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Name: Ever
Status: Student
Age: 14
Location: N/A
Country: N/A
Date: April 2004


Question:
I was wondering does everything get weaker the thinner you make it and does it get stronger the thicker you make it. In other words is possible to have a thick material be flexible and a thin material be sturdy?



Replies:
A direct answer to your questions is "no" and "yes", but it is a little more complicated than "making it stronger by making it thicker" and vice versa "making it thinner to make it weaker". There is also the issue of your definition of weaker and stronger and flexible and sturdy. In the study of material science and materials engineering there are some definitions of material properties that kind of cover the questions you are asking.

In terms of "strong" and "weak", there is ultimate tensile strength, yield strength, hardness, and fracture toughness just to name a few. Trust me, there are others out there. For flexibility there is modulus of rigidity for a mechanical property, but there is also cross section of the material (i.e. how it is built, thick or thinner) that plays into how stiff or flexible it is. Material science and materials engineering has developed over the centuries to understand how microstructure of the material influences these material properties and how a manufacturer of these materials can alter the properties by adding a little of this element, or heat treating it a certain way, or cooling it a certain way, etc. That is why you can have different types and grades of metals, different types of polymers, and different kinds of ceramics. It is also why you can have one material that is a certain thickness have a higher strength than one of the same size but different material. Also, you can manufacture a material a certain way and it be stronger than the same material of same composition manufactured a different way. For instance, you can actually make a turbine blade out of a single crystal of material and it will be stronger at higher temperatures than a turbine blade made out of multicrystaline material. It cost more to do it that way, but you have a safer turbine engine that can handle all the g accelerations an F-16 can put on it. Sometimes making a material thicker makes it weaker because it has more manufacturing voids in it that cause it to fail early.

Da Vinci actually did an experiment a long time ago where he was measuring the strength of iron rods. He concluded the longer the rods were the weaker they were. This was because the more material the rods had the more voids they had and thus the weaker they were. If you were to manufacture the rods without voids, this result would not hold true, but you pay more money to make sure the voids are not there.

Hopefully this has not confused you worse, but I hope that I have made you aware that material science and engineering is a fun, complicated science that is constantly changing. There are quite a lot of "no free lunch" scenarios in materials manufacturing. In other words, you may give up strength to make sure the material has a better fracture resistance or is more pliable (ductile in scientific terms). Likewise you may want it stronger so you do not have to have it as thick, but you make it more brittle (easily broken).

Thanks for using Newton

Christopher Murphy, P.E.



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