Static blade tests are performed in order to determine the structural properties of a blade including stiffness data and strain distribution.
The reported data enables certifying bodies to compare measured data to the calculated data of the design criteria, thus full-scale blade tests are an essential part of the approval process. The DANAK accredited static load tests performed by BLAEST comprise the following tests (incl. options):
Flapwise and edgewise proof test.
- Verification of changes in structural strength due to design changes.
- Determination of residual strength of the structure.
- Verification of changes in structural strength due to changes in production procedures.
- Verification of design details.
Figure 1 Up to 10 load points is possible for the test.
Strain gauges are applied to the blade skin and internal blade structure, in correspondence to the test-plan from the producer. The blade is bolted to the test rig and a root bending moment can be applied to the blade.
At the static proof test up to 10 loading clamps are attached to the blade. Loads are introduced in all points simultaneously.
Distance transducers measure the deflections at a number of positions along the blade. A strain gauge scanner processes strain gauge signals. All measured values are stored in the data acquisition system.
The most essential data obtained from the test are the strain values measured on the blade surface. Non-linearity of the graphs often indicates that structural buckling in the blade skin is building up. The slope of the strain graph is essential information for the verification of the structural blade design. (Figure 2)
Figure 2 Strain as function of local bending moment.
The length-wise strain distribution can reveal high gradients that may reduce the fatigue life of the blade. (Figure 3).
Figure 3 Strain distribution at maximum load.