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Wind Turbine Composites

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MIAT106 Inspections

on 24 October 2013

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Transcript of Wind Turbine Composites

Wind Turbine Composites

Inspections Day 5 Turbine Engine

Pulsed Thermography

Robotic Ultrasound Inspection

Manual Ultra-Sonic Inspection

Manual Ultra-Sonic Inspection

Visual Inspection

Visual Inspection

Visual Inspection

Visual Inspection

“… regardless of the resin, fiber type or fiber surface treatment, the interlaminar shear strength of a composite decreases by about 7% for each 1% of voids up to a total void content of about 4%”
(Judd and Wright SAMPE Journal , January 1978)

Composite wind blades must be inspected to ensure continued safe operation

Wind Blade Composites Inspection

Eddy Current Dovetails

Shaft Borescope

Thermal Cracking Of Coatings Using Fluorescent Dye Penetrant

Overheated Blade

Hot Corrosion

Blade Tip Clearance

Blade Clearance/Blade Stretch

Automated Ultra-Sonic Inspection

Ultra-Sonic transducers scan only a small area

A laser pulse is absorbed at the material surface and produces a transient and local surface heating.
When the laser heating is not uniform and concentrated over an area smaller than the size of the detached zone, localized thermal stresses are produced that cause a strong lifting and bending effect.
The disbonded layer or skin can then be set into vibration like a membrane
The modes of the vibration induced by laser heating are determined by the material elastic properties, the shape and the thickness of the detached area.

Laser Tapping Test

Manual Tapping Device

The tap testing procedure consists of lightly tapping the surface of the part with a coin or light special hammer
The acoustic response is compared with that of a known good area.
A “flat” or “dead” response is considered unacceptable.

Manual Tap Test

Visual Inspection of inside of blade half during manufacturing

Visual Inspection checks for:
Leading and trailing edge for:
Impact Damage
UV Cracking

Visual Inspection

Ultra-Sonic Inspection of Turbine Parts

Eddy Current Inspection Of Turbine Disk

Fluorescent Dye Penetrant

Most inspections done on turbines will be a type of visual inspection
Dye Penetrant
Fluorescent Dye Penetrant
Magnetic Particle
Dimensional measurements will also be used along with visual inspections to determine serviceability
Other types of inspections include
Eddy Current

Turbine Engine Inspections

Stress Rupture Cracks

Thermal Fatigue
Stressing of the metals thermally
Caused by:
Can’t always tell if over-temped visually
If known to have been over-temped, must follow manufacture’s recommendations for replacement
Too rapid of a change in temperature (Thermal Shock)
Usually seen as wide cracks on components

Turbine Engine Inspections

Blade Tip Clearance

Rotor to aft Stator Clearance
Checking Axial Movement

Turbine creep
Turbines experience extreme centrifugal loading
The natural tendency is for the blades to stretch
In the turbine section, high heat is added to the spinning blades
The amount the blades stretch is called creep
Stages of Creep:
Elastic Strain.- recover from deformation
Plastic Strain.- sustain deformation without rupture
Fracture or Rupture – Blades crack or rupture

Turbine Engine Inspections

Blade Failure

All turbine engines experience high levels of stress through out the engine
Centrifugal loading
Thermal stress
Sudden changes in loading
Metal fatigue
If proper inspections and measurements are not carried out, engine failure can happen with devastating consequences

Reasons For Inspection

Infrared image of a defective rotor blade. The yellow structures are air inclusions.

Thermography Testing

Thermography Inspections are used to detect faults
During manufacturing
As a NDT method
Mainly after damage is suspected

Thermography Inspections

In the past Ultra-Sonic inspections were mostly done on areas that had been noted as damaged
Blades have a large surface area but ultra-sonic transducers only scan a small area
With recent developments of the automated and robotic systems, entire blades are being routinely scanned

Ultra-Sonic Testing

Any damage found must further be investigated and determined safe for continued operation
Tap Testing
Ultra-Sonic Testing
Thermography Testing

Visual Inspection

All surfaces for:
UV cracking

Visual Inspection

Types of inspections:
Tap Testing
Acoustic Resonance Spectroscopy
Laser Tap Testing

Wind Blade Composites Inspection

Borescope Inspection

Stress Rupture Cracks

Wearing away of the component
Caused by:
Impingement of fast moving, hard particles through the engine
Flowing hot gasses across turbine components
Over-temping of parts in the gas path accelerates erosion

Turbine Engine Inspections

Corrosion is the oxidation of turbine metals
Caused by:
Ingestion of salts, sulfides, and pollutants from the atmosphere.
Introduction of salts and sulfur from fuels
Corrosion process is usually sped up with heat
Often referred to as Hot Corrosion

Turbine Engine Inspections

When inspecting a turbine engine, it is common to inspect all spinning parts for creep
Check compressor & turbine blades for contact with their housing
Using a feeler gauge, check for clearances per manufacture’s requirements
While checking for creep, you will also check rotor assemblies for axial movement

Turbine Engine Inspections

Creep varies with:
Centrifugal loading
Temperature of material
Time - temp and centrifugal loading applied
Today’s turbine blades do not experience as much creep as older blades did
Better / new alloy mixtures
Grain control of metals
Low Creep of less than 1% is desirable for a gas turbine blade.

Turbine Engine Inspections

There are four main problems that turbines must be closely inspected for:
Thermal fatigue

Turbine Engine Inspections

IR Cameras

Laser tapping inspection of an impact damage part. The first scan was made from the impacted side. The second scan from the opposite side

Laser Tapping Using Ultra-Sonic

Visual Inspections For Cracks and Distortion

Visual Inspection for cracks
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