NDT intro and ultrasound COPY

Question 1

what is detection window, and symbol

Answer 1

Tdw = time between damage being detectable and becoming critical

Question 2

Formula for inspection interval

Answer 2

∆t < Tdw / N + 1

N is number of required inspections to be certain of detection

Question 3

formula for longitudinal velocity (longitudinal wave propagation

Answer 3

CL = SQRT( (K+4G/3) / ρ ) = f λ

see notes if needed

K is bulk modulus
G is shear stiffness

Question 4

Acoustic impedance formula

Answer 4

z = p / u

p is pressure amplitude
u is velocity amplitude

Question 5

acoustic impedance formula using material parameters

Answer 5

z = ρ CL

Question 6

Formula for reflection coefficient between two materials

Answer 6

R = ( (z2/z1 - 1) / (z2/z1 + 1) ) ^2

Question 7

Formula for transmission coefficient between two materials

Answer 7

T = (4z2/z1) / (z2/z1 + 1)^2

Question 8

formula for reflected pressure amplitude

Answer 8

Pr = SQRT(R) x Pi

pr is reflected pressure amplitude
pi is pressure amplitude of initial wave?

Question 9

formula for transmitted pressure amplitude

Answer 9

Pt = SQRT(T) x Pi

pt is transmitted pressure amplitude
pi is pressure amplitude of initial wave?

Question 10

explain the process of B scans

Answer 10

1. transducer moves in straight line taking multiple A scans
2. A scans plotted next to eachother as colour maps
3. image produced of reflected signal as function of horizontal position and depth
4. can recover A scan data to zoom in on particular defects

Question 11

explain the process of C scans

Answer 11

1. transducer scans in 2 dimensions
2. produces amplitude data in 3D: two translations and horizontal position + depth
3. requires simplifocation for plotting
4. apply time window so that front and back reflections are ignored
5. measure largest reflected amplitude within sample
6. gives scanned data amplitude value over the 2 scanned dimensions
7. specific A scans for defects are retrievable

Question 12

list 3 coupling methods

Answer 12

1. suface contact coupling - commonly a gel
2. water coupling
3. wheel probes

Question 13

name two newer transducer developments

Answer 13

1. focussed transducer: curved element focusses at specific distances
2. phased array - customiseable real time beams - still in development

Question 14

differences between high precision and high power ultrasouns transducers

Answer 14

High Precision
- large bandwidth producing short pulses which allow accurate depth measurement
- achieved by adding backing to piezoelectric element to reduce amplitude
High Power:
- undamped transducer
- narrow bandwidth and long pulses, but at high amplitudes