Charpy Impact Test 33530

CHARPY IMPACT TEST AIM: To determine the impact energy of given specimen by using charpy impact tester. APPARATUS: Charpy impact testing machine, specimen, magnifying lens, annealed sample of steel. THEORY: This test uses charpy bar specimen with a square cross-section and a notch of 5mm depth. It is simply ed beam and loaded behind the notch by impact of pendulum. The specimen is forced to bend and fracture at a high strain-rate order. The principle measurements from impact test in the energy absorbed in fracturing the specimen. After breaking, the test bar the pendulum is rebounded in a height which decreases as the energy absorbed in the fracture energy measured by charpy test is only a relative energy and cannot be used directly in design equation. Another common measurement obtained from charpy test results from examination fracture surface to whether the fracture surface is fibrous, granular or a mixture of both. The different distinguishable zones of fracture surface helps in judging mode of fracture. A notch is supplied on specimen because it ensures that the specimen will break as a result of impact load to which is subjected without notch many materials would simply bend without breaking, so it would therefore impossible to determine their ability energy. DIFFERENT HEAT TREATMENTS GIVEN TO DIFFERENT SPECIMENS OF SAME MATERIAL ARE: ANNEALING: It is one of the most important and widely used heat treatment as it is restores the ductility to metal that has been severely strain-hardened. It involves heating of steel to 900 and cooling in furnace. NORMALISING: It involves heating of steel to 900°c, soaking for one hour and cooling in still air. HARDENING (WATER QUENCHED): This operation is applied to all tools and some important machine parts intended for especially heavy duty services. It involves heating of steel to 900°c followed by soaking for one hour and quenched in water or any liquid medium. TEMPERING: Here steel which is quenched component is reheated to a temperature below the transformation range followed by cooling at a desired rate. It restores the ductility and reduces brittleness due to quenching. The material can be heated to either 200 °c, 500°c,. PROCEDURE: 1) Specimen and swinging hammer are fixed in either position. 2) Pendulum is brought up and fixed at a particular position.

3) Centre of specimen notch is aligned to centre of by means of charpy setting gauge. 4) Pointer is adjusted to zero. 5) Pendulum is release from top, giving an impact blow to the specimen. 6) Energy absorbed is noted, through a magnifying glass lens to note extent of type of fracture surface. ADVANTAGES: 1) It is simple and utilizes simple and cheaper, small specimen. 2) This can be carried out over a range of sub-ambient temperatures. 3) This test can be used for comparing influence of alloy studies and heat treatment on notch toughness. 4) Used for quality control and material acceptance purpose. DISADVANTAGES: 1) The results of charpy test are difficult to use in design. 2) There is no correlation of charpy data with below size. 3) The large scatter inherent in test may make it difficult to determine well defined transition temperature curves. PRECAUTIONS: 1) Notch configuration should be carefully prepared as it affects notch-toughness value. 2) Centre of specimen notch should be aligned with centre of . 3) Impact energy reading should be taken without parallax error. RESULT: The impact energy absorbed by annealing specimen is The impact energy absorbed by normalizing specimen is The impact energy absorbed by tempering specimen is