Tensile test of an AlMgSi alloy. Aluminium alloys are Alloys of Aluminium, often with copper zinc manganese silicon or magnesium The local necking and the cup and cone fracture surfaces are typical for ductile metals.

Ductility is a mechanical property used to describe the extent to which materials can be deformed plastically without fracture. In Materials science, deformation is a change in the shape or size of an object due to an applied force. A fracture is the (local separation of an object or material into two or more pieces under the action of stress. Ductility is the most important parameter to consider in metal forming operations such as rolling, extrusion, and drawing. Metalworking is craft and practice of working with Metals to create individual parts assemblies or large scale structures Examples of highly ductile metals are silver, gold, copper, and aluminium. Silver (ˈsɪlvɚ is a Chemical element with the symbol " Ag " (argentum from the Ancient Greek: ἀργήντος - argēntos gen Gold (ˈɡoʊld is a Chemical element with the symbol Au (from its Latin name aurum) and Atomic number 79 Copper (ˈkɒpɚ is a Chemical element with the symbol Cu (cuprum and Atomic number 29 WikipediaNaming The ductility of steel varies depending on the alloying constituents. Steel is an Alloy consisting mostly of Iron, with a Carbon content between 0 Increasing levels of carbon decreases ductility, i. Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 e. , the steel becomes more brittle.

Ductility can be quantified by the fracture strain , which is the engineering strain at which a test specimen fractures during a uniaxial tensile test. Stress is a measure of the average amount of Force exerted per unit Area. Another commonly used measure is the reduction of area at fracture q. ^[1]

Scientific fields

Geology

In Earth science the brittle-ductile transition zone is a zone, at an approximate depth of 15 km in continental crust, at which rock becomes less likely to fracture and more likely to deform ductilely. Earth science (also known as geoscience, the geosciences or the Earth Sciences) is an all-embracing term for the Sciences related to the planet The brittle-ductile transition zone is the strongest part of the Earth's crust. The continental crust is the layer of granitic, Sedimentary, and Metamorphic rocks which form the Continents and the areas of shallow seabed In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere In glacial ice this zone is at approximately 30 metres depth. "Glacial" and "Glaciation" redirect here For the geological periods see Glacial period. Ice is a Solid phase, usually crystalline, of a Non-metalic substance that is liquid or gas at Room temperature, such as Ammonia It is not impossible for material above a brittle-ductile transition zone to deform ductilely, nor for material below to deform brittly. The zone exists because as depth increases confining pressure increases, and brittle strength increases with confining pressure whilst ductile strength decreases with increasing temperature. The transition zone occurs at the point where brittle strength exceeds ductile strength.

Materials science

Schematic appearance of round metal bars after tensile testing.
(a) Brittle fracture
(b) Ductile fracture
(c) Completely ductile fracture

In materials science the ductile-brittle transition temperature (DBTT), nil ductility temperature (NDT), or nil ductility transition temperature of a material represents the point at which the fracture energy passes below a pre-determined point (for steels typically 40 J^[2] for a standard Charpy impact test). Materials Science or Materials Engineering is an interdisciplinary field involving the properties of matter and its applications to various areas of Science and The Charpy impact test, also known as the Charpy v-notch test, is a standardized high strain -rate test which determines the amount of Energy DBTT is important since, once a material is cooled below the DBTT, it has a much greater tendency to shatter on impact instead of bending or deforming. For example, ZAMAK 3 exhibits good ductility at room temperature but shatters at sub zero temperatures when impacted. Zamak (formerly Trademarked as ZAMAK and also known as Zamac) is a family of Alloys with a base metal of Zinc and alloying elements DBTT is a very important consideration in materials selection when the material in question is subject to mechanical stresses. See the section on glass transition temperature for a related discussion. The glass transition temperature, T g is the temperature at which an Amorphous solid, such as Glass or a Polymer, becomes brittle

In some materials this transition is sharper than others. For example, the transition is generally sharper in materials with a body-centered cubic (BCC) lattice than those with a face-centered cubic (FCC) lattice. The cubic crystal system (or isometric) is a Crystal system where the Unit cell is in the shape of a Cube. The cubic crystal system (or isometric) is a Crystal system where the Unit cell is in the shape of a Cube. DBTT can also be influenced by external factors such as neutron radiation, which leads to an increase in internal lattice defects and a corresponding decrease in ductility and increase in DBTT. Neutron radiation is a kind of Ionizing radiation which consists of Free neutrons Sources Neutrons may be emitted during either spontaneous Crystalline solids have a very regular atomic structure that is the local positions of atoms with respect to each other are repeated at the atomic scale

The most accurate method of measuring the BDT or DBT temperature or a material is by fracture testing. Typically four point bend testing at a range of temperatures is performed on pre-cracked bars of polished material. For experiments conducted at higher temperatures dislocation activity increases. At a certain temperature dislocations shield the crack tip to such an extent the applied deformation rate is not sufficient for the stress intensity at the crack-tip to reach the critical value for fracture (K_iC). The temperature at which this occurs is the ductile-brittle transition temperature. If experiments are performed at a higher strain rate more dislocation shielding is required to prevent brittle fracture and the transition temperature is raised.

See also

• Malleability
• Work hardening, which reduces ductility

References

External links