Another type of mechanical testing, which we will consider in this series of articles, is called the fatigue test. This type of test allows you to determine the fatigue strength of the metal. The loading of the element during fatigue tests is cyclical. The fatigue tests help the constructor to determine the ability of the metal to resist fracture under cyclic load conditions. Usually, to achieve the fatigue limit of metal, the series of fatigue tests should be carried out. The tests are carried out at different stress levels, until the maximum possible voltage level is found, below which the metal has the unlimited fatigue life.
Since the quality of the surface treatment and the configuration of the element greatly affect its fatigue strength, the preparation of the fatigue test sample is of great importance. The minor surface defects can cause significant changes in the results. Thus, if it is not enough to thoroughly prepare at this stage, all the final results may be unreliable.
The numbers of different methods for performing fatigue tests are known. The choice of a particular type of test depends on the design load of the metal during operation. The load can be applied in the form of a bend in the plane, bending during rotation, torsion, axial extension, axial tension, or the combination of these kinds of loads. When the loaded in the axial (longitudinal) direction, the cyclic loading circuit can be selected in such a way that the load applied to the sample is created by alternating stretching and compression. This mode is, as a rule, considered to be the heaviest.