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Int. J. Engg. Res. & Sci. & Tech. 2017 Ch Meenakshi Devi et al., 2017

DESIGN AND ANALYSIS OF A LOW PASSENGERVEHICLE BUMPER IN AUTOMOBILES

In the present research paper mainly focusing on the design and analysis of a low passengervehicle bumper in automobiles. Day by day, the research on automotive design with economy,safety and aesthetics has been a great challenge to design engineers. The safety of thepassengers during vehicle crashes can be ensured to a certain limit by using good bumpers. Atthe same time these automotive parts should not be massive in terms of weight contributing tothe increase in total the weight of the vehicle. In this project impacts and collisions involving acar frame model are simulated and analysed using SOLIDWORKS and ANSYS softwares. Thematerials used for these analyses are Aluminium alloy, Chromium mild steel alloy and Carboncomposite. During static analysis, Carbon composite showed the lowest deformation andmaximum Vonmises stress value. During Modal analysis, Carbon composite showed the highestnatural frequency among the three. Mild steel showed the minimum value for the frequencywhich is due to the high density of the material. From all these analysis, it is concluded thatcarbon composite is the best bumper material among all the other materials used here.

Keywords: Automotive design, Model analysis, Aluminium alloy, Carbon composite, Mild steel

INTRODUCTIONIn automobile design, crash and structuralanalysis are the two most important engineeringprocesses in developing a high quality vehicle.The greatest challenges faced by the automotiveindustry have been to provide safer vehicles withhigh fuel efficiency at competitive cost. The safetyof the passengers during vehicle crashes can beensured to a certain limit by using good bumpers.1 Assistant Professor, Narasaraopeta Engineering College, Narasaraopet, Andhra Pradesh, India.2 Assistant Professor, Dire Dawa University, Dire Dawa, Ethiopia.3 Assistant Professor, D.V.R & Dr. H.S. MIC College of Technology, Vijayawada, Andhra Pradesh, India.

Int. J. Engg. Res. & Sci. & Tech. 2017

ISSN 2319-5991 www.ijerst.comVol. 6, No. 1, February 2017

© 2017 IJERST. All Rights Reserved

Research Paper

At the same time these automotive parts shouldnot be massive in terms of weight contributing tothe increase in total the weight of the vehicle.Computer simulation technologies have greatlyenhanced the safety, reliability, and comfort,environmental and manufacturing efficiency oftoday’s automobiles. This signif icantachievement was realized with the advancedsoftware and powerful computers that have been

Ch Meenakshi Devi1*, V Venkata Reddy2 and R Ranjith Kumar3

*Corresponding Author: Ch Meenakshi Devi [email protected]

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available in the last twenty years. The primaryconcern for drivers and passengers is safety.Governments have responded to this key concernand expectation with an increasing number ofregulations. Although the details may vary slightlyfrom country to country, the fundamentalrequirements are almost similar. A vehicle isexpected to provide adequate protection to driversand passengers in a not so serious accident. Toprotect the occupants of a car, there are manynew tangible safety features such as airbags; ABScontrol brakes, traction control. A less tangiblefeature that cannot easily be seen by drivers andpassengers is the crash response behaviour. Ina well-designed automobile, the car body andvarious components act as a protective layer forthe occupants of the vehicle. They serve as thecrumpling zone to absorb the energy of impact.The traditional approach involves multipleiterations of design, prototype and crash tests.This process is time consuming and expensive.The availability of high performance computersand crash simulation software has revolutionizedthe process. Instead of relying on experimentalvalidations, the safety design process issupplemented with computer simulation toevaluate the design. Since the inception of crashsimulation, the product cycle of a new automobilehas been reduced by half and the resultant vehicleis safer, better and more comfortable.

Lonny Thompson et al. (2001), determined thata high sensitivity value indicates a strong influenceon the torsional stiffness of the overall chassis.Results from the sensitivity analysis are used asa guide to modify the 2 base line chassis with thegoal of increased torsional stiffness withminimum increase in weight and low centre ofgravity placement. The torsional stiffness of thechassis with various combinations of added

members in the front clip area, engine bay, roofarea, front window and area behind the roll gaugewas predicted using FEA. They concluded thatwith strategic placement of structural membersto a base line chassis, torsional stiffness can bemore than tripled with only a 180 N increase inweight. A method for vehicle analysis based onfinite element technique has been proposed byJohansson and Gustavsson, Vehicle dynamicsand durability have been taken into account in theirwork and in house developed pre and postprocessor is used to achieve effective. Kirkpatrick(2000) has provided a method for force and stresscalculation using complete vehicle models inMSC.nastran, where variables such as roadprofile and curve radii are used as input. Accuratecalculations of force histories are of at mostimportance for reliable fatigue life estimates. Theforces are often calculated by the use of multi-body software (Mbs) and used as input for stressanalysis in fine element package. A drawback isthat Mbs calculations are very time consuming,especially if flexible bodies are included, and arethus not well suited for fast parameters studies.The stress analysis of truck chassis using rivetedjoints has been performed by Cicek Karaoglu andSefa Kuralay (2002), in order to achieve areduction in the magnitude of stresses near theriveted joints of the chassis frame. Side memberthickness, connection plate thickness andconnection plate length were varied. Numericalresults showed that stress on the side membercan be reduced by increasing the side memberthickness locally. In order to investigate thetransient response of a vehicle structureinteraction system in time domain, Tso-Chien Pan(2002) developed a Dynamic Vehicle Element(DVE) method. DVE method treats vehicle as amoving part of the entire system which considersthe vehicle influence at element level by

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incorporating detailed interaction between multiplevehicles and structure induced by irregular roadprofile. In addition a simplified decoupled DynamicNodal Loading (DNL) method is proposed. 11 DNLmethod generates a time series of concentratednodal loading which represents the vehiclereaction force on the structure. Parametricstudies for the effects of road roughness, speedparameter, mass ratio, and frequency ratio on thedynamic vehicle structure interaction are thencarried out using DVE and DNL methods. Arborio(1982) have developed a methodology tostimulate vehicle dynamic through ADAMS carand Mat lab co-simulation, to compare theperformance obtainable considering differentactive systems, a mechanical model of a newcar was implemented through Adams car. Themodel was completed with a power trainspecifically conceived in Mat lab environment toovercome problems due to Adams car modellingmost suitable to describe every operatingcondition, methodology developed was appliedto evaluate a control strategy developed to carryout vehicle dynamics control. Kinematics ofwheeled vehicles has been studied extensivelywith respect to automotive systems byAlexander and Maddocks (2008) for automotivesystems and robotic vehicles operation on eventerrain. Costa Netoetal describes the modellingand analysis process of a medium sized truckmanufacture with regard to vibration and comfortbehaviour. The vehicle model includes Hotchkisssuspensions front and rear with shackle and witha double stage with bump stops at the rear.Nonlinear shock absorber curves are alsorepresented for the vehicle and cabsuspensions. The effect on vehicle comfort ischanging as a design parameter, can bepredicted in the model and verif iedexperimentally.

OBJECTIVES OF THE WORKThe objective of the work is to identify the bestmaterial for bumper which will ensure passengersafety, with high strength to weight ratio throughthe static and modal analysis using differentengineering materials like Aluminium alloy,Chromium mild steel alloy and carbon composite.

• To reduce bumper weight.

• To determine the critical point which has thehighest stress.

• To find different mode shapes of Bumper forthe selected materials.

• To get an optimized in terms of reducing weightand deformation of selected materials ofbumper.

MODELLING AND ANALYSISOF THE STRUCTUREMaterials UsedMost auto bodies today use stamped sheet asstructural members that are spot weldedtogether to form a unitized body. This unitizedstructure is called the Body-In White (BIW). BIWstructural members support most of the loadsdesigned for strength, fatigue resistance,st if fness, as well crush loads forcrashworthiness.

Body materials should also possess sufficientstrength and controlled deformations under loadto absorb crash energy, yet maintain sufficientsurvivable space for adequate occupantprotection should a crash occur. Further, thestructure should be lightweight to reduce fuelconsumption. The majority of mass-producedvehicle bodies over the last six decades weremanufactured from stamped steel components.Manufacturers build only a few limited production

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Table 1: Material Properties of Steel

Table 2: Composition of Aluminum Alloy

Table 3: Composition of Mild Steel ChromiumAlloy

Table 4: Composition of Epoxy-Carbon FiberComposite

and specialty vehicle bodies from compositematerials or aluminum.

Crash WorthinessIn the automotive industry, crashworthinessconnotes a measure of the vehicle's structuralability to plastically deform and yet maintain asufficient survival space for its occupants incrashes involving reasonable deceleration loads.Restraint systems and occupant packaging canprovide additional protection to reduce severeinjuries and fatalities. Crashworthiness evaluationis ascertained by a combination of tests andanalytical methods.

Crashworthiness GoalsVehicle crashworthiness and occupant safetyremain among the most important and challenging design considerations in the automotiveindustry. Designers create vehicles to provideoccupant protection by maintaining integrity of thepassenger compartment and by simultaneouslycontrolling the crash deceleration pulse to fallbelow the upper limit of human tolerance. A crashdeceleration pulse with an early peak in time anda gradual decay is more beneficial for protectionof a restrained occupant. Therefore, the goal ofcrashworthiness is an optimized vehicle structurethat can absorb the crash energy by controlledvehicle deformations while maintaining adequate

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space so that the residual crash energy can bemanaged by the restraint systems to minimizecrash loads transfer to the vehicle occupants.

Real world vehicle collisions are uniquedynamic events where the vehicle may collidewith another vehicle of similar or different shape,stiffness and mass or it may collide with anotherstationary object such as a tree, utility pole orbridge abutment. Generally, for the purpose ofbody development, safety experts classify vehiclecollisions as frontal, side, rear or rollover crashes.

Further, the vehicle may experience a singleimpact or multiple impacts. Moreover, vehiclecrashes occur over a wide range of speeds,persisting for a fraction of a second, such as whena vehicle hits a tree, or for few seconds as inrollover events. These factors illustrate some ofthe complex tasks involved in the design of vehiclestructures to satisfy crashworthiness constraintsfor all collision scenarios.

Currently vehicle crashworthiness is evaluatedin four distinct modes: 1) Frontal, 2) Side, 3) Rearand 4) Rollover crashes

Crashworthiness TestsThere are three categories of tests:

Component Tests: The component testdetermines the dynamic and/or quasi-staticresponse to loading of an isolated component.These component tests are crucial in identifyingthe crush mode and energy absorption capacity.

Sled Tests: In a sled test, engineers use a vehiclebuck representing the passenger compartmentwith all or some of its interior components.Dummies or cadaver subjects are seated in thebuck to simulate a driver and/or passenger andsubjected to dynamic loads, similar to a vehicledeceleration-time pulse, to evaluate the occupant

response in a frontal impact or side impact. Theprimary objective of a sled test is evaluation ofthe restraints.

Full Scale Barrier Impact Tests: It involvescollision of a guided vehicle, propelled into abarrier at a predetermined initial velocity andangle. Typically a barrier test uses a completevehicle. Safety engineers run this barrier test toensure vehicle structural integrity and compliancewith government-mandated regulations.

Types of Crash Tests: All cars undergo front-and side-impact testing, which includes:

• 64 k ph (40 mph) Front impact test: to assesscar’s performance in severe accident.

• 50 k ph (30 mph) Side impact test.

• 29 k ph (18 mph) optional Pole impact test: todriver’s head.

• 40 k ph (25 mph) child and adult pedestrianimpact tests.

Crash Tests-Regulatory RulesThe following are the requirements for theconsumer rash tests conducted by

• Federal Motor Vehicle Safety Standard(FMVSS)

• Insurance Institute for Highway Safety (IIHS)

FMVSS Frontal impact requirements:

• 30 mph (48 kph) into a fixed barrier

Figure 1: Frontal Crash Tests

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• Uses SID dummy in front and rear seats

• Uses dummy injury measures for regulation

• TTI(d) <= 85 g for 4 door passenger cars

• TTI(d) <= 90 g for 2 door passenger cars

• Pelvic acceleration <= 130 g

• Where TTI(d) = 0.5 x (Gr + Gs)

– Gr = Max. Rib acceleration

– Gs = Lower spine acceleration

• IIHS Side impact requirements:

• Impactor mass = 1500 Kg

• Impactor shape derived from Ford F150 frontprofile

• 30 mph perpendicular impact

• Driver and rear passenger dummies

• Purpose is to represent crash type that posesgreatest risk to occupants (pickups/SUV asstriking vehicle)

• Promote head protection

ModelingThe model of the chassis frame has been createdusing the primitives approach usingSOLIDWORKS software.

1. Model is a uni-body structure

2. The figures shown in the literature review werethe basis of our model

3. A work plane is established (xy plane)

4. By using different geometrical primitives basicgeometry is obtained

5. By using different modeling options ofSOLIDWORKS for several times model iscreated according to dimensions as shown inFigure 3.

• Hybrid III in front driver and passenger seats

• Uses dummy injury measures for regulation

– chest G’s <= 60

– HIC <=1000

– Femur loads <= 10KN

• Protection must be automatic

• Purpose of this test is to examine theperformance of the occupant restraintsystems

– (seatbelts, airbags, etc.)

IIHS Frontal impact requirements:

40% offset, 40 mph (64 kph) into a deformablebarrier

• Male Hybrid III dummy in front driver seat

• Good, Acceptable, Marginal and poor ratingsto assess vehicle’s overall crashworthiness

• Rating based on:

– Dummy injury measures

– Structural performance

– Restraint/dummy kinematics

• Evaluates the structural performance of thevehicle

• FMVSS Side impact requirements:

• 33.5 mph (54 kph) crabbed impact

• Impactor mass 1367.6 kg (3015 lb)

Figure 2: Side Crash Tests

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Figure 3: Dimensions of Bumperwith Chassis Frame

Meshing of Model• By saving the file in igs format we can open

that in ANSYS WORKBENCH for doinganalysis

• In ANSYS WORKBENCH igs file is imported

• Now meshing is done using solid element 187

• Element division is taken as 10

• After meshing material is assigned for solidelement, the element solid187 (ANSYS library)is taken.

• Refined mesh is shown in Figure 5.

Figure 4: Solidworks Model of Car Front Part

Figure 5: Final Mesh of Car ChassisFrame-Bumper

ANALYSIS OF CAR CHASSISFRAME-BUMPERTypes of Analysis UsedThe following analysis has been carried out

• Static Analysis

• Modal Analysis

• The meshed model is initiated for analysis

Figure 6: Car Frame with Imposed BoundaryConditions

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• The boundary conditions are imposed on allthe end support edges in all DOF

• The final car frame with imposed boundaryconditions is shown in Figure 6.

Static AnalysisA static analysis calculates the effects of steadyloading conditions on a structure, while ignoringinertia and damping effects, such as thosecaused by time-varying loads. A static analysiscan, however, include steady inertia loads (suchas gravity and rotational velocity), and time-varying loads that can be approximated as staticequivalent loads (such as the static equivalentwind and seismic loads commonly defined inmany building codes).

Loads in a Static Analysis: Static analysis isused to determine the displacements, stresses,strains and forces in structures or componentscaused by loads that do not induce significantinertia and damping effects. Steady loading andresponse conditions are assumed; that is, theloads and the structure¡¦s response are assumedto vary slowly with respect to time. The kinds ofloading that can be applied in a static analysisinclude:

• Externally applied forces and pressures

• Steady-state inertial forces (such as gravity orrational velocity)

• Imposed (non-zero) displacements

• Temperatures (for thermal strain)

• Fluencies (for nuclear swelling)

A static analysis calculates the effects ofsteady loading conditions on a structure, whileignoring inertia and damping effects, such asthose caused by time-varying loads. A staticanalysis can, however, include steady inertia

loads (such as gravity and rotational velocity), andtime varying loads that can be approximated asstatic equivalent loads (such as static equivalentwind and seismic loads commonly defined inmany building codes.

Linear vs. Nonlinear Static Analysis: A staticanalysis can be either linear or non linear. All typesof nonlinearities are allowed-large deformations,plasticity, creep, stress stiffening, contact (gap)elements, hyper elastic elements, etc.

Figure 7: Schematic Diagram Showingthe Solid Model of the Bumper

RESULTS AND DISCUSSIONThe simulation results are shows the analysisrelated to the bumper of the vehicle in static andmodel analysis while using the different types ofthe composites.

Static AnalysisThe below results related to the static structuralanalysis with three different types, i.e., totaldeformation, equivalent stress and maximumprincipal elastic strain. It can be observed that inFigure 8a shows the maximum deformation ofthe bumper when using the Al alloy is 45.871 mm.In Figure 8b related to the maximum von-misses

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Figure 8: Schematic Diagram Showingthe Static Analysis on Al Alloy Bumper

(a) Total Deformation, (b) Equivalent Stress(c) Elastic Strain

(a)

(b)

(c)

Figure 9: Schematic Diagram Showingthe Static Analysis on Carbon Fiber CompositeBumper (a) Total Deformation, (b) Equivalent

Stress (c) Elastic Strain

(a)

(b)

(c)

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Figure 10: Schematic Diagram Showingthe Static Analysis on Mild Steel Chromium

Coated Bumper (a) Total Deformation,(b) Equivalent Stress (c) Elastic Strain

(a)

(b)

(c)

stress of the said material is 1792.3 Mpa and theFigure 8c represent the maximum principal elasticstrain of the Al alloy is 0.015131.

In Figure 9 shows the simulations related tothe static analysis of the carbon fibre compositematerial using on bumper. It can be observed thatthe deformation of the material is 42.847 mm,the stress of the material is 1905.1 Mpa and thestrain of the material is 0.016052.

In Figure10 shows the results related to thestatic analysis mild steel chromium coatedbumper. It can be observed that the deformationof the material is 17.697 mm, the stress of thematerial is 1811.4 Mpa and the strain of thematerial is 0.0059326.

Model AnalysisThe simulation result shows the modal analysis ofthree different materials is discussed in this section.The natural frequency of the different materials isdetermined in this section. It is a frequency at whichthe system tends to oscillate in the absence ofdriving and damping force. The free vibrations aredeveloped on any elastic body is called naturalvibration of the body. The natural frequency of thematerial is depends on the mass and stiffness ofthe material. The mass of the material is variedalways depends on the density of material. Similarly,the stiffness of the material is always depends onthe force and deflection of the geometry of thematerial. Since all the geometries taken in theseanalysis are identical, the chances for the variationof the frequencies are only due to the change in thedensity of the materials.

The natural frequency of the three differentmaterial models is given in Table 5. From theseresults it can be observed that the carbon fibrecomposite material has more natural frequencycompared to other two materials.

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Figure 11: Schematic Diagram Showing the Natural Frequency of Aluminum Alloy (a) Mode 1,(b) Mode 2, (c) Mode 3, (d) Mode 4, (e) Mode 5, (f) Mode 6, (g) Mode 7, (h) Mode 8,

(i) Mode 9 and (j) Mode 10

(a)

(b)

(c)

(d)

(e)

(g)

(h)

(i)

(j)

(f)

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Figure 12: Schematic Diagram Showing the Natural Frequency of Carbon Fiber Composite(a) Mode 1, (b) Mode 2, (c) Mode 3, (d) Mode 4, (e) Mode 5, (f) Mode 6, (g) Mode 7,

(h) Mode 8, (i) Mode 9 and (j) Mode 10

(a)

(b)

(c)

(d)

(e)

(g)

(h)

(i)

(j)

(f)

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Figure 13: Schematic Diagram Showing the Natural Frequency of Mild Steel Chromium Alloy(a) Mode 1, (b) Mode 2, (c) Mode 3, (d) Mode 4, (e) Mode 5, (f) Mode 6, (g) Mode 7,

(h) Mode 8, (i) Mode 9 and (j) Mode 10

(a)

(b)

(c)

(d)

(e)

(g)

(h)

(i)

(j)

(f)

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Table 5: Comparison of Natural Frequencies of Three Different Material Models

CONCLUSIONIn the present research work the authorsdiscussed the design and analysis of a lowpassenger vehicle of ambassador car bumper inautomobiles. Initially, the author modelled by usingsolid works and it is analysed by statically. In staticanalysis they compare the deformation, von-mises stress and strain of the three differentmaterials, i.e., Al alloy, Carbon fibre and mild steelmaterials. The carbon fibre composite obtainedhighest von-mises stress value and the lowestdeformation of the other two materials. In additionto, the model analysis due to low density and thenatural frequency is analysed of the threedifferent materials. Finally, the carbon fibrecomposite material is giving more naturalfrequency compare to other materials.

REFERENCES1. Alexander J C and Maddocks J H (2008),

“Kinematics of Wheeled Vehicles ofAutomotive Systems”, The InternationalConference on Vehicle Structural Mechanics.

2. Arborio N (1982), “Future Trend ofAutomobile and the High Strength SheetSteel”, Tetsu-to-Hagane, Vol. 68, No. 9,Japan.

3. Cicek Karaoglu and Sefa Kuralay N (2002),“Stress Analysis of a Truck Chassis withRiveted Joints”, Finite Elements in Analysisand Design, Vol. 38, pp. 1115-1130,Department of Mechanical Engineering,DEU Faculty of Engineering, 35100 Bornova,Izmir, Turkey.

4. Lonny L Thompson, Clifford C Chou, BahigB Fileta, Tawfik B Khalil, Albert King, HikmatF Mahmood, Harold J Mertz and JacWismans (2001), “Vehicle Crashworthinessand Occupant Protection”, Sponsored by:Automotive Applications Committee,American Iron and Steel Institute, Southfield,Michigan.

5. Kirkpatrick S W (2000), “Development andValidation of High Fidelity Vehicle CrashSimulation Models”, SAE Technical Paper2000-01-0627, doi: 10.4271/2000-01-0627.

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6. Tso-Chien Pan (2002), “Dynamic VehicleElement Method - Present and Future

Developments”, The InternationalConference on Vehicle Structural Mechanics.

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