Showing papers on "Photoelasticity published in 1990"
TL;DR: In this article, hybrid methods are developed for determining individual stress components under plane stress from thermo-elastically measured isopachics, which depend only on stress equilibrium and are independent of constitutive response.
Abstract: Hybrid methods are developed for determining individual stress components under plane stress from thermoelastically measured isopachics Some of the techniques depend only on stress equilibrium and are independent of constitutive response Applications are to a partially loaded half-plane, and tensile plates containing side notches and holes These are believed to represent the first examples of separating stresses from thermoelastically measured data
52 citations
TL;DR: In this paper, a grid technique was used to determine the inhomogeneous strain field associated with a steadily growing neck and an extension of photoelasticity was used in obtaining the stress variation along the line of symmetry in the neck.
50 citations
TL;DR: The computer-aided holophotoelastic method (CAHPM) is presented and validated and with it complete experimental stress analyses of transparent structures subjected to two-dimensional states of stress can be conducted based solely on experimental data without resort to either a hybrid, iterative, or other numerical procedure.
Abstract: The computer-aided holophotoelastic method (CAHPM) is presented and validated. With it complete experimental stress analyses of transparent structures subjected to two-dimensional states of stress can be conducted based solely on experimental data without resort to either a hybrid, iterative, or other numerical procedure. The stress analysis is determined from photoelastic and holographic data, i.e., isochromatic, isoclinic, and absolute retardation results. The experimental setup and procedures are discussed and the algorithms used for the data reduction are also presented. The method is validated using a disk in diametral loading.
46 citations
TL;DR: In this paper, an experimental procedure is presented for determining the mode I stress-intensity factor of an edge crack with a nearby rigid elliptical inclusion in a finite plate loaded in uniform tension.
Abstract: An experimental procedure is presented for determining the mode I stress-intensity factor of an edge crack with a nearby rigid elliptical inclusion in a finite plate loaded in uniform tension. The rigid inclusion was modeled by bonding two identical steel inclusions on to the faces of a thin plate of polycarbonate. Models were constructed with edge cracks and various inclusion geometries so that the effect of parameters such as inclusion shape, orientation, and cracktip position on the stress-intensity factors of the crack could be determined. Photoelasticity experiments were used for this investigation and the results were compared to the results of a similar theoretical analysis of the interaction between a crack and an inclusion in an infinite plate. A good correlation was found between the experimental and theoretical models indicating that the results may help provide a better understanding of the toughening mechanisms in materials such as short-fiber-reinforced composites and ceramics. This experimental method is relatively easy to use making it an attractive candidate to be applied to similar problems involving cracks and inhomogeneities.
22 citations
TL;DR: In this article, a hybrid experimental-computational study has been conducted in order to determine the propagational characteristics of mechanical waves in granular materials, and the experimental results provide special dynamic material constants necessary for the computational modeling, and they also provide data for comparison purposes.
Abstract: A hybrid experimental-computational study has been conducted in order to determine the propagational characteristics of mechanical waves in granular materials. The experimental investigation has used the method of dynamic photoelasticity to collect photographic data which provide information on the wave speeds, integranular contact loadings, and wave-spreading characteristics. The computational study employed the use of the distinct-element method whereby the motion of each granule in the material is modeled by rigid-body dynamics assuming each particle interaction has particular frictionless stiffness and damping forces. The experimental results provide special dynamic material constants necessary for the computational modeling, and they also provide data for comparison purposes. Results from the experimental and computational studies compare well with each other and indicate that local microstructure plays an important role in the wave propagation through such materials.
21 citations
TL;DR: In this article, the effects of stiffness and thickness of adhesive bonds on the stress distributions were demonstrated by numerical calculations, and the stress singularity caused at the edge of the interface was discussed.
17 citations
TL;DR: In this article, the photoelastic method was used to investigate the local stress field at a sharp corner of a wedge that was compressed against a larger body, and the experimental results were found to be in good agreement with the theoretical predictions.
Abstract: The photoelastic method was used to investigate the nature of the local stress field at a sharp corner of a wedge that was compressed against a larger body Planar wedge specimens made of photoelastic material were compressed against a half plane (larger body) of identical material at various load levels Several wedge angles were studied The nature of the singular stress field postulated by linear elastic analysis was verified and the strength of the singularity was obtained by plotting the variation of fringe order as a function of radial distance from the sharp corner on a logarithmic scale The experimental results were found to be in good agreement with the theoretical predictions The effect of interface friction and the effect of rounding off the sharp edge are brietly discussed
16 citations
TL;DR: In this paper, the loss of the square-root stress singularity of linear elastic fracture mechanics in some three-dimensional cracked body geometries is investigated with the aid of experimental data.
11 citations
TL;DR: In this article, photoelastic methods are used to analyze the stress intensity factors and crack trajectories for subsurface cracks that are relevant to the process of wear particle generation.
11 citations
TL;DR: In this article, both the strain gage technique and dynamic photoelasticity were employed to obtain stress wave velocity and its wavelength in a one-dimensional, relatively large-sized granular medium.
9 citations
Patent•
25 Jul 1990
TL;DR: In this paper, the presence or absence of an adhesive tape is detected through the utilization of polarization of light, depending on the uniform direction of the chemical treatment on the surface of the tape.
Abstract: PURPOSE:To detect an adhesive tape in a noncontact manner therewith irrespective of the reflectivity of said tape by a method wherein the absence or presence of said tape attached onto a sheet of paper is detected through the utilization of polarization of light CONSTITUTION:Even when an adhesive tape 2 is transparent and, the reflectivity of incident light from a light source 3 is equal between the surfaces with and without the tape, the reflected light of the incident light is polarized depending on the uniform direction of the chemical treatment on the surface of the tape 2 Therefore, when the plane of polarization of the reflecting light is rotated by changing a voltage applied to a variable polariscope 5, the quantity of light incident on a light receiving sensor 4 differs according to the deflection angle of the polariscope 5 and a fixed polariscope 6 The pattern of the reflected light is different between the surfaces with and without the tape 2, whereby the presence or absence of the tape 2 can be detected
01 Jan 1990
TL;DR: In this paper, the authors used photoelasticity for the analysis of elastic stress and strain, but it is not applicable for analysis of time and temperature dependent viscoelastic stress.
Abstract: Polymeric materials show remarkable time and temperature dependent viscoelastic behaviors, which are quite different from elastic ones, under certain conditions, for example, at the temperature ranging from the glassy state to the rubbery. Although photoelasticity is an useful experimental method for the analysis of elastic stress, it is not applicable for analysis of time and temperature dependent viscoelastic stress and strain.
01 Jan 1990
TL;DR: In this article, the intergranular contact forces and displacements of the assembly disks are determined through a series of calculations tracing the movements of each of the individual disks, and the results seem to indicate that the inclusions produced higher local wave attenuation.
Abstract: Theoretical and experimental studies have been conducted on the dynamic response of granular materials containing local discontinuities of voids and inhomogeneous inclusions. The granular medium was simulated by a specific assembly of circular disks which were subjected to explosive loadings of short duration. Voids were created by removing particular disks from the assembly, while inclusions were constructed by replacing certain disks with those of a higher impedance material. The computational simulation was accomplished through the use of the distinct element method in which the intergranular contact forces and displacements of the assembly disks are determined through a series of calculations tracing the movements of each of the individual disks. The experimental study employed the use of photoelasticity in conjunction with high-speed photography to collect photographic data of the propagation of waves in transparent assemblies of model granular media. Comparisons were made between the computational results and the experimental data for the local intergranular contact forces around each void or inclusion. Both voids and inclusions produce local wave scattering through various reflection mechanisms, and the results seem to indicate that the inclusions produced higher local wave attenuation.
TL;DR: In this article, an experimental investigation is conducted using dynamic photoelasticity and high speed photography to study the wave propagation due to blast loading in porous media as a function of fluid saturation.
Abstract: An experimental investigation is conducted using dynamic photoelasticity and high speed photography to study the wave propagation due to blast loading in porous media as a function of fluid saturation. The porous media have been modeled as a continuous solid containing particular arrays of holes or voids. The study has focused mainly on the effect of the porous structure on transient pulse propagation as well as the effect of the moisture in the pores on wave propagation. A series of experiments have been conducted using a sheet of Homalite 100 with different geometry of the periodic array of holes. A small amount of explosive was used to generate the stress wave. Dynamic photoelastic photographs were taken with the high speed camera as the wave propagated across the holes. These data are analyzed to obtain the wave velocity as well as the stress-wave attenuation in the porous media.
TL;DR: In this article, a grid mesh within the digitized boundary of a photoelastic specimen was generated from a single viewing through an overhead polariscope. Butler et al. presented a computerized method to generate a grid meshes within the boundary of an image.
Abstract: A computerized method is presented that generates a grid mesh within the digitized boundary of a photoelastic specimen as it appears in the single viewing through an overhead polariscope. The second-order partial differential equation for the first linear invariant of stress which satisfies the Laplace equation is solved from the boundary values for the digitized domain by the finite-difference method. Connectivity and the weighting functions that are required for the iterative solution of the systems of linear equations are generated from the digitized information along the boundary. Isochromatic values at each nodal point within the boundary are estimated from the digitized fringe patterns by a scanning technique, and the individual values of principal stresses are determined. To enhance convergence, the method of successive over relaxation is applied with an optimum accelerating factor determined in the course of the solution process. The accuracy and the speed of the solution are tested with three different examples.
01 Oct 1990
TL;DR: In this article, an analytical method to compute the optical errors due to three-dimensional photoelastic effect of isotropic transparent optical elements is presented, where a parametric finite element model which enables accurate stress, thermal and optical analyses for design study is presented.
Abstract: An analytical method to compute the optical errors due to three-dimensional photoelastic effect of isotropic transparent optical elements is presented. The finite element method is used to compute the stresses in optical elements of arbitrary shape due to general quasi-static mechanical/thermal loads. A parametric finite element model which enables accurate stress, thermal and optical analyses for design study is presented. Equations governing the stress birefringence of the optical element subject to general three-dimensional state of stress, material properties and non-normal beam incidence are derived. Each point in the aperture is characterized by a 2 x 2 complex matrix transformation relating the input beam to the output beam in terms of Jones optical vector. This method allows computation of output optical errors for the entire aperture, in terms of phase retardation and amplitudes of polarization, for an arbitrary input polarization.
TL;DR: In this paper, the relationship between physical properties and stress fringe values is suggested and used instead of the strain gauge to measure physical properties with stress fringe value, which is confirmed by experimentation in this study.
Abstract: Relationships between physical properties and stress fringe values are suggested in this paper. These can be utilized instead of the strain gauge to measure physical properties with stress fringe values. This is confirmed by experimentation in this study. Spemimens of CD are better those of BM for measurement of the stress fringe value of an orthotropic material
TL;DR: In this article, two-dimensional photoelastic experiments were conducted to obtain isochromatic fringe fields in the region between a crack tip and a concentrated load on the boundary of a half plane.
Abstract: Two-dimensional photoelastic experiments were conducted to obtain isochromatic fringe fields in the region between a crack tip and a concentrated load on the boundary of a half plane. An analysis method is developed to determine the mixed-mode stress-intensity factors due to two interacting stress singularities. The results obtained showed the dominance of the opening mode in extending a delamination crack by sliding surface loads.
TL;DR: The method presented in this paper has a good practical application and may be used in all cases of oblique-incidence measurements in reflection photoelasticity.
Abstract: The method presented in this paper has a good practical application, which may be used in all cases of oblique-incidence measurements in reflection photoelasticity. The calculation of separate values of stresses from two measurements is also quite straightforward and well known.
01 Jan 1990
TL;DR: In this article, a hybrid optical measuring technique is introduced to measure the whole field state of stresses and strains under dynamic loads using a combined optical bench, where displacements are recorded by in plane Moire technique and synchronously the isochromatics by photoelasticity.
Abstract: A hybrid optical measuring technique is introduced to measure the whole-field state of stresses and strains under dynamic loads. Using a combined optical bench the displace-ments are recorded by in plane Moire technique and synchronously the isochromatics by photoelasticity. To separate the Moire deformation data white-light processing is applied which also serves to multiply the Moire fringes and to encode the data for archival storage in color films. The application of the technique is demonstrated for the example of stress waves in plates to simulate solid-sound propagation in machine parts.
01 Jan 1990
TL;DR: A method for measuring automatically isoclinic parameters (i.e. principal stress directions) in the whole field of a model from photoelastic experiment has been developed and could be automatically determined with a high accuracy and without any interpolation.
Abstract: A method for measuring automatically isoclinic parameters (i.e. principal stress directions) in the whole field of a model from photoelastic experiment has been developed. A basic idea for obtaining the directions of principal stresses was to utilize that a time series curve of light intensity changes sinusoidally at each point in the model using a plane polari-scope in which a polarizer and analyzer were rotated, and the minimum location on the curve corresponds to the direction of principal stresses. The minimum location was detected by using the Fourier-series expansion of the curve. The above method was realized on an automatic polariscope with a TV camera, a personal computer, an image processing equipment etc. Using this system, the directions of principal stresses in the whole field could be automatically determined with a high accuracy and without any interpolation.
TL;DR: In this article, the R-wave induced micro-crack extension induced by both a single and two approaching surface or Rayleigh waves (R- waves ) is examined experimentally and theoretically.
TL;DR: In this paper, the photoelasticity method was used to investigate the effect of interaction of defects on the stress intensity factor, which can be used in rejecting components of equipment on the basis of the results of ultrasonic inspection.
Abstract: The authors describe the procedure and results of investigations by the photoelasticity method of the effect of interaction of defects on the stress intensity factor. The resultant data, essential for determining the permissible distances between the defects, can be used in rejecting components of equipment on the basis of the results of ultrasonic inspection.
TL;DR: This paper deals with selected aspects of some of the results obtained and evaluates the advantages and disadvantages of the methods used in the solution of the particular problems addressed.
Abstract: Photoelasticity has been used recently by the authors to conduct many tests related to the determination of stresses in the field of tall beams and to the optimization of those beams. Numerical methods (in particular, finite elements and solutions of Laplace's equation) have also been used to supplement or verify the results obtained photoelastically. This paper deals with selected aspects of some of the results obtained and evaluates the advantages and disadvantages of the methods used in the solution of
the particular problems addressed.
TL;DR: In this article, the relationship between the fringe order and the stress was investigated in both stress states using a tensile specimen with a central hole, and it was revealed that in the plate of polycarbonate, there is a linear relationship between fringe orders and the difference of principal strains in the plastic range.
Abstract: Photoplasticity is a possible method of analyzing the plastic behavior in a structural member. Various problems attendant with this technique, however, especially those concerning the fundamental relationship between the fringe order and the stress, and the photoelastic material in the plastic range remain to be investigated. A few studies on this relationship in a uniaxial stress state have been presented, but no evaluations have been made in a biaxial stress state, which is considered essential for practical application of the technique. Applying the photoelastic and the moire methods, the relationship is investigated in detail in this paper in both stress states using a tensile specimen with a central hole. It is revealed that in the plate of polycarbonate there is a linear relationship between the fringe order and the difference of principal strains in the plastic range.
TL;DR: In this paper, an experimental method for the determination of stress-intensity factors (SIF) at a crack tip under thermal loading is presented, where the experimental technique used is thermophotoelasticity.
Abstract: An experimental method for the determination of stress-intensity factors (SIF) at a crack tip under thermal loading is presented. The experimental technique used is thermophotoelasticity. Data were collected from whole-field patterns by means of a digital image analysis system. SIF values were extracted using the stress field equations obtained from Williams' stress function. The photoelastic fringe field corresponding to predicted SIFs was regenerated and superimposed onto the actual fringe field to verify the results.
Journal Article•
TL;DR: In this paper, the fracture mechanics solusion of the stress field near the tip of a closed crack under compression and shear is given and a new method for prefabricating closed cracks is developed.
Abstract: The fracture mechanics solusion of the stress field near the tip of a closed crack under compression and shear is given and a new method for prefabricating closed cracks is developed in this paper. The compression-shear closed crack is studied by means of photoelasticlty,and the changes of both the stress field near the crack tip and the distribution of friction on the closed crack are studied. Futhermore,the interaction of the singular stress field between,two initially closed collinear cracks is also studied by photoelasticity. The stress intensity factor (SIF) of the compression-shear closed crack is computed by the finite element nethod. It shows that the results in the paper are correct. Finally,some applications in the research on the seismic focus are discussed.
Patent•
14 Feb 1990
TL;DR: In this paper, a photoelastic image was taken by light transmitted through the plarizing plate 3, the object 7 to be inspected, a polarizing plate 11 and a camera section 15 are arranged on an optical axis of light emitted from a light source.
Abstract: PURPOSE:To achieve a measurement automatically and at a high accuracy in a short time pertaining to a photoelastic effect by preparing an isoclinic line with a main stress direction depicting a fixed locus based on a photoelastic image taken and a main stress line from a desired point on the isoclinic line. CONSTITUTION:A polarizing plate 3, an object 7 to be inspected, a polarizing plate 11 and a camera section 15 are arranged on an optical axis 2 of light emitted from a light source 1. The polarizing plates 3 and 11 are so arranged that polarization axes thereof are orthogonal to each other. When light is emitted from a light source 2, the camera section 15 takes a photoelastic image by light transmitted through the plarizing plate 3, the object 7 to be inspected and the polarizing plate 11. An image data 15a is outputted to a image processing section 17. The image processing section 17 consists of a main stress direction calculating section 20 to calculate a main stress direction and a main stress diagram preparing section 30 to prepare a main stress diagram and the main stress direction calculating section 20 calculates an isoclinic line with a main stress direction depicting a fixed locus while the main stress diagram preparing section 30 calculates a main stress line from a desired point on the isoclinic line and the results are shown on a display device 19.
TL;DR: In this paper, the presence of material birefringence in an arbitrarily selected group of unstressed cross-linked polymers was investigated and a means of their determination was presented.
Abstract: The photoelastic effect is cumulative, therefore the presence of material birefringence in unstressed transparent polymers might lead to erroneous photoelastic analyses. This presence is more influential in the scattered-light photoelasticity. Direct-transmission polariscopes are not suitable for detecting all material birefringence in normally illuminated plates because the birefringence in question coincides with the wave normal of the propagating light. The present paper describes phenomenologically the presence of the material birefringence in an arbitrarily selected group of unstressed cross-linked polymers and presents means of their determination. The material-birefringence information obtained can be used as a means of taking proper precautions for conducting faultless scattered-light photoelastic analyses. Octagonally shaped plates were machined to permit data acquisition using four different light-propagation directions. The orientation and diffusion of molecular chains appear to be the major source of the material birefringence observed.
01 Jan 1990
TL;DR: In this paper, three-dimensional frozen-stress photoelasticity was used to study two rectangular beams under pure bending loading, and the results for the V-notch profile Type A showed that Kn = 2.4 when the array was orientated at 90° to the applied stress, but the s.c.f. reduced to Kn = 1.6 when at ± 45°.
Abstract: Three-dimensional frozen-stress photoelasticity was used to study two rectangular beams under pure bending loading. Regular, orthogonal arrays of different shallow notches were cut in the top and bottom surfaces, aligned at 0°/90° and also at ± 45° to the applied stress direction. The s.c.f. Kn defined as the maximum stress/nominal stress at the roots of the notches, was measured and compared with previous 2D results for multiple notches. The results for the V-notch profile Type A showed that Kn = 2.4 when the array was orientated at 90° to the applied stress, but the s.c.f. reduced to Kn = 1.6 when at ± 45° (as it was on the implanted hip stems and bone plate orthopaedic devices). Prototype profiles Types B and C at ± 45° had only slightly lower Kn = 1.4.