Materials

Composite materials

Let's take a look at a beam. When you put something on the beam, it'll obviously experience a force of some kind, and will bend. As the beam bends, the particles on the inside of the beam (in this case the inside is the top) will move closer together. This is called compression. The particles on the outside of the beam (in this case the bottom) will move further apart. This is called tension.

Let's have a look at two different materials that we could potentially make our beam out of:

1) Concrete - Concrete has a high compression strength, which means that it fares well in situations where a force is trying to push its particles closer together. As a result, on the inside, where compression is experienced on the beam concrete will not buckle or deform in any way. This is good - we obviously don't want our beam to do this. Unfortunately, concrete does not have such a high tension strength - this means that at the bottom of the beam, where particles are moving away from each other, concrete will crack and fail in this way - this is obviously bad, and we cannot make the beam solely out of this material.

2) Iron - Iron tells the complete opposite story of the one above. Iron has a fantastic tension strength, and when a tensile force is added and tension is experienced, the iron will not crack and fail (within reason, of course). This makes it a fantastic material to use at the bottom of the beam. Iron, however, is not so good with compression. When put under a compression force, iron will tend to buckle and deform. This means that we cannot make the beam out of solely this material, either.

What we do, therefore, is form a composite material - we combine both materials together to form a new material, that adopts the most desirable aspects of both former materials. In this case, where concrete would fail at the underside of the beam when tension is experienced, iron stops the new composite material from cracking and deforming. If we take a look at the inside of the beam, we see that as this area experiences compression - a place where iron would regularly buckle and fail, concrete prevents this from occurring. Therefore, we are able to make a beam that can stand up to both compression and tension.