3-تقرير عن impact test

What is the Charpy Impact Test and why is it used?


Materials are used to build load-bearing structures. An engineer needs to know if the material will survive the conditions that the structure will see in service. Important factors that adversely affect the toughness of a structure include low-test temperatures, extra loading and high strain rates due to over pressurization or impacts and the effect of stress concentrations such as notches and cracks. These all tend to encourage fracture. To some extent, the complex interaction of these factors can be included in the design process by using fracture mechanics theory. Tests for the impact toughness, such as the Charpy Impact Test , were developed before fracture mechanics theory was available. The impact test is a method for evaluating the relative toughness of engineering materials. The Charpy impact test continues to be used nowadays as an economical quality control method to assess the notch sensitivity and impact toughness of engineering materials. It is usually used to test the toughness of metals. Similar tests can be used for polymers, ceramics and composites. The charpy impact test measures the energy absorbed by the high strain rate fracture of a standard notched specimen.

Figure 2. Typical Charpy Curves for various materials.

In the Charpy Impact Test, the specimen is supported as a simple beam with a notch in the center. The specimen is supported so that the notch is on the vertical face away from the point of impact. Figure 3 and 4 show the dimensions of the Charpy Impact Test specimen and the positions of the striking edge of the pendulum and the specimen in the anvil. The specimen is broken by the impact of a heavy pendulum hammer, falling through a fixed distance (constant potential energy) to strike the specimen at a fixed velocity (constant kinetic energy). Tough materials absorb a lot of energy when fractured and brittle materials absorb very little energy.

Figure 3. Charpy specimen

Figure 4. Position of the Charpy Impact Test specimen on the impact test machine

All content by Brad