The document discusses the mechanical properties of materials, emphasizing their relationship to forces, deformation, and factors such as temperature and microstructure. It outlines several hardness tests (Brinell, Rockwell, Vickers, Knoop) and tensile properties, explaining the measurement techniques and key parameters like yield strength and toughness. Understanding these properties is essential for various structural and engineering applications.

1. MECHANICAL PROPERTIES OF MATERIALS

2. Mechanical properties
 Mechanical properties are described as the relationship between
forces (or stresses) acting on a material and the resistance of the
material to deformation (i.e., strains) and fracture.
 The mechanical properties of a material are not constant and
often change as a function of temperature, rate of loading, and
other conditions.
 Examples are hardness, stress, strain, young’s modulus, yield
strength, UTM, shear modulus, ductility, plasticity, toughness,
creep, fatigue etc.

3. Mechanical properties
 Mechanical properties are highly dependent on microstructure
(e.g., grain size, phase distribution, second phase content),
crystal structure type (i.e., the arrangement of atoms), and
elemental composition (e.g., alloying element content, impurity
level).
 Mechanical property determination is important for a wide
variety of structural applications in metal working, in failure

4. Hardness
It is defined as the ability of a material to resist permanent
indentation or deformation when in contact with an indenter
under load. There are three different types of hardness
measurements but most acceptable in materials engineering is
indentation hardness.
1. Scratch hardness
2. Indentation hardness
3. Rebound hardness
Generally a hardness test consists of pressing an indenter of
known geometry and mechanical properties into the test material.

5.  The hardness of the material is quantified using one of
a variety of scales that directly or indirectly indicate the
contact pressure involved in deforming the test surface.
 Since the indenter is pressed into the material during
testing, hardness is also viewed as the ability of a
material to resist compressive loads.
 Hardness tests are no longer limited to metals, and the
currently available tools and procedures cover a vast
range of materials including polymers, elastomers, thin
films, semiconductors, and ceramics.

6. REBOUND HARDNESS IS EXPRESSED AS THE ENERGY OF IMPACT.
THE INDENTER OF DEFINED GEOMETRY IS DROPPED ONTO THE
MATERIALS’ SURFACE AND THE HARDNESS IS MEASURED IN
TERMS OF HEIGHT OF REBOUND.

8. INDENTATION HARDNESS
 It is measured using various kind of hardness testers. These
testers use indenters of specific material, shape and
dimensions. Indenters are allowed to penetrate into the
material’s surface for specified interval of time under
measured load. The type of indenter, the applied load and
selected time are all dependent on the type of material to be
tested.
 Indentation hardness testers are;
 Brinell hardness tester
 Rockwell hardness tester
 Vickers hardness tester
 Knoop hardness tester.

9. BRINELL HARDNESS TEST
 It consists of indenting the metal
surface with a 10mm diameter steel
ball under specific load and for very
hard materials the tungsten carbide
ball indenter is used.
 500kg load is applied for soft
materials.
 3000kg load is applied for ferrous
materials.
 Load is applied for 30sec for soft
materials and 10sec for ferrous
materials and the diameter is
measured with low power
microscope.

10. BRINELL HARDNESS TEST
 Here;
 F = applied load
 D = diameter of ball (mm)
 d = diameter of indentation (mm)
 t = depth of impression (mm)
 Example of the hardness number is "75 HB
10/500/30"
 Upper hardness limit with Hardened steel ball is
500HB.
 Tungsten carbide can be used up to ~650HB.

11. ROCKWELL HARDNESS TEST
 This test utilizes the depth of indentation, under constant load,
as a measure of hardness.

12. Indenter
 120 degree sphero-conical diamond indenter is used for
hard material.
 Hardened steel ball indenter with diameter of
1/16,1/8,1/4.1/2 inch.
WWW.07MET.TK

14. ROCKWELL HARDNESS TEST
 A minor of load of 10kg is applied first to seat the sample.
 The major load (60, 100, 150kg) is then applied and depth of
indentation is automatically recorded on a dial gage in terms of
arbitrary hardness numbers.
 HR = E - e

15. ROCKWELL SCALES
 There are 30 different scales
depending on the combination of
the indenter and the load.
 64 HRC means RHN of 64 on
C- scale, (diamond indenter and
150 Kg major load)
 100 HRB means RHN 100 on
B-scale (1/16 inch steel ball and
major load 100Kg )
 81 HR 30 N means SHN 81 on
30 N-scale (30 N diamond
indenter and major load 30 Kg)

16. ROCKWELL HARDNESS TEST
 Scale B and C are most
common.
 Selection of scale depends
upon the type of material to be
tested.

17. VICKERS HARDNESS TEST
 It is a micro hardness tester and
used to measure hardness of soft
and hard materials alike,
particularly used for extremely hard
surfaces.
 The surface is subjected to a
standard pressure ranging up to
approximately 1 to 120 kilograms-
force for a standard length of time
by means of a square based
diamond pyramid indenter. The
included angle between opposite
faces of the pyramid is 136o.

18. VICKERS HARDNESS TEST
 The size of the impression (usually no more than 0.5 mm) is
measured by measuring the lengths of diagonals, with the aid of a
calibrated microscope.
 HV =
𝟐𝑷𝒔𝒊𝒏 𝜽
𝟐
𝒅 𝟐 =
𝟏.𝟖𝟓𝟒𝑷
𝒅 𝟐
 Here;
P = applied load, kg
d = average length of diagonals, mm
θ = angle between opposite faces

19. VICKERS HARDNESS TEST

20. KNOOP HARDNESS TEST
 It is micro hardness tester and uses a diamond ground to a
pyramidal form that produces a diamond shape indentation with
long and short diagonals in the ratio of 7:1.
 The knoop hardness number is applied load divided by the
unrecovered projected area of indentation.
 The load vary from 1gf to 1kgf.
 KHN =
𝑷
𝑨 𝑷
=
𝑷
𝑳 𝟐 𝑪
 Here;
 P = applied load, kg
 Ap = unrecovered projected area, mm2
 L = length of long diagonal, mm
 C = a constant

21. KNOOP HARDNESS TEST

22. TENSILE PROPERTIES
 When a material of standard dimensions is subjected to an increasing
uniaxial tensile load, an engineering stress – strain curve can be
developed by load – extension measurements made on the test specimen.
 The engineering stress (S) used in this stress-strain curve is the average
longitudinal stress in the tensile specimen. It is obtained by dividing the
load (P) by the original area of the cross section of the specimen (A0)
𝑺 =
𝑷
𝑨 𝒐
 The engineering strain (e) used for the engineering stress-strain curve is
the average linear strain, which is obtained by dividing the elongation of
the guage length* of the specimen (δ) by its original length (L0)
𝒆 =
𝜹
𝑳 𝒐
=
∆𝑳
𝑳 𝒐
=
𝑳 − 𝑳 𝒐
𝑳 𝒐
 *guage length: The distance along the specimen upon which extension
calculations are made.

23. Stress: it is basically the measure of
the internal forces that resist the deformation in
response to applied forces.
Strain: it is defined as the change in length/area with reference to the original
length/area.

24. ENGINEERING STRESS – STRAIN CURVE

25. EXPLANATION OF THE CURVE
 The parameters that are used to describe the stress-strain curve
of a material are;
 elastic deformation
 plastic deformation
 modulus of elasticity
 yield strength or yield point
 tensile strength
 breaking strength
 percent elongation and reduction in area
 resilience and toughness

26.  Elastic deformation

27.  Plastic deformation

28.  Modulus of elasticity
It is measure of elasticity of the material and also known as elastic modulus. It
is defined as the ratio of stress to the strain with in elastic limit.
𝒀 = 𝑺
𝒆
 Ductility
It indicates the ability of the material to flow plastically before fracture. It is
measured as elongation in length or reduction in area.
𝒆 𝒇 =
𝑳 𝒇 − 𝑳 𝒐
𝑳 𝒐
𝒒 =
𝑨 𝒐 − 𝑨 𝒇
𝑨 𝒐
 Proportional Limit
It is the highest stress at which the stress is directly proportional to strain. It is
observed by the deviation from straight line of the curve

30. Stress – Strain Curve

32.  Elastic Limit
It is the greatest stress the material can withstand without any
measurable permanent strain remaining on the complete release of
load.
 Yield strength
It is the strength required to produce a small specified amount of
plastic deformation. It is measured at 0.2% or 0.5% of strain.
(strain = 0.002 or 0.005).
 Ultimate tensile strength (UTS)
It is maximum stress that the material can bear in tensile testing
before the necking starts.
 Breaking strength
The stress at which the material is fractured is called its breaking
strength.

33.  Necking
After UTS, the cross-sectional area begins to decrease in a
localized region of the specimen, instead of over its entire
length. This is called necking.
 Resilience
The ability of a material to absorb energy when deformed
elastically and to return it when unloaded is called resilience. This
property usually is measured by the modulus of resilience.
 Toughness
The toughness of a material is its ability to absorb energy in the
plastic range.

34. Comparison of Stress – Strain Curves

35. DUCTILE AND BRITTLE FRACTURE IN TENSILE
TESTING
Ductile fracture (cup and cone fracture) Brittle fracture