Properties are the way the material responds to the environment and external forces.
Mechanical properties – response to mechanical forces, strength, etc.
Electrical and magnetic properties - response electrical and magnetic fields, conductivity, etc.
Thermal properties are related to transmission of heat and heat capacity.
Optical properties include to absorption, transmission and scattering of light.
Chemical stability in contact with the environment - corrosion resistance.
Types of Materials:
Let us classify materials according to the way the atoms are bound together.
Metals: valence electrons are detached from atoms, and spread in an electron sea that "glues" the ions together. Strong, ductile, conduct electricity and heat well, are shiny
if polished.
An alloy is a combination of two or more metals usually produced to have new materials with improved properties.
Alloys like : Cu-Zn (brass) , Fe-C (steel) , Sn-Pb (solder) .
Semiconductors: the bonding is covalent (electrons are shared between atoms). Their electrical properties depend strongly on minute proportions of contaminants.
Examples: Si, Ge, GaAs.
Ceramics: atoms behave like either positive or negative ions, and are bound by Coulomb forces. They are usually combinations of metals or semiconductors with oxygen, nitrogen or carbon (oxides, nitrides, and carbides). Hard, brittle, insulators.
Examples: glass, porcelain.
Polymers: are bound by covalent forces and also by weak van der Waals forces, and usually based on C and H. They decompose at moderate temperatures (100 – 400 C), and are lightweight. Examples: plastics rubber.
Composite Materials: Consist of more than one material type (such as fiberglass) , display a combination of the best characteristics of each of the individual material.
Examples: Continuous carbon fibers in one or more orientations in a polymer matrix.
Concrete is another structural composite obtained by combining cement, sand, gravel.
Composites are classified according to their matrices into:
1- polymer-matrix composites : used for lightweight structures
(aircraft, sporting goods, wheelchairs, etc.) in addition to vibration damping.
2- Cement matrix composites
3-Metal-matrix composites : with aluminum as the matrix are used for lightweight structures, but they have a high cost of fabrication.
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 .