NDT Composite Components
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1 NDT FOR COMPOSITE MATERIALS
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NDT Composite Components
Transcript of NDT Composite Components
PowerPoint Presentation4. Potential Trans-IND techniques for
inspection of composite component for civil applications
2. Main techniques used on FRP Components
5. Beam inspection by Ultrasound system
6. Deck inspection by Thermography system
*
*
Always in evolution
It is important to have a normative to apply these techniques correctly
ASTM Standard
ASTM 543-04 norm report the list of all NDT norms
There are the lines guide to evaluate testing and safety agencies
There are a short description of the equipment for each nondestructive testing.
*
*
*
E 569-07 Practice for Acoustic Emission Monitoring of Structures During Controlled Stimulation
E 1106-07 (Includes change to title) Test Method for Primary Calibration of Acoustic Emission Sensors
E 1211-07 Practice for Leak Detection and Location Using Surface-Mounted Acoustic Emission Sensors
E 1816-07 (Includes change to title) Practice for Ultrasonic Testing Using Electromagnetic Acoustic Transducer (EMAT) Techniques
E 1888/E 1888M-07 (Includes change to title) Practice for Acoustic Emission Examination of Pressurized Containers Made of Fiberglass Reinforced Plastic with Balsa Wood Cores
E 1932-07 Guide for Acoustic Emission Examination of Small Parts
E 2192-07 Guide for Planar Flaw Height Sizing by Ultrasonics
REAPPROVAL OF STANDARD
Main techniques used on FRP Components
Ultrasonic testing is used to detect delaminations, porosities, cracks or inclusions. It is also possible to determine the thickness, fibre distribution, fibre alignment, and the curing state. The ultrasonic probe emits ultrasonic waves into the material. These waves are reflected by the face opposite to the probe. The probe collects these signals and they are visualised on a screen. So the thickness can be determined of the sonic velocity of the material is known. If there is a defect, an inclusion or a fibre in the material the waves are reflected by this object and it is visible on the screen.
Ultrasonic Testing (contact and non contact)
Frequency range: from 20 kHz to 25 MHz
The A scan display is similar to an oscilloscope display, giving the time of flight and reflection amplitude data.
The “C scan” requires additional scanning equipment and displays a plan view of the detected
The system can work, in the form of “A scan” or “C scan”.
Emitter
Main techniques used on FRP Components
Thermography is used to detect delaminations, bonding defects, and inclusions or to determine the fibre concentration. Therefore the surface of the part is heated. Inclusions or defects alter the flow of the heat. With an infrared camera the temperature distribution is recorded. With thermography only defects that are close to the surface can be detected.
Thermography
Passive thermography :
The features of interest are naturally at a higher or lower temperature than the background
An energy source is required to produce a thermal contrast between the feature of interest and the background
Active thermography :
Main techniques used on FRP Components
Radiography uses a penetrating radiation source such as X-rays or gamma rays and radiographic film to capture images of defects. Differential absorption of the penetrating radiation by the specimen will produce clearly discernible differences when recorded on radiographic film. Radiography requires access to both sides of the structure
With radiology not only voids, contaminants or trans laminar cracks can be detected but also the fibre orientation can be reviewed.
An alternative to traditional radiography is the real time radioscopy where the penetrating radiation produce an image on a video monitor The X-ray image is obviously limited to the image intensifier screen diameter.
The quality image as sharpness, contrast and noise depending on converts the analog signal of the sensor in to a digital data stream.
Radiography
Main techniques used on FRP Components
We consider the evolution of the technique for the automation, like a technology of artificial systems that extract information from images. This technology can be applied on controlling processes, superficial defects, detecting events, modeling objects or environments etc.. An optical access is necessary to apply this technique. Its performance depends on the optical sensor, illumination and processing system. The inspection can be made in real time during the production with immediately information on the anomalies.
Visual inspection by image analysis
*
Main techniques used on FRP Components
Shearography is an optical interferometric technique that measures the first derivative of the out of plane displacement of a deformed object. A shearography system is, in fact, generally composed of a Michelson interferometer with simple changes that allows shear application.
It belongs to the speckle measurements. A speckle visualises a raw surface as granules-like intensity distribution. The resulting intensity distribution is compared to the distribution of a loaded part. Its ability to measure large areas in one shot without contact.
Shearography
Main techniques used on FRP Components
In acoustic emission testing, an elastic wave is generated by the rapid release of energy from within a material. A structure under certain load levels produces acoustic sound, usually in the range between 20 kHz and 1 MHz. This sound generation is known as “acoustic emission”. Acoustic Emission is simply the stress waves generated in the materials due to deformation, crack initiation and growth, crack opening and closure, fiber breakage, and delamination in composite materials. The elastic waves come through the solid to the surface where they can be recorded by one or more sensors/transducers. Acoustic Emission listens for emissions from active defects and is very sensitive to defect activity when a structure is loaded.
Acoustic emission testing
Specification for NDT Methods in FRP component (2010)
Defect Size
Thickness inspection
Inspection Time
Potential Cost
Difficulty Use
Acoustic Emission
Defects with different dimensions but must be able to generate acoustic emissions
No restrictions
Low, but the cost depends on number of sensors
Technical expert, easy test, structure must be loaded; no feasible off-site
Radiography and Radioscopy
Around 5-7 mm
Real-time measurement up to 120s depending on load gradient and depth; typical inspection area 200x300 mm2
70.000 -100.00 €
Specification for NDT Methods in FRP component
In the inspection time the post processing time has not been considered.
The data of the Table are just indicative, the performance and the cost can change for each specific case, depending on optimization level of the technique, technology evolution and inspection level.
The potential costs in Table are only for the equipment of measure without the automation cost.
The automation cost can be variable depending on the technique choice and of the automation level.
Specification for NDT Methods in FRP component (2010)
Defect Size
Thickness inspection
Inspection Time
Potential Cost
Difficulty Use
Ultra- sound
Depending on material, structural components, probe frequency (e.g. up to 150-200 mm in FRP monolithic element)
Area of 100x100mm2 down to 1.5 min
15.000- 20.000 € without robot scanner, immersion system etc.
Technical expert, medium
20.000-40.000 €
Superficial defect
Real time
Technical expert, medium
Potential techniques for inspection of composite components for civil applications
The choice of the best technique, for each specific application, requires knowhow and a dedicated analysis of the specific case.
Operative conditions
Requirements
Analysis of the components to inspect
Objective:
Detect internal defects for Bridge Elements, in particular samples of the Beam and Deck, in composite material, on-site, for large areas
Characteristics of components:
Complex shapes
Beam sample
Deck sample
These characteristics limit the application of most common non destructive techniques
1
2
Requirements for the components to inspect
Techniques
Easy to use
Cost contained
It has the limit of thermal penetration (inspection depth: till 7-8 mm on CFRP)
Emissivity variation and external reflections affect the temperature pattern
Thermography
Thickness:
*
Requirements for the components to inspect
Full field technique
More sensitive to mechanic vibrations
Shaerography
Ultrasonics
The ultrasonic is the best technique to inspect high thickness and different materials
It can be applied adopting many configurations.
*
Lower frequency probes require larger size of each element -->
Air-coupled ultrasonic
easiness of movement
large gap of acoustic impedance between the FRP and air
attenuation more than 150 dB on CFRP components
No energy passes through a sandwich with a foam core
- Decrease of resolution
- Difficulty to move on raw surface
Ultrasonic phase array
no problem with raw surface
potentially applicable on complex shapes
potentially applicable to inspect high thickness
big basin required
difficult of apply off-site
potentially the best technique (pulse echo and trough transmission mode) to inspect high thickness elements.
High energy pass through the element
difficult to scan of raw surface
difficult of inspection on shapes with strong curvature.
inspection of high thickness components --> low frequency --> low resolution of the defect
complex system for big components:
Advantages
Disadvantages
Potential solutions for bridge elements with flexible installation and large area inspection
Laminate panels, monolithic elements
Air-coupled ultrasonic – transmission mode up to 1-3 cm
Contact ultrasonic – transmission mode over 3 cm
Ultrasonic with low frequency probes (100 kHz) need.
Air-coupled ultrasonic up to 15 mm in depth.
Contact ultrasonic probes in transmission mode are necessary for depth up to 15 mm.
Sandwich with PUR Core
Characteristics/limits for inspection:
2 skins in FRP (mix of Glass and Carbon Fibers)
1 low density PUR core (40 kg/m3)
High thickness
Complex shape
Curvilinear profile
Rough surface
Variable thickness
Rough surface
Technique of inspection: Contact Ultrasonic
66 mm
50 mm
The emitter
contact probe
The non-contact
receiver probe
Hybrid configuration
It generates a high energy ultrasound wave that travels through the element to be inspected
Low frequencies 100 kHz probe allows lower attenuation in high thickness components
It allows to have more freedom to follow the profile
It solves the problems of contact with bottom surface (coupled with water, oil, hanging)
It solves the problem to move on rough surfaces
Equipment
emitted signal: Burst; Max excitation voltage: 475 V pk-pk;
14-bit resolution; 100 MS/s real-time;
Contact emitter probe
Non-contact receiver probe
Further improvement solution
Further improvements, to overcome limits due to high curvature, rough surface and low spatial resolution, have been done.
In experimental stage a thin spherical cap (1 mm) on the low frequency contact probe (100 kHz) has been applied.
The thin thickness and the cap filled with water reduce interferences on the wave transmitted
The use of spherical element has also the objective of focusing and amplifying the beam
To support the sphere design and optimization a numerical simulation has already started
Contact emitter probe with spherical cap
Water
Simulated defects
The probes can be moved on the area of inspection by a Cartesian robot for planar shapes or by an anthropomorphic robot for complex shapes
In this work a Cartesian robot has been used
Core defect 10x3x30 mm
Skin defect 10x2.5x30 mm
Hybrid configuration
In both cases the skin defect and core defect have been detected
In the map with spherical cap, the edge effects and artefacts are reduced
The signal to noise ration (SNR) is lower with spherical cap (13 dB) but still good enough to detect defects
Core defect 10x3x30 mm; skin defect 10x2.5x30 mm
without spherical cap
SNR 19 dB
SNR 13 dB
with spherical cap
Skin Defective area
Core defective area
Improvement of the flexibility
Study the possibility to have more efficiency with a focusing ultrasonic beam on the contact point by using a sphere
ci
ct
Pa
Upgrade the spherical cap with the sphere to reduce the wear
Spherical cap - FEM simulation
Monolithic element
Triggering the ultrasound signal
*
3D map
Automatic system which scans the total area of the component allowing a complete structural integrity control including internal defects
2D map of the ultrasound signal amplitude
*
Hidden surface
Can be inspected using thermography techniques
IR
Deck profile inspection
To inspect hidden surfaces the solution can be the use of the mirror (aluminum)
Frame with the best contrast between the defective area and non defective area
Non defective area
Load lamp
Infrared camera
Anthropomorphic robot
*
Scan system configuration
The shape of the deck is complex and different configurations are request to inspect all deck surfaces
Scan of bottom surface
Scan of upper-right surface
Scan of upper-left surface
Simulated defect has been introduced to validate the inspection system
Defects: flat washers
Infrared images
*
Conclusions
Ultrasonic and thermography systems have been identified as the best techniques to inspect composite structural components for civil application due to their flexibility, cost and performances.
Innovative configuration such as hybrid ultrasonic and thermography with mirror have been studied to overcome the limits of inspection of complex structures.
A spherical cap has been applied on the ultrasonic transducer in order to increase the flexibility on curved profiles, rough surfaces and to improve the spatial resolution.
2. Main techniques used on FRP Components
5. Beam inspection by Ultrasound system
6. Deck inspection by Thermography system
*
*
Always in evolution
It is important to have a normative to apply these techniques correctly
ASTM Standard
ASTM 543-04 norm report the list of all NDT norms
There are the lines guide to evaluate testing and safety agencies
There are a short description of the equipment for each nondestructive testing.
*
*
*
E 569-07 Practice for Acoustic Emission Monitoring of Structures During Controlled Stimulation
E 1106-07 (Includes change to title) Test Method for Primary Calibration of Acoustic Emission Sensors
E 1211-07 Practice for Leak Detection and Location Using Surface-Mounted Acoustic Emission Sensors
E 1816-07 (Includes change to title) Practice for Ultrasonic Testing Using Electromagnetic Acoustic Transducer (EMAT) Techniques
E 1888/E 1888M-07 (Includes change to title) Practice for Acoustic Emission Examination of Pressurized Containers Made of Fiberglass Reinforced Plastic with Balsa Wood Cores
E 1932-07 Guide for Acoustic Emission Examination of Small Parts
E 2192-07 Guide for Planar Flaw Height Sizing by Ultrasonics
REAPPROVAL OF STANDARD
Main techniques used on FRP Components
Ultrasonic testing is used to detect delaminations, porosities, cracks or inclusions. It is also possible to determine the thickness, fibre distribution, fibre alignment, and the curing state. The ultrasonic probe emits ultrasonic waves into the material. These waves are reflected by the face opposite to the probe. The probe collects these signals and they are visualised on a screen. So the thickness can be determined of the sonic velocity of the material is known. If there is a defect, an inclusion or a fibre in the material the waves are reflected by this object and it is visible on the screen.
Ultrasonic Testing (contact and non contact)
Frequency range: from 20 kHz to 25 MHz
The A scan display is similar to an oscilloscope display, giving the time of flight and reflection amplitude data.
The “C scan” requires additional scanning equipment and displays a plan view of the detected
The system can work, in the form of “A scan” or “C scan”.
Emitter
Main techniques used on FRP Components
Thermography is used to detect delaminations, bonding defects, and inclusions or to determine the fibre concentration. Therefore the surface of the part is heated. Inclusions or defects alter the flow of the heat. With an infrared camera the temperature distribution is recorded. With thermography only defects that are close to the surface can be detected.
Thermography
Passive thermography :
The features of interest are naturally at a higher or lower temperature than the background
An energy source is required to produce a thermal contrast between the feature of interest and the background
Active thermography :
Main techniques used on FRP Components
Radiography uses a penetrating radiation source such as X-rays or gamma rays and radiographic film to capture images of defects. Differential absorption of the penetrating radiation by the specimen will produce clearly discernible differences when recorded on radiographic film. Radiography requires access to both sides of the structure
With radiology not only voids, contaminants or trans laminar cracks can be detected but also the fibre orientation can be reviewed.
An alternative to traditional radiography is the real time radioscopy where the penetrating radiation produce an image on a video monitor The X-ray image is obviously limited to the image intensifier screen diameter.
The quality image as sharpness, contrast and noise depending on converts the analog signal of the sensor in to a digital data stream.
Radiography
Main techniques used on FRP Components
We consider the evolution of the technique for the automation, like a technology of artificial systems that extract information from images. This technology can be applied on controlling processes, superficial defects, detecting events, modeling objects or environments etc.. An optical access is necessary to apply this technique. Its performance depends on the optical sensor, illumination and processing system. The inspection can be made in real time during the production with immediately information on the anomalies.
Visual inspection by image analysis
*
Main techniques used on FRP Components
Shearography is an optical interferometric technique that measures the first derivative of the out of plane displacement of a deformed object. A shearography system is, in fact, generally composed of a Michelson interferometer with simple changes that allows shear application.
It belongs to the speckle measurements. A speckle visualises a raw surface as granules-like intensity distribution. The resulting intensity distribution is compared to the distribution of a loaded part. Its ability to measure large areas in one shot without contact.
Shearography
Main techniques used on FRP Components
In acoustic emission testing, an elastic wave is generated by the rapid release of energy from within a material. A structure under certain load levels produces acoustic sound, usually in the range between 20 kHz and 1 MHz. This sound generation is known as “acoustic emission”. Acoustic Emission is simply the stress waves generated in the materials due to deformation, crack initiation and growth, crack opening and closure, fiber breakage, and delamination in composite materials. The elastic waves come through the solid to the surface where they can be recorded by one or more sensors/transducers. Acoustic Emission listens for emissions from active defects and is very sensitive to defect activity when a structure is loaded.
Acoustic emission testing
Specification for NDT Methods in FRP component (2010)
Defect Size
Thickness inspection
Inspection Time
Potential Cost
Difficulty Use
Acoustic Emission
Defects with different dimensions but must be able to generate acoustic emissions
No restrictions
Low, but the cost depends on number of sensors
Technical expert, easy test, structure must be loaded; no feasible off-site
Radiography and Radioscopy
Around 5-7 mm
Real-time measurement up to 120s depending on load gradient and depth; typical inspection area 200x300 mm2
70.000 -100.00 €
Specification for NDT Methods in FRP component
In the inspection time the post processing time has not been considered.
The data of the Table are just indicative, the performance and the cost can change for each specific case, depending on optimization level of the technique, technology evolution and inspection level.
The potential costs in Table are only for the equipment of measure without the automation cost.
The automation cost can be variable depending on the technique choice and of the automation level.
Specification for NDT Methods in FRP component (2010)
Defect Size
Thickness inspection
Inspection Time
Potential Cost
Difficulty Use
Ultra- sound
Depending on material, structural components, probe frequency (e.g. up to 150-200 mm in FRP monolithic element)
Area of 100x100mm2 down to 1.5 min
15.000- 20.000 € without robot scanner, immersion system etc.
Technical expert, medium
20.000-40.000 €
Superficial defect
Real time
Technical expert, medium
Potential techniques for inspection of composite components for civil applications
The choice of the best technique, for each specific application, requires knowhow and a dedicated analysis of the specific case.
Operative conditions
Requirements
Analysis of the components to inspect
Objective:
Detect internal defects for Bridge Elements, in particular samples of the Beam and Deck, in composite material, on-site, for large areas
Characteristics of components:
Complex shapes
Beam sample
Deck sample
These characteristics limit the application of most common non destructive techniques
1
2
Requirements for the components to inspect
Techniques
Easy to use
Cost contained
It has the limit of thermal penetration (inspection depth: till 7-8 mm on CFRP)
Emissivity variation and external reflections affect the temperature pattern
Thermography
Thickness:
*
Requirements for the components to inspect
Full field technique
More sensitive to mechanic vibrations
Shaerography
Ultrasonics
The ultrasonic is the best technique to inspect high thickness and different materials
It can be applied adopting many configurations.
*
Lower frequency probes require larger size of each element -->
Air-coupled ultrasonic
easiness of movement
large gap of acoustic impedance between the FRP and air
attenuation more than 150 dB on CFRP components
No energy passes through a sandwich with a foam core
- Decrease of resolution
- Difficulty to move on raw surface
Ultrasonic phase array
no problem with raw surface
potentially applicable on complex shapes
potentially applicable to inspect high thickness
big basin required
difficult of apply off-site
potentially the best technique (pulse echo and trough transmission mode) to inspect high thickness elements.
High energy pass through the element
difficult to scan of raw surface
difficult of inspection on shapes with strong curvature.
inspection of high thickness components --> low frequency --> low resolution of the defect
complex system for big components:
Advantages
Disadvantages
Potential solutions for bridge elements with flexible installation and large area inspection
Laminate panels, monolithic elements
Air-coupled ultrasonic – transmission mode up to 1-3 cm
Contact ultrasonic – transmission mode over 3 cm
Ultrasonic with low frequency probes (100 kHz) need.
Air-coupled ultrasonic up to 15 mm in depth.
Contact ultrasonic probes in transmission mode are necessary for depth up to 15 mm.
Sandwich with PUR Core
Characteristics/limits for inspection:
2 skins in FRP (mix of Glass and Carbon Fibers)
1 low density PUR core (40 kg/m3)
High thickness
Complex shape
Curvilinear profile
Rough surface
Variable thickness
Rough surface
Technique of inspection: Contact Ultrasonic
66 mm
50 mm
The emitter
contact probe
The non-contact
receiver probe
Hybrid configuration
It generates a high energy ultrasound wave that travels through the element to be inspected
Low frequencies 100 kHz probe allows lower attenuation in high thickness components
It allows to have more freedom to follow the profile
It solves the problems of contact with bottom surface (coupled with water, oil, hanging)
It solves the problem to move on rough surfaces
Equipment
emitted signal: Burst; Max excitation voltage: 475 V pk-pk;
14-bit resolution; 100 MS/s real-time;
Contact emitter probe
Non-contact receiver probe
Further improvement solution
Further improvements, to overcome limits due to high curvature, rough surface and low spatial resolution, have been done.
In experimental stage a thin spherical cap (1 mm) on the low frequency contact probe (100 kHz) has been applied.
The thin thickness and the cap filled with water reduce interferences on the wave transmitted
The use of spherical element has also the objective of focusing and amplifying the beam
To support the sphere design and optimization a numerical simulation has already started
Contact emitter probe with spherical cap
Water
Simulated defects
The probes can be moved on the area of inspection by a Cartesian robot for planar shapes or by an anthropomorphic robot for complex shapes
In this work a Cartesian robot has been used
Core defect 10x3x30 mm
Skin defect 10x2.5x30 mm
Hybrid configuration
In both cases the skin defect and core defect have been detected
In the map with spherical cap, the edge effects and artefacts are reduced
The signal to noise ration (SNR) is lower with spherical cap (13 dB) but still good enough to detect defects
Core defect 10x3x30 mm; skin defect 10x2.5x30 mm
without spherical cap
SNR 19 dB
SNR 13 dB
with spherical cap
Skin Defective area
Core defective area
Improvement of the flexibility
Study the possibility to have more efficiency with a focusing ultrasonic beam on the contact point by using a sphere
ci
ct
Pa
Upgrade the spherical cap with the sphere to reduce the wear
Spherical cap - FEM simulation
Monolithic element
Triggering the ultrasound signal
*
3D map
Automatic system which scans the total area of the component allowing a complete structural integrity control including internal defects
2D map of the ultrasound signal amplitude
*
Hidden surface
Can be inspected using thermography techniques
IR
Deck profile inspection
To inspect hidden surfaces the solution can be the use of the mirror (aluminum)
Frame with the best contrast between the defective area and non defective area
Non defective area
Load lamp
Infrared camera
Anthropomorphic robot
*
Scan system configuration
The shape of the deck is complex and different configurations are request to inspect all deck surfaces
Scan of bottom surface
Scan of upper-right surface
Scan of upper-left surface
Simulated defect has been introduced to validate the inspection system
Defects: flat washers
Infrared images
*
Conclusions
Ultrasonic and thermography systems have been identified as the best techniques to inspect composite structural components for civil application due to their flexibility, cost and performances.
Innovative configuration such as hybrid ultrasonic and thermography with mirror have been studied to overcome the limits of inspection of complex structures.
A spherical cap has been applied on the ultrasonic transducer in order to increase the flexibility on curved profiles, rough surfaces and to improve the spatial resolution.
