Contactless Interferometric Strain measurement

Contactless Interferometric Strain measurement

Fangjian Wang, M.Sc.

State of the art / Motivation

  • Conventional strain measurement with strain gauges:
    • Measuring errors due to contact (adhesives)
    • Sensitive towards strain perpendicular to the measuring direction
    • Influences of temperature at the measuring location
    • Complex measuring set-up with several measuring points
  • Current optical contactless strain sensors, e.g. Digital Image Correlation (DIC)
    • Low sampling rate
    • Higher noise
    • No electrical real-time measurement due to post-processing

Methods

  • Sensor principle of in-plane Laser Doppler Vibrometry transferred to strain measurement
  • The sensor is being researched within a ZIM project in cooperation with SincoTec GmbH. A stripe pattern is generated by two laser beams crossing each other on the measuring surface. The movement of the scattering body through the stripe pattern forms the intensity modulation, whose frequency is proportional to the velocity perpendicular to the stripe. In-plane deflection of each measurement point is proportional to the integration of the frequency. The strain results from the difference of the deflection at two measuring points in relation to the distance.

Results

  • Design of the principle of a novel contactless strain sensor
  • Simulation of the optimal sensor setup
  • Realization of an experimental setup of the sensor
  • Integration of strain sensor in resonance testing machine of SincoTec
  • The optical sensor provides comparable measurement results to a strain gauge

Prospects

  • Set sensor setup in high speed tear test

Publications

  1. F. Wang, S. Krause, und C. Rembe:
    Signal diversity for the reduction of signal dropouts and speckle noise in a laser-Doppler extensometer
    In: Measurement: Sensors, 2022. DOI: 10.1016/j.measen.2022.100377.
  2. F. Wang, S. Krause, J. Hug and C. Rembe:
    A Contactless Laser Doppler Strain Sensor for Fatigue Testing with Resonance-Testing Machine
    In: Sensors 2021, 21(1), 319. DOI: 10.3390/s21010319.
  3. F. Wang and C. Rembe:
    Kontaktloser interferometrischer Dehnungssensor.
    In: Tagungsband 3. Niedersächsisches Symposium Materialtechnik. pp. 51-65, 2019. DOI: 10.21268/20190312-3
  4. F. Wang and C. Rembe:
    Entwurf eines kontaktlosen interferometrischen Dehnungssensors.
    In: tm - Technisches Messen. Vol. 85, Issue s1, pp. 117-123, Sept 2018. DOI: 10.1515/teme-2018-0045.