General Properties of Engineering Materials
The principle properties of materials which are of importance to the engineer in selecting materials. These can be broadly divided into:
Physical properties of materials
1. Density
Density is defined as mass per unit volume for a material. The derived unit usually used by engineers is the kg/m3 . Relative density is the density of the material compared with the density of the water at 4?C. The formulae of density and relative density are:
density ( =
Relative density (d) =
2. Electrical conductivity
Figure 1 shows a piece of electrical cable. In this example copper wire has been chosen for the conductor or core of the cable because copper has the property of very good electrical conductivity. That is, it offers very little resistance to the flow of electrons (electric current) through the wire. A plastic materials such as polymerized has been chosen for the insulating sheathing surrounding the wire conductor. This material has been chosen because it is such a bad conductor, where very few electrons can bass through it. Because they are very bad conductors they are called as insulators. There is no such thing as a perfect insulator, only very bad conductors. For example, metallic conductors of electricity all increase in resistance as their temperatures rise. Pure metal shows this effect more strongly than alloys. However, pure metals generally have a better conductivity than alloys at room temperature.
The conductivity of metals and metal alloys improves as the temperature falls.
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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