The ETH Zürich – on of our longstanding customers – provides on the following website their research project. They analyse the accuracy of digital image correlation within the scope of reinforced concrete. To the project members belong Prof. Dr. Walter Kaufmann and Dr. Jaime Mata Falcón.
Full field strain measurement in rebar tension
test: failure phase.
Ravi Ranade
Test of a ECC (Engineered Cementitious Composites) Beam under 4-point loading.
Ravi Ranade
National Institute of Standards and Technology
In this example a Vic-3D measurement with 5MP CMOS Camera was performed. The acryl specimen is fixed in a tensile testing machine. A strain gauge is attached at the back in combination with a SCAD 500 strain gauge amplifier. The output of the SCAD 500 was connected to the DAQ of the DIC system. The strain results are recorded parallel with the Vic-3D measurement and plotted in a diagram. The camera type is equipped with Sony 5Mpx Pregius sensor, 75 fps.
Image 1: Vic-3D measurement of the acryl specimen
Image 2: Comparison of strain gauge data (red curve) and DIC Strain data (black curve)
The Vic-3D data match nearly perfect with the strain gauge data. Even at low strains the difference is less than 25 micro strain.
Results of a 2D fartigue test on a thick piece of notched steel. With the use of a 2,3MP camera and Vic-2D a high strain resolution of approximate 5-10 microstrain can be archieved.
The video shows the results of this fartigue test.
The graph demonstrates the bending load over time.
The following video clips show a deformation- or strain-measurement of a metal spring element, measured by using Vic-3D.
The first deformation measurement would be made in the X direction.
The second deformation measurement would be made in the Y direction.
The third deformation measurement would be made in the Z direction.
In the last case you see the result of the strain measurement.
The video shows an experimental setup of a strain measurement with digital image correlation. A segment of a 3 mm wide cable insulation is loaded by a tensile machine until failure.
The video shows the application of a stereo image correlation (phase synchronized) for a three-dimensional displacement measurement or movement analysis (Vic-3D).
The used stereo camera system is based on two 5 Mpixel cameras with a frame rate of 6Hz (at full resolution) in combination with the isi-sys synchronisation and trigger device for stroboscopic opservation of periodic events.
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Four measurement areas (hydraulic cylinder – below, wheel hub – left, swingarm – middle and linear unit – right above) with specle pattern were monitored for the evaluation. The vector arrows represent the current displacement state.
Application examples of a special stereomicroscope in combination with Vic-3D digital image correlation on electronic components.
Image 1: Measurement setup
Measurement set up: Stereo microscope mounted on x-y-z-microtable (backside) and tensile machine (right).
Image 2: Strain in x-direction
Image 3: Strain in y-direction
Strain distribution of a half cut capacitor-chip (left part) and its soldering area (round section). The board is under
bending load. The board is vertical on the right sight of the image. The local red area is showing a crack in the
soldering part. Image area approx. <2mm.
Image 4: The main strain of measuring a solder ball d=300µm under horizontal shear stress is shown.
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Reference coordinates and contour of the mobile phone.
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This article describes the measurement and analysis of the operation deflection shapes and rigid body vibration motions of a mobile phone excited by its vibration alert. The mearurement is done, using a non contact, 3D, full-field, high speed stereo image correlation system in combination with the new Vic-3D FFT module analyzes the recorded deformation data in the frequency domain by phase-separation method.
The measured deformations and displacements during the vibration alert are evaluated against the reference state for each stereo image pair. In this case the recording time covers about 5,5 seconds with 1000 FPS corresponding to about 5500 single measurements.
The following figure show the average vibration amplitude U.
The film shows a DIC Measurement using Vic-3D on a concrete beam during a three point bending test. The first crack opening <1µm is located at the lower right side of the beam.
Final conditions: Over the entire length of the concrete beam several cracks have formed.
