Material hardness represents the capability of resisting the penetration of a harder body. The harder material wears or scratches the softer material.
There are several methods to measure the hardness; commonly used in polymer industry (plastic, rubber, elastomer) is Shore A (soft), D (medium, hard), based on ASTM D 5470 and sometime Rockwell hardness is also used for harder materials.
The geometry of the indenter in Shore A and D are different, as shown in the following picture. The hardness is calculated based on the depth of the penetration.
Some parameters:
- Samples need to at least 6.4mm thick
- Indent force is 822g (8.064N), 4550g (44.64N) for shore A and D, respectively.
- The force direction must be perpendicular to the surface of the sample.
The following is a good video to understand the measurement procedure according to ASTM D2240.
Rockwell hardness measurement is for hard materials (refer to the following video).
The following table shows a rough comparison among different materials with different hardness.
