An Intelligent Hybrid Measurement Method for Steady Temperature Field

An intelligent hybrid measurement method, which is successfully developed for linear elastic deformation fields (Nishioka et al. Exp Mech 40:170–179, 2000), is investigated for steady-state temperature field. First, a variational principle is derived to minimize the errors and noises associated with experimental temperature measurements. This variational principle assures also the satisfaction of the governing steady-state heat conduction equation. On the basis of this variational principle, an intelligent hybrid experimental-numerical method is developed for the measurement of temperature field, and for the subsequent visualization of higher-order quantities such as the heat flux distribution. Furthermore, a concept is presented for self-restoring heat generation that automatically restores temperature field against experimental errors and noises. The present intelligent hybrid method successfully demonstrates automatic detection and automatic elimination of experimental measurement errors, and smooth visualization of heat flux distribution.     

New developments in the localized hybrid method of stress analysis

Developments of the localized hybrid method which combines an experimental technique, moiré interferometry, and a numerical method, finite-element analysis, are presented. In this localized hybrid method, the displacement fields which the moiré experiments provide in some local regions of interest are used as input data for finite-element stress analyses. Based on finite-element theory, several variations on this localized hybrid method, associated with different displacement boundary conditions, are developed. Applications and limitations of the localized hybrid method are discussed in detail. In particular, applications of the localized hybrid method of stress analysis are presented for three-dimensional problems in the mechanics of solids. It is shown that this localized hybrid analysis not only provides a powerful and efficient technique for the reduction of moiré experimental data, but also gives a good insight into the mechanics of the experimental observations.     

Constructing pure digital secondary moiré patterns

A new method of constructing pure digital secondary moiré patterns of equal-strain fringes is proposed in this paper. By this method, a pure secondary moiré pattern, without trace of primary moiré fringes, is obtained directly from common digital moiré patterns regardless of how low or high the fringe density. The pure secondary moiré patterns eliminate the backnoise of primary fringes and give the strain value at every point over the whole strain field. This technique can significantly increase the measurement accuracy and the range of moiré techniques.Paper was presented at the 1988 Spring Conference on Experimental Mechanics held in Portland, OR on June 5–10.     

Two-dimensional moiré method and grid method using Fourier transform

Formerly, the authors presented one-dimensional strain analysis by a moiré method using a Fourier transform. In the present work, the method is extended to two-dimensional strain analysis. The analysis is completely automated by introducing digital image processing. All of the laborious and subjective procedures required in the classical and conventional moiré method, such as separation of the two gratings, fringe-sign determination, fringe ordering and fringe interpolation, are completely eliminated; and objective, fast and accurate analysis can be made.currently Engineer, Kansai Electric Power Co. Inc.Paper was presented at the 1988 SEM Spring Conference on Experimental Mechanics held on June 5–10 in Portland, OR.     

Automatic analysis of moiré fringe patterns by using an image-processing system

This paper presents the whole process of analyzing moiré fringe patterns by using a computer-image-processing system. The main steps include: recording a fringe pattern, eliminating noise, thinning the fringes, assigning the fringes with fringe-order information, computing the strain field, outputing data tables, data curves, color two-dimensional computational displays and outputing in relief three-dimensional displays which represent strain and displacement. The method is highly automatic and gives visualized pictures and accurate results.     

An experimental investigation of losipescu specimen for composite materials

A detailed experimental evaluation of the losipescu specimen tested in the modified Wyoming fixture is presented. Moiré interferometry is employed to determine the deformation of unidirectional and cross-ply graphite-epoxy specimens. The results of the moiré experiments are compared to those from the traditional strain-gage method. It is shown that the strain-gage readings from one surface of a specimen together with corresponding data from moiré interferometry on the opposite face documented an extreme sensitivity of some fiber orientations to twisting. A localized hybrid analysis is introduced to perform efficient reduction of moiré data, producing whole-field strain distributions in the specimen test sections.     

Diffraction theory of optical interference moiré and a device for production of variable virtual reference gratings: A moiré microscope

Optical interference moiré methods are analyzed using Fraunhoffer diffraction theory to relate general large surface deformations to the fringes observed. This analysis determines the Almansl strain in the current configuration from the gradients of the fringe number function. The analysis shows the advantages of an experimental scheme that allows the virtual reference grating to be varied. The ability to vary the virtual reference grating results in a larger dynamic range and the ability to maintain a fringe spacing for maximum accuracy. A moiré microscope has been constructed which has this ability. Digital image processing coupled with optical filtering and phase control is used to enhance the accuracy of the fringe measurements. The variable virtual-reference-grating capability is demonstrated by using it to highlight several aspects of the deformation field near a crack tip in a single crystal of iron-silicon.     

Moiré holographic analysis of reinforced plate models

This paper deals with an extension of moiré holography for structural analysis on reinforced plate models. It is shown that unequal optical paths, caused by lack of uniform thickness, are compensated for and do not alter the moiré fringe patterns. Moreover, a simple technique is described for replicating high-sensitivity moiré gratings on Plexiglas models. The validity of the method has been satisfactorily tested on plate models with different geometries.Paper was presented at the 1988 SEM Spring Coinference on Experimental Mechanics, held in Portland, OR on June 5–10.     

Error analysis and thermal expansion measurement with electron-beam moiré

In this paper, the authors study erros incurred when using the experimental technique of electron-beam moiré. There are two sources of error: error manifested as an apparent magnificant drift and error due to fringe tracing. The error due to fringe tracing is nearly negligible in comparison to the error due to magnification drift. By investigating the thermal expansion of commercially pure copper, the authors demonstrate the usefulness of the error estimate. The average result for the coefficient of thermal expansion is within 1.8 percent of handbook values for this materials, with a possible error due to apparent magnification drift of 9 percent.     

Logical moiré and its application

Moiré fringes are generated using logical operations on one-bit binary gratings. A traditional moiré effect is observed using the AND operator while an enhanced moiré is observed using the XOR operation. Since the reference grating in this type of moiré is computer generated, fringe shifting to increase sensitivity can be easily accomplished. An alternative scheme, called the average step method, resulting from the logical operations with values averaged over the pitch of the reference grating, can also be used for fractional fringe-order determination. These principles with some applications are demonstrated in this paper.     

Electron beam moiré

A method of writing very high frequency line and dot pattems, in excess of 10,000 lines/mm, is described. This method uses a very small diameter, 10 to 20 nm, beam of electrons to sensitize a 100-nm thick layer of electron resist. The line and dot patterns are produced by etching the sensitized resist. Moiré fringe patterns occur when the line arrays are observed in the scanning electron microscope. Moiré fringes with excellent contrast have been produced at magnifications as high as 1900x. This capability permits e-beam moiré to be employed in micromechanics. Examples of line arrays, dot arrays and moiré fringe patterns on a brass disk and on a tensile specimen fabricated from glass-fiber-reinforced plastic are demonstrated to introduce the possibilities for micromechanics applications.     

Contouring by moiré interferometry

A double-exposure moiré-interferometry technique for topographic contour measurement of an arbitrarily curved object is presented. A curved surface coated with light-sensitive material is exposed twice in a volume of virtual gratings formed by the interference of two coherent light beams split from a laser. An adequate rotation of the curved surface relative to the virtual grating between the two exposures produces moiré fringes which reveal topographic contour, or contour under some conditions, of the surface. The advantage of the present method in comparison with others is that it offers both reasonably good fringe quality and easily adjustable high sensitivity. The sensitivity of the technique is shown to be from the order of micrometer to that of millimeter depending on the frequency of the virtual grating and the amount of the relative rotation. This technique was successfully applied to the topographic contour measurement of a cylindrical shell with and without a diametrical point loading.The principle of this paper and some early results were presented at the SPIE conference held at Dearborn, MI on June 27–30, 1988 and appeared in its proceeding.¹     

Hybrid elastostatic and thermostatic analysis from measured data

An effective hybrid method is demonstrated for stress analysis and heat transfer. Measured information is represented and differentiated analytically, while the number of unknown coefficients and amount of experimental input data needed are reduced through field equations. The approach is accurate, full-field, employs arbitrarily shaped elements, does not require a smoothing parameter and is well suited for computer-vision techniques. The concept is presently illustrated by moiré strain analysis, although it can be extended to other disciplines.     

Whole-field residual stress measurement in rail using moiré interferometry and twyman/green interferometry via thermal annealing

A novel whole-field residual stress measurement technique is developed using moiré interferometry and Twyman/Green interferometry coupled with thermal annealing. The technique is successfully applied to residual stress measurement in rail. In the measurement, a high temperature resistant 1200-lines/mm cross grating is made on a rail transverse slice surface. The whole-field residual stress relief is achieved by thermal annealing. Moiré interferometry and Twyman/Green interferometry are employed to obtain the in-plane and out-of-plane deformations generated by the residual stress relaxation. The whole-field strain redistribution due to the residual stress relief is calculated, and the whole-field residual stress distribution, including the possible stress concentration, is then obtained. Because of the three-dimensional nature of the residual stress relaxation and the measurement, the three-dimensional residual stress reconstruction sometimes becomes possible based on some plausible assumptions. In this paper, the principle of the experimental theory, technique and procedures are described. Three-dimensional residual stress reconstruction in a rail using a transverse slice is shown. Its comparison to the hole-drilling method with moiré interferometry is also presented.     

Measurement of bending stresses in shells of arbitrary shape using the reflection moiré method

The basic equation for fringe formation in the case of reflection moiré applied to surfaces of arbitrary curvatures is derived. A practical point-by-point solution for the application of this method is introduced, and the corresponding simplified equations are given. The technique is applied to an industrial problem, the stress analysis of a shell-shaped door.     

Measurement of energy release rates for delaminations in composite materials

Conventional measurements of energy release rates,G _I andG _II, for delaminations in composite materials, generally utilize loads, crack lengths and simple standard specimen geometries. In this work, a more widely applicable measurement method, using phase shifting moiré and the J integral, is presented. The experimental technique described requires only fringe-pattern information and the elastic constants for the measurements—thus it can be used when the standard methods are inapplicable. Using conventional double-cantilever beam and end-notched flexure specimens, the energy release rate has been measured simultaneously by the moiré method and the standard methods, with good agreement found between the two. This development will for the first time permit the experimental validation of new finite-element routines as they are developed.Paper was presented at the 1993 SEM Spring Conference on Experimental Mechanics held in Dearborn, MI on June 7–9.     

Phase-stepped fractional moiré

Two computer-aided methods have been developed for analysis of in-plane and out-of-plane surface displacements of structures under load. Both methods are whole-field techniques which combine phase-stepped geometric moire with video and computer technologies. With these methods, a displacement field of interest is determined by computer-processing phase stepped, geometric moiré image data with fringe ordering done automatically within the software. The theory of the techniques is described and results of accuracy tests and application problems are given. It is shown that very good agreement is obtained between theory and experiment for in-plane strain determinations. For out-of-plane displacement determinations errors are only a few percent over the entire field of view. The application problems discussed are: (1) the measurement of composite column buckling, and (2) the determination of the shape of a slightly distorted, thin aluminum plate.Paper was presented at the 1991 SEM Spring Conference on Experimental Mechanics held in Milwaukee, WI on June 9–13.     

Inversion of speckle interferometer fringes for hole-drilling residual stress determinations

Speckle interferometric fringe patterns record stress-relief displacements induced by the drilling of blind-holes into prestressed objects. The quantitative determination of residual stress state from such stress patterns is difficult because of the ambiguity in the order of the observed fringes. The plane stress magnitudes are provided directly from selected fringe positions using a stochastic, iterative least squares minimization approach. The inversion requires prior knowledge of the experimental geometry and an appropriate uniaxial stress-relief displacement basis function derived from three-dimensional finite element calculations. Superpositioning of the rotated and scaled displacement basis functions allows the stress-relief relaxation for any biaxial state of stress to be determined. In this paper, fringe patterns were forward modeled from a large ensemble of calculated biaxial stress-relief displacement fields. Inversion of these noise-free fringe patterns reproduced the biaxial stresses with negligible error. Analysis of more realistic fringe patterns that include speckle noise gave stress magnitude errors that diminished rapidly with the number of selected points to better than 3 percent for 100 points. Sensitivity of the optical method is influenced by a number of factors, but the ensemble of model fringe patterns studied indicates that the stress magnitudes (nomalized with respect to the material's Young's modulus) from 3×10^–4 to 10^–2 can accurately be determined with visible laser radiation. The method is amenable to automation and can easily be extended to study near surface gradients in the residual stresses or applied to other optical recording techniques such as moiré and phase-shifting interferometry.     

Grating interrogations: from small to large strain measurement

Our purpose is the direct strain measurement from the interrogation of a crossed grating marked on the surface of a specimen. The observation of the object through a master grid (as in moiré method) is replaced by a direct characterization of the pattern using a Fourier transform. This gives direct access to the modification of the pitches which leads to quantification of the strain without the intermediary of a fringe pattern. The comparison between the undeformed and deformed states allows the determination of the magnitude and orientation of principal strains and of the local rigid-body rotation. We describe three analysis techniques, one using the diffraction phenomenon, another utilizing a numerical spectral evaluation and third combining diffraction and phase-shifting procedure. These grid interrogations have different domains of application and a suitable choice of these analysis techniques allows a very large measurement range (10^–5 to high strain according to the grating resistance).     

Deformation measurement during powder compaction by a scanning-moiré method

The mechanical behavior of powders during compaction has been studied in previous papers. It has been shown that a moiré method may be used to determine the resulting strain distribution. Some difficulties were encountered, however, in the method used. In the present paper, therefore, an image-processing system employing a personal computer to analyze the moiré pattern is introduced. Many strain distributions obtained in this way from moiré-fringe patterns are presented. Further, using this image-processing system, a scanning-moiré technique is developed in which the master grating is replaced by the scanning lines of a television camera. The use of image processing in conjunction with the mismatch technique allows measurement of both small and large strains from one image picture.Paper was presented at 1982 SESA Spring Meeting held in Oahu and Maui, HI on May 23–28.