How do we know that graphene is really strong?
This one question has been answered a while ago but nobody seems to get it right or worse, know what it conveys. What I mean by that is that you will often hear people saying that it's either 10 times stronger than steel or sometimes 200 times stronger than steel. There's a lot of misconception here and to tell you the truth they are both right.
Wait a minute? How can they both be right?
The answer is it's a matter of reference first you must understand how they figured it out this strength of the graphene. To do that, what they basically did was to SHOOT it. They literally shot a graphene sheet. NO! Not with a gun but with a micro gun for what they called micro ballistics. This is nothing more than a membrane to which they attach a micro bullet made of silica balls. When the membrane expands the tiny bullet flies through space in speeds over a thousand meters per second. For reference, the fastest bullet reaches speeds of about 1250 meters per second however this is the fast as you can get. But normal bullets are well below that speed or about 762 meters per second.
The idea here is to calculate how much energy it is needed to break the graphene by acquiring the speed before the impact and after impact. By knowing the difference in speed, they can calculate the kinetic energy transfer or loss in the process and by that, we can tell how strong graphene is when compared with other materials.
In this case, what you are looking for in a strong material is its ability to absorb impact among the other things. For instance, when compared to steel on an equal weight basis (one gram of graphene against one gram of steel graphene), graphene is 10x stronger. However, this is a bit misleading for a few reasons. It's not that with ten times less material you can achieve the same thing. What happened in this experiment is that the bullet that is shot at both materials, at the exit, the bullet lost 10 times its speed or kinetic energy in comparison from one to another. However, because of the simplicity of this experiment you won't get the entire picture of how strong a material really is simply because you have other characteristics that can be way better. This is the part where you get the 200 times stronger the steel.
Now, you might be thinking what are the 200 times stronger all about? And the answer is the tensile strength. By definition, the tensile strength is the resistance of a material to breaking under tension. Stainless steel has a tensile strength of 505 Mega Pascals while graphene has a tensile strength of 130 Giga Pascals. Divide one by the other and you get more or less 257 times stronger than stainless steel. Just for the comparison, Kevlar is 375.7 Mega Pascals and if you compare to carbon steel which has a tensile strength of 370 Mega Pascals it's even more.
But a true comparison would be galvanized steel which was used in the Golden Gate Bridge and it has a tensile strength of about 600 mega Pascal's which will give you about 216 times stronger. That's why they say it's over 200 times stronger than steel. For you to quickly picture this, the diameter of the Golden Gate Bridge cable is 92.4 centimeters comprised of 27,572 wires as each wire is about 0.48 centimeters in diameter. Each of those wires can individually hold 8.8 kilograms per meter.
Here is the kicker.
According to one study of 2008 called "measurement of elastic properties and intrinsic strength of monolayer graphene", they concluded that the breaking strength of graphene is about 42 Newtons per meter. I will assume here that they are using a sample of 1 meter by 1 centimeter by 3.7 angstroms graphene sample to make my calculations. So if the cable and the bridge can hold about 600 million Newtons, this means that we would need about 14,285,714 layers of graphene which gives us a cable with a cross-section area of 0.52 centimeters squared.
This is mind-boggling.
We are talking about a cable that is 12,894 times less area when compared to the Golden Gate Bridge cable cross-section of 6705.54 centimeters squared. THIS IS ABSURD! Just to think about it and whether it is it even possible.
To be honest it is hard to picture this and this theory actually makes me more excited for the graphene revolution! It is something to theorize this case scenario, but what if this is actually possible?