In case of the here showed example of use, the strain distribution on a segment of a particularly reproduced foot of a fir tree of a blade under cyclic loading is inspected. The term of measurement have been given force guided due to a trigger signal, whereas the first ten cycle of load is recorded with a release of 80 measurements. The total number of measurements averages therewith 800 load cases. The first picture shows the test rig - consisting ofa devise of tensile test (reclined) and the aligned stereo camera system on the crossbar beyond.

To the resolution of the measuring problem, the stereo gray scale value correlation is used. The system hardware is based on isi-stereo camera system (release: 12 bit/Pixel, SXGA 1392x 1040 Pixel), mounted on a stand.

The attitude and choise of AOI is given by the perspective of the stereo-camera-system. Due to the limited accessibility, a compromise for the evaluable face had to be found. Both pictures below show the camera image of the left or the right camera of the cut-out of the object, preparated with speckled patterns.

The following picture shows the scaled color main strain distribution e_1 and the attendant main bearing of strain (lines of direction) of the AOI at the term of the first load cycle. The cutted area below and left to the chamfer (lila) stayes unloaded during the examination (expansion=0) and serves as reference point for the supervision and method of the noise component of the measurement. The maximum of the expansion (red) stands at  the curve of the tooth flank of the blade root. The direction of the main expansion telescopes there parallel to the tooth flank and devolves then to the right part into the direction of tension of the tensile test machine.

The next chart shows the main extention e_1 of a point near the maximum for the first ten load cicles. Because a force controlled triggering has been used, the horizontal axis advertises the number of measurements and should only be reckoned as limited time axis. It is clearly noticeable, that the extention retaines a relatively big ductile allotment already after ten load cycles. The purple area below at the left is the unstressed reference range as already in the picture above.

In the second picture, the reference block is represented. The AOI is square and red framed. The size of the measuring field averages about 8mm x 10mm. A special aspect of this test is the very small measuring face with high spatial release, by comparison with DMS. Compared with finite elements, a high accuracy could be achieved.

Stereo-
camera system

Lighting by
cold light source

Application strain measurement

- Next example     - Application strain measurement    - Used product (Image corr.)

Copyright by isi-sys GmbH, T:++49 (0) 561-739798-0, info@isi-sys.com, last update on 12. jul 2010

Information:
+49 5617397980
info@isi-sys.com
Impressum

News:
Vacuum hood
Suction cup tripod
NDT Set