*4.2.2 Hardness measurement*

Hardness is an easy method to assess the mechanical property of castings, and it is the measure of material resistance to deformation. Brinell hardness test is one of the standard techniques used for hardness measurement. The hardness was determined on the friction surface, and the hub of the failed rotor, and the measured value ranges from 163 to 180 HB. However, the design hardness specification is 160–220 HB. It can be said that the hardness of the disc is within the specification when the measured value is compared to the required hardness.
