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Available online 12 June 2011

Keywords:A. CompositeE. MechanicalH. Selection of components

e co

matrices can improve mechanical properties of natural bre composite. Moreover, geometric optimiza-

absorption, material consumption and cost [5]. The previous stud-ies did not completely full the impact strength requirement of thebumper PDS even in case where polybutylene terephthalate (PBT)was supplemented to the hybrid bio-composite material [6,7].Therefore, in this recent study the optimized concept selection isemployed to improve the impact stability of structure [8].

ers have done many investigations to expand the application pos-sibilities of natural bres in automotive industry such as front doorlinens, rear door linens, boot linens, parcel shelves, seat backs, sun-roof sliders, headliners, door-trim panel and trunk liner [1214]. Infact, the majority of their products are used in aesthetic and semistructural components. Mussig [15] utilized hemp and PTP bresin a body of bus as reinforcements, a vegetable-based thermosetresin as matrix, and sheet molding compound (SMC) as fabricatingmethod for structural components. Although, the earlier research-ers studied on energy absorption of wood for automotive structural

Corresponding author. Tel.: +60 16 65 65 296; fax: +60 3 8656 7122.E-mail addresses: makinejadm2@asme.org, davoodi@eng.upm.edu.my (M.M.

Materials and Design 32 (2011) 48574865

Contents lists availab

Materials an

elsDavoodi).Concept optimizations of the car bumper beam can improvestructural energy absorption to meet the PDS requirements. Bum-per system is composed of three main elements fascia, energy ab-sorber and bumper beam [1] (see Fig. 1). Bumper beam is the majordamping structure component in passenger cars. Besides, two en-ergy absorbers damp both the low and high impact energy by elas-tic deection between two traverse-xing points and crushingprocess respectively [2,3]. Due to safety requirements, in develop-ing the bumper beam, the careful design, optimized structure, highquality and consistent manufacturing must be considered [4]. Inaddition, bumper beam selection can improve structural energy

tual design of the automotive bumper system and used theweighted objective method to nd the best concept. Hosseinzadehet al. [9] conducted a research to substitute the high strength SMCwith common bumper beam material GMT to improve energyabsorption. Furthermore, Davoodi et al. [10] studied about com-posite elliptical energy absorber for pedestrian impact test withsystematic exploitation of proven ideas. Marzbanrad et al. [11]studied about the material, thickness, shape and impact conditionof the bumper beam to improve the crashworthiness and low-velocity impact. He offered to substitute SMC with GMT materialto absorb more structural impact. Also, European car manufactur-1. Introduction0261-3069/$ - see front matter 2011 Elsevier Ltd. Adoi:10.1016/j.matdes.2011.06.011tions have a signicant role in structural strength improvement. This study focused on selecting the bestgeometrical bumper beam concept to fulll the safety parameters of the dened product design speci-cation (PDS). The mechanical properties of developed hybrid composite material were considered in dif-ferent bumper beam concepts with the same frontal curvature, thickness, and overall dimensions. Thelow-speed impact test was simulated under the same conditions in Abaqus V16R9 software. Six weightedcriteria, which were deection, strain energy, mass, cost, easy manufacturing, and the rib possibility wereanalyzed to form an evaluation matrix. Topsis method was employed to select the best concept. It is con-cluded that double hat prole (DHP) with dened material model can be used for bumper beam of a smallcar. In addition, selected concept can be strengthened by adding reinforced ribs or increasing the thick-ness of the bumper beam to comply with the dened PDS.

2011 Elsevier Ltd. All rights reserved.

Conceptual design is the rst stage of product development tosatisfy customer requirements. Sapuan et al. [1] studied on concep-Received 10 March 2011Accepted 7 June 2011

technical and economic advantages. However, their low mechanical properties have limited their partic-ular application in automotive structural components. Hybridizations with other reinforcements orConcept selection of car bumper beam wbio-composite material

M.M. Davoodi a,, S.M. Sapuan a, D. Ahmad b, A. AidyaDepartment of Mechanical and Manufacturing Engineering, Universiti Putra Malaysia,bDepartment of Biological and Agricultural Engineering, Universiti Putra Malaysia, 4340cDepartment of Applied Physics and Mechanical Engineering, Lule University of Techno

a r t i c l e i n f o

Article history:

a b s t r a c t

Application of natural br

journal homepage: www.ll rights reserved.h developed hybrid

. Khalina b, Mehdi Jonoobi c

0 UPM Serdang, Selangor, MalaysiaPM Serdang, Selangor, Malaysia, Sweden

mposites is going to increase in different areas caused by environmental,

le at ScienceDirect

d Design

evier .com/locate /matdes

components [16], few studies have been conducted on applicationof natural bre in structural automotive components.

This research focused on analyzing, evaluating and selecting theoptimum concept among eight different bumper beam concepts,and particularly concentrated on safety purposes of a bumperbeam PDS. Based on the National Highway Trafc Safety Adminis-tration (NHTSA), car bumper low impact test was simulated by -nite element software, Abaqus Ver16R9, to address the highestenergy absorption and maximum possible deection. The samematerial properties and constant overall dimensions were consid-ered for whole concepts. Finally, decision matrix came up witheight alternatives against six criteria. Topsis method was ap-pointed for selecting the best concept of the bumper beam througheight systematic evaluation processes. It was concluded that Dou-ble Hat Prole (DHP) as a best concept. Moreover, this study dem-onstrated the feasibility of the nite element analysis in selectingthe best structural concepts to overcome the weak inherent prop-erties of natural bre, and to get better mechanical performancefor automotive structural application.

2. Basic design procedure

2.1. Conceptual design of bumper beam

The preliminary stage of product development start with con-ceptual design, which is derived from customer requirement voiceof the customer [17,18] to nd a solution to satisfy the functionaldesign problems [19]. Imprecise engineering calculation, designand material selection, might increase up to 70% the total productcost for redesigning [20]. Designer has to select the most suitableidea from different possible solutions or combination of materialselection and component design to meet the desired PDS in eachdesign stage to decrease the rework expense [2125].Therefore,many tools are developed to evaluate design concept selection(DCS) and compromise different effective factors, i.e. customerrequirements, designer intentions and market desire.

Decision matrix-based methods, offer the qualitative compari-son such as Pughs method [23] or quality function deployment(QFD) [26]. Fuzzy ANP-based, evaluate a set of conceptual designalternatives to satisfy both customer satisfaction and engineeringspecications [27]. Analytical Hierarchy Process (AHP) is a mathe-matically based technique for analyzing complex situations, whichwere sophisticated in its simplicity [28]. Multi criteria decision-making (MCDM) is an effective method for single selection amongmixed criteria. Multi-attribute decision-making technique(MADM) is a conicting preferences solution among criteria forsingle decision makers. Topsis is well suited technique to dealingwith multi attribute or multi-criteria decision-making (MADM/MCDM) problems in real world ideal solutions [29]. Its method is

Fig. 1. Bumper system components.

4858 M.M. Davoodi et al. /Materials and Design 32 (2011) 48574865Fig. 2. Selected parametersbased on chosen alternative has shortest distance from positiveideal solution and farthest distance from negative ideal solution.It helps to organize problems, compare, and rank alternatives tocarry out the analysis for better options [30]. This method has beenappointed to select the best concept in this research.for bumper beam PDS.

2.2. Product design specication (PDS)

To perform the customer requirements and expectation to a de-tailed technical document called PDS [31]. It is quite difcult to n-ish the exact PDS in the early stage of product development, whilethe knowledge of design requirements is imprecise and incomplete[32]. PDS originates by disorganized brainstorming team with var-ious prociency, i.e. manufacturing, designing, selling, assembling,maintaining, and might be improved due to new product changesand manufacturing limitations. Safety was the main goal amongdifferent bumper PDS specication in this study.

Bumper beam PDS consisted of safety, performance, weight,size, cost, environment issue, appearance (see Fig. 2). Whole PDSparameters can be classied into three main subdivisions such asmaterial, manufacturing and design. Since energy absorption ofdifferent concept is the core competency of this study, it is empha-sized in the PDS safety parameters. Some of the mechanical andphysical properties values are received from experimental resultsand others from existing PDS data.

Safety: There are different bumper safety regulations for pas-sengers car, issued by safety organization, insurance companiesor original equipment manufacturer (OEM) [33]. Insurance compa-nies usually offer more severe conditions in order to decrease theirown costs. This study follows safety criteria of the European carmanufacturer.

(1) Low impact test: Longitudinal pendulum impact test by4.0 km/h (2.5 mph), and corner pendulum impact test by2.4 km/h (1.5 mph) with any bumper visual, functional,and safety damages.

(2) High speed test: No bumper damage or yielding after 8 km/h(5 mph) frontal impact into a at, rigid barrier.

(3) Pedestrian impact test: In this test, a leg-form impactor ispropelled toward a stationary vehicle at a velocity of 40 km/h (25 mph) parallel to the vehicles longitudinal axis. The testcan be performed at any location across the face of the vehi-cle, between the 30 bumper corners. So the impact criteriafor 2010 should be a < 150 g and the shear d < 6 mm andbending a < 15

M.M. Davoodi et al. /Materials and Design 32 (2011) 48574865 4859Fig. 3. Bumper beam conceptual selection owchart.

[10]. In this study, bumper beam was placed after fascia and wasmounted to the main chassis through energy absorbers. Besides,are different effective parameters to improve the energy absorbingperformance in a bumper beam as follows.

(1) Frontal curvature: Frontal curvature increases the roombetween xing points and top extremity beam curvature. Itstrengthens the beam stability, and extends the requiredcollision displacement. Besides, the aesthetic purposes, thecurve facilitates better load impact distribution throughthe frontal beam and xing points during energy dampingprocess. When the impact load applied to the bumper, thebeam initial curvature intends to remove. So, some designer

4860 M.M. Davoodi et al. /Materials and Design 32 (2011) 48574865Since material development and its manufacturing method arediscussed in the previous study, this research emphasizes on design

Fig. 4. Overall dimensions of different concepts.parameters in PDS. Size: Dimension of the bumper beam dependson energy absorption value, which related to car size and weight.Maintenance: Design for assembly (DFA) and design for manufac-turing (DFM) should consider during product design. Performance:The dened goal of the product should be attainable [23]. Installa-tion: Design for manufacturing and assembly (DFMA) help to min-imize the bumper components in product or assembly tomake easyassembling with optimize xing point [34]. Material should be se-lect according to the required properties or desired problem solu-tion [35]. Materials of the bumper should be light, costcompetitive, accessible, producible, recyclable, and biodegradable.

2.3. Effective parameters in bumper beam energy absorption

Bumper beam acts as a plain simply supported beam. It usuallyxes to the frontal chassis sides to absorb collision energy. Thereare ve bumper system assembling methods for energy absorption

Table 1Finite element preliminary output data.

No. Properties Weight RCP COP CCP

Reverse Cprole

Closed obliqueprole

Curved Cprole

1 Material cost 0.15 24.40 29.00 18.602 Easy

manufacturing0.1 2 1 4

3 Product weight 0.2 2.44 2.9 1.864 Strain energy 0.3 2482.82 43419.92 38825.145 Add rib

possibility0.1 2 1 5

6 Min deection 0.15 16.92 29.86 21.34mounted a bar to link between beams xing points in orderto strengthen the outward motion and energy absorptiontendency [36,37]. Bumper beam is an offset of front bumperfascia to provide a consistent level of protection across thevehicle [38].

(2) Stress concentration: Stress concentration decreases fatiguelife, durability, and energy absorption of the bumper beamin instance loading. Numerical shape optimizations methodcould be employed to decrease stress concentration [39],which is not emphasized in this study. Manufacturing limi-tation cause to cut out some of the beam surface in orderto install the sensors, fog lamps, or make a hole to mountthe beam into the front-end, which makes some tiny crackinto the cutting area, increase the stress concentration anddecrease the performance. Sharp corners and less contactarea in xing points increase the stress concentration, whichshould be modied in design stage [40].

(3) Fixing method: Bumper beam has the main role in caring theweight of the bumper system. Proper xing method couldkeep the bumper system more stable and reliable duringthe energy absorption. Designer usually considers a C-chan-nel prole in frontal chassis to hold the bumper beam orabsorbers in order to increase the xing contact area anddecrease the stress. Additional xing point keeps the bum-per system more consistent, but extends the assembly time.The lateral xing points considered slide shape to let the fas-cia move safely in the desired gap to prevent the bumperside breaking.

(4) Strengthen rib: Strengthen rib increase distortion resistance,rigidity and structural stiffness by less material in slenderwalls [41] and provide the required impact severity [42].Pattern, thickness, tip and end llet of the ribs should bedesigned according to load direction, impact position, mate-rial and manufacturing process. Since the material thickness,increase at the ribs contact area, it causes sink marks; how-ever, this is not important for the bumper beam as non-aesthetic part. Strengthen ribs increase the impact energy

DHP DCC DCP SHP SCP

Double hatprole

Double Cclosed

Double Cprole

Simple hatprole

Simple Cprole

25.50 29.40 25.60 21.90 22.503 2 4 3 5

2.55 2.94 2.56 2.19 2.2576106.53 63671.64 44910.27 47231.52 2137.625 4 5 4 518.34 25.72 21.15 22.92 16.73

developed 3D model were imported to Abaqus Ver16R9 for niteelement analysis (see Fig. 4).

3.2. Low-speed impact simulation, boundary condition and meshing

There are three low-speed impact regulations to check thebumper performance. ECE Regulation No 42 [48], National High-way Trafc Safety Administration (NHTSA) - Code 49 Part 58[49], and Canadian Motor Vehicle Safety Regulation (CMVSR)[50]. Canadian safety regulation has the same limitation and safetydamage as NHTSA (pendulum test 4 km/h of bumper face and2.5 km/h bumper corner), but the speed is double. In this simula-tion method, pendulum with the same car weight tilted in speci-ed angle to make the linear speed 4 km/h at the contactposition. After the test, the lights must work, bonnet, boot, doorsoperate in the normal manner, and all the essential features forsafe operation of the vehicle must still be serviceable.

The block impactor is modeled according to the standard. Thedensity of the pendulum is modied to satisfy cars weight impactforce, which is between 700 and 950 kg for small city car. The blockis pivoted about its top left corner and rotates with 1.6859 rad/s tomake 4 km/h linear speed at contact position. Whole bumper beamconcepts are located at the dened height according to the stan-dard. Both traverse xing points were joined by spring- dampermechanism to their positions in order to tolerate the damping loaduntil car weight. If the load exceeds upon the car weight the bum-

and Design 32 (2011) 48574865 4861by 7% and decrease elongation by 19% [9,11,43]. The opti-mized reinforced ribs presented higher energy absorptionperformance compared with the empty and foam-lledbeams [44].

(5) Material properties: Material behavior, rigidity and ductility,has a great inuence in energy absorption. High rigidityincreases the car protecting capability, but decreases damp-ing capacity and causes impact load transmission to thecompartment. In low impact test, bending strength not letthe beam to go through the plastic region, so the materialshould withstand the impact load and keep their dimen-sional stability to stay intact.

(6) Cross-section: Optimizing cross-section of a bumper beammagnies the strength, dimensional stability and dampingcapability [36]. It has signicant effects in the energy damp-ing rate and bending resistance compare with other param-eters [45,46]. In this research, eight different cross-sectionswere investigated to select the optimum concepts in energyabsorption and deection during the low impact test, alongwith material weight, easy manufacturing, supplement ribpossibility and material cost.

(7) Manufacturing method: Manufacturing method should benalized in design stage. The applied pressure performs bet-ter adhesion between bre and matrix and makes the prod-uct more stable, stiffer, but heavier. Parting line, draft angle,bre direction, product warpage, cooling time, materialshrinkage, and post shrinkage are some effective parametersin selecting manufacturing method. Besides, production rateand material characteristic has a signicant effect in manu-facturing method selection.

(8) Thickness: Increasing the bumper beam thickness improvesthe strength and energy absorption, but it greatly increasesthe weight. However, additional thickness increases thestructural stability; it has some manufacturing limitation,especially in thermoplastic products. The ratio of strengthand weight improve by assigning the optimized thicknessand providing more effective energy absorption [47].

In this study, energy absorption improvement is originated bycross-section, material and manufacturing optimizations, whichhave less effect in weight enhancement, then other parameterssuch as strengthened ribs, and thickness, will be employed.

3. Materials and methods

In the previous studies, the hybrid composite material wasdeveloped and thermoplastic toughening was employed to im-prove the impact property, but it still less than common bumperbeam material GMT. Therefore, geometrical improvement wasused to comply with the dened PDS. This study focused on con-cept selection among eight-bumper beam prole based on six dif-ferent weighted criteria. The process of concept selectionillustrated as follows (see Fig. 3). First, whole concepts modeledand imported to the nite element analysis software, then thelow impact test was accomplished, and along with the result ofother criteria, the selection matrix was performed, and Topsismethod was employed to select the best concept.

3.1. Geometrical 3D model development

The idea of the geometrical 3D model came up with bench-marking different brand of passengers car, patents, industrial de-sign practice and car manufacturer products. Whole 3D concepts

M.M. Davoodi et al. /Materialswere designed in Catia V5R17 software symmetrically as similaras the real bumper beam with the same overall dimensions, i.e.height, breadth, thickness, radius and material model. Next, entireper together with car moves along the impact direction. Table 1shows the cross-section area, volume, number of nodes and ele-ments in each cross-section.

3.3. Topsis conceptual selection method

Six criterias are nominated for eight alternative concepts andspecialist appointed the weighted values are appointed for everycriterion. Topsis is an effective method for multi-criteria deci-sion-making (MCDM). Hwang and Yoon introduced the Topsis

Fig. 5. Strain energy in different cross sections in Abaqus.Fig. 6. The displacement graph of whole concepts.

method based on the idea that the best alternative should have theshortest distance from an ideal solution [51]. The algorithm con-siders ideal and non-ideal solution and help decision maker toevaluate ranking and select the best one. Topsis has been well uti-lized in project selection [52], material selection [53] and otherareas. The procedure of Topsis expressed in following steps:

D

C1 C2 CnA1 x11 x12 x1nA2 x21 x22 x2n... ..

. ... ..

. ...

Am xm1 xm2 xmn

1

W w1;w2; . . . ;wn;where A1, A2, . . ., Am are potential alternatives that decision makersneed to select and C1, C2, . . ., Cn are criterion, which evaluate thealternative performance are calculated, xij is the rating of alternativeAi with respect to criterion Cj when wj is the weight of criterion Cj[54]

(1) Determine the normalized decision matrix.

(2)

(3)

(4) Determine the separation measures, using the n-dimen-sional Euclidean distance. The separation of each alternativefrom the ideal solution is given as:

di Xnj1

v ij vj 2( )1=2

; i 1;2; . . . ;m 5

Similarly, the separation from the negative ideal solution isgiven as:

di Xnj1

v ij vj 2( )1=2

; i 1;2; . . . ;m 6

(5) Determine the relative closeness to the ideal solution. Therelative closeness of the alternative Ai with respect to A+ isdened as:

cli di

di di ;0 6 cli 6 1; i 1;2; . . . ;m 7

(6) Rank the preference order. For ranking alternatives usingthis index and rank alternatives in decreasing order.

Product w0.2

2

2

1.86

2.55

2.94

2.56

2

4862 M.M. Davoodi et al. /Materials and Design 32 (2011) 48574865ated with the cost criterion.

Table 2Evaluation matrix for selecting the best prole concept.

No. Concepts Name Material cost Easy manufacturing0.15 0.1

1 RCP 24.40 2

2 COP 29.00 1

3 CCP 18.60 4

4 DHP 25.50 3

5 DCC 29.40 2

6 DCP 25.60 4

7 SHP 21.90 38A minj

v ijji 2 I maxj

v ijji 2 J ji 1;2; . . . ;m

where I is associated with a benet criterion, and J is associ-A maxj

v ijji 2 I minj

v ijji 2 J ji 1;2; . . . ;n

4Vm1; . . . Vmj; . . . Vmn

where wj is the weight of the ith attribute or criterion, andPnj1wj 1:

Calculate the positive ideal and negative ideal solution:

V ND:Wnn V1i; . . . V1j; . . . V1n

..

. ... ..

.

3nij xijPmj1x

2ij

q ; i 1; . . . ;m; j 1; . . . ; 2Calculate the weighted normalized decision matrix.

SCP 22.50 5 2.19 47231.5 4 22.92.2576106.5 5 18.34

63671.6 4 25.72

44910.3 5 21.1538825.1 5 21.34.44 2482.82 2 16.92

.9 43419.9 1 29.86eight Strain energy Rib possibility Minimum deection0.3 0.1 0.154.1. Impact energy

Low-speed impact test is tested for whole bumper concepts inorder to nd the strain energy (see Fig. 5). The graph shows thatthe concept named double hat prole (DHP) has presented thehighest strain energy.

The longitudinal displacements (X direction) are demonstratedin Fig. 6. It shows the concepts single C prole (SCP) and closed ob-lique prole (COP) have displayed minimum and maximum deec-tion in low impact test respectively.4. Results

The safety parameters along with other PDS criteria are consid-ered as parameters in selecting the bumper beam concepts. Theabsorbed energy and deection are derived from simulated lowimpact test, and other criteria were assessed by scoring by the ex-pert to the converted qualied value to the quantify value andother calculation. The output information made a decision matrixfor selecting the best result by Topsis method to comply with thePDS requirement.2137.62 5 16.73

Table 5Weighted normalized decision matrix.

Material cost Easy manufacturing Product weight Strain energy Rib possibility Maximum deectionMC EM PW SE RP MD

0.05208 0.02182 0.06944 0.00563 0.01709 0.040730.06190 0.01091 0.08254 0.09847 0.00854 0.071870.03970 0.04364 0.05294 0.08805 0.04272 0.051360.05443 0.03273 0.07258 0.17261 0.04272 0.044140.06275 0.02182 0.08367 0.14440 0.03417 0.061910.05464 0.04364 0.07286 0.10185 0.04272 0.050910.04675 0.03273 0.06233 0.10712 0.03417 0.055170.04803 0.05455 0.06404 0.00485 0.04272 0.04027

Table 6The positive and negative ideal solution matrix.

Material cost Easy manufacturing Product weight Strain energy Rib possibility Maximum deection

MC EM PW SE RP MD0.039703 0.054554 0.05294 0.172606 0.042718 0.040270.062756 0.010911 0.08367 0.004848 0.008544 0.07184

Table 7Separation of each alternative from the ideal solution.

RCP COP CCP DHP DCC DCP SHP SCP

0.173306 0.104575 0.085973 0.033072 0.062324 0.076539 0.072094 0.1683310.038462 0.093637 0.105163 0.175352 0.142658 0.110778 0.112176 0.068367

Table 8The relative closeness to the ideal solution.

RCP COP CCP DHP DCC DCP SHP SCP

0.181614 0.472414 0.550201 0.841321 0.695954 0.591394 0.608758 0.288836

Table 3Decision matrix for selecting the concepts of bumber beam.

Subjective weight 0.15 0.1 0.2 0.30.1 0.15 0.15

No. Name Material cost MC Easy manufacturing EM Product weight PW Strain energy SE Rib possibility RP Maximum deection MD

1 RCP 24.4 2 2.44 2462.82 2 16.922 COP 29.0 1 2.90 43419.93 1 29.863 CCP 18.6 4 1.86 38825.14 5 21.344 DHP 25.5 3 2.55 76106.53 5 18.345 DCC 29.4 2 2.94 63671.64 4 25.726 DCP 25.6 4 2.56 44910.27 5 21.157 SHP 21.9 3 2.19 47231.52 4 22.928 SCP 22.5 5 2.25 21371.62 5 16.73

Table 4Normalized matrix.

Material Cost MC Manufacturing EM Product weight SE Strain energy Rib possibility RP Maximum deection MD

0.412682 0.109109 0.41268 0.328248 0.085436 0.479140.264686 0.436436 0.26469 0.293512 0.427179 0.342430.362876 0.327327 0.36288 0.575353 0.427179 0.294290.418374 0.218218 0.41837 0.481347 0.341743 0.412710.364299 0.436436 0.36435 0.339515 0.427179 0.339380.311646 0.327327 0.31165 0.357063 0.341743 0.367780.320185 0.545545 0.32018 0.016162 0.427179 0.26846

M.M. Davoodi et al. /Materials and Design 32 (2011) 48574865 4863

Table 2 shows eight different concepts along with six weightedcriteria. There are two qualitative criteria, easy manufacturing andrib possibility, which have changed to the quantitative in range oneto ve. One in the lowest and ve in the highest possibility as-signed to different concepts. Strain energy and minimum deec-tion have been derived from FEA results. Material estimated costcalculated based on the ingredient and material consumptionscost. Material weight was calculated according to the density ofthe material, which has been found in advance.

4.2. Selecting the best concept by Topsis method

There are three elimination phases to narrow down the possibledesign concepts to the nal concept, named initial screening phase,decision matrix phase and evaluation phase. Decision matrix basedon initial screening was made by eight concepts and six criterion.Material cost, product weight and maximum deection havenegative value, which should consider as a negative value andthe following present the evaluation phase (see Table 3), whereA1, A2, . . ., Am (Rows) are possible alternatives among which deci-sion makers have to choose and C1, C2, . . ., Cn (column) are criteriawith which alternative performance are measured, xij is the rating

strengthening ribs, and thickness. He found that the SMC can be re-

4864 M.M. Davoodi et al. /Materials andplaced by GMT material, while the strengthen rib removed andthickness decreased to 2.5 mm in order to increase 5% deectionto cover enough room after the impact as well as easy productionof alternative Ai with respect to criterion Cj while wj is the weightof criterion Cj. The matrix normalized between 01 to make itdimensionless by formula (see Tables 48).

5. Discussion

According to the automotive safety standards, all passengerscars have to overcome the frontal and rear low-speed impact testwithout any serious damage [9,11,55]. The severity of the barrierimpact load should not deform the bumper far more beyond theplastic region to fail the related parts function. Hosseinzadehet al. [9] compared impact property of the GMT and SMC bumperbeam by changing different parameters, i.e. material, shape,Fig. 7. Displacement prole of double hat prole after impact.6. Conclusions

Impact property of developed toughened hybrid bio-compositematerial did not completely fulll the common bumper beammaterial GMT. Therefore, in this study the geometric concept selec-tion is investigated to enhance structural energy absorption anddeection besides other criteria in the car bumper beam develop-ment. Eight bumper beam concepts with the same material modelunder low impact test standard conditions are simulated. It is con-cluded that proper concept selection has an important role instructural strength, while material is considered as a constant fac-tor. Moreover, it is resulted that bio-based composite material hasa potential to be used in automotive structural components bystructural optimization. The nominated concept (DHP) veried ascompared with some available car bumper beams prole. It pre-sented that the epoxy toughened hybrid kenaf/glass bre compos-ite can be employed in the small-sized car bumper beam.Although, adding strengthened ribs can enhance its performance,it may decrease the required room after impact. Moreover, authorbelieves that the real low impact test should be done to verify thestability of developed hybrid bio-composite material under theproposed concept.

Acknowledgements

The authors wish to thank Universiti Putra Malaysia for thenancial support to carry out this research through ResearchUniversity Fellowship Scheme to the principal author.

Referencesand cost reduction. Marzbanrad, et al. [11] presented 32 mmdeection for four mm thick un-ribbed GMT for big size car. In thisstudy, the deection of different concepts was between 17 to30 mm. The product was un-ribbed with four mm thickness andtest was conducted for small car size condition (700 kg). Since dif-ferent concepts have various contact areas with barrier, the energydamping, and stress distribution is distinctly different. Single CProle and Reversed C Prole present the lowest strain energyand stress because of high contact area, compare with other con-cepts (see Fig. 7).

Conceptual design selection is a systematic approach to evaluatea set of concepts to satisfy the customer needs and engineeringspecications. Edwards, [56] addressed design selection by inter-pretation and use of material test data. He told the designer has tomanipulate the experimental test data, while compared with stan-dard for an optimal design solution with minimal risk. Hoyle,et al. [57] utilized quality function deployment (QFD) and productattribute function deployment (PAFD) process for selecting theconceptual design of the car manifold. PAFD is a decision study toremove the need for the user scores and rankings of performance,priority, and attribute coupling in the QFD. Hambali, et al. [5] usedthe improved analytic hierarchy process (AHP) method to selectthe most appropriate bumper beam concept by expert choice soft-ware and consistency test. He found that the energy absorption asrst criteria and weight, strength and material as second criteriafor selecting the bumper beam concept. Topsis has been well usedin different particular selection areas and in conceptual designselection as well. It selected the Double Hat Prole with 0.841321score as a best concept among eight different concepts. The selectedconcept was conrmed by looking into the real bumper beam pro-le of some car manufacturer such as Peugeot.

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Concept selection of car bumper beam with developed hybrid bio-composite material1 Introduction2 Basic design procedure2.1 Conceptual design of bumper beam2.2 Product design specification (PDS)2.3 Effective parameters in bumper beam energy absorption

3 Materials and methods3.1 Geometrical 3D model development3.2 Low-speed impact simulation, boundary condition and meshing3.3 Topsis conceptual selection method

4 Results4.1 Impact energy4.2 Selecting the best concept by Topsis method

5 Discussion6 ConclusionsAcknowledgementsReferences