Selection criteria

Material failureProperties and applications of engineering materials

AimsTo explore extreme cases of material failure.

To raise awareness of the importance of design to help reduce the risk of failure in a material.ObjectivesBy 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 disaster15th January 191921 fatalities and 150 injuredMolasses 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 shipsBuilt to transport food and vital supplies from America to the UK in WWIIA 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 centre11th September 2001Terrorist 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 didnt help the situation

Mianus bridge collapse- Connecticut

Engineering is an activity other than purely manual and physical work which brings about the utilization of the materials and laws of nature for the good of humanity. R.E HellmundFailure modesBrittle FractureA brittle fracture occurs when the material exhibits little or no plastic deformation. This can be affected by temperature.

17Fatigue failure

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 failureCrack initiationCrack propagationFailure18Creep

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.

19Which failure mode is responsible?Liberty ShipsBrittle failureTemperature of the waterCracks would put pressure on additional weld lines

WTC CollapseCreepTemperatures from ignition of aviation fuel reached in excess of 800 degrees CelsiusCaused the structural beams to undergo creep deformation

Boston molassesFatigueExpansion and contraction of tank caused metal to fatigue and fail

DegradationType of material used prone to rustRust caused part of the bridge to collapseMianus Bridge 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.