optical measurement systems applied to wind turbine...

| Blade Workshop | July 2010

Optical Measurement Systems applied to Wind Turbine Blades for the Detection and

Characterization of Defects


• Dantec is the world’s leading supplier of optical measurement systems for air flows, liquid flows, combustion diagnostics and materials testing

• US Owned Company (Nova Instruments) Headquartered in Copenhagen,Denmark

• Wind Industry Applications in Air Flows- Aerodynamic Optimization- Computational Fluid Dynamics (CFD) Validation- Modeling of turbines and civil engineering projects

• Wind Industry Applications for Materials Testing- Inspection of blades using Shearography- Digital Image Correlation for R&D, new material characterization, Computer Aided Engineering

(CAE) validation, fatigue tests, QA

Introduction to Dantec Dynamics


How is Dantec Dynamics Involved in the Wind Industry?

• Several key customers using our technology including Vestas and Siemens Windpower

• Perform blade inspections in manufacturing and in-field• Working with Rope Partner, a leading inspection services

provider to develop shearography for up-tower use


What Dantec Dynamics has observed in the US market:

- Emphasis was on fulfilling orders and not on producing quality products

- European Manufacturers have been more proactive regarding quality inspection of blades

- Manufacturers who embraced quality controls are seeing the business benefits with products that require less maintenance

- Many valuable lessons can be learned from the Aerospace Industrythat apply to manufacturing, quality control and ultimate responsibility

- Blade Manufacturing defects are starting to manifest themselves in the field as cycle times increase and the damage propagates

- Several high profile failures and large scale mitigation efforts- Warranty periods will increase due to competitive pressures- Owners and Operators are beginning to understand what is required to

protect their assets


What can be measured?

• Digital Image Correlation- Strain- Displacement- Shape

• Shearography- Sub-surface defectse.g wrinkles, delaminations, disbonds,

porosity, core displacements


Digital Image Correlation (DIC) for Quantifying Defects

• Used for testing new materials, and blade testing

• Small and Compact- easily mounted to blades, gantry systems or test stands

• Results show strain distributions and ‘hot-spots’

• Quantitative results used to determine criticality of defects (accept/reject)


• Measurement of a standard Tensile Test sample

Coupon testing


Coupon with wrinkle

• Average Strain ~ 750με

• Max Strain ~ 2000 με

• Cracks will start in these areas


Tests on a full-size Blade

7500 data points (7500 strain gauges)

All strain gradients captured across wrinkles

Maximum strain 3 times higher!


Tests on Spar cap

Average strain 760με

Max strain 2300 με


How can DIC be used for QA?

• Measure strain distribution in critical areas of blade in production

• Measure strain on detected defects• System easily mounted on blade or gantry system

and moved to each measurement area• Real-time correlation can be used to monitor blades

under fatigue testing and detect damage growth• Blade can pass or fail based on maximum strain

criteria


Laser Shearography to find defects under the surface

• Technique to identify defects in almost any material• Slightest surface excitation leads to surface

deformations from the internal flaws• The shearography system can detect these very

small deformations• Full-field, non-contact and fast


The Shearography Principle

core skin

defect

Stress


Principle of Shearographic Measurement

= Differential displacement(between sheared points)

Camera

Shearelement

Laser

Deformation


Advantages of Shearography• Full-Field Results, not point or scanned

• Real-Time Results, instant judgment, no post processing

• Non-contact, no surface preparation or couplant

• Works with sandwich construction- foam or balsa core

• ‘Performance tests’ the material- only see weak areas

• High level of structural detail

• Proven to detect wrinkles, delaminations, disbonds, dry spots, porosity

Limitations: Material thickness, no depth information, stability


NDT Standards Shearography

• Incorporated in ASNT recommended practice 2006 (SNT TC-1-A) • Incorporated in European EN4179 and NAS410 (2008)• ASTM E2581 – 07 2007 Shearography Standard

• Training available to Level 1, 2 and 3


Shearography Applications-A giant step toward higher value inspection

• Production Inspection• Pre-installation inspection,

transportation damage• Condition monitoring• Damage assessment• Post Warranty Inspection

-> Commonly only visual inspections are made in-field


Systems for Lab, In-field or Production

• Customized solution for in-field

• 2 button operation up-tower

• Full Blade Inspection Systems in pipeline

• Automatic system covers 1m2 / 90s

• Focus on critical areas of blade only


Examples of Defects

Porosity

DelaminationsDisbonds


Examples of Wrinkles/ Waving

Image 5: Typical results of wrinkles in a laminate


Lightning Damage Strong material with visible lay-up direction

Large deformation measured

Boundary of damaged material


Cracks/ Wrinkles

• Visible cracks in gelcoat

• Shearography started where cracks stopped

• Wrinkles continued for more than 12ft


Correlation of Techniques -Wrinkles in Skin

Shearography Result

“Qualitative”Digital Image Correlation Result

“Quantitative”

Accept/ Reject Criteria


Correlation of Techniques –Wrinkles in Spar Cap

Shearography Result Digital Image Correlation Result


For wind to remain competitive as an energy source and manufacturers to remain competitive, blade quality must improve

The earlier the baseline inspection is performed in the life of a blade:• The sooner serial remediation issues will be eliminated• The cheaper the fixes will be if problems are found

Blade Quality would be improved if inspections were made a prerequisite by the customer and/or finance industry

Shearography is migrating from the Aerospace and Marine Industries to the Wind Industry and is a vital component to a complete Quality Inspection both in production and in the field

Digital Image Correlation can be used to charaterize defects or critical areas of the blade with full-field strain measurements

Conclusion:


Thank you for your attention!

Please come and see the live Shearography and Digital Image Correlation display

optical measurement systems applied to wind turbine...

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