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= Article Draft = Updates to Fracture.

As an existing article, only changed text is below with notes in [brackets] about which paragraphs are affected.

Also, the first and last External links don't work and should be deleted.

=Brittle fracture=

In brittle fracture, no apparent plastic deformation takes place before fracture. Brittle fracture typically involves little energy absorption and occurs at high speeds (up to 7000 ft/sec in steel). In most cases brittle fracture will continue even when loading is discontinued.

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.

[keep existing text except replace the last paragraph with the one below]

The basic sequence in a typical brittle fracture is: introduction of a flaw either before or after the material is put in service, slow and stable crack propagation under recurring loading, and sudden rapid failure when the crack reaches critical crack length based on the conditions defined by fracture mechanics. Brittle fracture may be avoided by controlling three primary factors, material fracture toughness (Kc), nominal stress level (σ), and introduced flaw size (a). Residual stresses, temperature, loading rate, and stress concentrations also contribute to brittle fracture by influencing the three primary factors.

=Ductile fracture= [new last paragraph]Under certain conditions, ductile materials can exhibit brittle behavior. Rapid loading, low temperature, and triaxial stress constraint conditions may cause ductile materials to fail without prior deformation.

=Fracture modes and characteristics = Main article: Fracture mechanics

There are three standard conventions for defining relative displacements in elastic materials in order to analyze crack propagation as proposed by Irwin. In addition fracture can involve uniform strain or a combination of these modes.


 * 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)

The manner by which the crack propagates through the material gives insight into the mode of fracture. With ductile fracture the crack moves slowly and is accompanied by a large amount of plastic deformation around the crack tip. The ductile crack will usually not propagate unless an increased stress is applied and generally cease propagating when loading is removed. In a ductile material, the crack may progress to a section of the material where stresses are slightly lower and stop due to the blunting effect of plastic deformations at the crack tip. On the other hand, with brittle fracture, cracks spread very rapidly with little or no plastic deformation. The cracks that propagate in a brittle material will continue to grow once initiated.

Another method of assessing crack propagation is the way in which the advancing crack travels through the material at the microscopic level. A crack that passes through the grains within the material is undergoing transgranular fracture. A crack that propagates along the grain boundaries is termed an intergranular fracture. Typically, the bonds between materials grains are stronger at room temperature than the material itself, so transgranular fracture is more likely to occur. As temperature increases, brittle behavior is more likely and intergranular fracture is the more common fracture mode.

=Notable fracture failures= Failures caused by brittle fracture have not been limited to any particular category of engineered structure. Though brittle fracture is less common than other types of failure, the impacts to life and property can be more severe. The following notable historic failures were attributed to brittle fracture:
 * Pressure vessels: Great Molasses Flood in 1919, New Jersey molasses tank failure in 1973
 * Bridges: King Street Bridge span collapse in 1962, Silver Bridge collapse in 1967, partial failure of the Hoan Bridge in 2000
 * Ships: Titanic in 1912, Liberty ships during World War II , SS Schenectady in 1943