Monitoring elastic characteristics could provide early warning of material fatigue

A significant percentage of the cost of wind energy is due to wind turbine failures, as components are weakened under turbulent air flow conditions and need to be replaced.

Until now, spectral analysis has been used to analyse turbines by looking at the different frequency responses. But these detection methods are distorted by the turbulent working conditions and may only detect major damage, such as a crack that covers more than 50% of a blade.

However, physicists at the ForWind Center for Wind Energy Research at the University of Oldenburg in Germany have developed a way to monitor the elastic characteristics of mechanical structures subjected to disturbance, akin to the turbulence affecting wind turbines.

The challenge for the team was to find a method for detecting fatigue in the wind turbines' parts without having to remove each of the components and while the turbine is in operation. Their solution used an experimental set up of undamaged and damaged beam structures, which were exposed to excitations, or noise, made by different turbulent wind conditions.

The analytical method allowed the team to distinguish between dynamics attributed to mechanical properties such as stiffness of the blade and those attributed to interfering noise, such as turbulence. The authors say they could detect precisely the changing mechanical properties of the beam material, based on an analysis of the mechanical vibrations.

When the method is further refined, the researchers believe it could be used to identify material fatigue or untightened screws, for example, and be applied to more complex structures, such as automotive or airplane parts.

Graham Pitcher

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