The Charpy Impact Test
and
Fracture Toughness
The Charpy Impact Test
Zero Setting
Fracture Energy vs. Temperature
for Various Metals
Source: J. Morrow, Univ. of Manchester (UK)
Fracture Energy and Mode Percentage
vs. Temperature for A36 Steel
brittle
ductile
DBT
Defining a Transition Temperature
• In general, there is no single specific
criteria for defining a transition
temperature; various definitions are
used:
brittle
ductile
– Fracture Transition Plastic (FTP) is the
temperature above which the fracture
is
100%
fibrous/shear
(0%
cleavage/ductile). This is the most
conservature estimate.
– Nil Ductility Temperature (NDT) is the
temperature below which the fracture
is 100% cleavage/shear.
– Fracture
Appearance
Transition
Temperature (FATT) is the temperature
at which the fracture surface is 5050% cleavage and fibrous. This can
alternativey be based upon the mean
of the “upper” and “lower” shelf
energies.
NDT
FATT
FTP
Fracture Surface Appearance vs. Temperature
(°Fahrenheit)
brittle
bright appearance, cleavage failure
ductile
dull appearance, plastic deformation
Carbon Content Effect on DBT Behavior
Increasing
Carbon
Note: Increasing %C decreases fracture toughness although increasing strength
Fracture Energy vs. Atomic Structure
• FCC structures exhibit no DBT, remain
ductile at all temperatures (e.g., Al and Cubased alloys)
• BCC/HCP structures do exhibit DBT
characteristics
ME124 Test Data from Spring 2000
ME124 Charpy Impact Test Data - Spr 2000
160
C1081 Steel
140
6061 Al
Brass
4340 Steel
120
A36 Steel
Fracture Energy (ft-lb)
Cast Iron
100
80
60
40
20
0
-250
-200
-150
-100
-50
0
50
Tem perature (deg C)
100
150
200
250
Fracture Surface Microstructure
brittle
ductile