Materials In Today's World



Hardness is a measure of a material's ability to resist plastic deformation. In other words, it is a measure of how resistant material is to denting or scratching. Diamond, for example, is a very hard material. It is extremely difficult to dent or scratch a diamond. In contrast, it is very easy to scratch or dent most plastics. As shown in the diagram below, hardness increases from the very soft plastics to the incredibly hard diamond with most other materials ranging between.

Increasing hardness soft to hard: plastics, brasses Al alloys, easy to machine steels, file hard, cutting tools, nitrided steels, diamond
Hardness increases from very soft plastics to the hard diamond with most other materials ranging between.
Credit: Callister

A common method for measuring the hardness of a material is outlined in the figure below. A very hard-sphere is pushed with a set force into the material. The resulting indent is measured for width and depth. A harder material will have a smaller width and depth, i.e., smaller indentation. Larger hardness results in a high resistance to deformation from compressive loads, i.e., resistance to scratches and dents, and better wear properties.

Measurement of hardness of materials. See text above for description. Apply known force, measure indent
A common method for measuring the hardness of a material.
Credit: Callister

To Read

Now that you have been introduced to the concept of hardness, please go to your e-textbook and finish the reading for this chapter (pages 90 to 97 in Chapter 4 of Materials for Today's World, Custom Edition for Penn State University). When finished with the reading proceed to the next web page.