Abstract:

：To counter the thermal fatigue failure of electrothermal actuator caused by the alternating temperature loading due to alternating current (AC), the failure mechanisms of the thermal fatigue failure is analyzed. The transient temperature analysis model and the mechanical model of the actuator are developed. The output displacement of actuator is measured and the experimental results are in good agreement with the theoretical predictions and finite element analysis. The relationships between temperature and the frequency or amplitude of the AC are analyzed. The results show that the structure and the applied voltage levels have significant influence on the temperature distributions and the value of the stress and the stress is not the dominant thermal fatigue failure mechanism for the maximum stress below the yield stress of the material. The relationships between displacement and number of cycles of the electrothermal actuator with AC loading are tested, it is indicated that the thermal fatigue failure won’t take place when electrothermal actuator working below ductile-brittle transition temperature, otherwise, thermal fatigue failure will occur after long-term cyclic loading. It is confirmed that the temperature between 300 ℃ to 600 ℃ is comparatively suitable for electrothermal actuator according to theoretical and experimental analysis, and the actuator is able to provide accurate and stable number of cycles for tens of millions. Thermal fatigue failure mechanism of electrothermal actuator is analyzed. The analysis indicates that high temperature deformation is the direct reason for thermal fatigue failure, and the frequency and amplitude of the AC which effect on thermal fatigue can be treated as the effects caused by temperature.

Key words: alternating temperature loading, electrothermal actuator, failure mechanisms, thermal fatigue failure, micro electro-mechanical system