- Impact tests are used to determine a material's impact energy, toughness, and tendency to fracture in a brittle manner. They are important for selecting materials that may experience sudden loading like collisions. - Common impact tests include the Charpy and Izod tests, which involve striking a notched sample with a falling pendulum. The Charpy test uses a simply supported beam setup while the Izod uses a cantilever. - Factors like yield strength, ductility, temperature, and strain rate can influence a material's impact performance and whether it fractures in a brittle or ductile manner. Many materials exhibit a ductile to brittle transition around a specific temperature.

1. Gaziantep universityGaziantep university
Department of Civil EngineeringDepartment of Civil Engineering
Impact Test on MetalsImpact Test on MetalsImpact Test on MetalsImpact Test on Metals
Present By
Omar Adnan

2. What is Impact or Impact ForceWhat is Impact or Impact Force ??
 In mechanics, an impact is a high force or shock applied over a short timeIn mechanics, an impact is a high force or shock applied over a short time
periodperiod when two or more bodies collide. Such a force or accelerationwhen two or more bodies collide. Such a force or acceleration
usually has a greater effect than a lower force applied over ausually has a greater effect than a lower force applied over a
proportionally longer period.proportionally longer period.
 At normal speeds, during a perfectly inelastic collision, an object struckAt normal speeds, during a perfectly inelastic collision, an object struck
by a projectile will deform, and this deformation will absorb most or allby a projectile will deform, and this deformation will absorb most or all
of the force of the collisionof the force of the collision
 The effect depends critically on the relative velocity of the bodies to oneThe effect depends critically on the relative velocity of the bodies to one
another.another.
 Example :Example : car crush, wind force, earthquakecar crush, wind force, earthquake etc.etc.

3. Impact test:- Is the test used for observing the
mechanics that a material will exhibit when it
experiences a shock loading that causes the
specimen to immediately:- (1)deform,
(2)fracture or rupture completely

4. Why impact test is necessary?Why impact test is necessary?
 To measure (A):-To measure (A):-Impact energyImpact energy - the energy required to break a- the energy required to break a
standard sized sample with a sudden, sharp load.standard sized sample with a sudden, sharp load.
 Joule is the unit used in measure the impact energyJoule is the unit used in measure the impact energy
 Find (B)Find (B)ToughnessToughness - the impact test is used to find a material's- the impact test is used to find a material's
toughness , it's ability to absorb energy without breaking.toughness , it's ability to absorb energy without breaking.
 Or the material's resistance to fracture when stressedOr the material's resistance to fracture when stressed
 To determine (C)the tendency of a material in aTo determine (C)the tendency of a material in a brittle mannerbrittle manner .It.It
detects difference between materials which are not in a tension test.detects difference between materials which are not in a tension test.
These values are important for the selection of materials that will beThese values are important for the selection of materials that will be
used in applications that require the material to undergo very rapidused in applications that require the material to undergo very rapid
loading processes such as in vehicular collisionsloading processes such as in vehicular collisions

5. Types of materials for impact testing
Nearly all materials may benefit from impact testing, but the most
common types used are metals, plastics, woods, composites,
ceramics, and polymers. Generally these materials take the form of
sheets of varying thicknesses or short rods depending on the test.
However, most materials will experience either ductile or brittle
failure depending on the (1)type of test, (2)the rate of loading and
(3)the temperature of the sample.

6. Test Method & Standard SpecimenTest Method & Standard Specimen
 The most common methods of performing impact test are -The most common methods of performing impact test are -
1. Charpy Test Method .1. Charpy Test Method .
2. Izod Test Method .2. Izod Test Method .
These are three tests all essentially determine the same
characteristics of the material but differs in the orientation of
the test sample
Fig : V notch Specimen

7. Charpy test MethodCharpy test Method
 The Charpy impact test, also known as the Charpy V-The Charpy impact test, also known as the Charpy V-
notch test, is a standardized high strain-rate test whichnotch test, is a standardized high strain-rate test which
determines the amount of energy absorbed by a materialdetermines the amount of energy absorbed by a material
during fracture.during fracture. This absorbed energy is a measure of a
given material's notch toughness and acts as a tool to
study
 It is widely applied in industry, since it is easy to prepare
and conduct and results can be obtained quickly and
cheaply

8. Charpy Impact Test Specimen
 Charpy test specimens normally measure
55x10x10mmwith 2mm deep notch at the middlewith 2mm deep notch at the middle
of a specified surface..of a specified surface..
 and have a notch machined across one of
the larger faces. The notches may be:
 • V-notch – A V-shaped notch, 2mm deep,
with 45° angle and 0.25mm radius along the
base
 • U-notch or keyhole notch – A 5mm deep
notch with 1mm radius at the base of the
notch.

9. The specimen is set like a simplyThe specimen is set like a simply
supported beam.supported beam.

11. Izod test MethodIzod test Method
 Izod impact is defined
as the kinetic energy
needed to initiate
fracture and continue
the fracture until the
specimen is broken.
This test can be used as
a quick and easy quality
control check to
determine if a material
meets specific impact
properties or to
compare materials for
general toughness.

12. Izod Impact Test Specimen
The Standard Size of IThe Standard Size of I zod zod
impact test Specimen is (64mm x impact test Specimen is (64mm x
12.7mm x 3.2mm) . The V notch 12.7mm x 3.2mm) . The V notch
Shaped bar is also used . Shaped bar is also used .
the Izod specimen is held
rigidly in a vice type fixture
with the notched side facing
the direction of impact. The
centerline of the notch must
be in the plane of the vice
top within .125 mm.
Once the specimen is in
place the hammer is
released from a preset
height and allowed to strike
the specimen thus fracturing
it at the vee notch

13. Izod test MethodIzod test Method
 The test piece is a cantilever, clamped upright in an anvil, with a V The test piece is a cantilever, clamped upright in an anvil, with a V
notch at the level of the top of the clamp. notch at the level of the top of the clamp.
 The test piece is hit by a striker carried on a pendulum which is The test piece is hit by a striker carried on a pendulum which is
allowed to fall freely from a fixed height, to give a blow of 120 ft lb allowed to fall freely from a fixed height, to give a blow of 120 ft lb
energy….energy….

14. ProcedureProcedure

15. Preparation ofof testtest piecepiece
ProcedureProcedure
Place the sample in positionPlace the sample in position

16. CalculationCalculation
 Impact energy Impact energy
= mgH-mghmgH-mgh ;
Where,
m=mass of pendulum.
g=acceleration due to gravity.=9.81ms-2
The absorb energy in Joule Unit.
Fig : Impact energy

17. Difference between Charpy & Izod testDifference between Charpy & Izod test
 In Charpy method the Specimen set is like aIn Charpy method the Specimen set is like a simply Supportedsimply Supported
beambeam
On other hand in Izod method the Specimen set is like aOn other hand in Izod method the Specimen set is like a CantileverCantilever..
Thus Why in Charpy method gives aThus Why in Charpy method gives a higher readinghigher reading than the Izodthan the Izod
method.method.

18.  The notch in the izod test is facing the striker,
fastened in pendulum, while in the charpy test;
the notch is positioned away from the striker.
 In the Charpy method, there are two kinds of
notches, the V-notch and the U-notch, while in
the Izod method; there is only one kind of
notch.

20. Factors Affecting Charpy Impact Energy
Factors that affect the Charpy impact energy of
a specimen as below:
1. Fracture mechanism
2. Notches
3.Yield strength and ductility
4.Temperature and strain rate

21. Notches
The notch serves as a stress
concentration zone and some
materials are more sensitive
towards notches than others. The
notch depth and tip radius are
therefore very important.

22. Yield strength and ductility
For a given material the impact
energy will be seen to decrease if
the yield strength is increased,
i.e. if the material undergoes
some process that makes it more
brittle and less able to undergo
plastic deformation. Such
processes may include cold
working or precipitation
hardening
The area under the stress-strain curve gives the
fracture energy of the material. A ductile
material has a greater fracture energy

23. Temperature and Strain Rate
Most of the impact energy is absorbed by means of plastic
deformation during the yielding of the specimen.
Therefore, factors that affect the yield behavior and hence
ductility of the material such as temperature and strain rate
will affect the impact energy.
This type of behavior is more prominent in materials with a
body centered cubic structure, where lowering the
temperature reduces ductility more markedly than face
centred cubic materials

24. The curve represents a change in fracture
behaviour from ductile at high temperature to
brittle at lower temperature

25. Brittle materials :-A material is said to be brittle, when subjected to
stress, it breaks without significant deformation (strain) for
examples are glasses and ceramics materials
Ductility materials:- is a solid material's ability to deform
under tensile stress .or those which could show plastic
deformation for examples are Carbon steel.

27. Ductile to Brittle Transition
Lower shelf
Transition –
mixed mode
Upper shelf

28. Some materials such as carbon steels undergo what
is known as a ‘ductile to brittle transition’. This
behaviour is obvious when impact energy is plotted
as a function of temperature. The resultant curve will
show a rapid dropping off of impact energy as the
temperature decreases. If the impact energy drops
off very sharply, a transition temperature can be
determined. This is often a good indicator of the
minimum recommended service temperature for a
material.
The increase in yield stress associated with low
temperature or high strain rates can results in a
material changing its mode of fracture from ductile
to brittle and this is very important when selecting
materials for engineering purposes.

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