1: Sound Flashcards
What property of a metal makes the propagation of ultrasonic waves possible?
Elasticity
Define cycle:
A particle displaced from rest position…. etc
Define frequency:
Number of cycles per second
Define wavelength:
Distance a wave travels during a cycle OR distance between 2 particles in same state of motion
What is the formula that relates velocity, frequency and wavelength?
LAMBDA = V/f
What is the approximate ratio of velocities of sound in steel as compared to water?
Sounds travels approx. 4X faster in steel than in water.
In theory, what is the smallest defect that an ultrasonic inspection can usually detect?
Approximately half a wavelength (LAMBDA/2)
What is meant by “period” of a cycle?
Time required to complete 1 cycle.
What is the maximum frequency that a human ear can hear?
20 KHz
What is the range of frequencies used in ultrasonic testing?
0.5 MHz to 25 MHz
What are the 2 factors that determine the velocity of a longitudinal wave in a medium?
Density and elasticity
What’s another name for a longitudinal wave?
Compression wave
What’s another name for a transverse wave?
Shear wave
What’s another name for a surface wave?
Rayleigh wave
What’s another name for a plate wave?
Lamb wave
What is approximate ratio of velocities of shear waves to longitudinal waves in a material?
Shear are approximately half the velocity of a longitudinal
What is the approximate ratio of velocities of surface waves to shear waves?
Surface waves are 3-15% slower than shear waves
What is the intensity of a surface wave at a depth of 1 wavelength below the surface?
Approx 4% or 1/25th intensity of wave at surface
What is the particle motion in surface waves?
Elliptical
What depth do surface waves usually penetrate?
About 1 wavelength in material.
What 5 factors influence velocity of a plate wave?
- Type of material
- Thickness of material
- Frequency of wave
- Angle if incidence of wave
- Mode of wave generated
What are the 2 most common types of lamb waves?
Symmetrical and asymmetrical
What type of waves can propagate in solids?
Compression, shear, surface and plate waves
What type of waves can propagate in liquids?
Only compression waves.
Under which conditions will a surface wave reflect back to the probe?
Surface discontinuities, grease, oil, or dirt.
Define the term “angle of incidence.”
Angle at which an incident wave strikes an interface.
What is meant by “normal incidence”?
Incident wave that strikes the interface at angle of 90 degrees.
What is condition necessary to produce reflection at an interface?
Sound waves hits an interface between 2 materials of different acoustic impedances
If the angle of incidence is known, how is the angle of reflection determined?
Equal to angle of incidence
What are the 2 characteristics of a material that determine its acoustic impedance?
Density and velocity
What symbol is used to represent density?
Rho (p)
