Test Rig for Wind Turbine Rotor Blades
To secure the service life of the 3-megawatt Aeolus II wind turbine, the fatigue strength of its composite rotor blades had to be proven beyond doubt. With standard testing machines reaching their limits, JSTec developed a bespoke test rig for highly complex static and dynamic four-point bending tests.
Fatigue Strength for the Megawatt Class
In wind energy, research and development are the indispensable precondition for technological progress. A central problem is mechanical energy conversion and mastering the enormous dynamic loads caused by local wind turbulence. For the Aeolus II turbine — a joint development by MBB and Kvaerner Turbin AB, and at the time of construction one of the largest wind energy converters in the world — the focus was on developing lightweight, high-strength rotor blades.
The design used an advanced sandwich construction of GRP spar caps and PVC foam. Qualifying the critical wrinkling strain of this composite under realistic, pulsating loads called for a special four-point bending test. Standard testing machines available on the market met neither the required load level nor the extremely high demands on load cycle counts within a reasonable budget.
The solution was a complete in-house development: a bespoke test rig combining mechanics, high-pressure hydraulics and control electronics in one modular system. The rigid frame was designed specifically for the immense continuous vibration loading. A static force generation system sets the mean load precisely, while a dynamic hydraulic power unit feeds in the required oscillation profile.
Proving Endurance, Not Just Calculating It
The goal of the development was to provide empirical proof that the composite rotor blades withstand the enormous forces of the wind over years of operation. At this scale, a purely computational approach is not enough.
The purpose-built test rig made it possible to determine reliable S-N curves for the material. The rig was able to load the specimens continuously and with high precision over hundreds of millions of oscillation cycles.
System Details & Construction
What the test rig delivered was far more than a measured value: it was the foundation for certifying the safe operation of the entire wind turbine. Frame, high-pressure hydraulics and control system were designed as a modular whole — durable across hundreds of millions of load cycles and dimensioned for a load level no off-the-shelf machine could reach.