Using the scanning infrared camera in experimental fatigue studies

Materials under cyclic loading dissipate energy in the form of heat due to hysteresis effects in the material. At locations of high stress levels, more heat is released than elsewhere, resulting in a local temperature rise in those areas. The scanning infrared camera has been used in this study to visualize the surface-temperature field on steel and fiberglass-epoxy composite samples during fatigue tests. The information achieved in this manner allows one to predict the probable location of the greatest fatigue damage well before such damage becomes visible in the form of a crack. The use of the scanning infrared camera for monitoring traveling cracks and mapping the temperature fields resulting from stress concentrations in cyclically loaded materials is also demonstrated. The results indicate that this instrument is of value in both nondestructive testing and crack-propagation studies.