Showing papers on "Photoelasticity published in 2004"
TL;DR: In this article, the effect of applied stress on the refractive index and birefringence of thin polymer films was investigated, and it was found that the applied stress in the out-of-plane direction of the thin films investigated leads to negative elasto-optic coefficients, as observed for all the three thin polymers.
Abstract: The use of thin polymer films in optical planar integrated optical circuits is rapidly increasing. Much interest, therefore, has been devoted to characterizing the optical and mechanical properties of thin polymer films. This study focuses on measuring the elasto-optical properties of three different polymers; polystyrene, polymethyl-methacrylate, and benzocyclobutane. The out-of-plane elastic modulus, refractive index, film thickness, and birefringence of thin polymer films were determined by means of the prism coupling technique. The effect of the applied stress on the refractive index and birefringence of the films was investigated. Three-dimensional finite element method analysis was used so as to obtain the principal stresses for each polymer system, and combining them with the stress dependent refractive index measurements, the elasto-optic coefficients of the polymer films were determined. It was found that the applied stress in the out-of-plane direction of the thin films investigated leads to negative elasto-optic coefficients, as observed for all the three thin polymer films.
58 citations
TL;DR: In this paper, the influence of anisotropy on the stress-optic coefficients and determination of the tensor components π11−π12 and π44 using an infrared polariscope and calibration with four-point bending of thin silicon samples were summarized.
Abstract: This paper summarizes the analysis of the influence of anisotropy on the stress-optic coefficients and the determination of the stress-optic tensor components π11−π12 and π44 using an infrared polariscope and calibration with four-point bending of thin silicon samples. Values obtained are π11−π12=9.88×10−13Pa−1 and π44=6.50×10−13Pa−1. A fringe multiplier was also introduced to increase the sensitivity of the infrared polariscope by up to seven times.
52 citations
TL;DR: In this article, a convex interface/joint design, inspired by the shape and mechanics of trees, will result in reduced stress singularities at bimaterial corners for most engineering material combinations.
Abstract: An integrated experimental and numerical investigation was conducted for removing the free-adge stress singularities in dissimilar material joints. A convex inter-face/joint design, inspired by the shape and mechanics of trees, will result in reduced stress singularities at bimaterial corners for most engineering material combinations.In situ photoelasticity experiments on convex polycarbonate-aluminum joints showed that the free-edge stress singularity was successfully removed. As a result, the new design not only improves the static load transfer capacity of dissimilar meterial joints, but also yields more reasonable interfacial tensile strength evaluation. For convex polycarbonate-aluminum and poly(methyl methacrylate)-aluminum joint specimens, the ultimate tensile load increased up to 81% while the total material volume was reduced by at least 15% over that of traditional butt-joint specimens with severe free-edge stress singularities.
45 citations
TL;DR: In this paper, a crack-tip stress, strain and displacement fields for a transient crack propagating along the direction of property gradation in functionally graded materials are obtained through an asymptotic analysis coupled with a displacement potential approach.
42 citations
TL;DR: In this article, a polariscope that allows simultaneous capture of multiple images is described, and a prototype instrument is evaluated using both transmission and reflection photoelasticity, offering the potential for real-time data acquisition and processing of high-speed events.
Abstract: The goal of recent research in digital photoelasticity has been fast, reliable, and accurate full-field photoelastic data that will allow the technique to play a valued role in assessing material and structural integrity. A novel design for a polariscope that allows simultaneous capture of multiple images is described, and a prototype instrument is evaluated using both transmission and reflection photoelasticity. The design offers the potential for real-time data acquisition and processing of high-speed events, using a number of different approaches to digital photoelasticity. The evaluation of the instrument arranged for the phase-stepping method demonstrated that it was capable of providing results of comparable quality and accuracy to manual analysis and more conventional methods of acquiring phase-stepped images.
39 citations
14 Dec 2004
TL;DR: In this paper, the second edition of the first edition, the authors presented a test and analysis of Fracture Toughness, a measure of the amount of stress required to break a fracture.
Abstract: PREFACE TO THE SECOND EDITION PREFACE TO THE FIRST EDITION HISTORICAL DEVELOPMENTS IN FRACTURE MECHANICS AND OVERVIEW Early Foundations of Strength of Material Concepts Development of Concept of Stresses Development of Modern Fracture Mechanics Basic Concepts of Stress and Strain Theory of Elasticity Strength Theories and Design Symbols References STRESS AND ENERGY CRITERIA AND FRACTURE Effects of Geometry Inglis Theory of Stress Advent of the Energy Concept Griffith Theory of Fracture Concept of Stress Intensity Plane-Strain Fracture Toughness Variation of Basic Parameters Symbols References CALCULATION OF STRESS INTENSITY Center Crack Double-Edge Crack Single-Edge Crack Collapse Stress Round Hole With Cracks Elliptical Notches With Cracks Edge-Notched Beams Flaws in Tension Superposition of Stress Intensity Factors Special Cases of Stress Intensity Closing Remarks Symbols References TEST AND ANALYSIS OF FRACTURE TOUGHNESS Overview of Theory and Practice Constraint and Thickness Testing of Fracture Toughness Determination of LEFM Parameters Correlation Techniques Symbols References CRACK MECHANICS General Comment Surface and Corner Cracks Elements of Fatigue Technology Initiation of Fracture Crack Propagation Special Effects Design Procedures Symbols References ELEMENTS OF STRUCTURAL INTEGRITY Ductile and Brittle Fracture Transition Temperature Approach Lower-Bound Stress in Design Crack Behavior in Weld Regions Criteria of Leak-Before-Break Plane Stress and Plastic Behavior CTOD Environmental Effects LEFM Symbols References EXPERIMENTAL DETERMINATION OF STRESS INTENSITY FACTOR KI General Comment Strain Gage Method Optical Method of Photoelasticity Shadow Method of Caustics Fiber-Optic Sensors and Fracture Mechanics Discussion Symbols References DYNAMIC FRACTURE Determination of Dynamic Initiation Toughness Crack Propagation Crack Arrest Symbols References FRACTURE TOUGHNESS OF FIBER REINFORCED COMPOSITES Introduction Measures of Fracture Toughness for Composites Experimental Measurement of Fracture Toughness Symbols References POST MORTEM FAILURE ANALYSIS Fractography Optical Microscopy Scanning Electron Microscopy Transmission Electron Microscopy (TEM) Interpretation of Fracture Surface Features Symbols References CASE STUDIES Typical Structural Failures in Service Crane Retrofit and Materials Control Integrity of Underground Structures Lessons From Structural Failures Symbols References INTRODUCTORY FRACTURE CONTROL Historical Perspective Analytical Options of Fracture Control and Failure Review Practical Elements of Fracture Control Limitations and Errors Symbols References DESIGN CONSIDERATIONS Basic Characteristics Selected Formulas and Definitions Special Problems Engineering Materials Glossary of Terms and Fundamentals Symbols References INDEX
34 citations
TL;DR: A new method is developed to remove ambiguity in the phase map using isoclinic–isochromatic interaction and a flexible algorithm for phase unwrapping is developed using tiling.
34 citations
TL;DR: A novel polariscope with electro-optic modulation that is capable of simultaneous measurement of the principal axis and the phase retardation of an optical linear birefringent medium by means of two phase-locked extractions is described.
Abstract: A novel polariscope with electro-optic modulation that is capable of simultaneous measurement of the principal axis and the phase retardation of an optical linear birefringent medium by means of two phase-locked extractions is described. A phase compensator is used to suppress the transmission phase-retardation effect of the beam splitter, thereby enhancing the precision of the measuring performance. The validity of the proposed design is demonstrated by measurement of the principal axis and phase retardation of a quarter-wave plate sample. There are absolute errors of 0.25° on average and 0.58° at maximum in the principal-axis measurement and of 0.75° (0.83%) on average and 3.11° at maximum in the phase-retardation measurement. Meanwhile, the retardation error lies within a 5% uncertainty range of a commercial wave plate. The root-mean-square resolutions for the principal-axis angle and phase-retardation measurements are 0.042° and 0.081°, respectively. Finally, the dynamic ranges of the principal-axis angle measurement and the phase-retardation measurement extend as far as 180°.
30 citations
TL;DR: In this paper, four optical techniques for evaluating stress intensity factors in opaque specimens are described in outline, and compared for both an artificial crack and a fatigue crack, and the results are compared to a standard solution for the geometry considered.
Abstract: Four optical techniques for evaluating stress intensity factors in opaque specimens are described in outline, and compared for both an artificial crack and a fatigue crack. The results are compared to a standard solution for the geometry considered. All the techniques gave acceptable results over a range of stress levels and crack lengths. The methods of caustics and strain gauges were less good, whilst photoelasticity gave consistent results over a wide range of stress levels. Comments on the ease of application and the resource implications are also made in order to assist practitioners.
28 citations
TL;DR: In this paper, the Iosipescu shear specimens and butt-joint specimens were employed to measure the shear and tensile strengths of five types of adhesive bonds for brittle poly(methyl methacrylate) and Homalite polymers.
27 citations
TL;DR: In this paper, the problem of finding unknown coefficients in linear combinations of holomorphic functions used for the representation of complex potentials in plane elasticity is reduced to the determination of unknown coefficients by fitting the data to the calculated principal directions.
TL;DR: In this paper, the authors describe an experimental study on full-field stress separation from thermoelasticity and photoelastic measurements and its application to estimation of stress intensity factor and the J-integral.
Abstract: This paper describes an experimental study on full-field stress separation from thermoelasticity and photoelasticity measurements and its application to estimation of stress intensity factor and the J-integral. Thermoelastic stress analysis (TSA) and photoelastic stress analysis (PSA) have been developed as full-field visualization methods of stress distribution. Only the sum of the principal stresses can be measured by TSA, while only the difference of the principal stresses can be measured by PSA. In this study, the hybrid stress separation measurement technique developed by the present authors using both of these methods was applied for determining distribution of all individual stress components in a center-cracked plate subjected to mechanical load. Stress intensity factor and the J-integral were calculated from the obtained stress distribution. In addition to the conventional calculation method, near-tip exclusive domain integral method was proposed, in which the J-integral was evaluated without using degraded experimental stress distribution data near the crack tip. It was found that these fracture mechanics parameters can be evaluated with good accuracies by the present technique.
TL;DR: In this paper, displacement-based finite element method formulations are coupled with stress-based photoelasticity analysis to generate high quality digital images acceptable for hybird experimental-numerical techniques.
Abstract: Displacement-based finite element method formulations are coupled with stress-based photoelasticity analysis. As the stress field is discontinuous at the interelement boundaries, the introduced smoothing procedure enables the generation of high-quality digital images acceptable for hybird experimental-numerical techniques. The proposed methods are applicable for the analysis of static and dynamic results of experimental photoelasticity.
TL;DR: In this article, the isochromatic fringe patterns obtained were analyzed using orthotropic photoelasticity to determine Mode-I stress intensity factors, and good agreement was found between the regenerated fringe patterns and the experimentally obtained patterns.
Abstract: Fiber-reinforced plastic composite materials are being widely used in a variety of load bearing and high-performance structures. Reliable use and optimum design requires accurate methods for predicating their fracture behavior, among other things. Fiber reinforced plastic composites are generally opaque and hence experimental fracture mechanics studies utilize surface measurements or post-fracture analysis. Hence quality transparent glass cloth reinforced polyester composites have been fabricated and transmission photoelasticity used to investigate quasi-static Mode-I fracture. The isochromatic fringe patterns obtained were analyzed using orthotropic photoelasticity to determine Mode-I stress intensity factors. Opening mode stress field equations in conjunction with an orthotropic stress-optic law were utilized to regenerate the isochromatic fringe patterns. Good agreement was found between the regenerated fringe patterns and the experimentally obtained patterns.
TL;DR: In this paper, a new common-path circular polariscope and the Senarmont setup with electro-optic modulation for measuring the optical linear birefringent media properties are presented.
TL;DR: This work presents an alternative load-stepping algorithm that is based on a nonlinear sinusoidal least-squares fitting based on the description of this technique together with its verification on simulated and real experiments.
TL;DR: The propagation of polarized light in an inhomogeneous birefringent medium is systematically studied to elucidate the relationships between the measurement data and the parameters of the stress field are non-linear.
Abstract: In recent years many authors have considered the possibility of using tomography for nondestructive determination of three-dimensional stress fields. A natural starting point for this is integrated photoelasticity. The problem is complicated since the stress field is a tensor field, and in the general case in integrated photoelasticity the relationships between the measurement data and the parameters of the stress field are non-linear. To elucidate these relationships, we have systematically studied the propagation of polarized light in an inhomogeneous birefringent medium. The inverse problem of integrated photoelasticity is formulated in the general form, and particular cases in which the polarization transformation matrix is exactly determined by integrals of the stress tensor components are considered. The possibility of using the Radon inversion for approximate determination of the normal stress field in an arbitrary section of the test object is outlined.
TL;DR: In this paper, the Poincare equivalence theorem is proved by explicitly proving a matrix decomposition theorem, from which the matrix equivalence result follows as a corollary.
Abstract: The Poincare equivalence theorem states that any optical element which contains no absorbing components can be replaced by an equivalent optical model which consists of one linear retarder and one rotator only, both of which are uniquely determined. This has many useful applications in the field of optics of polarized light. In particular, it arises naturally in attempts to reconstruct spatially varying refractive tensors or dielectric tensors from measurements of the change of state of polarization of light beams passing through the medium, a field which is known as tensor tomography. A special case is photoelasticity, where the internal stress of a transparent material may be reconstructed from knowledge of the local optical tensors by using the stress-optical laws. We present a rigorous approach to the Poincare equivalence theorem by explicitly proving a matrix decomposition theorem, from which the Poincare equivalence theorem follows as a corollary. To make the paper self-contained we supplem...
TL;DR: In this paper, it is shown how the ray transform emerges naturally in any attempt to reconstruct optical and stress tensors within a photoelastic medium from measurements on the state of polarization of light beams passing through the strained medium.
Abstract: We explain the main concepts centered around Sharafutdinov’s ray transform, its kernel, and the extent to which it can be inverted. It is shown how the ray transform emerges naturally in any attempt to reconstruct optical and stress tensors within a photoelastic medium from measurements on the state of polarization of light beams passing through the strained medium. The problem of reconstruction of stress tensors is crucially related to the fact that the ray transform has a nontrivial kernel; the latter is described by a theorem for which we provide a new proof which is simpler and shorter as in Sharafutdinov’s original work, as we limit our scope to tensors which are relevant to Photoelasticity. We explain how the kernel of the ray transform is related to the decomposition of tensor fields into longitudinal and transverse components. The merits of the ray transform as a tool for tensor reconstruction are studied by walking through an explicit example of reconstructing the σ33-component of the stress tensor in a cylindrical photoelastic specimen. In order to make the paper self-contained we provide a derivation of the basic equations of Integrated Photoelasticity which describe how the presence of stress within a photoelastic medium influences the passage of polarized light through the material.
15 Dec 2004-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the authors used infrared photoelasticity with the aim of clarifying the shielding effect due to crack tip dislocations on the steep increase of fracture toughness in the brittle-toductile transition (BDT).
Abstract: Stress fields around a crack tip in silicon crystals have been investigated by using infrared photoelasticity with the aim of clarifying the shielding effect due to crack tip dislocations on the steep increase of fracture toughness in the brittle-to-ductile transition (BDT). First, compact tension tests were carried out at room temperature to make in situ observation of elastic behavior of crack tip stress fields. The photoelastic images observed were in good agreement with those simulated for the usual elastic fields around the tip of a mode I crack. Next, to clarify the stress modification due to crack tip plasticity, three-point bending tests were also made by using notched specimens at high temperatures around 1000 K. After the high temperature test, in spite of the absence of the applied load, residual bright images were observed around the notch. Those images correspond to an internal stress due to dislocations multiplied around the notch, and they have an effect of shielding (accommodating) the stress concentration due to the applied load. The fracture toughness at room temperature was increased by the introduction of the residual stress.
16 May 2004
TL;DR: A novel design is proposed for a Si accelerometer sensor chip where a stress-tunable photonic crystal is used as the sensitive element to optically measure the deflection of a bulk-micromachined diaphragm with a boss.
Abstract: A novel design is proposed for a Si accelerometer sensor chip where a stress-tunable photonic crystal is used as the sensitive element to optically measure the deflection of a bulk-micromachined diaphragm with a boss. The photonic crystal may be 1D stack, 2D channel type, microbridge, etc. The photoelasticity effect is used instead of customarily utilized piezoresistivity and thus an all-optical readout is obtained. A feasibility analysis of the proposed structure is performed. 3D finite element modeling is used to determine the mechanical properties of the structure and the transfer matrix method to calculate its electromagnetic behavior. The advantages of the proposed concept are its simplicity, all-optical operation, monolithic integration with the sensor chip and compatibility with contemporary fiber-optic and integrated optics systems and devices.
TL;DR: In this article, the measurement of strain by the application of reflection photoelasticity is compared to an analytical and numerical results, and the final aim of this work is to determine the behavior of such structures by the exact knowledge of its mechanical properties deduced in part from edge effect results.
Abstract: Knowledge of edge effects in composite with honeycomb cores is essential for the design of sandwich structures. This paper deals with the measurement of strain by the application of reflection photoelasticity. Because of the geometry of honeycomb cores a classical method by strain gages is inaccurate and unsuitable. The measurements by photoelasticity is compared to an analytical and numerical results. The final aim of this work is to determine the behavior of such structures by the exact knowledge of its mechanical properties deduced in part from edge effect results.
TL;DR: In this paper, the interfacial shear strength of a pull out model between a thermoplastic fiber and a thermoset matrix was analyzed, and the method to analyze the quality in this kind of composite was photoelasticity.
Abstract: The interfacial shear strength of a pull out model between a thermoplastic fiber and thermoset matrix was analyzed. The method to analyze the interfacial quality in this kind of composite was Photoelasticity. The interfacial shear strength was measured localizing the isocromatic fringes. The Isochromatic fringe corresponds to the points along the specimen in which the principal stresses have the same value.
Journal Article•
TL;DR: In this article, the authors reviewed the photoelastic fringe refining and multiplication and the techniques for automatically determining photo-elastic parameters, including phase shifting, Fourier transform method, load stepping, spectral content analysis, and RGB photo elasticity etc.
Abstract: Digital photoelasticity combined the traditional photoelasticity with computer imaging techniques in order to acquire photoelastic data and analysis stress automatically, can improve experimental speed and precision In this paper, we firstly reviewed the photoelastic fringe refining and multiplication and the techniques for automatically determining photoelastic parameters, including phase shifting, Fourier transform method, load stepping, spectral content analysis and RGB photoelasticity etc The advancements in the last two decades reveal that the combination of the isoclinic parameter, which is calculated by the color-field phase shifting technique, and the ischromatic parameter, which is determined by the phase shifting in white light or three-color light, is expected to solve the static stress analysis of two dimensional models or three dimensional thin slices Moreover, the combination of designing a device to collect several photoelastic images real-timely or synchronously and acquiring photoelastic parameters by the phase shifting technique is one of the promising ways for the development of digital dynamic photoelasticity The review also gives us a future trend of digital photoelasticity and benefits for automating data-acquisition and stress-analysis
Patent•
02 Dec 2004
TL;DR: In this article, a photoelastic phase modulator is used to measure the photo-elasticity generated between a polishing tool surface and a workpiece in real-time by using a heterodyne polarimeter.
Abstract: PROBLEM TO BE SOLVED: To provide a polishing tool pressure distribution measuring method which enables a measurement of a pressure distribution generated between a polishing tool surface and a workpiece in real time by using a photoelastic phenomenon as a means for measuring the pressure distribution with high accuracy, in order to visualize and clarify a polishing process and carry out the polishing with high accuracy and high stability, and to provide a polishing tool and a polishing device. SOLUTION: In implementation of the polishing tool pressure distribution measuring method, a system is employed which comprises a photoelasticity generating optical system for measuring the pressure distribution, based on the polishing device, a heterodyne polarimeter for measuring the photoelasticity with high accuracy, a photoelastic phase modulator for enabling automatic measurement, a control system for controlling a measuring system location, an image signal processing computer for processing fetched signal data, etc. COPYRIGHT: (C)2005,JPO&NCIPI
TL;DR: In this article, the use of two digital photoelasticity methods for collecting these data is discussed and SIFs are evaluated using constant radius method and a least squares approach based on the singular stress field equation.
Abstract: The main sources of error in the determination of stress intensity factors (SIFs) for an interface crack in a bi-material by conventional photoelasticity are the measurement of the positional co-ordinates of the data point and the fringe order. In the present work, use of two digital photoelasticity methods for collecting these data is discussed. SIFs are evaluated using constant radius method and a least squares approach based on the singular stress field equation. The need for developing a multi-parameter stress field solution for evaluating SIF is highlighted.
TL;DR: In this paper, a non-destructive method for identifying boundary conditions applied on a 3D linear elastic body is developed based on the load incremental approach, which linearizes the nonlinear governing equation of photoelasticity by considering small increments in applied load.
Abstract: A new nondestructive method for identifying boundary conditions applied on a 3D linear elastic body is developed based on the load incremental approach, which linearizes the nonlinear governing equation of photoelasticity by considering small increments in applied load. Direct stress identification based on load incremental approach is highly sensitive to measurement errors and involves considerable amount of computations. On the other hand, identification of boundary conditions based on load incremental approach and thereby the state of stress is not only less sensitive to measurement errors but also involves less computation. This boundary conditions identification can be considered as an introduction of equilibrium condition and the property of linear elasticity to overcome the shortcomings of direct stress identification.
01 Jan 2004
10 Sep 2004
TL;DR: In this article, an algorithm of photoelastic tomography and its application for residual stress measurement in glass articles of complicated shape is described, which is based on a linearized solution of the equations of integrated photelasticity.
Abstract: The paper describes an algorithm of photoelastic tomography and its application for residual stress measurement in glass articles of complicated shape. The algorithm is based on a linearized solution of the equations of integrated photoelasticity. The problem of tensor field tomography is decomposed into several problems of scalar field tomography for normal stress components of the stress tensor. The method is implemented with an automated polariscope supplied with a rotary stage. Several examples illustrate application of the method. 1. INTRODUCTION Residual stress is one of the most important characteristics of glass articles from the point of view of their strength and residtance. 1,2 In the case of optical glass, birefringence caused by the residual stresses characterizes the optical quality of the article. During about a century, photoelasticity has been the most widely used method for quality control in the glass industry. 3,4 Two-dimensional photoelasticity permits the determination of the so-called form stresses (which are constant through the thickness in flat glass). As for the thickness stresses (which vary parabolically through the thickness), their distribution can be determined using the scattered light method. Specific methods have been developed for nondestructive determination of the stresses on the surfaces of the flat glass.
TL;DR: In this paper, the authors investigated the case when multiple reflection of the light is used to increase the rotation of the plane of polarization and showed that 2n multiple reflections correspond to a (2n+1)1/2)fold increase of the magnetic field.
Abstract: In magnetophotoelasticity, photoelastic models are investigated in transmitted light with the wave normal parallel to the magnetic field. Transformation of polarization in the model is caused both by stress birefringence and by the Faraday effect. Due to the latter, the integral Wertheim law is not valid and it is possible to measure stress distributions that are in equilibrium through the model like bending stresses in plates and parabolic residual stresses in glass plates. One of the drawbacks of magnetophotoelasticity is the need for very precise optical measurements since the angle of rotation of the plane of polarization is small. In this paper we investigate the case when multiple reflection of the light is used to increase the rotation of the plane of polarization. It is shown that 2n multiple reflections correspond to a (2n+1)1/2-fold increase of the magnetic field.