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Master of aerospace and aviation engineering

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Engineering sustainability in aviation

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AERO 2461

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12/10/2014

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Roberto Sabatini

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Guan Kai S3407535

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Metallic Composite Materials in

Aviation Industry

ASSIGNMENT

AERO 2461 Engineering Sustainability in Aviation

(Master of aerospace and aviation engineering)

Prepared by

Guan Kai No. 3407535

1

Table of Contents

Acronyms .......................................................................................................................................... 2

1.0 Introduction ...................................................................................................................... 3

1.1 Background ................................................................................................................... 3

1.2 Aim ................................................................................................................................ 4

2.0 Material applications ......................................................................................................... 4

2.1 Fibre metal laminates (FMLs) ........................................................................................ 4

2.1.1 Aramid Reinforced Aluminum Laminate (ARALL) .............................................. 6

2.1.2 Glass Reinforced Aluminum Laminate (GRALE) ................................................. 7

2.1.3 Carbon fiber aluminum laminates (CARALL) ................................................... 11

2.1.4 Advantages of using FMLs ............................................................................... 11

2.1.5 Challenges of FMLs .......................................................................................... 12

2.2 Sandwich structure ..................................................................................................... 15

2.2.1 Bonded repair of composite sandwich structures .......................................... 16

2.2.2 Advantages of using sandwich structure ......................................................... 17

2.2.3 Challenges of sandwich structure ................................................................... 18

3.0 Case study ....................................................................................................................... 19

3.1 Model description ....................................................................................................... 19

3.2 Application analysis ..................................................................................................... 20

4.0 Benefits and challenges of light weight metallic composite materials ........................... 23

4.1 Benefits ....................................................................................................................... 23

4.2 Challenges ................................................................................................................... 25

5.0 Conclusion ....................................................................................................................... 26

6.0 Recommendations .......................................................................................................... 27

7.0 References ....................................................................................................................... 29

2

Acronyms

ARALL Aramid Reinforced Aluminum

Laminate

ATSB Australian Transport Safety

Bureau

CARALL Carbon fiber aluminum laminates

CFRP Carbon-fiber-reinforced polymer

FAA Federal Aviation Administration

FMLs Fibre metal laminates

GLARE Glass Reinforced Aluminum

Laminate

3

1.0 Introduction

1.1 Background

Nowadays, traveling by air costs much less than decades before. As the

increasing of low cost carriers, people could even use $10 to travel between

Sydney and Melbourne (JetStar activities). As the transportations link

between airport and center of the city become more and more convenient and

efficient, traveling by air cost much less time than other transportations.

Businessman could travel and do business among different cities without any

delay. Therefore, more and more people prefer travelling by air to save time

and use time more efficient. As Boeing and Airbus reports, the airline traffic

RPKs will grow around 5% yearly in future 20 years. (Airbus 2014b; Boeing

2012) Therefore, to catch up with this growth, more and more aircrafts will

be produced and operated by airliners. More aircrafts and airline traffic could

help the world economy increase quickly, but it will also cause a huge

greenhouse gas pollution.

Aircrafts emissions are more serious than other transport because the

emissions will directly release into high altitude atmosphere. Emissions at

high altitude will cause much more damage to the atmosphere than ground

ones (Scelsi et al. 2010). Therefore, it is quite important to reduce the aircraft

emissions to make the development of aviation reach the sustainability. On

the other hand, as shows in Airbus’s report, the fuel price increase nearly 4

times in the past 10 years (Airbus 2014b). Thus, to make the airlines

operating economical, the aircrafts should be reduced of using jet fuel. Since

most of the aircraft emission comes from the engine burns fuel, the direct

approach to reduce the aircraft emissions and fuel cost is designing more

efficient and less emission engines. However, as the engine is one of the most

complex system of aircrafts, designing more efficient engine need huge

money and time. Thus, another direct way to reduce the emissions is reduce

4

the aircrafts weight. The aircrafts could burn less fuel to produce less power

with a lighter bodies. Also, using lighter materials, the aircrafts could be

designed larger and carry more passengers without increasing the propulsion.

1.2 Aim

The aim of the report is to point out the innovative metallic composite

materials using currently and analysis these materials in detail to find out

their advantages and challenges.

2.0 Material applications

The aluminum alloy is widely used in aircraft structure because it costs less to

produce, has high strength to support the aircraft structure and lighter than other

metals. However, as the development of aircraft technology, aluminum alloy

cannot meet people’s requirement of lighter aircrafts. At the same time, the fuel

prize increase multiply in recent decades. A most important issue to affect the

usage of fuel is the weight of the aircraft (Campbell 2006d). In addition, people

need more large aircrafts (such as A380) to meet the requirement of increasingly

busy airlines. Thus, people began to search for new materials which could take

place of aluminum alloy. Therefore, metallic composite materials which are first

been used in military after Second World War (Sinmazçelik et al. 2011), was

invented into civil aviation. The following chapter will point out these new

designed metallic composite materials and detailed analysis these applications.

2.1 Fibre metal laminates (FMLs)

FMLs are hybrid composite structures based on thin sheets of metal alloys

and plies of fibre reinforced polymeric materials (Cortés & Cantwell 2006).

Because fibre reinforced polymeric materials are lighter than aluminum

alloys, inserting fibre reinforced polymeric materials between aluminum

alloy sheets could help to reduce the weight of aluminum alloy much without

reducing its strength. The Figure 1 shows the FMLs classifications and the

most commonly applications are ARALL and GLARE. In 1978, the first

generation ARALL was introduced and CARALL was developed from

5

ARALL later. (Reyes Villanueva & Cantwell 2004) However, because the

CARALL shows poor fatigue performance during the test, it has not been

used. In 1990, another material developed from ARALL, GLARE was

introduced and became another main FMLs quickly. (Asundi & Choi 1997)

The following chapters will detailed claim these FMLs.

Figure 1: Classification of FMLs

Source: (Sinmazçelik et al. 2011)

6

2.1.1 Aramid Reinforced Aluminum Laminate (ARALL)

Figure 2: Schematic presentation of ARALL 2

Source: (Sinmazçelik et al. 2011)

The ARALL laminates use high strength aramid fibres embedded into

aluminium sheets to increase the material’s strength and reduce its weigh

at the same time (see Figure 2). Thus, using ARALL laminates could

help the aircraft reduce its weight. The aramid fibre is insensitive to the

loading just as Figure 3 shows, which gives the ARALL an advanced

ability on crack-grow protection. That means, the ARALL structure

could bear more load for longer time when crack occur. It makes the

aircraft safer on protecting fracture. At the same time, this ability makes

the ARALL has a longer life cycle comparing with aluminium alloys.

Therefore, the maintenance costs of ARALL will be lower than

aluminium alloys. Furthermore, the ARALL laminates also carries the

advantages of aluminium alloys, such as low cost and easy to produce.

(Sinmazçelik et al. 2011) Since the ARALL could protect fatigue better

than aluminium alloy, it is mainly used for fatigue dominated parts of

the aircraft, such as low wing skin, the pressurized fuselage cabin and

cargo doors.

7

Figure 3: Crack bridging mechanism of ARALL laminates

Source: (Sinmazçelik et al. 2011)

However, the ARALL laminates are weak in bending, buckling,

compression loading and transverse tension. Therefore, the using area

of ARALL is quite limited and it cannot use in the area where will

suffer complex loading. At the same time, the ARALL can only form

strong bonds with aluminium which limits the research area for

developing better FMLs based on aramid fibre. Furthermore, the

aramid fibre is easily to absorb moisture which makes the inner-

aluminium get corrosion easily. The corrosion inside materials are quite

hard to find out. Thus, ARALL laminates need high-tech equipment to

check for corrosion and the corrosion risk is higher than alumunium

alloys. (Sinmazçelik et al. 2011)

2.1.2 Glass Reinforced Aluminum Laminate (GRALE)

The structure difference between ARALL and GRALE is that ARALE

laminates use glass fibre instead of aramid fibre. The density of GRALE

laminate is at least 8% lighter than aluminium alloy (Wu & Yang 2005),

8

but it is higher than aramid fibre (Sinmazçelik et al. 2011). Thus, using

GLARE laminates cannot significant reduce the aircraft weigh as

ARALL laminates do. However, comparing with ARALL, glass fibre

has a better adhesion which could make the FMLs structure stronger.

Additional, the GLARE does not absorb moisture which makes it have

a good ability on protecting inner-corrosion. (Sinmazçelik et al. 2011)

On the other hand, because of the structure character of glass fibre, the

GLARE laminates has higher longitudinal strength but lower strength in

transverse direction for both tensile and compressive behavior.

Therefore, as Figure 4 shows, two glass fibre sheets will be put cross-

plied (such as 90° and 0° or +45° and -45°) to make sure the GRALE

laminates could have a higher strength in either directions. However, the

yield strength of GLARE laminates is still lower than aluminium alloy.

(Wu & Yang 2005)

Figure 4: Schematic illustration of a cross-ply GLARE laminates

Source: (Sinmazçelik et al. 2011)

From Figure 5 it could be seen that the GLARE laminates also have an

advanced ability on fracture protection when crack occurs than

aluminium alloys. It also makes the GLARE has good crack protection,

as Figure 6 shows. The GLARE crack-growth rates are 10-100 times

9

slower than aluminium alloys. Furthermore, From Figure 7, it could be

seen that GLARE has a quite higher impact behavior comparing with

other materials. (Wu & Yang 2005) However, the GLARE laminates

have low stiffness which makes it cannot defense elastic deformation

with very high loading. (Sinmazçelik et al. 2011)

Figure 5: The fracture behavior of GLARE laminates

Source: (Wu & Yang 2005)

Figure 6: The fatigue behavior of GLARE

Source: (Wu & Yang 2005)

10

Figure 7: The impact behavior of GLARE

Source: (Wu & Yang 2005)

11

2.1.3 Carbon fiber aluminum laminates (CARALL)

As the ARALL laminates have poor compressive strength, CARALL

which is developed base on ARALL was introduced. The CARALL uses

carbon fibre replace the aramid fibre (see Figure 8) which gives the new

materials higher specific modulus, but relatively low values of specific

strength, strain to failure and impact resistance.

Figure 8: schematic illustration of CARALL laminates

Source: (Sinmazçelik et al. 2011)

2.1.4 Advantages of using FMLs

Based the analysis before, it could be seen that FMLs are advanced

materials that could be used to replace aluminium alloys in some area of

the aircraft. An obvious benefit of using FMLs is that it could help to

reduce the weight of aircraft 20% - 50% (MRAZOVA 2013). The Boeing

787 Dreamliner, half of which use composite materials, is 10,000 lbs

lighter and burns 20% less fuel than a comparably-sized all-aluminium

aircraft (Massengill 2005). It is well know that less fuel burning means

less emission and less damage to environment. In addition, some

materials such as glass fibre, are not limited by the width of aluminium

12

alloys. Thus, these materials allow tailor-made skin of any size which

could help the aircraft become more streamlined and more suit for

aerodynamic. (ADVANCED GLASSFIBER YARNS LLC 2006) It

could also help to reduce the burning of fuel and emissions. Furthermore,

the FMLs could protect the inner-electrical-corrosion well by insert

insulating layer between aluminium sheets. The aircraft will be more

reliable and the corrosion protection maintenance work load could be

reduced. (MRAZOVA 2013) Moreover, the FMLs also have the ability

to reduce the crack-grow rates. The crack-grow rates reduction and

inner-electrical-corrosion, could help to extend the aircraft structure life-

circle much. A longer life-circle lead to less materials consumption and

maintenance work. The pollution for producing materials and the

pollution during maintenance which are also important pollution sources

of aviation industry could be reduced.

2.1.5 Challenges of FMLs

As FMLs are new high-tech materials, it still has many challenges which

need to solve by material improvements. The FMLs may have non-

visible impact damage which cannot be found out during visible A or B

check, just as Figure 9 shows in left side. It will increase the maintenance

work because these kinds of damage need high-tech equipment (such as

X-ray tomography, Laser shearography and infrared imaging) to find out.

(ATSB 2007) Additional, the reparations for FMLs will be different than

other metal structure. That means the engineerings need more training

and higher knowledge. (MRAZOVA 2013) On the other hand, the

nonrecurring cost for producing some of FMLs, such as GLARE, is

higher than aluminium alloys (Campbell 2006c). It will make the cost of

aircraft increase as well.

13

Figure 9: Delamination and disbonding in composite laminates

Source: (Werfelman 2007)

Furthermore, from the Figure 10, it could be seen that the GLARE are

much less environment friendly than Al 2024. That is because the Al

2024 is produced by 100% recycle aluminium and recycle aluminium

need much less energy. Even the recycle aluminium are not allowed to

be used on new aircrafts, with the cooperation, the manufacturing

technology for GLARE still has a large space to develop. (Scelsi et al.

2010) At the same time, from the Figure 10, it could be seen that the

introduction of Carbon-fiber-reinforced polymer (CFRP) is also a

challenge for FMLs. The CFPR is even lighter and more strength than

FMLs and it has less impact during manufacturing. Therefore, FMLs

still has many weakness need improvement to make it more widely used

and produce less environment impact.

14

Figure 10: Single score impact results for manufacturing and disposal of Al 2024,

CFRP and GLARE panels

Source: (Scelsi et al. 2010)

15

2.2 Sandwich structure

The sandwich structure was found from the nature environment and it was

first be described by W. Fairbairn in 1849 for the Britannia Tubular Bridge

in North Wales (Herrmann, Zahlen & Zuardy 2005). It could be seen quite

easily in the wild, such as the branches of the trees and the bones of animals.

The sandwich could make the whole structure more weight effectiveness.

Therefore, using sandwich structure on the aircraft could also reduce the

aircrafts weight much. From Figure 11, it could be seen that the sandwich

structure could be separated depending the different core inside. The

honeycomb cores (such as tails, flaps, spoilers and carbon floor panel) and

foam cores are the sandwich structures that current aircrafts mainly used.

Depending different materials used for the cores, the sandwich structure

could have much different characters and could be used in different

conditions. (Herrmann, Zahlen & Zuardy 2005)

Figure 11: Different sandwich core types

Source: (Herrmann, Zahlen & Zuardy 2005)

16

2.2.1 Bonded repair of composite sandwich structures

Based on the structure character of sandwich cores, the composite

sandwich structures could bonded repair by only replacing the failure

part. The Figure 12 shows the basic method of bonded reparation. It

could be seen that the reparation work cost long time because the surface

need to be polished and repaired piles by piles. In addition, after

complete the fixing, the repaired place needs to be dried and have an

intensity test. Therefore, repairing the sandwich structure is a complex

work and need to spend a long time. For further detail reparation, please

see (FAA 2004).

Figure 12: Schematic of a scarf repair applied to a sandwich component

Source: (FAA 2004)

17

2.2.2 Advantages of using sandwich structure

Similar with FMLs, sandwich structure also weight effectiveness which

makes the aircraft weight reduction become easier. Also, based on the

structure characters of sandwich cores, the sandwich structure is

continuous stiffness distribution. Thus, the sandwich structure does not

need complex cross-overs of stiffening elements, such as frames and

stringers, to support large surface. At the same time, complex frames

free also means that the surface of the structure could be smooth without

setting many rivets to fasten the frames as shows in Figure 13. In

addition, without complex structures, the production processes could

also become simple. (Herrmann, Zahlen & Zuardy 2005) Furthermore,

the Sandwich Structures have an excellent damping behavior and good

energy absorption (Majamäki 2002). Therefore, using sandwich

structure to make fuselage shells could reduce the cabin noise and give

passengers a better condition.

Figure 13: Aircraft wing

Moreover, with different core materials, the sandwich structure could get

different advantages. For example, using materials that are self-

extinguishable and nontoxic, the sandwich structure will have good

ability on protecting fire and smoke which could increase the survival

rate in accidents. Also, the core with low water absorption could help the

aircraft from increasing weight by absorbing water. Additional, non-

18

corrosive cores could help the sandwich structure to protect corrosion

significantly. Furthermore, as shows in last chapter, the cracks and

slamming damage could be repaired by partly replaced instead of replace

the whole structure. It makes the maintenance cost reduce much. (DIAB

Knowledge Series) Additional, the structure life cycle could also be

extended which could help to reduce the pollution for manufacturing and

the usage rate of unrenewable material.

2.2.3 Challenges of sandwich structure

The sandwich structure could get many benefits from different cores, but

it will also increase the complexity of the sandwich structure. Using

sandwich structure with different cores means more knowledge should

be learnt for engineers, and it will also make the sandwich structure

maintenance work more complex. In addition, similar with FMLs, the

sandwich structure also hardly to find out structural failures inside the

core. At the same time, although the sandwich structure could be

repaired partly, the reparation work are quite complex for novice and

cost long time to finish. (Herrmann, Zahlen & Zuardy 2005)

Furthermore, the sandwich structure has a good resistance for crack and

corrosion, but it is more sensitive to other types of damages. The damage

could cause disbonding, delamination, and internal crushing. (FAA 2004)

Thus, the sandwich structure still need complete failure check system to

make sure it work well. Therefore, to make the sandwich structure

become the primary structure of aircrafts, there are still many researches

need to be done to improve it.

19

3.0 Case study

Nowadays, the high-tech metallic composite materials have already been used on

the modern aircrafts. In this section, a detail model (A380) will be used to fully

analysis the high-tech metallic composite materials applied in current aviation

industry and how the light weight composite materials affect the aviation industry.

3.1 Model description

A380 is the largest commercial aircraft in the world. Its typical operating

empty weight is around 25 tons and it could carry more than 500 passengers.

(Airbus 2014a) Besides the more powerful engine and aerodynamic structure

design, using lighter materials to reduce the total weight of the aircraft is one

of the main reason that this large metal could fly into sky. The A380 is 15

tons lighter than it would be if made entirely of metal (Airbus).

20

3.2 Application analysis

The Figure 14 shows the different sandwich applications on A380. The

common character of these parts is that these parts stress load is simple and

comes from single direction. For example, the cabin floor panel is used

mainly support the load comes from the passengers weight, and the flaps are

mainly used for suffer the pressure comes from high speed air at the downside

surface. These sandwich applications help to reduce the weight of A380

effectively.

Figure 14: sandwich applications on A380

Source: (Herrmann, Zahlen & Zuardy 2005)

In the figure 15, the vertical tail plane (VTP) of A380 is separated into 5

major structural

Assemblies:

1. Leading edge fairings (including tip and dorsal fin)

2. Center box structure (including the interface to the fuselage)

21

3. Trailing edge fairings

4. Rudder

5. Fin – fuselage fairing

For the leading edge fairings, because the antennas are installed behind the

leading edge, the leading edge need to allow for electromagnetic

transmission. Therefore, this part is made by NOMEX® honeycomb and

GLARE which are good at transmit electromagnetic. (Herrmann, Zahlen &

Zuardy 2005)

Figure 15: VTP major structural assemblies

source: (Herrmann, Zahlen & Zuardy 2005)

The Figure 16 shows part of the fuselage of A380 which is made by GLARE.

The A380 has about 380 m2 GLARE fuselage which helps the A380 reduce

about 794 kg of weight (Wu & Yang 2005). It could be seen that with GLARE,

the aircraft fuselage block could be built quite large. As all know, the

reliability and strength would be much high for a complete structure than an

assembly structure. At the same time, the Figure 17 claims the benefits the

A380 gets from using GLARE instead of aluinium alloys. It could be seen

that the GLARE fuselage is more reliable than aluminium alloys. At the same

22

time, because the glass fibre inside GLARE is good at fire protection, using

GLARE to build the fuselage could help the aircraft protect the fire outside

and save the passengers. (Fokker Technologies)

Figure 16: Over 30 sq. metres of fuselage for the Airbus A380, including stringers

Source: (Fokker Technologies)

Figure 17: GLARE VS. ALUMINIUM Comparison Ratio

Source: (Fokker Technologies)

23

All of these new high-tech composite materials make the A380 could

strength its huge body and could be powered by its four engines with a lighter

weight. However, comparing with other two engines aircrafts, four engine

will produce double emission. Thus, the A380 still need to continually reduce

its weight so that the A380 could have three, even two engines to power.

4.0 Benefits and challenges of light weight metallic composite

materials

4.1 Benefits

Making aircraft lighter has many benefits. A FAA Advanced Materials

Research Program report claims that every pound of aircraft weight reduction

could save US$100-300 over the aircraft’s service life. (ATSB 2007) Lighter

aircraft lead to the reduction of propulsion to support the aircraft to fly. The

engine power could also be reduced which could lead to less emission and

less noise produced by engine. At the same time, on the premise of keeping

engine power, the aircraft could be designed larger with light materials. It

means the aircraft could carry more passengers in one time, and the flight

frequency could be reduced which could help to reduce the emission and

noise per passenger. The aircraft will become more efficient.

Moreover, the new high-tech metallic composite materials allows tailor-

made skins of any size. Thus, with these new materials, the aircraft could be

designed more suitable for aerodynamic. The resistance could be reduced

which could also help to reduce the engine power and the emission. At the

same time, the noise produce by air-friction could also be reduced. Moreover,

less propulsion also means less fuel burning. Thus, the usage rate of

unrenewable jet fuel could be reduced to meet the sustainability. Furthermore,

the higher weight efficient materials could support the next generation

aircraft’s design. The new materials could build a new aircraft body which is

24

totally different from current aircrafts as Figure 18 shows. This new aircraft

could carry much more passengers than current aircrafts and will significant

reduce the aircraft emission per passenger.

Figure 18: Cross section of future BWB ‘Clean Era’

Source: (Fokker Technologies)

In the life-long maintenance, the new lightweight materials also show

advantages comparing with aluminium alloys. Because the new materials

have good resistance for corrosion, crack and fatigue, the materials life time

will be much longer than aluminium alloys. That means the number of new

materials production which are used for replaced failure ones could be

reduced. Therefore, the pollution for producing new materials could also be

reduced. In addition, less failure materials could also reduce the maintenance

costs and pollutions. Therefore, during the whole service life of the aircrafts

with new materials, their total costs and pollutions will be much lower than

all-aluminium aircrafts. Moreover, long-life materials could also help to

reduce the usage rate of unrenewable metals to meet the sustainability.

25

4.2 Challenges

Besides of the benefits, there are still many challenges for the new

lightweight metallic composite materials. The firstly challenge is the training.

The introduction of new materials means a large number of new training

programs. No matter the design, manufactory and maintenance are also need

to be trained to make sure the aircrafts’ mechanical properties with new

materials are under control. These program will cost much money and take

long time. On the other hand, the metallic composite materials have many

new properties comparing with aluminium alloys, such as non-visible failure.

Thus, these new materials need new high-tech equipment to support the

maintenance. This will also cost much money for the new equipment.

Furthermore, even the newest high-tech Boeing 787 Dreamliner only use 50%

of composite materials by weight to replace aluminium alloys (ATSB 2007).

That is because the composite materials still has many weakness and

limitations which makes them cannot be widely used as aluminium alloys do.

Therefore, further research still need to be done to improve the widely

adaptive of the composite materials. Another challenge for using composite

materials is that the manufacturing cost is much higher than aluminium alloys.

That means more composite materials are used, higher the aircraft prize will

be. Higher prize will cost higher investment risk. Moreover, even the life

cycle for lightweight composite materials is much longer which reduce the

usage rate of unrenewable metals, the manufacturing of lightweight

composite materials will cost more fossil fuels and renewable materials

comparing with aluminium alloys. (Beck et al. 2008) From the figure 19, it

could be seen that the GLARE need a long time after manufacturing to

display its advance with aluminium alloys. Therefore, the manufacturing

processes also need to improve to make it more suitable for sustainability.

26

Figure 19: Schematic of “Break-even” in terms of fuel use for aluminium, GLARE

and carbon-fibre epoxy resin composite

Source: (Beck et al. 2008)

5.0 Conclusion

Depending the analysis before, it could be seen that the metallic composite

materials play an important role on reducing aircrafts’ weight and increase the

aircraft structure strength. With the high weight-strength efficient composite

materials, the aircraft could be designed more open. Many new design method

could come true, such as blended wing body aircraft. At the same time, light

weight composite materials could help to reduce much weight of aircraft which

gives many benefits to the environment and make the aviation industry meet the

sustainability. However, there are still many challenges for metallic composite

materials which block it be widely used on the whole aircraft. The challenges

both comes from the internal (such as structure limitation and complex structure)

and external (such as the competition from the recycle aluminium alloys and

cabon-fibre materials). Therefore, the metallic composite materials still have

much research need to be done.

27

6.0 Recommendations

Fully training engineers

As the metallic composite materials have much more complex structure and

need higher level maintenance equipment, the maintenance engineers also

need to have advanced knowledge, so that they could find out failure timely.

At the same time, because the composite materials may have non-visible

failure which need to use high-tech equipment to check, the engineers also

need have enough knowledge to use the equipment and know how to assess

the result comes out from these equipment. Furthermore, different with

aluminium alloys, some composite material could use bonded repair instead

of structure replace. Therefore, the engineers need to grasp the bonded repair

skill so that they could finish the maintenance work without any delay.

Further mezzanine metals and cores research

Currently, most common used mezzanine are fibre, glass fibre and carbon

fibre. All of those mezzanines have some limitation which makes them

cannot widely applied on whole aircraft. Therefore, further research still need

to be done to find out whether there are some other mezzanines that are even

better than the current ones. For the sandwich structure, because it has the

advantages that the Properties could be different with different cores, new

innovate core could be found to replace the aluminium alloys structure that

currently used. It could make the aircraft even lighter with more aluminium

alloys replaced by sandwich structure. Therefore, the aircraft could be design

even lighter and more sustainable.

Manufacturing processes development

As claimed in the report above, producing metallic composite materials will

cost more nonrenewable materials and cause more pollutions. Although the

environment benefits of composite materials could be seen in a long period,

the start environment impact could be reduced to make the composite

materials much more environment friendly than aluminium alloys. People

28

will more prefer to accept new materials that the benefits could be seen in a

short period. Therefore, it could indirectly promote the application of

composite materials on aircrafts. At the same time, the producing cost also

need to be reduced to reduce the total cost of aircraft so that the investment

risk could reduce as well to attract more airliners use newly lightweight

aircrafts. The whole aviation industry will meet the sustainability easily.

Develop the bonded repair processes

As shown before, the bonded reparation could help to save the usage of

materials and reduce the maintenance cost, but the reparation processes are

to complex and cost long time and need complex test after maintenance work.

These maintenance work is too complex for natives and much easy to make

mistakes. Therefore, the reparation process and the maintenance equipment

need to be improved to make the maintenance work more simple and efficient.

Additional, the improvement could help to increase the composite reliability.

Develop the failure check equipment

Because the composite materials are more likely to have non-visible failure

than aluminium alloys, the composite materials need to be taken care more

carefully. However, without large equipment, it is quite hard to find out non-

visible failure during A or B check. Thus, if the composite materials get

inner-failure between C and D check, it would be a serious hazard for the

aircraft. Therefore, the small equipment that could be carried by human to

check inner-failure for some failure frequency area during A check or daily

check, could help to increase the aircraft safety.

29

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