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Shearography / ESPI Systems

 

Shearog­ra­phy and elec­tron­ic speck­le pat­ter inter­fer­om­e­try (ESPI) are laser based, opti­cal mea­sure­ment meth­ods, work­ing full field and non contact.

The Shearog­ra­phy sys­tems are applied for non destruc­tive test­ing, but also for vibra­tion, defor­ma­tion and strain mea­sure­ment. The res­o­lu­tion of the dif­fer­en­tial defor­ma­tion is a frac­tion of the wave length only und thus in the nanome­ter range and below. The laser wave length is the ref­er­ence scale, so the res­o­lu­tion is inde­pen­dent of the field of view. The field of view is in the range of mm² to m². The prepa­ra­tion of the object in only required for sur­faces, which are opti­cal­ly non cooperative

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 Application: Non Destructive Testing

The main field of appli­ca­tion of the Shearog­ra­phy sys­tems of isi-sys is non destruc­tive test­ing (NDT).

The full field dif­fer­en­tial defor­ma­tion mea­sure­ment of shearog­ra­phy enables to locate espe­cial­ly struc­tural­ly and mechan­i­cal­ly rel­e­vant defects such as delamination’s, cracks or void due to local inho­mo­ge­neous defor­ma­tion and strain dis­tri­b­u­tion, when an exter­nal load is applied.

In the prac­ti­cal appli­ca­tion, this can be a ther­mal load via light sources or hot air guns, dynam­i­cal load via Piezoshak­ers or mechan­i­cal load­ing steps such as change of the inter­nal pres­sure of tubes and tanks or vac­u­um load­ing by vac­u­um cham­bers or vac­u­um hoods.

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DIC (Digital Image Correlation)

 

Dig­i­tal image cor­re­la­tion is applied in sol­id mechan­ics, mate­r­i­al research and devel­op­ment of mechan­i­cal­ly loaded mate­ri­als, com­po­nents and struc­tures. DIC con­tributes here espe­cial­ly due to the non con­tact and full field mea­sure­ment of defor­ma­tion and dis­place­ments and the derived quan­ti­ties such as strain, vibra­tion, motion and veloc­i­ties for analy­sis of the mechan­i­cal prop­er­ties. The results are use for val­i­da­tion of simulations.

 

The mea­sure­ment results orig­i­nate from the sur­face of the object itself usu­al­ly by stereo cam­era sys­tems and eval­u­at­ed with VIC 2D/VIC 3D soft­ware, but also with­in the sol­id by com­put­er tomog­ra­phy sys­tems (CT´s) and VIC Vol­ume. isi-sys is sys­tem inte­gra­tor for VIC soft­ware in Europe and close devel­op­ment part­ner of Cor­re­lat­ed Solu­tions, USA.

The res­o­lu­tion of the defor­ma­tion and strain as well as its spa­tial and time res­o­lu­tion is depend­ing on the sys­tem con­fig­u­ra­tion. DIC sys­tem of isi-sys reach nanome­ter sen­si­tiv­i­ty as well as time res­o­lu­tion in nanosec­ond range. They have been applied on field of view below one mm² und above 100m², such as on rotat­ing wind tur­bine blade with a diam­e­ter of 114m.

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Application Range of DIC for Strain and Deformation Measurement

DIC is applied for sta­t­ic and dynam­ic three dimen­sion­al strain and defor­ma­tion mea­sure­ment in the range of from 0,001% up to 1000% and above as well as for fatigue test­ing and mon­i­tor­ing. Using high res­o­lu­tion cam­eras with lin­ear and low noise sen­sor prop­er­ties a high spa­tial res­o­lu­tion can be achieved, too. Time res­o­lu­tion is actu­al­ly pos­si­ble up to 5 mil­lion frames per second.

DIC enabled a mea­sure­ment, which have not been pos­si­ble with con­ven­tion­al meth­ods such as at high tem­per­a­tures, at high strains or on small field of view with high spa­tial res­o­lu­tion. In a num­ber of cas­es DIC has replaced con­ven­tion­al meth­ods such as strain gauges or exten­some­ters – espe­cial­ly in the area lf devel­op­ment and research due to the full field and non con­tact work­ing principle.

Due to its advan­tages and due to the improved cam­eras and increas­ing com­pu­ta­tion pow­er the dig­i­tal image cor­re­la­tion sys­tems have dri­ven con­ven­tion­al opti­cal meth­ods for strain and defor­ma­tion such as Pho­toe­las­tic­i­ty and Elec­tron­ic Speck­le Pat­tern Inter­fer­om­e­try out of the mar­ket to a wide extend.

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Video Stroboscope

 

Used for sim­ple visu­al­iza­tion, mon­i­tor­ing and record­ing of vibra­tions and rota­tions in slow-motion. For quan­ti­ta­tive eval­u­a­tion in sub­pix­el range, it can be extend­ed with image cor­re­la­tion (see above).

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Application: Vibration Analysis

The com­bi­na­tion of Video Stro­bo­scopes or High Speed Cam­eras with dig­i­tal image cor­re­la­tion (see above) is used for vibra­tion mea­sure­ments apply­ing the phase res­o­nance or phase sep­a­ra­tion method. The VIC-FFT mod­ules enables to analyse oper­a­tion deflec­tion modes full field and 3D based.

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Piezoshaker Systems

 

 

Designed for vibra­tion exci­ta­tion in the range from 1–100kHz espe­cial­ly for non destruc­tive test­ing and vibra­tion analy­sis. The piezoshak­er exci­ta­tion sys­tems include spe­cial light weight high pow­er piezo ampli­fiers for mobile appli­ca­tion in NDT with shearog­ra­phy and thermography.

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Application: Non Destructive Testing

The video on the right shows the lamb waves, gen­er­at­ed by the piezoshak­er, that is attached at the bot­tom of the spec­i­men. The waves trav­el across the object sur­face and excite the five local sub­sur­face defects on the top. The local defects vibrate dif­fer­ent­ly, depend­ing on their local mechan­i­cal prop­er­ties (stiff­ness).

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