Ever wondered how airplane engines can withstand the heat and not bend? Or how the horizontal elements of a bridge stay in place for decades, or even centuries? Or maybe you do have some idea, but it is not quite clearly defined? Well, the secret is in the material – these things, and many others, use composite materials as opposed to basic ones, and here is a crash course in them!
What are composites to begin with?
Composites are complex materials – typically, construction or industrial materials – that are made by combining two (or more) basic ones into an advanced version. You can learn a little more about how we got around to them in this helpful educational article. What makes them different from a plain old mix (otherwise known as a “compound”) is that each component improves the others in some way, but each of them remains distinctly recognizable in the final hybrid.
This would probably be easier to understand if we had an example. Two of the most popular illustrations are concrete and fiberglass. In concrete, you have pebbles and stones of varying shapes and sizes dotted in, and throughout, a measurement of cement. In the case of fiberglass, you have a myriad of teeny tiny glass whiskers all glued in a messy bunch inside a mass of plastic. In both of these materials, however, the stones and the little glass shavings are still plainly visible inside the final material – they did not dissolve or melt into their fellow components (cement and plastic, respectively).
How are they actually made?
Like we mentioned above, composites are made by putting together two basic materials to form a better one. Sometimes there is a third component, which is referred to as an “additive”, but generally speaking, composites are regarded as a whole of two parts.
The first material is called a background material, a matrix, or a matrix phase. The second one is added to it in order to change the matrix’s properties, and so it is called a transforming material, or the reinforcement, or the reinforcing phase. The reinforcement can be something as tiny as the shavings of glass in fiberglass, or something as burly as the steel rods in reinforced concrete.It can also be particulates of something, or some granules, or even folded textile. The way you arrange it depends on what you are looking to achieve.
If you want your composite to be isotropic (equally strong in all directions, with the same mechanical properties throughout), you would need to scatter the reinforcing fibers, granules, or shavings all randomly oriented through the matrix, like the glass in fiberglass. If you are looking to make an anisotropic (a composite that is stronger in one direction, but weaker in the other, with different mechanical properties in different directions), you will have to make the reinforcing elements all face the same way (like the strands of fibers in wood).
While the reinforcement makes the background material stronger or more durable, the matrix phase serves to bind the reinforcing one securely in its place and protect it from environmental damage, pressure, heat, or water. Composites found incredibly versatile application in our modern society, as exemplified by the many experts specializing in them, such as Spartec fiberglass composite company – these guys and hundreds of their niche compatriots are finding new ways to implement these materials in every market sphere you can imagine.
What kinds of composites are there?
There are all sorts, actually, because there are myriad materials you can put together into a composite one. Moreover, you can edit them on the next tier and make a composite of a composite, so your possibilities are basically endless. However, for the sake of a simple explanation, we will divide them into natural, classic, and modern.
Natural composite materials have been around since forever, really. These refer both to naturally occurring composites, and human-made composites from natural materials (as opposed to hi-tech refined synthetic stuff). One excellent example, which we already mentioned, is wood. It has fibers (transforming material) growing inside a lignin matrix (organic polymers based on carbon). In bones, the background material is hydroxyapatite (a crystalline mineral which is a cousin of calcium), and it is reinforced by fibers of collagen. As for natural but man-made composites, think about the old age bricks – a clay or mud matrix reinforced using straw. You can read some interesting research into those at this page: https://www.researchgate.net/publication/289857770_STRAW_STABILIZED_LOCAL_CLAY_BRICKS
The label of classic composites refers primarily to carbon-fiber reinforced plastic and fiberglass (or glass-fiber reinforced plastic) which were introduced in the 1930s. they share the same kind of structure, and the same kind of logic: plastic is flexible but soft and weak, whereas glass and carbon are strong, but brittle. Therefore, they are a match made in heaven if you need a light, strong, durable, and rust-proof material.
The advanced modern composites are classified, based on their matrices, into metal matrix (MMC), ceramic matrix (CMC), and polymer matrix composites (PMC).
MMCs are made of light metals like aluminum reinforced with ceramic or carbon fibers. They are rust-proof, stiff, and strong, but hard to work with and pretty expensive. You would typically find them in jet engines, cutting tools, diesel engines (pistons), or reinforcing a military tank.
CMCs have a ceramic background (e.g. borosilicate glass), and a reinforcement of other ceramic or carbon fibers, just like MMCs, to compensate for the ceramic’s brittleness. They are used everywhere where you need a light material that can withstand insanely high temperatures: in jet engine exhaust nuzzles, gas turbines, heat exchangers, car brakes, clutches, and bearings, and even nuclear reactors.
Finally, PMCs, also known as composite plastics, are a little bit different. Rather than compensating for brittleness and weakness, the fibers here are aimed at adding stiffness and strength to the bendy and overly flexible plastic matrix. They are employed in car, plane, and boat parts, as well as various sports equipment like skis or golf clubs.