Laser
Testing includes three techniques, Holography,Shearography and Profilometry. As the method name implies, all three
techniques user lasers to perform the inspections.
Holographic
Testing
Holographic
Testing uses a laser to detect changes to the surface of a part as it deforms
under induced stress which can be applied as mechanical stress, heat, pressure,
or vibrational energy. The laser beam scans across the surface of the part and
reflects back to sensors that record the differences in the surface created by
that stress. The resulting image will be a topographical map-like presentation
that can reveal surface deformations in the order of 0.05 to 0.005 microns
without damage to the part. By comparing the test results with an undamaged
reference sample, holographic testing can be used to locate and evaluate
cracks, delaminations,disbonds,
voids and residual stresses.
Laser Profilometry
Laser Profilometry uses a high-speed rotating laser light
source, miniature optics and a computer with high-speed digital signal
processing software. The ID surface of a tube is scanned in two dimensions and
the reflected light is passed through a lens that focuses that light onto a
photo-detector, generating a signal that is proportional to the spot's position
in its image plane. As the distance from the laser to the ID surface changes,
the position of the focal spot on the photo-detector changes due to parallax,
generating a high resolution three-dimensional image of the part surface that
represents the surface topography of the part. This technique can be used to
detect corrosion, pitting, erosion and cracks in pipes and tubes.
Laser Shearography
Laser Shearography applies laser light to the surface of the
part being tested with the part at rest (non-stressed) and the resulting image
is picked up by a charge-coupled device (CCD) and stored on a computer. The
surface is then stressed and a new image is generated, recorded and stored. The
computer then superimposes the two patterns and if defects such as voids
or disbonds are present, the defect can be
revealed by the patterns developed. Discontinuities as small as a few
micrometres in size can be detected in this manner.
- Non-contact and remote, allowing
inspection of samples at high temperature, e.g. during welding with restricted
access
Small and adjustable footprint
- Enables inspection of small and
complex geometries
- High frequency capable of detecting
very small flaws
- Laser beam scanning method
for full coverage of inspection samples
- Industrial in-process measurements on
hot, hazardous, remote samples which may be moving at high speeds
- High-resolution measurement of small
parts
- Inspection of complex structures
- laser-ultrasonic projects involving the inspection of friction stir welds, laser material depositing andcomposite materials