MATSE 81
Materials in Today's World

Malleability and Ductility

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Malleability and ductility are related. A malleable material is one in which a thin sheet can be easily formed by hammering or rolling. In other words, the material has the ability to deform under compressive stress.

Malleability - Metal hammered into thin sheets
A malleable material is one in which a thin sheet can be easily formed by hammering. Gold is the most malleable metal.
Credit: Buzzle

In contrast, ductility is the ability of a solid material to deform under tensile stress. Practically, a ductile material is a material that can easily be stretched into a wire when pulled as shown in the figure below. Recall pulling is applying tensile stress.

Ductility text showing the starting point, ductility, (how far it can stretch) and the end point.
Ductility test.

If we pull on a rod of material, some of the possible profiles of the rods at fracture are shown in the figure below.

Breaking profiles: Snap w/ jagged edges. some contour and pulling then snap, pull all the way into smooth contours and points
Fracture Samples
Credit: Sigmund (Own work) [CC BY-SA 3.0], via Wikimedia Commons

Profile (a) is an example of the material that fractures with no plastic deformation, i.e., it is a brittle material. Profile (b) is an example of a material that fractures after very little plastic deformation. These two profiles would be classified as having low ductility. Profile (c) in contrast is a material that plastically deforms before fracture. This material has high ductility. The stress-strain curves for the brittle, profile (a), and the ductile material, profile (c), are shown in the figure below.

brittle materials have short and tall curves. Ductile materials rise quickly but level out for a long time
Ductile and Brittle Stress-Strain Curves
Credit: Amgreen (Own work) [CC BY-SA 3.0], via Wikimedia Commons

To Read

Now that you have learned a bit about the mechanical behavior of metals, please go to your e-textbook and read pages 75 to 84 in Chapter 4 of Materials for Today's World, Custom Edition for Penn State University to learn more about this subject. When finished with the reading proceed to the next web page.