J. Cent. South Univ. (2020) 27: 64-75

DOI: https://doi.org/10.1007/s11771-020-4278-1

Conceptual design of oil palm fibre reinforced polymer hybrid composite automotive crash box using integrated approach

N S B YUSOF^{1, 2}, S M SAPUAN^{1, 3}, M T H SULTAN^{1, 4}, M JAWAID¹

1. Laboratory of Biocomposite Technology, Institute of Tropical Forestry and Forest Products (INTROP), Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia;

2. Faculty of Information Sciences and Engineering, Management and Science University,Seksyen 13, 40100 Shah Alam, Selangor, Malaysia;

3. Advanced Engineering Materials and Composites Research Centre, Department of Mechanical and Manufacturing Engineering, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia;

4. Department of Aerospace Engineering, Universiti Putra Malaysia, 43400 UPM Serdang,Selangor, Malaysia

Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020

Abstract:

A hybrid conceptual design approach was introduced in this study to develop a conceptual design of oil palm polymer composite automotive crash box (ACB). A combination of theory of inventive problem solving (TRIZ), morphological charts and biomimetics was applied where the foremost requirements in terms of the material characteristics, function specifications, force identification, root cause analysis, geometry profile and design selection criteria were considered. The strategy was to use creations of nature to inspire five innovative conceptual designs of the ACB structure and the AHP method was applied to perform the pairwise analysis of selecting the best ACB conceptual design. A new conceptual design for a composite ACB was conceived bearing in mind the properties of natural fibre, unlike those of conventional materials such as steel alloys and aluminium alloys. The design with the highest ranking (26.6 %) was chosen as the final conceptual design, which was the one with a honeycomb structure for the outermost profile, reinforced with a spider web structure inside the part, supported by fibre foam structure extracted from the woodpecker sponge tissue at the centre to maximize the energy absorption capability. The new design could solve the problem of bending collapse which is a major cause of failure to absorb maximum impact energy for ACB during collision. However, the final conceptual design will still need several modifications for production and assembly purposes, which will be completed in a further study.

Key words:

conceptual design; automotive crash box; hybrid method; concept selection method；

Cite this article as:

N S B YUSOF, S M SAPUAN, M T H SULTAN, M JAWAID. Conceptual design of oil palm fibre reinforced polymer hybrid composite automotive crash box using integrated approach [J]. Journal of Central South University, 2020, 27(1): 64-75.

1 Introduction

Automotive crash box (ACB) is a part of crashworthy systems mounted in between a car beam and front rail. The crash box is designed to collapse while absorbing crash energy prior to collapse of other car body parts so that the physical damage to the cockpit of the occupant is minimized, thereby saving passengers [1].

Crash boxes are expected to collapse axially throughout crash deformation in order to have optimum performance [2, 3]. Currently, most researchers investigate the performance of a few basic cross-sections or the best profile shape for crash boxes which consistently use aluminium alloy or steel as a shown in Figure 1.

Figure 1 Automotive crash box design from different manufacturing companies [4]

DEMIRCI and YILDIZ [5] are researchers who actively perform research in crashworthiness and vehicle crash structural areas. They found that the geometry of ACB, number of spot welds, position of welding and the sheet metal thickness provided a significant effect on energy absorption performance, weight and manufacturing cost. Additionally, YILDIZ et al [6] also investigated the performance of vehicles using thin wall structures by using a hybrid optimization algorithm based on a gravitational search algorithm and the Nelder-Mead algorithm method. YILDIZ and SOLANKI [7] had introduced s particle swarm-based optimization method to produce the best structure capable of absorbing high crash energy. DEMIRCI and YILDIZ [8] also proposed a hybrid approach called hybrid gradient analysis (HGA) for the evaluation of both convex and concave constraint functions in reliability-based design optimization (RBDO). FUGANTI et al [9] used an aluminium foam square hollow double layer as a new ACB design to improve the energy absorbing efficiency. TOKSOY et al [10] used rectangular shell aluminium sheet alloy when analyzing the performance of ACB when using fully and partially-filled foam boxes as well as empty boxes relative to the material density. TANLAK et al [11] used 6061-T6 aluminium alloy and a honeycomb profile when observing ACB shape optimization under high impact frontal collision. Many believed that aluminium and steel materials with the correct cross-sectional profile could provide high energy absorption to an ACB. However, usage of metals such as aluminium and steel can negatively affect the environment during the extraction processes, particularly during the potential releasing of toxic gas, liquid and solid emissions [12, 13].

Thus, the implementation of a systematic approach in this paper could guarantee the excellent performance of the new design, particularly that it would not be affected by the aggressive approach. Therefore, in this study, the new ACB conceptual idea of geometry profile will be produced by introducing a hybrid method of TRIZ and biomimetics. Additionally, this paper highlights that the using of oil palm polymer composite material instead of aluminium and steel, which evidently produces low emissions of toxic fumes at the end of its life cycle, has recyclability features, is lightweight and is an economical material source [14, 15]. Finally, the AHP method will enable selection of the best ACB conceptual design.

2 Design brief

The importance of existing studies is to provide a guideline for the researchers in satisfying the standards and regulations stated in ACB product design specifications (PDS). The other important element of PDS is to provide geometry limitation guidelines to ACB geometry profiles. This is very important to determine the dimensions of a crash box, which should be long enough to offer sufficient deformation to dissipate more energy collisions, but should not occupy too much space before the deformation as it would gain more weight and reduce the product value from an economical point of view [16]. Apart from that, the information from PDS can be used as a reference to produce a product density lower than 0.19 g/cm³; material selection must be environmentally friendly and have biodegradable capability. Additionally, the ACB design must also fulfil the requirements regarding pedestrian protection as stated in National Highway Traffic Safety Administration (NHTSA) regulations, which propose strength requirements of the frontal structure in FMVSS Part 581 tests and FMVSS Part 208 mandatory testing for frontal impact. Moreover, the design must also consider the standards launched by the East European Constitutional Review (ECER) 42 and United Nation Economic Commission for Europe/Working Party 29(UNECE/WP29) and Research Council for Automobile Repairs (RCAR) test, which have established global technical regulations (GTR_S) for frontal impact structure and pedestrian safety. Finally, the new ACB design must be able to absorb more than a minimum energy of 1826 J, the plate thickness must be between 1.8 mm and 3 mm, the length of each side of hexagonal geometry must be 140 mm and the length of other shape must be in the range of 120 mm to 300 mm as shown in Table 1.

Table 1 Summary of product design specification for ACB [17-29]

3 Methodology

In engineering design, numerous design elements should be considered to satisfy the aim of product design quality [30, 31]. In this study, the design elements for ACB had been decided earlier in the design process to ensure that the design engineer would be able to produce a product which could fulfil the design objective as shown in Figure 2. The figure shows five design elements which have been determined before commencement of conceptual design, where one of the elements is material, as it will affect the properties of product, product performance and product manufacturability. Additionally, the shape of the product, also known as product geometry, is required to be identified as it will specify the product structure, the impact force applied to the product as well as the product functionality. Furthermore, by understanding cause and effect of product failure or product failure characteristics, it could guide and direct the designer to the exact problems of ACB design. Hence, it will help them to compute the most appropriate ACB geometry profile which suits the PDS without decreasing existing product quality.

Figure 2 Elements of ACB conceptual design

Generation of the concept was not a straight forward process. Figure 3 shows that the conceptual design generation phase began with the problem definition, followed by the process of determining the most appropriate material to be used in ACB design, which had already been described in a previous section. Then, the functional analysis diagram (FAD) had been developed to increase the understanding for the specific function of the product elements where a critical area in a design was highlighted and each of useful, harmful and useless functions had been identified. Next, impact forces acting on the ACB needed to be applied in order to recognise their fundamental operation. Subsequently, cause and effect analysis had to be performed in order to investigate the root cause of the problem. A few proposed new designs of ACB could be developed by using a hybrid method of TRIZ, morphological charts and biomimetics. Finally, analytic hierarchy process (AHP) was used to select the best new ACB design.

Figure 3 Process of conceptual design generation

4 Results and discussion

This section presents the problem definition of the study, material selection used for this case study, functional analysis diagramresults, impact force or failure analysis to determine how the forces would damage the ACB design, root cause analysis to understand the cause and effect of design element onthe ACB design and final geometry profile for the ACB [32].

4.1 Problem definition

Carbon fibre or glass reinforced compositeshavebeen proposed as alternative materials to fabricate ACB sdue to weight reduction and good mechanical properties [33]. However, poor recycling behaviour as well aspotentially hazardous effects to humans and the environment as a result of these particles have pushed natural fibre to be nominated as an alternative reinforcement material in the field of automotive component design. Additionally, recent awareness of the need for products which are environmentally friendly and sustainablehave proven that natural fibre reinforced composite (NFRC) could be an appropriate material to substitute aluminium and steel in terms of weight reduction. Furthermore, the properties of the material could be altered since the fibre orientation could be modified in the direction of principal stress to obtain higher structural productivity. In addition, the substitution of metal-based materials with NFRC materials offers more advantages based on high availability of raw materials and reduces the production cost, since the raw material is also relatively cheap [34]. Another advantage of using natural fibre compared with synthetics fibres is that natural fibre is fully biodegradable and less energy is consumed during the production process.

4.2 Material selection

During the materials selection process, an integrated analytic hierarchy process and 6 sigma method (AHP-6σ) were used. The AHP-6σ method follows five major steps of filtration before proposing the best natural fibre as reinforcement for the ACB design. These steps are: define, measure, analyse, improve and control (DMAIC). Following the final step of control, oil palm fibres had been decided as the best natural fibre for the ACB design. However, the process of material selection has not been included within the scope of this paper. The details of the material selection process will be explained in a following research paper.

4.3 Functional analysis

Functional analysis diagram (FAD) was selected to identify the functions of components in order to determine the real problem of the existing ACB design. FAD offers a systematic approach for technical problem solving by analysing the contact between parts. Additionally, FAD is able to visualize specific functions for each part of the ACB assembly which contributes to the crashworthiness management. The data from the analysis is also used to describe a product, the functions of the product and how its component elements will perform, specifically whether they functioned excessively, inadequately or normally [35].

As observed in Figure 4, all six components used for crashworthiness management were connected by using screws to hold them at their designated locations. During the collision, the first component hit by the impact force was the bumper fascia which had been purposely designed to absorb kinetic energy in a minor collision, where the function of a bumper fascia is to transfer that kinetic energy to the energy absorber, which would reduce impact to pedestrians [36]. The function of an energy absorber is to absorb minor collision energy by collapsing or crushing, thus reducing physical damage to the vehicle structure during low speed collision. Next, the bumper beam will absorb the bulk of kinetic energy and provide protection to the rest of the vehicle during low speed collisions below 16 km/h [18, 19]. Then, crash boxes were installed in between the bumper beam and the front rail. The main function of an ACB is to absorb maximum impact energy during low speed collisions below 16 km/h, or to transfer the minimum impact energy to the front rail to reduce a fatal damage to the expensive-to-repair parts like fenders, hoods, intercoolers and radiators as well as to save the occupants in the cockpit during high speed collisions [37, 38]. The function of crash boxes during receiving and transferring of the impact energy during collision could be refined, where that process has been represented by the dotted function arrow to indicate an inadequate function. Finally, the front rail will hold the crash box, these two parts connected by screws to provide protection to occupants during the crashing process. The front rail is a main component to absorb energy during high speed collisions, where this part is usually welded to the cockpit to protect the occupant [39].

Figure 4 Function model of automotive crash box ACB

4.4 Impact force identification

NAKAZAWA et al [40] used the concept of force analysis to explain how to recover the impact energy absorbedor how to obtain an axial collapse, which were based on three vital points:high buckling load at the ridge lines, minimization of buckling cycle time and minimization of load fluctuation. Free body diagram (FBD) as shown in Figure 5 illustrates the collapsing process for ACB during the collision. The folding process begins at a certain compression area of the ridge line. That compression area would then result in plastic buckling, or also known as wrinkling. The wrinkle would then fold and create another wrinkle at the ridge line under the earlierwrinkle. From the beginning of the collapse, the load would continuously grow until it reaches the supreme value point. The load would then return back to the lowest value once the wrinkle folds absolutely, where the subsequent deformation would repeat via the same process, producing fluctuating loads throughout the collapse, hence providing an axial collapse.

Figure 5 Impact force transferprocess during collision

4.5 Root cause analysis

Figure 6 presents a root cause analysis which is a structured process to assist in identifying fundamental aspects or causes of an adverse event. Understanding the causal failure factors can help develop corrective actions. The main task for the ACB is to absorb maximum energy during collisions, where the first cause identified for analysis to increase energy absorption level is the way the ACB collapses during absorption of the energy. The ACB must collapse in an axial direction, as opposed to acollapse in bending mode which could form a local hinge to the ACB. Wrong selection of cross section geometry would lead to premature buckling and loss of energy absorption [41, 42]. Selection of heavy materials such as steel and iron with low toughness properties could reduce the energy absorption capability for an ACB. LUKASZEWICZ [42] evidently proved it using specific energy absorption formula:

where W is total absorbed energy, which increases when alower material density (ρ) and small cross section (A) are used, multiplied by total crush displacement (δ). Therefore, materials recommended for use in this ACB design are aluminium alloy, synthetic composites and natural fibre composites. However, to add value to the ACB design, oil palm polymer composite, which is an environmentally friendly material with high biodegradable capability, will be used to fabricate this ACB design. Additionally, to obtain the maximum energy absorption for the ACB design, all design standards as well as rules and regulations of crashworthiness must be fulfilled while concurrently, engineering with a systematic approach must be selected. This could help in selecting the best ACB design, resulting in shortened product development time and improved productivity as well as reducing production costs [43, 44].

Figure 6 Fish bone diagram for ACB conceptual design root cause analysis

4.6 Stage 1: Geometry specification using an integrated method of TRIZ, morphological charts and biomimetics

Table 2 shows the TRIZ contradiction matrix developed with respect to the design goal of this study. The improving and worsening parameters were then accurately matched with the TRIZ list of the 39 engineering parameters, and the recommended solutions based on the 40 TRIZ inventive principles.

Based on the principle solutions recommended in Table 2, the most appropriate solutions were selected to be a guideline for development of a new ACB design. The aim of this project was to build a new conceptual design of oil palm polymer composite automotive crash box with high energy absorption capability. Therefore, this design needed to be a product with higher toughness and this could be achieved by reducing #2.Weight of stationary object. Thus, the inventive principles selected to be applied were #3.Local Quality, #26.Copying, #39. Inert atmosphere and #28.Mechanics substitution. The details of design strategy have been presented in Table 3.

Figure 7 shows an integrated method of TRIZ, morphological chart and niomimetics to generate a conceptual idea for a new ACB design. The TRIZ method provided a general solution which still needed to be interpreted further by the designers [45]. Thus, usage of a morphological chart could help to translate TRIZ recommended solutions to their specific ideas. In addition, the usage of biomimetics method based on the recommended solution “#26.Copying” would solve engineering problems with the help of nature’s wisdom approach [46, 47]. Hexagons were chosen as an external geometry profile, taking advantage of the honeycomb structure which could provide very low weight, high stiffness, durability and production cost savings [48, 49]. Combined geometry was used in this design generation by combination of two concepts of energy absorption from woodpeckers and spider webs. Woodpeckers have an impact- proof system, located at the unique hyoid bone inside the skull. It has been proven to bean original mechanism to absorb shock impact [50, 51]. Spider orb-web frame silk structure is stronger per unit weight, compared to high tensile steel and has very high toughness capability equal to 2.5×10⁸ J/m³ or usually expressed by 1.5×10⁵ J/kg [52]. This means that spider web structures are able to absorb very high shock impact energy during collision [53, 54]. Resin or adhesive will be used in fabrication of oil palm polymer composites and a straightslot profile will act as a crash bead leading to the axial collapse mode.

Table 2 TRIZ contradiction matrix for oil palm fibre composites ACB design

Table 3 ACB design strategy based on TRIZ recommended solutions

Figure 7 Integrated method of TRIZ, morphological chart and biomimetics for crash box concept generation

4.7 Stage 2: Concept design generation for ACB using integration method of TRIZ, morphological charts and biomimetics

Five new innovative ACB concept designs were developed by using a hybrid method of TRIZ, morphological charts and biomimetics generated as shown in Figure 8. The 3D model was developed in 1:1 scale for better visualization of product design features. The first concept idea labelled by P1 was copying the honeycomb structure for the outermost profile, reinforced by a spider web structure inside the part and with a multi-layer of fibre foam acting like a sponge in a woodpecker’s skull to protect its brain during a collision. In the second concept idea labelled by P2, the model still used a honeycomb structure for the outermost profile, reinforced by spider web structure inside the part. However, for this concept, only a single layer of spider web structure was to be used as a part-reinforcement supported by fibre foam at the center to optimize the energy absorption capability. The selection of the best design was to be performed using the AHP method. The concept for P3 model was almost similar to P2, but P3 only used a single structure to absorb energy by removing the fibre foam at the center to reduce the mass of the product design. Next, the concept design for P4 was similar to the P1 concept design, and the difference between these two designs was the removal of fibre foam at the center of the multi-layer spider web structure to obtain a lightweight component. Finally, the P5 concept design had an outer structure which was similar in concept to P1 and P4. The only unique part of the design for P5 was the fibre foam reinforcement structure at the middle which was substituted with ribs to strengthen the model. All concept designs were equipped with straight slot profiles as a crash bead to initiate the axial collapse during collision.

Figure 8 3D CAD model of new automotive crash box concept designs

4.8 Stage 3: Final selection of best ACB conceptual design

Four levels of analytic hierarchy process (AHP) were formulated using the available information as shown in Figure 9. Two main elements and their subsequent sub elements were extracted from the PDS main document which had been determined earlier in the design brief section to obtain the best performance of the ACB. Therefore, weight and cost were chosen for the concept design selection criterion. The lighter the part, the better the capability to absorb energy. Additionally, the design must be cost effective by eliminating unnecessary features while designing the part. At the top level, the goal of the project was defined. This was followed by the second level design selection of main criteria while the third level represented sub-criteria. Finally, alternatives at level 4 of the hierarchy listed all five design concept ideas for the automotive crash box design.

Figure 9 AHP hierarchy framework for oil palm fibre polymer composites automotive crash box concept design selection

Numerical values as observed in attributes for the overall ACB concept designs, as shown in Table 4, determined the relative importance for each of the compared criteria. The judgement process in the AHP method was made using pairwise comparison technique for all selection of main criteria and sub criteria. Values for the mass and part volume were calculated by using Solidworks 2015 software, which calculated the values numerically based on the oil palm material properties obtained from previous research studies. Cost for this project was divided into two elements which were raw material and manufacturing complexity. The designs for parts 1, 4 and 5 consumedless material and were therefore considered cheaper than the parts using more material such as designs for part 2 and part 3.

However, single layer reinforcement as inpart 2 and part 3 were considered less complex compared to thedesigns for parts 1, 4 and 5.

The overall evaluation results using the AHP method presented in Figure 10 had an excellent inconsistency ratio (CR) of 0.00 which is less than 0.1. If the consistency ratio exceeded the limit (more than 0.1), the designers would have to review and revise the pairwise comparison. Overall AHP results of the ACB concept design selection showed that the concept design P2 scored the highest priority value of 26.6 % as the most appropriate design or as thefirst choice. The second choice was the concept design P3 with a score of 26.1%, followed by concept design P1 with a score of 15.9%. The last choice was concept design P4 with a score of 15.5%. Therefore, concept design P2 was selected as the most appropriate ACB concept design to be fabricated using oil-palm fibre composite.

The advantage of using AHP by utilizing expert choice software was a sensitivity analysis. A sensitivity analysis was performed to study the effect of the different factors in selecting the best option. The final priorities of the design concepts were highly dependent on the priority vectors attached to the main criterion [58]. Sensitivity analysis was conducted to verify the results from weighting requirements using Expert Choice v.11.5 software. The stability of the results was thus observed by changing the main criteria priority value as shown in Figure 11. In this study, even though the priority value of each main criterion had been increased by 20%, design P2 still ranked first in the alternative ranking. This validated the earlier results.

Table 4 Attributes for overall concept design of oil palm polymer composite automotive crash box [21, 54] and [55-57]

Figure 10 Overall AHP results of ACB concept design selection

Figure 11 Sensitivity graph of main criteria with respect to goal when priority vector of cost is increased by 20% (25%-45%)

5 Conclusions

When comparing the highest priority vector value, concept design P2 was selected as the best design concept for the ACB at the end of the design selection process using the AHP method. The consistency value of less than 10% throughout the evaluation made the generated results acceptable. Apart from that, validation stability of the analysis results by changing the 20% sensitivity criteria still ranked the P2 design at the top compared to the other four designs. Hence, there was valid reason to accept the proposed design solution. Moreover, the hybrid method of the TRIZ–Morphological Chart–Biomimetics method, demonstrated the capability to be used in performing conceptual design idea generation and design enhancement as well as conceptual design development. Also, the AHP method was proven as a systematic approach for conceptual design selection processes in accomplishing the goal or design solution, particularly in undertaking conceptual design of oil palm polymer composite automotive crash boxes.

Acknowledgements

The authors wish to thank various individuals and institutions that made the publication of this paper possible. The cooperation of Universiti Putra Malaysia is highly appreciated. The contribution by Management and Science University (MSU) is highly appreciated.

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(Edited by HE Yun-bin)

中文导读

油棕纤维增强聚合物混合动力汽车防撞箱的概念设计

摘要：采用混合概念设计方法，对油棕复合材料汽车防撞箱进行了概念设计。结合创新问题解决(TRIZ)理论、形态图和仿生学，考虑材料特性、功能规格、力识别、根本原因分析、几何形状和设计选择标准等方面的首要要求。该策略是利用自然物来激发五种创新的ACB结构的概念设计，并运用层次分析法进行两两分析来选择最佳的ACB概念设计。复合ACB的新概念设计考虑到了天然纤维的特性，而不像传统材料如钢合金和铝合金。排名最高(26.6%)的设计被选为最终的概念设计，该设计的最外层具有蜂窝结构，内部结构由蜘蛛网结构强化，中心部位是由啄木鸟海绵组织中提取的纤维泡沫结构支撑，以达到能量吸收能力最大化。新的设计可以解决ACB在碰撞过程中无法吸收最大冲击能量的主要原因—弯曲塌陷的问题。但是，为了生产和装配需要，最后的概念设计仍需修改，这些修改将在今后研究中完成。

关键词：概念设计；汽车碰撞箱；混合方法；概念选择方法

Foundation item: Project(6369107) supported by the Ministry of Higher Education, Malaysia

Received date: 2019-01-13; Accepted date: 2019-06-26

Corresponding author: S M SAPUAN, PhD, Professor; Tel: +603-97696318; E-mail: sapuan@upm.edu.my; ORCID: 0000- 0003-0627-7951

Abstract: A hybrid conceptual design approach was introduced in this study to develop a conceptual design of oil palm polymer composite automotive crash box (ACB). A combination of theory of inventive problem solving (TRIZ), morphological charts and biomimetics was applied where the foremost requirements in terms of the material characteristics, function specifications, force identification, root cause analysis, geometry profile and design selection criteria were considered. The strategy was to use creations of nature to inspire five innovative conceptual designs of the ACB structure and the AHP method was applied to perform the pairwise analysis of selecting the best ACB conceptual design. A new conceptual design for a composite ACB was conceived bearing in mind the properties of natural fibre, unlike those of conventional materials such as steel alloys and aluminium alloys. The design with the highest ranking (26.6 %) was chosen as the final conceptual design, which was the one with a honeycomb structure for the outermost profile, reinforced with a spider web structure inside the part, supported by fibre foam structure extracted from the woodpecker sponge tissue at the centre to maximize the energy absorption capability. The new design could solve the problem of bending collapse which is a major cause of failure to absorb maximum impact energy for ACB during collision. However, the final conceptual design will still need several modifications for production and assembly purposes, which will be completed in a further study.