10:00
Speckle and Interferometry
Chair: Andreas Ettemeyer
10:00
20 mins
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DIFFERENTIAL INTERFEROMETRY FOR REAL-TIME MEASUREMENT IN HIGH CYCLE FATIGUE METAL TESTING
Josef Lazar, Miroslava Holá, Jan Hrabina, Ondřej Číp
Abstract: We present an interferometric method for measurement of strain induced deformation of metal samples in experiments inducing high-cycle fatigue. The motivation is to get real-time information about the deformation of a metal sample under test, its elongation imposed by fast vibrating actuator. The measuring setup was designed to measure only the deformation of the sample in a differential measuring configuration. The measurement technique uses laser interferometry, able to detect the absolute value of the displacement with a link to the fundamental etalon of length with nanometer resolution. The fast vibrations of the sample needed a design of a high-bandwidth detection chain and signal processing of the interference signal. A new concept of a compact differential interferometer is presented which compensates for small tilt of the reflecting surfaces in both reference and measuring paths and thanks to coaxial configuration is free from Abbe errors.
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10:20
20 mins
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6-AXIS LASER INTERFEROMETRY MEASUREMENT SYSTEM FOR A NANOMETROLOGY STANDARD
Jan Hrabina, Miroslava Holá, Josef Lazar, Ondřej Číp
Abstract: We present an overview of approaches to the design of nanometrology measuring setups with a focus on methodology of nanometrology interferometric techniques and associated problems. The design and development of a positioning system with interferometric multiaxis monitoring and control involved for scanning probe microscopy techniques (primarily atomic force microscopy, AFM) for detection of the sample profile is presented. Coordinate position sensing allows upgrading the imaging microscope techniques up to quantified measuring. Especially imaging techniques in the micro- and nanoworld overcoming the barrier of resolution given by the wavelength of visible light are a suitable basis for design of measuring systems with the best resolution possible. The system is being developed in cooperation with the Czech metrology institute and it is intended to operate as a national nanometrology standard combining local probe microscopy techniques and sample position control with traceability to the primary standard of length.
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10:40
20 mins
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PROCESSING TIME-AVERAGE VIBRATION PATTERNS USING LINEAR REGRESSION
Peter Somers
Abstract: When taking measurements on a harmonically vibrating object with an imaging interferometer device such as an ESPI or shearography system, vibration patterns can be obtained after processing at least 3 phase-stepped interferograms. The standard method is based on eliminating phase, yielding Bessel modulated fringe patterns that can be very noisy. Some improvement can be obtained by involving additional measurements in static conditions, but the nature of the fringe pattern remains the same: the vibration amplitude is an argument in the absolute value of a Bessel function. Removing noise by spatial filtering degrades the results at zero crossings of the Bessel function, since the derivative of its absolute value is not continuous there. An alternative method for processing vibration patterns using linear regression is proposed, yielding patterns where the vibration amplitude is an argument of a true Bessel function, not its absolute value. As a result, spatial frequencies associated with the vibration are only half of those obtained with standard methods, and results can be filtered and normalized conveniently.
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11:00
20 mins
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THE MEASUREMENT UP TO THE FOURTH ORDER MODAL DISPLACEMENT FIELDS USING DIGITAL SHEAROGRAPHY
Hernani Lopes, Jaime Monteiro, Mário Vaz
Abstract: This work presents the experimental measurement up to the fourth order derivative of modal displacements fields for free-free aluminum beam. The beam modal rotation fields are directly measured using digital shearography with temporal phase modulation technique and stroboscopic laser illumination. This is created by using two different methodologies: acousto-optic modulator, optical chopper system. The laser short pulses used to illuminate the beam are synchronized with vibration excitation of the beam in order to freeze interference speckle pattern, allowing the application of the temporal phase modulation technique to extract interference phase. The modal rotation of aluminum beam are presented for two different methods of stroboscopic illumination. The beam modal displacement field and their derivatives up to the fourth order are than obtained through numerical integration and differentiation process of experimental modal rotation fields, respectively. The quality of the results are evaluated by the comparison of the fourth order derivatives of the beam first four modal displacements fields with numerical solution, obtain using finite elements method.
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11:20
20 mins
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DYNAMIC SPECKLE INTERFEROMETRY OF MICRO - AND MACRO - PROCESSES ON A SCATTERING SURFACE UNDER HIGH CYCLE FATIGUE LOADING CONDITIONS
Alexander Vladimirov
Abstract: ABSTRACT: The theory of the time-averaging technique of dynamic speckles adapted for study of micro-damage accumulation and detection of plastic deformities under high cycle fatigue loading conditions was reviewed. The results of the theory were used to interpret the data obtained from fatigue testing of a prismatic Charpy-notched bar. The application of the technique to locate the nucleation area of a fatigue crack and determine its velocity was discussed
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