Monitoring of Piezoelectric Impedance for Bolt Loosening using General Regression Neural Network
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摘要: 压电阻抗法是一种有效的定量化检测局部螺栓预紧力变化的有效方法。然而,实际工程结构使用环境复杂,环境温度的变化同样会引起压电片测量到的阻抗信息的变化。准确的监测螺栓预紧力必须对温度影响进行补偿。机器学习方法近年来受到广泛关注,为此本文提出采用广义回归神经网络对阻抗信息进行温度补偿,进而实现了不同温度下螺栓预紧力的定量化监测。该方法利用少量不同环境温度下的健康状态阻抗实部信息,训练广义回归神经网络,则该网络可以输出任意环境温度下的阻抗实部的预测信息,将该预测数据作为该温度下的基准数据,与实测数据对比计算损伤特征参量,即可实现螺栓预紧力定量化监测的目的。试验研究验证了基于广义回归神经网络方法的有效性,并与常用的阻抗曲线有效频率移动方法进行了对比,表明了该方法的准确性。Abstract: Bolted joints are widely used in engineering structures.In the long-term service, the bolt pre-tightening force is likely to decrease due to the complex loading. This decrease will in turn induces loose connection failure. Piezoelectric impedance method is an effective method to detect the change of local bolt pre-tightening force quantitatively. However, the measured impedance also changes with temperature significantly, which brings great difficulty to the bolt pre-tightening monitoring. Hence, the temperature compensation in the bolt monitoringis necessary. In recent years, the machine learning methods have been received extensive attention. Therefore, the general regression neural network (GRNN) to compensate the temperature effect on the impedanceis proposed. Then the quantitative monitoring of bolt pre-tightening force at different temperatures was achieved. In this method, a small amount of data from different temperature was used to train a GRNN, and then impedance at any temperature can be predicted with GRNN. Furthermore, the predicted impedance is used as the benchmark to calculate the pre-tightening force indicator. Finally, the efficiency and accuracy of the present method are validated by the experimental results and common effective frequency shift method, respectively.
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表 1 不同工况的实际测量温度
扭距/Nm 温度/℃ 10 29.08 36.36 43.53 50.30 8 28.59 36.78 44.36 50.23 6 30.43 37.97 45.50 49.78 4 30.07 35.53 45.72 49.77 2 28.55 35.06 42.80 48.97 0 28.64 36.73 44.21 50.16 -
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