ASNT NDT Methods TEST(Quizzes
&soln)24|25 VERIFIED
Acoustic Emission Testing..
Acoustic Emission (AE) refers to the generation of transient elastic waves produced by
a sudden redistribution of stress in a material. When a structure is subjected to an
external stimulus (change in pressure, load, or temperature), localized sources trigger
the release of energy, in the form of stress waves, which propagate to the surface and
are recorded by sensors. With the right equipment and setup, motions on the order of
picometers (10 -12 m) can be identified. Sources of AE vary from natural events like
earthquakes and rockbursts to the initiation and growth of cracks, slip and dislocation
movements, melting, twinning, and phase transformations in metals. In composites,
matrix cracking and fiber breakage and debonding contribute to acoustic emissions.
AE's have also been measured and recorded in polymers, wood, and concrete, among
other materials.
Detection and analysis of AE sig - answer-100-300 kHz
2) Discontinuities that are not readily detectable by acoustic emission testing are: -
answer-rounded inclusions
The kaiser effect refers to: - answer-the behavior where emission from a source will not
occur until the previous load is exceeded. Kaiser effect is an absence of acoustic
emission at loads not exceeding the previous maximum load level when material
undergoes repetitive loading patterns. Discontinuities created in material during
previous steps do not move or expand until former stress is exceeded resulting in
Kaiser effect.
The felicity effect is useful in evaluating: - answer-fiber-reinforced plastic components
Felicity effect is an effect in acoustic emission that reduces Kaiser effect at high loads of
material. Under Felicity effect the acoustic emission resumes before the previous
maximum load was reached.
The total energy loss of a propagating wave is called: - answer-Attenuation
The Kaiser Effect is useful in distinguishing: - answer-mechanical noise from growing
discontinuities
The term "counts" refers to the : - answer-number of times a signal crosses a preset
threshold
The acoustic emission signal amplitude is related to: - answer-the band pass filters.
, Threshold settings are determined by the: - answer-background noise level
Background noise can be reduced by : - answer-electronic filtering
Electromagnetic Testing - answer-Electromagnetic Testing (ET), as a form of
nondestructive testing, is the process of inducing electric currents or magnetic fields or
both inside a test object and observing the electromagnetic response. If the test is set
up properly, a defect inside the test object creates a measurable response.
The term "Electromagnetic Testing" is often intended to mean simply Eddy-Current
Testing (ECT). However with an expanding number of electromagnetic and magnetic
test methods, "Electromagnetic Testing" is more often used to mean the whole class of
electromagnetic test methods, of which Eddy-Current Testing is just one.
Eddy-Current Testing (ECT) is used to detect near-surface cracks and corrosion in
metallic objects such as tubes and aircraft fuselage and structures. ECT is more
commonly applied to nonferromagnetic materials, since in ferromagnetic materials the
depth of penetration is relatively small.
Remote field testing (RFT) is used for nondestructive testing (NDT) of steel tubes and
pipes.
Magnetic flux leakage testing (MFL) is also used for nondestructive testing (NDT) of
steel tubes and pipes. At present RFT is more commonly used in small diameter tubes
and MFL in larger diameter pipes over long travel distances.
Wire rope testing is MFL applied to steel cables, to detect broken strands of wire.
Magnetic particle inspection (MT or MPI) is a form of MFL where small magnetic
particles in the form of a powder or liquid are sprayed on the magnetized steel test
object and gather at surface-breaking cracks.
Eddy Currents are circulating electrical currents induced in conductive materials by : -
answer-an alternating magnetic field
The method used to generate eddy currents in a test specimen by means of a coil can
most closely be compared with the action of a: - answer-transformer
Eddy current testing relies on the principle of : - answer-electromagnetic induction
When the electrical current in an eddy current coil reverses direction the: - answer-
direction of the eddy currents in the test part also reverses.
In order to generate measurable eddy currents in a test specimen the specimen must
be : - answer-an electrical conductor.
&soln)24|25 VERIFIED
Acoustic Emission Testing..
Acoustic Emission (AE) refers to the generation of transient elastic waves produced by
a sudden redistribution of stress in a material. When a structure is subjected to an
external stimulus (change in pressure, load, or temperature), localized sources trigger
the release of energy, in the form of stress waves, which propagate to the surface and
are recorded by sensors. With the right equipment and setup, motions on the order of
picometers (10 -12 m) can be identified. Sources of AE vary from natural events like
earthquakes and rockbursts to the initiation and growth of cracks, slip and dislocation
movements, melting, twinning, and phase transformations in metals. In composites,
matrix cracking and fiber breakage and debonding contribute to acoustic emissions.
AE's have also been measured and recorded in polymers, wood, and concrete, among
other materials.
Detection and analysis of AE sig - answer-100-300 kHz
2) Discontinuities that are not readily detectable by acoustic emission testing are: -
answer-rounded inclusions
The kaiser effect refers to: - answer-the behavior where emission from a source will not
occur until the previous load is exceeded. Kaiser effect is an absence of acoustic
emission at loads not exceeding the previous maximum load level when material
undergoes repetitive loading patterns. Discontinuities created in material during
previous steps do not move or expand until former stress is exceeded resulting in
Kaiser effect.
The felicity effect is useful in evaluating: - answer-fiber-reinforced plastic components
Felicity effect is an effect in acoustic emission that reduces Kaiser effect at high loads of
material. Under Felicity effect the acoustic emission resumes before the previous
maximum load was reached.
The total energy loss of a propagating wave is called: - answer-Attenuation
The Kaiser Effect is useful in distinguishing: - answer-mechanical noise from growing
discontinuities
The term "counts" refers to the : - answer-number of times a signal crosses a preset
threshold
The acoustic emission signal amplitude is related to: - answer-the band pass filters.
, Threshold settings are determined by the: - answer-background noise level
Background noise can be reduced by : - answer-electronic filtering
Electromagnetic Testing - answer-Electromagnetic Testing (ET), as a form of
nondestructive testing, is the process of inducing electric currents or magnetic fields or
both inside a test object and observing the electromagnetic response. If the test is set
up properly, a defect inside the test object creates a measurable response.
The term "Electromagnetic Testing" is often intended to mean simply Eddy-Current
Testing (ECT). However with an expanding number of electromagnetic and magnetic
test methods, "Electromagnetic Testing" is more often used to mean the whole class of
electromagnetic test methods, of which Eddy-Current Testing is just one.
Eddy-Current Testing (ECT) is used to detect near-surface cracks and corrosion in
metallic objects such as tubes and aircraft fuselage and structures. ECT is more
commonly applied to nonferromagnetic materials, since in ferromagnetic materials the
depth of penetration is relatively small.
Remote field testing (RFT) is used for nondestructive testing (NDT) of steel tubes and
pipes.
Magnetic flux leakage testing (MFL) is also used for nondestructive testing (NDT) of
steel tubes and pipes. At present RFT is more commonly used in small diameter tubes
and MFL in larger diameter pipes over long travel distances.
Wire rope testing is MFL applied to steel cables, to detect broken strands of wire.
Magnetic particle inspection (MT or MPI) is a form of MFL where small magnetic
particles in the form of a powder or liquid are sprayed on the magnetized steel test
object and gather at surface-breaking cracks.
Eddy Currents are circulating electrical currents induced in conductive materials by : -
answer-an alternating magnetic field
The method used to generate eddy currents in a test specimen by means of a coil can
most closely be compared with the action of a: - answer-transformer
Eddy current testing relies on the principle of : - answer-electromagnetic induction
When the electrical current in an eddy current coil reverses direction the: - answer-
direction of the eddy currents in the test part also reverses.
In order to generate measurable eddy currents in a test specimen the specimen must
be : - answer-an electrical conductor.
