Showing papers on "Photoelasticity published in 1986"
01 Jan 1986
TL;DR: In the following a method is proposed, which enables the complete extraction of photoelastic information at local picture elements (pixel) from series of related images of the same stress state, and was modified to meet the special requirements ofphotoelastic patterns.
Abstract: Computer-aided methods for evaluation of photoelastic patterns use video technique and digital image processing. They are based on localization of fringe centers [ 1, 2, 3, 4]. Neighbourhood operations are needed to reduce the influence of nonuniform illumination, inhomogeneous optical components and models, etc. Fractional orders of the relative retardation and of the isoclinic parameter at points between the fringes are computed by spline- functions, if the components of the plane stress state have to be derived from photoelastic data. In the following a method is proposed, which enables the complete extraction of photoelastic information at local picture elements (pixel) from series of related images of the same stress state. For this purpose the well-established phase-shifting technique (see e. g. [ 5,6]) was modified to meet the special requirements of photoelastic patterns.
78 citations
TL;DR: In this article, a theoretical method was developed for calculating the stress intensity factor (K ) for semielliptical surface cracks in shafts subjected to a constant moment load.
51 citations
TL;DR: In this article, a method for measuring axial residual stress profile in optical fibers is presented, where the axial stress profile on the fiber cross section is obtained from optical retardations of rays that travel laterally through the fiber.
Abstract: A method for measuring the axial residual stress profile in optical fibers is presented. The axial stress profile on the fiber cross section is obtained from optical retardations of rays that travel laterally through the fiber. The retardations are measured for a number of fiber orientations by rotating the fiber through 180°. The stress profile is reconstructed by performing a numerical inversion of the data. This paper describes the principle, experimental setup, and measured stress profiles, as well as measurement errors and spatial resolution. It is shown that the nonaxisymmetrical stress profile can be nondestructively measured with high accuracy by using the method.
49 citations
TL;DR: In this paper, a method for analyzing low-order moirefringe patterns of displacement fields is presented, which adapts the techniques of half-fringe photoelasticity to moire and extracts continuous displacement information in the regions between integral fringes.
Abstract: A new method for analyzing low-order moirefringe patterns of displacement fields is presented. This method adapts the techniques of half-fringe photoelasticity to moire and extracts continuous displacement information in the regions between integral fringes. The effectiveness of the technique is illustrated with three examples: a uniform uniaxial field, a tapered specimen in tension, and a disk in diametral compression.
33 citations
TL;DR: In this article, a series of dynamic experiments was performed to further investigate the relationship between the stress intensity factor and crack velocity for Homalite 100, and the results indicated that the stress field solution depends on the number of terms in the series representation.
31 citations
TL;DR: In this article, weak photoelastic patterns are resolvable in the near-infrared transmittance (typically near 1.4 μm) of semi-insulating GaAs wafers.
Abstract: Despite several detailed theoretical analyses of the stress distribution expected for Czochralski grown GaAs crystals, experimental verification of these calculations has hitherto relied on dislocation density measurements. The present work shows that weak photoelastic patterns are resolvable in the near‐infrared transmittance (typically near 1.4 μm) of semi‐insulating GaAs wafers. Mapping of these patterns reveals the contours of constant shear stress, with results generally supporting the calculated models for the stress distribution.
21 citations
TL;DR: In this article, the problem of representing crack speed behavior in terms of a K-ν relation is discussed and the belief that instantaneous crack speed depends on the past history of the crack tip stress field is supported.
14 citations
01 Jan 1986
TL;DR: In this paper, a certain radiation is passed through a section of the object in many directions, and properties of the radiation (intensity, phase, deflection, etc.) after passing the object are recorded for many rays.
Abstract: Tomography is a powerful method of determining the internal structure of various objects (Herman 1980). In tomography a certain radiation (X-rays, protons, acoustic waves, light rays, etc.) is passed through a section of the object in many directions, and properties of the radiation (intensity, phase, deflection, etc.) after passing the object are recorded for many rays. Experimental data for a certain value of the angle θ (Fig. 1) are named projection.
11 citations
TL;DR: In this paper, the shear stress fringe value of orthotropic birefringent model materials is used in an asymmetric four-point bend test that employs a notched specimen and is a modification of the Iosipescu test (1967).
9 citations
TL;DR: In this paper, a new separation method of principal stresses satisfying the above conditions was introduced, and the results obtained were in good agreement with the corresponding results obtained by theoretical or shear-difference method.
Abstract: In photoelasticity, it is desirable conditions of the method for obtaining the stress distributions (a) only isochromatic lines without isoclinic lines are used and (b) the principal stresses for arbitrary shapes can be separated easily. The present paper introduces a new separation method of principal stresses satisfying the above conditions. Stress distributions in several examples are obtained by the method which use only the prescribed values of the difference of principal stresses. The results obtained are in good agreement with the corresponding results obtained by theoretical or shear-difference method.
7 citations
Patent•
07 Nov 1986
TL;DR: In this paper, a method for obtaining quantitative data which relates the sound pressure distribution in a body to an ultrasound pulse waveform which propagates through the body, based on photoelastic measurement and analysis, is presented.
Abstract: A method for obtaining quantitative data which relates the sound pressure distribution in a body to an ultrasound pulse waveform which propagates through the body, based on photoelastic measurement and analysis. The method involves producing a first image of the body, into which the ultrasound pulse was launched, by recording the image of linearly polarized straboscopic light which is directed into the body. Thereafter, a second image is taken of the stroboscopic light with the principal axis of the linear polarizer offset by 45° relative to the first image. The first and second images are combined to produce a synthesized image and the above-mentioned quantitative data is derived from the synthesized image.
01 Jan 1986
TL;DR: In this paper, the same processes and changes which are developing rapidly in other fields of experimental mechanics and in experimental research in general are described in the context of photoelasticity.
Abstract: Photoelasticity, being one of the major fields of experimental research in mechanics, is subjected to the same processes and changes which are developing rapidly in other fields of experimental mechanics and in experimental research in general.
TL;DR: In this article, the interaction of the photoelastic parameters, the normalised light intensity In the characteristic angle ψ, and their link to the stress state parameters, such as the ratio of bending and direct stresses P and the angle of divergence θ of the stress components σM and σN have been examined by employing different wavelengths.
Abstract: The interaction of the photoelastic parameters, the normalised light intensity In the characteristic angle ψ, and their link to the stress state parameters, the ratio of bending and direct stresses P and the angle of divergence θ of the stress components σM and σN have been examined by employing different wavelengths. The analysis of the experimental data shows that the correlation diagrams of these parameters demonstrate similar characteristic curves. Measurements also show a preferable range of wavelength within which the wavelength of light source should be selected. So far the results are valid for thin plates, thin shells of rotationally symmetric conditions and similar structures.
01 Jan 1986
TL;DR: In this paper, the authors introduce nonlinear-elastic stress - strain relations between birefringence effects and stresses in photoelastic model materials, such as crack tips, notches and inclusions.
Abstract: As yet, in photoelasticity it has always been supposed Hooke’s theory of elasticity to be valid and consequently linear relations between birefringence effects and stresses to be existing [l]. However, in areas of high stress concentration, e. g. in the vicinity of crack tips, notches and inclusions, and with respect to some of the mainly used photoelastic model materials, considerable uncertainties may result. Therefore the following nonlinear-elastic stress - strain relations will be introduced.
TL;DR: In this article, a differential relationship for the variation of the separated stress components along a line of symmetry is derived by utilizing the compatibility and equilibrium field equations, in terms of only normal-incidence isochromatic data and does not use any isoclinic data.
Abstract: By utilizing the compatibility and equilibrium field equations a differential relationship for the variation of the separated stress components along a line of symmetry is derived. This is in terms of only normal-incidence isochromatic data and does not use any isoclinic data. Its application to two problems using experimental data is demonstrated.
TL;DR: In this article, a method for the determination of fringe orders and directions of principal stresses in the whole region of a 2-dimensional photoelastic model by image processing is described, where fringes (isochromatics, isoclinics) are extracted as points where the first derivative of the density distribution is zero.
Abstract: This paper describes a method for the determination of fringe orders and directions of principal stresses in the whole region of a 2-dimensional photoelastic model by image processing. The fringes (isochromatics, isoclinics) are extracted as points where the first derivative of the density distribution is zero. The determination of fringe orders or directions of principal stresses between extracted fringes uses the values and pattern of extracted fringes. The results obtained can be displayed as a shaded image on the monitor TV, and be utilized effectively for stress analysis by the finite element method, etc.
TL;DR: In this paper, a new method for stress analysis based on combination of two techniques: classical infrared photoelasticity and modern digital image processing is developed. But the method is not suitable for the analysis of polycrystal silicon ribbons.
Abstract: The brittleness of the polycrystal silicon ribbons is due to the residual stresses which appear in the material during the electron‐powder‐ribbon pulling process. We developed a new method for stress analysis based on combination of two techniques: classical infrared photoelasticity and modern digital image processing. The separation of principal stresses is achieved by means of a microcomputer: The sum of the principal stresses is determined which, combined with their differences, gives their values separately; by using these procedures it is possible to observe on a video analyzer the pseudocolor restoration of the stresses in the silicon ribbons. It may be noted that this method can be easily applied to other materials, such as InP for optoelectronic components.
TL;DR: In this article, the authors explored the stress distribution around a surface crack in a polyurethane rubber model subjected to axial pull using scattered light photoelasticity and showed that it can be solved in a completely non-destructive manner.
01 Jan 1986
TL;DR: In this article, the Boundary Integral Equation has been applied in photo-elasticity and the first stress invariant and its derivative on the boundary both can be obtained from photoelastic data.
Abstract: The Boundary Integral Equation has been applied in photo-elasticity. The first stress invariant and its derivative on the boundary both can be obtained from photoelastic data. The equation can be used to determine the stress tensor of any inner point directly, even if the model is acted by concentrated forces. The result shows that the photoelastic test contains full information about the stress tensors.
01 Jan 1986
TL;DR: The idea to study the transducer elastic elements by the finite element method (FEM) is a fairly novel one as mentioned in this paper, and the idea of using FEM to study transducers elastic elements is not new.
Abstract: The idea to study the transducer elastic elements by the finite element method (FEM) is a fairly novel one. Mitchell (6) has obtained good agreement between strain gauge and FEM results for the elastic column type, the difference being only 2.10−6. Bray (5) combined the theoretical (analytical and numerical calculation) and experimental (photoelasticity and strain gauges) techniques carrying out a complete research of a circular ring. Barbato (3) has studied by different methods the “square ring”, plotting the strain diagrams for various sets of parameters.
TL;DR: In this paper, a method for the determination of fringe orders and directions of principal stress in the whole region of a 2-dimensional photoelastic model by image processing is described, where fringes (isochromatics, isoclinics) are extracted as points where the first derivative of the density distribution is zero.
Abstract: This paper describes a method for the determination of fringe orders and directions of principal stress in the whole region of a 2-dimensional photoelastic model by image processing. The fringes (isochromatics, isoclinics) are extracted as points where the first derivative of the density distribution is zero. The determination of fringe orders or directions of principal stress between extracted fringes uses the values and pattern of extracted fringes. The results determined can be put out as a shaded image to monitor TV, and be utilized effectively to stress analysis by the finite element method, etc.
TL;DR: In this paper, a matrix method for describing fully depolarized light is proposed, and it is proved theoretically that this column matrix (Jones vector) can be used to describe unpolarised light as well.
Abstract: A matrix method for describing fully depolarized light is proposed. According to the properties of fully depolarized light it is proved theoretically that this column matrix (Jones vector) can be used to describe unpolarized light as well. Thus, it enables the problems of holographic photoelasticity, including holographic photoelasticity of unpolarized light, to be simply treated by using a unified matrix calculus (Jones calculus).
01 Jan 1986
TL;DR: The photostress method combines the best features of strain gages and classical photoelasticity by providing a visible picture of the surface stress distribution of the component and stress distribution which is accurately readable at any point for both direction and magnitude as mentioned in this paper.
Abstract: The Photostress and the photo-elastig coating technique weapply the Research Institute of Civil Engineering, Bratislava besides other experimental methods not only for the experimental stress analysis of models in laboratory but also during the construction and testing of bridges in situ. While the photoelastic model is still the only method for three-dimensional analysis, the surface coating technique permits the measurement of surface strains in the elastic or plastic ranges on structures, joints anchoring areas of pre-stressed concrete beams, atc., previously inaccessible to photo-elasticity. The use of experimental stress analysis techniques in situ is expanded in such fields as: establishment of design criteria, reduction of weight and cost of similar new structures or structural elements and improvement of product reliability. The photoelastic coatings, the photostress method combines the best features of strain gages and classical photoelasticity by providing a visible picture of the surface stress distribution of the component and stress distribution which is accurately readable at any point for both direction and magnitude.
01 Jan 1986
TL;DR: In several methods used in experimental mechanics an image is obtained as a result of an experiment, like various moire techniques, holographic interferometry or speckle, where the fringe pattern frequently appears on the inhomogenously bright background and image filtration would be much-desired.
Abstract: In several methods used in experimental mechanics an image is obtained as a result of an experiment. There are displacement measurement methods based on the phenomenon of light interference, like various moire techniques, holographic interferometry or speckle. In these methods a pattern of fringes appears on the specimen surface or in the camera. The fringes are contour lines of some specific deformation characteristics like in-plane displacements (e. g. intrinsic moire) or off-plane displacements (e. g. holographic interferometry). In the reflexion moire technique the contour map of the derivatives of the off-plane displacements is obtained. In all these methods usually specimen made of real structural materials are tested. Thus the fringe pattern frequently appears on the inhomogenously bright background and image filtration would be much-desired. There are also stress measurement methods based on the phenomenon of birefringence — various versions of photoelasticity. In these methods a pattern of fringes is also obtained. It is usually a contour map of the differences of principal stresses. Models made of special transparent materials are frequently tested instead of real structures or structural members. Thus, it is possible to assure homogenous background illumination and in many cases image filtration is not necessary. Further analysis is usually more complicated than in the previously mentioned methods, however, for fringe patterns in general the accurate determination of fringe axes is very important. The brittle lacquer technique can also be regarded as one giving visual information, although of a different type. The analysis of these images consists in the determination of densely cracked areas, thus being similar to texture analysis.
01 Jan 1986
TL;DR: Experimental stress intensity factors (SIFs) are evaluated for single, straight near edge cracks in a plate of finite width as mentioned in this paper, where cracks are positioned at various angles and distances with respect to the edge of the plate.
Abstract: Experimental stress intensity factors (SIFs) are evaluated for single, straight near edge cracks in a plate of finite width. The cracks are positioned at various angles and distances with respect to the edge of the plate. The far field stress is uniform tension parallel to the edge. On-line digital image analysis procedures are used to extract photoelastic data from the whole field isochromatic fringe patterns. Two different techniques are used to obtain information on the near crack tip stress field: (1) Half fringe photoelasticity (HEP), which requires adjusting the load to keep the maximum fringe order less than 0.5 in the data extraction zone, and (2) Trace, a digital fringe sharpening procedure, which accurately produces traces of all halfand full-order fringes. The load is adjusted to yield multiple fringes in the field of data extraction. Experimental SIFs from HFP and Trace are compared to each other and to the numerical results that are determined by the boundary integral equation method.
01 Jan 1986
TL;DR: The experimental method of photoelasticity has been widely applied to predict stress distribution in a model structure since the entire distribution can be observed visually as discussed by the authors, however, many elaborate techniques and much experience are required to obtain experimental results with a high degree of accuracy.
Abstract: The experimental method of photoelasticity has been widely applied to predict stress distribution in a model structure since the entire distribution can be observed visually[8]. However, many elaborate techniques and much experience are required to obtain experimental results with a high degree of accuracy. Furthermore, it is fairly troublesome and difficult to determine principal stresses throughout the model. Thus, the photoelastic method is not so commonly used, while numerical procedures have been broadly adopted for stress analysis.
01 Jan 1986
TL;DR: In this paper, the effect of depth/span ratio on bending stress wave propagation and on dynamic stress concentration factor in cantilever beam (dynamic load factor, DLF) under transverse impact load was studied by means of high speed photoelasticity.
Abstract: Effect of Depth/Span ratio on bending stress wave propagation and on dynamic stress concentration factor in cantilever beam (dynamic load factor, DLF) under transverse impact load was studied by means of high-speed photoelasticity. The photoelastic isochromatics for the entire impact duration were obtained, and propagation of bending stress waves was investigated. It was found that the upper limit of depth/span ratio for generating bending waves was about 0.57. Positive stress produced at the lower edge of the fixed end by stress wave going ahead of bending wave decreases with increasing h/1 and at h/l=0.55 and 0.91, this phenomenon is not observed. The results on DLF obtained from experiment were compared with theoretical solution by one dimensional equation for free vibrations of a beam in which transverse shear and rotary inertia were neglected. It was also shown that experimental results for DLF fell between theoretical solutions with the assumption of viscoelastic material and elastic material.
TL;DR: In this article, the problem of axi-symmetrical stresses can be analyzed by the scattered light photoelasticity, which need to obtain a stress equilibrium equation and three scattered isochromatic fringe patterns by three different incidences of polarized light beam.
Abstract: Formerly in the photoelastic experiments, indistinct isoclinic lines had to be applied in order to resolve the stresses in axi-symmetrical problem. The problem of axi-symmetrical stresses can be analyzed by the scattered light photoelasticity. This method need to obtain a stress equilibrium equation and three scattered isochromatic fringe patterns by three different incidences of polarized light beam. For the purpose of checking the accuracy of this experimental method, the author performed the stress analysis of a round shaft with a semicircular ring groove under the room temperature tensile loading, and also the author developed the epoxy resin of a new photoelastic material. This material had almost free stress initiation and photoelastic stress sensitivity of this material was higher value. As a result, it was proved that this technique led to a higher accuracy of the experimental stress analysis.