Ductility Defined
Imagine you take copper metal and stretch it into a thin piece of wire. Would you believe that the copper metal would resist breaking while being stretched? This is a great example of ductility. Ductility, by definition, is a material that can be stretched thin when tensile stress is applied. It is the way to describe a physical property of any material. Although very similar, be careful not to confuse ductility with malleability. Malleability is a material that can bend or change shape using compressive force, rather than tensile stress. Think of compressive force as the act of squeezing or pushing down on a material to change its shape. Some metals can be both ductile and malleable, or ductile (or malleable) only.
Tensile stress refers to a type of stress that changes the length of an object in the exact same direction as the force being applied. Using Diagram 1 as a guide (see video), think of tensile stress this way: you grab that piece of copper metal and begin pulling it with your pliers. The copper metal is experiencing stress because you are pulling it (lengthening the metal until it is stretched into a thin copper wire). Your action of pulling is the force that is being applied. Just keep in mind that tensile stress can contribute to the ability of a material (such as metal) to stretch into a thin wire.
Do you know the term for a material that is considered to be the opposite of a ductile material? This term is referred to as a brittle material. Brittle materials are quite different from ductile materials. Instead of stretching and lengthening, brittle materials can break when experiencing too much tensile stress. Let's look at different types of both materials.
Ductile Materials
The most common place to see ductility in action is through the use of metals. In metalworking, it is quite common to see a person pulling or stretching metal into a wire. Metalworking is simply the process of working with metals to create metal products. Goldsmiths and jewelers come to mind when thinking about metalworking. The types of metal commonly used, because of their high level of ductility, include the following: gold, silver, copper, and steel.
Earlier we discussed that the opposite of ductility is brittleness. Materials that are considered to be brittle include the following: concrete, cast iron, and some glass products. If you think about it, there is no way to pull and stretch these items without hearing a crack, break, or a shattering noise. Thus, they are not considered to be ductile.
Although metals dominate when discussing types of ductile materials, there is an example of a non-metal material that is ductile. Did a piece of gum come to mind? I know it seems odd but gum is actually a ductile material. Start chomping on a piece of gum. After a while, you will notice that when you stretch the gum (very thin), it lengthens without breaking. More importantly the gum stays at that length without returning to its original shape. That, my friends, is what we call a ductile material.