Fiber Reinforced Composites (FRC) – What Are They?
Ever since composites were first introduced, their use in airplanes as a material has been increasing.
Airbus was the first commercial manufacturer of airlines to use composites in its aircraft A310 in 1987. At that time composites contained only 10% of the total material that was used.
Boeing 787 Dreamliner that was introduced commercially on October 26, 2011, is made of materials that are 50% composites.
There is a military airplane that due to its amazing design and the use of FRC cannot be located easily in the sky. It’s the stealth.
It is not only the Airplanes. FRCs have also impacted the design of Super Cars.
There is one advantage that Fibre Reinforced Composites have that makes them stand apart from the rest of the materials like Steel, Aluminium, etc. It is this advantage that has made them transform the way airplanes and cars are being built today.
And if it wasn’t for this advantage, your long distance flight tickets wouldn’t have been so cheap.
More on this advantage, later.
What are Fiber Reinforced Composites?
“Fibre-reinforced composite materials consist of fibres of high strength and modulus embedded in or bonded to a matrix with distinct interfaces (boundaries) between them.”
Now, what does this mean?
There are only two MAIN components in FRC.
- The matrix/bonding (you can imagine it functioning as glue).
Carbon Fiber Zoomed In
What roles does each of them play?
The fibres provide the SUPER strength. Imagine each single fibre like a wooden stick. It can be broken easily. But combine a number of wooden sticks and breaking them becomes close to impossible. Fibres act in a same way. Take millions of fibres each of the size of microns, combine them with glue and what you have is a material with some amazing strength.
The matrix or the glue, other than keeping the fibres together also does the work of transferring loads evenly throughout the fibres and protects them from the environment.
Types of Fibre Materials Used
Some of the materials that you can use as fibres are
Types of Matrix Materials Used
Some of the materials that you can use as matrix are
- Vinyl Ester
Besides fibres and the matrix, some other components used in the manufacture of FRC are coupling agents, coatings and fibres.
Coupling agents and coatings are applied to the fibre which increases their wetting characteristics and helps promote the bonding across the fibre-matrix interface. Fillers are used with some polymeric matrices to improve their dimensional stability.
How are the Fibres and the Matrix combined?
A number of fibres when bundled together along with the matrix give us a lamina (0.1-1mm thickness).
When you take a number of laminas and stack them over each other you get a laminate.
The way in which these fibres are first bundled together to form a lamina varies. You can stack all the fibres parallel to each other, some normal to each other and some at varying angles to each other.
Once you get a lamina, you can stack a number of them in such a way that either all of them are of parallel series or normal series or having a mixture of both normal and parallel. It depends on what your objective is.
The following image shows how an FRC is made.
Methods Used To Incorporate Fibres into the Matrix
Depending upon the type of technique you choose in manufacturing, the following methods can be used.
1. When fibres and matrix processed directly into the finished product.
- Filament Winding
2. When Fibres are incorporated into the matrix to prepare ready-to-mold sheets.
- Autoclave Moulding
- Compression Moulding
(These ready to mould sheets are available in two basic forms 1. Prepegs and 2 Sheet moulding compounds which can later be processed to form laminated structures)
The above methods have been used to mass produce the composite in the automobile and aerospace industry. This has further reduced the cost of the composites. Earlier hand layup technique was used which was reliable but slow and labour intensive.
What makes the structure of FRC complex to analyse?
It is the fact that FRC is neither homogenous nor isotropic; the analysis of stress, strains and various other mechanics becomes complex and different.
Its analysis is done at two levels
- The micro-mechanics level (examination does on a microscopic level)
- The macro-mechanics level (examination does on a macroscopic level)
Comparing the strength of Composites with Aluminium and Steel
Tensile Strength (MPa)
SAE 1010 Steel
6061-T6 Aluminium alloy
High-strength Carbon Fibre–epoxy matrix (unidirectional)
One single BIGGEST Advantage that FRCs have over other Materials that has made it one of the most sort after materials on the planet today.
The biggest advantage that composites can give which no other traditional material can compete with it is HIGHER strength/ weight ratio. This means that if you replace a material for example aluminium with same strength of FRCs, you will get a material that is at least 5-10 times lighter.
In the TABLE NO 2 above where the comparison of steel, aluminium and fibres is done, you can easily see the sharp reduced density and higher strength carbon fibre offers as compared to steel and aluminium
This high strength/low weight property makes them highly important in the Aerospace Industry. The lighter the weight of an Airline, the less fuel consumed, the faster it can reach its destination and ultimately the lesser the cost of your ticket!
It has also speeded up Sports Cars. Cars can run faster if the drag presented by their weight is less. Since FRCs reduce the weight, if they replace steel or aluminium, the car becomes lighter and much faster.
Other Advantages of FRC
- It reduces the number of components and fasteners required which intern reduces fabrication and assembly costs
- Higher fatigue, chemical and corrosion resistance which reduces the maintenance and repair cost.
- Dimensional stability over wide temperature ranges.
Before going into the drawbacks of FRC let me recommend you a book.
I have read at least 5 books on this topic and according to me the most simplified and detailed one that I have come across is Fibre-Reinforced Composites by P.K. Mallick.
This book goes in-depth into the performance, manufacturing and design of the composites.
ONE SINGLE BIGGEST drawback that FRC has, that hasn’t made it a more common material.
Because of their strength and weight advantage FRCs can easily replace most of the components of our everyday life. They have the potential to easily replace most of the steel and aluminium in the world. So why hasn’t this happened?
It’s because they are EXPENSIVE.
To make them cheap, they need to be mass produced. But to mass produce them by making the mass public attracted towards them you need to make them cheap first. This has led to FRCs falling into the chicken and egg trap.
- When used along with aluminium and titanium, they can induce galvanic corrosion into them.
- They are difficult to inspect with Non Destructive Testing (NDT) methods like Ultrasonic Testing and Eddie Current Testing.
How to reduce the cost of FRC?
In order to reduce the cost of FRC, it is highly important to identify the materials and processes that lead to increase in cost. Some of them are
- Cost of fibre as well as the matrix.
- Cost of preparing the material i.e. prepeg or sheet metal compounding sheet
- Cost of fabrication and skilled labour.
- Tool cost which includes mould making and material used
- Cost of assembly.
- Cost of quality inspection.
It is important to seek for and discover new processes and technology in order to reduce the cost of FRC. Unless this happens, we won’t be able to make them a part of our everyday life.
Not getting confused with terms like CFRP and FRP
FR means Fibre Reinforced. Whatever comes before indicates the name of the material used as a fibre and whatever comes after it indicates the name of the matrix used as a binder.
Example, for CFRP, the material used is Carbon and indicates the matrix as Polymer. If now prefix is used before FR it means it can be any type of fibre material. E.g. FRP
APPLICATION EXAMPLE: Using Fibre Reinforced Composites to Increase the Strength of an Existing Bridge
Imagine that a Bridge is getting old. It can take the weight of only 10 cars over it at any given period of time. But since the last few weeks, the traffic has increased and your only chance is to break it down and build a new one or increase its strength.
Your local government is not very rich so you go with the decision of increasing its strength.
Now, you again have two options. Either use the traditional technique of jacketing (cheap and short term remedy) or you use the technique of applying FRC to the bridge (expensive and a long term remedy).
If you are able to convince the Local Mayor to go for the long term solution of using FRC, then you will get the following advantage over using the traditional method of jacketing.
Jacketing requires skilled labours who know how to fix the steel and pour the concrete. The process is complex to understand and perform.
Comparatively if FRC sheets are used, the process is as simple as taking a piece of paper and sticking it to the wall like glue.
You do not need highly skilled labour. Neither do you need expensive material to install it. You just have to take the FRC sheet and using an epoxy stick it to the column of the bridge.
1. Fibre Reinforced have two main components.
- The Fibre.
- The Matrix
2. Their BIGGEST advantage is strength/weight ratio that has resulted in creating commercial airlines like the Boeing 787 being 50% made out of composites.
3. Their BIGGEST drawback is the super high Cost. They have been used since the mid-20th Century. Even though more than half a century has passed their cost hasn’t come down drastically, they haven’t been mass produced and they haven’t replaced most of the traditional materials like aluminium and steel wherever possible.
4. The BIGGEST CHALLENGE that remains today is finding a way to reduce their cost and making them more common.