US3847481A - Photoelastic processes for examining mechanical stresses - Google Patents

Photoelastic processes for examining mechanical stresses Download PDF

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Publication number
US3847481A
US3847481A US00345896A US34589673A US3847481A US 3847481 A US3847481 A US 3847481A US 00345896 A US00345896 A US 00345896A US 34589673 A US34589673 A US 34589673A US 3847481 A US3847481 A US 3847481A
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United States
Prior art keywords
grid
images
polarizer
optical path
screen
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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US00345896A
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English (en)
Inventor
D Paraskevas
Hermite A L
G Bernard
J Guinet
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Centre Technique des Industries Mecaniques CETIM
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Centre Technique des Industries Mecaniques CETIM
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Priority claimed from FR7210617A external-priority patent/FR2179479B1/fr
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
    • G01L1/241—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet by photoelastic stress analysis
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
    • G01B11/18—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge using photoelastic elements

Definitions

  • 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 suc:
  • the present invention relates generally to photoelastic processes for examining mechanical stresses; and more especially relates to a process for visualizing the isostatic lines or lines of maximum-shear force in a body, and also to a device for carrying out such a process.
  • isostatic lines are envelopes of the directions of the principal stresses in a body. These are the field lines of the principal stresses, and they form two groups of curves, which are at all points orthogonal relative to each other.
  • the maximum-shear lines comprises two groups of orthogonal curves, intersecting the isostatics at 45.
  • Processes and devices are known, enabling direct viv sualization by means of successive superimposed photographs of the isostatics or maximum-shear lines, avoiding the long and painstaking point-by-point tracing, from the networks of isoclinic lines, in the case of examination by transmission of a model of transparent material placed between a polarizer and an analyzer.
  • a grid preferably having a square mesh, whose lines are parallel to the planes of polarization crossed by a polarizer and an analyzer.
  • the polarizer, the grid and the analyzer constitute an assembly which is rotatable relative to the modelsexamined.
  • the presentinvention proposesa process and device which obviates or mitigates the above drawbacks and enables direct visualization of the isostatics or maximum-shear lines more efficiently than in previous techniques, even in the observation of real structures.
  • the present invention can likewise be applied with advantage in the variant in which bytransmission, a model made of transparent photoelastic material is observed.
  • a process of visualizing the maximum-shear'lines or isostatics by observation under polarized light of the accidental double refractions appearing in a photoelastic material comprising obtaining, successive watered-silk images by observing simultaneously the material and a grid with lines parallel; to the plane of polarization. of the light superimposed for maximum-shear lines, orat 45 to the latter, for the isostatics for different successive orientations of the plane of polarization, one at least of the material. and the, grid being observed in the form of an optical image formed inv the plane of the other.
  • the said grid is made up by forming, in the same plane as the material observed, areal optical; image of a grid distant from the material.
  • the said material ismade up of a photoelastic film observed by reflection of the light on a reflective layer subjacent thereto, and: the real optical image of the grid isformed inthe plane of the refiective layer.
  • the real grid may also be arranged against a screen. on which the image of the material is formed.
  • a stroboscopic light is used as a light-source.
  • the speed of rotation: and the intervals, or the frequency of the'flashes may thenbe so selected that thespeed of the successionof the images observed is sufficiently rapidrelative to the retinal inertia,-so that an observer simultaneously seesthe successive images frequency of the flashes being a whole multiple of this number of the order of 40.
  • the networks of isostatics or of maximum-shear lines result ing from the watered-silk effects between the successive images super-imposed on the grid, are visible directly on a translucent screen without the necessity for photography.
  • the material may be progressively moved the whole surface of the piece thus being examined in a very short time.
  • a device for use in visualization of the maximum-shear lines or isostatics by observation under polarized light of the accidental double refractions appearing in a photoelastic material comprising means defining an optical path between a light source, a photoelastic material to be observed and a screen for observing or recording the images of the said material, a polarizer and an analyzer respectively arranged in the optical path between the source and the material, and the material and the screen, a grid distant from the material and superimposed on the said screen, or associated with means for forming therefrom an optical image in the plane of the material observed, or of its image on the screen, and means of synchronized rotation of the polarizer, the analyzer and the grid relative to the optical path axis.
  • the grid, the analyzer and even the screen are preferably mounted on the same rotary support on the optical axis, rotated in synchronism with the polarizer.
  • FIG. 3 shows diagrammatically a network of maximum-shear lines obtained by the visualization process according to the present invention
  • FIG. 4 also shows a network of isostatics
  • FIGS. 5a and Sb show the application of the processaccording to the present invention to the finishing of a profiled mechanical part
  • FIG. 6 shows diagrammatically a polariscope device according to another embodiment of the present invention.
  • a polariscope device shown in FIG. 1 is used for the observation of a structure 1, on which there has been placed a reflective layer 2, which is coated with a photoelastic varnish forming a transparent film 3.
  • the device comprises on thesame side relative to the structure 1, a light-source'4 and a camera photographic plate 5 receiving the image of the source, reflected at a slight angle of incidence on the structure 1, or more precisely by the reflective layer.
  • the structure 1 and the photographic plate 5 via lenses L1, L2, L3 and L4 there are arranged two polarizers whose planes of polarization are crossed, and which constitute respectively the polarizer proper 6 between the source and the structure 1 observed, and the analyzer 7 between the structure 1 and the photographic plate 5.
  • the light source 4 is at the focal point oflens L4, illuminating the structure by a parallel beam of light.
  • Lenses L2 and L3 focus the light on the polarizer6, and lens L1 focuses the light reflected on analyzer 7, in front of the objective lens 8 of the plate 5.
  • a grid 10 is arranged in the light-path perpendicularly to the optical axis, before the convergent lens L3.
  • This grid is mounted in a support whose position on the optical axis may be adjusted so that it is at a convergent point of the reflective layer 2, relative to the optical system of lenses L2 and L3.
  • the grid is oriented so that its lines are parallel and perpendicular to the plane of polarization of the light after the polarizer or at 45 to this plane, depending on whether it is required to obtain the maximum-shear lines or the isostatic lines of the structure It is possible to turn the plane of polarization of the light relative to the structure 1, which is presumed to remain fixed by causing synchronized rotation of the polarizer 6, the analyzer 7 and the grid 10, around the optical axis.
  • the device in FIG. 1a differs from that in FIG. 1 only in the fact that the two beams from polarizer 6 and an alyzer 7' are on opposite sides of the examined model 1' which is cut from a sheet of transparent photoelastic resin, and has neither a reflecting layer 2 nor a film 3 of photoelastic varnish.
  • the function of this device in FIG. la is otherwise identical with that in FIG. 1.
  • a mirror 11 allows the optical path to be deflected a first time before the polarizer, in order to render the assembly more compact.
  • the orientation of the grid is adjusted so that its lines are parallel and perpendicular to the crossed planes of polarization of the polarizer and the analyzer depending on the case. Then the grids position on the optical axis is adjusted so as to form a real image of the grid on the reflective layer 2 of the structure 1, causing this real image to coincide with its virtual image relative to the reflective layer. Finally, the camera is focused on this reflective layer.
  • Tracings such as those schematically shown in FIGS. 3 and 4 are obtained by observing a piece of beam under load, particularly under the following conditions:
  • FIGS. 50 before rectification
  • 5b after rectification
  • the rotation of the polarizer of the grid and of the analyzer and their positioning for each photograph taken may be effected manually or automatically.
  • the rotation may also be continuous, the light-source being made intermittent, at regular intervals, for example, with an electronic flash-gun when passing the desired inclinations, or if necessary, by causing the intensity to vary progressively according to a law of alternative varration.
  • FIG. 6 shows schematically a photoelastic device which comprises, like the embodiments described previously, a polarizer 21 and an analyzer 22, arranged in the optical path of a beam of light produced by a lightsource 23.
  • the model 24 is arranged between the analyzer and the pola'rizer, the beam of polarized light passing through the model.
  • An optical system illustrated by a lens-25 enables the image of the model to be formed in the plane of a screen 26 which is translucent'and against which there is arranged a grid 27.
  • This grid may be a simple positive or negative grid, with networks of orthogonal parallel lines. However, in this case it is doubled by another analogous grid whose lines form a variable angle with those of the first.
  • Thewatered-silk effect between the two superimposed grids constitutes a variable-stop grid as a function of the angle formed by the lines of the two grids, and by relative rotation of the latter, the stop may be adjusted at will, which in practice allows the contrast to be improved.
  • the analyzer 22, screen 26 and the grid 27 are mounted integrally on the same support 28, constituted by a rotary shaft arranged on the optical axis.
  • a synchronizer device 29 when functioning enables synchronization oftheir rotation with that of the polarizer 21 which is likewise rotary on the optical axis.
  • the screen 26 may be made up of a single sheet of tracing paper.
  • the watered-silk image, obtained by superimposition with grid 27, may be registered on the plate of a camera (not shown).
  • the network of isostatics or maximumshear lines are then obtained by recording successively on the same plate the watered,- silk images corresponding todifferent-angular positions of the polarizer/analyzer/gridassembly relative to the model. 7 7
  • these images are directly and simultaneously observableon the screen 26.
  • the light-source is then a flashinglight or a strobo scope and the analyzer/polarizer/g'rid-assembly likewise integral with the screen in the special embodiment under consideration, is continuouslyrotated at a speed sufficiently high for it to be possible to illuminate different angular positions relative to the model during the time when the images persist on theobservers retina.
  • the frequency of theflashes is a whole-multiple of the rpm. (revolutionsper'minute) .of this assembly.
  • a rotary speed'of 410 rpm. may be used with a flash frequency of 16,400 flashes per minute.
  • This method of operation enables the networks of isostatics or maximum-shear lines. to be seen directly such as those shown in FIGS. 3 and 4.
  • the screen may likewise be stroboscopically illuminated, instead of the photoelastic material.
  • the invention is in no way limited to the ex a screen for receivingthe-images from said material
  • a polarizer and an analyzer respectively arranged in the optical path between the source and the material, and the material and the screen, a grid distant from the materialand superimposed on said screen, and 7 means for synchronized rotationof the polarizer, the analyzer andthe grid'relative to the optical path axis to produce a succession-ofsaid imagesat'different angular orientations thereof.
  • a device for use in visualization of mechanical stress lines by observation, under a polarized light source, of the double refraction images from a photoelastic material comprising:
  • a polarizer and an analyzer respectively arranged in the optical path between the source and the material, and the material and the screen
  • a device for directly visualizing the mechanical stress lines caused by observing, under polarized light, the double refractions appearing in a photoelastic material comprising:
  • a method according to claim 14 including forming the successive moire images on an observation screen.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Eye Examination Apparatus (AREA)
  • Investigating Materials By The Use Of Optical Means Adapted For Particular Applications (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)
US00345896A 1972-03-27 1973-03-29 Photoelastic processes for examining mechanical stresses Expired - Lifetime US3847481A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR7210617A FR2179479B1 (xx) 1972-03-27 1972-03-27
FR7218422A FR2189705B2 (xx) 1972-03-27 1972-05-24

Publications (1)

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US3847481A true US3847481A (en) 1974-11-12

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US00345896A Expired - Lifetime US3847481A (en) 1972-03-27 1973-03-29 Photoelastic processes for examining mechanical stresses

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US (1) US3847481A (xx)
JP (1) JPS499286A (xx)
CA (1) CA977577A (xx)
CH (1) CH569267A5 (xx)
DD (1) DD102811A5 (xx)
DE (1) DE2314712C3 (xx)
FR (1) FR2189705B2 (xx)
GB (1) GB1412870A (xx)
SE (1) SE386264B (xx)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3971934A (en) * 1975-08-04 1976-07-27 Joseph Coatta Photoelastic load measurement alarm device
US3994719A (en) * 1973-03-24 1976-11-30 Bayer Aktiengesellschaft Resins for separating heavy metals consisting of thiourea-group-containing macroporous vinyl aromatic crosslinked matrixes
US4109515A (en) * 1976-05-10 1978-08-29 Chrysler Corporation Photoelastic stamping analysis
US5742392A (en) * 1996-04-16 1998-04-21 Seymour Light, Inc. Polarized material inspection apparatus
US6650405B2 (en) 2000-05-31 2003-11-18 Duhane Lam Method for detecting stress and strain

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2489957A1 (fr) * 1980-09-08 1982-03-12 Thomson Csf Dispositif de mesure de caracteristiques geometriques d'un barreau en materiau refringent, notamment d'une preforme utilisee pour la fabrication de fibres optiques
DE3516538A1 (de) * 1985-05-08 1986-11-13 Fa. Carl Zeiss, 7920 Heidenheim Verfahren und vorrichtung zur optischen spannungsmessung
DE19909516B4 (de) * 1999-03-04 2008-04-17 TÜV SÜD Automotive GmbH Verfahren zum Wahrnehmbarmachen von Meßdaten eines Versuchsablaufs sowie Versuchsdatenerfassungs-Auswertungssystem
CN107270234B (zh) * 2017-06-12 2019-04-16 中国农业大学 一种频闪仪

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3178934A (en) * 1963-07-18 1965-04-20 Bell Telephone Labor Inc Methods and apparatus for photoelastic strain analysis of structural members
US3477284A (en) * 1968-06-12 1969-11-11 Boeing Co Technique for deformation analysis
US3552856A (en) * 1968-06-12 1971-01-05 Boeing Co Technique for analyzing deformation in a test specimen

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3034395A (en) * 1956-11-26 1962-05-15 Budd Co Photoelastic testing and measurement of mechanical strains

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3178934A (en) * 1963-07-18 1965-04-20 Bell Telephone Labor Inc Methods and apparatus for photoelastic strain analysis of structural members
US3477284A (en) * 1968-06-12 1969-11-11 Boeing Co Technique for deformation analysis
US3552856A (en) * 1968-06-12 1971-01-05 Boeing Co Technique for analyzing deformation in a test specimen

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
General Radio Experimeter, The Polariscope for Dynamic Stress Analysis, Vol. XXV, No. 1, June 1950. *

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3994719A (en) * 1973-03-24 1976-11-30 Bayer Aktiengesellschaft Resins for separating heavy metals consisting of thiourea-group-containing macroporous vinyl aromatic crosslinked matrixes
US3971934A (en) * 1975-08-04 1976-07-27 Joseph Coatta Photoelastic load measurement alarm device
US4109515A (en) * 1976-05-10 1978-08-29 Chrysler Corporation Photoelastic stamping analysis
US5742392A (en) * 1996-04-16 1998-04-21 Seymour Light, Inc. Polarized material inspection apparatus
US6650405B2 (en) 2000-05-31 2003-11-18 Duhane Lam Method for detecting stress and strain

Also Published As

Publication number Publication date
FR2189705B2 (xx) 1978-03-31
DE2314712A1 (de) 1973-10-11
FR2189705A2 (xx) 1974-01-25
SE386264B (sv) 1976-08-02
CH569267A5 (xx) 1975-11-14
DE2314712C3 (de) 1975-08-28
DE2314712B2 (de) 1975-01-23
GB1412870A (en) 1975-11-05
JPS499286A (xx) 1974-01-26
DD102811A5 (xx) 1973-12-20
CA977577A (en) 1975-11-11

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