Jan T. Malmo

Interferometric measurements of high temperature objects by electronic speckle pattern interferometry

Electronic speckle pattern interferometry with a cw laser has been used to study objects at very high temperatures. Interference patterns were observable to 1700°C, while high contrast interference fringes could be recorded up to 1550°C. These temperature limits were mainly set by the onset of surface reactions and melting of the objects. Examples on how the technique can be used to study deformations, oxidation shell growth, and melting zones are presented.

Long-Distance Electronic Speckle Pattern Interferometry

Electronic speckle pattern interferometry has been used to measure the vibrations and deformations of objects located far from the optical head. Vibration recordings were made for a total path-length difference of up to 200 m with the object outdoors in bright sunshine. This limit was determined by practical considerations. For deformation recordings, turbulence and mechanical instabilities create a problem, and a more realistic limit is a path-length difference of about 50 m under stable, indoor conditions.

Interferometric measurements of objects in water by TV-holography

Abstract The use of full field interferometry in sub-water conditions is restricted by range, visibility, stability and turbidity. In this paper the authors discuss how the inherent stability and high sampling rate of TV-holography (ESPI) overcome most of these problems. Instrumentation for work under laboratory and field conditions is proposed. Examples of deformation and vibration recordings of submerged test objects are shown, including the use of digital image processing to provide end documentation of high quality, better resolution and easier interpretation.

Computerized vibration analysis of hot objects

A system for automatic data acquisition and fringe analysis based on phase shifting TV- holography is described. The system has been used to analyze vibrating objects heated to high temperatures.

Vibration Analysis And Deformation Measurements At High Temperature By TV-Holography

TV-holography is used in vibration analysis and surface inspection of very hot objects. Vibrational behavior (resonant frequencies, phase and amplitude of vibrations) has been studied as a function of increasing temperature. To reduce the effect of turbulence we use continuous averaging of TV-frames. Among typical applications of this technique is the testing of turbine components. We also show some examples of deformation measurements for various temperatures up to about 3000°C. The temperature limits are mainly set by the accessible laser illumination to suppress the background radiation. To block the background radiation we use narrow-band interference filters centered at the laser wavelength.

Deformation Measurements At Very High Temperatures By ESPI And Moire Methods

We describe two optical methods which have been used to measure the deformation and general behaviour of objects heated to high temperatures. TV-holography or ESPI has proven capable to follow and measure the surface behaviour and deformation with interferometric sensitivity to temperatures about +1600 °C, where the temperature limit is mainly determined by practical experimental problems and is not of fundamental character. Some preliminary results will be presented. The Moire method can be used to measure in-plane object movements to temperatures so far up to about +1300 °C by recording the variation in emissivity of an inscribed surface grating without external illumination.

TV-Holography at High Temperatures: In-Situ Observations of the Oxidation of Advanced Materials

TV-holography provides real-time mapping of the deformations and vibrations of surfaces, and is relatively immune towards object instability due to the combination of short exposure and high framing rate. By use of image processing the fringe pattern can be converted into absolute values of displacement or vibration amplitude and phase. Study of oxidation represents a new interesting application of the technique.

Interferometric Studies Of Very Hot Objects By Use Of Tv-Holography (ESPI)

In this paper we outline the problems encountered when doing interferometric testing of very hot objects. We show how the TV-holography (ESPI) system can be used to test objects heated to temperatures close to the melting point of the material. In the experiments we have monitored vibrations, and surface behaviour of objects heated to temperatures close to 3000C. The tertmratxre limits are apart from microstructure changes and excessive turbulence, set by the accessible laser illumination to suppress the background radiation.

Recent Application Of Electronic Speckle Pattern Interferometry At The Norwegian Institute Of Technology

The introduction of compact, robust and stable ESPI-instruments has opened for new applications of the technique outside the laboratory environments. We briefly describe a typical system and discuss how it may be used in hostile environments to measure on difficult objects.