Photoelasticity has been used recently by the authors to conduct many tests related to the determination of stresses in the field of tall beams, and to the optimization of those beams. Numerical methods (in particular finite-elements, and solutions of Laplace's equations) have also been used to supplement or to verify the results obtained photoelastically. The opportunity seems appropriate to weigh some of the advantages and limitations of the methods used. Photoelasticity gives readily the field solution of Tmax. An approximate method can be used to obtain normal stresses using equilibrium conditions and photoelastic data. The photoelastic test can also be used to determine the boundary conditions, or part of them when they are not known, as in the case of many hyperstatic structures. The complete and precise knowledge of the boundary conditions is not always necessary. Numerical solution of Laplace's equation which corresponds to the sum of the principal stresses can be obtained easily for the whole field with the computer. Knowledge of boundary condition is necessary. Complete solution in terms of individual principal stresses can be obtained using finite-elements. Knowledge of boundary conditions is necessary. When gradients are high, the size of the elements must be small which may require longer time in the computer. The decision on what method to use depends to a large extent on 1) The availability of a photoelastic laboratory; 2) The availability of a computer and the program; 3) The availability of personnel with the necessary experience; 4) The knowledge, or lack of knowledge of all the boundary conditions.

An early description of the photoelastic method was provided by Coker and Filon in 1931. Then, in 1937, Oppel introduced the concept of frozen stress photoelasticity. However, one of the first applications of photoelasticity to the field of fracture mechanics did not come until 1958, when Wells and Post conducted their photoelastic study of a running crack. In a discussion of this latter paper, Irwin described a method for extracting the Mode I stress intensity factor (SIP) hereafter referred to as K1, from the photoelastic stress fringe signatures. Subsequently, Fessler and Mansell were among the first to apply Oppel's frozen stress method to the extraction of K1 distributions from three dimensional cracked body problems.

Photoelastic measurements of residual strains are used extensively in the QC and inspection of transparent materials. A new method of measurements, based on Spectral Contents Analysis, is described in this paper. The method uses a personal computer for photoelastic data acquisition, eliminating personal skill and subjectivity. The new tool should make the measurements of residual strains for QC simpler and more reliable.

In the process of determining the complete state of stress at a general point in a three dimensional photoelastic model (in a non-destructive or a semi-destructive manner), the concept of optically equivalent model plays a very important role. There are three parameters that define an optically equivalent model and these are termed as characteristic parameters. In this paper, first a survey is given of the direct and indirect methods used to determine the three characteristic parameters and then a new indirect method to deter-mine these parameters is presented. An algorithm has also been developed to determine the characteristic parameters unambiguously by the new method. The new method is verified experimentally and compared with theoretically determined characteristic parameters using Jones calculus.

The use of methods of experimental mechanics to study physical behavior in elasto-dynamic problems requires high speed photographic recording systems capable of storing images of optical fringe patterns where features often propagate at or above the dilatational wave velocity. This paper discusses the requirements of a very high speed recording system for the dynamic photomechanics class of experiments. The requirements include: exposure time, framing rate, field size, image size and light intensity. The design of a new Cranz-Schardin photographic recording system which has recently been completed at the University of Maryland is described in some detail. The camera system incorporates a novel spark gap design with a reflecting and focusing mirror and a fiber optic output. The fiber-optic bundle adds considerable flexibility in adapting the optical system to a large number of different experiments. The optical system has been designed for operation in both the transmission and reflection modes. In the transmission mode the system records conventional photoelastic fringe patterns, moire and caustic images of transparent media. In reflected light the specimen is mirrored and the system records fringe patterns from birefringent coatings, moire and caustic images from opaque materials.

During the last few decades the authors have presented new kinds of polariscope referen-ced from l to 5. However in the described apparatus the electrical signal emitted by the photomultiplier tube was processed by an analog method. So we were forced to use a high speed of rotation for the polariser because of the electrical filters and it was impossible to coincide the incident laser beam with the mechanical axis of rotation of the polariser. This time we use a microcomputer and by an appropriate sampling of the signal and a suitable processing we are able to determine the deviator of the stress tensor at the studied point in the model when the Maxwell- Neumann Laws are valid. Moreover we can use a small speed of rotation for the rotating polariser and we can easely make the mechanical and optical axis coincide. In effect we determine the direction of the fast axis of the birefringent medium and also the optical phase difference. When the latter is more than π/2, it can be easier to use two wavelengths.

The technique of half-fringe photoelasticity (HFP) was used to study the applicability of the thin plate theory for cantilever rectangular plates subjected to transverse loading. Results are presented and discussed with those obtained from the finite element method (FEM) for three cases including plates with and without discontinuities.

A technique known as the half-fringe photoelasticity (HFP) was used for the determination of the stress intensity factors for edge-cracked plates in uniaxial tensile loading. The variation of the stress intensity factors with orientations and lengths of cracks are presented and compared with the available analytical and experimental results.

An image processing system has been developed around an APOLLO workstation, tailored to the needs of processing images of photoelastic models. Using this system, the authors have made a comparative study of some image processing algorithms in the analysis of a disc of araldite resin loaded in diametral compression. A differential zero crossing algorithm has been developed and the results obtained compared with those from the other algorithms. The algorithms used are described, and an analysis of their effectiveness in this problem presented, with the aid of a fringe analysis system developed to analyse output from the image processing system. The results are compared with results from finite element analysis and mathematical modelling.

A new and effective method of sandwich photo-carrier fringes is presented to separate principal stresses for both static and dynamic, especially for multi-frame recording, holographic photo-elasticity. It is the first to use digital image processing in dynamic holographic photo-elasticity.

The concept of photo-carrier moirefication is presented. The discussion is given on topics of photo-carrier modulation to moire,photoelasticity,speckle and holographic interferometry. Based on boundary conditions offered by the photo-carrier speckle method with the improved sensitivity and accuracy,the contact boundary restrain equantions are established. With the contact restrain and boundary conditions determined by the experiment ,the finite element method is used to analyse a frame structure with filled-wall. A simplified and rational mechanical model is given,which is more convenient to engineering designers.

A general light-intensity expression in terms of Stokes vectors is derived which can be used to calculate the light-intensity distribution in holographic Photoelastioity. It is shown that this expression is applicable to either conventional holophotoelasticity or polarization holophotoelasticity and can be applied to single-or double-exposure holophotoelasticity. Some typical examples are presented.

The theoretical basis of the new technique called "holospeckle interferometry" is laid out. Several schemes for this new technique are presented along with demonstrations showing its various applications.

Based on the principle of wave and statistical optics, shearography is analysed thoroughly. The auto-correlation function of the transmittance of the specklegram, which is the essence of speckle interference, is calculated. The ensamble average intensity distribution of the output fringe speckle field of the filtering system is derived. We have shown that, if some conditions are satisfied by the system parameters, better contrast of the fringe field will be obtained, but it still is a function of in-plane deformation fields and the system parameters. In addtion, we have found that the out-of-plane deformation gradient is measurable only when the in-plane deformation value is smaller than a value determined by system parameters.

An optical roughness measuring instrument has been developed for applications in the field of mechanical engineering. It is based upon the angular-speckle-correlation (ASC) method. Two-dimensional processing of the digitized speckle patterns is performed by means of a fast correlation algorithm. Alignment errors, which inevitably occur in practice and may impair the measurement, can be compensated by evaluating the position of the maximum value of the 2D-cross-correlation function of the speckle patterns. Experiments have been carried out using differently machined rough surface samples.

This paper introduces a method of measuring surface rougnness based on the average contrast of laser speckle, giving both theoretical analysis and description of the measurement system.

This paper presents some preliminary success in computerizing data deduction in shearography. Computeriza is made possible by the introduction of a fringe carrier technique which removes the ambiguities in fringe interpretation. The technique is based on superposing a set of carrier fringes upon the deformation fringes. The resulting fringe pattern has monotonically increasing fringe orders, thus allowing the fringe orders to be determined in a straightforward mariner and without ambiguity. It is demonstrated that the data deduction process can be computerized. By digitizing the deformed carrier fringe pattern, the displacement derivatives can be automatically deduced by means of digital image processing.

Statistical approach is utilised to analyse the formation of displacement gradient fringes created by shearing speckle interferometry in this paper. We calculated the impulse response function and studied the spectrum of shearing specklegram in detail. Then the optical filtering system of shearography is analysed and we found that the cosine fringes are related to the displacement gradient upon condition that the displacement component along the X-axis, can be negleected, and the fringe visibility depends on the size of filtering holes and the in-plane displacement components.

The actual engineering structures always possess the problems of large dimension, wide range of deformation, complex dynamic response and so on. Therefore, the practical applications of speckle techniques for actual engineering structures encounter some difficulties. Some new attempts have been made to resolve those problems by authors, and main achievements is reviewed in this paper. The focusing principle, evaluating equations and the experimental technique of the oblique-optic--axis speckle photography are presented.The stroboscopic laser speckle photography used for modal analysis, and the electronic speckle pattern interferometry applied to the measurement of the elastic-plastic deformation feild near the crack tip are introduced as well.

Objective speckle of sticking foil is a new approach to apply the objective speckle method into various materials for in-plane displacement measurememts. Specimen surface has been treated by sticking a thin layer of aluminium foil and scratching a random grating by relatively easy technique in order to form high reflectance and fine optical details. After double exposes by direct recording system without using lenses, the holographic film possesses a broad spatial spectrum range and displacement information. Full-field contour maps are obtained with clear lines of equal displacement, high sensitivity, and large adju-stable measurement range. It is available for practical engineering problems and for both plane and developable curved surfaces.

Basic principles and advances of the laser speckle strain gauge are described which optoelectronically detects speckle displacements caused by deformation of a diffuse surface and separates strain by means of differential optical systems. It is a perfectly non-contacting and automatic method. Several problems for practical application of the gauge are presented together with proposals for solving them.

The white light speckle method is used to study the in-plane and out-of-plane vibration of plates. By suitable choice of experimental set-up, the amplitude of vibration and location of the nodal or antinodal regions can be determined. For in-plane vibration studies, the object is coated with a layer of retro-reflective paint, which creates a random speckle pattern when illuminated by a beam of white light. Filtered time-averaged patterns recorded in this way gives the amplitudes of the sinusoidal oscillation. For out-of-plane vibration studies, the reflection speckle method and the projection speckle method provide the anti-nodal and nodal regions respectively.

An image processing system for the automatic analysis of double exposure laser speckle photographs is described. The "Young's fringes" diffraction pattern, formed by directing a narrow laser beam through a speckle photograph, is digitised by means of a mechanically scanned linear photodiode array. The displacement vector is calculated by spectral analysis of the fringe pattern using either the Fast Fourier Transform (FFT) or the Fast Walsh Transform (FWT) algorithms. The accuracy, reliability and computation time of the two algorithms are compared as a function of fringe visibility and image resolution. The paper is illustrated by three practical applications of the image processing system. In the first, small discs of plastic bonded explosive (PBX) underwent quasi-static diametral compression (the Brazilian test). Analysis of double exposure speckle photographs recorded during the deformation revealed the strain distribution at different load levels, and the strain-to-failure of the material under test. For the second and third examples, speckle photography was used to measure the displacement fields around the tips of stationary and moving cracks. Numerical methods for calculation of the stress intensity factor from the measured displacements are presented.

We describe a heterodyne readout system for the analysis of specklegrams arranged in the dual plate mode. We analyze the sources of error due both to the statistical nature of the detection scheme and to misalignement. In evaluating the contributions of the statistical errors we consider, besides the so called "scintillation noise", a recently described additional source called "speckle grain noise". With regard to the misalignment sources, the most critical parameters have been carefully analyzed to make the layout as insensitive as possible against drifts in the setting of the most crucial components. Tests have been performed with two identical specklegrams and the results show that the ultimate accuracy is only five times worst than the intrinsic noise limiting value.

A close-range objective white light speckle method has been used for strain determination on simply curved surfaces. The speckle field is not the artificially printed random dots but only the radiance distribution of object surface which was slightly treated before the test to produce fine structure of optical details. The holographic film, instead of holographic plate, is attatched to the curved surface when illuminated by a flash light. Whole field fringe patterns are obtained with high sensitivities and large adjustable range. There is no longer a requirement to derive the speckle movement on the image plane from the object furface. Defocusing problem has been avoided. It can be practically applied to engineering problems with considerable convenience because of the very simple recording system and little demand for environmental stability.

A new technique for determining the stress state in a three-dimensional transparent body is described. This method involves cast-ing dye molecules into a model material and using the fluorescent light to analysis the stress state. The techniques of scattered light photoelasticity and speckle interferometry are considered and the enhancement of these techniques by the use of fluorescent is reported. The amount of illumination is greatly increased and the wavelength red-shifted, which eliminates the undesirable boundary halo; however, at the expense of a loss of coherence and a degree of depolarization of the light. Rhodamine 6G dye molecules are cast into gelatin, epoxy resin (PLM-4) and urethane rubber (Solithane 113) model materials. The light scattering, fluorescent, and fringe formation processes of each material is investigated. It is observed that even for the standard scattered light photoelastic materials without dye molecules the scattering is not Rayleigh, but rather has a large amount of wavelength broadening, the center wavelength, is red-shifted, and a high degree of depolarization occurs. A theory of photoelastic fringe formation for fluorescent materials is proposed. Experimental results are presented and the use of digital image processor in filtering background illumination is shown to greatly enhance fringe visibility.

A laser speckle, differential strain measurement system has been built and tested for future applications in hostile environments. One-dimensional electronic correlation of speckle pattern movement allows a quasi-real time measure of strain. The system has been used successfully to measure uniaxial strain reaching into plastic deformation of a test specimen, at temperatures ranging to 450°C. A resolution of 16 microstrain is given by the photodiode array sensor pitch and the specimen to sensor separation. The strain meas-urement error is estimated to be ±18 microstrain ±0.3 percent of the strain reading. The upper temperature limit of the gauge is determined by air density perturbations causing decorrelation of the reference and shifted speckle patterns, and may be improved by limiting convective flow in the immediate vicinity of the test specimen.

A new optical visualization technique is discussed which provides a simple yet dramatic means to view local shape variations in quasi flat objects. Sensitivity of this technique is such that depressions or protrusions on the order of 0.025 mm are readily visible. Examples of several applications of this technique in industry are shown.

A fiber-ptic technique and the conventional photoelastic technique were applied to the investigation of pin-loaded specimens which simulate pin joints and bolted joints. The angle of contact between the pin and the hole was measured by these techniques and compared with finite element results. The stress distributions obtained from the otoelastic response were also compared with the finite element results. Such comparisons are needed to verify the finite element model and to assess the role of important joint variables such as friction.

The optical method of caustics has been successfully applied to several two dimensional elasticity problems. Up to now, this method can't treat of more complicated three dimen-sional elasticity problems. In this paper, the experimental technique of caustics is developed, and caustics are produced by annealing the stress-frozen slices. Applied the technique to Boussinesq's problem of a normal force and Cerruti's problem of a tangential force on the plane surface of a half-space, the experimentally obtained caustics for these problems were seen to be in satisfactory agreement with the corresponding theoretical forms. The treatment of more complicated three dimensional elasticity problems, including crack problems, by the author's method is also possible.

Two methods are presented in this study to optically assess the surface waviness of painted SMC (Sheet Molding Compound) panels. In both methods, a coarse grating is reflected by the panel surface and the resulting image is recorded for further evaluation. In the first method, the reflected grating image is superimposed on a reference grating to create a moire fringe pattern. A small rotational mismatch between the two gratings amplifies the grating distortions. The panel surface waviness is qualitatively assessed by visually evaluating the overall waviness of the moire fringes. In the second method, the reflected grating image is evaluated directly for the spacing variations, which are related to the variations in the panel surface waviness. A statistical parameter, called the Waviness Index, is proposed to provide an average measure of these variations and is shown to have a good correlation with overall surface waviness.

This paper describes a vernier-type optical encoder for absolute angular measurement. The vernier encoder has only two tracks, so it is much smaller and simpler than conven-tional Gray code encoders. Two "spatial filter" detectors are used with the vernier to provide interpolation between encoder slit positions. Each detector consists of a LED light source on one side of the disk, and two photodiode arrays (PDA) -- one for each track of the vernier -- on the other. The two detectors are placed at diametrically-opposed positions, and the intensities of the LED light sources are modulated in quad-rature by a sinusoidal signal. The signals from the detector arrays are combined to generate two vernier signals, and the difference between these vernier signals is a high-precision "absolute vernier" signal. The accuracy of angular measurement for a prototype encoder was as high as 1/10,000 (2.2 arc-min).

It is shown that unloaded transparent polymers, in contradiction with the available information, are optically anisotrope in certain directions. A polarized He Ne laser beam, moving in the planes of plate-samples, has been used in scanning plates of different polymers. Octagonally shaped plates were machined out to enable data acquisition from four different directions. The observed scattered radiation showed periodical extinction of light intensity in harmonic sense. This optic phenomenon which result in parallel fringes, is referred to the crystallographic system of the material. The number of fringes per unit length will be designated by Issa-number.

Triangulation based range sensors have long been used for making large scale measurements, however, when triangulation techniques are used in metrology applications with very tight tolerances, new concerns appear. In particular, the design of very high resolution range sensors requires an understanding of surface microstructure effects that can severely limit the accuracy of a system. For triangulation based sensors to enter the regime where interferometry has traditionally been used, the problems of surface microstructure induced noise must be overcome. In this paper we discuss the factors that limit the resolution of triangulation based range sensors, and the theoretical limitations on the accuracy of such sensors.

One of double grating diffraction systems, Moire deflectometry with a filtering system added behind the second grating is analysed in details based on diffraction theory. Both monochromatic and white light illuminations is considered, and some practical application such as adjustment of light collimation and measurement of flame field is introduced.

Commercial reflective optical switches, tilted strongly off-axis, can provide better than ±0.03 mm sensitivity in controlling the refill of a quiescent fluid container to some desired set-point level. The optics of this increased sensitivity is derived geometrically and a control sensor described and tested. Both set-point control sensitivity and sensor-surface working distance (inversely) are functions of tilt angle, so can be chosen or changed as required. Two such sensors, adjusted to give peak signals at two slightly different liquid levels (0.2 mm apart, e.g.), can then control not only a two-stage (fast/ slow) refill process but also provide high-sensitivity monitoring of any ripples or waves on the liquid surface after refill is complete.

This paper provides an optical method for determining the stress intensity factor. The optical properties of grating and wedge are used to form two images of a specime which stagger a small distance. The distance can be regulated stepless. Information of the partial derivative of the sum of principal stress around the crack tip is directly obtained by the shearing interference of two images and then the stress intensity factor is evaluated. This method is suited to both transparent and opaque material. Its sensitivity can be increased by multiplying technique.

By using aoperiphery camera which is capable of 360° viewing we have extended the in-plane, shadow and reflection moire methods and laser and white light speckle methods to cylindrical surfaces without the perspective effect.

The image photo-carrier theory as a new technique in photomechanics is described in this paper. The idea of high frequence photo-carrier which can transform the photoelasticity fringe into moire fringe and the single phase carrier method are presented by the author. According to the idea as mentioned above the physics and mathematics relation between the principal stress direction and moire fringe obtained from photo-carrier is established. The photo-carrier possesses some special functions which make it possible to determine automatically the fringe order and the fractional fringe value by the image processing system, in consequence of which provides an effective technique for collection and processing automatization in photomechanics.

The accuracy that can be achieved in the measurement of very small displacements in techniques such as moire, holography and speckle is limited by the noise inherent to the utilized optical devices. To reduce the noise to signal ratio, the moire method can be utilized. Two system of carrier fringes are introduced, an initial system before the load is applied and a final system when the load is applied. The moire pattern of these two systems contains the sought displacement information and the noise common to the two patterns is eliminated. The whole process is performed by a computer on digitized versions of the patterns. Examples of application are given.

Examination of various moire techniques from the perspective of communication theory provides insight into the inherent sensitivity and resolution limitations of the techniques. These limitations determine the suitability of the techniques for the study of micro-mechanics.

Moire, holography, speckle and thermographic (SPATE) stress analysis are used to analyze a variety of engineering problems involving man-made (fiber-reinforced) and natural (wood, paperboard) composites, metals and rubber. The photomechanical techniques are combined with computer-vision (digital-imaging) concepts. Some attention is devoted to hybrid methods for processing and differentiating recorded optical data. Applications involve both small and large (including nonlinear) strains, and hostile environments. Illustrations include those to fracture, stress waves, material behavior, knots in wood and energy storage.

In this paper, deformed cross gratings around crack-tip are recorded. The derivative fields of displacements (∂u/∂x, ∂u/∂y, ∂v/∂x, ∂v/∂y, ∂w/∂x ∂w/∂y) are obtained by optical spatial filtering of two shifted deformed gratings. From which, strain contours around crack-tips can be obtained directly.

The use of optical fibers has already found interferometric applications within holography,speckle photography and moire method. In this paper, multimode fiber-optic image bundle is used to time-averaged shadow-moire method for studying vibration, so that recoding surface deformation in remote areas of a structure is possible. The time-average shadow-moire method is also briefly viewed.

By shifting the discrete Fourier spectrum of the image of a deformed grating, we can obtain "the complex moire pattern", from which strain distribution is given as the derivatives of the phases of the complex moire fringes. The analysis is completely automatized by introducing the digital image processing. All of the laborious and subjective procedures required in the conventional analysis such as fringe sign determination, fringe ordering, fringe interpolation are so eliminated that objective, fast and accurate analysis can be made. Some applications for rubber plates are shown.

Moire technique using projected fringes is a suitable method for full field measurements of out-of-plane deformations and object contouring. In this paper a system using a TV-camera combined with a digital image processor is described. In this way a real-time system with the inherent possibilities of fringe interpolation for improving the accuracy and sensitivity is obtained. This system is very suitable for comparing the shape of different objects, e.g. for measuring the surface profile difference between a product specimen and a master object. An attractive alternative would be to measure the surface profile compared to a master object generated by means of CAD. An example of this method is presented. This technique offers a powerful tool for industrial production control.

One of the widely recognised limitations of moire topography is its inability to provide unambiguous data from objects which have discontinuities in their shape. Similar limitations arise when two parts of an object are separated by a region which is in shadow. This feature of moire topography has limited its use to the measurement of objects which have continuous surfaces. With the development of phase measuring techniques for fringe pattern analysis, moire fringe contour patterns can now be analysed to high levels of accuracy, the contour interval being subdivided into, perhaps, 200 increments of measurement by the phase calculation procedure. This paper describes a modified version of moire topography in which the contour interval has been greatly increased so that, in some cases, the entire depth of the object lies within one fringe. By applying high accuracy phase measuring techniques to the analysis of these moire fringe patterns, sub-millimetre accuracy can be obtained in measurements of objects which would normally be thought of as unmeasurable by moire topography.

An essential phase in moire techniques is the generation of strain fields from optical fringe patterns. In this effort we explore a finite element method based upon a new least-squares penalty-constraint variational principle, which will be shown to be extremely effective in producing accurate, two-dimensional displacement and strain fields over the full-fringe domain. The approach encompasses the full-field analyses of optical fringes, which include: (1) an effective and theoretically sound noise filtering/smoothing and differentiating of the optical intensity fringes, from which displacement fringes are accurately determined, (2) subsequent smoothing/differentiating of the displacement fringes, producing continuous displacement and strain fields of high quality, (3) computational efficiency, (4) the ability to routinely process distorted mismatch fields which occur, for example, with large fields of view, avoiding the need for any special care to eliminate such distortion, (5) ease of implementation within a conventional finite element program. Several examples are carried out which demonstrate the attractiveness of the methodology.

A microcomputer based moire strain gauge with high sensitivity is developed which is capable of measuring strain automatically .

From its inception, the technique of holographic interferometry has been continuously developed within the UK. Non-destructive testing (NDT) and metrological applications of holography have grown over the last 20 years, with major contributions coming from NPL, Loughborough University, Rolls Royce Advanced Research Laboratory and many others. More recently the technique of Electronic Speckle Pattern Interferometry (Electro-Optic Holography) has added to the list of available methods and given a spur to holographic metrology in industry. This paper will review recent developments within the UK, in optical systems and data analysis techniques (for both holographic and speckle interferometry). These are promising to provide the mechanical engineer with commercial products based on automated non-contacting optical measurement systems, for applications in industrial design and testing. Important developments include the use of fibre optics, CCD cameras, speckle averaging, heterodyning, 3-D deformation and strain measurement, together with a range of fringe analysis techniques. These will be discussed within the context of typical applications of holographic interferometry in the UK. Finally a view to the future will be given.

Dynamic double exposure holographic interferometry and sandwich holography were applied to the measurement of surface displacements resulting from the detonation of an explosive charge on the surface of rock models. A 10J state of the art ruby laser was used to illuminate three different rock models that were 0.75m on a side and 0.4m deep. In one model, a simulated tunnel was made by coring the rock specimen in a subsurface plane that was parallel to the face of the block. Another model involved the transmission and alteration of surface waves as they encountered a step change in the surface elevation. The remaining specimen consisted of an epoxy wedge overlaying the rock base. As the wave system passed into the epoxy layer of this last specimen, new waves were generated that produced dramatically increased displacements and particle velocities on the surface of the epoxy layer. These interferometric patterns were so complex that it was necessary to utilize sandwich holography to determine the wave types and the signs of the displacements.

A system appropriate to measure the displacement and deformation of the solid diffusely scattering objects is realized, with which an automatic measurement of high precision can be achieved.

In electronic speckle pattern interferometry, the visibility of resultant fringes are influenced by inhomogeneity of the object light and the reference light. Moreover, the resultant fringes have granularity, which is the drawback of ESPI. Two methods to improve the visibility of resultant fringes are proposed. One is a normalizing method and another is a phase scanning method. The experiments were carried out using a CCD image sensor, a digital frame memory and a 16-bit micro-computer, and the theoretical considerations were verified.

This paper deals with the mechanical structural analysis of the complete assembly system of the optics foreseen for the Italian Satellite for X-ray Astronomy SAX. Possible damages to the grazing incidence optical surfaces could have been induced by the strong environment during launch so that HNDT was adopted to obtain reliable data about amplitude and shape of the vibrational modes at some of the more critical expected frequencies. Computer simulation was also carried-out by the finite elements approach showing quite good agreement both in resonance frequencies and modes shaping with holographic analysis so that it was possible to take into account the attenuation factor resulting from holographic measurements.

The Fourier-transform method pointwisely determines the interference phase distribution of a digitally recorded and stored holographic interference pattern. Only one interference pattern is used, although the use of two patterns with an unknown mutual phase shift enables a sign correction with high reliability. The method offers means for filtering out disturbances such as speckle noise and background variations, especially when an image of the illuminated object-surface can be recorded before producing the interference fringes.

A technique for the fabrication of machine tool structures by epoxy resin bonding has been developed. The design principles and technical factors are discussed from tests of bonded joints. A model fabrication of a lathe spindle box was designed and manufactured. Infrared thermography was used to monitor and calculate the surface temperature distributions of the above structure. And the holographic quantitative analysis of three dimansional displacements was used to measure and calculate the thermal deformation. In this paper the advanced measuring techniques and real-time data of thermal characteristics of the above structure is presented.

A detailed investigation has been carried out into the application of digital phase stepping techniques in the computer analysis of Electronic Speckle Pattern Interferometry fringe data. The entire analysis process has been examined from its initial stages of video resolution and digitisation, through to the representation of phase data within a computer matrix for subsequent data analysis. These investigations have utilised standard video analysis equipment as well as specialised analogue and digital devices designed and built in-house. A high resolution, real time digital image processing system has been used in the analysis of the fringe data, for which specific applications software has been designed. A brief description of some of these devices is included, together with the details of their design philosophy and practical application. Each stage of the analysis method has been evaluated from a signal or image processing viewpoint and optimised to give the best results from a phase representation approach. The resulting processing method is described and example images are used to illustrate successive stages.

In this paper the theory of photocarrier holographic interferometry is presented to aeasure and analyze three dimensional displacements. From the photocarrier holographic interferogram, the fringe orders corresponding to object deformation can be easily determined by the demodulating process. By means of bi-needle projection method, utilizing the shadow and image parameters of the two needles in the hologram, the positions of the illuminating point and the observation point can be determined automatically. Taking advantage of these two methods, the interferograms could be analysed more quickly and accurately by the image processing system. The forenamed two methods were used to measure the thermal deformation field around a crack tip in a steel plate which subjected to a quasistatic thermal load at its two lateral sides. With combination of finite element method, J integral values were evaluated. By comparing with the theoratical value of J integral, good agreement was obtained.

We analyze the ultimate accuracy of interference phase neasrement that can be achieved by using heterodyne technique in conjunction with interfering speckle fields. We show that the mean square fluctuation of the measured phase depends not only on the traditionally introduced scintillation noise but also on the spatially random arrangement of the speckles over the detector aperture (speckle grain noise). Scintillation noise arises because the two speckle fields are partially decorrelated, in which case the interference pattern does not become completely dark even when the two speckle fields are out-of-phase since destructive interference is not complete. However, even in the case of perfect correlation, intrinsic random noise is to be expected, since the position of the speckles over the detector is random and therefore the total signal exhibits statistical fluctuations, which we call speckle grain noise. Our formula show, as expected, that scintillation noise can be reduced by enlarging the detector aperture which, however, cannot be larger than half of an interfringe spacing. On the contrary speckle grain noise cannot be reduced by enlarging the detect& aperture since the effect of increased sampling is cancelled by the increased range of phase variation.