Concept Selection of Car Bumper Beam With Developed Hybrid Bio-composite Material

Materials and Design 32 (2011) 4857–4865

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Concept selection of car bumper beam with developed hybrid bio-composite material M.M. Davoodi a,⇑, S.M. Sapuan a, D. Ahmad b, A. Aidy a, A. Khalina b, Mehdi Jonoobi c a

Department of Mechanical and Manufacturing Engineering, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia Department of Biological and Agricultural Engineering, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia c Department of Applied Physics and Mechanical Engineering, Luleå University of Technology, Sweden b

a r t i c l e

i n f o

Article history: Received 10 March 2011 Accepted 7 June 2011 Available online 12 June 2011 Keywords: A. Composite E. Mechanical H. Selection of components

a b s t r a c t Application of natural fibre composites is going to increase in different areas caused by environmental, technical and economic advantages. However, their low mechanical properties have limited their particular application in automotive structural components. Hybridizations with other reinforcements or matrices can improve mechanical properties of natural fibre composite. Moreover, geometric optimizations have a significant role in structural strength improvement. This study focused on selecting the best geometrical bumper beam concept to fulfill the safety parameters of the defined product design specification (PDS). The mechanical properties of developed hybrid composite material were considered in different bumper beam concepts with the same frontal curvature, thickness, and overall dimensions. The low-speed impact test was simulated under the same conditions in Abaqus V16R9 software. Six weighted criteria, which were deflection, strain energy, mass, cost, easy manufacturing, and the rib possibility were analyzed to form an evaluation matrix. Topsis method was employed to select the best concept. It is concluded that double hat profile (DHP) with defined material model can be used for bumper beam of a small car. In addition, selected concept can be strengthened by adding reinforced ribs or increasing the thickness of the bumper beam to comply with the defined PDS. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction Concept optimizations of the car bumper beam can improve structural energy absorption to meet the PDS requirements. Bumper system is composed of three main elements fascia, energy absorber and bumper beam [1] (see Fig. 1). Bumper beam is the major damping structure component in passenger cars. Besides, two energy absorbers damp both the low and high impact energy by elastic deflection between two traverse-fixing points and crushing process respectively [2,3]. Due to safety requirements, in developing the bumper beam, the careful design, optimized structure, high quality and consistent manufacturing must be considered [4]. In addition, bumper beam selection can improve structural energy absorption, material consumption and cost [5]. The previous studies did not completely fulfil the impact strength requirement of the bumper 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 is employed to improve the impact stability of structure [8].

⇑ Corresponding author. Tel.: +60 16 65 65 296; fax: +60 3 8656 7122. E-mail addresses: [email protected], [email protected] (M.M. Davoodi). 0261-3069/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2011.06.011

Conceptual design is the first stage of product development to satisfy customer requirements. Sapuan et al. [1] studied on conceptual design of the automotive bumper system and used the weighted objective method to find the best concept. Hosseinzadeh et al. [9] conducted a research to substitute the high strength SMC with common bumper beam material GMT to improve energy absorption. Furthermore, Davoodi et al. [10] studied about composite elliptical energy absorber for pedestrian impact test with systematic exploitation of proven ideas. Marzbanrad et al. [11] studied about the material, thickness, shape and impact condition of the bumper beam to improve the crashworthiness and lowvelocity impact. He offered to substitute SMC with GMT material to absorb more structural impact. Also, European car manufacturers have done many investigations to expand the application possibilities of natural fibres in automotive industry such as front door linens, rear door linens, boot linens, parcel shelves, seat backs, sunroof sliders, headliners, door-trim panel and trunk liner [12–14]. In fact, the majority of their products are used in aesthetic and semi structural components. Mussig [15] utilized hemp and PTPÒ fibres in a body of bus as reinforcements, a vegetable-based thermoset resin as matrix, and sheet molding compound (SMC) as fabricating method for structural components. Although, the earlier researchers studied on energy absorption of wood for automotive structural

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components [16], few studies have been conducted on application of natural fibre in structural automotive components. This research focused on analyzing, evaluating and selecting the optimum concept among eight different bumper beam concepts, and particularly concentrated on safety purposes of a bumper beam PDS. Based on the National Highway Traffic Safety Administration (NHTSA), car bumper low impact test was simulated by finite element software, Abaqus Ver16R9, to address the highest energy absorption and maximum possible deflection. The same material properties and constant overall dimensions were considered for whole concepts. Finally, decision matrix came up with eight alternatives against six criteria. Topsis method was appointed for selecting the best concept of the bumper beam through eight systematic evaluation processes. It was concluded that Double Hat Profile (DHP) as a best concept. Moreover, this study demonstrated the feasibility of the finite element analysis in selecting the best structural concepts to overcome the weak inherent properties of natural fibre, and to get better mechanical performance for automotive structural application.

Fig. 1. Bumper system components.

2. Basic design procedure 2.1. Conceptual design of bumper beam The preliminary stage of product development start with conceptual design, which is derived from customer requirement ‘‘voice of the customer’’ [17,18] to find a solution to satisfy the functional design problems [19]. Imprecise engineering calculation, design and material selection, might increase up to 70% the total product cost for redesigning [20]. Designer has to select the most suitable idea from different possible solutions or combination of material selection and component design to meet the desired PDS in each design stage to decrease the rework expense [21–25].Therefore, many tools are developed to evaluate design concept selection (DCS) and compromise different effective factors, i.e. customer requirements, designer intentions and market desire. Decision matrix-based methods, offer the qualitative comparison such as Pugh’s method [23] or quality function deployment (QFD) [26]. Fuzzy ANP-based, evaluate a set of conceptual design alternatives to satisfy both customer satisfaction and engineering specifications [27]. Analytical Hierarchy Process (AHP) is a mathematically based technique for analyzing complex situations, which were sophisticated in its simplicity [28]. Multi criteria decisionmaking (MCDM) is an effective method for single selection among mixed criteria. Multi-attribute decision-making technique (MADM) is a conflicting preferences’ solution among criteria for single decision makers’. Topsis is well suited technique to dealing with multi attribute or multi-criteria decision-making (MADM/ MCDM) problems in real world ideal solutions [29]. Its method is based on ‘‘chosen alternative has shortest distance from positive ideal solution and farthest distance from negative ideal solution’’. It helps to organize problems, compare, and rank alternatives to carry out the analysis for better options [30]. This method has been appointed to select the best concept in this research.

Fig. 2. Selected parameters for bumper beam PDS.

M.M. Davoodi et al. / Materials and Design 32 (2011) 4857–4865

2.2. Product design specification (PDS) To perform the customer requirements and expectation to a detailed technical document called PDS [31]. It is quite difficult to finish the exact PDS in the early stage of product development, while the knowledge of design requirements is imprecise and incomplete [32]. PDS originates by disorganized brainstorming team with various proficiency, i.e. manufacturing, designing, selling, assembling, maintaining, and might be improved due to new product changes and manufacturing limitations. Safety was the main goal among different bumper PDS specification in this study. Bumper beam PDS consisted of safety, performance, weight, size, cost, environment issue, appearance (see Fig. 2). Whole PDS parameters can be classified into three main subdivisions such as material, manufacturing and design. Since energy absorption of different concept is the core competency of this study, it is emphasized in the PDS safety parameters. Some of the mechanical and physical properties’ values are received from experimental results and others from existing PDS data.

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Safety: There are different bumper safety regulations for passenger’s car, issued by safety organization, insurance companies or original equipment manufacturer (OEM) [33]. Insurance companies usually offer more severe conditions in order to decrease their own costs. This study follows safety criteria of the European car manufacturer. (1) Low impact test: Longitudinal pendulum impact test by 4.0 km/h (2.5 mph), and corner pendulum impact test by 2.4 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 flat, rigid barrier. (3) Pedestrian impact test: In this test, a ‘‘leg-form’’ impactor is propelled toward a stationary vehicle at a velocity of 40 km/ h (25 mph) parallel to the vehicles longitudinal axis. The test can be performed at any location across the face of the vehicle, between the 30° bumper corners. So the impact criteria for 2010 should be a < 150 g and the shear d < 6 mm and bending a < 15°

Fig. 3. Bumper beam conceptual selection flowchart.

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

Fig. 4. Overall dimensions of different concepts.

Since material development and its manufacturing method are discussed in the previous study, this research emphasizes on design parameters in PDS. Size: Dimension of the bumper beam depends on energy absorption value, which related to car size and weight. Maintenance: Design for assembly (DFA) and design for manufacturing (DFM) should consider during product design. Performance: The defined goal of the product should be attainable [23]. Installation: Design for manufacturing and assembly (DFMA) help to minimize the bumper components in product or assembly to make easy assembling with optimize fixing point [34]. Material should be select according to the required properties or desired problem solution [35]. Materials of the bumper should be light, cost competitive, accessible, producible, recyclable, and biodegradable. 2.3. Effective parameters in bumper beam energy absorption Bumper beam acts as a plain simply supported beam. It usually fixes to the frontal chassis sides to absorb collision energy. There are five bumper system assembling methods for energy absorption

(1) Frontal curvature: Frontal curvature increases the room between fixing points and top extremity beam curvature. It strengthens the beam stability, and extends the required collision displacement. Besides, the aesthetic purposes, the curve facilitates better load impact distribution through the frontal beam and fixing points during energy damping process. When the impact load applied to the bumper, the beam initial curvature intends to remove. So, some designer mounted a bar to link between beam’s fixing points in order to strengthen the outward motion and energy absorption tendency [36,37]. Bumper beam is an offset of front bumper fascia to provide a consistent level of protection across the vehicle [38]. (2) Stress concentration: Stress concentration decreases fatigue life, durability, and energy absorption of the bumper beam in instance loading. Numerical shape optimizations method could be employed to decrease stress concentration [39], which is not emphasized in this study. Manufacturing limitation cause to cut out some of the beam surface in order to install the sensors, fog lamps, or make a hole to mount the beam into the front-end, which makes some tiny crack into the cutting area, increase the stress concentration and decrease the performance. Sharp corners and less contact area in fixing points increase the stress concentration, which should be modified in design stage [40]. (3) Fixing method: Bumper beam has the main role in caring the weight of the bumper system. Proper fixing method could keep the bumper system more stable and reliable during the energy absorption. Designer usually considers a C-channel profile in frontal chassis to hold the bumper beam or absorbers in order to increase the fixing contact area and decrease the stress. Additional fixing point keeps the bumper system more consistent, but extends the assembly time. The lateral fixing points considered slide shape to let the fascia move safely in the desired gap to prevent the bumper side breaking. (4) Strengthen rib: Strengthen rib increase distortion resistance, rigidity and structural stiffness by less material in slender walls [41] and provide the required impact severity [42]. Pattern, thickness, tip and end fillet of the ribs should be designed according to load direction, impact position, material and manufacturing process. Since the material thickness, increase at the rib’s contact area, it causes sink marks; however, this is not important for the bumper beam as nonaesthetic part. Strengthen ribs increase the impact energy

Table 1 Finite element preliminary output data. No.

1 2 3 4 5 6

Properties

Material cost Easy manufacturing Product weight Strain energy Add rib possibility Min deflection

Weight

RCP

COP

CCP

DHP

DCC

DCP

SHP

SCP

Reverse C profile

Closed oblique profile

Curved C profile

Double hat profile

Double C closed

Double C profile

Simple hat profile

Simple C profile

0.15 0.1

24.40 2

29.00 1

18.60 4

25.50 3

29.40 2

25.60 4

21.90 3

22.50 5

0.2 0.3 0.1

2.44 2482.82 2

2.9 43419.92 1

1.86 38825.14 5

2.55 76106.53 5

2.94 63671.64 4

2.56 44910.27 5

2.19 47231.52 4

2.25 2137.62 5

0.15

16.92

29.86

21.34

18.34

25.72

21.15

22.92

16.73

M.M. Davoodi et al. / Materials and Design 32 (2011) 4857–4865

(5)

(6)

(7)

(8)

by 7% and decrease elongation by 19% [9,11,43]. The optimized reinforced ribs presented higher energy absorption performance compared with the empty and foam-filled beams [44]. Material properties: Material behavior, rigidity and ductility, has a great influence in energy absorption. High rigidity increases the car protecting capability, but decreases damping capacity and causes impact load transmission to the compartment. In low impact test, bending strength not let the beam to go through the plastic region, so the material should withstand the impact load and keep their dimensional stability to stay intact. Cross-section: Optimizing cross-section of a bumper beam magnifies the strength, dimensional stability and damping capability [36]. It has significant effects in the energy damping rate and bending resistance compare with other parameters [45,46]. In this research, eight different cross-sections were investigated to select the optimum concepts in energy absorption and deflection during the low impact test, along with material weight, easy manufacturing, supplement rib possibility and material cost. Manufacturing method: Manufacturing method should be finalized in design stage. The applied pressure performs better adhesion between fibre and matrix and makes the product more stable, stiffer, but heavier. Parting line, draft angle, fibre direction, product warpage, cooling time, material shrinkage, and post shrinkage are some effective parameters in selecting manufacturing method. Besides, production rate and material characteristic has a significant effect in manufacturing method selection. Thickness: Increasing the bumper beam thickness improves the strength and energy absorption, but it greatly increases the weight. However, additional thickness increases the structural stability; it has some manufacturing limitation, especially in thermoplastic products. The ratio of strength and weight improve by assigning the optimized thickness and providing more effective energy absorption [47].

developed 3D model were imported to Abaqus Ver16R9 for finite element analysis (see Fig. 4). 3.2. Low-speed impact simulation, boundary condition and meshing There are three low-speed impact regulations to check the bumper performance. ECE Regulation No 42 [48], National Highway Traffic Safety Administration (NHTSA) - Code 49 Part 58 [49], and Canadian Motor Vehicle Safety Regulation (CMVSR) [50]. Canadian safety regulation has the same limitation and safety damage as NHTSA (pendulum test 4 km/h of bumper face and 2.5 km/h bumper corner), but the speed is double. In this simulation method, pendulum with the same car weight tilted in specified angle to make the linear speed 4 km/h at the contact position. After the test, the lights must work, bonnet, boot, doors operate in the normal manner, and all the essential features for safe operation of the vehicle must still be serviceable. The block impactor is modeled according to the standard. The density of the pendulum is modified to satisfy car’s weight impact force, which is between 700 and 950 kg for small city car. The block is pivoted about its top left corner and rotates with 1.6859 rad/s to make 4 km/h linear speed at contact position. Whole bumper beam concepts are located at the defined height according to the standard. Both traverse fixing points were joined by spring- damper mechanism to their positions in order to tolerate the damping load until car weight. If the load exceeds upon the car weight the bumper together with car moves along the impact direction. Table 1 shows the cross-section area, volume, number of nodes and elements in each cross-section. 3.3. Topsis conceptual selection method Six criteria’s are nominated for eight alternative concepts and specialist appointed the weighted values are appointed for every criterion. Topsis is an effective method for multi-criteria decision-making (MCDM). Hwang and Yoon introduced the Topsis

In this study, energy absorption improvement is originated by cross-section, material and manufacturing optimizations, which have less effect in weight enhancement, then other parameters such as strengthened ribs, and thickness, will be employed. 3. Materials and methods In the previous studies, the hybrid composite material was developed and thermoplastic toughening was employed to improve the impact property, but it still less than common bumper beam material GMT. Therefore, geometrical improvement was used to comply with the defined PDS. This study focused on concept selection among eight-bumper beam profile based on six different weighted criteria. The process of concept selection illustrated as follows (see Fig. 3). First, whole concepts modeled and imported to the finite element analysis software, then the low impact test was accomplished, and along with the result of other criteria, the selection matrix was performed, and Topsis method was employed to select the best concept.

Fig. 5. Strain energy in different cross sections in Abaqus.

3.1. Geometrical 3D model development The idea of the geometrical 3D model came up with benchmarking different brand of passenger’s car, patents, industrial design practice and car manufacturer products. Whole 3D concepts were designed in Catia V5R17 software symmetrically as similar as the real bumper beam with the same overall dimensions, i.e. height, breadth, thickness, radius and material model. Next, entire

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Fig. 6. The displacement graph of whole concepts.

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method based on the idea that the best alternative should have the shortest distance from an ideal solution [51]. The algorithm considers ideal and non-ideal solution and help decision maker to evaluate ranking and select the best one. Topsis has been well utilized in project selection [52], material selection [53] and other areas. The procedure of Topsis expressed in following steps:

A1 D ¼ A2 .. . Am

C1 x11 x21 .. . xm1

C2 x12 x22 .. . xm2

   .. . 

(4) Determine the separation measures, using the n-dimensional Euclidean distance. The separation of each alternative from the ideal solution is given as:

diþ ¼

( n  X

v ij  v þj

2

)1=2

;

i ¼ 1; 2; . . . ; m

ð5Þ

j¼1

Similarly, the separation from the negative ideal solution is given as:

Cn x1n x2n .. . xmn

ð1Þ di ¼

( )1=2 n X ðv ij  v j Þ2 ;

i ¼ 1; 2; . . . ; m

ð6Þ

j¼1

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

W ¼ ½w1 ; w2 ; . . . ; wn ; where A1, A2, . . ., Am are potential alternatives that decision makers need to select and C1, C2, . . ., Cn are criterion, which evaluate the alternative performance are calculated, xij is the rating of alternative Ai with respect to criterion Cj when wj is the weight of criterion Cj [54] (1) Determine the normalized decision matrix.

cliþ ¼

di ; 0 6 cliþ 6 1; ðdiþ þ di Þ

i ¼ 1; 2; . . . ; m

ð7Þ

(6) Rank the preference order. For ranking alternatives using this index and rank alternatives in decreasing order. 4. Results

xij nij ¼ qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Pm 2 ; j¼1 xij

i ¼ 1; . . . ; m;

j ¼ 1; . . . ;

ð2Þ

(2) Calculate the weighted normalized decision matrix.

V ¼ ND :W nn

   V 1i ; . . . V 1j ; . . . V 1n     .. .. ..  ¼ . . .   V ;... V ;... V  m1 mn mj

ð3Þ

where wj is the weight of the ith attribute or criterion, and Pn j¼1 wj ¼ 1: (3) Calculate the positive ideal and negative ideal solution:

    Aþ ¼ max v ij ji 2 I min v ij ji 2 J ji ¼ 1; 2; . . . ; n j j      min v ij ji 2 I max v ij ji 2 J ji ¼ 1; 2; . . . ; m A ¼ j

ð4Þ

j

where I is associated with a benefit criterion, and J is associated with the cost criterion.

The safety parameters along with other PDS criteria’ are considered as parameters in selecting the bumper beam concepts. The absorbed energy and deflection are derived from simulated low impact test, and other criteria were assessed by scoring by the expert to the converted qualified value to the quantify value and other calculation. The output information made a decision matrix for selecting the best result by Topsis method to comply with the PDS requirement. 4.1. Impact energy Low-speed impact test is tested for whole bumper concepts in order to find the strain energy (see Fig. 5). The graph shows that the concept named double hat profile (DHP) has presented the highest strain energy. The longitudinal displacements (X direction) are demonstrated in Fig. 6. It shows the concepts single C profile (SCP) and closed oblique profile (COP) have displayed minimum and maximum deflection in low impact test respectively.

Table 2 Evaluation matrix for selecting the best profile concept. No.

Concepts

Name

Material cost 0.15

Easy manufacturing 0.1

Product weight 0.2

1

RCP

24.40

2

2.44

2

COP

29.00

1

2.9

3

CCP

18.60

4

4

DHP

25.50

5

DCC

6

Strain energy 0.3

Rib possibility 0.1

Minimum deflection 0.15

2

16.92

43419.9

1

29.86

1.86

38825.1

5

21.34

3

2.55

76106.5

5

18.34

29.40

2

2.94

63671.6

4

25.72

DCP

25.60

4

2.56

44910.3

5

21.15

7

SHP

21.90

3

2.19

47231.5

4

22.92

8

SCP

22.50

5

2.25

5

16.73

2482.82

2137.62

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M.M. Davoodi et al. / Materials and Design 32 (2011) 4857–4865 Table 3 Decision 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 deflection MD

1 2 3 4 5 6 7 8

RCP COP CCP DHP DCC DCP SHP SCP

24.4 29.0 18.6 25.5 29.4 25.6 21.9 22.5

2 1 4 3 2 4 3 5

2.44 2.90 1.86 2.55 2.94 2.56 2.19 2.25

2462.82 43419.93 38825.14 76106.53 63671.64 44910.27 47231.52 21371.62

2 1 5 5 4 5 4 5

16.92 29.86 21.34 18.34 25.72 21.15 22.92 16.73

Table 4 Normalized matrix. Material Cost MC

Manufacturing EM

Product weight SE

Strain energy

Rib possibility RP

Maximum deflection MD

0.412682 0.264686 0.362876 0.418374 0.364299 0.311646 0.320185

0.109109 0.436436 0.327327 0.218218 0.436436 0.327327 0.545545

0.41268 0.26469 0.36288 0.41837 0.36435 0.31165 0.32018

0.328248 0.293512 0.575353 0.481347 0.339515 0.357063 0.016162

0.085436 0.427179 0.427179 0.341743 0.427179 0.341743 0.427179

0.47914 0.34243 0.29429 0.41271 0.33938 0.36778 0.26846

Table 5 Weighted normalized decision matrix. Material cost MC

Easy manufacturing EM

Product weight PW

Strain energy SE

Rib possibility RP

Maximum deflection MD

0.05208 0.06190 0.03970 0.05443 0.06275 0.05464 0.04675 0.04803

0.02182 0.01091 0.04364 0.03273 0.02182 0.04364 0.03273 0.05455

0.06944 0.08254 0.05294 0.07258 0.08367 0.07286 0.06233 0.06404

0.00563 0.09847 0.08805 0.17261 0.14440 0.10185 0.10712 0.00485

0.01709 0.00854 0.04272 0.04272 0.03417 0.04272 0.03417 0.04272

0.04073 0.07187 0.05136 0.04414 0.06191 0.05091 0.05517 0.04027

Table 6 The positive and negative ideal solution matrix. Material cost

Easy manufacturing

Product weight

Strain energy

Rib possibility

Maximum deflection

MC 0.039703 0.062756

EM 0.054554 0.010911

PW 0.05294 0.08367

SE 0.172606 0.004848

RP 0.042718 0.008544

MD 0.04027 0.07184

Table 7 Separation of each alternative from the ideal solution. RCP

COP

CCP

DHP

DCC

DCP

SHP

SCP

0.173306 0.038462

0.104575 0.093637

0.085973 0.105163

0.033072 0.175352

0.062324 0.142658

0.076539 0.110778

0.072094 0.112176

0.168331 0.068367

Table 8 The 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

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Table 2 shows eight different concepts along with six weighted criteria. There are two qualitative criteria, easy manufacturing and rib possibility, which have changed to the quantitative in range one to five. One in the lowest and five in the highest possibility assigned to different concepts. Strain energy and minimum deflection have been derived from FEA results. Material estimated cost calculated based on the ingredient and material consumption’s cost. Material weight was calculated according to the density of the 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 possible design concepts to the final concept, named initial screening phase, decision matrix phase and evaluation phase. Decision matrix based on initial screening was made by eight concepts and six criterion. Material cost, product weight and maximum deflection have negative value, which should consider as a negative value and the following present the evaluation phase (see Table 3), where A1, A2, . . ., Am (Rows) are possible alternatives among which decision makers have to choose and C1, C2, . . ., Cn (column) are criteria with which alternative performance are measured, xij is the rating of alternative Ai with respect to criterion Cj while wj is the weight of criterion Cj. The matrix normalized between 0–1 to make it dimensionless by formula (see Tables 4–8). 5. Discussion According to the automotive safety standards, all passenger’s cars have to overcome the frontal and rear low-speed impact test without any serious damage [9,11,55]. The severity of the barrier impact load should not deform the bumper far more beyond the plastic region to fail the related parts’ function. Hosseinzadeh et al. [9] compared impact property of the GMT and SMC bumper beam by changing different parameters, i.e. material, shape, strengthening ribs, and thickness. He found that the SMC can be replaced by GMT material, while the strengthen rib removed and thickness decreased to 2.5 mm in order to increase 5% deflection to cover enough room after the impact as well as easy production

and cost reduction. Marzbanrad, et al. [11] presented 32 mm deflection for four mm thick un-ribbed GMT for big size car. In this study, the deflection of different concepts was between 17 to 30 mm. The product was un-ribbed with four mm thickness and test was conducted for small car size condition (700 kg). Since different concepts have various contact areas with barrier, the energy damping, and stress distribution is distinctly different. Single C Profile and Reversed C Profile present the lowest strain energy and stress because of high contact area, compare with other concepts (see Fig. 7). Conceptual design selection is a systematic approach to evaluate a set of concepts to satisfy the customer needs and engineering specifications. Edwards, [56] addressed design selection by interpretation and use of material test data. He told the designer has to manipulate the experimental test data, while compared with standard for an optimal design solution with minimal risk. Hoyle, et al. [57] utilized quality function deployment (QFD) and product attribute function deployment (PAFD) process for selecting the conceptual design of the car manifold. PAFD is a decision study to remove the need for the user scores and rankings of performance, priority, and attribute coupling in the QFD. Hambali, et al. [5] used the improved analytic hierarchy process (AHP) method to select the most appropriate bumper beam concept by expert choice software and consistency test. He found that the energy absorption as first criteria and weight, strength and material as second criteria for selecting the bumper beam concept. Topsis has been well used in different particular selection areas and in conceptual design selection as well. It selected the Double Hat Profile with 0.841321 score as a best concept among eight different concepts. The selected concept was confirmed by looking into the real bumper beam profile of some car manufacturer such as Peugeot. 6. Conclusions Impact property of developed toughened hybrid bio-composite material did not completely fulfill the common bumper beam material GMT. Therefore, in this study the geometric concept selection is investigated to enhance structural energy absorption and deflection besides other criteria in the car bumper beam development. Eight bumper beam concepts with the same material model under low impact test standard conditions are simulated. It is concluded that proper concept selection has an important role in structural strength, while material is considered as a constant factor. Moreover, it is resulted that bio-based composite material has a potential to be used in automotive structural components by structural optimization. The nominated concept (DHP) verified as compared with some available car bumper beams profile. It presented that the epoxy toughened hybrid kenaf/glass fibre composite 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, author believes that the real low impact test should be done to verify the stability of developed hybrid bio-composite material under the proposed concept. Acknowledgements The authors wish to thank Universiti Putra Malaysia for the financial support to carry out this research through Research University Fellowship Scheme to the principal author. References

Fig. 7. Displacement profile of double hat profile after impact.

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