Temperature, Hardness
and
Toughness
Temperature Effects on
Material Properties
Temperature changes and extremes
affect the value of many engineering
properties

yield, modulus, toughness, corrosion
resistance, creep, relaxation, viscosity,
shrinkage, solubility…..
Temp Effect on Tensile Strength
Temp Effect on Other Properties
Thermal Expansion
Elevated Temperatures excite the
electrons at the atomic level of any
material
The excited atoms can more easily
move to a lower energy state and
change orientation of atomic planes
This leads to dimensional changes in
most materials
Temperature vs. Expansion
 temp  t t
t is the coefficient
of thermal
expansion.
Surface Properties
Hardness


Scratch hardness
Surface Hardness
Impact Energy
Hardness - Moh’s Scale
Moh scale is a surface scratch resistant scale based on
minerals
1
2
3
4
5
-
Talc
Gypsum
Calcite (CaCO3)
Flourite
Apatite
6
7
8
9
- Orthoclase (Feldspar)
- Quartz
- Topaz
- Corundum (or
sapphire)
10 - Diamond
Surface Hardness
Surface hardness is quantified by
determining the energy necessary to cause
localized plastic deformation.
A specific energy is imparted on a surface
of a material and the amount of plastic
deformation is quantified in most hardness
procedures.
Based on theory of plasticity.
Types of hardness tests
D

Brinell - 1900 - ball
original hardness
test
d
BHN 
D 
2 

Rockwell - 1919,
rounded cone most
common, (ASTM
E18)
P
D
D 2  d 2 
120°
Use of hardness
Surface hardness of heat treated metals
Quality control of heat treatment process
Correlated with other properties


Yield strength
“Brittleness”
Impact tests
Charpy V-notch
- Measure energy
required to
rupture specimen
Izod V-notch
- Same as Charpy but
different specimen
Test Specimen
and supports
Pointer
Pointer
Final
height, h’
Initial
height, h
Quantify resistance to
dynamic impacts and crack
sensitivity
Quantify the “transition
temperature” of an alloy
(ductile – brittle behavior)
Impact Energy, Joules
Use of impact resistance
Ductile
Brittle
Temperature