Hardness Toughness And dBTT Flashcards
Hardness=
A measure of a materials resistance to localised plastic deformation
What is the qualitative scale of hardness
1-10
Harder materials scratch softer ones
What is a quantitative hardness test
Small indenter forced into the surface under controlled load and rate of application
Depth and size of indent is measured
The indent in a hardness test is measured
Across 2 diagonals
4types of hardness test
Brinell(HB)
Vickers (HV)
Knoop(HK)
Rockwell(HRB)
Details of Brinell(HB) test
10 mm sphere of steel or tungsten carbide
Details of Vickers(HV)
Diamond pyramid
Details of Knoop (HK)
Diamond pyramid. Only used for thin sheets of metal
Details of Rockwell(HRB)
Diamond cone
3 Benefits of hardness tests
Simple
In-expensive
Non-destructive
High hardness= high
Strength
When is high hardness important
For applications that need good wear resistance
Toughness=
A measure of the amount of energy absorbed by a material as it fractures
How to measure toughness of smooth samples
Area under stress strain curves
How to measure notch toughness
Measure energy using fast fracture impact test(charpy)
How to measure fracture toughness (cracked sample)
Measure using critical load for failure
3 factors which affect toughness
Presence of notch
Strain rate
Environmental conditions
What is the charpy impact test
Sample hit with hammer
Measure energy absorbed size of machine relative to test material
Use standard sample size/geometry
DBTT stands for
Ductile- brittle transition temperature
K1c is
Fracture toughness
Which toughness is used in engineering calculations
Fracture toughness
How to test fracture toughness
Put a sample with a fatigue crack in a 3 or 4 point bend test at low strain rate
K1c is a
Material property
K1c equation
K1c=Y σ root (pi*a)
Critical crack length =
When failure occurs, they are a measure of damage tolerance
What values are used for an internal and edge crack
Internal =2a
Edge=a
For a pressure vessel we use
Hoop stress
Hoop stress=
Pr/t
(Internal pressure*radius)/wall thickness
2 characteristics of ductile failure
One piece
Large deformation
2 characteristics of brittle failure
Many pieces
Small deformations
