This presentation explains mechanical Properties of metals

1. Mechanical
properties of
metals
Prepared by:
Rebin Fakhir
Supervisor:
Mr.Aref ghaderi

2. Table Of Content
• Introduction
• Common States Of Stress
• Elastic Deformaation
• Anelasticity
• Poisson’s Ratio
• Plastic Deformation
• Hardness
• Types Of Hardness Testing Methods
• Design/Safety Factors

3. Introduction
How materials deform as a function of applied load →
Testing methods and language for mechanical properties of materials.

4. Common states of sterss

6. Stress-strain testing

7. Engineering stress

8. Engineering strain

9. Useful liner elastic relationships

10. Young’s moduli: comparison

11. Elastic deformaation

12. Anelasticity
(time dependence of elastic deformation)
• Have assumed elasticdeformation is time-independent
(appliedstress produces instantaneousstrain)
• Elasticdeformation takes time; can continueeven after load release.
Thisbehavioris known as anelasticity.
• Smalleffect in metals; can be significantfor polymers (visco-elastic).

13. Poisson’s ratio
Unloaded Loaded
Tension → shrink laterally
Compression → bulge

14. Poisson’s ratio
z
y
z
x









V dimensionless
Sign:
lateralstrain opposite to longitudinalstrain
Theoreticalvalue:
for isotropic material: 0.25
Maximum value:0.50,
Typicalvalue: 0.24 - 0.30

15. Shear Modulus
Shear stress to shear strain

16. Elastic Modulus
Poisson’s Ratio and
Shear Modulus
For isotropic material:
Single crystals are usually elastically anisotropic
Elastic behavior varies with crystallographic direction.

19. Plastic deformation
is the permanent distortion that occurs when a
material is subjected to tensile, compressive,
bending, or torsion stresses that exceed its yield
strength and cause it to elongate, compress,
buckle, bend, or twist.
Plastic Deformation

21. Yield point: P
Where strain deviates from
being proportional to stress
(the proportional limit)
Yield strength: oy
A measure of resistance to
plastic deformation
Permanent strain= 0.002

22. Elastic Recovery:
Metals can recover their original shape after being stretched to a certain limit determined by the metals yield strength.
Beyond that the metal experiences plastic deformation and cannot return to its original shape. Trying to bring the metal
back to its original shape results in a decrease in its length and diameter.

24. Tensile & yield Strength
Yield Strength is the stress a material
can withstand without permanent
deformation or a point at which it will no
longer return to its original dimensions
(by 0.2% in length).
Tensile Strength is the maximum stress
that a material can withstand while being
stretched or pulled before failing or
breaking.

25. Ductility
Some materials break very sharply, without plastic deformation, in
what is called a brittle failure. Others, which are more ductile,
including most metals, experience some plastic deformation and
possibly necking before fracture. In materials science, ductility is the
ability of a material to undergo large plastic deformations prior to
failure and it is one of very important characteristics that engineers
consider during design. Ductility may be expressed as percent
elongation or percent area reduction from a tensile test. Ductility is an
important factor in allowing a structure to survive extreme loads, such
as those due large pressure changes, earthquakes and hurricanes,
without experiencing a sudden failure or collapse. It is defined as:

27. True stress and strain

28. HARDNESS
Another mechanical property that may be important to consider is hardness, which is a
measure of a material’s resistance to localized plastic deformation (e.g., a small dent or
a scratch). Early hardness tests were based on natural minerals with a scale constructed
solely on the ability of one material to scratch another that was softer

29. Types of Hardness Testing Methods
Rockwell Hardness Test
During testing of hardness in Rockwell hardness tester, firstly applied minor load on a
specimen generally 10 KGF then applied major load according to their scale and
material
 These types of hardness testers are applicable for all types of materials.

30. Brinell Hardness Test
In these types of hardness tests, a round ball is used which is
forced on the work surface.
 These types of hardness tester are mostly applicable for material that is made up of
mild steel, aluminum, low carbon steel, and copper

31.  These types of hardness testers are mostly applicable for that material which is
made up of high carbon steel, silicon carbide, tungsten, carbide, etc.
Vickers Hardness Test
In these types of hardness testing methods, a mark is made by
applying a load with an Indentor tool (diamond pyramid) whose
point angle is 136°.

32. Knoop Hardness Test
These types of hardness tester are mostly used for very brittle and small thin metal and
also used for micro size materials like memory cards, sim cards.
 These types of hardness tests also used the diamond pyramid as an Indentor tool.

35. Correlation between Hardness and Tensile Strength
Both tensile strength and hardness are indicators of a
metal’s resistance to plastic deformation. Consequently,
they are roughly proportional, as shown in Figure 6.19, for
tensile strength as a function of the HB for cast iron, steel,
and brass. The same proportionality relationship does not
hold for all metals, as Figure 6.19 indicates. As a rule of
thumb, for most steels, the HB and the tensile strength are
related according to
For steel alloys,
conversion of Brinell
hardness to tensile
strength

36. Computation of Average and Standard Deviation Values
An average value is obtained by dividing the sum of all measured values by the number
of measurements taken. In mathematical terms, the average x of some parameter x is
Computation of
average value
where n is the number of observations or
measurements and xi is the value of a discrete
measurement.
 Furthermore, the standard deviation s is determined using the following expression:
Computation of
standard deviation
where xi, x, and n were defined earlier. A large
value of the standard deviation corresponds to a
high degree of scatter

39. design/safety factors