In selecting a material, the primary concern of engineers is to match the material properties to rthe service requirements of the component. Knowing the conditions of load and environment under which the component must operate, engineers must then select an appropriate material, using tabulated test data as the primary guide. They must know what properties they want to consider, how these are determined, and what restrictions or limitations should be placed on their application.www.mapeng.net 马棚网机械资讯

One means of distinguishing one material from another is by comparison of physical properties. These include such characteristics as density (weight); melting point; optical properties (such as transparency, opaqueness, or color); the thermal properties of specific heat, coefficient of thermal expansion, and thermal conductivity; electrical conductivity; and magnetic properties. In some case, the physical properties may be of prime importance when one is selecting a material.www.mapeng.net 马棚网机械资讯

Mechanical properties are those responses a material has to the application of mechanical forces. Of specific interest are: (1) deformation (strain) which occurs when a stress is applied. (2) bardness, and (3) toughness. These mechanical properties are determined by subjecting prepared specimens to standard laboratory tests designed to evaluate the material’s reaction to applied forces.www.mapeng.net 马棚网机械资讯

The properties of materials arise from their internal structures. If the engineer wants a specific set of properties, he must choose his materials appropriately so that they have suitable structures. Should the internal structure of a material be changed during processing of service, there are corresponding changes in properties.www.mapeng.net 马棚网机械资讯

A material’s thermal properties become apparent when energy, which is introduced by the inflow of heat, causes the atoms to vibrate more vigorously and raises the temperature of the material. The results are (1) thermal expansion, and (2) thermal conductivity.www.mapeng.net 马棚网机械资讯

Electrical properties are exhibited by materials which are subjected to applied electric fields. The more common electrical properties include: (1) electrical receptivity and conductivity, and (2) the relative dielectric constant, which relates the accumulated charge across an insulator to the electric field. These properties receive additional significance each year, since engineers must continually develop new and more automated products.www.mapeng.net 马棚网机械资讯