Hardness Toughness And dBTT

Question 1

Hardness=

Answer 1

A measure of a materials resistance to localised plastic deformation

Question 2

What is the qualitative scale of hardness

Answer 2

1-10

Harder materials scratch softer ones

Question 3

What is a quantitative hardness test

Answer 3

Small indenter forced into the surface under controlled load and rate of application
Depth and size of indent is measured

Question 4

The indent in a hardness test is measured

Answer 4

Across 2 diagonals

Question 5

4types of hardness test

Answer 5

Brinell(HB)
Vickers (HV)
Knoop(HK)
Rockwell(HRB)

Question 6

Details of Brinell(HB) test

Answer 6

10 mm sphere of steel or tungsten carbide

Question 7

Details of Vickers(HV)

Answer 7

Diamond pyramid

Question 8

Details of Knoop (HK)

Answer 8

Diamond pyramid. Only used for thin sheets of metal

Question 9

Details of Rockwell(HRB)

Answer 9

Diamond cone

Question 10

3 Benefits of hardness tests

Answer 10

Simple
In-expensive
Non-destructive

Question 11

High hardness= high

Answer 11

Strength

Question 12

When is high hardness important

Answer 12

For applications that need good wear resistance

Question 13

Toughness=

Answer 13

A measure of the amount of energy absorbed by a material as it fractures

Question 14

How to measure toughness of smooth samples

Answer 14

Area under stress strain curves

Question 15

How to measure notch toughness

Answer 15

Measure energy using fast fracture impact test(charpy)

Question 16

How to measure fracture toughness (cracked sample)

Answer 16

Measure using critical load for failure

Question 17

3 factors which affect toughness

Answer 17

Presence of notch
Strain rate
Environmental conditions

Question 18

What is the charpy impact test

Answer 18

Sample hit with hammer
Measure energy absorbed size of machine relative to test material
Use standard sample size/geometry

Question 19

DBTT stands for

Answer 19

Ductile- brittle transition temperature

Question 20

K1c is

Answer 20

Fracture toughness

Question 21

Which toughness is used in engineering calculations

Answer 21

Fracture toughness

Question 22

How to test fracture toughness

Answer 22

Put a sample with a fatigue crack in a 3 or 4 point bend test at low strain rate

Question 23

K1c is a

Answer 23

Material property

Question 24

K1c equation

Answer 24

K1c=Y σ root (pi*a)

Question 25

Critical crack length =

Answer 25

When failure occurs, they are a measure of damage tolerance

Question 26

What values are used for an internal and edge crack

Answer 26

Internal =2a

Edge=a

Question 27

For a pressure vessel we use

Answer 27

Hoop stress

Question 28

Hoop stress=

Answer 28

Pr/t

(Internal pressure*radius)/wall thickness

Question 29

2 characteristics of ductile failure

Answer 29

One piece

Large deformation

Question 30

2 characteristics of brittle failure

Answer 30

Many pieces

Small deformations