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AIM
To study the toughness property of the aggregates for concrete construction.
EQUIPMENT
Impact testing machine:
DESCRIPTION OF MACHINE
The Pendulum impact Testing Machine consists of the robust frame, the specimen support and measuring dial. The pendulum shaft is fitted in anti friction bearings. The pendulum is clamped to the pendulum shaft. The pendulum consists of the pendulum pipe and the pendulum hammer of U shaped design. Into this the striker is mounted for conducting Charpy Impact test. The range with in which the pendulum is swinging is partially protected by the guard. A latch is provided for operating the latch and releasing the pendulum. There is a dial attached concentrically with the pendulum shaft. The scale is designed such that the Impact energy absorbed in breaking the specimen can be read directly in joules. A separate striker for Izod test is provided.
THEORY AND PRINCIPE
Toughness depends fundamentally upon the strength and ductility. The property of the material relating to the work required to cause repute has been termed as toughness. In this experiment a specimen of definite dimensions are subjected to a hammer blow caused by a pendulum of known weight kept at a known height.
Let W -be the weight of hammer (w=21.025kg).
L -the length of the hammer (L=814.44mm)
- Angle measured from vertical up to the Initial position of the pendulum.
- Angle measured from the vertical up to the position of pendulum after breaking the specimen.
Initial potential Energy of the pendulum at A,
Final energy of pendulum at C,
But,
Initial position of the pendulum,
Energy loss,
Knowing the values of w, Land the energy loss can be calculated for various values of and calibration curve can be drawn by plotting energy loss on the Y- axis and on the x-axis and on the X- axis.
A. Izod Test.
Specimen
The Izod Impact test consists of notched test piece 75mm long, 10mm x 10mm cross section. The test piece is gripped vertically with the root of the notch in the same plain.
PROCEDURE
Fix the proper striker to the bottom of the hammer with the help of clamping device. Clamp the latching tube to the bearing housings at the side. Adjust the pointer along with the pointer carrier on 168.1 reading on the dial when the pendulum is hanging free vertically. Now simply raise the pendulum manually and latch in. The specimen for Izod test is firmly clamped in the specimen support with the help of clamping screw and setting gauge. Care is to be taken that the notch on the specimen should face the pendulum striker. Operate the lever so that the pendulum is released and the specimen is hit. Wait till the pendulum reverses its swing. Carefully retard the swinging pendulum by operating the brake. Note down the Impact energy. Remove the broken specimen by loosening the clamping screw.
Charpy test
Specimen
The Charpy U-notch impact test consists of test specimen notched in the middle and supported at each end. The test piece which is machined all over shall be 55mm long, 10mm x 10mm cross section and in the centre of length of flat, there will be a U notch of 5mm deep with 1mm root radius. The plain of symmetry of notch shall be perpendicular to the longitudinal axis.
PROCEDURE
Fix the Charpy striker firmly to the bottom of the hammer with the help of clamping device. Firmly clamp the latching tube to the bearing housing on the inclined face. Raise the hammer manually and latch in. Place the specimen should be placed in such a Way that the notch is opposite to the direction of impact of the pendulum. For correct centering of the specimen, the end stop is provided. Operate the lever so that the pendulum is released and the specimen is hit. Wait till the pendulum is reversing its direction of motion and begins to swing slow. Thereafter, bring the pendulum carefully to stand still position by applying the pendulum break. Note down the impact energy.
Fig: Specimen for the Charpy Test
