Fracture: Wikis

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Encyclopedia

Mechanical failure modes
Buckling
Corrosion
Creep
Fatigue
Fracture
Impact
Rupture
Thermal shock
Wear
Yielding

A fracture is the (local) separation of an object or material into two, or more, pieces under the action of stress.

The word fracture is often applied to bones of living creatures, or to crystals or crystalline materials, such as gemstones or metal. Sometimes, in crystalline materials, individual crystals fracture without the body actually separating into two or more pieces. Depending on the substance which is fractured, a fracture reduces strength (most substances) or inhibits transmission of light (optical crystals).

A detailed understanding of how fracture occurs in materials may be assisted by the study of fracture mechanics.

Types of fracture

Brittle fracture

Brittle fracture in glass.
Fracture of an Aluminum Crank Arm. Bright: Brittle fracture. Dark: Fatigue fracture.

In 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). In amorphous solids, by contrast, the lack of a crystalline structure results in a conchoidal fracture, with cracks proceeding normal to the applied tension.

The theoretical strength of a crystalline material is (roughly)

$\sigma_\mathrm{theoretical} = \sqrt{ \frac{E \gamma}{r_o} }$

where: -

E is the Young's modulus of the material,
γ is the surface energy, and
ro is the equilibrium distance between atomic centers.

On the other hand, a crack introduces a stress concentration modeled by

$\sigma_\mathrm{elliptical\ crack} = \sigma_\mathrm{applied}(1 + 2 \sqrt{ \frac{a}{\rho}}) = 2 \sigma_\mathrm{applied} \sqrt{\frac{a}{\rho}}$ (For sharp cracks)

where: -

a is half the length of the crack, and
ρ is the radius of curvature at the crack tip.

Putting these two equations together, we get

$\sigma_\mathrm{fracture} = \sqrt{ \frac{E \gamma \rho}{4 a r_o}}.$

Looking closely, we can see that sharp cracks (small ρ) and large defects (large a) both lower the fracture strength of the material.

Recently, scientists have discovered supersonic fracture, the phenomenon of crack motion faster than the speed of sound in a material. This phenomenon was recently also verified by experiment of fracture in rubber-like materials.

Ductile fracture

Ductile failure of a specimen strained axially.
Schematic representation of the steps in ductile fracture.

In ductile fracture, extensive plastic deformation takes place before fracture. Many ductile metals, especially materials with high purity, can sustain very large deformation of 50–100% or more strain before fracture under favorable loading condition and environmental condition. The strain at which the fracture happens is controlled by the purity of the materials. At room temperature, pure iron can undergo deformation up to 100% strain before breaking, while cast iron or high-carbon steels can barely sustain 3% of strain..

Because ductile rupture involves a high degree of plastic deformation, the fracture behavior of a propagating crack as modeled above changes fundamentally. Some of the energy from stress concentrations at the crack tips is dissipated by plastic deformation before the crack actually propagates.

The basic steps sample of smallest cross-sectional area), void formation, void coalescence (also known as crack formation), crack propagation, and failure, often resulting in a cup-and-cone shaped failure surface.

Crack separation modes

The three fracture modes.

There are three ways of applying a force to enable a crack to propagate:

• Mode I crack – Opening mode (a tensile stress normal to the plane of the crack)
• Mode II crack – Sliding mode (a shear stress acting parallel to the plane of the crack and perpendicular to the crack front)
• Mode III crack – Tearing mode (a shear stress acting parallel to the plane of the crack and parallel to the crack front)

Bibliography

• Dieter, G. E. (1988) Mechanical Metallurgy ISBN 0-07-100406-8
• A. Garcimartin, A. Guarino, L. Bellon and S. Cilberto (1997) " Statistical Properties of Fracture Precursors ". Physical Review Letters, 79, 3202 (1997)
• Callister, Jr., William D. (2002) Materials Science and Engineering: An Introduction. ISBN 0-471-13576-3
• Peter Rhys Lewis, Colin Gagg, Ken Reynolds, CRC Press (2004), Forensic Materials Engineering: Case Studies.

Quotes

Up to date as of January 14, 2010

From Wikiquote

Fracture is a 2007 legal/crime suspense film from both New Line Cinema and Castle Rock Entertainment, directed by Gregory Hoblit and starring Anthony Hopkins and Ryan Gosling.

If you look close enough, you'll find everyone has a weak spot.

Ted Crawford

• Even a broken clock is right twice a day.
• You look closely enough, you'll find that everything has a weak spot where it can break, sooner or later.

Gaming

Up to date as of February 01, 2010

From Wikia Gaming, your source for walkthroughs, games, guides, and more!

Amidst a backdrop of worldwide ecological and seismological chaos in the mid-2100s, the United States has been split in two by the "Great Flood". As a result of the polar ice cap melting, the Mississippi River has destroyed the central portion of the United States, causing an ill-equipped Federal Government to fail and literally cutting the country in half. These two halves are left to fend for themselves in the aftermath.

The East, now known as the Atlantic Alliance, symbolic of their union with Europe, puts its faith in surviving this new world in cybernetics, an established yet evolving technology now more than 150 years old. On the other side of the flooded continent, the Western states, now called the Republic of Pacifica and having allied with Asia, resort to solving their problems at the genetic level, effectively restructuring the DNA of its inhabitants -- a method the Atlantic Alliance finds morally reprehensible.

By 2161, it only takes a hint of unauthorized military preparation in Pacifica for the newly restored president to order a strike in the heart of Pacifican territory -- an outpost in the now dry San Francisco Bay. This strike leads to the unthinkable: an epic conflict with global implications fought on U.S. soil. As a soldier in this struggle, Mason Briggs uses explosive, terrain-deforming weaponry to change the face of battle: He not only destroys the land in his path, he outright transforms it to gain the strategic advantage in completely unscripted ways no game has ever seen. With such a devastating arsenal at hand, Briggs never leaves any battlefield the way he found it.

In addition to extraordinary weaponry that allows players to do things previously only imagined, each side of the conflict, Pacifica and the Atlantic Alliance, boast soldiers with powers beyond those of ordinary men. Genetic augmentations provide Pacifican forces with amazing abilities, while Atlantic Alliance soldiers like Briggs counter the threat with the more "traditional" method: cybernetics. The differing states of superhumanity result in balanced yet stylistically different combat tactics that have never been seen before.

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Simple English

A fracture is when some kind of material is split into multiple pieces, because stress is applied to it.

1. The general case, which explains this for materials is at Material fracture
2. In certain cases the mantle of the earth shows so called faults, explained at Fracture (geology)
3. Minerals can also break, as explained at Fracture (mineralogy)
4. This can also happen to bones of vertebrates, such as humans, and is explained as Bone fracture