PRObability distribution of FAtigue strength of Rotor blades: PROFAR

Coupon testing

Static and fatigue tests have been performed on coupons to derive material properties and strength distribution as a basis for further analysis. Within the Profar project 27 fatigue tests and 8 static tests have been performed. From FACT database 39 useful tests have been selected for comparison with Profar data.

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.
• 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.

Typical creep and stiffness development during coupon fatigue test Results of R=-1 tests fitted with a fatigue formulation using a Goodman modification using multiple non linear regression

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.