Resonance (5)

Question 1

Why is Resonance a key part of Ultrasonic Testing?

Answer 1

• Used to determine the thickness required of a crystal to produce a given frequency
• A form of thickness testing (Resonance Testing)

Question 2

What are Standing Waves?

Answer 2

The result of the superposition of two similar plane waves of identical frequency, amplitude and direction of oscillation but different direction of propagation.

• does not travel, vibrates up and down
• never the case in an ordinary or travelling wave!

Question 3

What are Nodes?

Answer 3

Points where the two waves (standing waves) cancel each other out.
- diagram: the point where to waves overlap one another.

• particles do not move

Question 4

What are Antinodes?

Answer 4

The maximum point of amplitude between two waves (standing waves)
- diagram: the vertical section where the two waves are farthest from one another

Question 5

When Standing Waves are formed, it results in a phenomenon called ___,

Answer 5

Resonance, which causes a drastic increase in the amplitude of the vibrations.

Question 6

When does Resonance occur?

Answer 6

When the thickness of the part is equal to 1/2λ or a multiple of 1/2λ.

Question 7

What is a Fundamental Frequency?

Answer 7

The minimum frequency at which resonance occurs, when: T = 1/2λ

Question 8

What are Harmonics?

Answer 8

Multiples of a Fundamental Frequency, when T= a multiple of 1/2λ

Question 9

What is Ultrasonic Resonance Testing?

Answer 9

Use the relationship between thickness and resonant frequency to measure thickness.

Induce a vibration into a part, compare the frequency to what frequency the part actually vibrates at to infer material thickness.

Question 10

How is Resonance Testing done?

Answer 10

Use continuous longitudinal waves, create Standing Waves by allowing both the transmitted and reflected waves to meet (nodes).

Control the frequency via UT resonance instrument until the part thickness is 1/2λ or a multiple of 1/2λ making the two waves meet, causing resonance and a signal is received.

Question 11

What is Resonance Testing used for?

Answer 11

• Thickness measurements for thin sheets
• Bond testing
• Detection of large front surface parallel discontinuities
• Testing integrity of composite and bonded structures (they appear as thin materials)