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Journal ArticleDOI

A stress-optic law for photoelastic analysis of orthotropic composites

01 May 1970-Experimental Mechanics (Kluwer Academic Publishers)-Vol. 10, Iss: 5, pp 210-215
TL;DR: In this article, a stress-optic law was formulated, based on the concept that the birefringence components contributed by each component of plane stress are combined according to a Mohr circle.
Abstract: The feasibility for utilizing transparent filament-resin composites for photoelastic stress analysis was investigated. Satisfactory photoelastic stress patterns were demonstrated in simple models with undirectional and bidirectional fiber orientations. A stress-optic law was formulated, based on the concept that the birefringence components contributed by each component of plane stress are combined according to a Mohr circle of birefringence. Applying this concept, the difference of the physical and optical principal directions was accounted for, and a general method of photoelastic solution for the plane-stress problem in orthotropic sheets was developed. The method of analysis is little more complex than the well-known procedures for isotropic materials, but at least three experimental measurements are required to characterize the optical response of the material to plane stress. Partial confirmation of the proposed stress-optic law was obtained by comparison of the theory to limited experimental data obtained in uniaxial-stress samples. It remains to establish a more positive verification by experiments in a variety of biaxial-stress conditions.
Citations
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Journal ArticleDOI
TL;DR: In this paper, the maximum in-plane local shearing stress Tau sub m and average fringe loop inclination Theta sub m near the crack tip in terms of the Mode 1 and Mode 2 stress intensity factors K1 and K2 and polar coordinates r and Theta measured from the crack point were derived.

139 citations

Journal ArticleDOI
TL;DR: In this paper, a transparent model material fabricated from glass fibers and a modified polyester matrix exhibits continuous relatively smooth fringe patterns which are linearly related to the state of stress, which can be treated as a homogenous medium with orthotropic properties.
Abstract: A method of producing transparent model materials for photo-orthotropic-elastic studies is presented. This material fabricated from glass fibers and a modified polyester matrix exhibits continuous relatively smooth fringe patterns which are linearly related to the state of stress. As such, the heterogenous material can be treated as a homogenous medium with orthotropic properties.

69 citations

Journal ArticleDOI
TL;DR: In this paper, a strain-optic law for a certain class of birefringent fiber-reinforced composite materials is developed, which requires both mechanical and optical characterization of the material.
Abstract: A strain-optic law for a certain class of birefringent fiber-reinforced composite materials is developed. The strain-optic law requires both mechanical and optical characterization of the material. Previous investigations have hypothesized the existence of three independent optical properties for the anisotropic birefringent material. The strain-optic relation developed in this study, however, requires only a single strain-optic coefficient, coupled with four independent mechanical material properties, for prediction of the optical response of a birefringent anisotropic material. Experimental results are presented which show good agreement with the developed strain-optic relation. Finally, the isoclinic parameter is investigated and preliminary evidence is presented which indicates a correspondence between principal-strain direction and optical isoclinic angle.

40 citations

Journal ArticleDOI
TL;DR: In this article, a hybrid method for stress analysis of orthotropic composite materials is proposed, which combines isochromatic information, complex stress functions and numerical nonlinear least-squares concepts.
Abstract: Ability to determine the individual stresses photoelastically in orthotropic composites from isochromatic data, but without employing isoclinics or isopachics, is developed and demonstrated. This new capability is achieved by combining isochromatic information, complex stress functions and numerical nonlinear least-squares concepts into a new and effective hybrid method for stress analyzing composite materials. Unlike previous methods of photo-orthotropic-elasticity, the present technique simultaneously smoothes the recorded isochromatic data, provides reliable boundary information, and separates the isochromatics into individual stress components throughout the area of interest. The method is illustrated by evaluating the three individual stresses throughout a region adjacent to a hole in a uniaxially loaded orthotropic composite plate from the measured isochromatics.

36 citations

Journal ArticleDOI
TL;DR: In this paper, photoelastic experimental hybrid methods using the external traction free boundary condition and that using the relative equation of two stress functions in contact problems were developed for the analysis of the contact stress of an O-ring under 10% or 20% squeeze rate.
Abstract: In this paper, photoelastic experimental hybrid methods using the external traction free boundary condition and that using the relative equation of two stress functions in contact problems are developed. The validities of these two methods are confirmed through experiments and discussions. Hertz’s contact theory and the two photoelastic experimental hybrid methods explained are applied to the analysis of the contact stress of an O-ring under 10% or 20% squeeze rate. The photoelastic experimental hybrid method using the relative equation of two stress functions in contact problems was found to be more effective. When the squeeze rates of an O-ring were 10% or 20%, the maximum of absolute σx was greater than the maximum of absolute σy, but was almost equal. Maximums of absolute τxy were 1/8 of absolute σx and 1/5 of absolute σx when the squeeze rates of the O-ring were 10% and 20%, respectively.

33 citations


Cites background from "A stress-optic law for photoelastic..."

  • ...(11) is the stress optic law for isotropic materials [18]....

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References
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Book
01 Jan 1934
TL;DR: The theory of the slipline field is used in this article to solve the problem of stable and non-stressed problems in plane strains in a plane-strain scenario.
Abstract: Chapter 1: Stresses and Strains Chapter 2: Foundations of Plasticity Chapter 3: Elasto-Plastic Bending and Torsion Chapter 4: Plastic Analysis of Beams and Frames Chapter 5: Further Solutions of Elasto-Plastic Problems Chapter 6: Theory of the Slipline Field Chapter 7: Steady Problems in Plane Strain Chapter 8: Non-Steady Problems in Plane Strain

20,724 citations

Book
01 Jan 1978
TL;DR: In this paper, elementary elasticity and fraction mechanics stress strain and the stress-strain relationships basic equations and plane-elasticity theory are discussed and an introduction to strain measurements electrical resistance strain gages strain gage circuits recording instruments strain analysis methods.
Abstract: Part 1: Elementary elasticity and fraction mechanics stress strain and the stress-strain relationships basic equations and plane-elasticity theory. Elementary fracture mechanics. Part 2: Strain-measurement methods and related instrumentation introduction to strain measurements electrical resistance strain gages strain gage circuits recording instruments strain analysis methods. Part 3: Optical methods of stress analysis basic optics moire methods theory of plasticity applied photoelasticity - two and three dimensional stress analysis optical methods for determining fracture parameters coating methods - photoelastic coatings and brittle coating statistical analysis of experimental data.

1,324 citations

Journal ArticleDOI
TL;DR: In this article, a theoretical and experimental investigation was made of the integrated photoelastic effect in a transparent fiber glass reinforced epoxy resin, where vacuum impregnation techniques were developed to render the material transparent.
Abstract: A theoretical and experimental investigation was made of the integrated photoelastic effect in a transparent fiber glass reinforced epoxy resin. Vacuum impregnation techniques were developed to render the material transparent. The integrated effect of the isochro matics and isoclinics in the material when subjected to both uniaxial and biaxial stresses was observed and compared to the predicted data. Isochromatic data proved to be representable by a proposed orthotropic stress-optic law. Isoclinics were predictable, but at a given point in a stressed model the isoclinic angle depends on both the fiber orienta tion with respect to the principal stress directions and the ratio of principal stress magnitudes. Thus, the isoclinics do not directly give the principal stress directions. At this point, the anisotropic photo elasticity solution has not been determined.

56 citations