Testing of strain-based sensorized bolts for loosening detection and condition monitoring

Abstract The installation of sensorized bolts in the main shaft bolt connection of wind turbines is an innovative approach that allows manufacturers and operators to gain insights into the operating conditions of the drivetrain. This article focuses on the use of sensorized bolts in the flange connections of wind turbines, particularly in the drivetrain. Fraunhofer IWES investigated the suitability of such sensors for determining the loads on the drivetrain and for monitoring the condition of the preload in the bolts of flange connections. In this context, to investigate the behavior of sensorized bolts equipped with strain gauges, a series of tests were carried out on a downscaled drivetrain test bench. Within the flange connection between the hub and the main shaft, four sensorized bolts and four non-sensorized bolts are used, alternating their positions in the flange. The use of these bolts for monitoring the preload in the flange connections is assessed and the results of tests with individual load conditions are evaluated. For this purpose, various load cases with combinations of bending moments and shear forces were applied. The load cases are reflected as cyclical changes in the bolts load due to the rotation of the drivetrain. These changes are captured by the sensorized bolts and the measurement results are presented in this paper.