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Showing papers on "Photoelasticity published in 1972"


Journal ArticleDOI
TL;DR: In this paper, the maximum in-plane local shearing stress Tau sub m and average fringe loop inclination Theta sub m near the crack tip in terms of the Mode 1 and Mode 2 stress intensity factors K1 and K2 and polar coordinates r and Theta measured from the crack point were derived.

139 citations


Journal ArticleDOI
TL;DR: In this paper, a set of stress freezing photoelastic experiments are conducted on plates containing through cracks and results are compared with the Westergaard solution in order to assess the effect of Item 2 using appropriate Item 3 locations.

72 citations


Book ChapterDOI
TL;DR: A series of tests were performed using the stress freezing and slicing technique of photoelasticity in order to obtain the stress fields near points of maximum flaw penetration and where the crack border intersects the tensile surface of the plate for naturally grown surface flaws under fields of remote cylindrical bending as discussed by the authors.
Abstract: A series of tests was performed using the stress freezing and slicing technique of photoelasticity in order to obtain the stress fields near points of maximum flaw penetration and where the crack border intersects the tensile surface of the plate for naturally grown surface flaws under fields of remote cylindrical bending. Geometrics investigated ranged over crack depth to crack length ratios of approximately 0.13 to 0.55 and over crack depth to plate thickness ratios of approximately 0.27 to 0.79. Results were compared with several approximate theories on the basis of graphs of normalized maximum in-plane shear stress versus normalized distance from the crack tip and stress intensity factor in order to assess the validity of the several field theories. A numerical technique for data conditioning was employed from which the stress intensity factors were computed and compared with theoretical values.

55 citations


Journal ArticleDOI
TL;DR: In this article, a more fundamental approach based on the application of Bhagavantam's theory of photoelasticity for the orthorhombic crystalline system, a theory which is well established in crystal physics, is proposed.

32 citations


Journal ArticleDOI
TL;DR: In this article, a 16-spark gap Cranz-Schardin camera system was used to determine certain conditions leading to fracture arrest by a circular hole ahead of a propagating crack.
Abstract: Dynamic photoelasticity employing a 16-spark gap Cranz-Schardin camera system was used to determine certain conditions leading to fracture arrest by a circular hole ahead of a propagating crack. Photoelastic models of 3/8×10×10-in. Homalite-100 plates with a 1/2-in. edge crack were loaded in a fixed-grip configuration and crack arrest was made possible by central holes of 1/2, 1/4, and 0.15-in. diameters. In one test of a uniformly loaded plate with a central hole of 0.15-in. diameter, the propagating crack continued through this hole. Changes in dynamic-stress-intensity factors, as the crack tip approaches the hole, as well as changes in the dynamic-stress-concentration factors at the far side of the hole were studied, and these results were compared with the corresponding static results determined by finite-element analysis. This comparison shows that the static analysis can be used to qualitatively assess the arrest capability of the hole using the maximum static-stress concept or the proposed concept of strain energy released as the crack penetrates the hole.

25 citations


Journal ArticleDOI
TL;DR: In this article, the authors give an interpretation to the fringes observed in holographic interferometry when plane-polarized light or circularly polarized light is utilized, and the obtained patterns are formed by the superposition of three families of fringes: the two families of absolute optical retardation and the family of relative retardation.
Abstract: The purpose of this paper is to give an interpretation to the fringes observed in holographic interferometry when plane-polarized light or circularly polarized light is utilized. It is shown that, when plane-polarized light is utilized and both the loaded and the unloaded states are considered, the obtained patterns are formed by the superposition of three families of fringes: the two families of absolute optical retardation and the family of relative retardation. The intensity distribution is also a function of the orientation of the plane of polarization, and along the points where the plane of polarization is parallel to one of the principal directions, only one of the families of absolute retardation is observed. By utilizing circularly polarized light, the dependence on the orientation of the principal axis is eliminated and patterns consisting of the superposition of the three above-mentioned families are obtained. If only the loaded state is considered, the holographic interferometer behaves as an ordinary polariscope with the reference beam playing the role of the analyzer. The relationships between the observed families are discussed. Examples of application to the disk and ring under diametral compression are also given.

24 citations


Journal ArticleDOI
TL;DR: In this paper, a holographic interferometer is used to obtain separate but simultaneous isochromatic and isopachic-fringe patterns for photoelastic models in states of plane stress.
Abstract: A shortcoming of the conventional holographic interferometer used in photoelasticity is that, for the double-exposure cases, the resulting fringe patterns are a complex combination of conventional isochromatic and isopachic fringes. This paper describes a holographic interferometer that may be used to obtain separate but simultaneous isochromatic- and isopachic-fringe patterns for photoelastic models in states of plane stress. The method requires a model with a partially reflecting front surface. Isopachics, which are proportional to the thickness change, are recorded using holographic interferometry from the transmitted light. The isochromatics are obtained from the transmitted light by conventional means. General equations relating the surface displacement of the specimen to the observed fringe patterns are developed, and examples of static and dynamic loadings are shown.

24 citations


Journal ArticleDOI
TL;DR: In this article, the authors describe the use of stroboscopic photoelasticity for visualization in solids, compares the method with its schlieren counterpart, and discusses possible applications relevant to ultrasonic ndt.
Abstract: The visualization of ultrasonic pulses in solids has particular relevance to ultrasonic ndt. This paper describes the use of stroboscopic photoelasticity for visualization in solids, compares the method with its schlieren counterpart, and discusses possible applications relevant to ndt.

22 citations


01 Sep 1972
TL;DR: In this article, the dynamics of Homalite-100 plates are discussed in the context of linear theory of fracture mechanics, where dynamic photoelasticity is used for dynamic analysis and finite element method is used to static analysis.
Abstract: : Fracture dynamics of Homalite-100 plates is discussed in the context of linear theory of fracture mechanics. Dynamic photoelasticity is used for dynamic analysis and finite element method is used for static analysis. Static and dynamic strain energy release rates and kinetic energy release rates for constant velocity, accelerating and decelerating cracks are determined for tension loaded and impacted pretensioned plates. (Author)

18 citations


Patent
21 Jun 1972
TL;DR: In this paper, a polariscope is described for detecting stresses in a transparent object, and means for moving the transparent object in a direction transverse to the direction of the scanning light beam are provided.
Abstract: A polariscope is described for detecting stresses in a transparent object. The polariscope comprises means for producing a beam of polychromatic plane polarized light, a condensing lens, an aperture, a quarter-wave retardation plate, analyzing means and a photocell. Changes in stress cause changes in the color and intensity of the light detected. Means are provided for scanning the polychromatic light beam back and forth in one direction across the transparent object that is being studied. Means are also provided for moving the transparent object in a direction transverse to the direction of the scanning light beam. The output of the photocell is applied through an amplifier to a chart recorder in order to produce a plot of the stresses in the object with respect to their position.

16 citations


01 Aug 1972
TL;DR: In this paper, a stress analysis of the lap joint is presented treating the problem as one of plane strain, and the potential energy of the joint is calculated and minimized to obtain linear, ordinary differential equations and boundary conditions.
Abstract: : A stress analysis of the lap joint is presented treating the problem as one of plane strain. The joint is subjected to a general loading, consisting of tension, shear force and bending moments. The variation in the material properties and thickness of the two adherends is considered. The displacement field in the adhesive layer is expressed in series form and the compatibility condition at the interface is used to express the displacement field in the adherends. The potential energy of the joint is calculated and minimized to obtain linear, ordinary differential equations and boundary conditions. The differential equations are solved on the computer. Photoelasticity is used to confirm the theory. Two specimens of lap joint using a 1/4 in. layer of a photoelastic plastic simulating the adhesive, are tested photoelastically. The agreement between the theoretical and the experimental results is found to be good. Design recommendations for the lap joint are made based on the results of this investigation.

Journal ArticleDOI
TL;DR: In this article, photoelastic problems involving optical activity are analyzed using Stokes parameters and a set of differential equations equivalent to the Maxwell-Neumann equations is derived which yields results with greater ease than other currently available methods.
Abstract: In this paper, photoelastic problems involving optical activity are analysed using Stokes parameters. A set of differential equations equivalent to the Maxwell-Neumann equations is derived which yields results with greater ease than other currently available methods. A few specific problems are solved by using these equations. A brief discussion on the use of scattered light methods in problems with optical activity is also included.

Journal ArticleDOI
01 Jun 1972
TL;DR: In this article, it is shown that spontaneous changes of birefringence appearing are disproportional to P2s, and the contributions of spontaneous deformation into optical constants anomalies at ferroelectric transitions are discussed.
Abstract: 2014 Temperature dependences of birefringence were measured in (NH4)2SO4, (NH4)2BeF4 and (CH3NH3)Al(SO4)2. 12 H2O crystals and the photoelastic constants of the crystals were estimated. The temperature behaviour of electro-optical and dielectric characteristics was investigated. It is shown that spontaneous changes of birefringence appearing are disproportional to P2s. The contributions of Ps and spontaneous deformation into optical constants anomalies at ferroelectric transitions are discussed. Tome 7 No 2 JUIN 1972 It is well known that in addition to the usual thermo-optical variations optical constant changes take place at ferroelectric phase transitions [1]-[3]. These changes can be considered phenomenologically as a result of spontaneous electro-optic effect [4]. Its components are linear and (or) quadratic electrooptic effects of paraelectric phase, and an elastooptic effect due to spontaneous deformation accompanying a Ps appearance. Temperature dependences of optical constants of KDP, BaTi03, TGS [5]-[7] and many other ferroelectrics were adequately described on this basis. However it was noticed many times [8]-[10] that in such crystals as and NaNO2 the birefringence changes below Tc appeared to be disproportional to P;, as it follows from this description. Up to now no satisfactory explanation of unusual An(P/) dependences in these crystals was suggested. Similar optical constant behaviour was observed recently by the author in (NH4)2504 (AS), (NH4)2BeF4 (AFB) and near the first order transitions at Tc = 223,5°, 179,6° and 177 OK respectively [3]. In an effort to determine the main reasons of this unusual behaviour the spontaneous birefringence changes in AS, AFB and MASD crystals were measured within a wide temperature range, including T,,. Photoelastic constants of the crystals were also estimated. The temperature dependences of a quadratic electrooptic effect in paraelectric phases were investigated. Dielectric properties (e, PS) were measured simultaneously with electro-optic experiments on the same samples. Birefringence measurements were made with a Berek compensator [11] on the samples where the light propagations coincided with [100], [010] and [001] in ortorhombic AS and AFB and 100 > directions in MASD crystals. Electro-optic experiments were carried out by the dynamic method [12] at a wavelength of 6 328 Å. The outer electric field with the frequency of 800 cps was applied along the polar directions of crystals. For comparison purposes we shall discuss the results obtained on the ferroelectric cuts. Birefringence 0394nc of AS is linearly dependent on temperature Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/rphysap:019720070207700

Journal ArticleDOI
TL;DR: In this article, an experimental technique utilizing high pressure gas from an exploding wire is used to load long, hollow, thick-walled cylinders from the inside, resulting in plane-strain cylindrical stress waves are one-dimensional in nature.
Abstract: An experimental technique utilizing high-pressure gas from an exploding wire is used to load long, hollow, thick-walled cylinders from the inside. Resulting plane-strain cylindrical stress waves are one-dimensional in nature. Asimultaneity of impact is studied with methods of high-speed photography and dynamic photoelasticity.

Journal ArticleDOI
TL;DR: In this article, the principal strain rates and the maximum shear stress from photoviscotity were determined for slow viscous flow about a cylindrical obstacle in a rectangular channel.
Abstract: Photoelasticity in solids is a well-developed technique for stress and strain analysis. Less progress has been made in applying a similar effect, photoviscosity, to flow analysis. This paper has three objects: (1) to simplify photoviscous methods; (2) to compare velocity profiles obtained from photoviscosity with those obtained by the double-exposure bubble technique; (3) to determine the principal strain rates and the maximum shear stress from photoviscotity. The problem of slow viscous flow about a cylindrical obstacle in a rectangular channel was selected for the comparison. The fluid was a suspension of milling yellow dye in water. Strain rates and stresses averaged over the path of ligh can be obtained easily using photoviscosity. The bubble technique is shown to be a very powerful tool that permits the determination of the velocity field in three-dimensional problems.

Journal ArticleDOI
TL;DR: In this paper, a complete, direct, full-field optical determination of dynamic stress distributions associated with the flexural waves is obtained by a combination of photoelastic and interferometric measurements.
Abstract: The dynamics of continuous media subjected to initial stress is of great interest in several fields of applied science and technology: geophysics, oceanography, underwater acoustics, and structural design. Pioneering analytical work in this field was done by Biot. Few contributions have been made, however, to the experimental treatment of the problems of determining dynamic stress distributions within statically prestressed continuous media. The present paper deals with an experimental analysis of the propagation of flexural waves in prismatic elastic bars with and without prestressing. A complete, direct, full‐field optical determination of dynamic stress distributions associated with the flexural waves is obtained by a combination of photoelastic and interferometric measurements. The effects of prestressing by axial tension, axial compression, and pure bending are illustrated. Comparisons are made with an approximate theory. The results are extended to bars of other materials by scaling laws.

Journal ArticleDOI
TL;DR: In this paper, the dominant wavelength of a narrow band of electromagnetic radiation in the visible and near-infrared ranges transmitted through a polariscope was determined based on the application of a Babinet compensator.
Abstract: A new technique has been developed for determining the dominant wavelength of a narrow band of electromagnetic radiation in the visible and near-infrared ranges transmitted through a polariscope. This technique is based on the application of a Babinet compensator, for which the spectral dependence of the refractive indices for both ordinary and extraordinary rays, that is, the spectral birefringence of crystalline quartz, is known or has been determined.


Journal ArticleDOI
TL;DR: In this paper, the authors applied the irradiation method to determine the thermal stresses in a thick-walled cylinder with a temperature gradient along the radius, and good agreement was obtained between the stress determined experimentally and those calculated analytically.
Abstract: It has recently been shown that a gamma-ray irradiation fixes the birefringence in photoelastic models of Araldite B. The method has hitherto only been used to fix the birefringence in specimens subjected to constant forces. This work applies the irradiation method to determine the thermal stresses in a thick-walled cylinder with a temperature gradient along the radius. The model behaved in the following way during the experiment. The material relaxed when the temperature gradient was applied, and the model was irradiated when it was stress free. Real stresses, which were equal to the thermal stresses but with opposite sign, appeared when the temperature gradient was removed. As the problem is mathematically two-dimensional, it is possible to determine the birefringence by means of the slicing technique. Good agreement was obtained between the stress determined experimentally and those calculated analytically.


Journal ArticleDOI
J.A. Hooper1
TL;DR: In this article, a glass cylinder compressed across a diameter can be used as an effective load transducer by utilizing the birefringent properties of the glass, and various factors affecting the design and performance of this type of load gauge are discussed.

Proceedings ArticleDOI
01 Jan 1972
TL;DR: In this article, a plane stress analysis on a static model has been made by photoelasticity and interferometry, and lines tangent to critical directions of supposed pre-existing cracks, and fracture initiation zones are described in the vicinity of the contact area.
Abstract: As an attempt to clarify the working process of drag bit blades, a plane stress analysis on a static model has been made by photoelasticity and interferometry. Induced stress concentration, lines tangent to critical directions of supposed pre-existing cracks, and fracture initiation zones are described in the vicinity of the contact area. High tensil stresses appear around the cutting edge. Their magnitude increases as the cutting angle increases and does not depend on the clearance angle. High-compression stress concentrations are induced under the tooth for clearance angles other than zero. Their magnitude increases with rake angles. In the grinding mechanism, a double compression stress state is perceived in the vicinity of contact. Tensile stress appears behind the tooth, and high-compression stresses are propagated in front of it. From the Griffith-Walsh failure initiation theory and the discussions of the fracture initiation patterns, in the cutting case, tooth efficiency is determined according to horizontal force. The bit is more efficient, when the rake angle increases.

Journal ArticleDOI
TL;DR: In this article, a detailed investigation has been conducted on a free-standing stairs model subjected to its own weight using photoelasticity, the results of which are reported in this paper.
Abstract: A detailed investigation has been conducted on a free-standing stairs model subjected to its own weight using photoelasticity, the results of which are reported herein. The photoelastic results have been compared with the results obtained from some of the approximate theoretical solutions, and the differences in the results have been brought out.

Journal ArticleDOI
TL;DR: In this paper, a series of five research programs dealing with the experimental determination of stresses, strains, and displacements in circular cylinders subjected to pressure are described, and the most important results are summarized in a table.
Abstract: This paper is a summary of a series of five research programs dealing with the experimental determination of stresses, strains, and displacements in circular cylinders subjected to pressure. The vessels have either constant thickness or transverse reinforcing ribs. Circular holes, with either plain or reinforced edges, are located in different positions of the vessels. The methods used for the analysis are: brittle coatings, three-dimensional photoelasticity ("freezing" technique), and electrical and mechanical strain gages. The most important results are summarized in a table. These results will be of interest to designers of underwater ships and of pressure vessels in general.