MATERIAL FAILURE
Properties and applications of engineering materials
AIMS
• To explore extreme cases of material failure.
• To raise awareness of the importance of design to
help reduce the risk of failure in a material.
OBJECTIVES
By the end of this session the learners should be able
to:
• List at least 3 instances in which the failure of a
material has led to loss of life.
• List the four main modes of material failure.
• Discuss and deduce the key mode of failure in at
least 2 of the cases presented.
THE BOSTON MOLASSES DISASTER
• 15th January 1919
• 21 fatalities and 150 injured
• Molasses was used in the production of ethanol. Consistency of
syrup.
• Fact: Killed humans and animals by blocking their airways.
THE BOSTON MOLASSES DISASTER
THE LIBERTY SHIPS
• Built to transport food and vital supplies from
America to the UK in WWII
• A ship could be built in just 42 days.
• Made from various grades of steel. One of the first
ships to be welded rather than riveted.
• Women were employed as welders.
• Fact: There were in excess of 1000 instances of
fracture.
THE WORLD TRADE CENTRE
• 11th September 2001
• Terrorist attack in which 2 planes were flown into the
towers.
• The south tower fell first; followed by the north.
• The way in which the towers collapsed raised
questions; conspiracy theories thrived.
• Are the conspiracy theories true? Or can the theory
of material failure provide a more valid
explanation?
PALAU BRIDGE COLLAPSE
BIG DIG CEILING COLLAPSE
TITANIC MATERIAL CHOICE DIDN’T HELP THE SITUATION
MIANUS BRIDGE COLLAPSE- CONNECTICUT
IS AN ACTIVITY OTHER THAN PURELY
“ ENGINEERING
MANUAL AND PHYSICAL WORK WHICH BRINGS
ABOUT THE UTILIZATION OF THE MATERIALS AND
LAWS OF NATURE FOR THE GOOD OF HUMANITY.
R.E Hellmund
”
Brittle/ Ductile
fracure
Creep
Fatigue
Degradation
FAILURE MODES
A brittle fracture occurs when the material
exhibits little or no plastic deformation. This
can be affected by temperature.
Fatigue failure is caused by cyclic stress, the stress
may not be applied in all instances but is
repeated over and over again. There are three
main stages to fatigue failure
• Crack initiation
• Crack propagation
• Failure
Creep occurs in materials that have been subjected to
high temperatures and forces causing deformation. For
example, in a jet engine, the blades may creep as the
temperatures and forces acting on the blades cause
deformation. This can lead to the blades extending,
rubbing the engine housing , leading to engine failure.
WHICH FAILURE MODE IS
RESPONSIBLE?
Liberty Ships
WTC Collapse
Brittle failure
Creep
- Temperature of
the water
- Temperatures
from ignition of
aviation fuel
reached in excess
of 800 degrees
Celsius
- Cracks would
put pressure on
additional weld
lines
- Caused the
structural beams
to undergo creep
deformation
Boston molasses
Fatigue
- Expansion and
contraction of
tank caused
metal to
fatigue and fail
Mianus Bridge
Degradation
- Type of
material used
prone to rust
- Rust caused
part of the
bridge to
collapse
ANY QUESTIONS?
Your next assignment is going to assess your knowledge on the following;
• Failure modes- Brittle/Ductile fracture, Fatigue, Creep and Degradation(rust,
corrosion, chemical attack, aging and thermal shock)
• Identify which failure mode caused/ occurred within given disasters.
• Description of the failure modes with regards to a specific material i.e. Creep
can occur in metal, concrete (composite)and plastic.