Examination of the Optimal Frequency of the Cyclic Load in the Inverse Analyses of the Heat Conduction of Infrared Thermography

Abstract

Infrared stress image analyses came to be used in a broad field as non-contact and the quantitative stress-analysis method by improvement in an infrared thermography technique in recent years. What can be measured by the infrared thermography is only the sum of the principal stresses, and cannot measure each stress component directly. Since evaluating each stress component is indispensable in order to evaluate the strength and the safety of the structure, the technique of principal stress separation of estimating individual stress components from the sum of the principal stresses has been studied. However, it became clear to have the influence by heat conduction on an infrared stress image in recent years. The temperature images were acquired by the superposition of the temperature field in about 100 cycles of the fixed amplitude of a cyclic load. Therefore, it is considered that those were obtained in a steady state. Then, the influence of heat conduction was investigated by the experiment which changed materials and a cyclic-load frequency. The optimum frequency of cyclic load for exact principal stress separation was examined about the viscoelastic material in which a frequency influences measurement greatly, and several kinds of metals in which heat conductivity differs greatly.