CN104573392B - A kind of welding spot fatigue Forecasting Methodology - Google Patents

Abstract

The present invention relates to a kind of welding spot fatigue Forecasting Methodology, it is characterised in that：Step 1, Full Vehicle Modelling, set up modularization solder joint FEM model；Step 2, derivation welding spot fatigue evaluation parameter：Mean stress intensity factorStep 3, the tack-weld to different materials carry out the fatigue test of system, willRegression analysis is carried out with the fatigue data of the tack-weld of different materials, different materials tack-weld is obtainedCurve.The present invention predicts welding spot fatigue using a kind of modularization solder joint model, in a particular application only need to overlap the node of modular solder joint model boundary unit with welding structure cell node, improves the efficiency that solder joint is modeled in Full Vehicle Modelling.

Description

A kind of welding spot fatigue Forecasting Methodology

Invention field

The present invention relates to a kind of solder joint fatigue failure prediction, more particularly to a kind of welding spot fatigue Forecasting Methodology.

Background technology

Resistance spot welding is the jointing form between most of part in traditional welding procedure in automobile assembling, automobile Designed according to resistance spot welding requirement, and resistance spot welding is highly suitable for the overlap joint of this thin-slab structure of vehicle body.According to system The fatigue problem of the vehicle structure of meter about 50% is relevant with solder joint, and about 80% vehicle body fatigue problem is relevant with solder joint, because This is it may be said that the fatigue strength of solder joint determines the durability of automobile component.Therefore, area of computer aided is used early stage design The means of analysis, fatigue life prediction is carried out to vehicle body solder joint, for effectively reduction production cost, shortens Automobile Design exploitation week Phase, improving the quality of product has important realistic meaning.

At present, welding spot fatigue prediction mainly has two methods：A kind of is the LBF methods based on power, and this method uses beam Unit simulation nugget, by acting on power and torque on nugget beam element, welded blank is calculated according to certain mathematical formulae On structural stress evaluate welding spot fatigue, torsional moment on shell unit can not be transmitted due to beam element, and structure should The calculating of power uses more empirical parameter, therefore precision of prediction is relatively low；Another is the LMS Forecasting Methodologies based on stress, should Method directly predicts that solder joint is tired using the solder joint model become more meticulous very much by the local stress of FEM calculation welded blank In the labor life-span, with certain precision of prediction, but applied in the solder joint fatigue prediction of vehicle, then modeling and computational efficiency are relatively low.

The content of the invention

It is an object of the invention to solve relatively low precision of prediction present in existing solder joint fatigue Forecasting Methodology, modeling and The problems such as computational efficiency is relatively low.

The technical scheme is that there is provided a kind of welding spot fatigue Forecasting Methodology, it is characterised in that：

Step 1, Full Vehicle Modelling, set up modularization solder joint FEM model；

Step 2, derivation welding spot fatigue evaluation parameter：Mean stress intensity factor

Step 3, the tack-weld to different materials carry out the fatigue test of system, willWith the spot welding of different materials The fatigue data of head carries out regression analysis, obtains different materials tack-weldCurve.

Further, in step 2, mean stress intensity factorDerivation is as follows：

(1) node of each node around solder joint nugget in whole vehicle model is can obtain under different working conditions by CAE analysis Power and torque, and the nodal force F under each node local coordinate system is converted into by coordinate transform_x、F_y、F_zWith node torque M_x、M_y、 M_z；

(2) by nodal force F_x、F_y、F_zBe converted to linear force f_x、f_y、f_z, node torque M_x、M_y、M_zBe converted to linear torque m_x、m_y、m_z；

(3) structural stress σ at respective nodes is calculated_m、σ_b, wherein, the linear force and torque of each node, are pressed around solder joint Formula (2) obtains the structural stress at respective nodes：

σ_m=f_y/t

σ_b=6m_x/t² (2)

In formula, σ_mFor the membrane stress around solder joint at each node, σ_bFor the flexure stress around solder joint at each node, f_y、m_xPoint Linear force and torque that Wei be under local coordinate system on y, x direction, t be the thickness of welding motherboard；

(4) Crack Extension angle α amendment is carried out to structural stress at node, wherein, by solder joint actual crack extended corner Spend the structural stress of α amendments：

σ_mxz=(f_y sinα-f_z cosα)sinα/t

σ_bxz=6m_x sinα²/t² (3)

In formula, σ_mxzFor the membrane stress corrected by α, σ_bxzFor the flexure stress corrected by α, t is welding motherboard thickness, α For actual crackpropagation angle, f_y、f_z、m_xLinear force and torque respectively under local coordinate system on y, z, x direction；

(5) to the stress intensity factor Δ K of membrane stress_m, flexure stress stress intensity factor Δ K_b, total stress intensity factor Δ K calculated, wherein total stress intensity factor：

In formula：ΔK_mFor the stress intensity factor of correspondence membrane stress, Δ K_bFor the stress intensity factor of correspondence flexure stress, Δ K For total stress intensity factor,The geometric corrections coefficient of membrane stress is corresponded to for stress intensity factor,It is strong for stress Degree factor pair answers the geometric corrections coefficient of flexure stress；

(6) to mean stress intensity factorCalculated, take crackle averagely should in expansion process on thickness of slab direction The force intensity factorIt is used as the evaluation parameter of welding spot fatigue：

Calculate：

Further, the nugget of solder joint uses two layer entities unit simulation, and every layer is made up of four solid elements, forms one Individual equilateral octagon, diameter takes the actual diameter of nugget, and nugget material assumes consistent with mother metal

Beneficial effects of the present invention：

(1), the present invention welding spot fatigue is predicted using a kind of modularization solder joint model, only need in a particular application by The node of modular solder joint model boundary unit is overlapped with welding structure cell node, is improved solder joint in Full Vehicle Modelling and is built The efficiency of mould.

(2) model, which carries out solder joint fatigue simulation analysis, mainly two advantages：One is to simulate weldering using many individual cells Core, and nugget, heat affected area and mother metal area have individually been distinguished, more conform to the actual physical geometric of solder joint；Two are due to Solder joint size of mesh opening is fixed using modularization model, the structural stress result of gained will not influenceed by sizing grid.

(3) in actual welding spot fatigue prediction, the section that finite element analysis obtains each node around nugget is first passed through Point power and torque, the corresponding structural stress of each node is obtained according to acting principle by nodal force and Calculating Torque during Rotary, and according to True extension angle of the crackle on thickness of slab direction is modified to it, and thus the structural stress by amendment, which can be calculated, obtains Stress intensity factor at respective nodes, and then it is strong to obtain a mean stress in solder joint crackle on its actual extensions path The factor is spent as the evaluation parameter of welding spot fatigue.

(4) due to using evaluation parameter of the mean stress intensity factor as welding spot fatigue, need to only calculate solder joint week The nodal force and torque enclosed considers the influence of crackle true extension angle in being calculated as input, and welding spot fatigue, therefore Computational efficiency and precision of prediction are of a relatively high.

Brief description of the drawings

Fig. 1 is a kind of flow chart of welding spot fatigue Forecasting Methodology of the present invention；

Fig. 2 is solder joint modular finite meta-model unit of the present invention；

Fig. 3 is node entirety of the present invention and local coordinate system；

Fig. 4 is typical spot welding lap joint fatigue failure mode schematic diagram；

Fig. 5 is the constituent schematic diagram for welding sheet metal structural stress；

Fig. 6 is fatigue test tack-weld specimen size schematic diagram；

Fig. 7 is load amplitude-fatigue life double-log distribution schematic diagram of sample obtained by fatigue test；

Fig. 8 is the tack-weld modular finite meta-model schematic diagram set up according to fatigue test tack-weld size；

Fig. 9 is the double-log distribution schematic diagram of mean stress intensity factor-fatigue life.

Embodiment

Technical scheme is described in detail below with reference to accompanying drawing 1-9

The invention provides a kind of welding spot fatigue Forecasting Methodology, comprise the following steps：

Step 1, Full Vehicle Modelling, set up modularization solder joint FEM model

In Full Vehicle Modelling, the modularization solder joint FEM model of foundation is as shown in Fig. 2 the nugget of solder joint is real using two layers Body unit is simulated, and in order to solve the problem of solder joint FEM model is matched with structured grid, every layer is made up of four solid elements, An equilateral octagon is formed, diameter takes the actual diameter of nugget, and nugget material assumes consistent with mother metal.Then, three circles are passed through Shell unit is progressively transitioned into 10 × 10mm basic grid size.

In nugget area, upper and lower surface covers a floor shell grid, is matched for solution shell grid with the physical grid degree of freedom on a node basis Problem, will weld circumnuclear first lap mesh definition for solder joint heat affected area, 2mm is taken along the width on spot size direction, weld Point heat affected area material thickness, type are consistent with welding base metal.Remaining two hoop nets lattice be solder joint mother metal area, its outermost boundary by Two element sides compositions, so as to complete solder joint size of mesh opening to the excessive of basic grid size.

Establish after whole vehicle model, it is possible to finite element analysis is carried out to it and obtains different operating mode under body solder joint nugget weeks Enclose the nodal force and torque of each node, then nodal force and torque be converted into mean stress intensity factor by Theory of Fracture MechanicsThen shouldCan as welding spot fatigue evaluation parameter, by the mean stress intensity factor around solder joint at each nodeThe tack-weld of corresponding materialCurvilinear correlation joins, and just can obtain the fatigue life N of corresponding solder joint.Below By butt welding point Fatigue Life Assessment parameterDerivation and different materials tack-weldThe acquisition of curve is made detailed Introduce.

Step 2, derivation welding spot fatigue evaluation parameter：Mean stress intensity factor

Set up using above-mentioned modularization modeling method after vehicle and solder joint FEM model, it is necessary to derive the solder joint fatigue longevity The evaluation parameter of life, specific derivation process is as follows：

(1) node of each node around solder joint nugget in whole vehicle model is can obtain under different working conditions by CAE analysis Power and torque, and the nodal force F under each node local coordinate system is converted into by coordinate transform_x、F_y、F_zWith node torque M_x、M_y、 M_z.Conversion coordinate is shown in Fig. 3, wherein (x ', y ', z ') is global coordinate system, (x, y, z) is the local coordinate system of certain node.

(2) by nodal force F_x、F_y、F_zBe converted to linear force f_x、f_y、f_z, node torque M_x、M_y、M_zBe converted to linear torque m_x、m_y、m_z

According to acting principle by formula (1) by nodal force F_x、F_y、F_zChange into the corresponding linear force f of each node_x、f_y、 f_z, following formula be from each node x around nugget to nodal force F_x1、F_x2、F_x3…F_x(n-1)Calculate obtain each node x to it is linear Power f_x1、f_x2、f_x3…f_x(n-1)Matrix Formula：

In formula:As shown in figure 3,1,2,3 ... n-1 are the numbering of each node around nugget, due to the solder joint mould used herein There are eight nodes around type nugget, so n takes 9, and because nugget is ring-type, node 1 is overlapped with n, so nodal force need to only take To n-1；F_x1、F_x2、F_x3…F_x(n-1)For each node x to nodal force；f_x1、f_x2、f_x3…f_x(n-1)For each node x to it is linear Power；l₁、l₂、l₃…l_n-1For each node spacing around nugget；It is similar therewith, around solder joint each node y to z to linear force Can from y to z to nodal force obtained by identical Matrix Formula, only the subscript x in formula need to be changed to y, z.

Likewise, node linear torque m_x、m_y、m_zAlso can be by node torque M_x、M_y、M_zObtained by identical transition matrix Arrive, only the F in Matrix Formula need to be changed to M, f is changed to m.

(3) structural stress σ at respective nodes is calculated_m、σ_b

The linear force and torque of each node around solder joint, the structural stress at respective nodes can be obtained by formula (2)：

σ_m=f_y/t

σ_b=6m_x/t² (2)

In formula, σ_mFor the membrane stress around solder joint at each node, σ_bFor the flexure stress around solder joint at each node, f_y、m_xPoint Linear force and torque that Wei be under local coordinate system on y, x direction, t be the thickness of welding motherboard.

(4) Crack Extension angle α amendment is carried out to structural stress at node

Caused by the fatigue failure of solder joint is due to through the Crack Extension of thickness of slab, but crackle is in thickness of slab direction Extension be not to be completely parallel to thickness of slab direction, but α at an angle, the size of angle [alpha] and material, the thickness of slab of solder joint joint Deng relating to parameters, Fig. 4 show the typical fatigue failure mode of overlap joint tack-weld.Then it can obtain real by solder joint by formula (3) The structural stress of border crackpropagation angle α amendments：

σ_mxz=(f_y sinα-f_z cosα)sinα/t

σ_bxz=6m_x sinα²/t² (3)

Fig. 5 show the constituent of welding sheet metal structural stress, wherein σ_mxzFor the membrane stress corrected by α, σ_bxzFor The flexure stress corrected by α, t is welding motherboard thickness, and α is actual crackpropagation angle, f_y、f_z、m_xRespectively local coordinate Linear force and torque on lower y, z, x direction of system.

(5) to the stress intensity factor Δ K of membrane stress_m, flexure stress stress intensity factor Δ K_b, total stress intensity factor Δ K is calculated

Total stress intensity factor can obtain by formula (4)：

Wherein Δ K_mFor the stress intensity factor of correspondence membrane stress, Δ K_bFor the stress intensity factor of correspondence flexure stress, Δ K For total stress intensity factor,The geometric corrections coefficient of membrane stress is corresponded to for stress intensity factor,It is strong for stress Degree factor pair answers the geometric corrections coefficient of flexure stress, and expression formula is as follows：

In formula, C₀=1.12152, C₁=-3.04057, C₂=10.49184, C₃=-36.6678, C₄=110.099, C₅ =-255.68184, C₆=421.97167, C₇=-440.50866, C₈=199.37326, C₉=123.93056, C₁₀=- 237.97164, C₁₁=136.17068, C₁₂=-28.91005；A is the crack length existed at certain moment, t_rIt is disconnected for fatigue Split critical crack length, t_r=t/sin α.

(6) to mean stress intensity factorCalculated

Because crack propagation life of the tack-weld on thickness of slab direction accounts for more than the 80% of its whole fatigue life, therefore We can reasonably assume fatigue fracture critical crack length t_r≈ t, and fatigue crack since a=0 up to expanding to a= It is broken during t, then can use mean stress intensity factor of the crackle on thickness of slab direction in expansion processIt is used as welding spot fatigue Evaluation parameter：

Calculate：

In above-mentioned calculation formula, identical letter represents repeated description in identical physical quantity, therefore no longer each formula The implication of corresponding letters.

Step 3, the tack-weld to different materials carry out the fatigue test of system, willWith the spot welding of different materials The fatigue data of head carries out regression analysis, obtains different materials tack-weldCurve.

The fatigue test of system is carried out to the tack-weld of different materials, willIt is tired with the tack-weld of different materials Labor test data carries out regression analysis, can obtain corresponding to different materials tack-weldCurve.With it is traditional tired S-N curves in labor analysis are similar, and these can be used in real vehicle analysis of fatigueThe fatigue life of curve butt welding point is carried out Finite element simulation is predicted, i.e., the mean stress intensity factor of the different solder joints of vehicle body is obtained by finite element analysis computationLead to again Cross correspondingCurve obtains corresponding fatigue life.

It is provided below one and DP600GI material tack-welds is obtained using context of methodsThe method of curve Example：

First have to design the shear fatigue test of tack-weld.A kind of high-strength steel material DP600GI is chosen as experiment pair As the thickness of slab of spot-welding sample being made into tetra- kinds of 0.8mm, 1.0mm, 1.5mm and 1.8mm, in order to ensure the tack-weld obtained Uniformity, the physical dimension of all samples is all consistent (see Fig. 6), and welding steel is all the combination of thickness of the same race, and nugget is straight Unified footpath is 7.0mm.

Because vehicle body solder joint is primarily subjected to shear-type load, experiment only focuses on the shear fatigue life-span of each solder joint exemplar, will The spot welding exemplar of 4 kinds of thickness of slab combinations of HSLA340GI carries out shear fatigue experiment on electo hydraulic servocontrolled fatigue testing machine, tests Loaded load is 0.1 than R in journey, and loading frequency is 10Hz.Fatigue data obtained by fatigue test can use load amplitude-fatigue The double-log distribution map in life-span is represented (see Fig. 7).

Next the Fatigue Life Assessment parameter of the tack-weld by finite element analysis acquisition different-thickness is needed The exemplar size for being first according to fatigue test sets up modularization tack-weld FEM model (see Fig. 8), to keep and fatigue examination The uniformity of condition is tested, Spot size takes 7.0mm, the whole six-freedom degrees of sample one end constraint, other end imposed load, load Stress point constraint is except whole frees degree of loading direction.Material properties are linear elasticity, and modulus of elasticity is 210GPa, and Poisson's ratio is 0.3, density is 7.85 × 10³kg/m³。

Finite element analysis is carried out to the model built up and different-thickness spot welding is obtained using this paper derivation method calculating The mean stress intensity factor of headAnd double-log regression analysis is carried out with the fatigue life data of solder joint, analysis result is shown in figure 9.From figure as can be seen that the fatigue life point of the solder joint exemplar of all different-thickness to be all closely distributed in fitting a straight line attached Closely, the degree of correlation of fitting a straight line reaches R²=-0.95, therefore we can obtain a masterCurve is as follows：

Then this curve is DP600GI tack-weldsCurve, other materials tack-weld Curve can also be obtained using same method by fatigue test.

Although refer to the attached drawing disclose in detail the present invention, it will be appreciated that, what these descriptions were merely exemplary, and The non-application for being used for limiting the present invention.Protection scope of the present invention may include do not departing from this by appended claims Various modifications, remodeling and the equivalents made in the case of invention protection domain and spirit for invention.

Claims (1)

1. a kind of welding spot fatigue Forecasting Methodology, it is characterised in that：

Step 1, Full Vehicle Modelling, set up modularization solder joint FEM model；

Wherein：The nugget of solder joint uses two layer entities unit simulation, and every layer is made up of four solid elements, forms one equilateral eight Side shape, diameter takes the actual diameter of nugget, and nugget material assumes consistent with mother metal；

In nugget area, upper and lower surface covers a floor shell grid, will weld circumnuclear first lap mesh definition for solder joint heat affected area, 2mm is taken along the width on spot size direction, solder joint heat affected area material thickness, type are consistent with welding base metal；

Step 2, derivation welding spot fatigue evaluation parameter：Mean stress intensity factor

Mean stress intensity factorDerivation is as follows：

(1) by CAE analysis can obtain under different working conditions in whole vehicle model around solder joint nugget the nodal force of each node and Torque, and the nodal force F under each node local coordinate system is converted into by coordinate transform_x、F_y、F_zWith node torque M_x、M_y、M_z；

(2) by nodal force F_x、F_y、F_zBe converted to linear force f_x、f_y、f_z, node torque M_x、M_y、M_zBe converted to linear torque m_x、m_y、 m_z；

(3) structural stress σ at respective nodes is calculated_m、σ_b, wherein, the linear force and torque of each node around solder joint, by formula (2) Obtain the structural stress at respective nodes：

σ_m=f_y/t

σ_b=6m_x/t² (2)

In formula, σ_mFor the membrane stress around solder joint at each node, σ_bFor the flexure stress around solder joint at each node, f_y、m_xRespectively Linear force and torque under local coordinate system on y, x direction, t are the thickness of welding motherboard；

(4) Crack Extension angle α amendment is carried out to structural stress at node, wherein, repaiied by solder joint actual crack expanded- angle α Positive structural stress：

σ_mxz=(f_y sinα-f_z cosα)sinα/t

σ_bxz=6m_x sinα²/t² (3)

In formula, σ_mxzFor the membrane stress corrected by α, σ_bxzFor the flexure stress corrected by α, t is welding motherboard thickness, and α is real The crackpropagation angle on border, f_y、f_z、m_xLinear force and torque respectively under local coordinate system on y, z, x direction；

(5) to the stress intensity factor Δ K of membrane stress_m, flexure stress stress intensity factor Δ K_b, total stress intensity factor Δ K enters Row reckoning, wherein total stress intensity factor：

$\mathrm{\Δ}K={\mathrm{\ΔK}}_m+{\mathrm{\ΔK}}_b=\sqrt{\mathrm{\π}a}\[{\mathrm{\σ}}_{mxz}{f}_m\left(\frac{a}{t_r}\right)+{\mathrm{\σ}}_{bxz}{f}_b\left(\frac{a}{t_r}\right)\]---\left(4\right)$

In formula：ΔK_mFor the stress intensity factor of correspondence membrane stress, Δ K_bFor the stress intensity factor of correspondence flexure stress, Δ K is total Stress intensity factor,The geometric corrections coefficient of membrane stress is corresponded to for stress intensity factor,For stress intensity because The geometric corrections coefficient of son correspondence flexure stress；

(6) to mean stress intensity factorCalculated, take mean stress of the crackle on thickness of slab direction in expansion process strong Spend the factorIt is used as the evaluation parameter of welding spot fatigue：

$\stackrel{\‾}{\mathrm{\Δ}K}={\∫}_{\frac{a}{t}=0}^{\frac{a}{t}=1}\mathrm{\Δ}Kd\frac{a}{t}={\∫}_{\frac{a}{t}=0}^{\frac{a}{t}=1}\sqrt{\mathrm{\π}a}\[{\mathrm{\σ}}_{mxz}{f}_m\left(\frac{a}{t}\right)+{\mathrm{\σ}}_{bxz}{f}_b\left(\frac{a}{t}\right)\]d\frac{a}{t}---\left(7\right)$

Calculate：

$\stackrel{\‾}{\mathrm{\Δ}K}=\sqrt{t/sin\mathrm{\α}}(32.87{\mathrm{\σ}}_{mxz}+11.87{\mathrm{\σ}}_{bxz}).---\left(8\right)$

Step 3, the tack-weld to different materials carry out the fatigue test of system, willWith the tack-weld of different materials Fatigue data carries out regression analysis, obtains different materials tack-weldCurve.