Showing papers on "Photoelasticity published in 1973"
TL;DR: First molars with full gold crown preparations and a shoulder geometry were idealized by an axisymmetric model and analyzed by the photoelastic, as well as the finite element method, and they were found to compare favorably.
144 citations
TL;DR: In this paper, an experimental method is described which can measure the direction and magnitude of residual and applied stress in metals using optical interference to measure the permanent surface deformation around a shallow spherical indentation in a polished area on the metal.
Abstract: An experimental method is described which can measure the direction and magnitude of residual and applied stress in metals. The method uses optical interference to measure the permanent surface deformation around a shallow spherical indentation in a polished area on the metal specimen. The deviation from circularly symmetrical surface deformations is measured at known values of applied stress in calibration specimens. This deviation from symmetry can then be used to determine the direction and magnitude of tensile residual stress in specimens of the same material. Determination of compressive residual stress is more limited.
48 citations
TL;DR: In this paper, the Taylor series correction for the maximum in-plane shear stress (TSCM) was used to determine the stress intensity factor photoelastically for three-dimensional problems.
Abstract: The philosophy of fracture mechanics is reviewed and utilized to formulate a simplified approach to the determination of the stress-intensity factor photoelastically for three-dimensional problems. The method involves a Taylor Series correction for the maximum in-plane shear stress (TSCM) and does not involve stress separation. The results are illustrated by applying the TSCM to surface flaws in bending fields. Other three-dimensional problems solved by the TSCM are cited.
37 citations
Book•
01 Jan 1973
TL;DR: In this article, the first part of this book deals with fundamental principles of the theoretical analysis of stress and strain, and applies these principles to common engineering problems, such as tension, compression and torsion.
Abstract: The first part of this book deals with fundamental principles of the theoretical analysis of stress and strain, and applies these principles to common engineering problems. The chapter headings of Part 1 are: (1) Statically determinate frames and beams; (2) Statically determinate stress systems; (3) Stress-strain relations; (4) Displacements in statically determinate structures; (5) Statically indeterminate stress systems; (6) bending: stresses; (7) Bending: slope and deflection; (8) Elastic strain energy; (9) Theory of torsion; (10) Statically indeterminate beams and frames; (11) Buckling instability; (12) Stress and strain transformation and relationships; (13) Analysis of variation of stress and strain; (14) Some applications of the equilibrium and strain-displacement relationships; (15) Theories of yielding; (16) Thin plates and shells; (17) Stress concentration; (18) Elementary plastic and viscoelastic analyses. Part 2 deals with mechanical properties and testing of materials, and consists of the following chapters: (19) Tension, compression and torsion; (20) Hardness and other tests; (21) Toughness and unstable fracture; (22) Fatigue; (23) Creep; (24) Non-metallic materials. Part 3 covers some of the most common methods used in experimental analysis of stress and strain, and is presented under the following chapter headings: (25) Resistance strain gauges; (26) Photoelasticity; (27) Other methods of strain measurement. /TRRL/
37 citations
TL;DR: The reflected method of caustics, which is based on geometric optics, was used to define the principal stress difference and the principal directions at the interior of any generalized plane stress field by defining the stress distribution around small perforations drilled in the plate.
Abstract: The reflected method of caustics, which is based on geometric optics, was used to define the principal stress difference and the principal directions at the interior of any generalized plane stress field by defining the stress distribution around small perforations drilled in the plate. A monochromatic coherent light beam, reflected on or transmitted through the plate at the neighborhood of the perforation, deviated by different amounts because of the refractive index variation and the thickness variation due to loading. The deviated light rays, received on a reference plane parallel to the plate, were concentrated along a singular curve, which enveloped a large part of the reflected or traversing rays and created a caustic. The properties of this singular curve were studied and found to depend on the biaxial stress field existing at the place of the perforation, as well as on the mechanical and optical properties of the material and the geometry of the optical setup. The double-kidney shape of the caustic presented a maximum diameter Dmax, which coincided with one of the axes of symmetry of the caustic. The other axis of symmetry, which passed through the cusps of the caustic, coincided with the axis of maximum principal stress, while the size of Dmax yielded the principal stress difference. Thus, the caustic constitutes a sensitive stress rosette, which defines the orientation and the size of the stress field.
29 citations
25 citations
TL;DR: In this paper, a photoelastic technique has been developed for simultaneous recording of the amount of birefringence in transmitted and in scattered light, and the theoretical foundation of the developed integrated polariscope has been deduced.
Abstract: A new photoelastic technique has been developed for simultaneous recording of the amount of birefringence in transmitted and in scattered light. This paper presents the basic theories of transmission and scattered-light polariscopes and hence deduces the theoretical foundation of the method and technique of the developed integrated polariscope.A laser is used as light source, or two identical lasers are used. In a one-laser system the linearly polarized ray is split into two beams, one of which is expanded and passes through the standard transmission polariscope, and the other, being about 1 mm in diameter, enters the photoelastic object parallel to its middle plane. An ‘integrating prism’ has been developed for simultaneous recording of the standard isochromatics and of three scattered light beams; a beam scattered parallel to the polariscope axis and two complementary beams scattered at angels of − π/4 and + π/4.
24 citations
01 Jan 1973
TL;DR: In this article, the fracture dynamics of Homalite-100 plates are discussed in the context of linear theory of fracture mechanics, where photoelasticity is used for dynamic analysis and finite element method for static analysis.
Abstract: The 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-energyrelease rates for constant-velocity, accelerating, and decelerating cracks are determined in fracturing tension plates and in pretensioned plates impacted by a projectile.
22 citations
TL;DR: In order to reduce the stress concentration around a hole in a plate, new, "analogue" reinforcements instead of reinforcing rings were used in this article, and the results showed that a definite reduction in stress concentration was observed on specimens containing analogue reinforcement.
Abstract: In order to reduce the stress concentration around a hole in a plate, new, “analogue” reinforcements instead of reinforcing rings were used in this investigation In two of these specimens, reinforcements with different volume fractions were arranged to coincide with the stress trajectories for an infinite plate with a hole under uniaxial tension Two other specimens containing straight rectangular-grid-type reinforcements were made by using a photofabrication method Specimens were then prepared by sandwiching these reinforcements between two epoxy-resin plates Plane specimens, ie, without reinforcement, were also made of the same epoxy resin for comparison The stress concentrations at the edge of the hole under uniaxial tension were determined by photoelastic techniques The measured stress-concentration factors were compared with well-known values for an infinite, isotropic, homogeneous plate containing a hole Results were also compared with published data on [90/0/90/0]s 7-ply laminated composite plates, and on plates strengthened with reinforcing rings A definite reduction in stress concentration was observed on specimens containing analogue reinforcement
13 citations
01 Jan 1973
TL;DR: In this article, the dynamic photoelasticity of tension plates composed of Homalite-100 sheets was studied by dynamic stress intensity factors, crack velocities and dynamic stress concentrations at the arresting hole.
Abstract: Crack propagation and arrest in impacted, edge-cracked, tension plates composed of Homalite-100 sheets were studied by dynamic photoelasticity. Dynamic stress intensity factors, crack velocities and dynamic stress concentrations at the arresting hole were determined and compared with corresponding static values which were computed by the method of finite element analysis. Significant influence of the reflected stress waves generated by the impact was noticed in this investigation. The otherwise stable crack appeared to run intermittently when the dynamic stress intensity factor exceeded the static fracture toughness of the material. The static stress field surrounding the arresting hole appeared relatively ineffective in influencing the path of crack propagation. Conclusions reached in this investigation are similar to those published previously except for the more pronounced stress wave effects in these series of experiments.
12 citations
Journal Article•
TL;DR: In this article, a review is made of the various elastic analytical methods available, and their assumptions are discussed, and the accuracy of each analysis is assessed on a plane wedge under separate application of normal force, shear, and bending moment, for a range of slopes and curvatures.
Abstract: Beams of varying depth are widely used in civil engineering structures, and are particularly suitable for large span prestressed concrete bridges. It is well known that the distribution of shear stress and hence principal tensile stress may be considerably affected by the variation in depth. A review is made of the various elastic analytical methods available, and their assumptions are discussed. The accuracy of each analysis is assessed on a plane wedge under separate application of normal force, shear, and bending moment, for a range of slopes and curvatures. The effect of curvature is shown to be unimportant for the values associated with bridges. The approximate forms of the solutions reached by Boussinesq and Wysiatycki are shown to be identical. These expressions are simple and give good agreement with the exast solution. Photo-elastic and finite element models are used to examine the accuracy of the various analytical methods applied to box-sections. /AUTHOR/
TL;DR: A four-exposure holographic technique is described that yields a moiré pattern representing the difference between two displacement solutions of an object, which lowered the sensitivity of the measurement and indicated an extension of the measurable range of deformations.
Abstract: In this Letter, a four-exposure holographic technique is described that yields a moiré pattern representing the difference between two displacement solutions of an object. In this manner, a full field comparison is obtained between a known displacement solution of an object and an unknown displacement solution of another object of similar geometry. The two specimens may be of different mechanical properties, or the same specimen may be elastically and then plastically deformed. Several moiré techniques which incorporate the use of holographic interferometry have been developed in the past few years. Hovanesian and Varner utilized a triple exposure moiré technique to determine bending moments in thin plates. Boone and Verbiest have created a moiré contour pattern of spatial derivatives of a plate deflection from multiple-exposure holograms. Rowe projected a fringe grating onto an object surface and obtained an interference with the holographic fringes due to surface deformations between exposures. The resulting moiré fringes lowered the sensitivity of the measurement and indicated an extension of the measurable range of deformations. In Rowe's analysis, the equation for the moiré intensity variation was expressed as the product of the intensity variation functions for the projected fringe grid and the holographic fringes. In pursuing this analysis for a fourexposure hologram intensity function, the moiré intensity variation is given by
TL;DR: In this article, the effect of the rotation of secondary principal axes on scattered light intensity has been investigated and a general formula for scattered-light intensity was developed. But the method is illustrated by the solution of the problem of a circular rod loaded by a combination of torsion and axial load.
Abstract: The lack of understanding of the effect of the rotation of secondary principal axes has been a severe limitation of the scattered-light method. The method of Poincare's equivalent system has been applied in order to develop a general formula for scattered-light intensity. Relationships among the orientation of eigenvectors and their phase retardation and stresses have been found. The method is illustrated by the solution of the problem of a circular rod loaded by a combination of torsion and axial load. An experimental procedure has also been suggested.
TL;DR: In this article, a composite cylinder consisting of two solid circular cylinders, made of dissimilar materials but having the same diameter, which are stuck together so that their axes coincide is considered.
Abstract: Experimental and theoretical investigations are reported concerning the stresses and deflections which occur in a composite cylinder due to a uniform rise in temperature. The composite cylinder consists of two solid circular cylinders, made of dissimilar materials but having the same diameter, which are stuck together so that their axes coincide. The interface between the two cylinders is a plane prependicular to their axes, and the lengths of both parts of the composite cylinder can vary. The composite cylinder is assumed to be free of stress initially.Theoretical results have been obtained by use of infinite-difference approximations to the governing equations and an iterative technique involving successive over-relaxation. These have been compared with experimental results obtained by a special application of the frozen-stress technique of photoelasticity.
TL;DR: In this paper, a dynamic polariscope was used to photographically stop the movement of the photoelastic-fringe patterns caused by the stress wave, and the results indicated that the scatter from duplicate shots performed with this technique is on the order of 3 percent.
Abstract: This paper describes a unique device that has been developed for the transient loading of models along straight and curved boundaries and that operates by discharge of a high-energy, high-voltage capacitor bank. In its present configuration, this device can generate uniform pressures from 1500 psi (10 MPa) to pressures that approach 100,000 psi (690 MPa) and that rise from zero to maximum pressure in 2 μs and decay to approximately zero in another 2 μs. The transient stress-wave patterns in photoelastic models loaded with this device have been recorded by a dynamic polariscope. The dynamic polariscope presently in use is identical to a static polariscope except that the light source is of a short enough duration (½ μs) to photographically stop the movement of the photoelastic-fringe patterns caused by the stress wave. With the stress-wave generator and the dynamic polariscope, transient photoelastic patterns have been recorded in a number of models. These patterns indicate that the scatter from duplicate shots performed with this technique is on the order of 3 percent. This represents considerable improvement over the 15-percent scatter normally experienced with sheet-explosive loading techniques. This improvement and the rapid turnaround between shots (approximately 5 min) are distinct advantages this system has over other methods of dynamic loading.
01 Aug 1973
TL;DR: In this article, a Taylor Series expansion of the in-plane maximum shearing stress is used to extract stress intensity factors from photoelastic data, which are then used to estimate stress intensity for complex 3D problems.
Abstract: : A technique is described for extracting stress intensity factors from photoelastic data which uses a Taylor Series expansion of the in-plane maximum shearing stress in conjunction with a digital computer program. By applying the method to a variety of problems including center cracked panels, compact tension specimens, part-circular surface flaws and flat bottomed surface flaws, characteristics of the method are demonstrated, and its strengths and weaknesses are delineated. It is concluded that stress freezing photoelasticity appears to be a potentially powerful tool for estimating stress intensity factors for complex three dimensional problems. (Author)
01 Mar 1973
TL;DR: In this article, a summary of stress concentration studies has been provided for the case of single and multiple openings in plate structures, as well as comments for modifications of the design criteria currently used for openings on ships.
Abstract: : A summary of stress concentration studies has been provided for the case of single and multiple openings in plate structures. The report summarizes some published theoretical studies as well as some previously unpublished photoelastic studies performed at the Center. Also included are comments for modifications of the design criteria currently used for openings on ships.
TL;DR: In this paper, the stresses in a ribbed cylindrical shell with a reinforced circular hole, when the shell is subjected to internal pressure, were obtained by several experimental methods: brittle coating, electrical strain gauges, and photoelasticity.
Abstract: The stresses in a ribbed cylindrical shell with a reinforced circular hole, when the shell is subjected to internal pressure, were obtained by several experimental methods: brittle coating, electrical strain gauges, and photoelasticity. The results obtained were compared with those corresponding to a non-reinforced hole in a ribbed and unribbed shell and also to a reinforced hole in an unribbed shell.
Patent•
29 Mar 1973
TL;DR: In this article, a process of visualizing the maximum shear lines or isostatics by observations under polarized light of the double refractions appearing in a photoelastic material comprises obtaining by means of a noval polariscope device moire images by observing simultaneously the material and a grid for the isostatic for different successive orientations of the plane of polarization.
Abstract: A process of visualizing the maximum-shear lines or isostatics by observations under polarized light of the double refractions appearing in a photoelastic material comprises obtaining by means of a noval polariscope device moire images by observing simultaneously the material and a grid for the isostatics for different successive orientations of the plane of polarization. The successive orientations are obtained by simultaneously rotating the plane of the polarized light and the grid. One at least of the material and the grid is observed in the form of an optical image formed in the plane of the other.
TL;DR: In this article, the authors describe the equipment, techniques and methodology used to study dynamic stresses in two-dimensional problems, and describe the techniques and techniques used to determine dynamic photoelasticity of parts or structures subjected to impact or shock loading.
Abstract: Dynamic photoelasticity is concerned generally with the determination of transient stresses and strains in machine parts or structures subjected to impact or shock loading. Progress in this field has paralleled the development and application of new advances in high-speed photography. This paper describes the equipment, techniques and methodology used to study dynamic stresses in two-dimensional problems.
TL;DR: In this paper, a rigorous method based on stress function in the form of Fourier series is presented for the stress analysis of the plate of infilled frames under in-plane diagonal loads.
TL;DR: In this paper, a theory for the photoelastic behavior of transparent polycrystalline aggregates consisting of randomly oriented anisotropic crystallites has been developed, and the elastic and the photo-elastic constants of the aggregates have been evaluated for both the stress continuity and the strain continuity conditions.
Abstract: A theory for the photoelastic behaviour of transparent polycrystalline aggregates consisting of randomly oriented anisotropic crystallites has been developed. Such an aggregate is isotropic but it becomes birefringent under the influence of a uniaxial load. The photoelastic constants of the aggregate are given by the components of the spatial average of the photoelastic tensor of the single crystal, and are worked out by assuming either the strain to be continuous (Voigt approximation) or the stress to be continuous (Reuss approximation). The components of the average photoelastic tensor are very different for these two limits. The elastic and the photoelastic constants of alkali halide aggregates have been evaluated for both the stress continuity and the strain continuity conditions. The maximum variation of the elastic constants in going from the Voigt to the Reuss condition is 50 per cent while the photoelastic birefringence can vary by as much as 300 per cent in alkali halides. In the case of KI and rubidium halides even the sign of the photoelastic birefringence is different for the two limits.
TL;DR: In this article, a special scattered-light polariscope with loading system was designed and constructed for this research, and two models were used in this investigation: a cylindrical tension model with a single discontinuous axially aligned aluminum fiber surrounded by a polyester matrix.
Abstract: This paper reports an investigation of three-dimensional stresses in models of composite materials with discontinuous fibers using the scattered-light photoelastic method. A special scattered-light polariscope with loading system was designed and constructed for this research. Two models were used in this investigation. The first was a cylindrical tension model with a single discontinuous axially aligned aluminum fiber surrounded by a polyester matrix. The second was a five-fiber cylindrical compression model with a central discontinuous fiber surrounded by four continuous ones and polyester matrix. The experimentally determined stress distribution from each model along chosen lines was presented. The stress distribution on the same lines in the single-fiber case was calculated using the finite-element method. The calculated result showed fair agreement with the experimentally determined results.
TL;DR: In this paper, the effect of the thickness/diameter ratios on the stress concentrations with thickness is investigated, and the experimental results are correlated with the existing three-dimensional theoretical solutions.
Abstract: In this study three-dimensional photoelasticity is used to analyse the stress variation through different layers of a thick plate containing a circular hole and subjected to uniform tensile loading. The effect of the thickness/diameter ratios on the stress concentrations with thickness is investigated. The experimental results are correlated with the existing three-dimensional theoretical solutions.The data establish, both experimentally and theoretically, the precise location of the maximum-stress layers in plates having different thickness/diameter ratios and thus resolves the discrepancies which existed in previous studies.
TL;DR: In this article, the authors deal with the contact pressure between a belt and the pulley to which it transmits force and with the bending and membrane stresses in the belt, taking the anticlastic configuration of the belt into consideration.
Abstract: This paper deals with the contact pressure between a belt and the pulley to which it transmits force and with the bending and membrane stresses in the belt. The anticlastic configuration of the belt is also taken into consideration. The commonly known simplified approximate analysis of the pressure, as well as the results of a more elaborated theory, are presented. Also given in the paper are the description and evaluation of several experimental stress analyses methods that can be used to solve the problem. Two and three-dimensional photoelasticity, thickness measurements and electrical strain gages were found to be the most practical approaches. The correlation of results obtained using the theories and the experimental methods is discussed. It is estimated that the peak contact pressure is 3.5 times the one computed using the plane stress assumption. Results obtained will also have application in the design of wire-ropes or cables transmitting forces to sheaves, or drums.
TL;DR: In this paper, the authors present a method that may help in the visualization of one form of behavior of buoy-cable systems loaded by the action of water waves, where the cable is modeled by a solid urethane rubber strip and the buoy by a floating plastic round can.
Abstract: A basic object of the paper is the presentation of a method that permits the experimental determination of stresses associated with vibrations in flexible members, immersed in a fluid, and subjected to prestress. The applied object of the paper is to present a method that may help in the visualization of one form of behavior of buoy-cable systems loaded by the action of water waves. Photoelasticity is used for the analysis. The cable is modeled by a solid urethane rubber strip and the buoy by a floating plastic round can. Waves of controllable frequency are produced by a device actuated by a shaker. Bending and axial stresses in the strip are determined and the possible extension of the experimental results obtained to prototypes by means of scaling laws is suggested.
01 Mar 1973
TL;DR: In this article, a monocoque cylinder was impulsively loaded around the circumference of one end, causing a compressive stress wave to propagate in the axial direction, and the resulting structural responses of two configurations of the cylinder (with and without a cutout) were recorded by photoelasticity, strain gages, and accelerometers.
Abstract: An experimental program was conducted to determine the feasibility of using subscale plastic models to determine the response of full-scale aerospace structural components to impulsive, pyrotechnic loadings. A monocoque cylinder was impulsively loaded around the circumference of one end, causing a compressive stress wave to propagate in the axial direction. The resulting structural responses of two configurations of the cylinder (with and without a cutout) were recorded by photoelasticity, strain gages, and accelerometers. A maximum dynamic stress concentration was photoelastically determined and the accelerations calculated from strain-gage data were in good agreement with those recorded by accelerometers. It is concluded that reliable, quantitative structural response data can be obtained by the experimental techniques described in this report.