Ductility
In materials science, ductility is a solid material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched into a wire. Malleability, a similar property, is a material's ability to deform under compressive stress; this is often characterized by the material's ability to form a thin sheet by hammering or rolling. Both of these mechanical properties are aspects of plasticity, the extent to which a solid material can be plastically deformed without fracture. Also, these material properties are dependent on temperature and pressure (investigated by Percy Williams Bridgman as part of his Nobel Prize–winning work on high pressures).
Ductility and malleability are not always coextensive – for instance, while gold has high ductility and malleability, lead has low ductility but high malleability. The word ductility is sometimes used to encompass both types of plasticity.
Materials science
Ductility is especially important in metalworking, as materials that crack, break or shatter under stress cannot be manipulated using metal-forming processes such as hammering, rolling, and drawing. Malleable materials can be formed cold using stamping or pressing, whereas brittle materials may be cast or thermoformed.
Ductility (Earth science)
In Earth science, ductility refers to the tendency of rock to deform to large strains without macroscopic fracturing. Such behaviour may occur in unlithified or poorly lithified sediments, in weak materials such as halite or at greater depths in all rock types where higher temperatures promote crystal plasticity and higher confining pressures suppress brittle fracture.
Ductile deformation is typically characterized by diffuse deformation (i.e. lacking a discrete fault plane) and on a stress-strain plot is accompanied by steady state sliding at failure, compared to the sharp stress drop observed in experiments during brittle failure.
Brittle-ductile transition zone
The brittle-ductile transition zone is characterized by a change in rock failure mode, at an approximate depth of 15 km (9 mi) in continental crust, below which rock becomes less likely to fracture and more likely to deform ductilely. It is still possible for material above the transition zone to deform ductilely, and for material below to deform in a brittle manner. 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 equals ductile strength. In glacial ice this zone is at approximately 30 m (100 ft) depth.
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