Charpy and Izod Tests

I was telling about Impact hardness earlier on this blog. The Charpy and Izod tests are useful in determining the Impact hardness of the materials.

The materials with high impact hardness are ductile in nature and the materials with low impact hardness are brittle in nature.

Charpy Test:

The specimen used is 55mmx10mmx10mm in size with a V notch (making 45 degrees) as shown in figure. The specimen is held horizontally and a hammer repeatedly strikes the specimen till the specimen fails

A hammer attached to pendulum strikes the specimen when released from a height. The pendulum swings back after striking the specimen. The angle from which the pendulum is released and the angle to which the pendulum raises back after breaking the specimen are noted down and used in calculation of Impact hardness.

A picture of apparatus used is shown in the figure. The formula for calculating the energy required for breaking the specimen is given by formula

     Enegry = WR(cosα  - cosβ)

with W => weight of pendulum and hammer

        R => distance between center of gravity of pendulum to its striking edge

         α  => Initial angle from which pendulum is released

          β => The angle to which the pendulum rose after breaking the specimen

Izod Test:

Here the specimen is of size 75mmX10mmX10mm with a V notch (making 45 degrees). The specimen is held vertically and the test is performed. The entire test is similar to Charpy Test.

The pictures in the post are taken from Vhttp://www.soawe.com/time/?tag=What-is-a-charpy-test

Don't forget to grab a copy of Material Science and Engineering book, which is essential for preparing for AMIE, Material Science.

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Impact hardness

  We have been speaking about tensile toughness. Tensile toughness can be defined as the resistance offered by material to plastic deformation i.e. the ability to resit indentation and penetration or abrasion. Here, the load is applied slowly and the strain rate is quite slow too.

But in real life materials are also subjected to sudden blows. The resistance offered by materials to such blows (or impacts) can be called as impact toughness.

Hard, strong materials with good tensile toughness also falter under sudden impacts and exhibit brittle nature and undergo brittle fracture. The brittleness of materials and the reliability of materials under impacts can be studied using Charpy test and Izod test.

The tests are described in the further sections of this blog. Please do take time to go through the same.

Don't forget to grab a copy of Material Science and Engineering book, which is essential for preparing for AMIE, Material Science.

with warm regards

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