1. by Norman E. Dowling. ISBN 0-13-186312-6.
Figure: 02-01
Mechanical Behavior of Materials: Engineering Methods for Deformation, Fracture, and Fatigue, Third Edition,
by Norman E. Dowling. ISBN
© 2007 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.
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2. Suspension bridge

3. Mechanical Properties of Metals - I
CHAPTER 6
Mechanical Properties of
Metals - I 3 3

4. Processing of Metals & Alloys
Most metals are first melted in a furnace.
Alloying is done if required.
Large ingots are then cast.
Sheets and plates are then produced from ingots by rolling Wrought alloy products.
Products manufactured by hot and cold working the metal from large ingots are called wrought alloy products
Channels and other shapes are produced by extrusion.
Some small parts can be cast as final product.
Example :- Automobile Piston. 4 4

5. Blast Furnace 5 5

6. Ingots 6 6

7. Classes of Processes
Figure 2.4

8. Classifying Processes
Choice of process is based on design requirements:
Material
Shape, dimensions, and precision
Number to be made
Process Families
Shaping - Primary
Shaping - Secondary
Joining
Surface Treatment
Primary process creates shapes
Secondary process modifies shapes or properties
Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon

9. Metal Shaping Process Hot Rolling of Steel
(I-beams, rails, sheet & plate)
Passing a piece of metal between two rolls
Hot rolling Greater reduction of thickness in a single pass.
Rolling carried out at above recrystallization temperature.
Ingots preheated to about 12000C.
Ingots reheated
between passes if
required.
Usually, series of
4 high rolling mills
are used. 9 9

10. Cold Rolling of Metal Sheet
Metal Shaping Process
Cold Rolling of Metal Sheet
Cold rolling is rolling performed below recrystallization temperature.
Hot rolled slabs have to
be annealed before cold
rolling.
Series of 4 high rolling
mills are usually used.
Less reduction of
thickness.
Needs high power. 10 10

11. Metal Shaping Process Extrusion
A plastic forming process in which a material under high pressure is reduced in cross section by forcing it through an opening in a die.
Hollow tube leaving the extrusion die

12. Metal Shaping Process Extrusion Metal under high pressure
Die
Metal under high pressure
is forced through opening
in a die.
Common Products are
cylindrical bar, hollow
tubes from copper,
aluminum etc.
Normally done at high
temperature.
Indirect extrusion needs
less power however has
limit on load applied
Container
Metal
Direct
Extrusion
Container
Metal
indirect
Extrusion 12 12

13. Sample metal products made from Extrusion (rods, tubings etc)

14. Metal Shaping Process Forging
A primary process method for working metals into useful shapes in which the metal is
hammered or pressed into shape.
Types:-
Open die: Dies are flat and
simple in shape
* Example products: Steel shafts
Closed die: Dies have upper
and lower impresion
* Example products: Automobile
engine connection rod.
Forging increases structural
properties, removes porosity
and increases homogeneity.
Direct
Forging
Metal
Indirect
Forging
Die 14 14

15. Basic Shapes for Open -die Forging
A set of closed forging dies used to produce an automobile connecting rod 15 15

16. Sample products made from forging (wrenches, crankshafts)

17. Metal Shaping Process Drawing
Wire drawing :- Starting rod or wire is drawn through several drawing dies to reduce diameter.
Deep drawing:- Used to
shape cup like articles
from flats and sheets of
metals
Change in cross-sectional area
% cold work =
X 100
Original area
Wire or rod
Carbide nib 17 17

18. Wire drawing (rods, wire tubing)
Wire is pulled from the die
rods, wire, tubing

19. Sample products made from wire drawing (rods, wire tubing)

20. Casting Metal Shaping Process
A fabrication process whereby a totally molten metal is poured
into a mold cavity having the desired shape; upon solidification,
the metal assumes the shape of the mold
Cast parts
Casting Process 20
Casting mold 20

21. Sample products made from casting large parts, e. g
Sample products made from casting large parts, e.g., auto engine blocks, turbine blades, jewelry, complex shapes

22. Process-property Interaction
Effects processing can have
on material properties:
Soft, stretchy rubber becomes hard and brittle when vulcanized
Annealing a metal increases its ductility
Glass becomes bullet-proof through a specific heat treatment
Electroplating improves corrosion resistance
Materials: engineering, science, processing and design, 2nd edition Copyright (c)2010 Michael Ashby, Hugh Shercliff, David Cebon

23. Stress and Strain in Metals
Metals undergo deformation under uniaxial tensile force.
Elastic deformation: Metal
returns to its original
dimension after tensile
force is removed.
Plastic deformation: The
metal is deformed to
such an extent such
that it cannot return
to its original dimension 23 23

24. Plastic deformation

25. During elastic deformation the metal atoms are displaced from their original positions but not to the extent that they take up new positions. Thus, when the force removed, the metal atoms return to their original positions and the metal takes back its original shape.
The ability of some metals to be extensively plastically deformed without fracture is one
of the most useful engineering properties of metals.

26. Five basic types of stress

27. Engineering Stress and Strain
F (Average uniaxial tensile force)
Engineering stress = ρ =
A0 (Original cross-sectional area)
Engineering stress σ =
Units of Stress are psi or N/m2 (Pascals) Δl A0
1 psi = 6.89 x 103 Pa
Change in length
Engineering strain = ε =
Original length A
Units of strain are in/in or m/m.
It is common to convert eng. Strain into percent strain or percent elongation:
% engineering strain= eng. Strain *100%=% elongation 27 27

28. Tensile test
Strength of materials can be tested by pulling the metal to failure.
Load Cell
Specimen
Extensometer
Force data is obtained from Load cell
Strain data is obtained from Extensometer. 28 28

29. pilot plant scale equipment

30. Tensile Test

31. In most cases engineering strain is determined by using a small length, usually 2 in., called the gage length, within a much longer, for example, 8 in.

32. Tensile test samples before and after testing, and the measurements required to calculate the percent elongation and the reduction in area

33. Sample Problems on Stress
Example 1: A 0.5 in diameter aluminum bar is subjected to a force of 2500 lbf. Calculate the engineering stress in pounds per square inch (psi) on the bar.
Example 2: A 1.25 cm diameter bar is subjected to a load of 2500 kg. Calculate the engineering stress in megapascal (MPa) on the bar.

34. Stress and Strain in metals
Engineering Strain ( ε epsilon):
Example 3:
A sample of commercially pure aluminum in. wide, in. thick, and 8 in. long that has gage markings 2.00 in. apart in the middle of the sample is strained so that the gage marking are 2.65 in. apart (Fig.) . Calculate the engineering strain and the percent engineering strain that the sample undergoes.