Fraunhofer Institute for Physical Measurement Techniques IPM
Fraunhofer Institute for Physical Measurement Techniques IPM
Optischen Dehnungs­messung in der Werkstoff- und Bauteilprüfung auf Basis von Echtzeit-Bildkorrelation (DIC)
© Fraunhofer IPM
Optisch dehnungsgeregelter Ermüdungsversuch bei 1000 °C: Das System RODiS ermöglicht sowohl integrale Dehnungsmessungen analog zu Messungen mit mechanischen Extensometern als auch vollflächige DIC-Messungen in einem Sensor.

Optical strain measurement and control in real time

The optical RODiS system measures contact-free even in settings that are not accessible to tactile systems.

© Fraunhofer IPM

RODIS – Optical displacement sensor

Optical strain measurement in material and component testing

Many parameters in material sciences can be attributed to changes in length or displacements. This applies to strain as well as crack contours and the opening and closing behavior of cracks in materials, and to gap variations between rotors and stators in machines. FE models are also used to simulate the displacement of surfaces that act as easily accessible measuring points. When designing structural components, strain and displacement measurements enable hypotheses to be tested during experiments under operational conditions. 

A single sensor records various parameters

Fraunhofer IPM’s RODiS optical measurement system allows many of these parameters to be recorded using a single sensor. Customized measuring points can be set within a camera image, either as individual points or for full-field mapping. 

State-of-the-art cameras resolve the microstructure of a workpiece surface while recording more than 1500 images per second.  Simultaneously, graphics cards evaluate up to 74,000 measuring points per second. This enables the system to use the microstructure on metallic surfaces as correlation pattern in a marker-free manner. Therefore, a surface treatment with speckle paint is not required. 

Integral strain measurements as with mechanical extensometers

The measurement accuracy meets the requirements of accuracy class 0.5 according to DIN ISO 9513. Turning points in cycle frequencies up to 10 Hz are sufficiently resolved for strain-controlled trials with triangular strain signal shape according to ASTM E606. Just like with mechanical extensometers, the analog strain signal can be directly passed to the test station’s PID controller. Other parameters, such as force, distance and temperature are synchronously recorded as analog signals.