Fracture Toughness
Alexander Werf , Guangmei Wu
Content
1. Definition
2. Fracture toughness value
-- Stress Intensity Factors of Cracks (KIC)
3. Notch-Impact tests
4. Factors influence on toughness
Definition
Toughness:
the ability of a material to
deform plastically and to
absorb energy in the
process before fracture
The key to toughness
is a good combination
of strength and ductility
Fracture toughness value
Stress Intensity Factors of Cracks KC
 C   a
KC is the fracture toughness in unit of MPa m
Y is a dimensionless factor depending
on the geometry of the specimen or
structural component
σ is the remote loading stress in MPa or psi
a is the crack length in meters or inches
Fracture toughness values
Stress Intensity Factors of Cracks KC KIC, KIIC, KIIIC
Mode I :
opening mode
Mode II :
sliding mode
Mode III :
tearing mode
Fracture toughness value
Stress Intensity Factors of Cracks KC
Crit. stress :
C 
K IC
Y a
Crit. crack length :
1  K IC 
ac  

  Y 
aC = critical crack length (surface crack),
one half crack length (intenal crack)
σ = the remote loading stress
KIC = the fracture toughness, when the
sample has a thickness less than B
Y = a dimensionless factor depending
on the geometry of the specimen
σC = critical applied loading stress
that causes the material to fail
Toughness tests
 Charpy test

Izod test

Compact tension specimen
Charpy test
Kimp is the impact toughness
KQ  W / S
W is the work, required for breaking the specimen
m is the pendulum mass
S is the cross section area of the specimen at the
notch
Izod test and ct-probe test
Izod test
ct-probe
Factors influence on toughness
 Temperature
 Strain rate (rate of loading)
 Thickness
 Microstructure
Temperature
 toughness decrease as the temperature lowered
Strain rate (rate of loading)
 toughness decrease as the rate of loading increase
Thickness
 K IC 
B  2.5

 Y 
 toughness decrease with increasing sample
thickness B
2
Microstructure
Ductile matrix
Brittle phase
Ductile matrix
Brittle phase
References
• Script HVAT Metalle, W. Reimers
• Mech. Behaviors of Materials, N. E. Dowling
• Mech. Verhalten der Werkstoffe, J. Rösler, H.
Harders, M. Bäker
• Werkstoffkunde, Bargel, Schulze
• Werkstofftechnik 1, W. Bergmann
• http://aluminium.matter.org.uk
• http://materials-welding.blogspot.com
• http://de.wikipedia.org/wiki/Bruchzähigkeit
Thanks for your attention !
To Alex,
ALLES GUTE ZUM
GEBURTSTAG !