The Phoenix and the The Phoenix and the SalamanderSalamander

The Power of Fire and HammerThe Power of Fire and Hammer

When and Why Things BreakHafid Aourag

LEPM, URMER, Université de Tlemcen, Algérie

The Most Important StoriesThe Most Important Stories• Aloha Airlines 28 April 1988, flight 243, Honolulu , 737 Boeing, The

accident investigation revealed the presence of small cracks at multiple rivet locations in a disbonded lap joint, which were sufficient in size and density to cause the accident. This phenomenon is referred to as widespread fatigue damage (WFD).

• Historically, we may look back to 1977 for what could be argued as the first ageing-airplane related accident; a Dan-Air Services Boeing 707-321C that crashed on final approach in Lusaka, Zambia.

• Whereas the accidents to date were raising awareness to ageing structural issues, it was not yet realized that aircraft systems ageing-related failures could be just as catastrophic. That all changed on July 17, 1996, when Trans World Airlines (TWA) flight 800, a 25-year old Boeing model 747-131, was involved in an in-flight break-up after takeoff from John F. Kennedy International Airport in New York, resulting in 230 fatalities.

In many respects, the term "ageing airplane" itself is getting long in the tooth. What is new is the approach now being taken to address design and maintenance issues associated with ageing structures, wiring and fuel tank safety.

Way Back in the Time:Way Back in the Time:Transformation just a story of failureTransformation just a story of failure

• Began 2500 years ago with the Greek• Two everyday phenomena « Conservation and Change » (Empedocles 445 b.c)

(Four kinds of atoms: earth, air, fire and water) Earth: solids Air:gazes Water:liquids The three states of matter, and the transformation is just the action of heating

• Meteorelogica (Aristotle) Origins of Materials Properties was descrideb by eighteen qualities of a substance (solidifiable, meltable, softenable by heat, softenable by water, flexible, breakable, fragmentable, capable of taling impression, plactic, squeezable, ductile, malleable, fissile, cuttable, viscous, compressible, combustible, and capable of giving off fumes)

• 12 among the 18 concerned the competition between fracture and deformation

• But At that time no notion of forces, gravity and electromagntism

Crystals and Polycrystals or theCrystals and Polycrystals or theNotion of GrainsNotion of Grains

Farm and a Forest : Notion of Direction ( Again the way it Broke)

Break to produce faces : Cleavage, (Interplay of light with fracture surfaces

Graphite

Grain BoundariesGrain Boundaries

Failure FractureFailure Fracture

• Failure theory is the science of predicting the conditions under which solid materials lose their strength under the action of external loads.

• Brittle Fracture : no apparent plastic deformation takes place before fracture. In brittle crystalline materials, fracture can occur by cleavage as the result of tensile stress acting normal to crystallographic planes with low bonding (cleavage planes).(Fracture)

• Ductile Fracture: In ductile fracture, extensive plastic deformation takes place before fracture. The terms rupture or ductile rupture describe the ultimate failure of tough ductile materials loaded in tension.(Yield)

Case StudyCase Study

• THE TITANIC

• Why did it sink so quickly?

OverviewOverview

• Case Study• The Titanic

• Fracture Mechanisms• Types of Fracture

• Metals/Ceramics/Polymers

• Composites

• Brittle/Ductile Transition• Charpy Impact Test

• Fatigue• Fatigue Life

• Environmental Effects• Stress Corrosion

• Creep

Fracture MechanismsFracture Mechanisms

• Fracture Mechanisms are differentin different materials.

• It’s important to understand• ductile and brittle failure, and • ductile and brittle fracture mechanisms.

DUCTILE FAILURE : HIGH ENERGYBRITTLE FAILURE : LOW ENERGY

Case Study - The TitanicCase Study - The Titanic

• Maiden Voyage• April 10th 1912

• Struck an Iceberg• 11.40pm, April 14th 1912

• Sank with over 1500 lives lost• 2.20am, April 15th 1912

Case Study - The TitanicCase Study - The Titanic

The Iceberg

The Damage

The TitanicThe Titanic

• The iceberg caused damage over a distance of 100m along the side of the Titanic.

• The damage area was 1.1m2

• This flooded 6 compartments

This damage was sufficient to sink the Titanic

The TitanicThe Titanic

• Titanic Steel• 0.2% Carbon Steel

• Yield Strength: 190 MPa

• Tensile Strength: 420 MPa

• Elongation: 29%

• Modern Steel• 0.2% Carbon Steel

• Yield Strength: 205 MPa

• Tensile Strength: 380 MPa

• Elongation: 26%

150 µm 20 µm Modern steel has smaller grain structure

Averagegrain size 26 µm

Averagegrain size 42 µm

The TitanicThe Titanic

-100 0 100 200

Temperature (ºC)

200

150

100

50

0

Modern Steel

Titanic SteelC

harp

y Im

pact

Ene

rgy

(J)

Titanic Steel, 0ºC

Seawater temperature(14th April 1912)

-2ºC• Titanic Steel• Low toughness

• Large grains• Low purity steel

• (High Phosphorus and Sulphur content)

Would a modern ship survive?

The TitanicThe Titanic

• Summary• The Titanic Steel was brittle at low temperature.• This probably increased the amount of damage

when the iceberg collided.• A modern ship might survive!

• less damage

• better design (water-tight bulkheads)

• better navigation equipment

Was the Titanic Steel Brittle?Was the Titanic Steel Brittle?

• New evidence suggests another cause for the sinking of the Titanic…...

RMS Olympic and HMS Hawke(collided 1911)

Evidence for brittle fracture under impact, but ductile tearing at lower speeds

Splitting of the steel hull unlikely…..

Was the Titanic Steel Brittle?Was the Titanic Steel Brittle?The Titanic steel was brittle, but no more so than any other ship of its time…..

Failed Titanic Rivet

MnS inclusions

Paramagnetic susceptibility of ferrite and cementite obtained from ab initio calculations  , Journal of Magnetism and Magnetic Materials, Volume 299, Issue 1, April 2006, Pages 64-69 Y.D. Zhang, H. Faraoun, C. Esling, L. Zuo and H. Aourag

Grain BoundariesGrain Boundaries

• Atomic mismatch in the transition from crytalline orientation of one grain to that of the adjacent one

• Small angle grain boundary

• Interstitial or grain boundary energy similar to surface energy • more chemcially reactive• impurity atoms tend to segregate here• lower in large or coarse-grained materials than in

fine-grained materials

Boron, SulfurBoron, Sulfur

Intermetallics, Volume 14, Issue 2, February 2006, Pages 142-148 A. Kellou, T. Grosdidier and H. Aourag

Acta Materialia, Volume 52, Issue 11, 21 June 2004, Pages 3263-3271 A. Kellou, H. I. Feraoun, T. Grosdidier, C. Coddet and H. Aourag

Study of stability of twist grain boundaries in hcp zinc  • ARTICLEScripta Materialia, Volume 54, Issue 5, March 2006, Pages 865-868 H. Faraoun, G. Vincent, C. Esling and H. Aourag

Liberty Ships : Arc WeldingLiberty Ships : Arc Welding

By High Seas and Low Air Tempereture : 140(2100)

Problem of Hydrogen

Brittle Failure

Crack Arrestors

Critical Stress Intensity FactorCritical Stress Intensity Factor

• When Things Break

• Irwin Griffith Naval Research Lab

• Able to clarify crack growth and provide designers with the information they needed to understand when cracks would become instable and run

• Fracture Mechanics

Challenger ExplosionChallenger ExplosionJanuary, 26, 1986January, 26, 1986

O – Rings : 1977

Thermal Effects

Malouines Islands : Malouines Islands : Exocet against AluminiumExocet against Aluminium

HMS Sheffield Dassault Etendard

Aluminium Hull