Showing papers on "Photoelasticity published in 1994"

Low-cost digital polariscope for dynamic photoelasticity

Abstract: A low-cost dynamic polariscope is presented. The experimental arrangement is based on the delayed-microflash technique. A LED is used as the flash source. Dynamic photoelastic patterns are recorded after different time delays from the loading point using a CCD camera operating in the time-delay and integration mode. Unlike the conventional photographic techniques, the experiments need not be performed in total darkness. Digital recording provides instantaneous visualization of the patterns and rapid repeatability.

Stress intensity factors for cracks at fastener holes

Abstract: — Transmission and reflection photoelasticity has been used to determine the stress intensity factors for artificial cracks emanating from a hole in two-dimensional tensile plates. Three geometries were investigated, namely a free hole, a pin-loaded hole and a hole with an interference-fit pin. All these cases relate to situations commonly found in aircraft structures. The results have been compared where possible with analytical data and a good correlation was found for these cases.

Analytical phase-measuring technique for retardation measurements.

Abstract: An analytical method for phase detection in retardation measurements is proposed. The experimental setup is based on a simple linear polariscope with a λ plate. The intensity modulation at the output of the polariscope is measured when the wavelength is changed and a grid of phase-shifted intensity values is recorded. The phase difference between the components of the light propagating along the principal axes of the birefringent sample is determined with Greivenkamp’s algorithm employed in phase-stepping interferometry. Error analysis for the new method is performed. Simplified algorithms for faster data analysis are proposed. The accuracy attained is comparable with the accuracy of known phase-detection methods used in retardation measurements.

The variational principles of coupled systems in photoelasticity

Abstract: This paper presents an energy principle, zero different principle of coupled systems in photoelasticity, from which the potential energy, the complementary energy, generalized potential energy and generalized complementary energy variational principles of the coupled systems in photoelasticity are derived.

Stress Concentrations Associated with Circular Holes in Cylinders and Bone in Torsion

Abstract: Experimental studies were undertaken to determine the torsional stress concentration factors (Kt) associated with circular holes in bone Reflective photoelasticity was used to determine the stress field around a circular hole through one wall of the bone A single adult sheep femur was used as the torsional model, in which six circular holes were concentrically machined through the posterior cortex These holes ranged from 104 percent to 664 percent of the mediolateral bone diameter From the photoelastic data, a stress concentration curve was developed for bone The maximum stress location on the boundary of the hole was found to shift from the previously expected 45-deg location Studies on tubes made of steel and plastic, both coated with photoelastic coating, were also performed Three different pieces of steel tubing with similar inner to outer diameters were coated with different thicknesses of photoelastic coating The variation in coating thickness did not appear to influence the stress-concentration factors in steel TheKt in steel for 10 percent and 20 percent defects agreed with theKt associated with similar defects in bone A single piece of plastic tubing was used in which six holes from 10 percent to 60 percent of the tube's outer diameter were concentrically machined through one wall The location of the maximum stress around the boundary of the hole was found to shift, and this agreed with the maximum stress shift found in the bone

Stress-optic effect in ice

Abstract: It is demonstrated in this letter that single‐crystal ice exhibits stress‐optic effect or temporary stress‐induced birefringence. This effect can be used in the exploration of the stresses using the standard techniques of photoelasticity. The photoelastic sensitivity of ice is quite high compared to glass and thus, should be quite useful in the determination of stresses in polycrystalline materials particularly near grain boundaries and in the vicinity of cracks.

Polariscope using the phase-shifting technique

Abstract: Two-dimensional birefringence measurement method using phase shifting technique has been already proposed. However, it has some problem that 16 images data are required for one birefringence distribution analysis and that its accuracy is not highly enough. To overcome this problem, the birefringent distribution measurement method using two special phase shifting techniques to reduce the collected images and to get the high sensitivity relative retardation are established. One is a local-sampling phase shifting technique using the Babinet-Soleil compensator as a phase shifter in order to get high sensitivity. The other is using the one-step phase shifting technique for quick birefringence distribution measurement using a birefringence wedge plate. In this method, only 2 images are enough to analyze the two- dimensional birefringence distribution. These experimental procedures and the results that are compared with the Babinet-Soleil compensator and of the optical components are discussed.

Separation of principal stresses in dynamic photoelasticity

Abstract: A new and effective method used to separate the transient principal stresses for dynamic photoelasticity is proposed. This is a hybrid method combining the optical method of dynamic caustics and the boundary element numerical method. Firstly, a modified Cranz-Schardin spark camera is used to record simultaneously the isochromatic fringe patterns of photoelasticity and the shadow spot patterns in the dynamic process. By means of the isochromatic fringe patterns, the difference between transient principal stresses in the whole domain and the principal stresses along the free boundary can be solved. In addition, the method of caustics is a very powerful technique for measuring the concentrative load. Then, the sum of the principal stresses is calculated by the boundary integral equation obtained from the Laplace integral transform of the wave equation. So, the transient principal stresses can be determined from the experimental and numerical results. As an example, the transient principal stresses in a polycarbonate disk under an impact load are resolved.

Finite Element Analysis and Mechanical Testing of External Fixator Designs

Abstract: Experimental and theoretical stress analysis methods are used to evaluate the mechanical behaviour of external fixation devices as load-bearing structures For the experimental part, a modular assembly was fabricated from which unilateral and bilateral fixators of different design configurations were assembled and tested under various loading conditions A reflective photoelasticity technique was used to study the effect of frame configuration on the stress patterns generated around the pin-bone interface Finite element models of each design were also generated using three-dimensional beam and shell elements Spring elements were used to model the pin/sidebar clamp It is shown that close correspondence between the experimental and theoretical methods of investigation is obtained when the flexibility of the pin/side-bar clamp is taken into account It is also shown that a unilateral design, modified by attaching a second side-bar to the first and connecting them by means of a semicircular component, can

The Effect of Bending on the Normalized Stress at Roots of Threaded Connectors

Abstract: Three-dimensional photoelasticity was used to analyze the effect of bending on the normalized stress at the roots of threaded connectors. Loading was effected by steel cages and a combination of eccentric weights (to provide the bending load) and concentric weights (to provide the axial load). The ratio of the bending stress to the axial stress was determined and various levels of this stress ratio, R[sub o], were tested. The connections were analyzed by taking thin slices in the plane of bending and perpendicular to it. The position of the maximum fringe order at the roots was determined using Mesnager's theorem and the maximum fringe order found by Tardy compensation. The fringe orders were normalized using the nominal axial stress and compared to those in connections without bending, exhibit a lower and broader peak of normalized stress values plotted against the helix length. The normalized stress values are also periodic in relation to the bending plane due to the variation in stress around the longitudinal axis of the bolt. It was found that bending in connectors will affect the normalized stress and that it is possible to determine this effect in a similar way to the method used for axially loadedmore » connections.« less

The multi-load method of determining discrete system parameters in a loaded three dimensional photoelastic model

Abstract: The determination of the secondary principal stress difference and their orientations for a discrete slice of thickness dz along a particular light path in a loaded three dimensional photoelastic model is discussed in this paper. It is well known that once the geometry of the loaded member and the geometry of loading on the member are fixed, the secondary principal stress directions at any particular point along any line of consideration remain constant. The secondary principal stress values will get multiplied by the factor through which the loading on the component is increased. This has been made use of in the present method and from the characteristic parameters obtained at the end of any light path for different loadings on the three dimensional model, the secondary principal stress difference and their orientations are obtained. The method proposed is a fully non-destructive method of testing and involves measurements only on a transmission polariscope.

Manufacture of x-ray mask and instrument for measuring stress of x-ray mask

Abstract: PURPOSE:To measure the stress distribution on an X-ray mask with high accuracy by performing intrasurface stress distribution measurement by using photoelasticity caused by infrared rays while the X-ray mask is controlled to the temperature used for X-ray lithography CONSTITUTION:Infrared rays emitted from a light source 21 are made incident to a sample 26 through a polarizing plate 24a and 1/4-wave plate 25a after they are monochromatized through a filter 22 and transformed into parallel rays through a lens 23a The title stress measuring instrument circulates an He gas 29b in a measuring container 28, is provided with an He temperature adjuster 29a for controlling the temperature of the He gas, and controls the temperature rise of the sample caused by the irradiation of infrared rays by performing the irradiation in a temperature-controlled He atmosphere having a large coefficient of thermal conductivity The controlled temperature is set at the temperature at which the X-ray mask is used for X-ray lithography Therefore, the stress distribution on the X-ray mask can be measured with a high density

Mueller fringes as a stress measurer

Abstract: We found that any uniform stressed area in loaded birefringent material observed in a polarized, white light shows an extinction effect for different light wavelength (lambda) . The shape and spectral position of the fringes depends on the value of the applied force and the type of material. The new effect is like the Mueller fringes, but we have observed the changing of the material birefringence rather than the thickness. We have studied the interference effect for a `disc-like' whole cylinder of different materials loaded by uniaxial forces acting along the diameter. The cylinder posses a uniform stress area in its center and that area is under study. The measurements were made for various materials on a computer aided spectrometer, (specially constructed for the research), under different loading conditions. The results of the measurements are discussed and compared with theoretical predictions. The effect can be utilized for construction of an optical force sensor.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Investigation of faulted tunnel models by combined photoelasticity and finite element analysis

Abstract: Models of square and circular tunnels with short faults cutting through their surfaces are investigated by photoelasticity. These models, when duplicated by finite element analysis can predict the stress states of square or circular faulted tunnels adequately. Finite element analysis, using gap elements, may be used to investigate full size faulted tunnel system.

Measurement of absolute retardation in photoelasticity using a digital image processing system

Abstract: A new method for measuring the isoclinics and absolute retardations along the principal stress directions at a point in a loaded photoelastic specimen is presented. In this method, a plane polariscope is used with the digital image processing system. Two images of a loaded specimen are captured at different angular positions of the polarizer and analyzer. Isoclinics and retardations at a point are evaluated from the light intensity values measured on these recorded images. The present method for the measurement of absolute retardations overcomes the difficulties in the measurement of retardations in birefringent specimens using the conventional interferometric methods. To verify the effectiveness of this method, principal stresses are directly evaluated using the values of retardations and these principal stresses are verified with the theoretical solutions. The photoelastic specimens -- a circular disk under diametral compression and a simply supported beam with a load at its center -- are analyzed.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Quantifying the Tooth-Food Interface with Finite-Element Analysis and Photoelasticity

Abstract: s from the Fourth International Congress of Vertebrate Morphology, Chicago, Illinois, July 31–August 4, 1994. Quantifying the Tooth-Food Interface with FiniteElement Analysis and Photoelasticity Freeman, P. W. Weijs, W. N. University of Nebraska–Lincoln, NE, USA. We are interested in the tooth-food interface and the functioning of teeth. The cross-sectional shapes of canine teeth of bats can be triangular or polygonal. The vertices of the triangle or polygon represent edges that extend longitudinally from tip to cingulum. One of us proposed there should be differences in how cracks are propagated in the substance being penetrated based on the shape of the tooth. To test this idea we have used finite-element analysis to simulate the effect of an edged tooth versus a non-edged or circular tooth as it penetrated a substance. To see what actually happens we have used oversized metal models of edged and non-edged teeth and the materials science technique of photoelasticity. A unique aspect of our approach is to use photoelastic plastic, to test the stress in a photoelastic “food.” Here we stress-freeze the oversized model in the plastic and document the patterns of stress with a polariscope. From our preliminary results we can now verify experimentally what was simulated with finite-element analysis. It is not surprising that there is an increase of surface energy at the edge of an edged tooth and no such build-up with a circular or non-edged tooth. We have now established a protocol to examine more subtle shapes of teeth and can analyze the tooth marks in three dimensions.

Analyzing method of stress of conductor and terminal pressure welding part

Abstract: PURPOSE:To obtain a method for making it possible to use experimental data as quantitative data as they are without modification (correction) CONSTITUTION:A photoelastic sample 23 being isotropic, transparent and analogue substantially to a pressure welding terminal is formed and a jig 24 for pressure prepared by making a pressure welding part of a conductor be in the same ratio as the photoelastic sample is inserted into a position corresponding to the conductor in a pressure welding groove 23a of the photoelastic sample In this state, the state of a stress applied to the photoelastic sample is recorded by a method of photoelasticity The jig 24 being removed, subsequently, a pair of jigs for tension are brought into contact with the same position, a plane stress is applied by impressing a tensile force on the photoelastic sample by a tensile tester and a tensile stress which brings about the same state of the stress as that by the aforesaid jig for pressure is determined by the method of photoelasticity

Studies of the Effect of Microstructure on the Dynamic Behavior of Granular and Particulate Media (First Year Report)

Abstract: : A combined experimental-numerical investigation is being conducted to study dynamic load transfer in particulate materials due to explosive loadings. The primary emphasis in the study is to relate the microstructural features of the particulate media tot he load transfer process. The experimental techniques of dynamic photoelasticity is used to investigate the effect of cementation and of the particle shape on the local contact stress fields. The stiffness of the cement relative to that of the particle controls the location of the peak contact stresses. Strong cementation increases the load transfer velocity and also promotes fracture of the particles. The particle shapes as presently studied in this research program seem to have little influence on the load transfer process. The applicability of the fiber optic sensors and the speckle techniques to contact stress measurements is evaluated. Fiber optic sensors show promise of future applications to three dimensional problems. Discrete element numerical wave simulation has been conducted for saturated granular materials through the introduction of a new contact law using elastohydrodynamic theory. Pore fluid acts to decrease the wave speed and increase the attenuation. Future numerical studies will focus on additional changes of the interparticle contact response through cementation and particle shape effects.

支台材料がCeramics Jacket Crownの応力分布に及ぼす影響

Abstract: A photoelastic stress analysis technique has been conducted for many years as a test to analyze stress distribution of porcelain jacket crowns under a load. The purpose of this study was to evaluate the alteration of stress distribution on ceramic jacket crowns by each abutment material of different elasticity. On the assumption that the jacket crown consists of castable ceramics (DICOR) and three different abutment materials had metal cores (12% Au-Ag-Pd alloy), a resin core (photocuring composite resin) and a natural tooth, the crown and the abutment tooth model were made of epoxy resin. And the stress analysis of the ceramic jacket crown was studied by three-dimensional stress freezing photoelasticity experimental technique.The boundary stress in the portion with the added load reached the maximum value in all abutment teeth. The magnitude of boundary stress increased with the decrease in the elastic modulus of the abutment material. Especially, when the abutment was a resin core or a natural tooth, high boundary stress was observed around the labial cervix.

Ccd automated polariscope system and the stress analysis methods

Abstract: A Linear CCD (change coupled device) automated measurement system and the stress analysis methods are presented in the present paper. The skeleton and the orders of photoelastic fringes can be acquired rapidly, precisely and in real time by the system. The automatic stress analysis methods in the paper only uses a small amount of known data to analyze the stress precisely.

Experimental analysis of nonlinear problems by optical methods

Abstract: As an example of a geometrical nonlinear problem a thin plate-in-bending under large deflection is considered. To determine the inplane- as well as the bending stress-state the photoelastic reflection method and Ligtenberg's moire method are used; the measured information is evaluated according to the principles of integrated photoelasticity. As yet in photoelasticity it has always been supposed Hooke's law of elasticity is valid and consequently linear relations between birefringent effects and stresses are existing. However, in areas of high stress concentration and with reference to some of the mainly used photoelastic material nonlinear strain-stress relations must be introduced. A proper constitutive equation yields an advanced principal photoelastic equation, the solution of which is performed in an iterative procedure. It should be mentioned that extended material testing is demanded to get the various material parameters. Finally proper algorithms and the respective numerical evaluation procedures are described, to analyze plane stress-states, if the material shows viscoelastic response. Then the mechanical as well as the optical rheological response of material must be considered.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Stress induced frequency shift of dielectric resonators with magnetic wall

Abstract: This paper presents a perturbation analysis on the stress or strain induced frequency shift through piezooptic or photoelastic effect in dielectric resonators with open circuit boundary or magnetic wall. Based on the availability of the frequency and mode when stress is not present, prediction on first order stress induced frequency shift is obtained for a resonator of arbitrary shape and with general dielectric permittivity tensor. The result is in fact also valid for resonators with short circuit boundary or electric wall, or resonators with partial open circuit boundary and partial short circuit boundary. >

Dynamic material properties in birefringent materials

Abstract: Dynamic photoelasticity is a full field technique which has been used by various researchers as an aid to improve understanding of problems that involve stress wave propagation. Birefringent materials that exhibit sufficient sensitivity to loading for stress wave propagation studies are typically polymers. Glass, which is not nearly as viscoelastic as polymers does not exhibit enough sensitivity for easy measurements, thus it is unsuitable for most dynamic studies. The effect of loading rate on material properties is more pronounced in polymers, hence accurate measurement of these properties is essential in a dynamic photoelastic study. The problem associated with the determination of the dynamic material properties of a polymer is the determination of the exact location of the wavefront. Digital image analysis can be used to locate the wavefront with a great deal of accuracy. The results from the digital image analysis can then be used to determine dynamic material properties for the polymer.