Basic elements › Units of measurement

HARDNESS

Hardness is the resistance a Material offers against penetration. Resistance to impact, wear, scratches, the coefficient of friction, etc. are all factors that directly depend on the hardness of a material. There are numerous hardness tests suited to families of materials or to specific requirements. Each test has its own system of units. These tests fall into several main families:

• Macroindentation tests (Vickers hardness, Rockwell hardness, Knoop hardness, etc.)
• Tribological / scratch tests (Mohs scale, etc.)
• Pendulum damping tests (Persoz hardness, König hardness)

Macroindentation tests

Macroindentation tests consist of measuring the imprint left by the indenter (usually a Diamond pyramid), of a given weight, falling from a given height onto a material sample of given dimensions. The shape and weight of the indenter, its Drop (impact) height, and the sample dimensions are specific to each test.

Tribological / scratch tests

The best known and most widely used scale for tribological tests is the Mohs scale, which determines the Hardness of minerals. It has 10 degrees, from the least hard (talc) to the hardest (Diamond), and ranks minerals by comparing their ability to scratch another mineral. Diamond scratches corundum, which scratches topaz, which scratches Quartz, etc.

Pendulum damping tests

Pendulum damping tests are valued for measuring the Hardness of coatings and surface treatments even though they also apply directly to materials. The pivot feet of the Pendulum rest on a sample with given dimensions. The Pendulum is released at a defined angle (6° or 12°). A soft Material will absorb the Amplitude of the Pendulum more quickly than a hard Material.