Showing papers on "Photoelasticity published in 1975"

On photoelastic response of composites

Abstract: Using the theory of the unitary system of retarders, it is shown that two seemingly different theories of photoelasticity (Sampson’s phenomenological theory and Dally and Prabhakaran’s stress-proportioning concept) are identical if the heterogeneous nature of the composites is respected. It is also shown that the optical isoclinic parameter can be accurately predicted even if the initial birefringence is present in the unloaded specimen.

Experimental Determination of Side Boundary Effects on Stress Intensity Factors in Surface Flaws

Abstract: A technique consisting of stress-freezing photoelasticity coupled with a Taylor Series Expansion of the maximum local in-plane shearing stress known as the Taylor Series Correction Method (TSCM) is applied to the determination of stress intensity factors (SIF’s) in flat bottomed surface flaws of flaw depth/length ratios of approximately 0.033. Flaw depth/thickness ratios of approximately 0.20 and 0.40 were studied as were plate width/crack length ratios of approximately 2.33 and 1.25, the former of which corresponded to a nearly infinite width. Agreement to well within 10 percent was found with the Rice-Levy and Newman theories using a depth-modified secant correction and equivalent flaw depth/length ratios. The Shah-Kobayashi Theory, when compared on the same basis, was lower than the experimental results. Using a modified net section stress correction suggested by Shah, agreement with the Shah-Kobayashi Theory was greatly improved but agreement with the other theories was poorer. On the basis of the experiments alone, it was found that the SIF was intensified by about 10 percent by decreasing the plate width/crack length from 2.33 to 1.25.

Fracture initiation and propagation from a center of dilatation

Abstract: Stress wave propagation, crack initiation, crack motion, crack arrest and the interaction of stress waves and cracks were examined in an experimental study. Dynamic photoelasticity used in conjunction with ultra-high speed photography provided full-field visualization of the several phases in the dynamic fracture process. Two fundamental problems were examined—the full-plane and the half-plane with a tensile type center of dilatation. The fracture process was characterized for both of these problems for the case where the pressure pulse at the dilatational source was of extremely short duration. The importance of the reflected stress waves in extending the fracture zone is clearly established.

Improved stressing apparatus for photoelasticity measurements

Abstract: An improved, direct reading stressing apparatus has been constructed for measuring photoelastic constants. Highly uniform stresses are obtained with minimal specimen tilt.

Measurement of stress birefringence patterns in molten polymers flowing through geometrically complex channels

Abstract: Measurements were taken of stress birefringence patterns in molten polymers flowing through geometrically complex channels. Six different flow channels were constructed for experiment, some representing the flow geometries of spinnerettes encountered in fiber spinning, and others representing mold cavities encountered in injection molding. All the flow channels had two glass windows, which permitted one to take photographs of the flow birefringence patterns of molten polymers with the aid of a polariscope. Quantitative information on the stress distributions in a flow channel was obtained, with the aid of the stress-optical laws, from the pictures taken of both isochromatic and isoclinic fringe patterns. The significance of flow birefringence measurement is discussed from the standpoint of die design for extrusion operation and mold design for injection molding operation.

Stresses and Strains in Tires

Abstract: Stress and strain patterns developed in each of several regions of automobile tires have been mapped by using methods particularly suited to each region. Miniature force transducers were u...

A note on special photographic techniques applicable to photoelasticity

Abstract: Equidensity techniques used increasingly in photoelasticity are based on pseudo-solarization effects. These and related photographic phenomena are defined, the classical procedure and improvements described, basic experimental results and calibration methods demonstrated.

Photoelasticity Using Double-exposure Polarization Holography

Abstract: A holographic method for reconstructing the polarization of light from a photoelastic model is presented Three typical patterns associated with the principal stresses, that is, Nisida and Saito's pattern in a Mach-Zehnder inter-ferometer, Fourney and Mate's pattern in double-exposure holographic inter-ferometry and dark-field isochromatics in conventional photoelasticity, are obtained from one double-exposure hologram by observing the reconstructed image having information of the original model's polarization Though the experimental condition is more stringent than that of Fourney and Mate's method, the intensity pattern obtained here is simpler than theirs The present method can completely separate dark-field isochromatics from other patterns and does not require an optically flat and parallel plane model The analytical description of the method and the experimental verification are described

Photoelastic Investigation on the Crack-Arrest Capability of Pretensioned Stiffened Panels.

Abstract: Dynamic photoelasticity, employing a 16-spark-gap Cranz-Schardin camera system, was used for dynamic analysis of propagating cracks in stiffened panels. The method of finite elements was used for a corresponding static analysis. Photoelastic models included 0.009525×0.25×0.25 m Homalite-100 plates with 10- and 25-percent pin-joined and bonded stringers. Static and dynamic strain-energy release rates, kinetic-energy release rates and stringer-load concentration factors were determined in stiffened panels that were pretensioned and then impacted by a projectile. It was found that the arrest capability of a stiffened panel could be assessed through the kinetic-energyrate concept. Also bonded stiffeners were found to be more effective in arresting a propagating crack than a corresponding pin-joined stiffened panel.

Fracture Dynamics of Wedge-Loaded DCB Specimen.

Abstract: : Dynamic photoelasticity was used to analyze the Battelle-type wedge-loaded DCB specimen machined from Homalite-100 sheets of 3/8-inch (9.5mm) thickness. Dynamic stress intensity factors, dynamic strain energy release rate, crack velocities of straight and curved crack were determined. Corresponding static stress intensity factors were calculated by the method of finite element analysis. These results were compared against Kanninen's analytical results and experimental results by Hahn et al., using steel specimen. While dynamic photoelasticity results show qualitative agreement with Kanninen's results, the two differ in detail.

Photoelastic Stress Analysis of a Nematode Stylet

Abstract: To study the mechanics and design of the tylenchid stylet, stress-distributions were determined photoelastically in transparent plastics models representing longitudinal sections of the stylet of Heterodera cruciferae. Models loaded to represent natural stresses were viewed in a plane polariscope and lines of principal stress (compressive and tensile) constructed from the resulting patterns of isoclinic lines. The plane polariscope is described and details of the method are given. With a symmetrical axial load, compressive stress lines run from the tip along the shaft and fan out into the knobs, and form an arched group with the feet of the arch on the posterolateral faces of the knobs. Tensile stress lines join the protractor muscle attachments to each other and also run across the shaft. Stress lines loop round a positive isotropic point between the knobs, where there is maximum bending moment, and diverge from a negative point at the shaft base where bending moment is least. Bending of stylets when probing food cells is illustrated and changes in stress-direction, when bending is simulated in models, are shown. Compressive stress values and elastic (Young's) modulus of stylet material are calculated and suggest that the material is a collagen. Design of stylets, relative to their mechanical requirements, is discussed, taking account of shaft and tip taper, aperture placement, muscle attachment areas, orientation of knobs and form of the transition curve between knobs and shaft.

Photoelastic and analytical investigation of stress in toroidal magnetic field coils

Abstract: A series of two-dimensional photoelastic stress analyses on circular and oval toroidal magnetic field coils for fusion reactors were made The circumferential variation of the coil's magnetic force was simulated by applying different pressures to sixteen segmented regions of the inner surface of the models Isochromatics and isoclinics were measured at selected points on the loaded model in a transmission polariscope using a microphotometer Separate principal stresses were obtained using the combination of photoelastic information and isopachic data measured from the solution of Laplace's equation by the electrical analog method Analysis of the same coil geometries, loadings, and boundary conditions were made using the finite element method General agreement between theory and experiment was realized From this investigation several variations of coil geometry and methods of support were evaluated Based upon this experiment, suggestions for optimum structural design of toroidal field coils are presented (auth)