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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Advances in Moire interferometry for thermal response of composites

An experimental technique for the precise measurement of the thermal response of both sides of a laminated composite coupon specimen uses Moire interferometry with fringe multiplication which yields a sensitivity of 833 nm (32.8 micro in.) per fringe. The reference gratings used are virtual gratings and are formed by partially mirrorized glass prisms in close proximity to the specimen. Results are compared with both results obtained from tests which used Moire interferometry on one side of composite laminates, and with those predicted by classical lamination theory. The technique is shown to be capable of producing the sensitivity and accuracy necessary to measure a wide range of thermal responses and to detect small side to side variations in the measured response. Tests were conducted on four laminate configurations of T300/5208 graphite epoxy over a temperature range of 297 K (75 F) to 422 K (300 F). The technique presented allows for the generation of reference gratings for temperature regimes well outside that used in these tests.

Brooks, E. W., Jr.↗
NASA NTRS1983

Moire deflectometry with deferred analysis

A simplified version of moire deflectometry for flow visualization is presented. The modification comprises replacement of the second grating, the ground glass screen, and the camera with a plate film holder to obtain a shadow picture. Postanalysis proceeds by placing a grid transparency of the same periodicity of the remaining glass grating on the negative for projection viewing. The rotational angle between the grating and the plate alters the moire fringe periodicity. Use of the method in studying flows is predicted to reveal weak density gradient areas and shocks.

Rhodes, D. B.↗
NASA NTRS1983

Edge effects in composites by moire interferometry

The very high sensitivity of moire interferometry has permitted the present edge effect experiments to be conducted at a low average stress and strain level, assuring linear and elastic behavior in the composite material samples tested. Sensitivity corresponding to 2450 line/mm moire was achieved with a 0.408 micron/fringe. Simultaneous observations of the specimen face and edge displacement fields showed good fringe definition despite the 1-mm thickness of the specimens and the high gradients, and it is noted that the use of a carrier pattern and optical filtering was effective in even these conditions. Edge effects and dramatic displacement gradients were confirmed in angle-ply composite laminates.

Czarnek, R.↗
NASA NTRS1984

Deformations and strains in adhesive joints by moire interferometry

Displacement fields in a thick adherend lap joint and a cracked lap shear specimen were measured by high sensitivity moire interferometry. Contour maps of in-plane U and V displacements were obtained across adhesive and adherent surfaces. Loading sequences ranged from modest loads to near-failure loads. Quantitative results are given for displacements and certain strains in the adhesive and along the adhesive/adherend boundary lines. The results show nonlinear displacements and strains as a function of loads or stresses and they show viscoelastic or time-dependent response. Moire interferometry is an excellent method for experimental studies of adhesive joint performance. Subwavelength displacement resolution of a few micro-inches, and spatial resolution corresponding to 1600 fringes/inch (64 fringes/mm), were obtained in these studies. The whole-field contour maps offer insights not available from local measurements made by high sensitivity gages.

Post, D.↗
NASA NTRS1985

A comparison of electronic heterodyne moire deflectometry and electronic heterodyne holographic interferometry for flow measurements

Electronic heterodyne moire deflectometry and electronic heterodyne holographic interferometry are compared as methods for the accurate measurement of refractive index and density change distributions of phase objects. Experimental results are presented to show that the two methods have comparable accuracy for measuring the first derivative of the interferometric fringe shift. The phase object for the measurements is a large crystal of KD*P, whose refractive index distribution can be changed accurately and repeatably for the comparison. Although the refractive index change causes only about one interferometric fringe shift over the entire crystal, the derivative shows considerable detail for the comparison. As electronic phase measurement methods, both methods are very accurate and are intrinsically compatible with computer controlled readout and data processing. Heterodyne moire is relatively inexpensive and has high variable sensitivity. Heterodyne holographic interferometry is better developed, and can be used with poor quality optical access to the experiment.

Decker, A. J.↗
NASA NTRS1985

Electronic heterodyne readout of fringes in moire deflectometry

An electronic heterodyne technique is described for the readout of fringes in moire deflectometry. The technique is based on phase measurements of signals generated by a photodetector observing the light transmitted through a traveling moire fringe pattern. The phase of the signal is proportional to the fringe deviation and thus to the deflection angle of the light ray. The phase is measured on line by a standard phase meter with an accuracy of 1 deg or 1:360 of a fringe. The technique, which is precise and sensitive, is demonstrated by detecting and measuring a fringe shift of 0.15 mm corresponding to 0.029 of a fringe.

Stricker, J.↗
NASA NTRS1985

Moire deflectometry with deferred electronic heterodyne readout

The electronic heterodyne technique is applied to the task of deferred readout of phase objects' moire fringes. In combination with the heterodyne readout technique, moire deflectometry constitutes a powerful tool for the study of phase objects, exhibiting high sensitivity, ease of automation and recording, low cost, use of incoherent illumination, and independence from fringe contrast variations.

Stricker, J.↗
NASA NTRS1986

Diffraction effects and special advantages in electronic heterodyne moire deflectometry

Effects of diffraction on the performance of electronic heterodyne readout of moire fringes are investigated. The sensitivity, accuracy, and resolution of the system are calculated, and it is shown that these features are significantly improved compared with the conventional intensity moire readout technique. The sensitivity of the system can be tripled without changing the distance between gratings. The system was evaluated experimentally by measuring the refractive-index derivatives of a weak phase object consisting of a large KD(asterisk)P crystal. Effects of nonlinear fringe modulation were studied both theoretically and experimentally. It is shown that in this case the electronic phase is not linearly related to the fringe shift, and calibration of the system is necessary.

Stricker, J.↗
NASA NTRS1985

A comparison of electronic heterodyne moire deflectometry and electronic heterodyne holographic interferometry for flow measurements

Electronic heterodyne moire deflectometry and electronic heterodyne holographic interferometry are compared as methods for the accurate measurement of refractive index and density change distributions of phase objects. Experimental results are presented to show that the two methods have comparable accuracy for measuring the first derivative of the interferometric fringe shift. The phase object for the measurements is a large crystal of KD P, whose refractive index distribution can be changed accurately and repeatably for the comparison. Although the refractive index change causes only about one interferometric fringe shift over the entire crystal, the derivative shows considerable detail for the comparison. As electronic phase measurement methods, both methods are very accurate and are intrinsically compatible with computer controlled readout and data processing. Heterodyne moire is relatively inexpensive and has high variable sensitivity. Heterodyne holographic interferometry is better developed, and can be used with poor quality optical access to the experiment.

Decker, A. J.↗
NASA NTRS1987

Moire interferometry, 1986

Current capabilities of moire interferometry are described. Several examples illustrate this whole-field optical technique for measurements of in-plane displacements. Sensitivity corresponds to moire measurements with gratings of 2400 lines/mm. The examples are taken from studies of composite members, material anomalies, plasticity, joints, micromechanics and strain concentrations. The abundance of high-sensitivity displacement information permits calculation of normal strains and shear strains in the field, including critical zones of very high gradients.

Post, D.↗
NASA NTRS1988

Compressive creep strain measurements using moire interferometry

Uniaxial compressive creep loads were applied to quasi-isotropic composite laminates at room temperature. The x and y displacement fields were measured using moire interferometry. Moire fringe patterns were recorded photographically; these photographic records were subsequently digitized and reduced to in-plane strain levels numerically. Strain contours were plotted, providing a whole-field representation of in-plane strain distribution. Slight viscoelastic behavior was observed over the time period considered, except in one test in which time-dependent delamination failures were observed.

Tuttle, M. E.↗
NASA NTRS1989

Error sources in deferred heterodyne moire deflectometry - An analytical study

The effects of the aperture size and shape of the photodetector and of the structure of the grating lines on the performance of deferred electronic heterodyne moire deflectometry are studied. It is shown that scanning of a moire fringe pattern parallel to an unshifted fringe yields periodical variations in the heterodyne phase and amplitude, which cause severe errors in the measurements.

Stricker, Josef↗
NASA NTRS1989

Utilization of Moire patterns as an orbital docking aid to space shuttle/Space Station Freedom

Moire patterns are investigated as possible docking aids for use between the National Space Transportations System (Space Shuttle Orbiter) and the Space Station Freedom. A sight reticle placed in optical conjunction with a docking target can generate moire fringes from which position and alignment can be inferred. Design specifications and a mathematical development to meet those specifications are discussed. A motion based simulator and experimental hardware have been constructed.

Dottery, Edwin L.↗
NASA NTRS1990

Compression creep of graphite/epoxy laminates monitored using moire interferometry

Uniaxial compressive creep loadings were applied for ten hours to various graphite/epoxy laminates with a hole. All tests were performed at room temperatures. In-plane displacements were monitored using moire interferometry. Moire fringe patterns were reduced to in-plane strain fields numerically. The fiber-dominated laminates tested exhibited little or no viscoelastic behavior during the ten hour period. Conversely, the matrix-dominated laminates tested did exhibit viscoelastic behavior during the ten hour test time.

Tuttle, M. E.↗
NASA NTRS1991

Three-Dimensional Moire Pattern

Use of moire patterns to determine positions extended to three dimensions. Concept requires two moire templates or grids, separated from each other. Template on side closer to observer contains alternating black and transparent areas. Template farther from observer contains alternating black and white areas. Observer determines position of center of perspective, also receiving indication of depth even without stereoscopic view. Used in rangefinding applications in which precision not required. Also used to gauge location of mobile robot in environment hostile to humans.

Juday, Richard D.↗
NASA NTRS1992

Optical-precision alignment of diffraction grating mold in moire interferometry

A high-precision optical method is presented for aligning diffraction grating molds with the edges of specimens in moire interferometry. The alignment fixture is simple and convenient to operate. The conventional method of grating-mold alignment has a wide band of uncertainty in the range of error which is not compatible with the required precision of high-sensitivity moire interferometry. Following a description of the alignment technique, both the single-edge and parallel-edge guide bar optical alignment methods are introduced and compared.

Joh, D.↗
NASA NTRS1991

Variable sensitivity moire interferometry

This paper demonstrates that optical microlithography can be used to produce a crossed grating which diffracts light into multiple orders sufficient to record moire interferograms with sensitivities ranging from 2.0 to 0.285 micron/fringe. The grating profile produced by the method is analyzed to establish the diffraction efficiency in each diffraction order, and generalized expressions are given for variable sensitivity moire interferometry. Experimental tests are conducted to verify analytical arguments. In one of these tests, two different diffraction order pairs are used simultaneously to verify that surface displacement can be measured at different sensitivities.

Johnson-Cole, Helen↗
NASA NTRS1995

X-Ray Moire Techniques For Measuring Strain

X-ray moire method provides for measurement of strains throughout relatively large regions and in locations invisible or inaccessible to measurement by other techniques. For example, used to measure strains between layers of material in rubber tires. Method exploits body of knowledge already developed for optical moire measurement of strains. Offers advantages over optical methods of measuring strains within depths of objects, in that x-ray imaging not restricted to optically transparent materials. Also offers advantages over strain-gauge method that gauge wires not needed and measurements not limited to discrete gauge points.

Madaras, Eric Irvine↗