Rivets are proven to join aluminum sheets or fasten them to the support structure in light weight constructions.

To install and test a new ordered ARAMIS system in the Testing Technology laboratory of AIRBUS, Bremen, Mr. Torben Kluwe prepared a simple test set-up, consisting of two aluminum sheets (material 3.1364-T3), joined together using three rows of rivets.

The sample was spray-painted using an aerosol can with black mat acrylic paint. The spray button was pressed very gently to produce a high-contrast splash pattern on the area to be measured (figure 1).

Then, the sample was installed in the tensile testing machine and the ARAMIS 3D system was calibrated and positioned in front of the sample. During the tensile test, the cameras are to observe and record the 3D displacement of the rivet area and the corresponding tensile force, in regular time intervals. In addition, the applied tensile force is read in and stored. The value of the actual force is also assigned to each snapped image pair. Then, the behavior of the sample during the test shall be evaluated and displayed graphically.

Fig. 2 shows the resulting load displacement diagram. Immediately visible is the shearing of the rivets shortly after load step 60 and the total failure shortly after load step 80.

The deformation of the sample is visible in the captured image series (fig. 3). However, to get detailed results, the graphical plot of the measured deformation is used. First, the coordinate system of the gathered data was adjusted to the actual measuring set-up and the lower end of the front sheet was used to define the location of zero movement.

Figure 4 shows the local deformation of the rivets and the asymmetrical and non-uniform displacement of the sheet.

Masking the rivets shows the deformation of the sheet very clearly. As often in tensile tests of riveted sheet metals, the sample under load starts tilting in Z-direction (vertical to the sheet surface). In vertical direction, only small displacements are measured.

Strain data often give an easier understanding of the behavior of a sample under load. Therefore, figure 6 displays the differentiated displacement values (strain values) of the load stage 80 graphically. For the actual calculation of the strain values in the left image, a short base length of 0.57 mm was used, showing local strain maxima and inhomogeneities. To show the averaged deformation in the sheet metal, a longer base length of 1 mm was used.

Figure 7 shows the sample shortly before the failure, with clearly visible rivets, at load stage 80, in the left image, and after the failure, at load stage 84, in the right image.

Figure 8 shows the strain distribution shortly before the failure of the rivets (load stage 80). Clearly visible is pressure-strain in the area of the lower rivets and tensile strain in the area of the other rivets. The area of high strain is caused by the bending of the sheet under load.

In figure 9, the strain values in a section parallel to the tensile direction, as indicated in figure 8, is shown. Here, the total strain before the failure and the remaining strain after the complete failure is clearly visible.

This test set-up was made to install and test the newly ordered ARAMIS system. Of course, the measuring set-up as well as data gathering and analysis could be optimized. However, this test demonstrated that already with a minimal preparation reasonable measuring can be carried out within a short time visualizing the behavior and the characteristics of the actual probe under load.

By courtesy of AIRBUS Bremen, Testing Technology