A fracture is the (local) separation of an object or material into two, or more, pieces under the action of stress. In Engineering, buckling is a failure mode characterized by a sudden failure of a structural member subjected to high Compressive stresses where Corrosion means the breaking down of essential properties in a material due to Chemical reactions with its surroundings Creep is the tendency of a solid material to slowly move or deform permanently under the influence of stresses It occurs as a result of long term exposure to levels of An impact force is a high Force or shock applied over a short time period Melting is a process that results in the phase change of a substance from a Solid to a Liquid. The failure or fracture of a product or component in a single event is known as mechanical overload. Thermal shock is the name given to cracking as a result of rapid temperature change In Materials science, wear is the erosion of material from a Solid Surface by the action of another substance The yield strength or yield point of a Material is defined in Engineering and Materials science as the stress at which a material Stress is a measure of the average amount of Force exerted per unit Area.

The word fracture is often applied to bones of living creatures, or to crystals or crystalline materials, such as gemstones or metal. Bones are rigid organs that form part of the Endoskeleton of Vertebrates They function to move support and protect the various organs of the body produce In Materials science, a crystal is a Solid in which the constituent Atoms Molecules or Ions are packed in a regularly ordered repeating A gemstone or gem, also called a precious or semi-precious stone, is a piece of attractive Mineral, which &mdash when cut and polished &mdash The M acro E xpansion T emplate A ttribute L anguage complements TAL, providing macros which allow the reuse of code across 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). In Materials science, the strength of a material refers to the material's ability to resist an applied force In Telecommunications transmission is the process of sending propagating and receiving an analogue or digital information signal over a physical point-to-point or Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700

A detailed understanding of how fracture occurs in materials may be assisted by the study of fracture mechanics. Fracture mechanics is the field of Mechanics concerned with the study of the formation of cracks in materials

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). Cleavage, in Mineralogy, is the tendency of crystalline materials to split along definite planes creating smooth surfaces of which there are several named types Stress is a measure of the average amount of Force exerted per unit Area. In amorphous solids, by contrast, the lack of a crystalline structure results in a conchoidal fracture, with cracks proceeding normal to the applied tension. An amorphous solid is a Solid in which there is no Long-range order of the positions of the Atoms (Solids in which there is long-range atomic order are 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)

where: -

E is the Young's modulus of the material,

γ is the surface energy, and

r_o is the equilibrium distance between atomic centers. In Solid mechanics, Young's modulus (E is a measure of the Stiffness of an isotropic elastic material Surface energy quantifies the disruption of intermolecular bonds that occurs when a surface is created

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

(For sharp cracks)

where: -

σ_applied 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

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. Supersonic fractures are Fractures where the fracture velocity moves faster than the Speed of sound in the 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. Ductility is a mechanical property used to describe the extent to which materials can be deformed plastically or "stretched" into "wires" without 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. Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 Cast iron usually refers to grey cast iron, but identifies a large group of Ferrous Alloys which solidify with a Eutectic. Carbon steel, also called plain carbon steel, is Steel where the main alloying constituent is Carbon. .

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 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.

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)

For more information, see fracture mechanics. Stress is a measure of the average amount of Force exerted per unit Area. A shear stress, denoted \tau\ ( Tau) is defined as a stress which is applied Parallel or tangential to a face of a material A shear stress, denoted \tau\ ( Tau) is defined as a stress which is applied Parallel or tangential to a face of a material Fracture mechanics is the field of Mechanics concerned with the study of the formation of cracks in materials

See also

• Bone fracture
• Brittle-ductile transition zone
• Environmental stress fracture
• Fracture mechanics
• Fracture (mineralogy)
• Fracture (geology)
• Fracture toughness
• Fractography
• Forensic engineering
• Forensic materials engineering
• Rupture (engineering)
• Structural failure

Bibliography

• Dieter, G. A bone fracture (sometimes abbreviated # or Fx or Fx) is a medical condition in which a Bone is cracked or broken The brittle-ductile transition zone is the strongest part of the Earth's crust. In Materials science, environmental stress fracture or environment assisted fracture is the generic name given to premature failure under the influence Fracture mechanics is the field of Mechanics concerned with the study of the formation of cracks in materials In the field of Mineralogy, fracture is a term used to describe the shape and texture of the surface formed when a Mineral is broken A fracture is any local separation or discontinuity plane in a Geologic formation, such as a joint or a fault that divides the rock into two or more 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 Fractography is the study of fracture surfaces of materials Fractographic methods are routinely used to determine the cause of failure in engineering structures especially in product Forensic Engineering is the investigation of materials, products, Structures or components that fail or do not operate/function as A branch of Forensic engineering, the subject focuses on the material evidence from crime or accident scenes seeking defects in those materials which might explain why an accident occurred 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 E. (1988) Mechanical Metallurgy ISBN 0-07-100406-8
• A. Garcimartin, A. Guarino, L. Alessio Guarino is an Italian physicist born in Florence Italy in 1970 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.

External links

• Web postings at http://www.jwave.vt.edu/crcd/farkas/lectures/Fract1/tsld006.htm
• Virtual museum of failed products at http://materials.open.ac.uk/mem/index.html
• Fracture and Reconstruction of a Clay Bowl
• Ductile fracture