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In this paper, a technique for improving the accuracy of a dissipated energy measurement based on the phase information-called the phase 2f lock-in infrared method-is proposed. In the conventional 2f lock-in infrared method, the dissipated energy is obtained as the double frequency component of the measured temperature change. In this work, a phase analysis of the double frequency component has been conducted. It is found that the double frequency component includes the influence of the energy dissipation and harmonic vibration of the fatigue testing machine, and the phase difference between the thermoelastic temperature change and the double frequency component is a specific value. The phase 2f lock-in method utilizes a specific phase of the dissipated energy and is effective for removing the noise component such as the thermoelastic temperature change due to the harmonic vibration of fatigue testing machine. This method provides an improvement in the accuracy of the fatigue-limit estimate and the detection of future crack initiation points based on the dissipated energy.

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Fatigue limit estimation based on the dissipated energy measurement using 血 frared thermography has been gening an attention in various indusUies ． In this study ， phase information of temperature change due to energy dissipation was used fbr accuracy provement of dissipa 重 ed energy measurement which is called phase lock − in method ． Fatigue limit estimation us血 g phase lock − in method for dissipated energy measurement was conducted for pre − s廿ained JlS 卵 e 316L austenitic steel specimen ． 正 t is found that the increasing rate of dissipated energy near fhtigue limit for pre − strained specimcn is smaller than that丘 )r as − received sp imen ， The estimated value of fatigue limit obtained 肋 m new e 飢 ima髄on sch e coincides wi 止 that obtained from conventiona1 fatigUe test．