CN102435514B - 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 identifying 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 impact of resistance heat, the material behavior of welding region can change, and this just makes this regional performance also be different from mother metal, welding region can be divided into three sub regions according to the feature of hardness: mother metal district, heat-affected zone, solder joint district.Because the size of general mother metal is compared enough large with the heat-affected zone, so in the past to research in this respect, all ignored the material behavior of heat-affected zone, namely the conode connected mode is adopted in the finite element numerical modeling often or the mode that is rigidly connected directly links to each other with mother metal in that welding region is carried out, can not consider in this case obviously the material behavior at solder joint place, 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, namely 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 mechanical property parameters and the non-uniform Distribution of solder joint by mixcrohardness test, thereby can not be a fixed value with each regional mechanical property design of material of solder joint simply.In sum, the disposal route of present butt welding point can not satisfy the demand of Practical Project.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 of whole simulation analysis, the Obtaining Accurate 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 complexity and the zones of different place has different microstructures, for ferrous metal, place's metallographic structure comprises martensite and bainite in the middle of the solder joint, and there is the mixing metallographic structure heat-affected zone, existing martensite, bainite, ferrite and pearlite is arranged again, these different metallographic structures have caused the different material behavior in solder joint place, further research finds that mechanics parameter herein can present Heterogeneous distribution, it is solder joint, can there be the parameter attribute of graded at the place, heat-affected zone, so only stretch or the very difficult concrete mechanics parameter of determining solder joint zones of different place of compression test by simple, and the stress-strain relation at this place is difficult to obtain by conventional method, so can not carry out inverse problem of parameter to it according to the thinking of curve.

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, how the material dynamic mechanical characterisitic parameter of Obtaining Accurate 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 for traditional metal materials or the new material as 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 by dynamic indentation test, less sign size or even nano level strength of materials characteristic are measured and estimated to the dynamic stiffness indentation test for we provide, it is 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 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 has reflected that conscientiously material opposing pressure head dynamically is pressed into the ability of distortion, and this test is efficient and convenient, sample is without 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 by 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 recognition detection as this each regional material behavior of solder joint, the initial cross sectional of regional to be measured is amassed A ₀Be difficult to determine, therefore, can not directly obtain stress-strain relation according to the fundamental equation of appeal by dynamic indentation test, and then can not directly simulate this regional dynamic mechanical parameter.

Summary of the invention

The technical problem to be solved in the present invention just is: for the technical matters that prior art exists, the 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 by the following technical solutions:

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

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

(2) choose several points 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 calculation 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 respectively 22mm and 18mm, and such advantage is to optimize the quality of grid, reduces scale of model; On the other hand, because drop bar is only for generation of the effect of stress pulse, so need not consider drop bar in the indentation test finite element numerical model, the method for replacement is directly to apply uniform stress pulse at the input end of incident bar.

(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 with corresponding test findings, according to the analog result of indentation test finite element numerical model and corresponding experimental result to obtain the optimized mathematical model at solder joint zones of different place;

(6) in conjunction with optimized Genetic Algorithm, set this algorithm initial value, initial parameter has certain impact to solving result and the solution efficiency of genetic algorithm, and the parameter that needs to set in advance has: Population Size M, be the quantity of contained individuality in the population, generally get 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 in the process of iteration, then iteration stops, and the mechanics parameter under this iteration step namely is the optimum solution under certain suitable interval.

As a further improvement on the present invention:

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

Described optimized 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,

Respectively the upper and lower bound of parameter to be asked,

Be the continuous indentation load that obtains by 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 local mechanics parameter of material in millimeter even the micron-scale scope, have especially the engineering structure of stronger non-uniform Distribution 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 grade of picture spot area characterizes size in the Practical Project; The present invention considers the characteristic attributes such as the material of solder joint zones of different and size, more can truly reflect the material behavior at spot area place, has higher practical value and stronger engineering significance.

Description of drawings

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

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

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

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

Fig. 5 is the dynamic indentation test two-dimensional axial symmetric finite element model in the inventive method;

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

Embodiment

Below with reference to Figure of description and specific embodiment the present invention is described in further details.

Because usually strengthening model with the widest Johnson Cook, the distortion of most of engineering polycrystalline metal material under impact loading simulate, so the present invention adopts this model as the constitutive relation of this embodiment, shown in (1), can find out from formula, the J-C model representation is three product, has reflected respectively strain hardening, rate of strain sclerosis and temperature softening (annotating: use J-C correction of the model form here).

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

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 parameter value corresponding 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 simplicity, present embodiment is not considered the temperature softening effect, and namely temperature remains room temperature, and A is so just arranged, B, and n, four parameters of C are as the required dynamic mechanics parameter of the present invention.

As shown in Figure 1, be the application example of the present invention in instantiation, used welding spot structure is by 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 as follows:

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

(2) choose several points 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 being subject to 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 Indentation Process protuberance between two adjacent test points or the impact of depression, distance on every line between two adjacent measuring points is 0.12mm, to satisfy GB/T4340.1 to the standard-required of two measuring point centre distances, get afterwards its mean value as last True Data, the hardness number that records as shown in Figure 3, carry 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 large, and then can indirectly judge its material behavior larger 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, again according to the one dimension elastic wave theory, derive stress-strain relation by measuring two strains on the depression bar, this thinking can only be for the uniform situation of material behavior, for needing to consider that as solder joint is this regional has the special construction of dissimilar material properties, the initial cross sectional at each zone to be asked or unknown point place is amassed A ₀Very difficult obtaining even may do not obtained, 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, ensure at least three testing sites;

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, need at diamond penetrator of incident bar place installation, by applying the single compression pulse at adamas Vickers pressure head, the excitation pressure head dynamically is pressed into some points of reference line, obtain the dynamic impression of these points, record from the depth value at 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 etc., a kind of similar curve form is 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 converted to by the signal of piezoelectric sensor output; D is the mean value (mm) of impression catercorner length.

Present embodiment is divided into Three regions 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, the loading and unloading curve that obtains respectively 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 indentation test according to the physical process of impression examination, in order to reduce calculation scale, whole finite element model and load all are axisymmetric about center line, in addition, in order not make model too huge, here adopt 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 respectively 22mm and 18mm, such advantage is to optimize the quality of grid, reduces scale of model; On the other hand, because drop bar only plays the effect that produces stress pulse, so need not consider drop bar in finite element model, the method for replacement is that direct input end at incident bar applies uniform stress pulse, as shown in Figure 5;

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

This optimized 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,

Respectively the upper and lower bound of parameter to be asked, Be the continuous indentation load that obtains by dynamic indentation test, The dynamic indentation load of trying to achieve during for finite element simulation, m are time increment step sum.

For choosing different reference points, according to the mechanics parameter that constantly changes in optimizing process, just can obtain the finite element load depth relationship under the particular combination parameter, then by optimization method, constantly call the indentation test FEM model, and then obtain target response function, due to the required elastic-plastic mechanical parameter A of the present embodiment, B, n is initial yield stress, strength factor and the strain hardening exponent of corresponding welded seam area material respectively, C is dynamic empirical strain rate sensitivity coefficient, therefore the Mathematical Modeling 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),

Be the continuous indentation load that obtains by nano indentation test,

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

(6) in conjunction with optimized Genetic Algorithm, set this algorithm initial value, initial parameter has certain impact to solving result and the solution efficiency of genetic algorithm, and the parameter that present embodiment needs to set in advance has: Population Size, be the 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.According to the selected target response function of step (5) continuous test load-depth curve of each selected point of iterative approach progressively, Fig. 6 is progressively iteration synoptic diagram of physical test value and limited simulation value, 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 by genetic Optimization Algorithm itself is constantly upgraded required elastic-plastic mechanical parameter automatically, when certain step, iteration reached this convergence criterion, just can judge the A under this iteration step, and B, n, C are exactly the optimized parameter solution that will seek.Can draw the plasto-elasticity parameter of each regional institute reconnaissance by above-mentioned solution procedure, as shown in table 1 below, these points have comparatively significantly variation and rule, and have step-characteristic, and the strength factor at place, fusion area is obviously greater than the heat-affected zone.From present embodiment as can be known, the method can comparatively accurately identify the material dynamic mechanical performance parameter at solder joint zones of different place, this is just so 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 provides good CAE basis, have preferably reference and a reference value 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 above-described embodiment, 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 the some improvements and modifications not breaking away under the principle of the invention prerequisite should be considered as protection scope of the present invention.

Claims (2)

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

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

(2) choose several points 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 loading-depth curve at each place, testing site in the zones of different;

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

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

(6) adopt global optimization approach that the optimized mathematical model of step (5) is found the solution, the value of constantly automatically adjusting parameter to be asked in the optimizing process makes the empirical curve of the corresponding experimental point of the continuous iterative approach of loading-depth curve of realistic model, if reach the optimization convergence criterion of appointment in the process of iteration, then Optimized Iterative stops, mechanics parameter under this iteration step namely 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;

Described optimized mathematical model is shown in the following formula:

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

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

K=1,2 ... n is respectively lower limit and the upper limit of parameter to be asked,

(x ₁, x ₂..., x _n) be the continuous indentation load that obtains by dynamic indentation test,

(x ₁, x ₂..., x _n) the dynamic indentation load of trying to achieve during for finite element simulation, m is time increment step sum.

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

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