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喜歡就充值下載吧，，資源目錄下展示的全都有，，下載后全都有，dwg格式的為CAD圖紙，有疑問咨詢QQ：414951605 或1304139763 400 Commonwealth Drive, Warrendale, PA 15096-0001 U.S.A.Tel: (724) 776-4841 Fax: (724) 776-5760SAE TECHNICALPAPER SERIES982309Door Structural Slam DurabilityInertia Relief ApproachS. BaskarGM - Midsize and Luxury Car GroupReprinted From: Proceedings of the IBEC 98, Volume 1Advanced Body Design and Engineering(P-330)International Body EngineeringConference & ExpositionDetroit, MichiganSeptember 29 - October 1, 1998Downloaded from SAE International by Birmingham City Univ, Monday, August 20, 2018The appearance of this ISSN code at the bottom of this page indicates SAEs consent that copies of thepaper may be made for personal or internal use of specific clients. This consent is given on the condition,however, that the copier pay a $7.00 per article copy fee through the Copyright Clearance Center, Inc.Operations Center, 222 Rosewood Drive, Danvers, MA 01923 for copying beyond that permitted by Sec-tions 107 or 108 of the U.S. Copyright Law. This consent does not extend to other kinds of copying such ascopying for general distribution, for advertising or promotional purposes, for creating new collective works,or for resale.SAE routinely stocks printed papers for a period of three years following date of publication. Direct yourorders to SAE Customer Sales and Satisfaction Department.Quantity reprint rates can be obtained from the Customer Sales and Satisfaction Department.To request permission to reprint a technical paper or permission to use copyrighted SAE publications inother works, contact the SAE Publications Group.No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior writtenpermission of the publisher.ISSN 0148-7191Copyright 1998 Society of Automotive Engineers, Inc.Positions and opinions advanced in this paper are those of the author(s) and not necessarily those of SAE. The author is solelyresponsible for the content of the paper. A process is available by which discussions will be printed with the paper if it is published inSAE Transactions. For permission to publish this paper in full or in part, contact the SAE Publications Group.Persons wishing to submit papers to be considered for presentation or publication through SAE should send the manuscript or a 300word abstract of a proposed manuscript to: Secretary, Engineering Meetings Board, SAE.Printed in USAAll SAE papers, standards, and selectedbooks are abstracted and indexed in theGlobal Mobility DatabaseDownloaded from SAE International by Birmingham City Univ, Monday, August 20, 20181982309Door Structural Slam DurabilityInertia Relief ApproachS. BaskarGM - Midsize and Luxury Car GroupCopyright 1998 Society of Automotive Engineers, Inc.ABSTRACTThe automotive industry faces many competitive chal-lenges including weight and cost reduction to meet CAFEstandards. In particular, a thin door panel optimized forweight reduction can cause high manufacturer warrantiesand durability problems. Traditionally, the assessment ofdoor slam durability is accomplished by tests rather thanusing computer aided techniques. Many simple CAEtechniques such as simple linear static and dynamicanalyses have been used to evaluate the door structuralintegrity. However, the door slam event requires complexanalysis due to the transient impact phenomenon. Tosolve this complex door slam event with a computerbased technique is a challenging and interesting problemfor CAE engineers. However, a simplified technique hasbeen developed to anticipate the potential durability prob-lem in the door. This technique involves the use of thecomputer- based finite element method incorporatinginertia relief and fatigue life prediction. Actual testing vali-dated the analytically predicted results. This method pro-vides an inexpensive way of predicting door slamdurability reducing development time and product cost.As a result, the new approach aided the door designrobustness.INTRODUCTIONIn recent years, higher fuel economy and manufacturingcost drove the automotive industries to reduce the massand the number of parts for assembly. This forces auto-motive engineers to design lighter structures and meetperformance requirements without sacrificing quality andsafety. However, a lightweight door design that satisfiescost, quality, and safety requirements must also meetwarranty and slam durability goals also. Traditionally, the slam durability test assessed the doordesign in the prototype phase. Any design modificationsat this stage will increase lead time and cost. However,use of up-front analytical prediction can reduce develop-ment cycle time and down-stream quality problems suchas warranty, and on-line inspection for door fit and finish.Computer based analyses have been used extensively toevaluate the door system performance such as stiffness,strength, frequency and the Federal Motor Vehicle SafetyStandards (FMVSS 214, static and dynamic side doorintrusion). However, a comprehensive computer-basedanalysis has not been developed for door slam durability.In fact, the door slam event is a complicated transientimpact loading phenomenon and it is a challenging prob-lem for the CAE engineers. This inspired the CAE com-munity to develop a slam durability analysis that canidentify the critical problem areas in the early designphase.The door slam analysis is a transient dynamic impact aswell as a repeated type of loading in nature. The impactloading produces appreciable shock or vibration andinduces accelerations in addition to inertial accelerationsdue to rigid body motion. Further, if the rate of loading(forcing frequency) approaches the natural frequency ofthe part, the vibration excited due to resonance producesnot only high deflections but also large stresses in thepart. Several approximate analytical techniques havebeen used in the aircraft and automotive industries topredict dynamic loads in a structure.Recently, a dynamic transient finite element analysis(FEA) and a nonlinear dynamic transient contact FEAmethods have been used extensively in both automotiveand aerospace industries to predict the dynamic loads.Door trim panel flutter analysis uses the first method tostudy the trim response due to a slam. However, theaccuracy of the trim response depends on the number ofmodes included in the analysis. Recently, bumper designused the second method to evaluate the dynamic loadsdue to pendulum impacts. Both methods required longlead time and intensive computational effort in calculatingand sorting the high stresses. On the other hand, CAEengineers seek a robust technique to predict dynamicloads in the structure due to slam. An approximate ana-lytical technique is the Inertia Relief Technique thatincludes the dynamic effects and solves by using a staticconventional analysis to evaluate the dynamic (inertia)Downloaded from SAE International by Birmingham City Univ, Monday, August 20, 20182loads. The aerospace and automotive industries appliedthis method successfully in the aircraft wing design 1,and in the automotive hood structure 2 and the bodyjoint structural durability 3. Furthermore, the reference4 addressed the limitations and usefulness of thismethod extensively.The objective of this paper is to develop an inertia relieftechnique and couple the fatigue analysis to predict doorinner panel crack initiation locations and fatigue life dueto slam. In the inertia relief technique, the inertia loadsare calculated due to door slam and multiplied by a loadfactor to compensate for a door slam energy. Based onthe inertia loads, the conventional static analysis methodcalculated the stresses, and the in-house computer codeestimated the fatigue life of the door inner panel. Further-more, the methodology correlated the coupe door testand aided the new sedan door design in the early designphase. Finally, the sedan slam test validated the analysispredictions and enhanced the CAE confidence. Based onthe above study and the test, the generic design guide-lines were developed to achieve door design robustness.INERTIA RELIEF APPROACHUsually, the conventional finite element method cannotbe performed on any unconstrained structures. However,these structures can be analyzed using the methodknown as Inertia Relief 5. It analyzes the structure byassuming that an approximate state of equilibrium existsbetween the external forces and the inertia forces due torigid body accelerations produced by unconstrainedmotion. However, the state of equilibrium statement holdsonly if the rate of change of the external force (forcing fre-quency) is small compared to the lowest natural fre-quency of the structure. On the other hand, if the forcingfrequency (load) coincides with the natural frequency, theprediction of inertia force will be non-conservative.During the slam, door components undergo a rigid bodymotion, vibration and elastic deformation. The equationof motion of the free body can be written M+ k X = P(Eq. 1)M and k are the mass and stiffness of the door system. , X, and P are the acceleration, the displacement andthe force vector, respectively. The above equation can bepartitioned as follows:(Eq. 2)where prime (T) shows the matrix transposition. f and rrepresent degree of freedom (dof) for the unrestrainedand restrained motion, respectively. Here, the dof rrefers to the free body supports such as hinge axis rota-tion in the door. By incorporating the inertia relief, the equation of motionis modified as M*rr = P*r(Eq. 3)and the expanded matrices (*) are explained in the refer-ence 4. The eqn. 3 solves the accelerations of thedegree freedom of r and were used in the calculation ofthe accelerations of all other dofs.An inertia load vector PI can be calculated as follows:PI = - M (Eq. 4)where M and are the mass matrix and the accelerationvector of the door system. Once the inertia loads werecomputed at all other points in the door, it is added to theoriginal load vector (Pf) to solve for displacements. Byrestraining the door structure at the latch location, thedisplacements are solved using the equation 5.Kff Xf = Pf + PI (Eq. 5)Once the displacements (Xf) are solved, the stresseswere evaluated in the conventional manner.X.X.MMMMxxKKKKxxPPfffrfrTrrfrfffrfrTrrfrfr&+ = Xr.X.X.Downloaded from SAE International by Birmingham City Univ, Monday, August 20, 20183Figure 1. Door Slam Durability Analysis - Flow ChartSLAM DURABILITY METHODOLOGY In this paper, the door slam durability methodology cou-pled the dynamic load prediction and the fatigue life esti-mation. The inertia relief approach predicted the dynamicloads due to slam and the in-house fatigue code evalu-ated the damage or fatigue life of the door structure.However, the inertia relief methodology is applicable onlywhen the rate of change slam loading is sufficiently small(10 Hz, forcing frequency) compared to the lowest doorinner panel natural frequency (22 Hz). Based on theabove assumption, the CAE process flow chart in figure 1shows the following four steps to evaluate the door slamdurability.1. Evaluate the Inertia load due to slam2. Compute the latch force and the strain energy3. Select the load factor for stress evaluation4. Compute the fatigue life of the inner panel1. EVALUATION OF INERTIA LOAD The door finiteelement model incorporated all components such asdoor in white, window glass, window regulator motor,glass run and regulator channels, beltline seals, andhinges to evaluate the inertia loads. The door inner andouter weld connections were modeled by RBE2 elementswith zero lengths. However, a careful consideration suchas nearly normal and minimum length was given in mod-eling rigid elements. The seals were represented byspring elements and furthermore, masses such as regu-lator motor, trim and latch were lumped as concentratedmasses in the model. A moment was applied on thehinge axis to represent the door rotation and chosen as aSUPORT degree of freedom for the inertia relief run.Nastran analysis used Solution 101 along with the speci-fied ALTER to calculate the inertia loads and punchedDMIG file for further use. The accuracy of the solutionwas checked carefully using the error parameters suchas epsilon and strain energy. The user information message such as epsilon andstrain energy in the Nastran outlist file are provided forerror check. Under a no-strain condition, the epsilon andstrain energy are zero for good accuracy, and when non-zero indicate errors due to incompatible multipoint con-straints, or nonaligned scalar elements with the basiccoordinate axes.2. COMPUTATION OF LATCH FORCE AND STRAINENERGY The DMIG file consisting of inertia load at allgrid points was used as input loads for the latch force andthe strain energy. In this run, the solution 101 along withthe specified ALTER (load multiplication factor) evaluatedthe latch reaction force and the strain energy. By con-straining the latch points and removing the SUPORT dof(hinge axis rotation), the model will become a staticallydeterminate structure for the evaluation of latch force andInertia Relief RunEnergy FactorCompare with Input Slam EnergyLatch Load Factor Latch Force Crack/ Fatigue Life PredictionEvaluation Of Stress/StrainInertia LoadApplicationStrain EnergyLoad Factor EvaluationFactor SelectionConfirm With The TestDesign ModificationYesNoCompare with Test ValueMet Desired Life and/ or PerformanceDownloaded from SAE International by Birmingham City Univ, Monday, August 20, 20184the strain energy. Furthermore, the initial latch reactionforce and the strain energy were calculated using theload factor of 1.0 for the load factor selection.3. LOAD FACTOR SELECTION The latch factor selec-tion plays an important role in evaluating the stress.Before evaluating the stresses, the inertia loads areadjusted to compensate for door slam energy. The slamdurability schedule (figure 2) consists of various slamenergies that include several environmental conditions,and glass window positions. In this paper, the durabilityslam energy of 30 J was considered in the evaluation ofinertia load factor selection based on one of the followingmethods.Figure 2. Slam Durability Schedulea. Energy Method The slam energy (kinetic energy ,KE) and the strain energy (SE) is related to the angularvelocity () and the hinge axis moment (M) as in eqn. (6) KE/SE1= ( / 1)*2 = (M/M1)*2 (Eq. 6)The subscript 1 represents the value due to latch factorof 1.0. The moment about the hinge axis is written asMoment, M = 1/2 I , (Eq. 7)where I and are the door mass moment of inertia aboutthe hinge axis and the door angular acceleration, respec-tively. Since the moment is directly proportional to load,the energy load factor can be written(Eq. 8)In this approach it was assummed the slam energy (KE)had been converted completely into door strain energyand thereby, produced a higher energy load factor. How-ever, during the slam event, the slam energy is dissipatedas airbind, seal absorption, noise, heat, etc., into the doorsystem and are likely to yield a lower value.b. Latch Force Method In this method, the forces (in-out, lateral, and vertical) at the striker location are mea-sured on a similar production door for various slamenergy levels. The latch force factor calculation uses onlythe in-out force for the chosen energy level and it isrelated as (Eq. 9)Figure 3. Fatigue Life or Damage Calculations - Flow ChartThe latch force due to 30 J slam energy was selected toevaluate the stress on the door inner panel. Finally, thein-house fatigue code estimates the fatigue life or dam-age of the door structure based on the door inner panelstress.4. FATIGUE LIFE PREDICTION In the automotiveindustry, the durability of the structure was assessed bythe safe-life design criterion rather than the fail - safe criterion used in the aerospace industry. The safe-lifecriterion allows us to design for finite fatigue life and islimited to the crack initiation stage only. On the contrary,the fail-safe design allows cracks to occur without anyfatigue failure before they are detected and repaired.Fatigue is the process of progressive, localized, perma-nent material deformation, due to cyclic stress and strain,which may lead to cracks or fracture after sufficient num-ber of cycles. The fatigue process consists of threestages: crack initiation, crack propagation, and suddenConstantAmplitudeNeubersRule for KFMaterialModelStrain - Life &Mean StressCorrectionTotal Life = 1/ Total DamageMiners RuleLoad (Stressor Strain ) InputNominal History(Stress/ Strain)Notch Strain ()HistoryCycle Count onStrain Vs # of Cycles to FailureDamageNominal To NotchDownloaded from SAE International by Birmingham City Univ, Monday, August 20, 20185fracture. As in the safe-life design, the door inner panelcomponents are designed such that the fatigue is limitedto the crack initiation stage only.An analysis procedure for fatigue life prediction of doorinner panel was developed using the in-house computercode, the Corporate Fatigue System (CFS). The CFSuses the strain-life approach to forecast crack initiation interms of repetitions of the specified load history. How-ever, in the fatigue analysis, a repeated load may causefatigue cracking at stress lower than the material yieldstrength. The CFS code uses the load history, the scalefactor, fatigue notch factor, cyclic and hystersis stress-strain curves, and the material strain-life, for the evalua-tion of fatigue life or damage. Figure 3 outlines the dam-age calculations step-by-step. Additionally, this method isused in the assessment of load histories for damagecomparison, and also, in the design improvement of acomponent that has cracked on a road or lab durabilitytest.The durability schedule consists of many slam energylevels, various environmental conditions, and differentwindow positions. In this paper, the durability schedulehas been simplified to one slam energy level (30 J) atambient condition with the glass window positioned low inthe door during slam. The maximum load occurred in the30 J slam energy was chosen for the load factor calcula-tion in the inertia relief approach. The inertia relief wascoupled with the fatigue analysis to evaluate the damageor fatigue life of the coupe and sedan front door. Thefatigue code used the constant stress history to evaluatethe damage or fatigue life of the inner panel. Further-more, the slam durability test verified the inertia reliefapproach.METHODOLOGY VERIFICATIONThis method was developed after witnessing durabilityproblems on a coupe door. Hence, it is essential to corre-late the new methodology with the available coupe doortest data before evaluating the new door design.CORRELATION STUDY - COUPE DOOR Figures 4and 5 show the FEM door system model and the fullytrimmed coupe door. Due to availability of the latch forcefrom the test, the force load factor was selected to calcu-late inertia loads on the door structure. The inertia loadscalculated the element Von Mises stresses and wereused in the fatigue calculations. Figure 6 shows the innerpanel stress and the possible crack initiation locations. Figure 4. Coupe Door System FEM ModelFigure 5. Fully Trimmed Coupe DoorDownloaded from SAE International by Birmingham City Univ, Monday, August 20, 20186Figure 6.Coupe Door - Possible Crack Initiation LocationsFigure 7 compares the coupe door crack initiation loca-tions between the test and the prediction. The resultsshowed a very good correlation in identifying the loca-tions. However, the tested door showed some loss offunction and a lesser target fatigue life. To improve thefatigue life of the inner panel, the fatigue life estimationanalysis as shown in figure 8 was used to achieve the tar-get life of 1.5 lives. The CFS estimated the safe stresslevel for the target life for the known parameters such asfatigue notch factor, test life, and FEM stress. Here, theCFS calculated not only the fatigue notch factor from theknown test life and the peak element stress but also eval-uated the scale factor vs. life as shown in figure 9. Usingthe scale factor vs. life plot, a s