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Encyclopedia > Fracture
Mechanical failure modes
Buckling
Corrosion
Creep
Fatigue
Fracture
Melting
Rupture (engineering)
Thermal shock
Wear
Yielding
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A fracture is the (local) separation of a body into two, or more, pieces under the action of stress. Look up fracture in Wiktionary, the free dictionary. ... This article is about engineering. ... For the hazard, see corrosive. ... Creep is the term used to describe the tendency of a material to move or to deform permanently to relieve stresses. ... In materials science, fatigue is the progressive, localised, and permanent structural damage that occurs when a material is subjected to cyclic or fluctuating strains at nominal stresses that have maximum values less than (often much less than) the static yield strength of the material. ... In physics, melting is the process of heating a solid substance to a point (called the melting point) where it turns into a liquid. ... Rupture, or ductile rupture describes the ultimate failure of tough ductile materials loaded in tension. ... Thermal shock and thermal loading refer to the disfuntion (and perhaps, crack) of a material due to the heating, especially non-stationary and non-uniform. ... In materials science, wear is the erosion of material from a solid surface by the action of another solid. ... Yield strength, or the yield point, is defined in engineering and materials science as the stress at which a material begins to plastically deform. ... Stress is a measure of force per unit area within a body. ...


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). This article is about the skeletal organs. ... For other uses, see Crystal (disambiguation). ... For other uses, see Gemstone (disambiguation). ... This article is about metallic materials. ... Strength of materials is materials science applied to the study of engineering materials and their mechanical behavior in general (such as stress, deformation, strain and stress-strain relations). ... In telecommunications, transmission is the act of transmitting electrical messages (and the associated phenomena of radiant energy that passes through media). ... This article does not cite any references or sources. ... See also list of optical topics. ...


A detailed understanding of how fracture occurs in materials may be assisted by the study of fracture mechanics. This does not cite its references or sources. ...

Contents

Types of fracture

Brittle fracture

Brittle fracture in glass.
Brittle fracture in glass.

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. Image File history File links Metadata Size of this preview: 800 × 600 pixelsFull resolution (1600 × 1200 pixel, file size: 391 KB, MIME type: image/jpeg) Its a crop from an image in the series at http://ctho. ... Image File history File links Metadata Size of this preview: 800 × 600 pixelsFull resolution (1600 × 1200 pixel, file size: 391 KB, MIME type: image/jpeg) Its a crop from an image in the series at http://ctho. ... A material is brittle if it is subject to fracture when subjected to stress i. ... For other uses, see Plasticity. ... Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite planes, creating smooth surfaces, of which there are several named types: Basal cleavage: cleavage parallel to the base of a crystal, or to the plane of the lateral axes. ... Tensile stress (or tension) is the stress state leading to expansion; that is, the length of a material tends to increase in the tensile direction. ... Wax and paraffin are amorphous. ... Conchoidal fracture describes the way that brittle materials break when they do not follow any natural planes of separation. ...


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: -

  • σapplied is the loading stress,
  • 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.[citation needed] This phenomenon was recently also verified by experiment of fracture in rubber-like materials. Supersonic fractures are fractures faster than the speed of sound in a material. ... This does not cite any references or sources. ...

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

Image File history File links Metadata Size of this preview: 652 × 599 pixelsFull resolution (2316 × 2129 pixel, file size: 470 KB, MIME type: image/jpeg) File historyClick on a date/time to view the file as it appeared at that time. ... Image File history File links Metadata Size of this preview: 652 × 599 pixelsFull resolution (2316 × 2129 pixel, file size: 470 KB, MIME type: image/jpeg) File historyClick on a date/time to view the file as it appeared at that time. ...

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.[citation needed]. Ductility is the physical property of being capable of sustaining large plastic deformations without fracture (in metals, such as being drawn into a wire). ... This article is about the deformation of materials. ... For other uses, see Iron (disambiguation). ... Cast iron usually refers to grey cast iron, but can mean any of a group of iron-based alloys containing more than 2% carbon (alloys with less carbon are carbon steel by definition). ... Plain-carbon steel is a metal alloy, a combination of two elements, iron and carbon, where other elements are present in quantities too small to affect the properties. ...

Ductile failure of a specimen strained axially.
Ductile failure of a specimen strained axially.

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. Image File history File links Metadata Size of this preview: 800 × 438 pixelsFull resolution (2812 × 1540 pixel, file size: 2. ... Image File history File links Metadata Size of this preview: 800 × 438 pixelsFull resolution (2812 × 1540 pixel, file size: 2. ...


The basic steps of ductile fracture are necking (which results in stress localization at the point on the 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.

Schematic representation of the steps in ductile fracture.
Schematic representation of the steps in ductile fracture.

Image File history File links Ductile_fracture. ...

Crack Separation Modes

There are three modes of fracture. Mode I, or the opening mode, is characterized by a stress normal to the crack faces. Mode II, the sliding mode or forward shear mode, has a shear stress normal to the crack front. Finally Mode III is the tearing mode, with a shear stress parallel to the crack front.


For more information, see fracture mechanics. This does not cite its references or sources. ...


See also

The brittle-ductile transition zone is the zone in the Earths crust, at an approximate depth of 10-15 km (18-20km) at which rock becomes less likely to fracture, and more likely to deform ductilely by creep. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... This does not cite its references or sources. ... In materials science, fracture toughness is a property which describes the ability of a material containing a crack to resist fracture, and is one of the most important properties of any material for virtually all design applications. ... Rupture, or ductile rupture describes the ultimate failure of tough ductile materials loaded in tension. ... Structural failure refers to loss of the load-carrying capacity of a component or member within a structure or of the structure itself. ...

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.

It is proposed that this article be deleted, because of the following concern: Likely failure of WP:AUTO and WP:BIO If you can address this concern by improving, copyediting, sourcing, renaming or merging the page, please edit this page and do so. ...

External Links


  Results from FactBites:
 
Bone fracture - Wikipedia, the free encyclopedia (1221 words)
A bone fracture is a medical condition in which a bone becomes cracked, splintered, or bisected as a result of physical trauma.
A greenstick fracture occurs because the bone is not as brittle as it would be in an adult, and thus does not completely fracture, but rather exhibits bowing without complete disruption of the bone's cortex.
To this end, a fractured limb is usually immobilized with a plaster or fiberglass cast which holds the bones in position and immobilizes the joints above and below the fracture.
Fracture - Wikipedia, the free encyclopedia (381 words)
The word fracture is often applied to bones of living creatures, or to crystals or crystalline materials, such as gemstones or metal.
Depending on the substance which is fractured, a fracture reduces strength (most substances) or inhibits transmission of light (optical crystals).
In amorphous solids, by contrast, the lack of a crystalline structure means that any direction may be considered a cleavage plane; the result is a conchoidal fracture, with cracks proceeding normal to the applied tension.
  More results at FactBites »

 
 

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