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Author: Ibrahim Al-Qassab

Combinaton of Multiple Stereo Systems

Parallel use of stereo systems

Apply­ing mul­ti­ple sys­tems enables the enlarge­ment of the FOV and/or to increase the spa­tial res­o­lu­tion. Dif­fer­ent meth­ods are avail­able for com­bin­ing their results and coor­di­nates by the VIC soft­ware. A unique method with high­er accu­ra­cy than  onven­tion­al ones enables to com­bine any obser­va­tion direc­tions — in this exam­ple, side by side sys­tems (right image) — even with­out an over­lap of the FOV, which is required for the con­ven­tion­al stitch­ing method. This dou­bles the spa­tial resolution.

 

 

Flexibility in combination of multiple systems

Here, opposed sys­tems oper­ate at dif­fer­ent field of view ranges. Click for the high-res­o­lu­tion mea­sure­ment of prin­ci­pal strain ε1 and ε2 tak­en from the backside.

 

 

 

 

 

 

 

Spatial resolution and accuracy

VIC-3D Pro­fes­sion­al Sys­tems deliv­er full­field, high­ly accu­rate shape, motion and defor­ma­tion mea­sure­ments. Lim­its can be traced for indi­vid­ual setups by sim­ple pro­ce­dures out­lined in the VDI-2626 direc­tive espe­cial­ly devel­oped for dig­i­tal image cor­re­la­tion (DIC). This exam­ple shows prin­ci­pal strain ε1 and ε2 (click to start video). In cas­es with local high peaks, a high spa­tial res­o­lu­tion can be the key to achiev­ing pre­ci­sion and accu­ra­cy for peak strain, in addi­tion to excel­lent SNR and cal­i­bra­tion of VIC. Video gen­er­at­ed with­in VIC iris work­space by isi-sys.

 

A high opti­cal res­o­lu­tion com­bined with suit­able speck­le size and den­si­ty is not only required to resolves the spa­tial strain dis­tri­b­u­tion as in the case before, but also improves accu­ra­cy in par­tic­u­lar for strain peak deter­mi­na­tion (upper right sketch), due to the fact that sub­set and strain fil­ter sizes (in pix­el scale) are fur­ther reduced (in absolute scale) com­pared to the peak strain dis­tri­b­u­tion. This fact also mat­ters for strain gauge size, as they are also not point strain mea­sure­ment device but inte­grat­ing over their length. The low­er right image is zoomed down to the pix­el  size range in VIC. It shows a high end case using the Blue-Fal­con. The lit­tle grey val­ue squares (two marked green) cor­re­sponds to the inten­si­ty val­ue of a pix­el and cov­er an area of 1.83 μm2. The vis­i­ble speck­le diam­e­ters are in the range between 3 to 8 pix­el. The red and yel­low squares also indi­cate the pix­el size oper­at­ing with larg­er FOV (mag­ni­fi­ca­tion 1:7 and 1:14), which would even not resolve speckles.

 

 

Outdoor, Long Distance from Small to Large FOV (Field Of View)

FOV Ranges for Stereo-DIC

The stan­dard FOV ranges from 40 to 400 mm, 4, 8 and 16 m can be extend­ed to very large FOVs not only using mul­ti­ple stereo sys­tems in com­bi­na­tion but also by a sin­gle stereo sys­tem. There­fore, VIC offers spe­cial cal­i­bra­tion meth­ods for large and very large FOV mea­sure­ments that exceed the size of the hand-held cal­i­bra­tion pan­els (> 1 m). We offer the suit­able lens­es and the required hard­ware such a bat­tery dri­ven sys­tems or water pro­tec­tion even for under water applications.

Wind Turbine Blade (FOV > 100 m)

Spe­cial sys­tems for out­door appli­ca­tions, such as for mea­sur­ing bridges or (rotat­ing) wind tur­bines blades with Ø > 100 m are avail­able with cam­era dis­tances of 200 m, con­trolled from a Lap­top oper­at­ing on bat­tery pow­er. Mea­sure­ments by Jan Wind­stroth, Han­nover Uni­ver­si­ty, Insti­tute for Tur­bo­maschin­ery and Flu­id Dynam­ics, Germany.

 

Below: Fea­si­bil­i­ty of the mea­sure­ment in a mod­el study back in 2013. Mea­sure­ments by Jan Wind­stroth, Han­nover Uni­ver­si­ty, Insti­tute for Tur­bo­maschin­ery and Flu­id Dynam­ics, Germany.

 

 

Outdoor Wave Measurement ( FOV 75 m x 30 m)

Full Scale CFD Validation using Ship Performance and Wave Pattern Measurements of a Mega Cruise Ship

Anoth­er appli­ca­tion, in col­lab­o­ra­tion with the Mar­itime Research Insti­tute of Nether­lands, involved record­ing the wave for­ma­tion behind a 330 m long cruise ship sail­ing at 20 knots. Start the video of the stern wave mea­sure­ment (Video gen­er­at­ed with­in VIC iris work­space by Marin.NL).

Sources:
(1)https://asmedigitalcollection.asme.org/OMAE/proceedings-abstract/OMAE2022/85925/V007T08A041/1147961
(2)https://www.marin.nl/en/news/full-scale-cfd-validation-using-ship-performance-and-wave-pattern-measurements-of-a-mega-cruise-ship

Long Distance Small FOV (Stereo-DIC)

Out­door mea­sure­ment on small field of view  (FOV) at long work­ing dis­tance with high sen­si­tiv­i­ty and/or accu­ra­cy require not only spe­cial cal­i­bra­tion meth­ods for 2D and 3D appli­ca­tions but also spe­cial record­ing and eval­u­a­tion meth­ods, as these appli­ca­tion under­lay­ing high noise influ­ences such as ther­mal air waves result­ing into opti­cal Schlieren.

 

 

 

 

 

 

Bending Test

The video exam­ple shows a four point bend­ing test set­up for a met­al beam with drilled holes (side view). The beam sur­face is mea­sured by a VIC-3D Pro­fes­sion­al stereo sys­tem from below via a sur­face coat­ed mir­ror. The mea­sured prin­ci­pal strain are pro­ject­ed on the mir­rored image of the sam­ple sur­face. Mea­sure­ment of 9/2023, Uni­ver­si­ty of Lübeck.

VIC-Gimbal

VIC-Snap APP and tar­get fixtures:
The cal­i­bra­tion pro­ce­dure of VIC can be done eas­i­ly done mov­ing the tar­gets man­u­al­ly. How­ev­er for small field of view where man­u­al posi­tion­ing of the tar­gets and the influ­ence of motion blur­ring becomes dif­fi­cult we offer the BCTF 50 and now new the VIC cal­i­bra­tion gimbal.

test

The VIC cal­i­bra­tion gim­bal for auto­mat­ed cal­i­bra­tion of VIC-3D sys­tems via USB & VIC-Snap or Wifi & VIC-Snap App, which espe­cial­ly is use­ful for non reach­able areas such as cli­mat­ic chambers

Automated NDT system for filament wound tubes

This sys­tem is used for auto­mat­ed, non-destruc­tive test­ing of fil­a­ment wound pipes. The pipes are rotat­ed in 90° steps around their axis to mon­i­tor four cir­cum­fer­en­tial seg­ments. Two SE4 sen­sors with 2 x 4000 px are applied per seg­ment along the tube axis. For a tube length of 1m @ 8000 px, this leads to 0.125 mm/px spa­tial pix­el res­o­lu­tion for all 8 image seg­ments. After insert­ing the pipes the ends are auto­mat­i­cal­ly sealed and inter­nal pres­sure is used as the load­ing method. Since this cor­re­sponds to the usu­al oper­at­ing load of the tubes, the mea­sured defor­ma­tion dis­tri­b­u­tion visu­al­izes main­ly the rel­e­vant struc­tur­al defects in con­trast to oth­er load­ing meth­ods such as ther­mal load­ing.

Due to the high defor­ma­tion sen­si­tiv­i­ty of the SE4 sen­sors com­bined with the high spa­tial pix­el res­o­lu­tion even the small­est defects can be detect­ed. An oper­a­tor final­ly cat­e­go­rizes the object as IO / NIO. Auto­mat­ed or AI-based image analy­sis is pos­si­ble, but it depends on the appli­ca­tion and detec­tion require­ments. At the end of the mea­sure­ment, a report is gen­er­at­ed and auto­mat­i­cal­ly stored as a PDF in a direc­to­ry spec­i­fied by the user.

The tubes are insert­ed and removed man­u­al­ly. An exten­sion with col­lab­o­ra­tive robots or inte­gra­tion into pro­duc­tion lines is pos­si­ble. Sev­er­al thou­sand tubes have already been test­ed per year with­out prob­lems and maintenance.

Automated NDT on a guide vanes ring of a jet engine

Here the SE4 Sen­sor is used in com­bi­na­tion with an auto­mat­ic attached Piezoshak­er for dynam­ic exci­ta­tion. The SE4 is oper­at­ed in time aver­age mode dur­ing fre­quen­cy sweep­ing for detect­ing local defect res­o­nances of the sol­der­ing of the seal­ing band. The two mea­sure­ments on the left show pre­pared defects. Upper left: hor­i­zon­tal shear­ing, time aver­age mode; Below: ver­ti­cal shear­ing and stro­bo­scop­ic mode for phase reconstruction.

 

Blue-X-Lite (LED light source)

The Blue-X-Lite is a entry-level professional flicker free lighting solution for DIC. Short wave length, small bandwidth, pulse mode, focusable.

  • The Blue-X-Lite can be used in con­tin­u­ous wave mode (CW) or in pulsed mode (Pulse) with 20 W. Due to its fast rise times < 100 ns in com­bi­na­tion with spe­cial trig­ger unit it is also suit­able for syn­chro­niza­tion with DIC sys­tems with stro­bo­scop­ic illumination.
  • Light inten­si­ty can be con­trolled step­less up to  60% light inten­si­ty for con­tin­u­ous wave mode (CW) and 100% light inten­si­ty for pulse mode (Pulse).
  • Frame rates: Two ver­sions are avail­able with trig­ger fre­quen­cy up to 1,000 Hz or 10,000 Hz.
  • The Blue-X-Lite can be eas­i­ly attached direct­ly to the stereo bar by flex­i­ble arms for indi­vid­ual adjust­ment of the light direction.
    The fan­less design offers the advan­tage of no vibra­tions trans­mit­ted to the stereo bar.
  • Mount­ing: 1/4″, 3/8” and M6 threads for tri­pod or flex­i­ble mount­ing arms (bot­tom). M4 threads (front) for mount­ing to VIC-Pro­fes­sion­al fine adjust­ment cam­era mounts.

Application for Optimization of Laser Beam Welding by Ultrasonic Wave Superposition

The poten­tial of ultra­son­ic wave super­po­si­tion to improve the prop­er­ties of laser beam weld­ing was inves­ti­gat­ed using sta­tion­ary and mov­ing Piezoshak­er-Sys­tem at the Depart­ment of Cut­ting and Join­ing Man­u­fac­tur­ing Process­es (tff) at the Uni­ver­si­ty of Kas­sel. An exam­ple of this is the test on the high-strength steel alloy 22MnB5, which is pre­sent­ed here. Adap­ta­tion to oth­er weld­ing process­es and mate­ri­als is possible. 

The influ­ences of the var­i­ous exci­ta­tion para­me­ters of the Piezoshak­er on the ultra­son­ic wave super­po­si­tion were inves­ti­gat­ed, e.g. the dis­tri­b­u­tion of the AlSi-coat­ing par­ti­cles with­in the join­ing zone as well as the weld seam prop­er­ties [1].

The isi-sys Piezoshak­er-Sys­tem was used for the mov­ing wave super­po­si­tion, as shown in Fig. 1 The sys­tem con­tains a 2‑channel Piezoam­pli­fier of the HPDA‑0–180-2C series and two Piezoshak­ers of the PS-W-02 series. The Piezoshak­ers are firm­ly con­nect­ed to the laser optics via a mount and are moved rel­a­tive to the com­po­nent sur­face at a defined dis­tance from the laser beam. These are pressed onto the com­po­nent sur­face with a defined force using pneu­mat­ic cylin­ders. Uneven­ness and dif­fer­ences in the thick­ness of the join­ing part­ners can be compensated.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. 1 (left): The dis­tri­b­u­tion of the AlSi-coat­ing in com­par­i­son with­out (a) and © and with (b) and (e) influ­ence of an ultra­son­ic wave super­po­si­tion by isi-sys Piezoshak­er dur­ing laser beam weld­ing with false-col­or images of EDS-analy­sis (d) and (f) [1]

Fig. 2 (right): Super­im­posed SEM-images and sec­tioned inverse pole fig­ure map­pings (IPFM) of a weld seam with­out (a) and with ultra­son­ic super­po­si­tion (b) mea­sured with elec­tron backscat­ter dif­frac­tion shown as inverse pole fig­ure in Z‑direction [1]

[1] Pub­lished in: C. Wolf, S. Völk­ers, I. Kryukov, M. Graß, N. Som­mer, S. Böhm, M. Wun­der, N. Köh­ler und P. Mäck­el, „Enhance­ment of Weld­abil­i­ty at Laser Beam Weld­ing of 22MnB5 by an Entrained Ultra­son­ic Wave Super­po­si­tion,“ In: Mate­ri­als 2022, Bd. 15, 4800.