Olympus BondMaster 600, Руководство пользователя

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DMTA-10045-01EN, Rev. E, August 2016
Chapter 2 24
Defect detection in pitch-catch mode is achieved by detecting a greater amplitude
oscillation at the receiving crystal. In the pitch-catch mode's RF and IMPULSE test
techniques (fixed frequency test), near-surface and far-surface disbonds can be
detected. The IMPULSE technique applies an envelope filter to the receiving signals.
(The name “IMPULSE” originates from earlier BondMaster products.) The pitch-catch
mode's SWEPT test technique, however, sweeps over a range of frequencies, which is
more suitable, for example, for the varying thicknesses of aircraft flaps or stabilizers.
The pitch-catch SWEPT test technique is also particularly well-suited for aluminum
core honeycomb composites.
In Mechanical Impedance Analysis (MIA) mode and Resonance mode, the oscillations
generated by the probe's emitting crystal are also transferred into the test specimen,
but in a more rigid way. The probe uses the specimen's oscillations to sense changes in
mechanical impedance, rather than using the membrane vibrations as with pitch-
catch mode and test techniques.
In MIA mode, the mechanical impedance is detected through the restricted movement
of a receiving crystal that is included in the mechanical drive circuit. The receiving
crystal is coupled to the test specimen by means of a solid shaft (the probe tip). The
other side of the receiving crystal is coupled to the emitting crystal through a semi-
elastic material. As a result, the receiving crystal becomes more or less restricted as
the mechanical impedance of the test specimen changes. If a defect is present, the
probe tip oscillates more freely, and the receiving crystal is subjected to a lower
alternating mechanical pressure, which generates a weaker amplitude voltage that is
detected by the instrument. However, if the test specimen has a greater mechanical
impedance (for example, for honeycomb composite potted repairs) the receiving
crystal's movement becomes even more restrained, which results in increased
pressure and amplitude signals at the receiving crystal. MIA mode is therefore an
excellent way of identifying potted repairs and crushed cores in honeycomb
composites. Typically, MIA mode is able to detect smaller disbonds than the pitch-
catch mode.
Resonance mode, like MIA mode, can also be used to monitor the mechanical
impedance of the test specimen. (Incidentally, the term “resonance” may be
misleading, as it refers to probe resonance and NOT part resonance.) In resonance
mode, the probe's crystal is coupled to passive electronic components that form a
resonant filter. The single crystal must be coupled to the test specimen using a low
viscosity couplant. Because the crystal becomes part of the resonant circuit, any
changes in its electrical impedance will affect the resonant point (phase and
amplitude). The crystal's electrical impedance is affected by the mechanical
impedance of the test specimen, which is coupled to the crystal when a resonance test
is performed. Changes in mechanical impedance occur when disbonds or interply