In this application video, a 3-cam (5 Mpx) TestDIC system is used to measure the deformation and strain of an aluminium coupon
with a centric hole cutout undergoing a tensile test. The sample is loaded from 0 N to 1500 N.
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 need to perform any adjustment of the camera and/or lenses. It also relinquishes the need to calibrate
the projection, each time, before a new test setup is used. 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. A real-time overlay of the speckle pattern quality can be seen, indicated the standard deviation with respect to
a selected facet/subset size.
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 3rd 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, a 2D-overlay of the Y-displacement (in um) with rigid body motion removed, can be seen.
(Y-displacement direction is along the loading axis) At 1500N, the total displacement was ca. 140 um and eng. strain was 1.3
mstrain, as shown in the temporal plots of the virtual line gauge.
From the 2D-overlay, of the LaGrangian principal strain 1 (major strain) (in mstrain), the strain concentration around the middle
centric hole can be seen, reaching a max of 3.3 mstrain.
Tensile test of an aluminium coupon with a centric hole cutout 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.
