Hardness TestingSection 6.10

Hardness“A measure of a material’s resistance

to localized plastic deformation.”

Early arbitrary hardness indexing◦What scratches what? Which is “softer?”◦Mohs Scale

Hardness

Hardness

Hardness

Hardness

Hardness

Hardness

Hardness

Hardness

Hardness

Hardness

Diamonds are “hard”Talc is “soft”

◦You can scratch talc with a diamond◦Cannot scratch a diamond with talc

(Frypans and Metal Spatulas) (Sharpening tools) (Whet stones)

Hardness

Hardness test performed more frequently than any other mechanical test.◦Simple and inexpensive

Little preparation for specimens Machinery not quite as expensive as others

◦Little deformation Small bump or indentation, not large fracture

◦Can sometimes estimate tensile strength

Hardness

Most common◦Simple◦Little skill required

Uses◦Indentors and weights

Allow testing of alloysand some plastics

Normal or Superficial

Rockwell Hardness

Depend on normal or superficialNormal

◦B – 1/16” tungsten carbide ball, 100 kg◦C – “Brale” conical diamond, 150 kg

Superficial◦15N – “Brale”, 15 kg◦15T – 1/16” ball, 15 kg

Brale scales used for hardest materials

Rockwell (Indenters)

10.00 mm ballLoads

◦500 and 3000 kgLoaded for ~10 sHB scale

Brinell Hardness

Small diamond shape1 to 1000 g loadsMicroindentation

◦Requires microscopeHK and HV scalesKnoop – ceramics

Knoop and Vickers

Diamond tipped hammerMeasures rebound

from a fixed height

Scleroscope

Shore DurometerTests polymers, elastomers, and

rubber

Conversions Between scales

◦Figure 6.18◦Charts in the lab

Between Hardness and Tensile ◦TS(MPa) = 3.45 x HB

Steel alloys only