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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.〔 Includes definitions from ''American Heritage Dictionary of the English Language'', ''Collins English Dictionary: Complete and Unabridged'', ''American Heritage Science Dictionary'', and ''WordNet 3.0''.〕 == 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. High degrees of ductility occur due to metallic bonds, which are found predominantly in metals and leads 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 .〔Dieter, G. (1986) ''Mechanical Metallurgy'', McGraw-Hill, ISBN 978-0-07-016893-0〕 The ductility of steel varies depending on the alloying constituents. Increasing levels of carbon decrease 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.〔Vaccaro, John (2002) ''Materials handbook'', Mc Graw-Hill handbooks, fifteenth edition〕〔Schwartz, M. (2002) ''CRC encyclopedia of materials parts and finishes'', second edition〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「ductility」の詳細全文を読む スポンサード リンク
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