The Replacement Of Metallic Component

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02 Nov 2017

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In recent years, the composite industries have begun to recognize that their business opportunities offer to various commercial applications is much larger than they have ever thought of. The introduction of newer polymer resin matrix materials and other high performance reinforcement fibres has shown a steady increased in usage and volume. A summary of genealogy for polymeric composites are shown below:

In mid 1930’s - first known composite product was using a fiber-glass fabric and polyester resin laid in a foam mold producing a boat hull.

In early 1940’s - fiber-reinforced polymer (FRP) composite materials were used in aerospace and naval applications for defence industry.

In 1960’s - the marine market was the next largest consumer of composite materials.

In 1970’s - the automotive market surpassed marine sector as the number one market; a position it retains until now.

In 1980’s - new development of FRP for construction sector that needed special requirement in areas that were subjected to chemical attack.

In early 2000 - polypropylene nanocomposites had come into use for large scale automotive applications such as engine covers and fuel lines.

In Figure 1, a schematic diagram has shown the relative importance of polymers and composites as a function of time.

Figure 1 - Schematic diagram show the relative importance of polymers and composites as a function of time. The time scale is nonlinear. (Source: Ashby, 1987)

The drivers for this change

Polymeric composites can be used for metal replacement; however there are several key differences in terms of their properties. They must be able to meet numerous design requirements with significant weight savings as well as high strength-to-weight ratio as compared to conventional materials.

Table 1 - Comparsion between aluminium, steel and polymer. (extracted from 2012 CES software database)

General

Properties

Aluminium (7075, wrought, T6)

Steel (coated steel, terne coated)

Polymer (Kelvar 149, aramid fiber)

Density

2.65e3 - 2.71e3 kg/m^3

7.85e3 - 7.9e3 kg/m^3

1.46 e3 - 1.48e3 kg/m^3

Price

3.99 - 4.39 SGD/kg

1.81 - 1.98 SGD/kg

115 - 286 SGD/kg

Mechanical

Young’s modulus

69 - 76 GPa

185 - 200 GPa

170 -190 GPa

Flexural modulus

69 - 76 GPa

185 - 200 GPa

170 - 190 GPa

Shear modulus

26 - 28 GPa

79 - 84 GPa

1 - 1.3 GPa

Tensile strength

434 -580 MPa

345 - 580 MPa

3.2e3 - 3.6e3 MPa

Flexural strength

359 - 530 MPa

250 - 395MPa

2.5e3 - 3e3 MPa

Hardness

152 - 168 HV

107 - 170 HV

25 - 30 HV

Fatigue strength at 10^7 cycles

152 - 168 MPa

107 - 223 MPa

2.5e3 - 3e3 MPa

Durability

Flammability

Non-flammable

Non-flammable

Highly flammable

Fluids (fresh water)

Excellent

Acceptance

Acceptance

Fluids (salt water)

Acceptance

Acceptance

Acceptance

Weak acids

Excellent

Acceptance

Limited use

Strong acids

Excellent

Limited Use

Acceptance

Weak alkalis

Acceptance

Excellent

Acceptance

Material Recycling

Recycle fraction in current supply

40.5 - 44.4 %

52.3 - 57.8 %

0.0475 - 0.0525 %

Downcycle

Yes

Yes

Yes

Landfill

Yes

No

Yes

Biodegrade

No

No

No

Some of the comparisons for polymer versus aluminium and steel are shown in Table 1, there are:

Tensile strength in polymer is around 6 -7 times greater than steel or aluminium;

Polymer are around 60-70% lighter than steel or aluminium which can be designed to meet the same functional requirements as steel or aluminium;

Lower embedded energy in polymer as compared to steel or aluminium;

Polymer are more versatile than steel and aluminium as they are easier to meet to complex design requirements;

Long life in polymer as it can offers excellent fatigue, impact, environmental resistance and reduced in maintenance; and

Polymer enjoys reduced life cycle cost compared to steel and aluminium.

Aramid fibers, of which Kelvarâ„¢ is best known example, are aromatic polyamide polymers strengthened by a backbone containing benzene rings and examples of liquid-crystalline polymers in the polymer chains are rod-like and very stiff. They have excellent strength and stiffness but are limited to low-temperature use. In Figure 2, composite materials are shown by comparing tensile strength vs density.

Figure 2 - Tensile strength vs Density in Material Graph extracted from 2012 CES software database

Many manufacturers in the world provide excellent and high performance applications. For example:

Americhem Inc.- Infinity Compounding

Infinity Compounding Corp. is based in Logan Township, New Jersey. While they offers glass and carbon fiber reinforced and mineral and process additive filled structural compounds, they are also specializes in various manufacturing industries like medical, electrical, disk drive, and aerospace.

Meggitt PLC - Polymers & Composites

Meggitt Polymer & Composites has been a leader in the design, engineering and manufacture of robust, cost effective, sealing solutions, for almost 40 years. Seals for aircraft and oil platforms; flexible fuel tanks and their coatings; ice protection systems and sub-assemblies; and helicopter interior panels and accessories are some of the products produced by this company.

The technological advances and its limitations

There are many new technological advancement for polymeric materials globally, however I have name 2 of them together with their limitations below.

Polymeric materials like nano-materials, sol-gel materials, conductive and functional polymeric materials, and biomaterials have been used as electron mediators and immobilizing matrices in the design for sensors and biosensors.

However, there are a number of limitations in fulfilling for such applications.

While there are difficulties in production of pure and defective-free polymers, it is also very costly;

Processing of carbon nano-tubes is still in initial stage, prevention of aggregations for such tubes are not yet achievable;

Tube lengths are not reproducible, insoluble in most solvents; and

Long laboratory time and high costs are involved in the production such polymeric materials.

The nano-composites have recently shown many potential applications such as structural components for aircraft bodies, wind turbine blades, light-weight materials for electromagnetic interference (EMI) shielding and materials for strong and flexible fibers.

However, limitations for such composite materials have cost delay in manufacturing.

Reinforcing fillers has been restricted due to the drawback of Carbon Nano-Tubes (CNT) during its fabrication process.

Enhancing the compatibility of and their interfacial adhesion between CNT and Liquid crystalline polymers (LCP) matrix.

Separation individual CNTs from agglomeration and stabilizing them in an LCP matrix to avoid the secondary agglomeration.

Potential new development

Complex Integrated Technologies

Complex technologies such as white biotechnology and green chemistry can be used with less waste and energy consumption which make polymers having very low impact on environment.

Examples of some companies globally uses this kind of technology are shown below:

Cargill-Dow’s production of polymer reduced dependency from fossile resources and exhaust gases;

DuPont’ s new polymer (SONORAR) produced from glucose derived from corn starch;

Novamont’s mater-Bi; BASF’s EcoflexR; and Solvay Interox, Union Carbide’s polycaprolacton.

Biodegradable polymers

Growth in using biodegradable polymers has become more cost competitive due to various government legislation and the industries promoting their usage. An increase in public awareness on the reduction of petroleum based raw materials and current focus on the climate change has also contributes to the growth. Use of such polymers is highly driven by their low carbon footprint and it will make more economic and environmental sense to compost and recycle more.

Recycling of Composites Waste

Issues such as recyclability of polymeric materials & their environmental safety have becoming an increasing importance in the introduction of new composite materials and products. Efforts are also undergoing in developing matrix systems based on natural resources for the development of true bio-composites.

Recycling technology for thermoset composites had some success in applications such as vacuum assisted resin transfer moulding, centrifugal casting and reaction injection moulding. From the composite waste, resin could be utilized as raw material for producing the cement.

Some of the recycling solutions are being developed to suit specific processes and markets, for example:

Milling of the waste to powder can used as filler for polyester resin systems in injection moulding;

Milling of the waste can form granules in an open mould as these granules could be sprayed together with resin system directly on a laminate;

Milling of the waste with chemical processing can recovered the depolymerised on of the resin. Fibres and some of the depolymerised resin components could also be reused; and

Packing of such waste in a sandwiched structure can used as flat textile sheets such as veil, mat and fabrics.

Manufacturing Technology

The fabrication of composite structures and products is very labour intensive as compared to automated manufacturing methods. However, a major new breakthrough in manufacturing technology is not likely to occur in the near future. It is more likely that there will be an increase in improving to the existing manufacturing technologies. For composites to become competitive with metals, cost reduction has to occur besides its superb properties.

Word Count: 1474



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