page_title: Ductility
section_title: Materials science
hierarchical_section_title: Ductility / Materials science
caption_attribution_description: Time variation of the Au ASW formation process observed using the in situ HRTEM method
context_page_description: Ductility is a measure of a material's ability to undergo significant plastic deformation before rupture or breaking, which may be expressed as percent elongation or percent area reduction from a tensile test. According to Shigley's Mechanical Engineering Design significant denotes about 5.0 percent elongation.
  Percent elongation, or engineering strain at fracture, can be written as:
  Percent reduction in area can be written as:
  , where the area of concern is the cross-sectional area of the gage of the specimen. Ductility is sometimes also characterized by a material's ability to be stretched into a wire.
  Other definition require a ductile material to have a measurable yield strength, at which unrecoverable plastic deformation begins, and also must satisfy one of the following conditions: either have an elongation to failure of at least 5%, or area reduction to rupture at least 20%, or true strain to rupture at least 10%.
  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.
context_section_description: 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, drawing or extruding. Malleable materials can be formed cold using stamping or pressing, whereas brittle materials may be cast or thermoformed.
  High degrees of ductility occur due to metallic bonds, which are found predominantly in metals, leading to the common perception that metals are ductile in general.  In metallic bonds valence shell electrons are delocalized and shared between many atoms.  The delocalized electrons allow metal atoms to slide past one another without being subjected to strong repulsive forces that would cause other materials to shatter.
  Ductility can be quantified by the fracture strain , which is the engineering strain at which a test specimen fractures during a uniaxial tensile test. Another commonly used measure is the reduction of area at fracture . The ductility of steel varies depending on the alloying constituents. Increasing the levels of carbon decreases ductility. Many plastics and amorphous solids, such as Play-Doh, are also malleable.
  The most ductile metal is platinum and the most malleable metal is gold. When highly stretched, such metals distort via formation, reorientation and migration of dislocations and crystal twins without noticeable hardening.
caption: Gold is extremely ductile. It can be drawn into a monatomic wire, and then stretched more before it breaks.[8]
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