ESG also offers acoustic emission and ultrasonic equipment for field
and laboratory applications such as non-destructive testing of material
properties.

Our systems are used extensively in industry and research environments,
including international universities, industry associations, government
and non-government organizations.

Acoustic Emission & Ultrasonic Systems

Acoustic emissions (AEs) are sound waves emitted by micro-cracks as
they are created or propagate inside material that can deform through
brittle fracture such as rock, concrete, or metals.

AEs can be detected and recorded by a data acquisition system either in
a laboratory setting (e.g. testing material samples), or in-situ (e.g.
monitoring bridge support beams or a dam structure). The number and
placement of sensors in the acquisition system dictates the monitoring
volume. For testing material samples, the volume can be as little as a
few cubic centimeters. For in-situ monitoring, the volume can be
several cubic meters.
AE systems typically operate in ultrasonic frequency ranges. ESG’s
Hyperion Ultrasonic System (HUS) and GIGA Recorder operate at frequency
ranges from 30 kHz to 5 MHz.

Capabilities
After a data acquisition system captures the relevant AE data,
processing techniques, similar to those used by seismologists, are
applied in order to determine information concerning the AE abundance,
locations and mechanics. This leads to an analysis of the cracks that
have created them.

• AE counts and magnitudes (energy release) show the amount and intensity of fracturing occurring in the material.
• AE
  locations delineate regions of damage. Micro-crack distributions,
  mapped three-dimensionally through time, describe damage accumulation,
  crack coalescence and macro-fracture propagation.
• AE
  mechanisms (fault-plane solutions and moment tensors) show micro-crack
  orientations and failure properties (tensile crack growth, frictional
  sliding, grain crushing).

Ultrasonic studies artificially generated sound waves to examine the
sample. Transmitters induce sound into the sample and receivers record
the sound after it has propagated through the material. The sound’s
behavior (velocity and attenuation) is a function of the properties of
the medium. As these properties change, due to crack or pore-space
closure, stress loading, saturation or heating, then the recorded
signals change. Through analysis of the signals, the changing
properties of the sample can be examined.

• Ultrasonic velocities provide quantification of dynamic elastic moduli
• Velocity and attenuation measurements with time show changes in medium properties three-dimensionally through the sample
• Tomography techniques map zones of differing material properties
• The
  dedicated ESG Hyperion Ultrasonic System (HUS) and GIGA Recorder
  perform full-waveform AW acquisition and AE Hit Counting with
  synchronized triggering over the array. Full waveform storage allows
  detailed processing of the data to be performed after the experiment.
  Both systems are easily configured using Windows based software and
  once operating, require little or no intervention. They can be set to
  provide automatic on-line AE locations and relative magnitude estimates.
• The
  HUS provides three-dimensional ultrasonic surveys using multiple
  transmitters pulsing to the entire array and storing full-waveform
  data. Surveys can be user operated or set at user-defined intervals.
• The
  GIGA Recorder also captures a continuous stream of data from up to 16
  channels and is ideal for loading systems that test samples to failure.
• Acquisition software provides graphical display of AE Hit
  counts, waveforms, locations and provides data base support. Waveforms
  can be easily accessed for data quality assessment.

As full waveforms are recorded during the experiment, detailed
post-processing of the data can be performed. ESG’s processing software
provides techniques tailor-made to the testing application. They
include:

• Velocity interferometry using waveform cross-correlation to give precise changes in sample velocity
• Elastic moduli and crack density calculations
• AE mechanism studies to give fracture orientations and fracture types
• Signal attenuation analyses for fracture investigations