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Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering http://pid.sagepub.com/ Characterization of an injection-moulded car audio chassis made of polycarbonate−(acrylonitrile− butadiene−styrene)-based composite using metal-coated carbon fibre Seong Ho Jeon, Chin Hun Chung, Heon Mo Kim, Won Hee Han, Il-Eui Jung and Byoung-Ho Choi Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 2012 226: 881 originally published online 4 January 2012 DOI: 10.1177/0954407011430183 The online version of this article can be found at: http://pid.sagepub.com/content/226/7/881

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Original Article

Characterization of an injectionmoulded car audio chassis made of polycarbonate–(acrylonitrile– butadiene–styrene)-based composite using metal-coated carbon fibre

Proc IMechE Part D: J Automobile Engineering 226(7) 881–894 Ó IMechE 2012 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0954407011430183 pid.sagepub.com

Seong Ho Jeon1, Chin Hun Chung2, Heon Mo Kim3, Won Hee Han1, Il-Eui Jung2 and Byoung-Ho Choi1

Abstract Engineering plastics are widely used as a substitute for stainless steel in the automobile industry to reduce weight and to improve fuel efficiency. In this paper, a polycarbonate–(acrylonitrile–butadiene–styrene)-based composite with nickelcoated carbon fibre was developed, and the application of the composite to a lightweight car audio chassis was examined. The mechanical and electrical properties of the composite were evaluated through various physical tests, i.e. tensile, impact, flexural and electromagnetic interference shielding effectiveness tests. In addition, the characteristics of this material were compared with those of a material previously developed by the present authors, i.e. a polycarbonate– (acrylonitrile–butadiene–styrene)-based composite with metal fibre and glass fibre. Finally, the actual car audio chassis was made by injection moulding under various moulding conditions pertaining to the injection speed and the tool temperature to find the optimum injection-moulding conditions. Two required key tests, i.e. a full-scale electromagnetic interference shielding effectiveness test and vibration analysis, were conducted to confirm the applicability of the polycarbonate–(acrylonitrile–butadiene–styrene)-based composite with nickel-coated carbon fibre as a material for a car audio chassis.

Keywords Polycarbonate–(acrylonitrile–butadiene–styrene), nickel-coated carbon fibre, car audio, injection moulding, vibration, electromagnetic interference shielding effectiveness

Date received: 31 July 2011; accepted: 19 October 2011

Introduction The automobile industry requires eco-friendly strategies to reduce carbon dioxide (CO2) emissions because of environmental regulations such as the 2005 Kyoto Protocol.1 For this reason, engineering plastics have become very popular because they have been considered a good substitute for conventional heavy stainless steel. Thus, ‘green car’ research is being pursued in many countries.2–4 In this study, as part of green car research, a car audio chassis that originally was made of stainless steel was produced using a polycarbonate– (acrylonitrile–butadiene–styrene) (PC–ABS) composite to reduce the weight of the car audio and to improve the fuel efficiency.

The PC–ABS composite in this research was obtained by mixing PC–ABS with nickel-coated carbon fibre (NCF). PC–ABS is generally known to have good mouldability5 and balanced mechanical strength.6 Therefore, in 2009, General Motors and Delphi (USA) 1

School of Mechanical Engineering, Korea University, Seoul, Republic of Korea 2 LG Electronics, Pyeongtaek-si, Kyounggi-do, Republic of Korea 3 Technology Center, LG Chem, Daejeon, Republic of Korea Corresponding author: Byoung-Ho Choi, School of Mechanical Engineering, College of Engineering, Korea University, 1 5-ga Anam-dong, Sungbuk-gu, Seoul 136713, Republic of Korea. Email: [email protected]


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developed an engineering plastics car audio chassis made of PC–ABS with 16 wt% glass fibre (GF).7 The plastic chassis satisfied the required electromagnetic interference (EMI) shielding effectiveness (SE) because it enclosed the car audio with a mesh Faraday cage. However, their technique requires a complicated insert moulding process as well as a mesh Faraday cage for shielding. The present authors developed a PC–ABSbased composite with metal fibre (MF) and GF to make a new resin for the simple injection moulding of a car audio chassis, and it was confirmed that most of the required physical and electrical properties were satisfied.8 However, the car audio chassis made of this material did not show a stable EMI SE and mechanical strength once it was injection moulded because the material could not be pelletized uniformly owing to the low filler content and unexpected permanent deformation of the MFs, which led to an uneven distribution of the fillers.9 Therefore, instead of MF and GF, carbon fibre (CF) was added to the PC–ABS. Generally, CF has been used in many ways as carbon-fibre-reinforced plastic (CFRP) owing to the high strength-to-weight and stiffness-to-weight ratios, high damping and good corrosion resistance properties. Thus, CFRP has been thought to be an alternative to stainless steel and other materials. Also, it has been applied in many industrial fields such as aerospace engineering.10 In this study, NCF was considered to improve the EMI SE since the EMI SE is highly regulated in electronic devices because of electromagnetic wave disturbance and human health problems. In this paper, a PC–ABS-based composite with NCF was developed, and the application of the composite to a lightweight car audio chassis was studied. The mechanical and electrical properties of the composite were evaluated through various physical tests, i.e. tensile, impact, flexural, rheology and EMI SE tests. In addition, the characteristics of this material were compared with those of a material previously developed by the present authors, i.e. PC–ABS with MF and GF.8 Finally, actual car audio mould chassis were made by injection moulding under various moulding conditions pertaining to the injection speed and the tool temperature to find the optimum injection-moulding conditions. Two required key tests, i.e. a full-scale EMI SE test and vibration analysis, were conducted to confirm the applicability of the PC–ABS–NCF composite as a material for car audio chassis.

Composite materials, test methods and car audio structure Composite materials Engineering plastic as a material for car audio chassis requires the following conditions: first, superior mechanical properties against external vibration and

impact; second, a good EMI SE; third, lightness of weight. In a previous study, two functional fillers, i.e. MF and GF, were selected to meet these requirements. MF was expected to control the mechanical properties and the EMI SE.11 Also, GF was good for enhancing the mechanical strength without increasing the specific gravity too much12 and costs less than any other materials.13 However, a car audio made of PC–ABS with MF and GF did not satisfy the vibrational stiffness and EMI SE requirements constantly once it was injection moulded. Because the composite material could not be pelletized uniformly owing to a low filler content and unexpected permanent deformation of the MFs, functional fillers were not dispersed well in PC–ABS. Therefore, stable mechanical strength and EMI SE were not guaranteed. Therefore, in this paper, CF was selected because it can be pelletized with PC–ABS unlike the previous composite material. In other words, CF was expected to show a relatively more even distribution than MF and GF once the car audio chassis was injection moulded, and PC–ABS with CF was assumed to display better mechanical and electrical characteristics. Also, instead of using conventional CF, NCF was considered to further improve the EMI SE. Tzeng and Chang14 reported that PC–ABS with NCF has a better EMI SE than PC–ABS with normal CF, and they also reported that the EMI SE of PC–ABS–NCF varied depending on the ABS content. The EMI SE regulatory limit for a car audio is 40 dB.15 Thus, the material of a car audio chassis should have an EMI SE of more than 40 dB. In this study, two types of composite material were prepared with NCF contents of 10 wt% and 12 wt%, because a small amount of fillers did not yield a higher EMI SE; the EMI SE of PC–ABS with 3 wt% MF was not higher than 40 dB. PC–ABS–10 wt% NCF and PC–ABS–12 wt% NCF are denoted materials A and B respectively. For reference purposes, the basic properties of PC–ABS are shown in Table 1.8

Test methods First of all, basic mechanical tests, i.e. tensile, impact and flexural tests, were conducted. With these test results, the improvements in the mechanical properties of the PC–ABS–NCF composite were evaluated through a comparison with those of the conventional PC–ABS–MF–GF composite. Also, an EMI SE test was conducted to check whether the material could be applied to a car audio chassis by verifying the EMI SE regulation limit that should be higher than 40 dB. In general, the EMI SE is a measure of the material’s ability to attenuate the intensity of EMI waves. The higher the SE value, the better is the attenuation. The EMI SE is expressed in decibels (dB). For electromagnetic radiation of a specific power, the EMI SE is the logarithm


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Table 1. Mechanical and electrical properties of PC–ABS. Properties Physical Specific gravity Moulding shrinkage (flow), 3.2 mm Melt flow rate Mechanical Tensile strength, 3.2 mm, yield Tensile elongation, 3.2 mm, break Flexural strength, 3.2 mm Flexural modulus, 3.2 mm Izod impact strength, 3.2 mm, notched Rockwell hardness

Test conditions

Test method

Units

Typical value

250 °C, 2.16 kg

ASTM D792 ASTM D955 ASTM D1238

% g/10 min

1.14 0.4– 0.6 5

ASTM D638 ASTM D638 ASTM D790 ASTM D790 ASTM D256

MPa % MPa MPa J/m

54.91 100 88.26 2255.53 588 490 111

O/sq dB

. 1013 0

50 mm/min 50 mm/min 10 mm/min 10 mm/min 223 °C 223 °C R scale

Electrical Surface resistance EMI SE (1 Hz), T = 3 t

ASTM D785 IEC 60112 ASTM D4935

EMI SE: electromagnetic interference shielding effectiveness.

of the ratio of the incident power P1 to the transmitted power P2, i.e. SE = 10 log(P1/P2). The incident power is equal to the transmitted power when there is no shielding.16 Also, in the rheology tests, the glass transition temperature Tg was observed through data from phase difference versus temperature curves and from stored modulus versus temperature curves. In addition, the car audio chassis was made of the PC–ABS–NCF composite by injection moulding under various conditions relating to the injection temperature, the tool temperature and the injection speed. An analysis of the dispersion of NCF fillers, vibration analysis and the EMI SE test were executed to confirm the PC– ABS–NCF composite as the prospective material for car audio chassis. Injection moulding was performed under four various settings: the reference setting, an increase in the injection speed, an increase in the tool temperature and an increase in the injection temperature. This was to find an optimum injection-moulding condition. A hydraulic catapult was used in this study based on previous studies.9,17 Previous studies arrived at the conclusion that the hydraulic catapult generated a better filler distribution than a high-speed catapult.9,17 After the injection moulding, the dispersion of the fillers of the car audio mould chassis was studied. Fifteen specimens from the upper parts of the mould chassis were taken from three regions, namely left, centre and right. Then, nine scanning electron micrographs of each specimen were captured. Using these micrographs, the number of NCFs was counted. Finally, the dispersion of fillers was analysed statistically through matrix contour drawing. Subsequent to injection moulding and an analysis of the dispersion of fillers, vibration analysis and base excitation tests were executed. Vibration analysis is based on the mode frequencies, and these values check the stability of a car audio (a commercial software

package NASTRAN was used for this purpose). Figure 1 shows a schematic diagram of a car audio. External sweep frequencies of 0–100 Hz were applied to the bracket points; then, the mode frequencies of the decks were extracted (see Figure 1(b)). The deck is a very important part of a car audio because the CD–DVD player is mounted in the deck; therefore, the deck should be safe from external impact and shocks. The safe first-mode frequency should be higher than 100 Hz because all external frequencies are less than 100 Hz; otherwise, the acceleration in those ranges has to be lower than 5 g according to technical reports from LG Electronics and the recommendations of engineers in the relevant industry. As well as this, a base excitation test was conducted on the basis of18 ai ar car audio acceleration = base acceleration

Tir =

ð1Þ

Equation (1) also can be expressed in terms of the displacement Xi of the car audio and the displacement Xr of the base, according to18 Xi Xr car audio displacement = base displacement

Tir =

=

1 + (2§r)2 2

(1 r2 ) + (2§r)2

ð2Þ

with r = vn/vb, where vn is the natural frequency of the car audio and vb is the frequency of the excited base; also, § is the damping ratio. In equation (2), when the frequency ratio r is 1 (i.e. the natural frequency vn of the car audio equals the frequency vb of the excited base), the transmissibility Tir will have the highest value


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Figure 1. The schematic diagram of a car audio: (a) bracket points where external vibration is applied; (b) deck points.

and will cause severe fluctuations of the car audio. In extreme cases, this phenomenon may badly damage the car audio. As a final key test, an EMI SE test of the full car audio with the injection-moulded chassis was carried out. The EMI SE test of the full car audio measured the capability of blocking the electromagnetic signal sent by an antenna that was located about 1 m away from the car audio.

Test results Characterization of the PC–ABS–NCF composite material Figure 2 shows the results obtained from the tensile tests. The results indicate that the tensile strength and Young’s modulus increase with increasing CF content. Young’s modulus was measured as 2.40 GPa and 2.84 GPa for material A and material B respectively, and the tensile strength was about 80 GPa for both materials. In comparison with the previous PC–ABS–MF–GF composite material (PC–ABS with 3 wt% MF and 7 wt% GF),8 which had a tensile strength of 58 GPa and Young’s modulus of 1.66 GPa, it can be observed that the mechanical properties improved noticeably. Thus, from this finding, it is expected that the mechanical stiffness and vibrational stability of a car audio chassis made of PC–ABS–NCF composite material will increase in comparison with those of a car audio chassis made of the previous PC–ABS–MF–GF composite material. In Table 2, other key physical and electrical properties of the PC–ABS–NCF composite material are

Figure 2. Stress–strain curves of material A (10 wt% NCF), material B (12 wt% NCF) and the reference material (PC–ABS– MF). NCF: nickel-coated carbon fibre; PC–ABS–MF: polycarbonate– (acrylonitrile–butadiene–styrene)–metal fibre.

summarized. Generally, the flexural modulus and strength, as well as the impact strength, increase with increasing CF content. In particular, the EMI SE of material B (12 wt% NCF) is satisfactorily above 40 dB for specimens that are at least 2 mm thick. However, material A (10 wt% NCF) does not satisfy the EMI SE regulation (the EMI SE should be higher than 40 dB). From these results, it can be observed that material B is an appropriate material that will be applied for injection-moulded car audio chassis. In addition, EMI SE increases for NCF; therefore, it can be shown that


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Table 2. Comparison between the mechanical properties of material A, material B and PC–ABS–3 wt% MF. Value for the following

Impact test (J/m) Flexural strength (kg/cm2) Flexural modulus (kg/cm2) EMI SE (dB) at 1 t EMI SE (dB) at 2 t EMI SE (dB) at 3 t Mould chassis weight (g)

Material A

Material B

PC–ABS– 3 wt% MF

500 1100 45,000 22.6 32.5 32.5 215.5

500 1200 54,000 37.4 47.3 49.8 219.2

140 1010 31,700 26 45 46 227

PC–ABS– 3 wt% MF: polycarbonate–(acrylonitrile–butadiene–styrene)–3 wt% metal fibre; EMI SE: electromagnetic interference shielding effectiveness.

Figure 3. Rheology properties of PC–ABS–NCF: (a) phase difference; (b) stored modulus. NCF: nickel-coated carbon fibre; PC–ABS–MF: polycarbonate–(acrylonitrile–butadiene–styrene)–metal fibre.

nickel is an effective material for increasing the EMI SE, as Tzeng and Chang14 observed. In addition, the use of lightweight CF as opposed to GF did reduce the weight of the chassis. In addition, Figure 3 displays the results of rheology tests. From the graphs in Figure 3, the glass transition temperature Tg of PC–ABS–NCF is around 150 °C.

Injection moulding and dispersion of the fillers of the car audio chassis Using materials A and B, car audio chassis were produced by injection moulding. Figure 4 shows a mould chassis model. This model is the same as the mould chassis model that was designed in an earlier study. Initially, three models were selected, and the results of vibration analysis yielded the reference for selecting an appropriate model.9 The model in Figure 4 showed a higher first-mode frequency than the other two models. Following the selection models, two types of

injection-moulding analysis were conducted. The first was the pinpoint method (four points were placed at the corner of the rear side) in Figure 4(a), and the second type of analysis was the side-gate method shown in Figure 4(b). In this analysis, the side-gate method resulted in lower deformation and moulding pressure than the pinpoint method.9 In other words, lowpressure injection moulding is a cost-effective near-netshaping process and has several significant advantages such as lower mould cost, energy consumption and wear rate of the flow, besides nearly no density gradient in the mould product.19 Table 3 summarizes the injection-moulding conditions for four different cases regarding each material. The injection speed, the tool temperature and the injection temperature were selected as the variables for injection moulding to find the optimal conditions for injection moulding. Injection moulding was carried out for three temperature conditions, i.e. 265 °C, 280 °C and 300 °C. The mould chassis produced at injection temperatures of


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Figure 4. Two cases of injection-moulding analysis: (a) pinpoint method; (b) side-gate method.9

Table 3. Summary of injection-moulding conditions.

Case A1 Case A2 Case A3 Case A4 Case B1 Case B2 Case B3 Case B4

NCF (wt%)

Injection temperature (°C)

Tool temperature (°C)

Injection speed (mm/s)

Remarks

10 10 10 10 12 12 12 12

285 285 285 300 285 285 285 300

50 50 70 50 50 50 70 50

50 100 50 50 50 100 50 50

Reference Increase in the injection speed Increase in the tool temperature Increase in the injection temperature Reference Increase in the injection speed Increase in the tool temperature Increase in the injection temperature

NCF: nickel-coated carbon fibre.

280 °C and 300 °C both had a higher average and a higher standard deviation of fillers compared with that produced at 265 °C. In addition to the injection temperature, two other variables, namely the injection speed and the tool temperature, were considered. The selection of the optimum condition should be decided by the dispersion of fillers given that an even distribution of fillers ensures high strength and stable properties. Figures 5 and 6 show NCF using energy-dispersive X-ray spectroscopy and the cross-sections of the mould car audio chassis. In the upper photographs in Figure 6, the core area of the sample is shown, and the surfaces of the sample are indicated in the lower photographs of Figure 6. In the core areas, NCF is generally mixed well with PC–ABS without any specific orientation in the central regions. However, in the surface regions, the fibres were oriented along the PC–ABS material. This is mainly because of the skin-core effect, which produces a morphological difference between the central and surface regions. The fillers in the surface regions were aligned more parallel to the surface than those in the central regions because of the high shear stress during the injection-moulding process.20 To determine a suitable injection-moulding condition, the dispersion of fillers was analysed. An even distribution

of fillers is very important because the mechanical strength and the EMI SE are dependent on it. This analysis was conducted by counting the number of fibres of specimens at the top surface of the mould chassis. Then, the average and the standard deviation of the right, centre and left sides of the top surfaces were calculated. Finally, through an overall comparison of the average and the standard deviation of the number of fibres at each injectionmoulding condition, the appropriate injection-moulding conditions were evaluated. Figures 7 and 8 show the distribution of fillers in each case through matrix contour drawings. As shown in these figures, an increase in the injection speed (cases A2 and B2) and an increase in the tool temperature (cases A3 and B3) are needed to improve the filler distribution because the density of fillers is higher than in any other condition. In addition, Figure 9 indicates the number of fibres in each case through the average value and the standard deviation. Cases A3 and B3 show the highest values of fillers of all cases. Therefore, considering the matrix contour drawing and the number of fillers, the injection-moulding conditions of cases A3 and B3 (an injection temperature of 285 °C, a tool temperature of 70 °C and an injection speed of 50 mm/s) are the most suitable for a mould chassis with PC–ABS–NCF.


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Figure 5. (a) NCF; (b) energy-dispersive X-ray analysis indicating ‘nickel’. EDX: energy-dispersive X-ray.

Figure 6. Cross-section of mould car audio chassis: (a) central part; (b) surface area. SEM: scanning electron microscopy.


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Figure 7. Distribution of fillers in material A.

EMI SE test The EMI SE test is essential because it judges the commercialization of mould car audio chassis. If a mould car audio chassis does not pass the EMI SE regulation, it will not be accepted in the market. Figure 10 shows the EMI SE test setting. The EMI signals generated from the car audio are measured by an antenna and recorded. All eight cases of mould chassis that were produced under different injection-moulding conditions were measured for their EMI SEs; further, the reference steel chassis and the normal PC–ABS chassis were measured to yield a comparison (Figure 11). In the case of steel chassis, most signals do not exceed the EMI SE limit (red lines) except for some ranges because stainless steel blocks or absorbs electromagnetic signals. However, the result for the normal PC–ABS chassis is concerning since most signals surpass the limit because there are

no other conductive materials or fillers. Figure 12 displays the representative EMI SE test results for mould chassis A3 and B3 among the eight cases. These chassis show the most stable results; most signals are under the EMI SE limit, and their signal magnitudes are lower than for other mould chassis. This supports the theory that nickel is the appropriate conductive coating material on CF and can increase the EMI SE. From these results, chassis B3 (12 wt% NCF with increasing tool temperature) will be selected for the base excitation test because both material B and its mould chassis satisfy the EMI limit and regulation.

Vibration analysis and the base excitation test Vibration analysis has been considered to be important to check the applicability of a car audio because the performance of the car audio is determined by whether the CD–DVD player operates smoothly. An


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Figure 8. Distribution of fillers in material B.

Figure 9. Averages and standard deviations of fillers in materials A and B. STDEV: standard deviation; NCF: nickel-coated carbon fibre.


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Figure 10. EMI test setting.

Figure 11. EMI test results of steel car audio chassis and PC–ABS mould car audio chassis. PC–ABS: polycarbonate–(acrylonitrile–butadiene–styrene).

Figure 12. EMI test results of mould chassis A3 and B3. NCF: nickel-coated carbon fibre.


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Figure 13. Vibration analysis results (material B).

Figure 14. (a) Base excitation model (xr is the displacement of the base, xi is the displacement of the material M, ar is the acceleration of the base and ai is the acceleration of the material); (b) base excitation test and measuring points in this test.9


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Figure 15. Test results of base excitation: mould chassis A3 and B3.

automobile CD–DVD deck, where the CD player, MP3 player and/or radio are fitted, should be run in a harsh environment because cars are driven sometimes on rugged roads and under bad-weather conditions. In other words, when products are designed, it is essential in a car audio design that the CD–DVD deck runs smoothly in a harsh vibrational environment.21,22 Therefore, the first-mode frequency should be as high as possible to avoid resonance23 during the operation of the car audio. If resonance occurs, the inner and outer components of the car audio may become damaged because of unacceptable levels of vibration, which will cause discontinuous dynamic behaviour.24 In terms of the vibration standard, the first-mode frequency should be higher than 100 Hz, and the acceleration should be lower than 5 g, as mentioned before. The current chassis model made of stainless steel has a first-mode frequency of 147 Hz with 32.5 g; hence, this model satisfies the vibration standard. However, the previous mould chassis achieved a first-mode frequency of 87 Hz with 9.5 g,25 and this result did not meet the requirement. This is one of the main reasons why NCF was applied for a mould chassis instead of MF and GF. Young’s moduli, obtained from the stress–strain curves (Figure 2), were about 2.32 GPa (material A) and 2.77 GPa (material B) respectively. Given that Young’s modulus of the previous PC–ABS–MF–GF was 1.66 GPa, the improved vibration results could be predicted partially by the improvement in the modulus. Figure 13 shows the results for car audio mould chassis with material B; the first-mode frequency was found to be at 72 Hz with 4.50 g, which is quite satisfactory compared with the results for the previous PC–ABS–MF– GF composite.9 While the highest acceleration within 100 Hz is 5.66 g at 94 Hz, when this result is compared

with results from the previous study,9 the vibration response appears to be more stable because the acceleration is significantly lower even though the first-mode frequency is slightly lower than 100 Hz. Therefore, it is concluded that PC–ABS–NCF could be a reasonable substitute for stainless steel. To verify the improved vibration response, a base excitation test (actual vibration test) was executed. This test was performed using the two samples chosen from the previous EMI test results (cases A3 and B3) to verify the vibrational stability of the mould chassis model that was assembled with the car audio components. The base excitation test method measures the transmissibility between the base and the car audio. The schematic diagram of the base excitation model and the test setting of the base excitation test are shown in Figure 14.9 Figure 15 shows the results of the base excitation test when measured from two positions (see Figure 14(b)) of the car audio with a mould chassis made from the PC– ABS–NCF composite. For the PC–ABS–NCF mould chassis, the first-mode frequency occurs at 92 Hz at approximately 6 g for chassis A3, whereas all measurements for chassis B4 are well below the required 5 g limit in the range 10–100 Hz. These outcomes prove the findings from vibrational analysis that the addition of NCF has made the mould chassis more rigid, enabling it to withstand vibration in a much more efficient manner than the PC–ABS–MF mould chassis where the peak is at 16 g at 95 Hz.9

Conclusion In this study, PC–ABS-based composite materials with NCF were developed and pelletized to realize improved dispersion of fillers in the mould chassis. The


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application of this new material in a car audio chassis was analysed through tests on mechanical properties and morphology, EMI testing and vibration analysis. NCF was used to balance both the mechanical and the electrical properties of the composites. The role of this filler was specifically investigated and compared with the results from previous studies, namely a mould chassis using a PC–ABS composite with 3 wt% MF and 7 wt% GF. The following conclusions are drawn from this study. 1.

2.

3.

4.

The tensile strength and the impact strength of the test materials are far superior to those in the previous study. Also, 12 wt% NCF is a more appropriate proportion than 10 wt% NCF because the EMI SE of PC–ABS–12 wt% NCF is higher than 40 dB, which is the EMI SE regulation for car audio. Although the EMI results of this study are not perfectly conclusive as appropriate hardware needs to be developed for the use of moulded chassis, the EMI SE results were very stable under both the sample specimen measurements and the actual car audio chassis measurements owing to the improved dispersion of fillers by the pelletization of the PC– ABS–NCF composite. Vibration measurements (both computer-aided engineering and actual results) show that the requirement of less than 5 g in the 10–100 Hz frequency range is met; hence, the design is appropriate in a general vehicle driving environment. Considering all the results, the new mould chassis using PC–ABS–NCF has improved mechanical and electrical properties. In other words, the application of this new model in car audio is possible, and only the cost aspect has to be overcome.

Funding This work was supported by LG Electronics, Republic of Korea and by Korea University. Acknowledgements This research was accomplished through academic– industrial cooperation with LG Electronics and the Department of Mechanical Engineering in Korea University, Seoul, Republic of Korea. The research on polymer and injection moulding was carried out with LG Chem, Ltd. The authors would like to acknowledge the researchers of LG Chem, Ltd and LG Electronics for supporting this work successfully. References 1. Moriarty P and Honnery D. The prospects for global green car mobility. J Cleaner Prod 2008; 16(16): 1717– 1726.

2. Hayes J. What price the green car? Reinf Plast 1990; 34(4): 48. 3. Rosato DV. Advances in moulding reinforced plastic parts for automotive applications: a review of the industry in the USA. Composites, 1990; 4(5): 208–217. 4. New plastics techniques used in UK car: Reliant Motor PLC Tamworth Staffordshire B77 1HN. Mater Des 1984–1985; 5(6): 271–272. 5. Yin ZN, Fan LF and Wang TJ. Experimental investigation of the viscoelastic deformation of PC. ABS and PC/ ABS alloys. Mater Lett 2008; 62(17–18), 2750–2753. 6. Joseph K, Randy WS and Peter PP. Physical property retention of PC/ABS blends. Polym Degradation Stability 1994; 43(2): 285–291. 7. SPE Automotive Innovation Awards. Soc Plast Engrs, Plast Engng 2010; 66(1): 38. 8. Jeon SH, Kim HM, Park TH, et al. Development of polycarbonate/acrylonitrile–butadiene–styrene copolymer based composites with functional fillers for car audio chassis. Mater Des 2011; 32(3): 1306–1314. 9. Jeon SH, Park TH, Kim HM, et al. Development of a new light-weight car audio using polycarbonate/acrylonitrile–butadiene–styrene copolymer based hybrid material. Int J Precision Engng Mfg 2012 (in press). 10. Karnik SR, Gaitonde VN, Campos Rubio J, et al. Delamination analysis in high speed drilling of carbon fibre reinforced plastics (CFRP) using artificial neural network model. Mater Des 2008; 29(9): 1768–1776. 11. Donald MB. Mechanical, thermal and electrical properties of metal fibre filled polymer composites. Polym Engng Sci 1979; 19(16): 1188–1192. 12. Lee NJ and Jang J. The effect of fibre content on the mechanical properties of glass fibre mat/polypropylene composites. Composites Part A: Appl Sci Mfg 1999; 30(6): 815–822. 13. Talib ARA, Ali A, Badie MA, et al. Developing a hybrid carbon/glass fibre-reinforced, epoxy composite automotive drive shaft. Mater Des 2010; 31(1): 514–521. 14. Tzeng S-S and Chang F-Y. EMI shielding effectiveness of metal-coated carbon fibre-reinforced ABS composites. Mater Sci Engng A 2001; 302(2): 258–267. 15. International Electrotechnical Commission, International Special Committee on Radio Interference. Information technology equipment – radio disturbance characteristics – limits and methods of measurement. International Standard CISPR 22, 5th edition, 2005–2004. 16. Al-Saleh MH, Gelves GA and Sundararaj U. Copper nanowire/polystyrene nanocomposites: lower percolation threshold and higher EMI shielding. Composites Part A: Appl Sci Mfg 2011; 42(1): 92–97. 17. Jeon SH, Lee HJ, Park TH, et al. Analysis of injection moulding conditions of car audio mould chassis using PC/ ABS based composites. In: KSPE spring conference, Jeju, Republic of Korea, 2010, pp. 1225–1226. Seoul: KSPE. 18. Inman DJ. Engineering vibration, 2nd edition. Upper Saddle River, New Jersey: Prentice Hall, 2001. 19. Zhang X, Zheng Y and Han J. Low-pressure injection moulding and SHS–HIP without envelope of AlN–TiB2 ceramic slender tube with blind hole. Mater Des 2005; 26(5): 410–416. 20. Lawrence WE, Manson JAE and Seferis JC. Thermal and morphological skin-core effect in processing of


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thermoplastic composites. Composites 1990; 21(6): 475– 480. 21. Lee TK and Kim BS. Vibration analysis of automobile tire due to bump impact. Appl Acoust. 2008; 69(6): 473–478. 22. Choi SB, Kim HS and Park JS. Multi-mode vibration reduction of a CD-ROM drive base using a piezoelectric shunt circuit. J Sound Vibr 2007; 300(1–2): 160–175. 23. McFadden PD and Smith JD. Vibration monitoring of rolling element bearings by the high-frequency resonance technique – a review. Tribol Int 1984; 17(1): 3–10.

24. Ji JC and Zhang N. Suppression of the primary resonance vibrations of a forced nonlinear system using a dynamic vibration absorber. J Sound Vibr 2010; 329(11): 2044– 2056. 25. Jeon SH, Park TH, Jung EI, et al. Analysis of vibration characteristics of car audio chassis using PC/ABS hybrid composites. In: KSPE fall conference, Daegu, Republic of Korea, 2009, pp. 431–432. Seoul: KSPE.


Engineering Engineers, Part D: Journal of Automobile ...

Engineering Engineers, Part D: Journal of Automobile ...

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