What are the differences between Shore, DIDC, Micro DIDC hardness scales?

The hardness of rubbers and plastics according to the shore, DIDC and micro DICD scales consists of the resistance to penetration into the sample of a punch of a certain geometric shape under a defined force.

The distance the indenter has moved is measured and then converted to hardness.

Thus for Shore A or Shore D hardness, the maximum displacement of the indenter is 2.5 mm (hardness = 100). 1 point of hardness will then correspond to a displacement of 25 µm of the indenter.

There are different hardness measurement scales:

Shore hardness:

Shore hardness scales were developed by Albert Ferdinand Shore in the 1920s. They meet the ASTM D2240 - 15e1 Standard Test Method for Rubber Property — Durometer Hardness which describes 12 shore hardness scales: A, B, C, D , DO, E, M, O, OO, OOO, OOO-S, and R

Depending on the measurement scale, the shape of the indenter is different.

For example, the Shore A scale uses a truncated cone type indenter with an angle of 35 ° and the Shore D scale uses a cone with an angle of 30 °

IRHD / DIDC hardness:

This scale is described in ISO 48: 2010 Rubber, vulcanized or thermoplastic - Determination of hardness

IRHD stands for International Rubber Hardness Degree or in French: Degree International de Dureté des Caoutchoucs

This scale uses a ball

Micro Hardness - IRHD / Micro DIDC:

This scale is also described in ISO 48: 2010 Rubber, vulcanized or thermoplastic - Determination of hardness

It is perfectly suited to measuring the hardness of thin products and / or small dimensions (example: O-ring).

The maximum displacement of the indenter is in fact 0.3 mm.

This scale uses a needle extended with a micro ball of 395 µm in diameter.

Differences between Shore, DIDC and Micro DIDC scales

In the following table, depending on the measurement scale, the geometry of the indenter, the displacement stroke, the pressure force, the minimum recommended sample thickness, etc.