Accuracy improvement in dissipated energy measurement by using phase information

Abstract

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.

Energy Dissipation Measurement in Improved Spatial Resolution Under Fatigue Loading

“…1 (a), the temperature changes due to the thermoelastic effect (T E ) and dissipated energy (T D ) are schematically shown as solid and broken lines in Fig. 1 (b), respectively [17]. As the significant increase in temperature due to dissipated energy occurs twice during one loading cycle, the frequency of the related temperature component is two times greater than that of the loading frequency.…”

“…In this study, a time-series temperature change of the specimen surface, measured by infrared thermography, was analyzed in the frequency domain. The range of temperature change due to dissipated energy (ΔT D ) can be obtained as a temperature component with a frequency twice as high as that of the load signal by the lock-in algorithm [17,25] using eq. 1.…”

“…The waveform and frequency of the loading were set to sinusoidal and 5 Hz, respectively. The applied stress amplitude (σ a ) was increased in steps, which is known as Bstaircase-like^stress level testing [17]. At each step, 1150 loading cycles shown in Fig.…”

“…Fatigue damage causes local plasticity, which leads to irreversible energy dissipation in the form of heat. In recent years, 2f lock-in thermography has received increasing interest on account of the improved performance of infrared cameras [17]. This technique utilizes the specific temperature increase due to plastic deformation by analyzing the measured temperature signals in a frequency domain [25].…”

Advanced Infrared Technology and Applications 2015

“…The paper 'Accuracy improvement in dissipated energy measurement by using phase information' by Shiozawa et al [1] presents a technique for improving the accuracy of a dissipated energy measurement based on the phase information-called the phase 2f lock-in IR method. The phase 2f lock-in method utilizes a phase difference between the thermoelastic temperature change and the temperature change due to the energy dissipation and is effective for eliminating the noise component unrelated to the dissipated energy.…”