In this application video, a 3-cam (5 Mpx) TestDIC system is used to analyse the displacement and strain of a wooden sample
with various holes sizes undergoing a 3-point bending test. The sample is loaded from 0 N to 1500 N, then unloaded.
The TestDIC is a fixed setup system whereby the cameras are permanently mounted, and the lenses are fixed in both focus and
aperture. This removes the needs to perform any adjustment of the camera and/or lenses. It also relinquishes the need to
calibrate the projection of the test setup. Two laser pointers are used to aid the user in adjusting the correct distance-to-object
(DtO). At the point of intersection between the two laser pointers, the correct distance and point of focus has been set.
In the measurement, the acquisition speed/camera frame rate of 15 Hz is selected. The recording procedure is used, from
an available template, whereby every 5th image is saved at the frame rate.
After acquisition of the measurement images, the correlation evaluation is performed whereby the central camera is selected to
be the reference camera, known as the Central Reference Camera Perspective (CRCP). This approach defines the facet/subset
generation on the camera with the lowest stereo angle, reducing perspective distortion, and maximizing both in-plane sharpness
and out-of-plane depth-of-field (DoF). It also improves measurement accuracy by 30%, as opposed to using a 2-camera setup.
In the graphical visualization, the total displacement with rigid body motion removed, can be seen. It is clear that about the
point-of-contact from the die, the right-side of the circle deforms slightly more compared to the left-side. However the
distribution seems relatively symmetrical across both sides. This indicates that there has been local plastic deformation on the
right-side of the circle. After observation of the line gauge result, is clear that permanent deformation has occurred, in that
the sample has plastically expanded (along the gauge line) of ca. 25 um.
From the 2D-overlay of the engineering principal strain 1 (major strain) and from the virtual circle gauges #1 (underneath the die)
and #2 (above the resisting die), the strain is ca. 4 mstrain higher above the resisting die, however after unloading the strain
recovers more than directly under the die. The (red) strain concentrations around circle #2 indicate the direction and location
of premature fracture & failure.
3-Point bending test of a wooden sample with various hole sizes using the TestDIC system in Istra4D V4.11
To learn more about how Dantec Dynamics can help you solve your testing challenges, contact us today.
