Introduction:
In determining the fabrication and possible practical applications, the mechanical properties of materials, their strength, rigidity and ductility are of vital importance. The important mechanical properties of materials are: elasticity, plasticity, strength, ductility, hardness, brittleness, toughness, stiffness, resilience, malleability, fatigue, creep, etc. Materials exhibit a wide range of mechanical properties ranging, e.g., from the ductility of pure copper to the hardness of diamond and most surprising elastic behaviour of rubber. There are several materials behave quite differently when stressed in different ways, e.g. steel and wood are stronger in tension whereas cast iron, cement and bricks are much stronger in compression. Obviously, stresses can produce a shape change and may also cause a material to break or fracture. For materials which have to withstand high temperatures, the melting point is also of importance.
The combination of high yield strength and good fracture toughness or ductility makes steel an excellent structural material. Modern high strength low alloy (HSLA) steels have a very fine grain size around 10 micro-meters which provides both high strength and good crack growth resistance or fracture toughness.
In addition to mechanical properties of materials, the following properties are also important for an engineer, to enable him in selecting suitable metals for various jobs:
1- Physical Properties: These properties of materials include shape, size, colour, lusters, specific gravity, porosity, structure, finish, etc.
2- Technological Properties: We may note that all the technical properties of a metal are essentially its mechanical properties, which include properties like malleability, machinability, weldability, formability or workability, castability, etc.
3- Thermal Properties: Specific heat, thermal conductivity, thermal expansion, latent heat, thermal stresses, thermal shock, etc. fall under thermal properties of materials.
4- Electrical Properties: These include conductivity, resistivity, relative capacity, dielectric strength, etc.
5- Chemical Properties: These properties include atomic weight, equivalent weight molecular weight, atomic number, acidity, alkalinity, chemical composition, corrosion, etc.
Common Terms:
(i) Isotropy: A body is said to be isotropic if its physical properties are not dependent upon the direction in the body along which they are measured.
(ii) Anisotropy: The quality of variation of a physical property with the direction in a body along which the property is measured.
(iii) Elasticity: It is the property of a material which enables it to regain its original shape and size after deformation within the elastic limit. However, in nature no material is perfectly elastic, i.e., a certain limit exists for every material beyond which it will not be able to regain its original shape and size. This limit is termed as elastic limit. Materials with high elastic limit are called as more elastic than the others. This property is always desirable in metals used in machine tools and other structural constituents. Steel and rubber are amongst the common examples of materials having elasticity.
(iv) Plasticity: It is the ability of material to be permanently deformed (without fracture) even after the load is removed. It is of importance in deciding
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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