Module-1_Lesson-2 - 1 Fundamentals of machine design...

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Version 2 ME, IIT Kharagpur Module 1 Fundamentals of machine design
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Version 2 ME, IIT Kharagpur Lesson 2 Engineering Materials
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Version 2 ME, IIT Kharagpur Instructional Objectives At the end of this lesson, students should know Properties and applications of common engineering materials. Types and uses of ferrous metals such as cast iron, wrought iron and steel. Types and uses of some common non-ferrous metals. Types and uses of some non-metals. Important mechanical properties of materials. 1.2.1 Introduction Choice of materials for a machine element depends very much on its properties, cost, availability and such other factors. It is therefore important to have some idea of the common engineering materials and their properties before learning the details of design procedure. This topic is in the domain of material science or metallurgy but some relevant discussions are necessary at this stage. Common engineering materials are normally classified as metals and non- metals. Metals may conveniently be divided into ferrous and non-ferrous metals. Important ferrous metals for the present purpose are: (i) cast iron (ii) wrought iron (iii) steel. Some of the important non-ferrous metals used in engineering design are: (a) Light metal group such as aluminium and its alloys, magnesium and manganese alloys. (b) Copper based alloys such as brass (Cu-Zn), bronze (Cu-Sn). (c) White metal group such as nickel, silver, white bearing metals eg. SnSb7Cu3, Sn60Sb11Pb, zinc etc. Cast iron, wrought iron and steel will now be discussed under separate headings.
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Version 2 ME, IIT Kharagpur 1.2.2 Ferrous materials Cast iron - It is an alloy of iron, carbon and silicon and it is hard and brittle. Carbon content may be within 1.7% to 3% and carbon may be present as free carbon or iron carbide Fe 3 C. In general the types of cast iron are (a) grey cast iron and (b) white cast iron (c) malleable cast iron (d) spheroidal or nodular cast iron (e) austenitic cast iron (f) abrasion resistant cast iron. (a) Grey cast iron - Carbon here is mainly in the form of graphite. This type of cast iron is inexpensive and has high compressive strength. Graphite is an excellent solid lubricant and this makes it easily machinable but brittle. Some examples of this type of cast iron are FG20, FG35 or FG35Si15. The numbers indicate ultimate tensile strength in MPa and 15 indicates 0.15% silicon. (b) White cast iron - In these cast irons carbon is present in the form of iron carbide (Fe 3 C) which is hard and brittle. The presence of iron carbide increases hardness and makes it difficult to machine. Consequently these cast irons are abrasion resistant. (c) Malleable cast iron - These are white cast irons rendered malleable by annealing. These are tougher than grey cast iron and they can be twisted or bent without fracture. They have excellent machining properties and are inexpensive. Malleable cast iron are used for making parts where forging is expensive such as hubs for wagon wheels, brake supports. Depending on the
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This note was uploaded on 11/10/2010 for the course AEROSPACE AE 1202 taught by Professor Dr.adib during the Spring '10 term at Sharif University of Technology.

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Module-1_Lesson-2 - 1 Fundamentals of machine design...

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