Showing papers on "Photoelasticity published in 1983"

Half-fringe photoelasticity: A new approach to whole-field stress analysis

Abstract: This paper presents a new method for whole-field stress analysis based on a symbiosis of two techniques—classical photoelasticity and modern digital image analysis. The resulting method is called ‘half-fringe photoelasticity (HFP)’. Classical photoelasticity demands materials with high birefringence, which leads to extensive use of plastics as model materials. Since the behavior of these materials is often different from that of the prototype materials, their use distorts the similitude relationships. In many contemporary problems this distortion is untenable. HFP offers a way out of this dilemma. It permits materials and loads to be chosen so that no more than one half of a fringe order appears in the area of interest. Thus, for example, glass, which behaves linearly up to high stress levels and over a wide range of temperatures, could be used as model material. Alternatively, models from polymeric materials could be used under very low load in order to stay within the linear part of the stress-strain diagram and to prevent large deformations. The half-fringe-photoelasticity system, which is described here, utilizes the resulting low levels of birefringence for effective stress analysis. This paper describes the system. It outlines a calibration routine and illustrates its application to two simple problems using glass models.

Reduction of stress concentration around a hole in a uniaxially loaded plate

Abstract: The stress concentration around a circular hole in a plate can be reduced by up to 21 per cent by introducing auxiliary holes on either side of the original hole. But this approach of auxiliary holes creates two more regions of stress concentration in the plate.In the present study, the hole geometry has been modified to effect stress reductions as high as 22 per cent. The problem has been analysed numerically by the finite element method and experimentally by two-dimensional photoelasticity. It has been observed that by making the hole oblong in the direction of loading, a high order of reduction in stress concentration around the hole can be obtained.

Nondestructive residual-stress measurement in a wide-flanged rolled beam by acoustoelasticity

Abstract: X-ray stress analysis is a standard nondestructive stress-measurement technique, but its use is limited in the sense that only a surface layer is surveyed. Recently, acoustoelasticity has emerged as a technique for nondestructive stress analysis. Acoustoelasticity makes use of stress-induced acoustic-birefringent effects. It gives stress distributions averaged through the thickness of a specimen. This technique is attractive because it does not require a transparent plastic model as photoelasticity does. However, much should be done before this method is established as a standard nondestructive technique of stress analysis. The most important among them is to separate stress-induced birefringence from that introduced by texture structure. For special cases, such as axisymmetric stress distributions and when a stress-free region is knowna priori, residual-stress distributions can be evaluated nondestructively. In this paper, we measured residual-stress distribution in a wide-flanged rolled beam by using a recently developed T-type transducer. The results were compared to those obtained from conventional destructive methods.

Ionic photoelasticity of GaAs

Abstract: The dispersion of photoelastic and elasto-optical coefficients of GaAs in the infrared region of the spectrum is calculated. The basic physical parameters entering the calculation correspond to the strain derivatives of the transverse phonon effective charge and of the transverse and longitudinal optical phonon frequencies. They are all deduced from existing piezospectroscopic data. The calculation extends to other physical parameters such as the pressure derivatives of the effective charge and index of refraction. The dispersion of the integrated intensity for ionic Brillouin scattering is also computed. Both the linewidth of the transverse optical phonon and its strain dependence are taken into account explicitly. They are shown to have a substantial effect on the profile of the dispersions.

Stress compensation in laser diodes

Abstract: Stress compensation in GaAs‐(Ga,Al)As laser diodes is discussed. The stress distributions in the laser diodes are theoretically simulated by the finite element method. The photoelastic effect is used to observe the actual strain fields. It is found by simulation that the stress can be minimized by optimizing the Si submount thickness. Lasers fabricated with the optimized submount successfully exhibit low strain fields.

Determination of mode I stress intensity factors in surface-flawed plates by scattered-light photoelasticity

Abstract: The scattered-light photoelastic technique was utilized to determine Mode I stress intensity factors associated with a semi-elliptical surface flaw in a plate subjected to uniaxial tension. Stress intensity factors were experimentally determined for the point of maximum flaw penetration and the point of intersection of the flaw border with the free surface of the plate. Experimental results are compared to those obtained in a three-dimensional finite element analysis with reasonable agreement being shown.

A Stress Separation Technique for Photo-Orthotropic Elasticity

Abstract: A stress separation technique using an approximate strain-optic law has been developed for photo orthotropic elasticity. The technique is similar to the shear difference method of stress separation used in photoelasticity of isotropic materials and involves stepwise numerical integration. The technique has been illustrated through its application to the analysis of a circular disk of orthotropic material under diametral compression.

Visualization of Ultrasonic Pulse in Glass by the Technique of Photoelasticity

Abstract: A stroboscopic photoelastic system has been applied to visualize ultrasonic pulses propagating and reflecting in glass. It is revealed that the longitudinal-shear mode conversion caused by the reflection of ultrasonic wave at a free boundary of glass yields many spurious echo signals.

Dynamic Crack Growth in Polymers

Abstract: : Over the past several years, considerable effort has been directed towards developing two-dimensional, finite-element computer codes to predict crack propagation behavior in large structures. One of the input parameters to these computer codes is the relationship between the crack extension force (or the stress intensity factor) and the velocity of crack propagation in the material. Experimental investigations of the dynamic behavior of crack propagation and arrest in several different polymers, epoxies, and structural steels have been conducted. This paper summarizes briefly the highlights of the work performed at the University of Maryland over the period 1972-1982 using dynamic photoelasticity, high speed multi-flash photography, and finite element modeling to study crack propagation.

Rayleigh wave interaction with inhomogeneities—Part II: The buried cavity and inclusion

Abstract: The elastodynamic interaction between an explosively generated Rayleigh pulse and a buried imperfection such as a cavity or an inclusion in a half plane is investigated. Dynamic photoelasticity was employed to obtain full field information for data analysis. Measurements of the stress distribution along the free boundary of the half plane and the cavity and along the cavity/inclusion interface have been made. Results show that fractures occur for shallow as well as for deeper burial depths initiating from the cavity boundary.

Axial force management of bolt utilizing photoelasticity

Abstract: PURPOSE:To enable accurate and simple management of axial force of a bolt by measuring the density of a stripe pattern generated from a photoelastic film pasted on the surface of a bolt hand with the irradiation of light thereon to determine the distortion of the bolt head CONSTITUTION:A reflective film 13 made of an elastic resin-like film is applied and formed on a bolt head 7 A photoelastic film 14 with a thickness of several mm, for example, is pasted on the top surface of the reflective film 13 A polarizing plate 15 is arranged between the light source and the photoelastic film 14 and a polarizing plate 15' between the film 14 and a scope while 1/4 wavelength plates 16 and 16' are mounted on the polarizing plates 15 and 15' As entering the photoelastic film 14 through the polarizing plate 15 and the 1/4 wavelength plate 16, light projected from the light source is refracted in the directions X and Y inside and reflected on the reflective film 13, passing through the 1/4 wavelength plate 16' while a circular polarized light changes to a plane polarized light with respect to the main surface of the polarizing plate 15 This polarized light can be seen in a stripe pattern as passing through the polarizing plate 15'

The Acousto-Optical Properties and Photoelasticity of PbBr2 Single Crystals

Abstract: Comparaison des proprietes acoustooptiques de PbBr 2 et PbCl 2 . Mesure de l'indice de refraction de PbBr 2 dans le visible : forte birefringence et large region de transparence. Mesure des vitesses de propagation des ondes acoustiques longitudinales. Mesure des coefficients du tenseur de photoelasticite

Fracture behavior of brittle circular rings subjected to concentrated impulsive loading

Abstract: The influence of impact velocity and ring geometry in the fracture patterns produced by in-plane concentrated impulsive loading on brittle circular rings has been studied both experimentally and theoretically. The experiments were performed by impacting circular rings made of plaster with a steel plate. The fracture behavior was photographed by a camera with a flash, and the crack-initiation time was measured using a memoriscope. The fracture behavior is explained using dynamic photoelasticity and the theory of flexural motion of a circular ring. With the addition of an impact-fracture criterion to this theory, the fracture patterns of brittle circular rings are predicted.

Strain measurement with asymmetric oblique-incidence polariscope for birefringent coatings

Abstract: A method for measuring principal-strain components is presented Retardation in the birefringent coatings is measured with a compensator in normal and oblique-incidence In order to reduce the errors and increase the angle of oblique incidence, a prism made of optically homogeneous material with an asymmetric polariscope is used The plane of incidence of light is arbitrarily chosen and does not have to be changed during the measurement Jones calculus is used to analyze the light transformation in the polariscope and in birefringent coatings

A rational theory of oblique incidence and its extension to stress-separation in birefringent composites

Abstract: A rational theory of oblique incidence for a birefringent medium is developed. The theory rules out the concept of secondary principal stresses as an arbitrary one and provides more adequate interpretation of isochromatics and isoclinics in oblique incidence. The method is shown to be applicable for stress-separation in an anisotropic-birefringent composite, and the stress-optical equations deduced require an additional stress-fringe constant to those involved in normal incidence. The stress-birefringence relations for isotropic photoelasticity are obtained as a particular case of the general theory.

Another Method to Separate Principal Strains in Photoelastic Coatings

Abstract: It is shown that the combination of a prism and a reflection polariscope provided with a Babinet-Soleil compensator offers a simple practical solution to the problem of separation of the principal strains in photoelastic coatings.

Comparison of Stress Distributions in a Simple Tubular Joint Using 3-D Finite Element, Photoelastic and Strain Gauge Techniques

Abstract: Combined strip and rosette gauge measurements and results from three-dimensional, finite element calculations are in excellent agreement with frozen stress photoelastic results for an efficient shape of cast-steel node under axial, brace loading. Three different meshes showed that two layers of elements through the thickness are needed.

Holes for shrouding

Abstract: In this communication we present the results of investigations of the state of stress of plates with inclined holes subjected to bending. The investigations were carried out by the method of photoelasticity with "freezing" of the deformations in the models made of the optically sensitive material ED-20M, with geometric and force similarity being maintained. The obtained data were mathematically processed on a Mir-i computer. The object of the investigation was to study the stress field in the zone of the holes for shrouding when the model was exposed to the effect of flexural forces, and to reveal the nature of the change of the maximum values of the stress concentration factor across the thickness of the plate. We also studied the case of different angles of inclination of the axis of the hole to the surface of the plate, with and without rounding off of the edge formed by the hole and the surface of the plate (hole opening). The bending moments were applied at both ends of the plate, and it was ensured that they acted in the yz plane in such a way that the plate underwent cylindrical bending.

Dynamic Photoelasticity and Holography Applied to Crack and Wave Propagation

Abstract: The field of elastodynamics covers the class of problems in solid mechanics where the inertia term on the right hand side of the equations of motion where e is the dilatation and ω is the in-plane rotation of an element, may not be neglected because of rapid changes of stress and displacement in time. These variations of the stresses are due to loads or displacements which change in time, or they are due to relatively sudden changes in the geometry of the body. From the broad field of elastodynamics only stress wave propagation, fracture propagation and their interaction, and penetration (high speed impact) problems will be highlighted here.

Three Dimensional Photoelastic Investigations on Thick Rectangular Plates

Abstract: Thick rectangular plates are investigated by means of three-dimensional photoelasticity using the stress-freezing technique. Plate with two opposite edges simply supported and the other two edges free subjected to a central line load is studied as a specific example. Three different thicknesses to include the range of thin to moderately thick to thick plates are considered and it is shown that by employing a judicious slicing pattern stress variation at the critical sections of the plate can be obtained. Numerical results obtained are compared with those from a thin plate theory and a higher order thick plate theory.

Single-polarization single-mode optical fiber with internal stress application part

Abstract: PURPOSE:To obtain excellent polarization conserving properties by arranging a stress application part at a local part between a clad and a coating part separately from a core. CONSTITUTION:At the circumference of an optical fiber which has a core 10 with a diameter 2a and clad 20 with a diameter 26, two stress application parts which has a large coefficient of thermal expansion are arragned symmetrically at an angle 2theta centering on the center of the core 10. Further, its outside is coated with a coating part 13 having round strcuture. When the coefficient of photoelasticity of core glass is P and main stresses in a main axis direction are sigmax and sigmay, an index of mode double reflection B is p(sigmax-sigmay). The angle 2theta of each stress application part is preferably <=90 degrees and the stress application part may be composed of plural circular bodies.

Ground Vibration Studies

Abstract: Many attempts have been made to quantify the propagation and interaction of elastic waves. Woods [1], for example, examined the role of trenches in isolating a building from vibration. Dally and Lewis [2] studied the effects of a slit on a propagating Rayleigh wave through the use of dynamic photoelasticity. Gupta and Kisslinger [3] observed the surface displacements in an explosively generated Rayleigh wave, by modeling a half space with a plane and employing capacitor probes to measure the vertical and radial displacement. DeBremaecker [4] studied the transmission and reflection of Rayleigh waves at corners. All of the above have their shortcomings.