Non-Destructive Evaluation/Testing - NDE/NDT
Testing - VT
Visual inspection is one
NDT method used extensively to evaluate
the condition or the quality of a weld or
component. It is easily carried out, inexpensive
and usually doesn't require special equipment.
It requires good vision, good lighting and
the knowledge of what to look for. Visual
inspection can be enhanced by various methods
ranging from low power magnifying glasses
through to boroscopes.
Thermography is the use of an infrared
imaging and measurement camera to "see"
and "measure " thermal energy
emitted from an object.
Thermal, or infrared energy,
is light that is not visible because its
wavelength is too long to be detected
by the human eye; it's the part of the
electromagnetic spectrum that we perceive
as heat. Unlike visible light, in the
infrared world, everything with a temperature
above absolute zero emits heat. Even very
cold objects, like ice cubes, emit infrared.
The higher the object's temperature, the
greater the IR radiation emitted. Infrared
allows us to see what our eyes cannot.
thermography cameras produce images of invisible
infrared or "heat" radiation and
provide precise non-contact temperature
measurement capabilities. Nearly everything
gets hot before it fails, making infrared
cameras extremely cost-effective, valuable
diagnostic tools in many diverse applications.
And as industry strives to improve manufacturing
efficiencies, manage energy, improve product
quality, and enhance worker safety, new
applications for infrared cameras continually
The objective of conventional
thermography is the measurement of surface
temperatures. Using passive thermography,
one can get contactless information about
is applicable for the detection of deep-seated
defects in materials with low temperature
conductivity. The sample is heated up
over a long period of time in a furnace
(non-destructive temperature, e.g. 50°C).
After that it is brought into a normal
climate and at the same time the surface
temperature is gathered with an infrared
camera. Because the sample is losing heat
to the environment due to convection and
radiation, the surface is cooling down.
Heat is flowing from the inside to the
surface of the sample. A defect, typically
a delamination or a cavity, is a thermal
barrier for the heat flow. This leads
to an inhomogeneous temperature distribution
on the surface, which is detected from
the infrared camera. Only one way, from
the defect to the surface of the sample,
is relevant for the measurement: The heat
has to cover only half the distance compared
to other thermal methods. This explains,
why it is possible to detect deep-seated
defects in short time with this method.
Shearography is a variation
of holography specifically designed for
NDT applications. Shearography provides
full-field, non-contact nondestructive
testing for rapid wide-field inspection
of composites, bonded structures and other
advanced materials. Shearography is an
optical video strain gauge and an appropriately
applied stress is used to locate strain
concentrations caused by internal defects.
is an imaging method, which records the
amplitude and phase of light reflected
from an object as an interferometric pattern
on film. It thus allows reconstruction
of the full 3-D image of the object. In
HNDT, the test sample is interferometrically
compared in two different stressed states.
Stressing can be mechanical, thermal,
vibration etc. The resulting interference
pattern contours the deformation undergone
by the specimen in between the two recordings.
Surface as well as sub-surface defects
show distortions in the otherwise uniform
pattern. In addition, the characteristics
of the component, such as vibration modes,
mechanical properties, residual stress
etc. can be identified through holographic
inspection. Applications in fluid mechanics
and gas dynamics also abound.