Coke cans are made of aluminum and juice cans are made of iron because the two materials have different yield strengths and tensile forces. Aluminum stretches easily, making it ideal for thin cans, while iron is stronger but harder to stretch and is used for thicker cans.
Coke cans and juice cans are made of different metals. Soda cans are mainly made of aluminum, while non-carbonated beverage cans are made of iron. So why are soda cans made of aluminum, even though iron is cheaper than aluminum for the same volume? The reason is that the carbon dioxide gas from the soda keeps the pressure inside the can high, so it can support some of the structure of the can, allowing it to be thin enough to hold up. It would be nice to be able to stretch iron thinner, but iron doesn’t stretch as easily as aluminum, so it would be expensive to make it thinner. Aluminum, on the other hand, stretches better than iron, which makes it perfect for making thin cans. So, when you factor in the cost of the manufacturing process, it’s the most economical choice to make cola cans out of aluminum and juice cans out of iron.
By knowing which materials stretch better, you can choose the right materials during the manufacturing process and save a lot of money. Understanding how materials react when subjected to a pulling force is very important, and these properties are applied in many different areas of real life. In the construction industry, for example, choosing the right material is an important factor in determining the durability of a building.
To find out how well a material stretches, you need to pull on it from both sides. This pulling force from both sides is called the ‘tensile force’, and the experiment to find out how a material responds to this force is called a ‘tensile test’. In other words, it’s a bit like playing tug-of-war with a material instead of a rope. In this test, a rod-shaped material called a “specimen” is gradually pulled from both sides, which initially stretches and then breaks when it reaches a certain length. In tensile testing, the length of the specimen is initially stretched at a constant rate by the tensile force, i.e., there is an “elastic zone” where the amount of stretch is proportional to the pulling force. When the pulling force is removed, the specimen returns to its original length. In this elastic zone, the material behaves like a spring.
However, if you apply a larger force beyond the elastic zone, you enter the ‘plastic zone’. This is where the specimen is permanently deformed, meaning that even if no further force is applied, the specimen will not return to its original length, but will remain stretched. If you continue to apply force, a section of the specimen will become thinner and thinner until it eventually breaks at that point. This is the same principle as if you pull a fingernail from both sides, it will get thinner and thinner until it finally breaks at the weakest point.
The force at the point of transition from elasticity to plasticity is called the yield strength, meaning that the material will remain permanently stretched without returning to its original state until a force greater than the yield strength is applied. To thin a material, it must be stretched with a force greater than its yield strength to remain thin. Iron has a very high yield strength and requires a lot of force to make it thin. Aluminum, on the other hand, has a lower yield strength and can be easily stretched and thinned with less force.
Yield strength is also a very important concept in construction. The main material for buildings is concrete, which is strong in compression but very weak in pulling forces. It’s not safe to build a building with concrete alone because it cracks easily with the slightest pull. In particular, high-rise buildings are highly exposed to external forces such as wind, so it is essential to use materials with high yield strength. This is why reinforced concrete is nowadays used. Reinforced concrete has a high yield strength, which makes it resistant to external forces. On the other hand, buildings that don”t use enough reinforcement due to poor construction can easily collapse. This shows how important the role of rebar is.
To summarize, the greater the yield strength, the stronger the material resists pulling forces and the harder it is to stretch it. This is why we use aluminum with a low yield strength to make cola cans economically, and reinforced concrete with a high yield strength to build strong buildings. In this way, we choose materials with higher yield strengths, or sometimes vice versa, depending on the specific situation. We need to measure the yield strength of a material through tensile testing and choose the right material based on that data. If we look around us once again, we can see that materials are chosen for their yield strength, not only for the reason that aluminum is used for cola cans and iron for juice cans, but also for the variety of products and buildings that are made of them.
Finally, in addition to yield strength, other mechanical properties of a material also play a role. For example, materials need to be selected for different conditions, such as shock absorption or resistance to heat. Therefore, a comprehensive consideration of the material’s properties in terms of more than just yield strength will help to select the optimal material.
