Scope:

Knoop indenters are used to make indentations in advanced ceramics as according to ASTM  C1326. One of the parameters used to characterize advanced ceramics is the Knoop indentation hardness. Knoop indents can also be used to measure the coating hardness of advanced ceramics. It is primarily used to prevent cracking in brittle materials and to make hardness testing of thin layers easier. In this ASTM C1326 test technique, the indentation load is aimed at creating indentations as large as feasible with traditional micro hardness equipment, but not so large as to cause breaking. 

Test Procedure:

This ASTM C1326 testing procedure outlines an indentation hardness experiment that involves forcing a pointed, rhombic base, pyramidal diamond indenter with specified face angles into the surface of the material under test while applying a predetermined load, and measuring the surface projection of the long diagonal of the resulting impression after the load is removed. 

Specimen Size : 

The surface of the ASTM C1326 test specimen is ground and polished. The specimen has a  roughness of less than 0.1 µm and a thickness of 0.50 mm. 

Data:

As per ASTM C1326, the ratio of the applied force divided by the projected indentation area on the specimen surface is used to compute Knoop hardness. Ceramics’ Knoop hardness decreases as the size or force of the indentation increases.