IMPACT TEST

Impact Test

     An impact test determines the behavior of material when subjected to high rates of loading.  In an impact test a specimen machined or surface ground and usually notched, is struck and broken by a single blow in a specially design testing machine fig (1).  The quantity measured is the energy absorbed in breaking the specimen by a single blow

     The ideal impact test would be one in which, all the energy of the blow is transmitted the test specimen.  And impact test gives an indication of the relative toughness of the material.

Fig 1

 Two specimens are used on an impact testing machine namely (1) IZOD and (2) CHARPY 

      The CHARPY specimen is placed in the vice so that it is just a simple beam supported at the ends. The Izod specimen is placed in the vice vertically which has V notch kept facing the hammer.

Procedure of the impact testing:- 

Fig 2

Refer fig a, b & c

1. The swing pendulum weight is raised to standard height depending up on the type of specimen to be tested
2. With reference to the vice holding the specimen, the higher the pendulum, the more potential energy it has got
3. As the pendulum is released its PE is converted to KE. Until it strikes the specimen
4. The charpy specimen is hit behind the ‘U’ notch, but izod test specimen is kept facing the pendulum will be hit above the v-notch
5. A portion of the energy possessed by the pendulum is used to rupture the specimen and the pendulum rises on the other side of the machine to a height lower than its initial height on the opposite side of the impact-testing machine.
6. The energy consumed in breaking the specimen is the weight of the pendulum times the difference into heights of pendulum on either side of the machine.
7. This energy in meter-kilogram is the notched impact strength and can be read from the dial of the impact-testing machine.

Standard Charpy & Izod test specimen

The following Fig gives the dimension of standard Charpy and Izod test specimen.