Speckle-Holographic Stresses-and-Defects Inspection
Tech Area / Field
- INS-MEA/Measuring Instruments/Instrumentation
- PHY-OPL/Optics and Lasers/Physics
3 Approved without Funding
Vavilov State Optical Institute (GOI) / Research Institute for Complex Testing of Optical Devices, Russia, Leningrad reg., Sosnovy Bor
- Leningrad NPP, Russia, Leningrad reg., Sosnovy Bor
- International Atomic Energy Agency, Austria, Vienna\nThe University of Warwick / The School of Engineering, UK, Coventry\nInstitute of Physical and Chemical Research (RIKEN), Japan, Saitama, Wako\nUniversity of Portsmouth, UK, Portsmouth\nMetroLaser,Inc, USA, CA, Irvine\nUniversity of Portsmouth / School of Mathematics and Computer Science, UK, Southsea\nHOLOGRAPICS INC., USA, NY, Long Island City\nIllinois Institute of Technology / Armour College of Engineering & Science, USA, IL, Chicago\nLaboratorium Soete, Belgium, Gent\nFachbochschule Ulm IAF Automatisierungssysteme/ Labor Technische Optik, Lasertechnik, Optoelektronik, Germany, Ulm\nCentre Spatial de LIEGE, ULg, Belgium, Liege\nUniversity of Aberdeen, UK, Aberdeen\nMD Diffusion, France, Schiltigheim
Project summaryPurpose of the project: scientific solution of the problem of non-contact non-destructive control over residual stresses and defects on the base of combination of: a) holographic and speckle-interferometric methods for defects measurements and b) lasers methods of acoustic waves and local heat fields generation in the object under control, creation and study of an operating prototype of portable instrumentation illustrating the validity of this approach.
The methods of residual stresses and defects inspection (cracks, caverns and etc) should be in compliance with the following requirements needed for reliable and prompt detection of degraded sections in constructions and places of possible destruction: high accuracy in measurements, ease of data interpretation, non-contact measuring method, non-destructive measuring technique, applicability for a wide range of materials.
Analysis of the methods and means being used for inspection of residual stresses and defects reveals that the potential of holographic interferometry and speckle interferometry complies the set of requirements given above contrary to the known methods of inspection like X-rays, acoustic, magnitoelastic and eddy current methods. Available holographic and speckle interferometric methods provide high accuracy in measurements, ease of data interpretation and possibility to use them for inspecting a wide range of materials. However, drawbacks of these methods restrict their practicality.
Holographic methods devised by now are partially destructive due to contact mechanical probing actions like drilling of non-through holes, forcing an indent and etc. Application of mechanical probing actions renders the measuring process non-technological. In this case to perform the mechanical action it is necessary to remove the interferometer from the section under control upon recording the hologram of surface initial state and then to replace it on its original position with a sub-micron accuracy for taking measurement of deformation in the area of the probing action. It calls for complicated cinematic devices and extra time for interferometer adjustment. A version of experimental-calculation speckle interferometric method devised by now for inspection of residual stresses with local laser heating probing action can be used only for measuring residual stresses exceeding 0.9Y, where -yield point. The existing holographic and speckle interferometric methods allow to measure only one component of displacement: normal or tangential one. It provides incomplete data about the nature of the revealed defects and field of residual stresses under control and also limits the range of measurements.
The problem of non-contact non-destructive inspection of residual stresses and defects is proposed to solve by a new approach using a two-stage principle when a combination of methods of holographic interferometry, electronic speckle interferometry and non-contact laser method for generating acoustic waves and local heat fields is of key importance.
First stage - data retrieval about areas of the section under control with the increased level of deformations under vibration load. Vibration load on the operating equipment is realized automatically. Vibration in the section under control on the non-operating equipment is excited by laser radiation. To measure deformation at this stage the combination of holographic interferometry and electronic speckle-interferometry methods is used. The second stage - determination of value, sign and spatial orientation of the residual stresses and defects available. At this stage the combination of holographic interferometry, electronic speckle-interferometry and non-contact laser methods for acoustic waves and local heating fields generation is used.
The combination of speckle-interferometric and holographic methods will make possible to measure normal and tangential displacement components at a time. As a result the accuracy in determination of residual stresses and defects parameters will increase more than twice. Integration of the holographic and speckle-interferometric measuring schemes in a portable unit is proposed to perform by employing recording media with the switching-on sensitivity (for example, photothermoplastic media) and non-conventional optical elements based on holographic optics.
Development of the new method for residual stresses determination from registration of the beginning of non-linear interaction between residual stresses and thermal stresses due to local laser heating and more general theory for arbitrary magnitudes of these stresses in the context of the proposed project will allow to extend significantly the measuring range to the direction of lesser values of residual stresses and in doing so to decrease the detection threshold for construction sections dangerous in respect to their destruction.
Unlike the destructive contact probing actions (holes drilling and indents forcing etc) application of lasers to generate probing acoustic waves and local heating fields permits to exert measurements by non-contact non-destructive methods. In doing so labor input to the measurements will be considerably reduced.
Participants of the project have a wealth of experience in development and application of holographic interferometry for solving the problems of defense and civil purpose. In particular, since 1975 the participants have developed the following: holographic methods for inspection of tapers in hollow blades, a set of holographic interferometers with continuos and pulsed lasers for dynamic deformations detection and control over residual stresses in welded seams, techniques and devices for photothermoplastic recording of holograms, technology of holographic optical elements making for holographic interferometers. Since 1997 a holographic strain-measuring device for control over welding and operational residual stresses made in cooperation between RICTOD and Leningrad NPP has now been in use at LNPP.
Now the participants of the proposed project keep working in the fields related with the basic lines of the project, including development and investigation in holographic means of control over the quality of products, development and investigation in laser radiation sources, development and investigation in methods and means for photothermoplastic recording of holograms, elaboration of methods and means for automated interferograms decoding, elaboration of analytical, experimental - calculation and numerical methods for analysis of stressed-deformed state under different thermoforce quazistatic and dynamic loads, elaboration of calculation methods for residual stresses and deformations, analysis of residual stresses and thermodeformations fields by numerical simulation methods, elaboration and investigation in manufacturing technology for holographic optical elements.
Theoretical and experimental basis for non-contact non-destructive speckle-holographic control over residual stresses fields and defects detection will be developed as a result of the project execution. The methods being devised will allow to remove the restrictions peculiar to the existing holographic and speckle-interferometric control methods: they will broaden the range of measurements, allow to vary measurement sensitivity and exert measurements by non-contact non-destructive methods. A prototype of electronic speckle-holographic instrumentation exhibiting the validity of the approaches proposed will be created and tested. It will make the basis for developing the advanced instrumentation.
The instrumentation and technique proposed are of most importance for prompt control over residual stresses and defects in pipe-line welding seams made from austenite steels in the circle contours at Nuclear Power Plants. Reliability of these pipe-lines operation determines the reliability of NPP operation in whole. Judging from the information obtained at Smolensk NPP the expenses for welding seams preparation and repairs in these pipe-lines during maintenance from 28.08.97 to 05.02.98 made up $ 3.8 mln, losses due to underproduction of energy and heat were not included. The methods and means being devised will be able to reduce these expenses.
The given methods and instrumentation will find use in optimization of welding technological processes in many other industries: aircraft- ship- and bridge-building, oil and gas industries etc. Their application will provide high operational reliability of welded elements and constructions.
Besides, the devised methods and means including separate units will find use in electronic industry for non-destructive chip control, for laser treatment of materials, for vibration diagnostics of various units and equipment, for automated interferograms decoding.
The project will allow the specialists of weapon industries to take part in peaceful fundamental and applied investigation for creating new methods and instrumentation capable of solving the problems of constructions reliability for nuclear power, oil, gas industries and motor-car, ship- and aircraft-building. The work on the project will aid in international integrating of scientists.
Foreign collaborators may help the participants of the project: a) to improve execution of the project, b) to involve in conducting parallel research effects carrying out in other countries, c) to assist in identifying the most appropriate sources of specialized materials and equipment which are to be used in our project. Foreign collaborators will: a) take part in discussions and analysis of the results obtained and preparation for joint publications, b) comment upon technical reports being presented to ISTC by the participants of the Project, c) take part in cross-checking of the obtained results with the use of Doppler interferometry, d) collaborate on commercialization of the results after the project has been completed, e) take part in exchange of information about new optical methods of non-destructive control; f) share of materials to manufacture photothermoplastic layers and layers of dichromate gelatin, g) test electronic speckle-holographic system.
The Project will include the following stages: a) theoretical study of mechanisms for displacements field formation on the surface of the object under control in respect to the parameters of residual stresses and defects, characteristics of the probing acoustic wave on laser excitation and characteristics of local laser heating (radiation energy distribution in laser beam, heating duration and size of the heated area), b) preparation of experimental base for the investigations, c) experimental study of mechanisms for displacements field formation on the surface of the object under control in respect to the parameters of residual stresses and defects, characteristics of the probing acoustic wave on laser excitation and characteristics of local laser heating, d) making and study of the prototype of electronic speckle-holographic system for non-destructive control over residual stresses and defects.
For the theoretical study of mechanisms for displacements field formation on the surface of the object under control on local laser heating an approach based on solving a thermoelasticplastic problem by the finite elements method will be used. Displacement fields in relation to: residual stresses characteristics, material characteristics, local laser heating power, duration and heated area will be calculated. The following results will be obtained: a) calcula tion - analytical relationships for determining residual stresses from interferograms of displacements, b) estimation of method's sensitivity and range of measurements, c) requirements to spectral, power, time and geometric parameters of local laser heating.
For the theoretical study of mechanisms for displacements field formation on the surface of the object with defects on laser excitation with probing acoustic wave an approach based on solving the dynamic elastic-plastic problem by the finite elements method will be used. Displacement fields in relation to: type of a defect and depth of its location; materials characteristics; power, duration and size of laser excitation area of probing acoustic wave; local temperature conditions for probing acoustic wave propagation will be calculated. The following results will be obtained: a) calculation-analytical relationships for determining the defect's nature and parameters, b) estimations of method's sensitivity and range of measurements, c) requirements to spectral, power, time and geometric parameters of probing acoustic wave laser excitation.
In experimental studies of mechanisms of displacements field formation on the surface of the object's section under control when laser generation of probing acoustic and thermal fields an approach using nature samples with the known characteristics of residual stresses and defects will be applied.
In creating the prototype of electronic speckle-holographic system with separate measuring of normal and tangential components of displacement an approach based on integration of holographic and correlation speckle-interferometric schemes will be used. To integrate these schemes it is proposed to develop and investigate an integral element containing CCD- camera, holographic recording medium with switching-on sensitivity for prompt reverse hologram recording, an opto-fiber unit for communication with laser radiation source, a device for light beams formation for illuminating the object's section under control and reference beam formation in hologram recording. Photothermoplastic layer with switching-on sensitivity is proposed to be used as a recording medium and holographic optical elements with dichromate gelatin are to be used as forming optical elements. Optical calculations will be performed by a "Demos" program available in RICTOD. The given program allows to exert calculations both conventional and holographic optical elements. Software for quality improvement of correlation electronic speckle-interferograms will be worked out.
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