Introduction to Measurement Technology Using Thermography (Infrared Cameras) (2)

Fatigue Limit Measurement

The main advantage of fatigue limit measurement using an infrared camera is its speed. While conventional methods typically require anywhere from one week to one month, the fatigue limit can be determined in approximately half a day using this technique. This significant reduction in testing time is particularly beneficial for screening during the development and design stages, where various materials and geometries must be evaluated.

Because the infrared camera method measures the energy associated with the early stages of damage, it is considered a highly effective approach. In addition, the two-dimensional thermal images allow the locations related to the fatigue limit to be visualized, helping to identify the effects of component geometry, weld bead defects, and other factors.

The principle of this method is based on the deviation from Equation (1), which describes the thermoelastic effect explained previously in the section on stress measurement. As the cyclic stress level is increased, heat generation rises sharply beyond a certain stress level, indicating an increase in microscopic damage energy caused by fatigue, also known as dissipated energy. The inflection point in the graph plotting cyclic stress against dissipated energy can be used to estimate the fatigue limit (Figure 6).

Introduction to Measurement Technology Using Thermography (Infrared Cameras) (1)