Structural design and test of automobile bonnet with natural flax composite through impact damage analysis

Accepted Manuscript Structural Design and Test of Automobile Bonnet with Natural Flax Composite through Impact Damage Analysis Gilsu Park, Hyunbum Park PII: DOI: Reference:

S0263-8223(16)31879-7 https://doi.org/10.1016/j.compstruct.2017.10.068 COST 9043

To appear in:

Composite Structures

Received Date: Revised Date: Accepted Date:

18 September 2016 13 October 2017 21 October 2017

Please cite this article as: Park, G., Park, H., Structural Design and Test of Automobile Bonnet with Natural Flax Composite through Impact Damage Analysis, Composite Structures (2017), doi: https://doi.org/10.1016/ j.compstruct.2017.10.068

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1

Structural Design and Test of Automobile Bonnet with Natural Flax Composite through Impact Damage Analysis Gilsu Parka and Hyunbum Parkb,* a

Department of Aerospace Engineering, Chosun University 375 Seosukdong, Donggu, 502-759, Gwangju, Rep. of Korea b Department of Defense Science & Technology-Aeronautics, Howon University 64 Howondae 3gil, Impi, 54058, Gunsan, Rep. of Korea *Corresponding author e-mail:[email protected]

Automobile light weight is an important

Abstract In this study, it was performed structural

area in structural design. It is a direct factor

design and analysis of the automobile bonnet

of enhancing accelerating force and braking

with natural flax composite. The composite

power that are the basic performance. Light

structure is weak to external impact damage.

weight

Therefore, the structural design through

accelerating force and braking power in the

impact damage analysis was performed. For

case of having identical power. Since

manufacturing

applied

automobile light weight can maximize

composite, RTM (resin transfer molding),

engine efficiency and reduce the weight ratio

which is a manufacturing process suitable for

per power to be handled even in the case of

light weight and mass production, was

having relatively lesser power, it can ensure

applied. The impact test of specimen was

superior

performed to analyze the safety of structure

performances compared to that of heavier

from impact. In addition, compression

vehicle.

strength test was performed for specimen

improvement has become essential resulting

applied with impact to measure residual

from recent environmental regulations and

strength of structure after impact to analyze

the arrival of high oil price era. Since 10%

structural behavior. Through the structural

weight reduction is known to improve fuel

design and test, it is confirmed that the

efficiency

designed bonnet structure is acceptable.

manufacturers are seeking to achieve light

flax/vinyl

ester

is

advantageous

for

acceleration

In

addition,

by

and

fuel

5-7%,

enhancing

motion

efficiency

automobile

weight and related parts manufacturers are Keywords: B. Mechanical properties, B.

also developing light weight materials in

Impact behavior, C. Finite element analysis

collaboration with automobile manufacturers.

(FEA)

Recently, there has been a growing interest in the use of natural fibers for

1. Introduction

composites design and manufacturing[1-8].

2

M. M Davoodi et al. performed various

chemical treatment

on the

mechanical

research works of bio-composites. In 2010,

properties of woven kenaf–aramid hybrid

investigation on mechanical properties of

laminated composites was carried out[18]. In

hybrid

epoxy

the same year, review study of natural fiber

composite was carried out[9]. In 2011, study

function was conducted[19]. In 2016, review

on car bumper beam design with developed

of

hybrid

crashworthiness

kenaf/glass

reinforced

bio-composite

material

was

industrial of

applications

and

bio-composites

was

performed[10]. And also, study on effect of

carried[20-21]. In the same year, research on

polybutylene terephthalate (PBT) on impact

effect of fiber orientations on the mechanical

property improvement of hybrid kenaf/glass

properties

epoxy composite was conducted in 2012[11].

composites for spall-liner application was

S. M. Sapuan et al. performed many

studied[22]. In 2017, moisture absorption

research works of design and analysis for

and thickness swelling behavior of sugar

natural

palm

fiber

composite.

In

2008,

of

fiber

kenaf–aramid

reinforced

hybrid

thermoplastic

investigation on effect of alkaline treatment

polyurethane was performed[23]. Recently,

on tensile properties of sugar palm fiber

manufacturing process of natural composite

reinforced epoxy composites was carried

is performed[24].

out[12]. In 2012, study on defect detection in Kenaf/Epoxy

natural

composite

Other research on natural fiber composite

was

was carried out by M. R. Mansor et al. In

performed[13] and also, study on influence

2013, automotive brake lever design using

of fiber content on the mechanical and

natural and glass fiber was conducted[25].

thermal properties of Kenaf fiber reinforced

In 2014, study on design and analysis using

thermoplastic polyurethane composites was

Kenaf fiber was performed and review of

carried out[14].

In 2013, research of

engineering approach applied to composite

mechanical properties of sugar palm tree was

was presented[26-27]. In 2017, study on

conducted[15]. In 2014, investigation on

design characteristics, codes and standards of

mechanical,

natural fiber composites was performed[28].

thermal and

morphological

properties of durian skin fiber reinforced

In this study, the design of eco-friendly

PLA bio-composites was conducted[16].

automobile bonnet structure using natural

And also, study on penetration and ballistic

fiber was performed. Many research works

properties

hybrid

of bonnet design using metal or glass

composites was performed[17]. In 2015,

composite were performed in an early stage

study on effect of layering sequence and

of research[29-33]. However, little research

of

kenaf–aramid

3

work has been carried out to apply natural

capacity. In particular, flax fiber of natural

composite for automobile structure.

fiber has most superior tensile strength and

In this study, properties of flax/vinyl ester

modulus of elasticity. Accordingly, flax fiber

composite that is being researched in various

was applied in this study to perform

ways as eco-friendly material was evaluated

structural design. Fig. 1 is a graph comparing

to perform structural design and analysis of

the performances of materials used for

compact

automotive parts compared to their prices.

automobile

manufacturing

bonnet.

flax/vinyl

ester

For applied

Resins used for natural fiber are mainly

composite, RTM (resin transfer molding),

divided into

thermoplasticity resin and

which is a manufacturing process suitable for

thermosetting resin. As for resin applied for

light weight and mass production, was

composite fiber, thermosetting resin is often

applied. Specimen was manufactured to

applied. As for thermosetting resin, epoxy,

analyze the mechanical properties of material,

vinyl ester and phenolic are used. In this

and specimen impact test was performed to

study, vinyl ester with relatively cheaper

analyze the safety of structure from impact.

price was selected as resin to be applied for

In addition, compression strength test was

flax fiber.

performed for specimen applied with impact

Applying RTM manufacturing method,

to measure residual strength of structure after

specimen selected was manufactured. The

impact to analyze structural behavior.

tensile, compression, flexure and shear tests were performed to evaluate its properties.

2. Investigation on Mechanical Properties

The

tension

strength

is

109MPa

of Natural Fiber

compression strength is 90MPa.

and

Natural fiber composites are being used in various industries in recent. In automotive

3. Structural Design and Head Impact

industry, natural fiber composites are being

Analysis

applied for light weight of structure by replacing existing metal materials such as

3. 1 Structural Design of Bonnet

door panel, seat back support, dashboard,

In this study, comparative analysis was

truck liner, etc. Natural fiber has somewhat

conducted with the panel of domestic

lesser strength compared to that of glass fiber

compact care manufactured with ordinary

but natural fiber is more advantageous than

metal to compare the structural motion of

glass fiber when comparing their price,

automobile panel designed with flax fiber. As

specific

for mechanical properties, flax fiber analysis

gravity

and

energy

absorbing

4

results previous analyzed were applied. Since

and wrapped around with skin viscoelasticity.

panel is a plate structure with a characteristic

The headform consists of 165mm in diameter

of flexing when load is applied at the center

and 4.9kg in weight, as shown in Fig.

of panel, flexural strength of structure design

3.According to the European pedestrian

with ordinary metal was analyzed to design

protection regulation, impact analysis was

similar flexural strength of structure that

performed

applied natural fiber similar [34].

colliding at the center, which is most

Thickness of the metal panel of compact

at

40km/h

speed

vertically

structurally vulnerable area.

automobile is 1.8mm and flexural strength is

The impact analysis result showed that the

146.52Nm. Flexural strength of structure that

displacement at the center of panel was

applied 1ply of flax/vinyl ester is 0.86Nm.

54.6mm. In the case of vertical direction

For the purpose of obtain flexural strength

displacement exceeding 120mm, it indicates

equivalent to ordinary metal panel, it was

that head damage and engine damage could

designed with 6plies thickness of 2-D fabric

be maximized during headform impact

flax fiber for the panel structure that applied

through direct interference with engine. The

flax/vinyl ester. The stacking sequence is

result confirmed that it is safe since the

[±45]6. Fig. 2 shows the structural shape of

vertical direction displacement of panel did

automotive panel. Structural analysis was

not exceed 120mm. The result of stress

performed to verify the structural design

analysis showed 151MPa.

results through 3-D modeling of the structure panel.

For the purpose of comparing structural motion of panel that applied flax/vinyl ester, impact analysis of ordinary steel panel was

3. 2 Impact Analysis of Adult Headform

performed. It was performed in the same way

For the purpose of analyzing the safety of

as that of flax/vinyl ester panel colliding at

designed panel against impact, modeling was

the center of panel in vertical direction at

performed for adult headform to perform

40km/h speed. The thickness of steel panel

impact analysis. It analyzed the displacement

was 2mm.

and stress of panel in the case of male adult

The impact analysis result of steel panel

head colliding at the center of panel at

showed 53.9mm of displacement at the

40km/h speed. As for the adult headform, it

center of panel with 223MPa stress. In

needs to be a globe shape in accordance with

comparison with panel that applied natural

the European pedestrian protection regulation.

fiber, natural fiber panel showed higher

Aluminum shall be applied for the main body

displacement by 1.29%, while showing lesser

5

stress by 32.28%. In terms of panel weight,

energy. After moving impactor to the

natural fiber panel was lighter by 32%,

location that corresponds to the calculated

thereby

of

energy, specimen will be fastened with clamp

flax/vinyl ester panel in place of steel panel

at the lower part of support to drop it to place

for achieving light weight of structure. Table

impact. Impactor mass is 5.0kg and the

1 shows the comparison of impact results

diameter of hemispherical striker tip is

between steel panel and flax fiber panel. The

12.7mm that were applied according to the

comparison analysis result of impact was

standard of ASTM D7136 [35]. For the

shown in Fig. 4, 5.

purpose of determining the impact energy

showing

the

applicability

placed to specimen, energy during adult head colliding with panel at 40km/h speed was

4. Investigation on Impact Damage For verifying the analysis result of

calculated.

automobile panel applied with flax fiber, it is

The specimen was manufactured by RTM

necessary to manufacture adult headform

method. In regards to the size of specimen, 2-

impactor

D

and

perform

impact

test

to

fabric

type

fiber ±45°was

fabricated

in

layered

in

specimen. Since special equipment is needed,

100mm×150mm

a research was conducted in this study to

0°direction. Since energy is proportional to

analyze trend before manufacturing specimen.

volume, energy during the collision of adult

After manufacturing miniature specimen,

headform with panel was calculated to

specimen impact test was conducted to verify

determine the energy to be placed to

the validity of analysis by comparing

specimen. Energy during the collision of

experiment and analysis results. Since energy

adult headfrom with panel is 301J and impact

is proportional to volume, value proportional

energy to be placed to specimen is 8.8J.

to energy when adult headform collided with

Accordingly, three types of impact test of

panel was calculated to perform specimen

8J/9J/10J were performed.

impact test. After the specimen impact test,

Prior to performing impact test, simulation

any damage to specimen was examined.

of impact test was performed to review the

Compression

result. The stress and displacement of

strength

test

was

also

performed after the impact test to analyze the

specimen

after

impact

were

analyzed.

safety of structure after damage.

Impactor mass is 5.2kg and the diameter of

As for the impact tester applied in this

impact contact surface is 12.7mm for

study, weight drop impact method will be

modeling identical to impact test impactor.

used to convert impact energy into potential

Fig. 6 shows impact analysis modeling. As

6

for the specimen impact speed, 1.76m/s,

performed according to ASTM D7137 [36].

1.86m/s, 1.96m/s were applied to place

As

impact energy of 8J / 9J / 10J. The analysis

supplementing test environment vulnerable

result was shown in Table 2 and Fig. 7, 8

to buckling according to the characteristic of

show the analysis result of displacement and

composite, buckling prevention system was

stress of specimen placed with 10J of impact.

devised and applied according to the ASTM

Using impact equipment for impact test, flax/vinyl ester specimen was placed with 8J

for

the

compression

test

jig

for

test regulation. Specimen

test

result

showed

that

/ 9J / 10J of impact. The weight of impactor

compression strength after applying 8J / 9J /

is 5.2kg. As for the drop location, it was

10J of impact to flax/vinyl ester specimen

dropped at the height of 0.16m, 0.18m,

deteriorated respectively by 9.55% / 17.08%

0.20m respectively for 8J / 9J / 10J. In terms

/ 29.26% compared to the strength of

of

was

specimen without any damage. Since 1.5

respectively 1.76m/s, 1.87m/s, 1.98m/s. Fig.

safety rate was applied during the panel

9 shows configuration of impact test. The

structural design, the area where strength is

result of analyzing specimen after impact

reduced by 33% from damage is an area that

showed that its back side was also damaged.

requires maintenance and repair. It was found

Fig. 10-12 show fracture configuration of

that the area where strength is reduced by 33%

specimen before and after impact by SEM.

from damage requires maintenance and

Fig. 11 and 12 show fiber breakage of

repair that is needed during impact exceeding

specimen after impact. The maximum load

10J. Table 4 shows the compression strength

and energy of impact was shown in Table 3.

comparison result after impact of 8J/9J/10J.

the

speed

during

impact,

it

For the purpose of analyzing the degree of strength deterioration of structure after impact

damage,

compression

5. Manufacturing and Structural Test

strength

In this study, after investigation on

measurement test was performed in this

structural analysis of bonnet, the prototype

study after the specimen impact test. As for

was manufactured using flax/vinyl ester. In

the compression strength test, flax/vinyl ester

order to manufacture the prototype, the RTM

specimen was placed with 8J / 9J / 10J of

method

impact to measure its compression strength,

manufacturing process of bonnet using RTM

along with the compression strength of

method. The manufactured bonnet is shown

specimen without any damage. In terms of

in Fig. 14.

compression strength test after impact, it was

is

adopted.

Fig.

13

shows

7

In this work, the headform impact test was performed. The

manufactured

after impact test. As for specimen impact

prototype

energy, energy in proportion to volume was

bonnet was set on the test rig and impacted

calculated to conduct test and it was found

by headform

and

that maintenance and repair are needed in the

deflections ofthe bonnet were measured. As a

case of impact exceeding 10J. Compared to

load for the impact test, the designed load

ordinary steel panel, flax/vinyl ester panel

was applied. The weight of adult headform is

designed in this study showed 31.7% of

4.9kg and the impact velocity is 40km/h

weight reduction rate and it was found that it

speed.

can be applied in place of ordinary steel

impact,

According

evaluation result,

to

and

the

strains

impact

test

structural safety was

panel.

confirmed. Fig. 15 shows impact test rig of bonnet. The prototype bonnet was set on the test rig and impacted by headform impactor.

Acknowledgements This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF)

67. Conclusion In this study, natural fiber flax/vinyl ester

funded by the Ministry of Education(No.

composites were applied to automobile

2014R1A1A2054842).

This

study

was

bonnet to perform structural design, analysis

supported by research funds from Howon

and impact test. As for structural design of

University.

bonnet, it was performed based on flexural strength. For the purpose of designing in

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12

Fig.3. Modeling for headform impact analysis

Fig.1. Performance and price comparison of competing materials for automotive applications[7]

Fig.4. Stress analysis result under impact load of flax/vinyl ester composite bonnet

Fig.2. Configuration of automobile bonnet

13

Fig.5. Stress analysis result under impact load of steel bonnet

Fig.6. Impact analysis modeling for specimen test

Fig.7. Impact analysis result of specimen : 8J deformation

Fig.8. Impact analysis result of specimen : 8J stress

14

Fig.11. Flax fiber surface morphology after 8J impact damage

Fig.9. Configuration of impact test

Fig.12. Flax fiber surface morphology after 10J impact damage

Fig.10. Flax fiber surface morphology before impact

15

Fig.13. Prototype manufacturing using RTM method

Fig.14. Manufactured Prototype bonnet

16

Fig.15. headform impact test

17

Table 2 Impact analysis results Table 1 Mechanical properties of natural fibers Steel panel

Flax/vinyl

V[m/s]

1.76

1.86

1.96

E[J]

8

9

10

Deformation [mm]

4.4665

4.925

5.2255

Stress[MPa]

117.84

134.07

142.8

Comparison

ester panel Mass

6.48kg

4.4kg

-32.0%

Thickness

2mm

6mm

200.0%

54.6mm

1.29%

151MPa

-32.28%

Deformation 53.9mm Stress

223MPa

Table 3 Impact test results Max. load Impact velocity Energy to max [kN]

[m/s]

load [J]

8J

3.3994

1.7616

6.3935

9J

3.4546

1.8767

8.3112

10J

3.4503

1.9898

8.27795

18

Table 4 Compressive strength test results after impact No

8J

9J

10J

89.87

81.28

74.51

63.56

-

-9.55

-17.0

-29.26

damage Compressive Strength [MPa] Strength reduction [%]