mt4101=06-2

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Hardness
• Resistance to permanently indenting the surface.
• Large hardness means:
--resistance to plastic deformation or cracking in
compression.
--better wear properties.
e.g., 
10 mm sphere
apply known force measure size 
of indent after 
removing load
dD
Smaller indents 
mean larger 
hardness.
increasing hardness
most 
plastics
brasses 
Al alloys
easy to machine 
steels file hard
cutting 
tools
nitrided 
steels diamond
• Hardness test:
– Simple and inexpensive
– Non-destructive test
– Estimating other mechanical properties from hardness data.
• Brinell
– Hard spherical steel indenter (D=10mm)
– Standard load (500-3000kg)
– HB is a function of the load and the diameter of the 
resulting indentation
Hardness: Measurement
Hardness: Measurement
• Knoop and Vickers (diamond pyramid)
– Diamond indenter (pyramidal geometry)
– Smaller load (1-1000kg)
– Hardness numbers are designated by HK &HV
– HK&HV approximately equivalent
– Microindentation-test
Hardness: Measurement
• Rockwell
– Each scale runs to 130 but only useful in range 20-100. 
– Minor load 10 kg
– Major load 60 (A), 100 (B) & 150 (C) kg
• A,C&D=diamond, B,F&G = 1/16 in.ball, E,H&K = 1/8 in.ball
• Superficial Rockwell
– Minor load 3 kg
– Major load 15, 30, 45
• N= diamond, T= 1/16 in. ball, W= 1/8 in. ball.
• Examples:
– 80 HRB, 60 HR30W
Hardness: Measurement
Table 6.5