电动汽车车架及电池箱轻量化设计（含三维图SW及CAD图纸）
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电动汽车车架及电池箱轻量化设计（含三维图SW及CAD图纸）,电动汽车,车架,电池,量化,设计,三维,SW,CAD,图纸
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doi: 10.1111/j.1460-2695.2011.01615.xLightweight design of vehicle components based on strengtheningeffects of low-amplitude loads below fatigue limit Z. SONGLIN and L. XICollege of Mechanical Engineering, University of Shanghai for Science and Technology, No. 516 Jungong Road, Shanghai, 200093, ChinaReceived in final form 28 June 2011ABSTRACTA new lightweight design method for vehicle components is proposed based on thestrengthening effects of low-amplitude loads below the fatigue limit. The new methodis technically based on the strength feature of strengthening and damaging of vehiclecomponents under loading spectrum, while combining dynamic strength equations withthe residual strength of vehicle components. It ensures the maximum exploitation of thematerials strength potential and fully realises the lightweight design of vehicle compo-nents at a low cost. As an application of the new lightweight design method, a light trucksfront axle was redesigned. The lightweight potential of the front axle was first estimatedby fatigue and static strength experiments of four-point bending. Then the lightweightdesign was realised by finite element analysis and experimental results. The weight of thisfront axle was reduced by 5.5 kg.Keywordslightweight design; residual strength; strengthening; vehicle component.NOMENCLATURESB= the minimum strengthening loadSC= the maximum strengthening loadSmax= the maximum residual strengthS0= the original strengthS = the load variableFB= the minimum load with the characteristic of slalFD= the maximum load with the characteristic of slalFC= the critical load with the characteristic of slalQ0= the virgin static strengthQb= the residual static strengthpa= the load amplitude of the standard testp0= the critical load which has a fatigue life of 107cycles, similar to the fatiguelimit of the vehicle components or parts and will keep static strengthconstant for any long cyclen = the cyclescm= the correction coefficient of mean stresspm= the load amplitudecq= the material coefficientINTRODUCTIONThe rapid increase in energy and resource consump-tion has forced people to make more stringent demandsfor vehicle fuel economy, which requires improvementin the lightweight structure of vehicles to a certain de-gree.12Substitution with a new lightweight material isCorrespondence: L. Xi. E-mail: luxi_the most direct and simple method in achieving a vehi-cle lightweight design. The greatest barrier in applyingthese new lightweight materials is the cost.34Therefore,it is very important and necessary to investigate a newlightweight design method for vehicle components madeof traditional material at a low cost.To design lightweight vehicle components or parts re-quires comprehensive consideration of the interactionsc ?2011 Blackwell Publishing Ltd.Fatigue Fract Engng Mater Struct35, 269277269Fatigue & Fracture of Engineering Materials & Structures270Z. SONGLIN and L. XIamong service loads, material properties, geometry,manufacturing technology and cost. These interac-tions determine the strength and durability of vehiclecomponents or parts. There are thus various methodsand techniques in lightweight vehicle design, such aslightweightdesignbygeometrystructure,lightweightde-sign by manufacturing technologies and lightweight de-sign by material substitution.56In the existing fatiguedamage theories, the strengthening effects of some smallloads below the fatigue limit are not considered.79Thestrength potential of components or parts could not befully exploited even if the new lightweight material andoptimisation method are applied. The possibility of real-ising more lightweight vehicle components or parts stillexists.Experimental results have shown that the mechanicalproperties, including fatigue strength, static strength,yield strength, and the fatigue life of vehicle componentsor parts, such as front axle, transmission gear, and driveshaft, can be clearly increased and improved by strength-ening under low-amplitude loads below the fatiguelimit (SLAL).1013This strengthening phenomenon isalso known as understressing or the coaxing effect.1415Experimental results also showed that only the metal ma-terial being capable of strain aging, such as iron and steel,have the phenomenon of the SLAL.15This paper focusesonmassreductionthroughadvancesintheuseofironandsteel (ferrous materials), because they are the dominantmaterial(64%ofatypicalfamilyvehicle),formthecriticalelements of structure for the vast majority of vehicles, andare low-cost materials with an extensive experience baseand familiarity to the industry.16The SLAL is the coretechnology of the new lightweight design method withlow cost for the iron and steel parts and structure. Theobject of the new lightweight design method is to exploitthe materials strength potential as much as possible.DESIGN THEORY AND METHODStrength strengtheningThe strengthening phenomenon of low-amplitude loadsbelow the fatigue limit was early investigated in the lastcentury by Smith.17To this day, the phenomenon andmechanism behind the SLAL are still under investiga-tion.1013,1820However, the engineering application ofthe SLAL, such as lightweight design, has not been pub-licly reported, except for the running-in specification oftransmission gears first proposed and successfully ap-plied.11In order to completely consider the strengthening anddamagingcharacteristicofloadsintraditionalfatiguethe-ory, except the gigacycle fatigue, three load regions aredefined by the studys authors in the process of structurestrength and reliability design. They are the damagingregion, the strengthening region, and the useless region.These different load regions and their strengthening ordamaging characteristic are shown in Fig. 1a. The char-acteristics of strength change in different load and life areshown in Fig. 1b.21In Fig. 1, the traditional SN curve and the fatigue limitare introduced. The ultra high cycle fatigue behaviour,whichthefatiguelifeisgreaterthan107cycles,isnotcon-sidered. SB, SCand Smaxare the minimum strengtheningload, the maximum strengthening load and the maximumresidual strength, respectively. S0and S are the originalstrength and the load variable, respectively. The regionSB S SCis the strengthening region, S SCis the damaging region.According to the experimental results of ferrous ma-terials and structures, the authors also put forward thestrength characteristics of part and structure in differentfatigue loads, including static strength, tensile strength,fatigue strength and residual strength, shown in Fig. 2.In Fig. 2, S0is the virgin strength. The FB, FDand FCare the minimum load, maximum load and critical loadwith the characteristic of SLAL The meaning of criticalload is a maximum load that the strength is not changedin unlimited cycles or 107cycles. The curve of Fig. 2 isthe strength change of fatigue process in different loads.Certainly,thegigacyclefatigueisnotincludedbecausethefrequency of structure or part experiments is very low.In strengthening region, the strength of the materialor component can be obviously increased if the low-amplitude loads below the fatigue limit are repeatedlyFig. 1 (a) Load region; and (b)Characteristics of strength change.c ?2011 Blackwell Publishing Ltd.Fatigue Fract Engng Mater Struct35, 269277LIGHTWEIGHT DESIGN271S0SmaxA B DCE0 FB FD FC FELoad Strength Fig. 2 Strength characteristics in different fatigue loads.subjected up to certain times. When the loads locate inthe useless region, it is neither the strengthening effectsnorthedamagingeffects.Theseloadscouldthusbeomit-ted in the loading spectrum analysis and processing. Ithas an essential difference from the existing criterion ofthe small load omitted, in which the SLAL is not con-sidered.2223The loads within the damaging region areabove the fatigue limit. The component or part will failwhen the repeated cycles reach a certain time. In this re-gion, it is need to investigate the damage line, which wasa mystery for decades by Schlitz.24The strengthening characteristics of material or com-ponent, which is the precondition of a new vehiclelightweightdesign,mainlyincludearegionofstrengthen-ing loads and strengthening cycles, the optimal strength-ening load and strengthening cycles, and the three-dimension strengthening equation. They can be obtainedby a series of fatigue experiments and strengtheningexperiments. One object of the SLAL investigation isto ascertain the strengthening effects and strengtheningboundary of different material and heat treatment pro-cess. Through fatigue experiments and data processing,the typical three-dimension strengthening surface of afront axle made of low strength steel and a transmissiongear made of high strength steel are shown in Fig. 3.1113In Fig. 3, the strengthening loads and strengthening cy-cles are independent variables; the verified life, which isthe fatigue life of overload after SLAL, is a function ofthese variables. The strengthening effects will be exhib-ited if the verified life is much higher than that of fatiguelife of overload in the original S-N curve.According to the characteristic of the SLAL, it is knownthatthematerials strengthpotentialcouldbeexploitedasmuch as possible if the strength of vehicle components orparts is rationally designed. That is, if the design stress iscontrolled within the strengthening loads region, as timeelapses, both the fatigue strength and the static strengthof vehicle components or parts could be strengthened andimproved because of the SLAL.Dynamic strength equationsThe vehicle components or parts must be evaluated bythe experimental result of static strength and fatiguelife under different standard test specifications. How-ever, the design level and the lightweight degree are notassessed using these specifications because the residualstrength of vehicle components or parts after the standardtest being completed is not restricted in these standardspecifications.Inordertoguidelightweightdesign,thestrengthchangeand residual strength of vehicle components or parts thusneed to be investigated in depth and reasonably restrictedafter the standard test has been completed on a test rig.When the product test is completed using the productFig. 3 Three-dimensional strengthening surface of low-amplitude load.c ?2011 Blackwell Publishing Ltd.Fatigue Fract Engng Mater Struct35, 269277272Z. SONGLIN and L. XItest specifications, and the product is not fractured, thereare three different conditions of residual static strength asfollows:1 The residual static strength is equal to the virgin staticstrength.2 The residual static strength is greater than the virgin staticstrength.3 The residual static strength is less than the virgin staticstrength.If the residual static strength of the vehicle compo-nents or parts increased after the standard test hasbeen completed, it implies that the test load, which hascomparatively higher amplitude, is still a small load ascompared to the virgin strength of the vehicle compo-nents or parts. The most rational condition is that theresidual static strength initially increases then decreasesto the peak value, which is equal to the test load, afterthe standard test has been completed. However, if thestrength is a great surplus, the test load is much less thanthe virgin static strength, and the residual static strengthwill remain constant after the standard test has been com-pleted. In this condition, the strength is not strengthened,that is, it does not suffer the process of increasing anddecreasing, and there is a large capability of lightweightdesign.To obtain the ideal residual static strength of the vehiclecomponents or parts after the standard test has been com-pleted; the virgin strength must be designed and limitedrationally. The equations of strength change, includingthe strengthening and damaging, should be established.According to the results of some fatigue and strength-ening tests, two experiential dynamic strength equations,strength increase and strength degradation, are put for-ward by this studys authors, following one of the basicprinciples for evaluating the level of lightweight design.The dynamic strength equations, using to estimate theinstantaneous strength of ferrous materials and parts, areexpressed by Eqs (1) and (2).25Equation of strength increaselgQbQ0= lgp0palgn105(pa p0).(1)Equation of strength degradationlgcmQbQ0= lgcqp0palgn104(p0 pa).(2)cm= epmQ0The parameters of Eqs (1) and (2) are given in Table 1.Although two experiential dynamic strength equationsneed to be investigated and proven in depth, the changeTable 1 The parameters of Eqs (1) and (2)ParameterMeaningQ0The virgin static strengthQbThe residual static strengthpaThe load amplitude of the standard testp0The critical load which has a fatigue life of 107cycles, similar to the fatigue limit of the vehiclecomponents or parts and will keep static strengthconstant for any long cyclenThe cyclescmThe correction coefficient of mean stresspmThe load amplitudecqThe material coefficientin static strength ofthevehiclecomponentsorpartscouldbe quantitatively predicted. In the equation of strengthincrease, the original strength will increase from Q0to Qbafter the test load amplitude pais performed by n cycles,and the quantitative relationship among static strength,fatigue load and cycles of the vehicle components or partsis established.Using dynamic strength Eqs (1) and (2), as well as theexperimentalresultsofresidualstaticstrength,theleveloflightweightdesigncanbequantitativelyevaluated,andthenew lightweight design can be realised to some degree.Lightweight design methodThe new lightweight design method is technically basedon the strengthening and degenerating properties ofstrength while combining dynamic strength equationswith the strength test of vehicle components or parts.The foundation of the new lightweight design is the crit-ical load of components, which is calculated by the dy-namic equations and acts as the lightweight design ob-ject. However, the critical load could also be estimatedby the feature of SLAL if there is not enough strengthexperimental data in the new vehicle components orparts.In the new design method, other design characteristicssuch as vibration, mode, structure optimisation, and pro-cessing techniques retain their existing technology. Theprocedure sketch of the new lightweight design based onthe SLAL is shown in Fig. 4.In the new lightweight design method, both the relia-bility and safety of vehicle components or parts could besatisfied, and the strength potential could be exploited asmuch as possible. The cost of design and manufactureis not increased. In addition, the vehicle components orparts have a finite fatigue life, unlike the infinite fatiguelife in traditional strength design.c ?2011 Blackwell Publishing Ltd.Fatigue Fract Engng Mater Struct35, 269277LIGHTWEIGHT DESIGN273Evolution standard Design and analysis Experiment Evolution FEASLALPro-design Fatigue life Residual strength Critical load Calculating surplus of light-weight Evaluating surplus of light-weight Checking surplus Accept Light-weight structure Pro-design Fig. 4 Lightweight design procedure based on strength feature.A DESIGN CASEStrength testUsing the new lightweight design method, a front axle oflighttruck-TY1105isredesigned.Theexperimentalfrontaxles made by YTO Group Corporation are randomly se-lected. The material of the front axle is 45 forged steel,which the heat treatment process is quenched and an-nealed. The cross-section of the front axle is the I-axle.The chemical composition and the mechanical propertiesof the material are given in Tables 2 and 3, respectively.The basic parameters of strength design are also given inTable 4.Chinese Automobile Industry Standard was introducedin the strength test of the front axle. The fatigue teststandard of front axle (QC/T 5131999) in China is givenin Table 5.Four-point bending experiments were performed bySaginomiyaWT-30fatiguemachineinStructureStrength laboratory of Luoyang Tractor Research Insti-tute. A sinusoidal waveform signal with a frequency of5 Hz was used for the constant stress amplitude control,and the stress ratio is 0.15. The repeated cycles of thefront axle fractured are the fatigue life. The (residual)Table 3 Mechanical properties of 45 steelTensileYieldElongationPercentageImpactstrengthstrengthratereduction oftoughness(MPa)(MPa)(%)area (%)(J)600355164031Table 4 Basic parameters of the truck and front axleUnladenMaximumStatic fullvehiclepay loadload of frontmass (kN)(kN)axle (kN)54.050.032.0Table 5 The fatigue test standard of front axle (QC/T 5131999)ProjectContentTest conditionPerpendicular loadingLoading conditionFour-point bending, Constant amplitudesinusoidal waveLoading regionMaximal load is 3.5 times as large as thestatic full load and Minimal load is 0.5times as large as the static full loadLife regionMedian Fatigue Life is 700,000 cycles andfatigue life of 95% survival probability is300,000 cyclesstatic strength is the maximum value of front axle frac-tured. The test is also stopped when the repeated cyclesof the front axle is over 106cycles. Under this condition,the front axle is considered infinite life. The test field andtest specimen is shown in Figs. 5 and 6.The whole experimental procedures are first, the staticstrength is tested in four-point bending. Second, the fa-tigue experiments are performed according to our stan-dard test specification. Third, using the unfractured frontaxle,whichthefatigueexperimentiscompleted,theresid-ual static strength is tested.In the lightweight design of the front axle, some staticstrength and fatigue strength experiments have been per-formed according to our standard test specification. Thevirgin static strength is the average value of three testspecimens. The residual static strength is the averagevalue of five specimens after the fatigue experiment hasbeen completed in the standard test specifications, whereTable 2 Chemical composition of 45 steel, mass%CSiMnPSNiCrCu0.420.500.170.370.500.800.0350.035c ?2011 Blackwell Publishing Ltd.Fatigue Fract Engng Mater Struct35, 269277274Z. SONGLIN and L. XIFig. 5 Test field of front axle.Fig. 6 Test specimen of front axle.the fatigue life of the front axle is not less than 800,000cycles under standard test loads. In our experiments,however, the residual static strength is also measuredwhen the number of standard test reaches 106cycles.The experimental results for the front axle are shown inTable 6.Table 6 shows that the residual static strength of thefront axle is increased from 276.0 to 309.2 kN, an in-crease rate of about 12%, after the fatigue test had beencompleted by standard test specifications. Based on thedynamic strength equations and the experimental results,thecriticalloadofthefrontaxlecanbedetermined,whichTable 6 Experimental results of the front axleFatigue testOriginalAverageaverage staticresidual staticstrengthAverageAmplitudestrength(kN)(kN)(kN)Cycles(kN)276.064.048.01 000 000309.2is about 52.52 kN. This means that the front axle couldwithstand the load amplitude of 52.52 kN for any longcycle without damage. The original designs front axleobviously has infinite fatigue life because the test load isc ?2011 Blackwell Publishing Ltd.Fatigue Fract Engng Mater Struct35, 269277LIGHTWEIGHT DESIGN275Fig. 7 Locations of stress measured of front axle.less than the critical load. Thus, there is a great capa-bility of reducing the front axles weight using the newlightweight design method.In our criterion, the fatigue life of the front axle isnot less than 800 000 cycles when the load amplitude is48.0 kN. In oversea company standards, the average fa-tigue life is not less than 106cycles when the load am-plitude is 32.0 kN. Therefore, there is great space forlightweight improvement for the front axle even if therigorous evaluation standards are used.Lightweight designFor the first step of weight reduction, the front axlesshould only withstand the load amplitude of 48.0 kN, not52.52 kN, with more than 800,000 cycles and maintainconstant strength. A higher stress level needs to be estab-lished under the load amplitude of 48.0 kN for the frontaxle. The goal of weight reduction maybe to redesign thefront axles based on the reduction of critical load from52.52 to 48.0 kN in the new design.The stress of dangerous point was calculated and mea-sured in four-point bending of the front axle. Becausein working the front axle is approximately under in-planebending, the plane loading is imposed in Anysis FEA soft-ware, which the vertical displacements of two supportingpoints and two loading points are restricted and the otherdegrees of freedom are not restricted. The measured lo-cations are shown in Fig. 7. The results measured andanalysed are given in Table 7.From Table 7 and Fig. 7, location 6 is revealed to bethe dangerous point; its stress value becomes the designreference criterion. In Table 7, the relationship betweenload and stress of the front axle is provided by FEA, whichshowsthat the100kNloadscorrespondtothe320.2MPastress in the dangerous point.For the original structure, the stress at location 6 incritical load of 52.52 kN is 168.2 MPa, which is calculatedby the relationship between load and stress. The originalstress of the most dangerous point in the fatigue testingload of 48.0 kN is 153.7 MPa.Table 7 Results of stress measured and analysedExperimentCalculationRelativeLocationsstress (MPa)stress (MPa)error (%)1184.1190.23.32217.4221.92.13341.2352.73.44262.4282.67.75312.1322.33.36320.2329.73.07304.1313.63.18228.7247.98.4Notes: “”refer to compress stress; “+” refer to tension stress. Theload calculated stress is 100 kN.In the new lightweight design, the critical load is48.0 kN. The critical load can be cut down by decreasingthe strength of the original structure, such as by materialreplacement, in which the cost can be reduced becausethe lower strength material can be utilised. Similarly, thedimension reduction of the cross-section, which conse-quently causes the component weight to be reduced, andthe lightweight design are realised.After the lightweight design, the stress of the most dan-gerous point in the fatigue testing load of 48.0 kN shouldbe increased from 153.7 to 168.2 MPa. The new relation-ship between the applied loads and the response stressesshould be 350.4 MPa and 100 kN.The decrease dimension of the front axle is the mainmethod used to realise the lightweight design, whereinthe stress can be increased. As a safety component, struc-tural durability requirements must be satisfied in thelightweight design of the front axle. In addition, thereis enough stiffness in the front axle, including vertical,longitudinal, and lateral stiffness.After iterative calculation, the decrease dimension ofcross-section for the middle post is 3 mm, 3 mm forthe width of the upper and down limbs, and 2 mm forthe height. The calculation stress of the most dangerouspoint becomes 347.75 MPa in the new lightweight de-sign. There is little difference from the theoretical analy-sis, which is 350.34 MPa. A weight of approximately 5.5kg is removed in the new lightweight design of this frontaxle. When the dimension of the front axle is reduced,the results of static strength and residual static strengthafter the fatigue test being completed can be predicted, asshown in Table 8.In Table 8, the static strength of the front axle will re-main constant or will slightly increase after the fatiguetest is completed in standard test specification. Althoughthe results of the lightweight design need to be provenin engineering, the lightweight effect, as indicated by the5.5 kg weight reduction, is very remarkable.c ?2011 Blackwell Publishing Ltd.Fatigue Fract Engng Mater Struct35, 269277276Z. SONGLIN and L. XITable 8 Predicted results of re-designed front axleFatigue test loadOriginalResidual staticstaticstrength afterstrengthAverageAmplitudefatigue(kN)(kN)(kN)Cyclestest (kN)201.064.048.01 000 000203.0RESULTS AND DISCUSSIONThe very remarkable lightweight results also imply thatthe studys product design is irrational to some extentand has great capability for achieving further lightweightdesign. The main reasons could be that the current de-sign method is similar to the experience design and thesimilitude design. A large safety factor is selected in thedesign to ensure safety and reliability. In the developedcountry, vehicle design evolved from experience design tosimilitude design, to strength and reliability design, andto the current lightweight design. The design level is veryhigh, but it could be predicted that the further capabilitiesof lightweight design still exist because the SLAL is notconsidered in the existing design theory of strength andreliability. In addition, the material strength could be stillexploited by SLAL.However, many problems need to be investigated andproven in depth in the new method of vehicle lightweightdesign, such as experiential dynamic strength equationsand the reliability of lightweight design. Although theseexperientialequationscanprimarilyassesswhetheravehi-cle component or part is overweight, the precise strengththeory still needs to be established, and the strengtheningcharacteristics of different materials need to be continu-ally accumulated if this new method is to be applied invehicle engineering. In addition, strength design is onlyone aspect in vehicle lightweight design. Other aspects,such as vibration, mode, manufacturing, and the like alsoneed to be considered. The ideas of new lightweight de-sign, including fully exploiting the strength limit of a ma-terial and utilising low-amplitude loads below the fatiguelimit, are worthy of further attention and investigation invehicle engineering.A new lightweight design method is proposed in thispaper. The new method is technically based on strength-ening under low-amplitude loads below the fatigue limit,while combining dynamic strength equations with theresidual strength test results of vehicle components. Thenew method can ensure the maximum exploitation ofthe materials strength potential and fully realise thelightweight design of vehicle components at a low cost.The new lightweight design method was successfullyapplied to redesign a front axle of light truck, which theweight reduced by 5.5 kg. In our design case, the 5.5 kgweight reduction is theoretically redesigned according tothe results of experimental strength. The result primar-ily showed that the lightweight design of vehicle com-ponents could be realised by the strengthening effects oflow-amplitude loads below the fatigue limit.AcknowledgementsThisworkwassupportedbytheNationalNaturalScienceFoundation of China (50875173), Shanghai Natural Sci-enceFoundation(09ZR1422000),ShanghaiInternationalCooperation project (10520711500), Key Basic ResearchProject of Shanghai Committee of Science and Tech-nology (10JC1411600) and the Innovation Program ofShanghai Municipal Education Commission (11YZ114).All the investigations, except the fatigue experiments,were completed in the Machinery Industry Key Labo-ratory for Mechanical Strength & Reliability Evaluationof Auto Chassis Components.REFERENCES1Li, Y. X., Lin, Z. Q., Jiang, A. Q. and Chen, G. L. (2003) Useof high strength steel sheet for lightweight and crashworthycar body. Mater. Design 24, 177182.2Yamane, K. and Furuhama, S. (1998) A study on the effect ofthe total weight of fuel and fuel tank on the drivingperformances of cars. Int. J. Hydrogen Energ. 23, 825831.3Schubert, E., Klassen, M., Zemer, I., Walz, C. and Sepold, G.(2001) Light-weight structures produced by laser beamjoining for future applications in automobile and aerospaceindustry. Mater. Process Technol. 115, 28.4Zhang, Y., Zhu, P., Chen, G. L. and Lin, Z. Q. (2007) Studyon structural lightweight design of automotive front side railbased on response surface method. J. Mech. Design 129,553557.5Sonsino, C. M. (2007) Lig
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