Showing papers on "Photoelasticity published in 1999"

Optical Methods of Measurement: Wholefield Techniques

Abstract: Waves deffraction phase evaluation methods detectors and recording materials holographic interferometry speckle metrology photoelasticity the Moire phenomenon

Single-fibre Broutman test: fibre–matrix interface transverse debonding

Abstract: The single-fibre Broutman test was used to study the fibre–matrix interface debonding behaviour when subjected to a transverse tensile stress. During testing, damage was detected using both visual observation under polarized light and acoustic emission (AE) monitoring. Separation of failure mechanisms, based on AE events, was performed using time domain parameters (amplitude and event width) and fast Fourier transform (FFT) frequency spectra of the AE waveforms. The latter can be considered as a fingerprint allowing to discriminate fibre failure, matrix cracking, fibre–matrix interface debonding, friction and ‘parasite noise’. Stresses in the specimens were evaluated using a two-dimensional finite element model (FEM) and monochromatic photoelasticity was used to verify the simulated stress distribution. Two failure mechanisms appeared to be in competition in the Broutman test: fibre failure under compressive stresses and fibre–matrix interface debonding under transverse tensile stresses. For systems in which the interfacial adhesion is not so ‘good’, like glass fibre–polyester systems for instance, fibre–matrix debonding was observed, and the progression of the debonding front with the interfacial transverse stress was recorded. Thermal stresses are also discussed, and a FEM simulation shows that they encourage fibre failure under compressive stresses.

Phase-shifting method with a normal polariscope

Abstract: In many laboratories of universities and industrial organizations, commercial polariscopes have the feature that the relative position of the two quarter-wave plates is fixed. This is due to the requirement of transforming a plane polariscope to a circular polariscope with greater precision and ease. Unfortunately, these polariscopes cannot implement Patterson and Wang's [Strain 27, 49-56 (1991)] phase-shifting algorithm because this algorithm requires that the second quarter-wave plate and the analyzer of the circular polariscope be capable of independent rotation. A new phase-shifting method that can be applied under these constraints is proposed. A comparative study with Patterson and Wang's [Strain 27, 49-56 (1991)] algorithm shows very good agreement. Furthermore, it is shown that four phase steps are sufficient to determine both the isoclinic and the isochromatic parameters.

Two-wavelength method for full-field automated photoelasticity

Abstract: A new method for the whole-field determination of the isoclinic angle α and the isochromatic parameter ϕ is presented. The problems appearing during the calculation of these two parameters are solved with the use of two different wavelengths. Indeed, when a monochromatic light is used as an incident light, α is not measurable at the points where ϕ is equal to 2kπ. In this method, each monochromatic light can compensate for the influence of ϕ to obtain the isoclinic angle for the entire model. Also, most of the methods calculate the fractional fringe order that is unwrapped afterward to obtain the isochromatic parameter. This unwrapping process needs an initialization, which cannot be automatic with only one isochromatic fringe pattern. The use of two wavelengths permits a complete automatic unwrapping of the isochromatic parameter, even for the initialization of the process.

Validation of finite element modelling through photoelastic fringe contours

Abstract: In finite element modelling, apart from proper element selection, selection of an appropriate discretization scheme is crucial in correctly evaluating the intended variables. The role of photoelasticity in selecting an appropriate discretization scheme for modelling problems in stress analysis is presented in this paper.

Rayleigh pulse-dynamic triggering of fault slip

Abstract: We present an experimental and numerical investigation of the interaction of a Rayleigh (R) pulse with a partially contacting strike-slip fault between similar and dissimilar materials. This study is intended to offer an improved understanding of the earthquake rupture mechanisms. The fault is subjected to static normal and shear prestresses. Utilizing two-dimensional dynamic photoelasticity in conjunction with high-speed cinematography, the evolution of time-dependent isochromatic fringe patterns (contours of maximum in-plane shear stress) associated with Rayleigh pulse-fault interaction is experimentally recorded. It is shown that fault slip (instability) can be triggered by a pulse that propagates along the fault interface at Rayleigh wave speed (about 90% of the relevant shear wave speed) and that the direction of the static shear preloading has an influence on the initiation of fault slip. For the numerical studies, a finite-difference wave propagation simulator SWIFD (solids wave impact fracture damage) is used for a quantitative analysis of the problem under different combinations of contacting materials. Dynamic rupture in laterally heterogeneous structures is discussed by considering the effect of the acoustic impedance ratio of the two contacting materials on the wave patterns. The results indicate that upon fault rupture, Mach (head) waves, which carry a relatively large amount of concentrated energy, can be generated that propagate from the fault contact region into the acoustically softer material. Such Mach waves can cause concentrated damage in a particular region located inside an adjacent acoustically softer area. This type of damage concentration might be another possible reason for the generation of the damage belt in Kobe, Japan, on the occasion of the 1995 Hyogo-ken Nanbu earthquake.

The development of simultaneous thermo- and photo-elasticity for principal stress analyses

Abstract: A technique is developed for determining the individual principal stresses by measuring experimentally the sum and the difference of the principal stresses over a surface of an engineering component. This application, which results from previous research on the thermoelastic response of polycarbonate coatings typically used in reflection photoelasticity, is based upon the simultaneous use of thermoelastic stress analysis and automated photoelasticity. Full field patterns of the individual principal stresses can be evaluated, even over complex geometric surfaces, by properly processing the data obtained by the independent experimental techniques.

The stress optical behavior of PET fibers and films

Abstract: The use of stress-optical measurements to characterize oriented PET fibers is reviewed. The implications of a molecular network for the development of orientation in spun fibers, cold drawn and hot drawn fibers are also considered. Early research made use of the Kuhn and Grun theory of photoelasticity, and their model has been shown by many workers to be a useful starting point for understanding the development of molecular orientation in PET provided that it is suitably modified for high chain extension at high draw ratios. The principal thrust of recent research at Leeds has been to explore the applications of more precise molecular modelling using the Monte Carlo rotational isomeric state model developed by Stepto and Taylor, and applying it to the development of optical birefringence with strain, as well as the shrinkage stress. It has been shown that the Kuhn and Grun theory, where the actual network is replaced by a model network of freely jointed random links, cannot provide a consistent description of the shrinkage stress and the optical birefringence.

Use of multiple loads to extract continuous isoclinic fringes by phase shifting technique

Abstract: Using a monochromatic light source for illumination, a new approach is proposed which uses two different loads to get continuous isoclinic fringes A new set of optical arrangements in a plane polariscope setup is proposed for this purpose The intensity equations are obtained by Jones calculus The methodology is verified for the problem of a disc under diametral compression

Two-Dimensional Transient Thermal Stress Analysis of Adhesive Butt Joints

Abstract: Transient thermal stress distribution in an adhesive butt joint is considered. It is assumed that both the upper and lower end surfaces of the joint are maintained at different temperatures at a certain instant in time and that no heat transfers between the side surfaces of the joint and ambient air. In the analysis, two adherends were replaced with finite strips and unsteady temperature distribution in the joint was obtained theoretically. Then the transient thermal stress distribution in the joint was analyzed using a two-dimensional theory of elasticity. The effects of the ratios of the coefficient of thermal expansion and Young's modulus of the adherend to those of the adhesive on the thermal stress distribution were clarified from numerical calculations. Furthermore, the transient stress distribution in the adhesive was measured by a photoelastic experiment on a joint where the adhesive was modelled by an epoxy plate. The experimental results were consistent with the analytical results.

Polarizing plate protective film and polarizing plate

Abstract: PROBLEM TO BE SOLVED: To provide a polarizing plate excellent in optical characteristics and a polarizing plate protective film causing no irregular display and contrast degradation even under a high-temperature or high-temperature humid environment when used for the polarizing plate. SOLUTION: This polarizing plate protective film is laminated with a resin layer having a smaller hygroscopicity than tri-acetyl cellulose and a positive photoelasticity constant, and with a resin layer having a smaller hygroscopicity than tri-acetyl cellulose and a negative photoelasticity constant, so that the photoelasticity constant of the polarizing plate protective film is not more than 10.0×10-7 cm2/kgf.

Photoelastic Imaging of Process Induced Defects in 300mm-Silicon Wafers

Abstract: Process induced crystal defects in silicon wafers can be detected by their stress fields. The nondestructive photoelasticity based on laser polarimetry is applied to visualize the stress fields of temperture gradient induced lattice defects like sliplines or extended defect areas around boat marks. The quantitative evaluation of the defects allows their characterization by a specific danger potential for further evolution causing upstream problems in IC manufacturing.

The magnetophotoelastic analysis of residual stresses in thermally toughened glass

Abstract: The determination of individual stress values in the multiaxial residual stress distributions found in toughened glass is a problem of major practical importance in the glass industry In spite of many years of development, conventional experimental stress analysis techniques have not been able to provide a generally applicable means of obtaining this information However, a unique method has now been developed for this purpose, based on the principles of magnetophotoelasticity, in which the combined optical retardation effects due to (i) the stress-birefringence of the material and (ii) a superimposed magnetic field, are utilized The paper summarises the basic theory of magnetophotoelasticity and describes experimental verification work using simple uniaxial systems of constant and linearly varying stress Two important developments follow First, a solution technique is developed whereby principal stress differences can be determined at any position through the thickness of a toughened glass plate, for an assumed biaxial residual stress distribution consisting of a combination of parabolic and linear stress variations Second, an oblique incidence technique is employed to obtain individual stresses from the previously determined principal stress differences A polariscope, designed and built for the implementation of the technique at any position over the area of an automotive windscreen, is described Typical experimental results are presented and shown to compare well with the limited information available from conventional techniques

Phase difference plate, elliptically polarizing plate, separation element for circularly polarized light and liquid crystal display device

Abstract: PROBLEM TO BE SOLVED: To provide a phase difference plate with which a liquid crystal cell can be accurately optically compensated even when the temperature and humidity change. SOLUTION: The phase difference plate has an optical anisotropic layer formed from liquid crystal molecules on a transparent support. In the plate, the transparent support has 10 to 1,000 nm phase difference in the plane or thickness direction, and the absolute modulus of photoelasticity of the transparent support is controlled to <1×10-6 cm2/kg.

Determination of resudual stress fields beneath a Vickers indentation using photoelasticity

Abstract: Static Vickers indentation tests were performed on Homalite specimens with an intent to obtain the residual stress distribution beneath the indentation. The indented specimens were placed in a circular polariscope to view the fringe patterns corresponding to the induced residual stress. Similitude analysis was later employed to identify the functional relationship between the various parameters related to an indentation test. The analysis resulted in a unified relationship that can assist in the determination of residual stress in nontransparent materials subjected to similar geometric and loading conditions. The shear stress contours provided here can also be used as guidelines to verify constitutive models under complex three-dimensional loads.

Variational method for the solution of the problems of tomography of the stressed state of solids

Abstract: We study the problem of reconstruction of the stressed state of piecewise-homogenous solids on the basis of the data of measuring of the effects of interaction of external physical fields with the stress field. The general mathematical model includes three main elements: a model of stressed state, the data of nondestructive testing obtained by one or several methods, and a model of interaction of the sounding radiation with the stress field. Within the framework of this model, the problem of reconstruction of the stressed state is reduced to the problem of minimization of a quadratic functional taking into account both the experimental data obtained by different physical methods and the conditions imposed on the surface of the body and the interfaces of its components of different nature. This approach enables one to perform the numerical realization of both direct and inverse problems on the basis of a single algorithm. We establish the analytic structure of the beam integrals of the stress field determined according to the results of polarization-optical measurements. On this basis, we apply the proposed method to the solution of problems of integral photoelasticity and present an example of the applicability of our method to the investigation of the stress concentration near the interface of bodies of different nature.

Evaluation of Time-Dependent Fracture Mechanics Parameters of a Moving Crack in a Viscoelastic Strip

Abstract: The present work studies time-dependent stress fields around a moving crack tip in a viscoelastic strip and crack extension resistance. Photoviscoelastic technique is employed for the evaluation of the time-dependent stress state around a crack tip. For the fringe pattern analysis, a new technique using an elliptically polarized white light, which can determine isochromatic and isoclinic parameters simultaneously from a colored image obtained by a single acquisition, is applied. The time-dependent stress intensity factor K * I which is extended for linearly viscoelastic materials is evaluated using a method based on least-squares. The results show that the proposed crack extension resistance K* IC may be considered as a characteristic property of the material under monotonically increasing load.

Integration of spectral and phase-stepping methods in photoelasticity

Abstract: The theoretical description of spectral contents analysis is extended to red-green-blue (RGB) photoelasticity. The integration of the resultant methodology for spectral analysis with phase stepping is used to achieve automatic analysis of photoelastic fringe patterns containing a minimum fringe order of no greater than four, and without the requirement for a zero-order fringe order to be present in the pattern.

Photoelastic Analysis from a Single Image Using Elliptically Polarized Tricolored Light.

Abstract: In this paper, the authors describe a new method for determining the fringe order and the principal direction of birefringence from a single image. Using an elliptically polarized tricolored light and color image processing, the fringe order and the principal direction of birefringence are obtained from data of a color image obtained by a single shot. The theory of the proposed method and the entire experimental and analytical system are described. Then, a successful application of the method to 2-D photoelastic analysis is demonstrated. It is emphasized that this method can be applied to time-dependent phenomena, since multiple exposures are not necessary for sufficient data acquisition in the completion of stress analysis.

Combined Thermoelastic and Photoelastic Full-Field Stress Measurement

Abstract: Accurate determination of stress distributions is essential in assessing the structural integrity of a component. Photoelasticity and thermoelasticity are full field nondestructive methods used to measure the stress state of an object.

Photoelastic studies for composite dynamics

Abstract: The orthotropic birefringent composites suitable for the study of dynamic photoelasticity are investigated and the determination of residual birefringence in the materials is briefly described. A stress-optic law for dynamic photoelastic analysis of orthotropic birefringent composites is postulated based on the static stress-optic law of Hyer and Liu. Subsequently, practical methods of calibrating dynamic mechanical constants and dynamic stress-fringe values are proposed. With dynamic strain measurements and time domain BEM for anisotropic media, three calibration specimens (0°, 90° and 45°) are used to verify the proposed stress-optic law in uniaxial-stress fields and a plate of unidirectional fiber-reinforced birefringent composite under impact loading, with the loading direction parallel, perpendicular and at 45° to the fiber direction, is analyzed to verify the proposed stress-optic law in biaxial-stress fields. Results show that the dynamic stress-optic law for orthotropic birefringent composites is valid in the two cases.

Measurement of Bonding Stress in Silicon High Power Device Structures by Infrared Photoelasticity Method

Abstract: Silicon high-power devices are commonly bonded to Mo electrodes using Al films. Bonding stress will inevitably be introduced into the Si substrate by such a process. In this work, the infrared (IR) photoelasticity (PE) method was employed to measure the stress distribution in the Si substrates induced by high temperature bonding process of Si/Al/Mo structures commonly used in the production of silicon thyristors. It is demonstrated that quantitative information on both the directions and magnitudes of the stress can be obtained. The dependence of the magnitude of the stress on the geometrical parameters of the structure has also been studied. The experimental results are shown to agree well with the calculated results derived from a theory of interlaminar stresses in composites.

Stress analysis method considering piezoelectric effects and its application to static strain optic devices

Abstract: A stress analysis method considering piezoelectric effects based on the finite-element method (FEM), which can be applied to arbitrarily anisotropic material-based optical waveguide devices, is newly formulated. To produce a two-step analysis of static strain optic (SSO) and electrooptic (EO) modulations of optical waveguide devices, this stress analysis is linked to the guided mode analysis and the beam propagation analysis taking into account the refractive index changes. Numerical examples are shown for strain-induced optical waveguides and strain-induced polarization mode converters on LiNbO/sub 3/ substrates.

Catalogue of photoelastic fringes for a biaxially loaded infinite plate with a hole

Abstract: This paper presents a typical catalogue of “virtual” photoelastic isochromatic fringes around the hole of a biaxially loaded infinite plate for two problems. Problem 1 relates to an infinite plate in which the circular hole is drilled first and then the loads are applied. Problem 2 is the residual stress problem in which the hole is drilled after the biaxial load is applied to the infinite plate. Use of this catalogue allows visualisation of the stress distribution around the hole, and a first approximation to the solution of the inverse problem using photoelasticity.

Optical element and its manufacture

Abstract: PROBLEM TO BE SOLVED: To provide an optical element made of glass and having very low photoelasticity constant by forming the same with the glass including the specific amounts of a plurality of specific materials as the glass composition, and having a specific range of the photoelasticity constant to a specific range of wavelength. SOLUTION: 5-28 wt. % of SiO2 , 0-10 wt.% of B2 O3 , 0-5 wt.% of Al2 O3 , 0.3-2.5 wt.% of Na2 O+K2 O, 69.5-83.7 wt.% of PbO, 0-50 wt.% of As2 O3 +Sb2 O3 and 16-28 wt.% of SiO2 +B2 O3 +Al2 O3 are included as the glass composition. The optical element is made of the glass satisfying that the photoelasticity constant to the wavelength of 0.24-0.8 μm, is -1×10 ∼+1.0×10 (nm/cm) (kgf/cm ). Whereby the glass having the refraction factor for making the photoelasticity constant substantially zero in the desired wavelength within a range of 0.24-0.8 μm can be manufactured, and the optical element of small photoelasticity constant in a using wavelength area can be provided.

Misfit strain induced reflection of light from magnetic-nonmagnetic interfaces

Abstract: We have theoretically investigated changes in reflection coefficients induced by misfit strain located near the interface between an iron-yttrium garnet magnetic film and a nonmagnetic gadolinium-gallium garnet substrate in a transverse magneto-optical configuration.