Blade materials, testing methods and structural design - Wind Power Generation and Wind Turbine Design - page 436

Residual
Strength

σ u

σ max

Fatigue
Failure

σ min

N f

(a) Number of Cycles, N

Average

Fatigue
Limit

σ fl

Design
line

Run-out

Number of Cycles to Failure, N f

(b)

Figure 10: Description of fatigue of materials experiencing damage. (a) The num-
ber of cycles to failure, N f , is determined by cycling specimens to a pre-
selected maximum stress, s max . (b) A schematics of an S-N curve,
which is the relationship between the maximum applied stress and the
number of cycled to failure.

Sa m ple: Opti m at, UD2, R=0.1, Fatigue test
R = 0 . 10
R = 0 . 10 r u n o ut
Pow e r (S i n d e p e n d e n t)
Lowe r 95 % co n fi.

1.20

1.00

0.80

0.60

0.40

0.20

0.00

1000 10000 100000 1000000 10000000

Number of cycles to faliure

Figure 11: S-N curve for tension-tension fatigue of a glass fi ber/epoxy composite [40].