MMRB-Repair-Care

• Damage to rotor blades is detected with the help of structural health monitoring (SHM) systems, which compare an initial and a damaged condition.
• Following repairs, the initial condition must be adapted in the system in order to be able to make reliable statements about damage and life spans. The SHM systems currently in use are not in a position to do this.
• The MMRB-Repair-Care research project aims to close this gap by further developing the SMH systems and can draw on valuable data from the predecessor project MultiMonitorRB (MMRB).
• Fraunhofer IWES is responsible in a subproject for the further development of the structure-borne sound-based acoustic emission testing (AET) technique.

The challenge
In order to be able to identify and repair damage on rotor blades as early as possible, they are monitored using SHM systems. These systems check the mechanical properties in the structural behavior by comparing an initial and a damaged condition and react to changes.

The complex layer structure of the rotor blades means that damage assessment is by no means a trivial matter. In addition, there is the issue of a new initial condition following every repair, which would have to be taken as the basis for further monitoring. In practice, however, this is not the case, meaning that only little is known about the effects of the structures’ new initial condition on further damage monitoring and the fatigue damage behavior.

The solution
This is where the MMRB-Repair-Care research project comes in, investigating the effects of repairs on the structural monitoring and fatigue damage behavior. To this end, researchers can re-equip and test two 30- and 60-meter-long rotor blades tested in the predecessor project MultiMonitorRB following repair and revision work. Existing measurement data and evaluations relating to SHM and the fatigue damage behavior of the two rotor blades prior to the repairs can be compared with new measurements and evaluations performed following fully documented repairs. The aim is to further develop different SHM methods and numerical fatigue predictions for monitoring wind turbine rotor blades so that they take the effects of repairs into consideration.

Fraunhofer IWES is responsible in a subproject for the further development of the structure-borne sound-based acoustic emission testing (AET) technique, where transient material deflections caused by sudden material changes, such as the appearance of a crack, are detected by sensors. Following laboratory tests for the validation of the new technology, the SHM systems will be tested in operation at an offshore wind farm.

The added value
The failure of a rotor blade often means long wind turbine downtimes and high costs for the operator. The more precisely and reliably that SHM systems detect damage and numerical fatigue predictions function, the better repairs can be planned and costs avoided. The further developed SHM system should be able to provide reliable information about the condition of the repaired rotor blade and detect renewed damage at an early stage.