CN105447268A - Method for designing car front longitudinal beam with hat section - Google Patents

Abstract

The invention, for the deficiencies in existing car front longitudinal beam design, proposes a method for designing a car front longitudinal beam with a hat section, and aims to realize controllable design of a front collision deformation mode of a front longitudinal beam with a section analysis and calculation method in an overall deformation mode of a planned longitudinal beam. The design method comprises the following steps: A, planning an overall deformation mode of the front longitudinal beam in a front collision condition: dividing the front longitudinal beam into a front telescopic crushing section, a middle Y-direction bent section, a rear micro-deformation supporting section and a rear stable extension section in sequence from front to rear; B, deriving an average crushing counterforce expression of the front longitudinal beam with the hat section; C, according to the requirements of the sections of the front longitudinal beam, designing the sections of the front longitudinal beam in sequence from front to rear; and D, according to a design result in the step C, performing simulation analysis by utilizing a computer, and according to a simulation result, confirming or modifying the design. The design thought of the method has very high practicality, so that the method also can be applied to the design of other car parts.

Description

A kind of automobile front longitudinal beam method for designing of hat section

Technical field

The invention belongs to automotive safety design field, before relating to front longitudinal, touch structural design, specifically, the present invention relates to a kind of automobile front longitudinal beam method for designing of hat section.

Background technology

Along with the swift and violent growth of urban and rural residents' automobile pollution, road traffic accident has become the serious public hazards threatening human life in worldwide.According to WHO analyses and prediction: to the year two thousand twenty, road traffic accident will become be only second in the world angiocardiopathy and hypochondriacal the third-largest the person threaten, for this reason, each flourishing state of the world has all made Compulsory Feature to Crash Safety Design of Vehicles, establish respective Legal System, and successively implement NCAP (NCAP:NewCarAssessmentProgramme), be intended to the raising promoting Crash Safety Design of Vehicles energy further.

When automotive SBC can refer to automobile generation traffic hazard, vehicle can be protected the occupant in car or the pedestrian outside car, to prevent injury or to make injury be down to the performance of minimum level.Designer adopts various method to make every effort to automotive body structure can be out of shape in a predetermined manner in an impact, thus effectively absorbs collision energy, produces good collision waveform and impacts injury, for the coupling of occupant restrain system lays the foundation to alleviate suffered by occupant.The framed structure that the minibus of body structure is mainly made up of thin-walled beam-shaped structure and joint determines, they be also absorb in collision process collision impact can leading, simultaneously for crew module provides most rigidity.Front longitudinal is the important longitudinal stress component of passenger vehicle body structure, its basic structure is thin walled beam shape, usually, safe vehicle body requires that front longitudinal absorbs the energy of 30%-50% in head-on crash, and there is certain Stability Analysis of Structures performance, guarantee that front-end architecture is out of shape in a particular manner, ensure the structural intergrity of crew module.Therefore, appropriate design front longitudinal can be out of shape and energy-absorbing in a predetermined manner, is the main contents of body structure minibus design.

For the design of passenger car front rail structure, the analysis relevant due to impingement designed in engineering and theory perfect not at present, ubiquity more trial and error fashion method for designing consuming time and structured material redundancy phenomena in design.

Notification number is the method for designing that the Chinese patent of CN201310039923.3 discloses a kind of front longitudinal, comprising: 1, obtain acceleration-time curve during mark car head-on crash and conquassation distance-time curve; 2, target carriage front longitudinal arrives the length of power assembly front end is foremost X; The the first moment t started when producing conquassation is obtained in conjunction with conquassation distance-time curve ₀, and the second moment t corresponding when conquassation distance is X ₁; 3, obtain at t ₀~ t ₁to the constant equivalent acceleration a of mark car in time period; 4, target carriage test mass m is obtained; Obtain target carriage at t ₀~ t ₁the average eguivalent impact force F be subject in time period; 5, according to the proportion of the impact force that front longitudinal is born in the energy-absorbing section that front longitudinal arrives power assembly front end foremost, front longitudinal is obtained at t ₀~ t ₁the equivalent impact force be subject in time period; 6, according to front longitudinal at t ₀~ t ₁the equivalent impact force be subject in time period obtains the length of front longitudinal xsect, width, wall thickness and material parameter.This method truly has some reference value in reverse engineer field, but does not have too many directive significance for brand-new positive development.

Notification number be 201310388342.0 Chinese patent disclose a kind of front longitudinal beam anti-collision performance design method for passenger vehicle, be intended to overcome prior art traditional " trial and error ", namely need during design vehicle front longitudinal repeatedly to revise computer simulation model, repeatedly carry out the problems such as experimental test.Described front longitudinal beam anti-collision performance design method for passenger vehicle is divided into four steps: many right-angle cross-section of 1, deriving thin walled beam average conquassation counter-force expression formula; 2, front longitudinal conquassation crushed element cross section is designed; 3, the average Expression of Moment formula of derivation square-section thin walled beam; 4, front longitudinal flexural deformation partial cross section is designed.This method is only applicable to the stringer designs of square-section, in fact, current, hat section front longitudinal has obtained and extensively and has successfully applied, and this invents the bulk deformation pattern shortage general plan of described method to front longitudinal, not for the controlled design proposal of front longitudinal deformation pattern.

Summary of the invention

The present invention is directed to the deficiency that above-mentioned existing automobile front longitudinal beam design exists, propose a kind of automobile front longitudinal beam method for designing of hat section, being intended to the bulk deformation pattern by planning longeron, using cross-section analysis and computing method, realizing the controlled design of front longitudinal head-on crash deformation pattern.

The automobile front longitudinal beam method for designing of hat section of the present invention comprises the steps:

A: planning front longitudinal is front touching the structural strain's pattern under operating mode: front longitudinal is divided into from front to back successively front portion and collapses conquassation section, middle part Y-direction bending section, rear portion Light deformation supporting section and posterior stabilization extension;

B: the average conquassation counter-force expression formula of derivation hat section front longitudinal;

C: according to the requirement of each section of front longitudinal, designs each section of front longitudinal from front to back successively;

D: according to the design result of step C, utilizes computing machine to carry out sunykatuib analysis, and to confirm design according to analog result or change.

Specifically, in described step B, the average conquassation counter-force expression formula of described hat section front longitudinal is as follows:

$F_m=32.90M_0{\left(\frac{L}{t}\right)}^{1/3};$

In formula: F _mfor average conquassation counter-force, unit is kN; M ₀=σ ₀t ²/ 4, unit is N.mm; σ ₀for longeron Metal plate yield strength, unit is Mpa; L=2a+2b+4f, unit is mm; A is longitudinal beam front section inner panel width, and b is plate height in longitudinal beam front section, and f is side rail welding edge width, and t is girder plate material thickness.

Further, summarize, the design process that front portion in described step C collapses conquassation section is as follows: according to front longitudinal overall collapse energy-absorption target and effective conquassation distance, tentatively determine the average conquassation counter-force of front longitudinal front end, and then according to the hat section front longitudinal average conquassation counter-force expression formula in step B and boundary condition design hat section thin-walled depth of beam, width and welding edge width.

Specifically, the design process that the front portion in described step C collapses conquassation section is as follows: a, determine the yield strength σ of material therefor ₀; B, tentatively determine that front longitudinal collapses depth of section a, the length b of conquassation segment structure and nominal perimeter L according to arrangement space; C, utilizing hat section front longitudinal average conquassation counter-force expression formula and front longitudinal to collapse the average conquassation counter-force formula of conquassation section, collapsing the average conquassation counter-force of target of conquassation segment structure for reaching front longitudinal, optimize front longitudinal B ₁perimeter L, the wall thickness t of section collapse structure, determine the design load of each design variable; The average conquassation counter-force formula that described front longitudinal collapses conquassation section is as follows: 0.73DF _m=E _t, wherein D is the longitudinal length that front longitudinal collapses conquassation segment structure, and unit is mm; E _tfor front longitudinal collapses the energy-absorbing desired value of conquassation segment structure, unit is kJ, Fm is the average conquassation counter-force of front longitudinal; D, the anterior limit element artificial module collapsing the axial conquassation of conquassation segment structure of foundation, carry out the axial conquassation simulation analysis that front portion collapses conquassation segment structure, the front portion of extracting emulation gained collapses the average crushing force of conquassation segment structure, and checking is anterior collapses the design object whether conquassation section average conquassation counter-force reaches hat section front longitudinal average conquassation counter-force expression formula.

Further, the design process of the middle part Y-direction bending section in described step C is as follows:

A, according to the size of the longitudinal force suffered in complete automobile collision of Y-direction bending section bending position in the middle part of front longitudinal and simulation analysis moment values, draw design object function:

$\mathrm{\σ}=\frac{F_x}{A}+\frac{M_y\×d_y}{I_y}+\frac{M_z\×d_z}{I_z}>{\mathrm{\σ}}_s;$

Wherein, A is the thick area of material in Y-direction bending section cross section in the middle part of front longitudinal; M _yand M _zbe respectively the Y-direction in the middle part of front longitudinal suffered by Y-direction bending section cross section and Z-direction moment of flexure; I _yand I _zbe respectively the moment of inertia of sectional view for Y-axis and Z axis; d _yand d _zbe respectively certain point on cross section and arrive the distance of the moment of inertia of centroidal principal axes Y-axis and Z axis, σ is the longitudinal force that in the middle part of front longitudinal, Y-direction bending section bending position is suffered in complete automobile collision, σ _sfor the yield strength of Y-direction bending section bending position material in the middle part of front longitudinal;

B, yield strength σ according to Y-direction bending section bending position material in the middle part of design object function determination front longitudinal _s, select the material of Y-direction bending section bending position in the middle part of front longitudinal accordingly;

C, in conjunction with front deck general arrangement space, collapse based on conquassation segment structure sectional dimension by the front longitudinal designed, consider the connection of Y-direction bending section and lower curved longeron in the middle part of front longitudinal simultaneously, tentatively determine the height in Y-direction bending section bending position cross section in the middle part of front longitudinal, width and nominal girth; Based on front longitudinal leading portion Cross Section Morphology, in conjunction with front deck design space (as tire envelope size, power assembly size and installation site, the planning of longeron bending position), and longitudinal load requires to determine cross section Z-direction height and Y-direction width in the middle part of front longitudinal and then determines the nominal girth in cross section;

D, in conjunction with the design object function described in a step, for meeting Y-direction bending section bending position maximum （normal） stress design object in the middle part of front longitudinal, determine the wall thickness t of Y-direction bending section bending position in the middle part of front longitudinal; Above-mentioned a, b, c tri-step carry out successively from front to back physical logic, in the middle part of front longitudinal, the wall thickness t of Y-direction bending section bending position is based in conjunction with the design object function described in a step, the known maximum （normal） stress of a step, M _y, M _z, I _y, I _z, d _y, d _z, reverse goes out A accordingly, and step c have also been obtained the nominal perimeter L in cross section, and according to physical knowledge, the critical value of wall thickness t just can obtain (t=A/L), and concrete value is obtained by iteration optimization;

Based on the geometry of the bending position cross section structure gone out designed by e, the moment values that requires and input by the axially loaded set and material parameter, set up complete automobile collision realistic model, carry out complete automobile collision analysis, and extract the moment values of Y-direction bending section bending position in the middle part of front longitudinal and longitudinal force-time curve;

Y-direction bending section bending position cross section longitudinal force maximal value F in the middle part of f, checking front longitudinal _x-maxwhether reach design object F _x-max>F, wherein, F is the longitudinal stress threshold value of bending section in the middle part of front longitudinal;

G, repetition section optimal step, whole process iterates is to meeting F _x-maxtill >F;

H, from front to back, makes successively to use the same method and to design the cross section of each crooked place of Y-direction bending section in the middle part of front longitudinal.

Further, in described Step d, the wall thickness t < A/L of Y-direction bending section bending position in the middle part of front longitudinal, wherein A is the thick area of material in Y-direction bending section cross section in the middle part of front longitudinal, and L is the nominal girth in Y-direction bending section cross section in the middle part of front longitudinal.

Further, if when the demand calculating Y-direction bending section each crooked place cross section destruction trend and strategic planning in the middle part of discovery front longitudinal is inconsistent, adjust by following method: a, increase inside cavity stiffening plate, to adjust cross sectional moment of inertia and principal axis of inertia angle, thus change section stress maximum point position; B, front longitudinal surface increase inducement structure, to change the moment direction suffered by crooked place.

The design process of described rear portion Light deformation supporting section is as follows: the design process of rear portion Light deformation supporting section and the design process of middle part Y-direction bending section similar, just keep this region few distortion or Light deformation as far as possible, wall thickness t generally gets and is greater than A/L for this reason, and concrete value also continuous iteration optimization obtains.

The design process of described posterior stabilization extension is as follows: the design of posterior stabilization extension and the design process of middle part Y-direction bending section similar, just keep this region indeformable, wall thickness t is greater than A/L for this reason.Method repeats no more.

Mentality of designing of the present invention is as follows:

Head-on crash part in current domestic main flow C-NCAP security evaluation criteria comprises the collision of front rigid wall and 40% liang of class is tested, and the final evaluation criterion of these two kinds of collision experiments is dummy and injures index and meet the demands.And in CAE simulation analysis, conveniently assess, then need dummy to be injured index decomposition and be transformed in vehicle body index.The simulation analysis vehicle body evaluation index that Frontal offset impact is corresponding is structure intrusion volume, and the simulation analysis vehicle body evaluation index of front rigid wall collision correspondence is the equivalent acceleration of B post root position.

Automobile front longitudinal beam is the key structure part of head-on crash operating mode, and its structural arrangement, cross section geometric parameter and material properties directly affect the Impact Resisting Capability of car load under head-on crash operating mode.The analysis relevant due to impingement designed in engineering and theory perfect not at present, ubiquity more trial and error fashion method for designing consuming time and structured material redundancy phenomena in design.If research contents of the present invention is by planning front longitudinal deformation pattern, uses cross-section analysis and computing method, realize the controlled design of front longitudinal collision deformation pattern.

Be illustrated in figure 1 a kind of typical front longitudinal beam structure of automobile, the present invention by its from left to right (namely along automobile by front backward directions) be divided into four parts: front portion collapses conquassation section (i.e. B1 section), middle part bending section (i.e. B2 section), rear portion Light deformation supporting section (i.e. B3 section) and posterior stabilization extension (i.e. B4 section).The Main Function of its B1 section, B2 section is to absorb collision energy by self-deformation in collision process; B3 section then requires to have certain strength and stiffness to support the collision impact in next front, ensures that the folding produced in collision process turns distortion as far as possible little, and crew module's front apron intrusion volume is kept in the reasonable scope; The Main Function of B4 section, for transmit and to disperse collision impact to body in white rear portion, is made every effort to eliminate body in white local stress concentrations, is ensured that body structure intensity distributions is reasonable.

When B3 section ensures some strength, if B1 section, B2 section are designed on the weak side, as by minimizing rail inner stiffening plate structure, increase the method such as inducement structure, reduction material thickness, make B1 section, B2 section fully can be out of shape energy-absorbing, so can meet Frontal offset impact requirement well.But do not reach the B1 section of sufficient intensity, B2 section can cause front rigid wall collision operating mode in, the X that B1 section, B2 section can be born declines to (namely headstock points to tailstock direction) power, in front 60ms, Absorbable rod collision energy is less, thus B post root position equivalence acceleration improves after causing the 60ms moment, the result embodied in an experiment is exactly that dummy is subject to grievous injury.If B1 section, B2 section intensity are excessive, the intensity of obvious B3 section should corresponding improve, so just can bear B1 section, collision impact load that B2 section passes over.Thus by producing unnecessary waste of material, design seriously more can be caused not realize.Therefore can be set as that the X bearing a certain size is to impact force to B1 section, the designing requirement of B2 section, can not be too large, in order to avoid exceed Frontal offset impact performance of operating condition needs; Can not be too little, in order to avoid do not meet the requirement of front rigid wall collision performance of operating condition.This value can be used as the Performance Evaluating Indexes of front longitudinal B1 section, B2 section.

In complete automobile collision process, second peak value occurrence cause of accelerating curve is that front longitudinal occurs to destroy first in collision process.Occur in front longitudinal B2 section, front longitudinal B2 section bending thus premature loss energy absorption ability if destroyed first, when power assembly will be caused to contact crew module, vehicle also has very large kinetic energy.And power assembly almost can be considered the rigid body of the energy-absorbing that do not deform in an impact, therefore accelerating curve after an impact half way will produce a very high acceleration peak value, thus make final equivalent accekeration become large, cause occupant to be subject to serious secondary collision injury.For avoiding this type of situation to occur, just require to make to destroy first to occur in front longitudinal B1 section, and make first peak value of accelerating curve before 20ms high as best one can, make it as far as possible close to desired acceleration curve, thus reach the object reducing equivalent acceleration.

Due to reasons such as load, structure or boundary constraints, front longitudinal all can not realize " concertina " from front to back and axially collapse conquassation, usually shows as and realizes destroying with bending form.Therefore at predevelopment phase, need the deformation pattern planning front longitudinal B1 section, B2 section, the present invention plans that front longitudinal B1 section axially collapses conquassation, the deformation pattern overall control strategy of B2 section left and right directions bending.Wherein B1 section is designed to stable axis and collapses conquassation, to absorb collision impact kinetic energy as much as possible.B2 section, because the reason of the arrangement of parts such as accumulator, engine mounting, cannot realize concertina and axially collapse conquassation distortion, therefore be designed to the left and right bending pattern outside car.B3 section needs remain unchanged shape or few distortion as far as possible, to guarantee that engine and wheel box do not contact or contact crew module's sheet metal structural less; B4 section is indeformable.

As Fig. 2, for the ease of studying the deformation pattern of each section of front longitudinal, planning setting 5 key points.Specific as follows: P0 point is positioned at the front end of B1 section, P1 point is positioned at the intersection of B1 section and B2 section, and P2 point is positioned at the middle part of B2 section, and P3 point is positioned at the rear end of B2 section, and P4 point is positioned at the intersection of B3 section and B4 section.

For during guarantee B1 section conquassation, P2, P3 point does not destroy, the X that P2, P3 point can bear before bending destroys is greater than the axial conquassation counter-force of B1 section to power, the X suffered when the bending of P2, P3 point destroys must not more than the load limit value of B3 section to power simultaneously.

After structure occurs plastic hinge somewhere, the moment of flexure that this place bears and axial force can not continue to increase, and therefore purpose of design is that before plastic hinge occurs, the axial force of longeron can reach designing requirement.According to initial plan, destruction order is P1, P2, P3, and therefore when P1 occurs to destroy, P2, P3 need to remain on elastic deformation stage, to keep car load longitudinal holding power.And when the moment of destruction occurs P2, P3 needs to continue to remain on elastic stage.According to such thinking, if only study the stressing conditions before the generation plastic yield of certain cross section destroys, the Cross section calculation method of the equal Available Material mechanics in cross section of P1, P2, P3 tri-points carries out proximate analysis.

After B1 ~ B3 segment structure is determined, namely mean that the born longitudinal holding power (X is to power) as front longitudinal performance index is determined.This has directive significance to needing the design of failure position P2, P3 point forming plastic hinge.Longitudinal force is the evaluation index of each key point Cross section Design of front longitudinal, and damages and determine that its cross section being destroyed the principal element that first position occurs is the moment that in collision process, this cross section is subject to.Due to the difference of front deck general arrangement, the moment situation that the car load front longitudinal B2 section of different structure is subject in collision process is also different, therefore be optimized design to the front rail structure of concrete vehicle just to need by car load sunykatuib analysis to obtain moment, and using input that gained moment is optimized as Cross section Design.

Hat section thin-walled front longitudinal is reliable as a kind of structure, and technique simple front longitudinal Cross section Design mode, is extensively adopted by industry.For this reason, the present invention focuses on hat section thin walled beam design.

1, the expression formula of hat section thin walled beam by its super folding unit energy dissipation during responsive to axial force is determined:

Theoretical according to the super folding unit of Abramowicz and Wierzbicki scholar, the symmetry produced under the effect of axial force for hat section thin walled beam collapses conquassation disrepair phenomenon, hat-shaped structure can be divided into several " L " types and surpass folding unit.

Relative to the elastic strain of panel beating, the plastic strain that front longitudinal B1 section axially collapses region is much bigger, and therefore, can think that axially collapsing folding wavelength 2H in Collapse of Concrete be constant, the average conquassation counter-force of super folding unit can be expressed as

$F_m=\frac{t^2}{4}\left\{{\mathrm{\&sigma;}}_0^{\left(1\right)}{A}_1\frac{r}{t}+{\mathrm{\&sigma;}}_0^{\left(2\right)}{A}_2\frac{C}{H}+{\mathrm{\&sigma;}}_0^{\left(3\right)}{A}_3\frac{H}{r}+{\mathrm{\&sigma;}}_0^{\left(4\right)}{A}_4\frac{H}{t}+{\mathrm{\&sigma;}}_0^{\left(5\right)}{A}_5\right\}\frac{2H}{{\mathrm{\&delta;}}_e}---\left(1\right);$

Wherein, δ _e=0.73 × 2H, be i-th Plastic Flow region equivalent stress; R is the upset radius in region 4; C=(a+2b+2f)/4.

Get A ₁=8I ₁, A ₂=p, A ₃=2I ₃, A ₄=0, A ₅=0, then the interior energy that each super folding unit in thin walled beam inner panel hat section absorbs can be expressed as

$E_{\mathrm{int}}=P_m\&times;{\mathrm{\&delta;}}_e=\frac{t^2}{4}\left\{{\mathrm{\&sigma;}}_0^{\left(1\right)}8I_1\frac{r}{t}+{\mathrm{\&sigma;}}_0^{\left(2\right)}\mathrm{\&pi;}\frac{C}{H}+{\mathrm{\&sigma;}}_0^{\left(3\right)}2I_3\frac{H}{r}\right\}2H---\left(2\right);$

The interior energy that thin walled beam outside plate folded deformation absorbs can be expressed as

$E_{p1}=\frac{\mathrm{\&pi;}}{2}\&times;4\&times;M_0\&times;(a+2f)=\frac{t^2}{4}{\mathrm{\&sigma;}}_0^{\left(2\right)}2\mathrm{\&pi;}(a+2f)---\left(3\right);$

The gross energy dissipation that hat section collapses distortion is

E _T＝4E _int+E _pl

$E_T=\frac{t^2}{4}\left\{4\&times;{\mathrm{\&sigma;}}_0^{\left(1\right)}8I_1\frac{r}{t}+{\mathrm{\&sigma;}}_0^{\left(2\right)}\mathrm{\&pi;}\frac{(2a+2b+4f)}{H}+4\&times;2{\mathrm{\&sigma;}}_0^{\left(3\right)}{I}_3\frac{H}{r}\right\}2H---\left(4\right);$

If the nominal perimeter L=2a+2b+4f in cross section, by E _t=P _m× δ _e, I ₁=0.555, I ₃=1.148, then have:

$F_m=\frac{t^2}{4}\left\{{\mathrm{\&sigma;}}_0^{\left(1\right)}17.76\frac{r}{t}+{\mathrm{\&sigma;}}_0^{\left(2\right)}\mathrm{\&pi;}\frac{L}{H}+{\mathrm{\&sigma;}}_0^{\left(3\right)}9.184\frac{H}{r}\right\}\frac{2H}{{\mathrm{\&delta;}}_e}---\left(5\right);$

For perfectl plastic material, definition σ ₀for the yield strength of material, then have:

${\mathrm{\&sigma;}}_0^{\left(i\right)}={\mathrm{\&sigma;}}_0---\left(6\right);$

Effective conquassation distance δ of super folding unit _ethe pass folding wavelength 2H with super folding unit is

δ _e＝0.73×2H(7)；

Simultaneous formula (5) ~ (7), the expression formula obtaining the average conquassation counter-force of hat section thin walled beam is

$F_m=\frac{M_0}{0.73}\{A_1\frac{r}{t}+A_2\frac{L}{H}+A_3\frac{H}{r}\}---\left(8\right);$

Wherein, A ₁=17.76, A ₂=π, A ₃=9.184, M ₀=σ ₀t ²/ 4.

According to minimum energy principle, local derviation is asked to formula (8):

$\frac{\&part;F_m}{\&part;H}=0,\frac{\&part;F_m}{\&part;r}=0---\left(9\right);$

The final expression formula obtaining hat section thin walled beam average conquassation counter-force is:

$F_m=32.90M_0{\left(\frac{L}{t}\right)}^{1/3}---\left(10a\right);$

$\frac{H}{t}=0.3926{\left(\frac{L}{t}\right)}^{2/3}---\left(10b\right);$

$\frac{r}{t}=0.4506{\left(\frac{L}{t}\right)}^{1/3}---\left(10c\right);$

Design front longitudinal B1 section collapses collapse structure cross section:

1, require and longitudinal available crush space according to its energy-absorbing in car load head-on crash, calculate its average conquassation counter-force by formula (11), and using this value as design object;

0.73DF _m＝E _t(11)；

In formula (11), D is the longitudinal length of front longitudinal B1 segment structure, and unit is mm; E _tfor the energy-absorbing desired value of front longitudinal B1 segment structure, unit is kJ, Fm is average conquassation counter-force, and unit is N.

2, the yield strength σ of material is determined ₀, and select the material of suitable front longitudinal B1 section accordingly;

3, depth of section a, the length b of front longitudinal B1 segment structure and nominal perimeter L is tentatively determined according to arrangement space;

4, utilizing hat section thin walled beam average conquassation counter-force expression formula (10a), is the average conquassation counter-force Fm of the target reaching front longitudinal B1 segment structure, optimizes perimeter L, the wall thickness t of front longitudinal B1 section collapse structure, determines the design load of each design variable;

5, as Fig. 6 sets up the limit element artificial module of the axial conquassation of front longitudinal B1 segment structure, carry out the axial conquassation simulation analysis of front longitudinal B1 segment structure, extract the average crushing force of the front longitudinal B1 segment structure of emulation gained, whether the average conquassation counter-force of checking front longitudinal B1 section reaches the design object of expression formula (10a).

Design front longitudinal B2 segment structure cross section:

1, derivation front longitudinal B2 section bending breakdown point maximum stress expression formula:

Front longitudinal B2 segment structure is planned to the cross section of bending damaged deformation pattern, before plastic yield destroys generation, the stress expression formula that on cross section, maximum （normal） stress point position is subject to is

σ＝σ _Fx+σ _My+σ _Mz(12)；

Wherein: ${\mathrm{\&sigma;}}_{Fx}=\frac{F_x}{A}---\left(13a\right);$

${\mathrm{\&sigma;}}_{My}=\frac{M_z\&times;d_y}{I_y}---\left(13b\right);$

${\mathrm{\&sigma;}}_{Mz}=\frac{M_z\&times;d_z}{I_z}---\left(13c\right);$

If cross section is divided into four quadrants, as shown in Figure 7, so, according to the mechanics of materials, for σ with principal axis of inertia _fx, being evenly distributed in whole cross section in theory, is namely all negative stress at all four quadrants; For σ _my, first, second quadrant stress and the 3rd, fourth quadrant stress are contrary in theory; And for σ _mz, then in theory first, fourth quadrant is contrary with second, third quadrant symbol.

According to the force request of setting and the moment values Iterative Design front longitudinal B of input ₂section bending failure position cross section:

Due to the effect of moment, what the maximum point of stress bore must be compressive stress, and first the quadrant residing for it can destroy, and shows on front rail structure, is the bending phenomenon occurred to this side.In engineering, the approximate criterion as material damage in collision operating mode of conventional 3rd strength theory (i.e. maximum shear stress theory):

σ＞σ _s(14)；

If namely stress suffered by somewhere is greater than the yield stress of this place's material, then can think that structure is destroyed at this place.

As Fig. 8, the step of design front longitudinal B2 section bending position structural section is as follows:

1, according to size and the simulation analysis moment values of the longitudinal force suffered in complete automobile collision of front longitudinal B2 section bending position structure, simultaneous formula (13) ~ (14) draw design object function

$\mathrm{\&sigma;}=\frac{F_x}{A}+\frac{M_z\&times;d_y}{I_y}+\frac{M_z\&times;d_z}{I_z}>{\mathrm{\&sigma;}}_s---\left(15\right);$

Wherein, A is the thick area of material in cross section; M _yand M _zbe respectively the Y-direction suffered by thin walled beam cross section and Z-direction moment of flexure; I _yand I _zbe respectively the moment of inertia of sectional view for Y-axis and Z axis; d _yand d _zbe respectively certain point on cross section and arrive the distance of the moment of inertia of centroidal principal axes Y-axis and Z axis.

2, the yield strength σ of material is determined _s, select the material of front longitudinal B2 section breakdown point P2 position accordingly;

3, in conjunction with front deck general arrangement space, based on the front longitudinal B1 segment structure sectional dimension designed, consider the connection of front longitudinal B2 section and lower curved longeron simultaneously, tentatively determine the height in B2 section bending structure cross section, width and nominal girth;

4, convolution (15), for meeting front longitudinal B2 segment structure maximum （normal） stress design object, determines the wall thickness t of front longitudinal B2 fragment position structure;

Based on the geometry of the breakdown point position cross section structure that the moment values 5, requiring by the axially loaded set and input is designed and material parameter, set up complete automobile collision realistic model, carry out complete automobile collision analysis, and extract the moment values of front longitudinal B2 section bending position and longitudinal force-time curve;

6, front longitudinal B2 segment structure cross section longitudinal force F is verified _x-maxwhether maximal value reaches design object

F _x-max>F(16)；

Wherein, F is the longitudinal stress threshold value of bending section in the middle part of front longitudinal.

7, repeat section optimal step, whole process iterates is to the longitudinal force that this cross section can be born meets formula (16).

8, from front to back, the cross section used the same method to front longitudinal B2 section each bending point position is made to design successively.

Find that the demand of cross section destruction trend and strategic planning is inconsistent if calculated, then adjust by following method: 1, increase inside cavity stiffening plate, to adjust cross sectional moment of inertia and principal axis of inertia angle, thus change section stress maximum point position.2, inducement structure is increased, to change the moment direction suffered by the failure position point of cross section on front longitudinal surface.

The design process of described rear portion Light deformation supporting section is as follows: the design process of rear portion Light deformation supporting section and the design process of middle part Y-direction bending section similar, just keep this region few distortion or Light deformation as far as possible, wall thickness t generally gets and is greater than A/L for this reason, and concrete value also continuous iteration optimization obtains.

The design process of described posterior stabilization extension is as follows: the design of posterior stabilization extension and the design process of middle part Y-direction bending section similar, just keep this region indeformable, wall thickness t is greater than A/L for this reason.Method repeats no more.

The automobile front longitudinal beam method for designing of hat section of the present invention is by planning the bulk deformation pattern of longeron, use cross-section analysis and computing method, achieve the controlled design of front longitudinal head-on crash deformation pattern, its mentality of designing has good practicality, also can be applicable to the design of other parts of automobile.

Accompanying drawing explanation

Fig. 1 is front longitudinal beam structure of automobile stepwise schematic views of the present invention.

Fig. 2 is automobile front longitudinal beam deformation pattern of the present invention planning schematic diagram.

Fig. 3 is front longitudinal method for designing process flow diagram of the present invention.

Fig. 4 is front longitudinal of the present invention anterior body hat section schematic diagram.

Fig. 5 is that hat section of the present invention inner plate structure is subject to responsive to axial force " to collapse " the super folding unit schematic diagram produced when being out of shape, and wherein numeral 1 ~ 5 represents in super folding unit respectively according to 1st ~ 5 the Plastic Flow regions being out of shape severe degree and position division.

Fig. 6 is that the thin walled beam conquassation operating mode set up based on thin walled beam minibus theory of the present invention loads schematic diagram.

Fig. 7 is hat section of the present invention subregion schematic diagram.

Fig. 8 is the Cross section Design process flow diagram of bending section in the middle part of front longitudinal of the present invention.

Fig. 9 is the front longitudinal deformation pattern car load sunykatuib analysis result of embodiment 1.

Embodiment

Contrast accompanying drawing below, by the description to embodiment, the effect and principle of work etc. of the specific embodiment of the present invention as the mutual alignment between the shape of involved each component, structure, each several part and annexation, each several part are described in further detail.

Embodiment 1,

The automobile front longitudinal beam method for designing of hat section of the present embodiment is adopted to design the process of certain automobile front longitudinal beam as follows:

1, plan that front longitudinal is front touching the structural strain's pattern under operating mode:

Front longitudinal deformation pattern is planned, totally as shown in Figure 2: B1 section is stable collapses conquassation; Y-direction bending in B2 section plane; It is little as much as possible that B3 section folding turns distortion; B4 section is indeformable, with underbody strength matching.

2, derivation hat section thin walled beam average conquassation counter-force expression formula:

According to the derivation in embodiment, obtaining hat section thin walled beam average conquassation counter-force expression formula is

$F_m=32.90M_0{\left(\frac{L}{t}\right)}^{1/3};$

In formula: F _mfor average conquassation counter-force, unit is kN; M ₀=s ₀t ²/ 4, unit is N.mm; σ ₀for Metal plate yield strength, unit is Mpa; With reference to Fig. 4, nominal girth is L=2a+2b+4f, and unit is mm; A is front longitudinal B1 section inner panel body height, and unit is mm; B is front longitudinal B1 section inner panel body width, and unit is mm; F is side rail body welding edge width, and unit is mm; T is girder plate bulk material thickness, and unit is mm.

3, front longitudinal B1 segment structure cross section is designed:

As Fig. 1 passenger car front longitudinal arrangement space is determined, be divided into four sections according to the deformation pattern of front longitudinal in head-on crash: be followed successively by B1 section-front longitudinal front portion and collapse conquassation section; Bending section in the middle part of B2 section-front longitudinal; B3 section-front longitudinal rear portion Light deformation supporting section; B4 section-front longitudinal posterior stabilization extension.

The length of front longitudinal B1 section is 400mm, according to formula (11) 0.73DF _m=E _t, effective conquassation length of front longitudinal B1 section is 292mm, and in order to the collision energy enabling front longitudinal B1 section absorb 15 ~ 20kJ, its average conquassation counter-force is 51 ~ 68kN.In ensuing design, the present invention plans the target average conquassation counter-force of 60kN as front longitudinal B1 section.

By formula (10a) known, the average conquassation counter-force of hat section thin walled beam and selected material, cross section three factors such as name perimeter L and wall thickness t etc. are relevant, latter two factors is relevant with the quality of hat section thin walled beam, in order to alleviate the quality of designed structure as much as possible, selection yield strength is the material of plow-steel as front longitudinal B1 section of 325MPa.

According to the arrangement space of front longitudinal, the ratio of width to height of front longitudinal B1 section is 0.6, selects cross section name girth 530mm as initial value, in order to make average conquassation counter-force be 60kN, and can by formula (10a) calculate the combined result of some groups of hat section sizes and wall thickness.

According to arrangement space adjustment depth of section, width and the nominal perimeter L of structure.As Fig. 4, determine the height a=136mm of front longitudinal B1 section, width b is 82mm, and front longitudinal girder inner plate body welding edge width f is 26mm, and section thickness t is 1.8mm.

Consult Fig. 6, utilize business software LS-DYNA to calculate the mean pressure feedback counter-force of front longitudinal B1 section.When front longitudinal B1 section thickness is 1.8mm, mean pressure feedback counter-force is 58kN, can reach the requirement that front longitudinal B1 section absorbs collision energy, can meet the requirement of average conquassation counter-force.

4, derivation front longitudinal B2 section bending breakdown point maximum stress expression formula:

$\mathrm{\&sigma;}=\frac{F_x}{A}+\frac{M_y\&times;d_y}{I_y}+\frac{M_z\&times;d_z}{I_z};$

Wherein, A is the thick area of material in cross section; M _yand M _zbe respectively the Y-direction suffered by thin walled beam cross section and Z-direction moment of flexure; I _yand I _zbe respectively the moment of inertia of sectional view for Y-axis and Z axis; d _yand d _zbe respectively certain point on cross section and arrive the distance of the moment of inertia of centroidal principal axes Y-axis and Z axis.

5, the cross section of front longitudinal B2 section bending failure position is designed:

Front longitudinal B2 section is because the reason of the arrangement of parts such as accumulator, engine mounting, and cannot realize concertina and axially collapse conquassation deformation pattern, front longitudinal B2 section is designed to the left and right bending pattern outside car by the present invention.B3 section needs remain unchanged shape or few distortion as far as possible, to guarantee that engine and variator do not contact or contact the sheet metal structural of crew module less.

In the present embodiment, planning front longitudinal B2 section has two bending breakdown points (i.e. P2, P3 point), therefore gets n=2; Arrange and initial model simulation result according to space, try to achieve front longitudinal P2 point position and P3 point position when bearing longitudinal 100kN acting force respectively, the moment around Z axis is respectively 2150N.mm and 3400N.mm.Therefore the present invention is next using these two values as front longitudinal P2 point position and front longitudinal P3 point position initial torque data input values.

Step is as follows:

1, select the material identical with front longitudinal B1 section as the material of front longitudinal B2 section, the yield strength of namely drawing materials is 325Mpa;

2, in conjunction with front deck general arrangement space, based on front longitudinal B1 section collapse structure sectional dimension, tentatively determine that the width a in B2 section bending structure cross section is 82mm; Height b is 136mm; Welding edge width f is 26mm; Thickness t is 1.8mm;

3, bending breakdown point position (P2, P3 point) place's Cross section Design:

P2 point place Cross section Design:

1) according to front longitudinal P2 point position around Z axis initial torque value 2150Nmm, the B2 section bending structure cross section parameter tentatively determined and boundary condition, set up head-on crash realistic model, carry out complete automobile collision sunykatuib analysis, and extract front longitudinal P2 point position deformation pattern, front longitudinal P2 point position moment values and longitudinally hold force-time curve;

2) contrast the demand of front longitudinal B2 section P2 point position deformation pattern and deformation pattern strategic planning, if find inconsistent, adjust by following method:

A, increase inside cavity stiffening plate, to adjust cross sectional moment of inertia and principal axis of inertia angle, thus change section stress maximum point position;

B, beam surface increase inducement structure, to change the moment direction suffered by breakdown point cross section.

3) the longitudinal load F in front longitudinal B2 section P2 dot structure cross section is verified _x-maxwhether maximal value reaches design object

F _x-max>F(16)；

4) repeat section optimal step, whole process iterates meets formula (16) to the longitudinal force that this cross section can be born.Finally, the cross section parameters of front longitudinal B2 section P2 point Position Ontology is height a=139mm, width b is 81mm; Welding edge width f is 43mm; Thickness t is 1.8mm.The longitudinal force that front longitudinal B2 section P2 point bears is 101kN; Moment around Y-axis is 2272N.mm; Moment around Z axis is 2151N.mm.

P3 point place Cross section Design:

1) according to front longitudinal P3 point position around Z axis initial torque value 3400Nmm, the B2 section bending structure cross section parameter tentatively determined and boundary condition, set up head-on crash realistic model, carry out complete automobile collision sunykatuib analysis, and extract front longitudinal P3 point position deformation pattern, front longitudinal P3 point position moment values and longitudinally hold force-time curve;

2) contrast the demand of front longitudinal B2 section P3 point deformation figure and deformation pattern strategic planning, if find inconsistent, adjust by following method:

A, increase inside cavity stiffening plate, to adjust cross sectional moment of inertia and principal axis of inertia angle, thus change section stress maximum point position.

B, beam surface increase inducement structure, to change the moment direction suffered by breakdown point cross section.

3) the longitudinal load F in front longitudinal B2 section P3 dot structure cross section is verified _x-maxwhether maximal value reaches design object

F _x-max>F(16)；

4) repeat section optimal step, whole process iterates meets formula (16) to the longitudinal force that this cross section can be born.Finally, the cross section parameters of front longitudinal B2 section P3 point Position Ontology is height a=140mm, width b is 73mm; Welding edge width f is 42mm; Thickness t is 1.8mm.The longitudinal force that front longitudinal P3 point position is born is 95.3kN; Moment around Y-axis is 575N.mm; Moment around Z axis is 3434N.mm.

6, sunykatuib analysis result:

Design certain vehicle left front girder according to said method, show in sunykatuib analysis as shown in Figure 9 after completing, can clearly see in the drawings from front longitudinal front axle to the overall process crushing to P2, P3 point and destroy successively.And front longitudinal deformation pattern and Fig. 2 in advance strategic planning mate good.

Claims (7)

1. an automobile front longitudinal beam method for designing for hat section, is characterized in that comprising the steps:

A: planning front longitudinal is front touching the structural strain's pattern under operating mode: front longitudinal is divided into from front to back successively front portion and collapses conquassation section, middle part Y-direction bending section, rear portion Light deformation supporting section and posterior stabilization extension;

B: the average conquassation counter-force expression formula of derivation hat section front longitudinal;

C: according to the requirement of each section of front longitudinal, designs each section of front longitudinal from front to back successively;

D: according to the design result of step C, utilizes computing machine to carry out sunykatuib analysis, and to confirm design according to analog result or change.

2. the automobile front longitudinal beam method for designing of hat section according to claim 1, is characterized in that in described step B, and the average conquassation counter-force expression formula of described hat section front longitudinal is as follows:

$F_m=32.90M_0{\left(\frac{L}{t}\right)}^{1/3};$

In formula: F _mfor average conquassation counter-force, unit is kN; M ₀=σ ₀t ²/ 4, unit is N.mm; σ ₀for longeron Metal plate yield strength, unit is Mpa; L=2a+2b+4f, unit is mm; A is longitudinal beam front section inner panel width, and b is plate height in longitudinal beam front section, and f is side rail welding edge width, and t is girder plate material thickness.

3. the automobile front longitudinal beam method for designing of hat section according to claim 1, the design process that the front portion that it is characterized in that in described step C collapses conquassation section is as follows: according to front longitudinal overall collapse energy-absorption target and effective conquassation distance, tentatively determine the average conquassation counter-force of front longitudinal front end, and then according to the hat section front longitudinal average conquassation counter-force expression formula in step B and boundary condition design hat section thin-walled depth of beam, width and welding edge width.

4. the automobile front longitudinal beam method for designing of hat section according to claim 3, the design process that the front portion that it is characterized in that in described step C collapses conquassation section is as follows: a, determine the yield strength σ of material therefor ₀; B, tentatively determine that front longitudinal collapses depth of section a, the length b of conquassation segment structure and nominal perimeter L according to arrangement space; C, utilizing hat section front longitudinal average conquassation counter-force expression formula and front longitudinal to collapse the average conquassation counter-force formula of conquassation section, collapsing the average conquassation counter-force of target of conquassation segment structure for reaching front longitudinal, optimize front longitudinal B ₁perimeter L, the wall thickness t of section collapse structure, determine the design load of each design variable; The average conquassation counter-force formula that described front longitudinal collapses conquassation section is as follows: 0.73DF _m=E _t, wherein D is the longitudinal length that front longitudinal collapses conquassation segment structure, and unit is mm; E _tfor front longitudinal collapses the energy-absorbing desired value of conquassation segment structure, unit is kJ, Fm is the average conquassation counter-force of front longitudinal; D, the anterior limit element artificial module collapsing the axial conquassation of conquassation segment structure of foundation, carry out the axial conquassation simulation analysis that front portion collapses conquassation segment structure, the front portion of extracting emulation gained collapses the average crushing force of conquassation segment structure, and checking is anterior collapses the design object whether conquassation section average conquassation counter-force reaches hat section front longitudinal average conquassation counter-force expression formula.

5. the automobile front longitudinal beam method for designing of hat section according to claim 3, is characterized in that the design process of the middle part Y-direction bending section in described step C is as follows:

A, according to the size of the longitudinal force suffered in complete automobile collision of Y-direction bending section bending position in the middle part of front longitudinal and simulation analysis moment values, draw design object function:

$\mathrm{\&sigma;}=\frac{F_x}{A}+\frac{M_y\&times;d_y}{I_y}+\frac{M_z\&times;d_z}{I_z}>{\mathrm{\&sigma;}}_s;$

Wherein, A is the thick area of material in Y-direction bending section cross section in the middle part of front longitudinal; M _yand M _zbe respectively the Y-direction in the middle part of front longitudinal suffered by Y-direction bending section cross section and Z-direction moment of flexure; I _yand I _zbe respectively the moment of inertia of sectional view for Y-axis and Z axis; d _yand d _zbe respectively certain point on cross section and arrive the distance of the moment of inertia of centroidal principal axes Y-axis and Z axis, σ is the longitudinal force that in the middle part of front longitudinal, Y-direction bending section bending position is suffered in complete automobile collision, σ _sfor the yield strength of Y-direction bending section bending position material in the middle part of front longitudinal;

B, yield strength σ according to Y-direction bending section bending position material in the middle part of design object function determination front longitudinal _s, select the material of Y-direction bending section bending position in the middle part of front longitudinal accordingly;

C, in conjunction with front deck general arrangement space, collapse based on conquassation segment structure sectional dimension by the front longitudinal designed, consider the connection of Y-direction bending section and lower curved longeron in the middle part of front longitudinal simultaneously, tentatively determine the height in Y-direction bending section bending position cross section in the middle part of front longitudinal, width and nominal girth;

D, in conjunction with the design object function described in a step, for meeting Y-direction bending section bending position maximum （normal） stress design object in the middle part of front longitudinal, determine the wall thickness t of Y-direction bending section bending position in the middle part of front longitudinal;

Based on the geometry of the bending position cross section structure gone out designed by e, the moment values that requires and input by the axially loaded set and material parameter, set up complete automobile collision realistic model, carry out complete automobile collision analysis, and extract the moment values of Y-direction bending section bending position in the middle part of front longitudinal and longitudinal force-time curve;

Y-direction bending section bending position cross section longitudinal force maximal value F in the middle part of f, checking front longitudinal _x-maxwhether reach design object F _x-max>F, wherein, F is the longitudinal stress threshold value of bending section in the middle part of front longitudinal;

G, repetition section optimal step, whole process iterates is to meeting F _x-maxtill >F;

H, from front to back, makes successively to use the same method and to design the cross section of each crooked place of Y-direction bending section in the middle part of front longitudinal.

6. the automobile front longitudinal beam method for designing of hat section according to claim 5, it is characterized in that in described Step d, the wall thickness t < A/L of Y-direction bending section bending position in the middle part of front longitudinal, wherein A is the thick area of material in Y-direction bending section cross section in the middle part of front longitudinal, and L is the nominal girth in Y-direction bending section cross section in the middle part of front longitudinal.

7. the automobile front longitudinal beam method for designing of the hat section according to claim 5 or 6, it is characterized in that if when the demand calculating Y-direction bending section each crooked place cross section destruction trend and strategic planning in the middle part of discovery front longitudinal is inconsistent, adjust by following method: a, increase inside cavity stiffening plate, to adjust cross sectional moment of inertia and principal axis of inertia angle, thus change section stress maximum point position; B, front longitudinal surface increase inducement structure, to change the moment direction suffered by crooked place.