Composite Materials -structure and properties

by engineering101 (student)

Introduction

Definition of a composite material.

A composite material is made up of two or more distinct materials, usually a base, binder, filler, and reinforcement. When they merge they do not do not lose their individual identities, but still take on their properties and making the products properties stronger.

Exampled of composite materials and where are they commonly used.

Carbon Fiber –

Carbon Fibre is an extremely strong, thin fibre, consisting of long, chainlike molecules of pure carbon that are made by charring synthetic fibres such as rayon in the absence of oxygen. Carbon fibres are used in high-strength composite materials in aircraft, automobiles, architectural structures, and in other applications where light materials capable of withstanding high stress are required.

Fiberglass –

Fibreglass is a material consisting of extremely fine glass fibres, used in making various products, such as yarns, fabrics, insulators, and structural objects or parts.

Reinforcement –

The role of the reinforcement in a composite material is fundamentally to increase the mechanical properties of the well-ordered resin system. All of the different fibres used in composites have different properties and so affect the properties of the composite in different ways.

Matrix –

A matrix is the material that binds together the reinforcing fibres of a composite. The matrix is usually a viscous material that hardens to give shape to the composite part and to protect the fibres from damage.

Material 1 – Carbon Epoxy HexMc/c/2000/R1A (Random Mat (No Weave)).

Carbon fibres are the stiffest and strongest reinforcing fibres for polymer composites, the most used after glass fibres. They are made of pure carbon in the graphite form, they have low density and a negative coefficient of longitudinal thermal expansion.

Carbon fibres are very expensive and can give galvanic corrosion in contact with metals.
They are generally used together with epoxy, where high strength and stiffness are required, for example race cars, automotive and space applications, and sport equipment.

Random Mat –

This is when the fibres are arranges in a random fashion. This can potentially be quite strong as a strain in any direction can more than likely be dealt with.

Epoxy Resin –

This is a heat-set resin with appropriate toughness, adhesiveness, chemical resistance, dielectric properties, and dimensional stability; several modified types are used as denture base material.

The diagram above shows the Mer unit commonly found in an epoxy resin.to form an epoxy polymer this Mer unit must repeat to form a long chain structure (commonly cross linked). The Epoxy Mer unit will now be described from left to right; on the left of the Mer unit we have benzene, aromatic ring. A benzene ring is 6 carbon atoms attaches together with alternating double and single bonds and each have their own hydrogen atoms. To the right of the benzene ring on the main back bone of the Mer unit, we have another carbon atom. The carbon atom has two side branches containing carbon and hydrogen atoms. Next we have a further benzene ring. Followed by a long chain of carbon, oxygen and carbon atoms, with a side branch of oxygen and hydrogen.

Material 2 – HexForce 104 Glass Fibre (Plain Wave) with Hex Ply 200 Phenolic Resin.

Glass Fibre –

Glass fibres are made of silicon oxide with addition of small amounts of other oxides.
Glass fibres are characteristic for their high strength, good temperature and corrosion resistance, and low price. There are two main types of glass fibres: E-glass and S-glass.

E-glass is the most used, and takes its name from its good electrical properties. S-glass is very strong, stiff, and temperature resistant. Used as reinforcing materials in many sectors, for example automotive and naval industries, sport equipment etc.
They are produced by a spinning process, in which they are pulled out through a nozzle from molten glass.

Phenolic Resin –

Phenolic resin is a heat-cured plastic formed from a reaction of a carbon-based alcohol and a chemical called aldehyde. Formaldehyde is a common raw material for this type of resin, but others related chemicals can be used. The resin is hard, heat resistant, and can be mixed with a wide range of materials for industrial and residential uses.

Plain Weave –

This is a preview of the whole essay

Phenolic Resin –

Plain Weave –

In plain weave fabric each warp fibre is woven alternatively over and under each weft fibre. This fibre type has reasonable porosity and good stability. The plain weave has poor drape ability due to the high level of crimp that exists between the fibres. The high level of crimp results in poorer mechanical properties of the finished component when compared to other weave types.

In the middle of the Mer Unit is a Benzene / Aromatic ring. A benzene ring is 6 carbon atoms attaches together with alternating double and single bonds and each have their own hydrogen atoms. From here there are 4 side branches. The top branch consists of an oxygen and hydrogen atom. The bottom branch has a carbon atom and three hydrogen atoms. The left branch has a hydrogen, oxygen and Carbon atom also, 2 extra hydrogen atoms. The Right branch a carbon atom with two hydrogen atoms attached with an oxygen and hydrogen atom.

Material 3 – HexForce 353 Aramid Fibre (4 Harness Satin Weave) combined with Hex Ply F650 BMI resin

Aramid Fibre –

Technically, aramid fibers are long-chain synthetic polyamides. Aramid fibers have extremely high tensile strength, which is why they are commonly used in armor and ballistic protection applications. With a distinctive yellow color, aramid fibers are frequently used in advanced composite products which require high-strength and light-weight properties. Products made with aramid fibers include: bulletproof vests, space craft components, fire suits, football pads, boats, and more.

Harness Satin Weave –

Satin weave is basically the same as twill weave. The difference in the two lies in the number of warp and weft intersections. The satin weave has less intersections between fabrics and hence less crimp. This results in a weave that produces good mechanical properties, drape ability and good wet out characteristics. The satin weave suffers from lower structural stability than the other weave types due to its asymmetric nature. The asymmetric pattern needs to be considered when laying up multiple layers of the fabric as it may result in more fibres running in one direction than the other.

BMI Resin –

Bismaleimide (BMI) resins are polyimides used in high-performance structural composites that require superior toughness and high-temperature resistance. BMI resins have processing characteristics similar to epoxy resins, and are used as laminating resins, and adhesives. Epoxy blends of bismaleimide (BMI) resins can withstand use-temperatures as high as 245-̊̊C without a decrease in thermal stability.

On the left of this Mer unit there are 2 hydrogen atoms and a nitrogen atom. From here there is a benzene ring. A benzene ring is 6 carbon atoms attaches together with alternating double and single bonds and each have their own hydrogen atoms. Moving further right there are two more Hydrogen atoms and a carbon atom. There is another Benzene ring and finally there are 2 hydrogen atoms and a nitrogen atom.

Composites have many properties that make them better than traditional materials in certain situations. They are generally lighter than most traditional materials such as steel and aluminium. Even though the composites are lighter they are on power and in some cases even stronger than steel. This makes them a grate material to use for high performance tasks such as F1 cars, Planes etc. Their tensile modulus is also on power with materials such as steel and titanium.

From the table above we can see that high modulus carbon is by far the most expensive but it also has the highest tensile modulus. It would probably be used in the manufacture of aircraft where price is not an issue but strength is. We can also see that High strength carbon has a low density making it very light for uses such as a car body panel. It has a decent tensile modulus but it is a lot cheaper than high modulus carbon.

Aramid is very light, it’s not too expensive but apart from this it is a pretty average material on its own. R-Glass and E-Glass are both quite heavy but are also enormously cheaper than the other materials. R-Glass has the best Tensile strength making is a grate material to be used in surfboards.

The graph above shows the properties of some common epoxies. The BMI polyimide has excellent heat and fire resistance while also having a good structure. The Phenolic epoxy has a very weak structure and mid-range heat resistance. 120ºC curing epoxy systems has a good mix of structure and heat resistance although is no match for 180ºC curing epoxy systems. This has the best structure and can have a better heat resistance than phenolic.

Material 1 – Carbon Epoxy Hex MC/C/2000/R1A

Properties of the Reinforcement
Properties of the Matrix
Properties of overall composite material
Applications of such a material.

Carbon is the reinforcement in this material. Carbon has many properties that make it perfect in most applications, for example it is stronger than concrete, and most other alloys and composites, yet it is still lighter than metals such as steel and aluminium. It has a tensile strength of 2000-5000 MPA putting it in line with materials such as aluminium. All of this gives it a great strength to weight ratio for reinforcement.

Epoxy resin is used at the resin for this material. It has a few properties that make it suitable for this material, for example it is Non-Flammable so it can be used at high temperatures and also has good electrical insulation properties. The graph above shows its limitations and strengths compared with other matrixes.

The overall material is very light yet strong enough to do be used in aircrafts. The material scan can withstand a heat of around 140 degrees. The structure of the material makes it hold together extremely well and can resist impact.

Due to its properties it has many uses but in the practical sense it is manly used in automotive and aerospace industries. It is not limited to this as you can see it used to make golf club because it is very rigid and can resist impact but also light as to allow for a clean swing.

Material 2 – Hex Force 104 Glass Fibre (Plain Weave) combined with Hex Ply 200 Phenolic resin

Properties of the Reinforcement
Properties of the Matrix
Properties of overall composite material
Applications of such a material.

Glass fibre is used as reinforcement in this material; it has many properties that make it perfect. It is quite light but still has a tensile strength that could rival that of light alloys. It also has great strength that is just as good as any plastic. The table above shows that it is a strong material that costs very little, making it a viable option for mass production.

Phenolic resin is the matrix used which, just like epoxy is fire resistant but its structure is not as good, making it susceptible to cracking. They are distinguished by their high adhesive stability and good mechanical properties. Furthermore they show good heat-resistance up to around 250° c.

The overall material inherits the properties of both the reinforcement and the matrix. This makes it light, strong and heat resistant never mind the cost being so low. The structure is not as strong as some other composites, this limits its uses but it fits the bill for many products.

The positive properties of this material make it a good choice for many products such as light tube. This is because of its ability to resist heat while being opaque and allowing light to travel through it.

Material 3 – Hex Force 353 Aramid Fibre (4 Harness Satin Weave) combined with Hex Ply F650 BMI resin

Properties of the Reinforcement
Properties of the Matrix
Properties of overall composite material
Applications of such a material.

Aramid fibre is used as the reinforcement because it has very good physical properties, for example, it has a better tensile strength than both plastic and glass but is just below carbon (You can see this in the diagram above) although it density and cost both excise that of carbon.

BMI resin, also known as Bismaleimide is used as the matrix in this composite. It brings a number of properties to the material, but most notably its heat resistance of around 290 degrees. It has very good structural strength making it ideal in high performance situations.

The final material has a good mixture of strength and weight. It has a good structure combined with it being strong, light and very heat resistant, making it perfect for most applications.

It has many modern day applications in the aerospace industry because of its outstanding strength to weight ratio. It is also used to make damage replant products such as kneepads and helmets.

- For a given product which may be manufactured from composite materials or traditional materials discuss the advantages and disadvantages of each material.

Advanced composites have been asked to produce the chassis of a new sports car. This chassis was traditionally made from an aluminium alloy. Advanced composites are planning to produce the chassis from a high modulus carbon fibre combined with a 180° epoxy matrix system.

The traditional material of aluminium alloy has many advantages and disadvantages that make it good and bad for the chassis.

Advantages of using Aluminium Alloy –

Low Density

A low density of around 2.7g per cm3 makes the material easy to process, which are essential while making such an intricate product.

Easy to Get

Aluminium allow is in abundance and so it is readily available making it perfect for bulk orders.

Relativity Cheap

It is cheap allowing for lower production cost and increasing profits.

High Degree of Malleability

This makes the material very easy to shape, which is a good property to have while making an intricate product such as this.

Good Strength

It is a very strong material with a tensile strength of around 710 MPA; this makes it very good as withstanding impact.

High melting point

The high malting point makes the material very heat resistant; this is useful in products such as this due to the heat generated from stress.

Range of finishes

There is a range of finishes, this allows for a range of testers to find the perfect one for this particular product.

Will resist corrosion

This is extremely important when you are making any product for the automobile industry as corrosion can lead to failure in any part of the car.

Disadvantages of using Aluminium Alloy –

Moderate Rigidity

The rigidity of a material can cause it to become too brittle or the other extreme it that it will become too soft.

Chassis will need to be made in a number of bits.

The chassis has many parts to it and aluminium would have points of weakness in it if it was all done as one part.

Parts need joined

Aluminium is hard to weld, expensive to weld and points of weakness appear from joining/welding.

Not very hard

The hardness value is 100 HRY; this is low and so could cause dents and scrapes in the chassis causing it to weaken.

Advantages of using Carbon Fibre and epoxy resin –

High strength

It is a very strong material with a tensile strength of around 6370 MPA; his makes it very good as withstanding impact.

Low density

It has a density of around 1.80 g/cm3; this is very low and so allows the product to be light yet strong.

Resist corrosion

This is extremely important when you are making any product for the automobile industry as corrosion can lead to failure in any part of the car.

Good impact properties

Being able to resist impact is one of the main uses for the chassis and so good impact properties are essential.

Good Rigidity

The rigidity of the material will allow for it to be used in high positions of high stress such as the chassis.

No need for a paint/finishing process

This saves time and money while allowing every intricate section to be clearly defined to the final assembly team.

Chassis made in one piece

This means that no Joints are needed; this prevents weaknesses and also lowers the cost.

Material can be tailored to suit forces

This allows for tests and simulations to be run to find the prefect combination for the job, in this case the chassis.

Disadvantages of using Carbon Fibre and epoxy resin –

There are a high range of options making it hard to choose the right one

Although this can also be seen as an advantage it can set you back while trying to find the perfect combination.

Limited knowledge of the materials

This is a relatively new material and so some staff may have limited knowledge and need to be trained or new staff need to be brought in, both costing the company money.

From the above advantages and disadvantages I feel that carbon fibre is the appropriate choice for this job.

Justify your selection of an engineering composite for a given application describing the reasons the selection meets the required criteria.

Advanced composites are planning to produce a new range of bath tubs. What material (reinforcement & matrix) would you suggest they use. Comment on criteria such as:

Cost
Properties required
Ease of manufacture
Availability of materials

Cost –

Because of the common price of a bath tub being quite low, the choice of materials is quite low, for example carbon fibre would be far too expensive to make a bathtub out of, there are a couple on the market costing £4,000.

Properties required –

It must be strong enough to hold a lot of weight and the force of the water pushing up against. Must be moisture resistant. Has to withstand a certain amount o heat, approximately 70 degrees. Must be non-toxic. Must be modern and aesthetically pleasing.

Ease of manufacture –

Must be easy to mass-produce, this will save money rather than an intricate design whit many different processes needed to make it. More than likely a moulding process would be the easiest and most efficient way to produce this product.

Availability of Materials –

Should be made from materials that are easy to acquire, possibility a plastic such as acrylic. Importing a material or having scares amounts will both add to the cost of production. Mass production also requires a bulk quantity of material.