This document discusses testing methods for analyzing the bending and torsional behavior of wind turbine blades. It describes testing a wind turbine blade box girder section under bending-torsional loading to better understand the material properties and structural response. The testing apparatus applies bending or torsional loads individually or together to the blade section sample, which is simply supported at its ends. Strain responses are measured to analyze the nonlinear deformation behavior and effects of various parameters on structural performance.

1. • Non-metal materials: FRP, Foam, Resin, Wood
• V-shaped notches
•Transversely shear stress-strain curve
• Shear modulus, shear strengthObjective
Bending-torsional
load
Bending-torsional
supported
National Lab of Wind Turbine Blade R&D Center, Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190
• Material properties
• Geometric structure
• Load configuration
General
Parameters
Bending/
Torsional Load
PRODUCE
Local Strain
Response
ANALYZE
Nonlinear
Deformation
Structure Design
of Blades
INPROVE
CONTENT /
OBJECTIVE
Law of Structure
Properties
AFFECT
Patent NO.: 201410532785.7
TEST PLATFORM
• Test Sample
Box Girder of wind turbine composite blade
• Support
Simple support for bending loading
Torsional support for torsional loading
• Load
Only one hydraulic cylinder for applied load
Install a distributive beam to transfer bending
load and torsional load.
Test Sample
Support
INNOVATION • Results applied more widely
Suitable for various wind blades except their root and transition regions.
• More insights can be obtained
The type and mechanism of nonlinear deformation.
The relationship between the deformation and bending-torsional load.
The effect of general parameters on structure performance.
• Simple and versatile (pure bending, pure torsion, bending+torsion )
Root
region
Transition
region Applicable region for test
• As size of wind turbine increases, the bend-twist coupling effect of blade is more
significant. It is important to understand the bending and torsional behavior.
Structural test of wind blade box girder under bending-torsional loading is meaningful and promising.
BACKGROUND
• The shapes and materials of blade are complex, so it is difficult to establish general rules for structural property
characteristics.
• The Box Girder is the main load carrying element of a wind turbine blade.
Rotating
inner pipe
Fixed
outer pipe
Patent NO.: 201410752065.1
Patent NO.: 201410752062.8
Box girder
Root
Shear web
Trailing edge
Aft panel
Spar capLeading Panel
Leading edge
Some new material and component testing technologies and equipment developed at IET-Wind are presented here.
• Rotor blades are one of the most critical components in wind turbine system, they are thin-walled composite structures with airfoil
cross-sectional profiles. Aerodynamic and structural performance of rotor blades determines the overall performance of wind turbines.
In order to improve their structural performance, the primary job is to understand the material and structural properties of blades.
• Typical construction of blades
Leading panel & Aft panel: Sandwich constructions to provide aerodynamic profiles of blade cross section
Spar cap: Composite laminates to carry primary bending moments
Shear web: Sandwich constructions to support two spar caps and transfer shear forces
Box girder
• Transversely isotropic material
• Thin-walled tubular shape
Test Sample
Ⅰ
Ⅱ
Ⅲ
Sample
adhesion
Twisting
force
Transversely
pure shear
τ23
Approach
• Fixed the sample
Clamping angle plate fixed for thin-plate sample
Bonding plate fixed for thick-plate sample
Test
Sample
Approach
Test Section
Sample
Strain
rosette
Load
Clamping
angle plate
Thin-plate
Sample
Advantage
• More uniform shear stress
distribution.
• Reduce stress concentration.
• Easy handling and assembly.
• Applied load
Longitudinal Shear in test section.
• Sawtooth in blade leading edge
Reduce Slippage
Reduce material damage
Improve strain measurement accuracy
• Multiple notch in blade trailing edge
Adapt to the different dimensions of samples
Feature
Rubber band
Sample
Extensometer
fixture
ACKNOWLEDGEMENTS This study is partly financed by National Natural Science Foundation of China (NO.51405468) and
Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.
Thin-plate Sample
Clamping angle plate
Applicable Scope : Low-density porous materials
Patent NO.: 201420578940.4
Sawtooth leading edge
Notch trailing edge
Blade
TANG Jing, CHEN Xiao*
*chenxiao@iet.cn