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How can the defect be sized using the time of signals?
a = cosθ*(Δt*v/2)
How can the frequency spectrum of combined signals help to size a defect?
PICTURE

a = cosθ*(Δt*v/2)
What can velocity and attenuation of material be used for?
Estimating material characteristics such as
- grain size and concentration
- porosity content
- material anisotropy
- residual stress
What can variations in velocity be used for in material characterisation?
v prop root(avgElasticModulus/avgDensity)
this could be porosity content, grain characteristics, material mix
What can variations in attenuation be used for in material characterisation?
scattering induced attenuation is related to size, shape and volume fraction of simple scatterers
How would residual stress or anisotropic characteristics be detected?
Mechanical working affects velocity. Therefore accurate velocity measurements techniques are required
What are the most common methods of ultrasound generation?
- Piezoelectronic transducers
- Magnetostrictive transducers
- EMATs (Electromagnetic Acoustic transducers)
- Laser generation
- Impact
What are magnetostrictive transducers?
Transducers which have material which changes shape due to the influence of a magnetic field
How does an Electromagnetic Acoustic transducer work?
Eddy currents induced by coil on material surfaceinteract with permanent magnet which result in the vibration of specimen surface
What are the most important features of Electromagentic Acoustic transducers?
- The wave generation process is reciprocal
- Non-contact method whic his good for hot-surface inspection
How does laser generation of ultrasonic waves work?
Surface is struck by laser pulses which heats the specimen locally and thus expands. Ultrasonic waves created due to expansion and contraction of material
What is an advantage of laser generation ultrasonic waves?
Non-contact
What are the disadvantages of ultrasonic waves?
- Material damage may occur
- Detection is complex
Draw the set-up of a piezoelectronic transducer
IMAGE
Draw the set-up of a shear wave transducer
IAMGE
Draw a B-scan system
IMAGE
draw an A-scan system
IMAGE
draw a shear wave EMAT
Image
Draw a compressional wave EMAT
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