Impact toughness testing (Part 2).

The Charpy impact test machine consists of the pendulum, support, lever, arrow and the scale. Since the task is to measure the energy absorbed during the destruction of the sample, the initial energy reserve is accumulated by raising the pendulum to the given height. After releasing the pendulum falls and continues its motion to the highest point on the other side of its trajectory. If it does not meet resistance, it rises to the height, which is called the point of zero energy absorption. When contracting a pendulum with the Charpy sample, some amount of energy is expended on the nucleation and propagation of the crack. Therefore, the pendulum rises to the height slightly below the point of zero energy absorption. The scale bar indicates the maximum height of this oscillatory motion of the pendulum. Since the scale is graduated, it is possible to find out from it the amount of energy that is required to destroy the sample.

This value is called the fracture energy, is the basic information obtained as a result of the Charpy impact test. This energy is expressed in foot-pound-force (J). Although in most cases the test results of the Charpy test are expressed in foot-pounds of energy absorbed, there are other ways of representing the viscosity characteristics. They are determined by measuring the various characteristics of the Charpy specimen destroyed by the test. These include expansion in the transverse direction. The expansion in the transverse direction is a measure of deformation, which resulted from the formation of a break in the sample. The expansion is measured in thousandths of an inch.

Regardless of the methods used for measurements, we are usually interested in the result of a series of tests. After testing on several samples at different temperatures, it is possible to determine the nature of the change in the results as the function of temperature. If we build the curve for this temperature dependence, we obtain curves with upper and lower planar sections and practically vertical sections in the intervals. For each measurement category, there is a certain temperature at which a sharp decrease in the values ​​is observed. Such temperatures are referred to as transition temperatures, which means the transition of a metal from a relatively ductile state to an embitter state at a given temperature. In this case, the constructor knows that the metal characteristics will remain acceptable at the temperature above this level.

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