Lecture 10- Hardness and toughness

Question 1

define hardness

Answer 1

a materials resistance to localised plastic deformation (dent or scratch)

Question 2

how is hardness measured?

Answer 2

using an indentor

Question 3

what dictates hardness in testing?

Answer 3

the depth and size of an indent

Question 4

define toughness

Answer 4

the amount of energy absorbed by a material before it fractures

Question 5

how is toughness measured for smooth samples?

Answer 5

area under stress-strain curve

Question 6

how is toughness measured for notched samples?

Answer 6

Charpy impact test

Question 7

how is toughness measured for cracked samples?

Answer 7

critical load for failure

Question 8

what 3 factors affect toughness?

Answer 8

presence of notch or other defects
strain rate
environmental conditions like temperature and chemicals

Question 9

describe the charpy impact test

Answer 9

sample is hit with a hammer and energy absorbed is measured

Question 10

what does it mean if a material displays dbtt behaviour when toughness is tested at different temperatures?

Answer 10

as temperature increases, the material goes frpm brittle to ductile eg carbon steels