AIM
The objective is to investigate the toughness characteristic of aggregates that are commonly used in the construction of concrete structures. This study aims to analyze the resistance of the aggregates to fracture and impact, which are critical factors that affect the durability and reliability of the concrete. By assessing the toughness of the aggregates, we can determine their suitability for specific construction purposes and ensure that the resulting concrete structures can withstand various stresses and loads over time. Therefore, this study can provide valuable insights for engineers and contractors who are involved in designing and building concrete structures.
EQUIPMENT
Impact testing machine:
DESCRIPTION OF MACHINE
The Pendulum Impact Testing Machine is composed of a sturdy frame, specimen support, and measuring dial. Anti-friction bearings hold the pendulum shaft, onto which the pendulum is fastened. The pendulum is made up of a pendulum pipe and a U-shaped pendulum hammer that houses the striker used for conducting Charpy Impact tests. The pendulum’s swinging range is partially shielded by a guard, and a latch is used to operate and release the pendulum. A dial is attached concentrically with the pendulum shaft, allowing for direct reading of the Impact energy absorbed in breaking the specimen in joules. Additionally, there is a separate striker provided for conducting Izod tests.
THEORY AND PRINCIPE
Toughness is a property of a material that depends on its strength and ductility. It is defined as the amount of work required to cause a material to fracture. In order to measure toughness, an experiment is conducted where a specimen with specific dimensions is subjected to a hammer blow caused by a pendulum with a known weight that is kept at a known height.
The weight of the hammer used in the experiment is denoted by W, which is equal to 21.025 kg. The pendulum used in the experiment has an initial potential energy at point A. The length of the pendulum used in the experiment is denoted by L and is equal to 814.44 mm.
Two angles are measured in the experiment. The first angle is measured from the vertical up to the initial position of the pendulum. The second angle is measured from the vertical up to the position of the pendulum after the specimen has been fractured. The difference between these two angles is used to determine the amount of work required to fracture the specimen, which is a measure of its toughness.
Final energy of pendulum at C,
But,
Initial position of the pendulum,
Energy loss,
The Izod Impact test is a method of measuring energy loss in a material specimen. The test involves using a notched test piece that is 75mm long and has a cross section of 10mm x 10mm. The specimen is gripped vertically with the root of the notch in the same plane. By knowing the values of w, L, and the energy loss, it is possible to calculate the energy loss for various values of the test piece. This can be used to create a calibration curve by plotting energy loss on the Y-axis and the value of the test piece on the X-axis.
PROCEDURE
To perform an Izod test, first attach the proper striker to the bottom of the hammer using a clamping device. Then, clamp the latching tube to the bearing housings at the side. Adjust the pointer along with the pointer carrier to 168.1 on the dial while the pendulum is hanging free vertically. Afterward, manually raise the pendulum and latch it in place. The specimen for the Izod test should be firmly clamped in the specimen support using a clamping screw and setting gauge. Ensure that the notch on the specimen faces the pendulum striker.
Next, operate the lever to release the pendulum and hit the specimen. Wait until the pendulum reverses its swing, and carefully retard the swinging pendulum by operating the brake. Note down the impact energy and remove the broken specimen by loosening the clamping screw.
The Charpy U-notch impact test involves a test specimen that is notched in the middle and supported at each end. The specimen should be machined to a length of 55mm and have a cross-section of 10mm x 10mm. At the center of the length of flat, there should be a U notch that is 5mm deep with a 1mm root radius. The plain of symmetry of the notch should be perpendicular to the longitudinal axis.
PROCEDURE
To prepare for the Charpy impact test, it is important to properly secure the Charpy striker to the bottom of the hammer using a clamping device. Additionally, the latching tube should be firmly clamped to the bearing housing on the inclined face. Once the apparatus is set up, the hammer can be manually raised and latched in place.
When placing the specimen, it is crucial to ensure that the notch is positioned opposite to the direction of impact of the pendulum. To ensure proper centering, an end stop is provided. Once the specimen is in place, the lever can be operated to release the pendulum and strike the specimen.
After the specimen has been struck, it is important to wait until the pendulum begins to slow down and reverse direction. The pendulum should then be carefully brought to a standstill position using the pendulum break. At this point, the impact energy can be noted down for further analysis.
Fig: Specimen for the Charpy Test