PRObability distribution of FAtigue strength of Rotor blades: PROFAR

Blade testing

In order to get a deeper understanding of the blade to blade variations and to determine the statistical distribution of the fatigue strength of rotor blades, 37 small rotor blades have been tested in static and fatigue loading. Next to these blades, a number of coupons of identical material as that of the blades has been tested statically and under fatigue loading.

Testing

Static and fatigue tests on rotor blades:

• Flapwise prismatic tip section
• Flapwise root section
• Edgewise root section

Static and fatigue tests on coupons:

• Fatigue R= 0.1
• Fatigue R= -1
• Static tensile
• Static compression

Analysis

• Fatigue formulation with Goodman modification has been used.
• Comparison coupon data with existing data from literature.
• Non-linear regression analysis of coupon results based on maximum stress for the whole population R=0.1 and R=-1; slope and UTS value are the results.
• Non-linear regression analysis of blade data with UTS value found from coupons substituted; slopes of each test series are the results.

Conclusions

• Fatigue formulation with Goodman modification describes influence of stress ratio very well.
• PROFAR test results are in good agreement with FACT results when divided by the UTS-value of the relevant material.
• Slopes of regression lines are close to 10 for blade and coupon tests as well.
• Scatter found from blade tests are comparable with that from coupon tests.