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Kombination von digitaler Bildkorrelation und Thermografiemessung

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The combination of measuring results from the digital image correlation (ARAMIS, DIC)
and temperature measuring data from infrared cameras permits the simultaneous
analysis of the thermal and mechanical behavior of test specimens in the materials
and components testing field.

GOM ARAMIS – Digital image correlation (DIC)
The ARAMIS system measures by using a contact-free
and material-independent method based on the
principle of digital image correlation.

The images of the test specimens under load that were
recorded with high-resolution cameras or high-speed
cameras are evaluated. The system determines the gray
value distribution for thousands of subsections in each
camera image and gives the subpixel-accurate positions
of the corresponding measuring points in all images,
from which then the 3D coordinates are calculated by
triangulation. The evaluation of this surface information
for all load levels during the time in the 3D space delivers
the exact X, Y and Z displacements, velocities and
accelerations. Furthermore, ARAMIS determines from
the 3D coordinates the surface strains, such as, major
and minor strain.

Proceeding from these measuring data, material parameters
are determined, numerical simulations are validated
and component motions and deformations are analyzed.
The ARAMIS system can be used for specimen sizes in
the range from several square millimeters to several
square meters and supports both high-definition and
high-speed cameras with frame rates up to more than
1,000,000 Hz.

InfraTec – Thermography
The thermography systems of the VarioCAM® HD series
and the ImageIR® series with the latest detector technology
are characterized by excellent metrological
properties. The thermography cameras achieve a spatial
resolution of up to (2,560 × 2,048) IR pixels. This allows
images and sequences to be created with unmatched
spatial resolution, effectively avoiding geometrical
measuring errors. Due to the excellent thermal resolution
of up to 20 mK, even the smallest temperature
differences can be accurately represented.

The optical channel of the cameras consists of exchangeable
infrared lenses, which can be equipped
with a motor focus unit. Fast and precise focusing is
achieved via the camera operating software. You can
choose between the autofocus function and manual
focusing. The use of infrared lenses with F/1 concept
and very high luminous intensity enables the creation
of thermograms that are free of undesired warm aperture
effects or image inhomogeneities.

The specially developed calibration algorithm, featuring
one main and two secondary characteristic curves,
serves to compensate for varying ambient temperatures
and enables repeatable measurements even
under changing thermal conditions.

Control and data storage are carried out via industrial
Ethernet interfaces (GigE and 10 GigE). Thus, high-frequency
infrared sequences can be recorded fully
radiometrically with up to 105 kHz. The temperature
data are stored with the X/Y coordinate. Due to the
delay-free triggering, synchronization with external
processes as well as external cameras is possible, which
enables clear assignment of the resulting data (temperature
values and digital image data).

The modular basic concept of the thermography
systems consisting of optical, detector and interface
modules allows an individual system configuration
and an optimal adaptation of the performance data
to the respective task. The light metal housings with
their compact design and high protection degree (up
to IP67) enable easy integration into existing systems,
even in harsh industrial environments.

In order to be able to combine the two measuring
results, the ARAMIS 3D sensor and the IR camera are
pointing to the same area of the specimen surface that
is to be measured, and the image acquisition of both
systems is synchronized with an electrical trigger signal.

The temperature and the 3D coordinate results are
combined in the ARAMIS Professional software, so that
a temperature value is assigned to each 3D coordinate.
In this way, the temperature change on the surface is
analyzed over the entire test period and is evaluated
in relation to the 3D displacements and the 3D surface
strains. Thus, the separate analysis of the thermal and
mechanical deformations is possible.

Application example of a tensile test
The determining of the material parameters in quasistatic
tensile tests with ARAMIS is described under, so that in this application
example only the further results from the combination
of ARAMIS and the thermography are dealt with.

In the quasistatic tensile test, the combination of the
two measurement methods makes the synchronized
and place-bound analysis of the strain results with the
temperature of the test specimen surface possible.

During the initial phase of the tensile test (elastic strain
area and shortly afterwards – the above diagram), it
can be established with the help of the thermographic
evaluation at greater deformation a cooling off of the
specimen due to the thermo-elastic effect (the diagram
in the middle).

On the other hand, in the further course of the experiment,
due to the effect of the deformation force in the
area of plastic deformation, a constant heating of the
specimen up to fracture takes place.

Application example of the components testing
In the area of testing of components or parts, the GOM
ARAMIS system and the InfraTec infrared cameras can
be used in the same way to obtain valuable information
about the thermal and mechanical component behavior,
so that the temperature and deformation data can
be used for validation of the numerical simulations.
Further information about the validation of numerical
simulations can be found in the GOM webinar under:

Founded in 1991, the owner-managed Dresden
company InfraTec GmbH offers a wide range of high-quality,
innovative products and services in the field of
infrared technology. Approx. 200 employees regard
the demands of the market as a challenge, which
they meet with sound specialist knowledge, daily
commitment and high quality awareness. Optimal
consultation, exemplary service and individual product
design by internal development and manufacturing
capacities are used, in order to fulfill the requirements
of the customers in the best possible way and support
thereby their lasting success.

GOM develops, produces and distributes software, machines and systems for 3D coordinate measuring technology and 3D testing based on latest research results and innovative technologies. With more than 60 sites and more than 1,000 metrology specialists, GOM guarantees professional advice, as well as support and service across the globe. More than 17,000 system installations improve the product quality and manufacturing processes in the automotive, aerospace and consumer goods industries.

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