고온 조건에서의 마찰 댐퍼의 마찰 특성

초록

The vibration of turbines leads to high cycle fatigue due to the high thermal stress and blade vibrations. Those blades are operating under periodically fluctuating conditions. Such working conditions will increase the maintenance cost and weaken the reliability. Therefore, it is necessary to reduce the amplitude of vibration by dissipating vibration energy. Friction is one of the sources that effectively dissipates the vibration energy. Friction damping has been widely used to control the dynamic characteristic of blades. It is important to know the friction characteristics of friction damper under high temperature and micro slip conditions. In this study, friction test rig is designed to enable a wide range of normal load, relative displacement and excitation frequencies. Two specimens are attached to the upper and lower holder of the test rig, respectively. The upper holder is attached to moving support and lower holder is fixed. The relative displacement is generated using the natural frequency of moving support. The range of generated relative displacement is from ±5um to ±40um. The contact surfaces are both cylindrical in line contact. Cartridge heaters are also inserted in the both holders to provide high temperature up to 800℃. Numerous tests are carried out under different relative displacement and temperature conditions. Contact hysteresis is measured, and friction coefficient is calculated using a set of obtained results. The results are statistically analyzed to estimate the friction characteristics under varying vibration amplitude and temperature conditions. Friction coefficient rapidly decreases to 300℃ and then gradually becomes stable. These results can be used to estimate the dynamic behavior of turbine blades with friction damper under high temperature conditions.