Using the IEC Simple Load Model for Small Wind Turbines - Small Wind Turbines: Analysis, Design, and Application - page 181

Table 9.7 Partial safety
factors for SLM loads from
IEC 61400-2

Load determination method Safety factor

for fatigue
loads, c f

Safety factor
for ultimate
loads, c f

Simple load calculation 1.0 3.0

Aero-elastic modelling
with design
data (rpm, power)

1.0 1.35

Load measurements
with extrapolation

1.0 3.0

Table 9.8 Partial safety
factors for material
characterisation form IEC
61400-2

Condition Full

characterisation

Minimal
characterisation

Fatigue strength 1.25 10.0

Ultimate strength 1.1 3.0

9.3.2 Partial Safety Factors

Ref. IEC 61400-2 defines partial safety factors for the load case calculations based
upon the analysis method used. These factors, shown in Table 9.7 , reflect the
judgement that the SLM is less accurate than a full aero-elastic analysis. The
second set of partial safety factors for the component materials are shown in
Table 9.8 . To use the full characterisation factors, i.e. the lower safety factors, the
material properties must have been estimated with 95% probability at a 95%
confidence level. The other requirements are:
• the properties have been obtained from materials and configurations represen-
tative of the final structure,
• the test samples come from the same process as the final product,
• static and fatigue testing have been done with appropriate load spectrum and
rate effects,
• environmental effects, such as ultra-violet degradation, have been included, and
• any appropriate geometry effects, such as fibreglass orientation in composite
blades, have been adequately accounted for.

9.3.3 Ultimate Stress Analysis

The safety factors and the ultimate material strength determine the allowable
design stress, r d , in any component according to 31 :

31

(IEC 47).