Выпишите 1 предложение в активном залоге, 1 предложение в пассивном залоге и 1 предложение с модальным глаголом. mechanical properties of metals. all metals possess certain mechanical properties. it is necessary to study them because later, when discussing treatment, we shall see how great is the influence of treatment on those properties. brittleness is the property of breaking without much permanent distortion. it may be due to brittleness of the grain boundaries or of the crystals themselves. cast iron is brittle because its structure is split up by flakes of graphite which is a brittle material. brittleness is often referred to as shortness. hot-or red-shortness in steel is when it is brittle in the red-hot state. it is caused by too much sulpher, which is present as iron sulphide and forms a brittle membrane surrounding the steel crystals. cold-shortness means that a metal is brittle when cold. in steel cold-shortness is produced when the phosphorous content is too high. ductility. a metal is ductile when it may be drawn out in tension without rupture. wire drawing depends upon ductility for its successful operation. a ductile metal must be both strong and plastic; e.g. lead wire is difficult to draw because the strength of lead is low. elasticity. the elasticity of a metal is its power of returning to its original shape after deformation by force. a material may be stretched, compressed, or its volume changed by pressure on all sides. many materials behave to some extent like powerful elastic, and, within limits will recover their shape when the load on them is removed. the elastic limit is the limit of the elasticity of a material, and is expressed in pounds or tons per square inch of area.

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