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This standard was developed in accordance with the rules given in GB/T 1.1-2009.
This standard replaces GB/T 25384-2010 Turbine blade of wind turbine generator systems Full-scale structural testing of rotor blades. In addition to editorial changes, the following main technical changes have been made with respect to GB/T 25384-2010:
——The static load tests after fatigue tests are added (see Clause 1);
——The description of infrequently used strength-based test methods is deleted (see Clause 8 of Edition 2010);
——The influence of load introduction is adjusted (see Clause 9; Clause 10 of Edition 2010);
——The description of failure patterns is revised (see Clause 11; Clause 11 of Edition 2010);
——The content of component test in Chapter 14 of the Edition 2010 of the standard is deleted;
——The description of sample test equipment in Appendix D of the Edition 2010 of the Standard is deleted;
——The appendix A for introduction of test substitution, Appendix B for introduction of test area, Appendix D for confirmation of test load, and Appendix F for introduction of error coefficient for fatigue formula are added.
This standard is identical to IEC 61400-23:2014 Wind turbines - Part 23: Full-scale structural testing of rotor blades by means of translation.
For convenience of use, this standard includes the following editorial changes:
This standard name is changed to Wind turbines - Full scale structural testing of rotor blade.
This standard was proposed by the China Machinery Industry Federation.
This standard is under the jurisdiction of National Technical Committee 50 on Wind Power Machinery of Standardization Administration of China.
The previous editions of this standard are as follows:
——GB/T 25384-2010.
Introduction
The blades of a wind turbine rotor are generally regarded as one of the most critical components of the wind turbine system. In this standard, the demands for full-scale structural testing related to certification are defined as well as the interpretation and evaluation of test results.
Specific testing methods or set-ups for testing are not demanded or included as full-scale blade testing methods historically have developed independently in different countries and laboratories.
Furthermore, demands for tests determining blade properties are included in this standard in order to validate some vital design assumptions used as inputs for the design load calculations.
Any of the requirements of this standard may be altered if it can be suitably demonstrated that the safety of the system is not compromised.
The standard is based on IEC TS 61400-23 published in 2001. Compared to the TS, this standard only describes load based testing and is condensed to describe the general principles and demands.
Wind turbines
Full scale structural testing of rotor blade
1 Scope
This standard defines the requirements for full-scale structural testing of wind turbine blades and for the interpretation and evaluation of achieved test results.
The standard focuses on aspects of testing related to an evaluation of the integrity of the blade, for use by manufacturers and third party investigators.
The following tests are considered in this standard:
•static load tests;
•fatigue tests;
•static load tests after fatigue tests;
•tests determining other blade properties.
The purpose of the tests is to confirm to an acceptable level of probability that the whole population of a blade type fulfils the design assumptions.
It is assumed that the data required to define the parameters of the tests are available and based on the standard for design requirements for wind turbines such as GB/T 18451.1 or equivalent. Design loads and blade material data are considered starting points for establishing and evaluating the test loads. The evaluation of the design loads with respect to the actual loads on the wind turbines is outside the scope of this standard.
At the time this standard was written, full-scale tests were carried out on blades of horizontal axis wind turbines. The blades were mostly made of fibre reinforced plastics and wood/epoxy. However, most principles would be applicable to any wind turbine configuration, size and material.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 2900.53-2001 Electrotechnical terminology - Wind turbine generator systems (IEC 60050-415:1999, IDT)
GB/T 18451.1-2012 Wind turbine generator systems - Design requirements (IEC 61400-1:2005, IDT)
GB/T 27025-2008 General requirements for the competence of testing and calibration laboratories (ISO/IEC 17025:2005, IDT)
ISO 2394:1998 General principles on reliability for structures
3 Terms and definitions
For the purposes of this document, the terms and definitions related to wind turbines or wind energy given in GB/T 2900.53-2001 and the following apply.
3.1
actuator
device that can be controlled to apply a constant or varying force and displacement
3.2
blade root
that part of the rotor blade that is connected to the hub of the rotor
3.3
blade subsystem
integrated set of items that accomplishes a defined objective or function within the blade (e.g., lightning protection subsystem, aerodynamic braking subsystem, monitoring subsystem, aerodynamic control subsystem, etc.)
3.4
buckling
instability characterized by a non-linear increase in out of plane deflection with a change in local compressive load
3.5
chord
length of a reference straight line that joins the leading and trailing edges of a blade aerofoil cross-section at a given spanwise location
3.6
constant amplitude loading
during a fatigue test, the application of load cycles with a constant amplitude and mean value
3.7
creep
time-dependant increase in strain under a sustained load
3.8
design loads
loads the blade is designed to withstand, including appropriate partial safety factors
3.9
edgewise
direction that is parallel to the local chord
See 4.4.
3.10
elastic axis
the line, lengthwise of the blade, along which transverse loads are applied in order to produce bending only, with no torsion at any section
Note: Strictly speaking, no such line exists except for a few conditions of loading. Usually the elastic axis is assumed to be the line that passes through the elastic center of every section. This definition is not applicable for blades with bend-twist coupling.
3.11
fatigue formulation
methodology by which the fatigue life is estimated
3.12
fatigue test
test in which a cyclic load of constant or varying amplitude is applied to the test specimen
3.13
fixture
component or device to introduce loads or to support the test specimen
3.14
flapwise
direction that is perpendicular to the surface swept by the undeformed rotor blade axis
See 4.4.
3.15
flatwise
direction that is perpendicular to the local chord, and spanwise blade axis
3.16
full-scale test
test carried out on the actual blade or part thereof
3.17
inboard
towards the blade root
3.18
lead-lag
direction that is parallel to the plane of the swept surface and perpendicular to the longitudinal axis of the undeformed rotor blade
See 4.4.
3.19
load envelope
collection of maximum design loads in all directions and spanwise positions
3.20
natural frequency, eigen frequency
frequency at which a structure will vibrate when perturbed and allowed to vibrate freely
3.21
partial safety factors
factors that are applied to loads and material strengths to account for uncertainties in the representative (characteristic) values
3.22
prebend
blade curvature in the flapwise plane in the unloaded condition
3.23
R-value
ratio between minimum and maximum value during a load cycle
3.24
S-N formulation
method used to describe the stress and/or strain (S) vs. cycle (N) characteristics of a material, component or structure
3.25
spanwise
direction parallel to the longitudinal axis of a rotor blade
3.26
static test
test with an application of a single load cycle without introducing dynamic effects
3.27
stiffness
ratio of change of force to the corresponding change in displacement of an elastic body
3.28
strain
ratio of the elongation (or shear displacement) of a material subjected to stress to the original length of the material
3.29
sweep
blade curvature in the lead-lag plane in the unloaded condition
3.30
tare loads
gravitational or other loads that are inherent to the test set-up
3.31
target load
load that is developed from the design load and is the ideal test load
3.32
test load
forces applied during a test
3.33
tested area
region of the test object that experiences the intended loading
3.34
twist
spanwise variation in angle of the chord lines of blade cross-sections
3.35
variable amplitude loading
application of load cycles of non-constant mean and/or cyclic range
3.36
whiffle tree
device for distributing a single load source over multiple points on a test specimen
4 Notation
4.1 Symbols
C: conversion factor for material strength.
D: theoretical damage.
F: load.
Fa: flatwise shear force (chordwise co-ordinates).
Fb: edgewise shear force (chordwise co-ordinates).
Fc: spanwise (tensile) force (chordwise co-ordinates).
Fx: flapwise shear force (rotor co-ordinate system).
Fy: lead-lag shear force (rotor co-ordinate system).
Fz: spanwise (tensile) force (rotor co-ordinate system).
Ma: edgewise bending moment (chordwise co-ordinates).
Mb: flatwise bending moment (chordwise co-ordinates).
Mc: blade torsion moment (chordwise co-ordinates).
Mx: edgewise bending moment (chordwise co-ordinates).
My: flapwise bending moment (rotor co-ordinate system).
Mz: blade torsion moment (rotor co-ordinate system).
N: cycle.
S: strain or stress
4.2 Greek symbols
γ: partial factor or test load factor
σ: applied stress or strain
4.3 Subscripts
design: design loading conditions
df: design load: fatigue
du: design load: static
ef: uncertainty in fatigue formulation of test load
f: load.
lf: environmental effects (fatigue)
lu: environmental effects (static)
m: material
n: consequence of failure
nf: consequence of failure (fatigue).
nu: consequence of failure (static).
sf: blade to blade variation: fatigue test load.
su: blade to blade variation: static test load.
target: target loading conditions
test: test loading conditions
4.4 Coordinate systems
Two different coordinate systems may be used for reference during structural testing. The first, shown in Figure 1, references the local blade chord directions. The second, shown in Figure 2, references the global rotor plane directions.
Foreword I
Introduction III
1 Scope
2 Normative references
3 Terms and definitions
4 Notation
4.1 Symbols
4.2 Greek symbols
4.3 Subscripts
4.4 Coordinate systems
5 General principles
5.1 Purpose of tests
5.2 Limit states
5.3 Practical constraints
5.4 Results of test
6 Documentation and procedures for test blade
7 Blade test program and test plans
7.1 Areas to be tested
7.2 Test program
7.3 Test plans
7.3.1 General
7.3.2 Blade description
7.3.3 Loads and conditions
7.3.4 Instrumentation
7.3.5 Expected test results
8 Load factors for testing
8.1 General
8.2 Partial safety factors used in the design
8.2.1 General
8.2.2 Partial factors on materials
8.2.3 Partial factors for consequences of failure
8.2.4 Partial factors on loads
8.3 Test load factors
8.3.1 Blade to blade variation
8.3.2 Possible errors in the fatigue formulation
8.3.3 Environmental conditions
8.4 Application of load factors to obtain the target load
9 Test loading and test load evaluation
9.1 General
9.2 Influence of load introduction
9.3 Static load testing
9.4 Fatigue load testing
10 Test requirements
10.1 General
10.1.1 Test records
10.1.2 Instrumentation calibration
10.1.3 Measurement uncertainties
10.1.4 Root fixture and test stand requirements
10.1.5 Environmental conditions monitoring
10.1.6 Deterministic corrections
10.2 Static test
10.2.1 General
10.2.2 Static load test
10.2.3 Strain measurement
10.2.4 Deflection measurement
10.3 Fatigue test
10.4 Other blade property tests
10.4.1 Blade mass and center of gravity
10.4.2 Natural frequencies
10.4.3 Optional blade property tests
11 Test results evaluation
11.1 General
11.2 Catastrophic failure
11.3 Permanent deformation, loss of stiffness or change in other blade properties
11.4 Superficial damage
11.5 Failure evaluation
12 Reporting
12.1 General
12.2 Test report content
12.3 Evaluation of test in relation to design requirements
Annex A (Informative) Guidelines for the necessity of renewed static and fatigue testing
Annex B (Informative) Areas to be tested
Annex C (Informative) Effects of large deflections and load direction
Annex D (Informative) Formulation of test load
D.1 Static target load
D.2 Fatigue target load
D.3 Sequential single-axial, single location
D.4 Multi axial single location
Annex E (Informative) Differences between design and test load conditions
E.1 General
E.2 Load introduction
E.3 Bending moments and shear
E.4 Flapwise and lead-lag combinations
E.5 Radial loads
E.6 Torsion loads
E.7 Environmental conditions
E.8 Fatigue load spectrum and sequence
Appendix F (Informative) Determination of number of load cycles for fatigue tests
F.1 General
F.2 Background
F.3 The approach used
