c}{x}_1^L\≤x_1{\≤x}_1^U\\ x_2^L\≤x_2\≤x_2^U\\ \·\·\·\\ x_n^L\≤x_n\≤x_n^U\end{array}\right.\end{array}\right.$

In the formula, x ₁, x ₂..., x _nBe parameter to be asked,

Be respectively the upper and lower bound of waiting to ask parameter,

Be the continuous indentation load that obtains through dynamic indentation test,

The dynamic indentation load of trying to achieve during for finite element simulation, m are time increment step sum.

Compared with prior art, the invention has the advantages that:

The angle of the indentation test method when 1, the present invention is from mensuration hardness; In conjunction with finite element numerical simulation technology and inversion technique; The short-cut method of the MATERIALS ' DYNAMIC plasto-elasticity parameter at a kind of accurate acquisition solder joint zones of different place is provided; Have very strong engineering use value, widened the usable range of indentation test.The present invention can measure the localized forces mathematic(al) parameter of material in millimeter even the micron-scale scope; Have the engineering structure of stronger non-uniform Distribution especially as this mechanics parameter of spot area, overcome the deficiency that material in measuring this range of size is tested in traditional simple extension.

2, the present invention be substituted in most cases can only judge and exosyndrome material macroscopic behavior meaning on unilateral stretching or compression test, overcome and be difficult to accurately to obtain the technical bottlenecks such as performance parameter that this millimeter level of picture spot area characterizes size in the actual engineering; The present invention considers characteristic attributes such as material and the size of solder joint zones of different, more can truly reflect the material behavior at spot area place, has higher utility and stronger engineering significance.

Description of drawings

Fig. 1 is the schematic flow sheet of detection method of the present invention;

Fig. 2 is an indentation hardness test test point position view of the present invention;

Fig. 3 is the synoptic diagram of the hardness number and the subregion situation at RP of the present invention place;

Fig. 4 is the load depth curve synoptic diagram of the zones of different that obtains through indentation test in the inventive method;

Fig. 5 is the dynamic indentation test two dimension rotational symmetry finite element model in the inventive method;

Fig. 6 is that the present invention finds the solution the iterative process synoptic diagram.

Embodiment

Below will combine Figure of description and specific embodiment that the present invention is explained further details.

Because the distortion of most engineering polycrystalline metal material under impact loading usually used the widest Johnson Cook to strengthen model and simulated; So the present invention adopts the constitutive relation of this model as this embodiment; Shown in (1); Can find out that from formula the J-C model representation is three a product, reflect strain hardening, rate of strain sclerosis and the softening (notes: the correction form of using the J-C model here) of temperature respectively.

$\mathrm{\σ}=(A+B{\mathrm{\ϵ}}^n)[1+\mathrm{CIn}(1+\frac{\stackrel{\·}{\mathrm{\ϵ}}}{{\stackrel{\·}{\mathrm{\ϵ}}}_0})](1-T^{*m})---\left(1\right)$

Comprise A in the model shown in the formula (1), B, n; C, five parameters of m, wherein first three parameter A; B; N is initial yield stress, strength factor and the strain hardening exponent of corresponding spot area material respectively, and these values can not simply be equivalent to corresponding parameters value under the static condition, because can increase along with the raising of rate of strain at the dynamic condition lower yield stress; C is dynamic empirical rate of strain sensitivity coefficient; M is for characterizing the index of temperature effect.General hypothetical reference rate of strain

T in the formula ^{* m}Be the temperature of nondimensionalization, suc as formula (2);

$T^{*m}=\frac{T-T_r}{T_m-T_r}---\left(2\right)$

Wherein, T _rBe room temperature, T _mBe the fusing point of material, the J-C model all is effective in the scope of temperature from room temperature to the material melting point temperature variation.For for simplicity, present embodiment is the account temperature softening effect not, and promptly temperature remains room temperature, and A is so just arranged, B, and n, four parameters of C are as dynamic mechanics parameter that the present invention asked.

As shown in Figure 1, be the application example of the present invention in instantiation, used welding spot structure is through being that the high-strength steel sheet of two kinds of different materials is welded among this embodiment, is respectively DP600 and DP980, and thickness is 2mm, and its concrete steps are following:

(1) preparation is used for the solder joint sample that hardness test is used, and to the solder joint surface of carrying out the hardness test side polish, operation such as polishing, make the solder joint surfacing, bright and clean of test side, roughness reaches the requirement of test.

(2) choose some spots in the whole spot area on the spot size direction and carry out hardness test; Sample should be placed on the rigid support thing reposefully in the process of the test; And make ram axis vertical with specimen surface, to avoid sample to produce displacement, indentation equipment and to avoid receiving shock and vibration.Fig. 2 has provided the position of indentation test test point, in order to reduce test error, measures four hardness numbers on the diameter line here; In order to alleviate in the impression process protuberance or the influence of depression between two adjacent test points, the distance on every line between two adjacent measuring points is 0.12mm, to satisfy the standard-required of GB/T4340.1 to two measuring point centre distances; Get its mean value afterwards as last True Data; The hardness number that records is as shown in Figure 3, carries out rationalization partition according to this real hardness number, can be divided into the molten bath district; The heat-affected zone; The mother metal district, the hardness number that therefrom can obviously find out the solder joint place is compared difference with mother metal very big, and then can judge its material behavior indirectly bigger difference is also arranged;

(3) carry out dynamic indentation test in the institute subregion, read solder joint zones of different indentation test result, obtain the load depth curve of zones of different, test count what with that what subregions are whole spot area be divided into is relevant.It should be noted that; Here be not to obtain volt-time curve according to common dynamic Hopkinson pressure bar test; According to the one dimension elastic wave theory, derive stress-strain relation through measuring two strains on the depression bar again, this thinking can only be directed against the uniform situation of material behavior; For needing to consider that as solder joint is this each zone has the special construction of dissimilar material properties, the long-pending A of initial cross sectional that each is waited to ask the zone or waits to ask a place ₀Very difficulty is obtained, and even possibly not obtain, and then can not derive its stress-strain relation.So the present invention only need record the load depth curve at testing site place, test is counted in this step what with whole spot area to be divided into what subregions relevant, in each subregion, assurance has three testing sites at least;

In the process of carrying out the test of separate type Hopkinson (Hopkinson) depression bar, because survey region involved in the present invention is less, about 3-6mm; So can not directly select traditional SHPB test unit for use, need a diamond penetrator to be installed, through on adamas Vickers pressure head, applying the single compression pulse at the incident bar place; The excitation pressure head dynamically is pressed into some points of reference line, obtains the dynamic impression of these points, records the depth value from solder joint center line different distance place; This load depth relationship is for the pressure head of any one shape; Such as pyramid type, triangular pyramid type (Berkovich pressure head and Vickers pressure head), cylinder is flat, ball-type or the like; A kind of similar curve form is all arranged, shown in (3);

$\mathrm{DH}=C\frac{P}{d^2}---\left(3\right)$

Wherein the C value is the constant that depends on indenter shape and material behavior, and P is the stress pulse peak value under the dynamic load conditions, i.e. load (N) is obtained by the conversion of signals of piezoelectric sensor output; D is the mean value (mm) of impression catercorner length.

Present embodiment is divided into three zones with whole spot area; Wherein get test point 1-3 in the heat-affected zone 1; Get test point 4-6 in the district of molten bath, test point 7-9 is got in heat-affected zone 2, and the loading and unloading curve that obtains respectively is as shown in Figure 4; Here adopt the Vickers pressure head, so the indentation load degree of depth has the curve form suc as formula (4);

$\mathrm{DH}=0.1891\frac{P}{d^2}---\left(4\right)$

Wherein the C value is 0.1891.

(4) set up dynamic indentation test and simplify finite element model: adopt finite element business software Abaqus and set up the finite element model of impression experiment according to the physical process of impression examination, in order to reduce the calculating scale, whole finite element model and load all are axisymmetric about center line; In addition; In order not make model too huge, adopt here to physical size suitable carry out scaling, length is reduced to 1000mm by original 3040mm; Increasing diameter is added to 25mm; The length of test specimen and diameter also are changed to 22mm and 18mm respectively, and such advantage is to optimize the quality of grid, reduce the model scale; On the other hand, because drop bar only plays the effect that produces stress pulse, so in finite element model, need not consider drop bar, substituted method is that direct input end at incident bar applies the stress pulse that is uniformly distributed with, and is as shown in Figure 5;

(5) the choosing and setting up of objective function: on the basis of step (3), (4);, optimize in the mathematical model and comprise objective function and constraint function to obtain the target response function optimization mathematical model at solder joint zones of different place according to the analog result of indentation test finite element numerical model and corresponding experimental result.

This optimization mathematical model is following formula (5):

$\left\{\begin{array}{c}\mathrm{Minmize}:\mathrm{\Δf}(x_1,x_2,\·\·\·,x_n)=\sqrt{\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{\left(\frac{F_i^{\exp }(x_1,x_2,\·\·\·,x_n)-F_i^{\mathrm{sim}}(x_1,x_2,\·\·\·,x_n)}{F_i^{\exp }(x_1,x_2,\·\·\·,x_n)}\right)}^2}\\ \mathrm{Subject\; to}:\left\{\begin{array}{c}{x}_1^L\≤x_1{\≤x}_1^U\\ x_2^L\≤x_2\≤x_2^U\\ \·\·\·\\ x_n^L\≤x_n\≤x_n^U\end{array}\right.\end{array}\right.---\left(5\right)$

In the formula (5), x ₁, x ₂..., x _nBe parameter to be asked,

Be respectively the upper and lower bound of waiting to ask parameter,

Be the continuous indentation load that obtains through dynamic indentation test,

The dynamic indentation load of trying to achieve during for finite element simulation, m are time increment step sum.

To choosing different RPs; Mechanics parameter according to constantly changing in the optimizing process just can obtain the finite element load depth relationship under the particular combination parameter, constantly calls the indentation test finite element model through optimization method then, and then obtains the target response function; Because present embodiment is asked the elastoplasticity parameter A; B, n is initial yield stress, strength factor and the strain hardening exponent of corresponding welded seam area material respectively, and C is dynamic empirical rate of strain sensitivity coefficient; So the mathematical model here is suc as formula shown in (6)

$\left\{\begin{array}{c}\mathrm{Minimize}:\mathrm{\Δf}(A,B,n,C)=\sqrt{\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{\left(\frac{F_i^{\exp }(A,B,n,C)-F_i^{\mathrm{sim}}(A,B,n,C)}{F_i^{\exp }(A,B,n,C)}\right)}^2}\\ \mathrm{Subject\; to}:\left\{\begin{array}{c}200\mathrm{MPa}\≤A\≤1000\mathrm{MPa}\\ 500\mathrm{MPa}\≤B\≤2000\mathrm{MPa}\\ 0.001\≤n\≤0.5\\ 0.01\≤C\≤0.5\end{array}\right.\end{array}\right.---\left(6\right)$

In the formula (6);

continuous indentation load for obtaining through nano indentation test; The indentation load that

tries to achieve during for finite element simulation, m are time increment step sum.

(6) combine optimized Genetic Algorithm, set this algorithm initial value, initial parameter to the solving result of genetic algorithm with find the solution efficient certain influence all arranged, the parameter that present embodiment needs to set in advance has: population size, the i.e. quantity of contained individuality in the colony, M=100; The termination of iterations number of times T=500 of heredity computing; Crossover probability P _c=0.70; The variation probability P _m=0.05.Test load-depth curve according to continuous each selected point of iterative approach of the selected target response function steps of step (5); Fig. 6 is physical test value and limited simulation value iteration synoptic diagram progressively; In the time of iteration according to certain convergence criterion, adopt here the objective function of formula (6) enough little for convergence criterion be that residual value Δ f among Fig. 6 restrains verification less than certain enough little constant ε.Advantage through genetic Optimization Algorithm itself is constantly upgraded the elastoplasticity parameter of being asked automatically, when certain step, iteration reached this convergence criterion, just can judge the A under this iteration step, B, n, C be exactly the optimized parameter that will seek separate.Can draw the plasto-elasticity parameter of each regional institute reconnaissance through above-mentioned solution procedure, as shown in table 1 below, these points have comparatively obvious variation and rule, and have step-characteristic, and the strength factor at place, fusion area is obviously greater than the heat-affected zone.Can know from present embodiment; This method can comparatively accurately identify the material dynamic mechanical performance parameter at solder joint zones of different place; This just makes that the finite element modeling of relevant welding spot structure is more accurate such as the modeling of front stringpiece of vehicle body collision process; For welded further Computer Simulation research provides good CAE the basis, have reference and a reference value preferably for engineering is actual.

Table 1:

The position	The A value	The B value	The n value	The C value
					Test point
1	447	923.6	0.0802	0.0146
					Test point 2	497	958.8	0.0844	0.0157
Test point 3	548	1015.1	0.9123	0.0182
					Test point 4	691	1026.9	0.1025	0.0212
Test point 5	704	1109.3	0.1058	0.0227
					Test point 6	683	1158.9	0.1102	0.0231
Test point 7	672	1053.0	0.1072	0.0219
					Test point 8	654	1042.4	0.1062	0.0208
Test point 9	642	981.1	0.1047	0.0189

Below only be preferred implementation of the present invention, protection scope of the present invention also not only is confined to the foregoing description, and all technical schemes that belongs under the thinking of the present invention all belong to protection scope of the present invention.Should be pointed out that for those skilled in the art some improvement and retouching not breaking away under the principle of the invention prerequisite should be regarded as protection scope of the present invention.

Claims (3)

1. detection method of discerning solder joint zones of different material dynamic mechanical performance parameter is characterized in that step is:

(1) preparation is used for the solder joint sample that hardness test is used, and the solder joint surface of carrying out the hardness test side is polished, polished;

(2) choose some spots in the whole spot area on solder joint pilot diameter direction and carry out static hardness test, carry out subregion according to the gained hardness number;

(3) in the institute subregion, carry out dynamic indentation test, obtain the load depth curve at each place, testing site in the zones of different;

(4) set up the indentation test finite element numerical model;

(5), optimize and comprise objective function and constraint function, parameter and each parameter range to be detected in the mathematical model according to the analog result of indentation test finite element numerical model optimization mathematical model with corresponding experimental result structure solder joint zones of different place;

(6) adopt global optimization approach that the optimization mathematical model of step (5) is found the solution; Constantly adjust the empirical curve that values of parameters to be asked makes the corresponding experimental point of the continuous iterative approach of load depth curve of realistic model in the optimizing process automatically; In the process of iteration if reach the optimization convergence criterion of appointment; Then optimize iteration and stop, the mechanics parameter under this iteration step promptly is the optimum solution under certain suitable interval, repeats the dynamic mechanical parameter that this process can be obtained the solder joint zones of different.

2. the detection method of identification solder joint zones of different material dynamic mechanical performance parameter according to claim 1 is characterized in that: in the said step (3), carry out at least three indentation tests in the institute subregion.

3. the detection method of identification solder joint zones of different material dynamic mechanical performance parameter according to claim 1 is characterized in that said optimization mathematical model is shown in the following formula:

$\left\{\begin{array}{c}\mathrm{Minmize}:\mathrm{\Δf}(x_1,x_2,\·\·\·,x_n)=\sqrt{\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{\left(\frac{F_i^{\exp }(x_1,x_2,\·\·\·,x_n)-F_i^{\mathrm{sim}}(x_1,x_2,\·\·\·,x_n)}{F_i^{\exp }(x_1,x_2,\·\·\·,x_n)}\right)}^2}\\ \mathrm{Subject\; to}:\left\{\begin{array}{c}{x}_1^L\≤x_1\≤x_1^U\\ x_2^L\≤x_2\≤x_2^U\\ \·\·\·\\ x_n^L\≤x_n\≤x_n^U\end{array}\right.\end{array}\right.$

In the formula, x ₁, x ₂..., x _nBe parameter to be asked,

Be respectively the upper and lower bound of waiting to ask parameter, Be the continuous indentation load that obtains through dynamic indentation test,

The dynamic indentation load of trying to achieve during for finite element simulation, m are time increment step sum.

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