Non-Destructive Techniques Flashcards
(42 cards)
Define infrastructure resilience
The capacity of infrastructure to mitigate, adapt, or positively respond to chronic and acute stresses, transforming in ways that restore, maintain and even improve their essential functions
Simplified: robustness of a structure to withstand hazards
Give an example of resilient infrastructure
Tokyo Underground Floodwater Tunnels
Channels excess water to river
Define Non-Destructive Techniques
Process of inspecting, testing, or evaluating materials, components or assemblies for discontinuities/differences in characteristics, without destroying the serviceability of the part/system
What are NDT methods used for?
To locate the exact location and characteristics of damage.
Usually done after continuous monitoring detects the general location of damage
Give an overview of visual inspection methods
Can be by direct viewing, using line-of-sight vision, or using optimal instruments.
Used to detect corrosion, misalignment of parts, physical damage and cracks.
Examples include underbridge units (image), elevating platforms and truck cranes
What are the advantages of visual inspection methods?
- Easy to apply
- Quick
- Low-cost
Give an overview of the UAV (unmanned aerial vehicles) inspection method
UAVs are autonomously/semi-autonomously controlled aircrafts that can be equipped with cameras.
What are the advantages of UAV methods?
- Only need an operator on the ground (safety)
- Use low cost technologies whilst reaching high level of complexity
- Capability of fast real time data acquisition and the storage of all relevant flight data
What are the limitations of UAV methods?
- Small payload; only small format/light cameras can be used for photos and videos
- Low weight makes flight sensitive to harsh weather
- Restrictions/permissions needed to be used in some areas (e.g. around electrified railway)
What are the principles behind acoustic inspection methods?
Materials ‘talk’ when they are in trouble.
Acoustic emission equipment can ‘listen’ to the sounds of cracks growing, fibres breaking, and more
Name the different types of acoustic methods
- Chain Drag (mechanical)
- Impact Echo (mechanical)
- Ultrasonic Pulse Velocity
- Ultrasonic Pulse Echo
What is the chain drag method used for?
Identifying cracks, delaminations and other surface defects, in combination with visual inspection
Effective in locating shallow delaminations on uncovered decks
What are the limitations of the chain drag method?
- Requires lane closures
- Labour intensive
- Dependent on user and traffic volume (noise)
- Can’t be used to locate delaminations in the concrete below bituminous material
Give an overview of the Impact Echo method
What materials is it used to test?
Uses impact-generated stress (sound) waves, which propagate through the material and are reflected by internal flaws and external surfaces
Used to test concrete and masonry structures
Give example uses of the Impact Echo method
- Measuring the thickness of new highway pavements and concrete slabs
- Bridge deck delamination detection
- Finding the location and extent of flaws, including cracks, delaminations, voids in plain, reinforced, and PT concrete structures
- Determining thickness/locating cracks and other defects in masonry structures (where the brick or block units are bonded together with mortar)
What are the advantages of the Impact Echo Method?
- Not user intensive
- Provides data regarding top and bottom surface delamination
- Cost-effective; saves lots of money on repair/retrofit costs on bridges, retaining walls, and other large structures
What are the disadvantages of the Impact Echo Method?
- Requires lane closures
- Interpretation of results requires experience
Give an overview of (general) ultrasonic testing
- Ultra-high frequency sound introduced
- If sound hits a material with a different acoustic impedance, some of it is reflected (and presented on display)
- Distance to the reflector determined by knowing the speed of the sound and the time taken for it to return
What are the most common sound frequencies used in UT?
How do lower frequencies perform with respect to sensitivity and penetrating power?
Between 1.0 and 10.0 MHz
Lower frequencies have greater penetrating power but less sensitivity (ability to ‘see’ small indications)
Give an overview of the Ultrasonic Pulse Velocity Method
- Ultrasonic pulse of 50 to 54kHz produced by electro-acoustical transducer
- Measures travel time T of the pulse; with path length L, finds the pulse velocity (V = L/T)
- The material is held in contact with one surface of the concrete member under test, and receives the same pulse by a similar transducer in contact at the other end
- Ultrasonic pulse velocity depends on the density and elastic material properties
What is the Ultrasonic Pulse Velocity method used for?
- Qualitative assessment of strength of concrete/its gradation in different locations
- Any discontinuity in the cross-section (cracks, cover concrete delamination etc)
- Depth of surface cracks
What pulse velocity gives an excellent concrete quality grade?
What is done if the results indicate the concrete quality is ‘doubtful’
Above 4.5 km/second
If doubtfoul (below 3.0), a core test is done
What are the limitations of the Ultrasonic Pulse Velocity method?
- High operator skill needed
- Defects may be masked in certain materials (e.g. austenitic steel; large grain size found in welds can cause attenuation)
- Misreading of signals can result in unnecessary repairs
Give an overview of the Ultrasonic Pulse Echo method
What materials is it used on?
- Very commonly used for inspecting steel structures
- Mechanical waves (ultrasound) generated by a piezo-magnetically excited element at a frequency between 2 to 5 MHz
- Can detect cracks and determine crack depth with a high degree of accuracy
