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Principle of Testing

The document discusses Charpy impact testing which is used to determine the toughness and ductility of materials. It describes the key components of an impact testing machine and the specifications for testing speed and energy. Test results are used to classify materials as brittle or ductile based on the amount of energy absorbed and features of the fracture surface. Lateral expansion and percentage shear measurements provide additional information on a material's ductility.

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Melvin Ariel Bautista
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49 views4 pages

Principle of Testing

The document discusses Charpy impact testing which is used to determine the toughness and ductility of materials. It describes the key components of an impact testing machine and the specifications for testing speed and energy. Test results are used to classify materials as brittle or ductile based on the amount of energy absorbed and features of the fracture surface. Lateral expansion and percentage shear measurements provide additional information on a material's ductility.

Uploaded by

Melvin Ariel Bautista
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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PRINCIPLE OF TESTING

• Toughness is the ability of the material to withstand crack i.e., to prevent


the transfer or propagation of the cracks across its section hence causing
failure.
• Impact testing machine consists of a pendulum suspended from
a short shaft that rotates in ball bearing and swings midway
between two rigid upright stands supported on a rigid base.
• According to Indian Standard the speed of pendulum at the
instant of striking shall be 4.5 - 7 m/s and the plane of swing
of the striker shall be vertical and within 0.5 mm of the plane
midway between the supports.
• The striking energy of the testing machine should be
300±10J for standard testing.

(NEXT SLIDE)

Fracture Energy = mgh(h0 - hf)


KE = PE
𝒎𝒗𝟐
= 𝒎𝒈𝒉
𝟐
Where:
• m is the mass of the hammer
• v is its tangential velocity at impact=2gh
• g is gravitational acceleration (9.806 m/s2)
• h is the height through which hammer falls.

This value is called impact toughness or impact value, which will be measured per
unit area at the notch.
(NEXT SLIDE)

Charpy tests show whether a metal can be classified as being either brittle or ductile.

DUCTILE BRITTLE
• Large amount of energy • Small amount of energy
• High temperature • Low temperature
• Dull and fibrous. • Bright and crystalline

(NEXT SLIDE)

In addition to the impact energy there are two other features that can be measured and
may be found as a requirement in some specifications. These are lateral expansion
and percentage shear

LATERAL EXPANSION

• Lateral expansion is a measure of the ductility of the impact specimen.

• When a ductile material is impact tested, it will deform before breaking to create
shear lips.
• The amount that the specimen deforms normally to the fracture face is measured
in millimeters with a digital test indicator.

(NEXT SLIDE)
PERCENTAGE SHEAR

• Percentage shear measures the amount of ductile and brittle fracture on the
fracture face of the broken specimen.

• The fracture surface is indicative of the type of fracture that has occurred.
REFERENCE:

https://justenergy.com/blog/potential-and-kinetic-energy-
explained/#:~:text=You%20now%20know%20that%20potential,energy%2C
%20and%20then%20back%20again

https://sm-
nitk.vlabs.ac.in/exp6/index.html?fbclid=IwAR3DCS4jRUZrUvJ5SpH51ulo89
FOlkUDvnJhGGEGoJj-4YG_stiYnFpq8qc

https://www.twi-global.com/technical-knowledge/faqs/faq-what-is-charpy-
testing#:~:text=The%20Charpy%20impact%20test%2C%20also,by%20the%
20specimen%20during%20fracture

https://www.asams.co.uk/testing/charpy-impact-testing

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