photo elasticity
TRANSCRIPT
PRESENTATION MEMBERS ARE;1)- Syed Anis Badshah
UW-09-ME-BE--012)- Hafiz Abul Rafay
UW-09-ME-BE--113)- Muhammad Ashiq
UW-09-ME-BE--374)- Muhammad Hashim
UW-09-ME-BE--465)- Hammad Habib
UW-09-ME-BE--43
OutlineDefinition and methodology of
photoelasticity?Theory of PhotoelasticityThe application of photoelasticityPhotoelastic materialsProducts GFP2000 for real-time
photoelasticity PhotoStress Measurement Limitations Conclusions
PHOTOELASTICITY:It is an indirect method of stress analysis, in that a
study is made of the stress conditions in a scale model made from a transparent plastic material, and from this the stresses in a metal component can be deduced, both quantitatively and qualitative results being obtain..
METHODOLOGY: Polarized light is passed through the model in
stress condition and changes the passage of light are thus effected , which are observed on the image of the model at the end of the optical system.
The appearance of an optical stress pattern is illustrated in figure for a pair of mating gear teeth.
These optical results are Related to 1.Stress distribution2.Magnitude and3.Direction in the modelThis provides stresses in the Actual metal component. Model is made of plasticAnd component of metal isOf no significance in Determination of stress in the elastic rangebecause widely different elastic constants would only affect the
determination of deformations and not stresses.
Theory of PhotoelasticityPhotoelasticity applying a given stress state to model utilising the induced birefringence of the transparent material by polarized light examining the stress distribution Natural and polarized light
Light Vector (Amplitude, Direction, Phase Angle), mixed of rays of different frequency
Birefringence(Double Refraction) A transparent material like mica, calcite etc is
birefringent if a ray of light passing through it experiences two refractive indices, usually two rays are “ordinary and extra ordinary rays” The effect of this is to change the polarization state of the transmitted light to form interference fringes
o
e Transparent material
Different refractive indices
Double Refraction
According to snell law
i
t
i
t
t
i
ttii
n
n
nn
sin
sin
sinsineo nn
Optic Mechanics :” the refractive indices are depended on the existing stress state in transparent material”
nlV 2
Phase Angle is
Isochromatic fringes are lines of constant principal stress difference, (P – Q).
Isoclinic fringes happens when principal stress direction coincides with the axis of polarization of the polarizer. The front figure shows appearance of isoclines in a beam during bendingAt 60°, 45°,30°.ORIENTATION Of the polarizer And analyzer withRespect to aVertical datum.
“Photoelasticity can provide both magnitude and direction of principal stress and strain”
Stress trajectories:Isoclines in themselves do not provide a clear
picture of direction of stresses in the model. However from them it is possible to construct a set of curves known as stress trajectories.
Basic Instrumentation for polarized light employed:
Basically three types that isa) Plane polarized, b) circular polarized and c) elliptical polarized
Simplest , but no light pass throughThe analyzer.
Circular Polariscope for Stress Opticon
ColorsLight source Polarize
r
Circular Polarizer
Circular Polarizer
Specimen induced stressed
Analyzer
Fringes in circular polariscope:
Figures are the fringe pattern for a beam built in each end and carrying a uniformly distributed load.
Fig(A) represents whole order fringes and Fig(B)
represents half order fringes
The application of photoelasticity Non-contact optical method for determining stresses and load paths in components or structures
coating 2D investigation 3D investigation
Impact Testing Assembly Stress Analysis Glass Inspection Flaw Detection Residual Stress Analysis FEA Model Verification
Residual Stress in Glass
Photoelastic Materials:Most widely used photoelastic material is an
“epoxy-based resin known as ARALDITE, which is also termed a thermosetting resin”.
In U.S.A several well tried and successful materials for both two and three dimensional work namely “ BAKELITE, FOSTERITE AND KRISTON..” however these materials are rather expensive and show little advantage over ARALDITE.
Materials such as celluloid and Perspex , while exhibiting birefringence , are optically too insensitive for normal photoelastic use, although they are sometimes convenient when determining isoclines.
Requirements for good photoelastic materials
High optical sensitivity.Tensile strength and modulus.Absence of optical and mechanical creepTime edge stressAbility of casting and machining.
Although photoelastic properties tend to vary somewhat from one batch of material to enother , some typical values for various substances are given in the table below.
substances Tensile strength.(lbf/in2)
Modulus of elasticity(lbf/in2)
Poisson’s ratio Material fringe value, lbf/in2. per fringe for 1 in. λ = 5461 A
ARALDITE(U.K) 20 ºC 135 ºC
12000300
0.45 * 10^60.0019 * 10^6
0.3 -
521.4
BAKELITE(U.S.A) 20ºC 110ºC
16000400
0.62 * 10^60.0011 * 10^6
0.360.5
853.3
FOSTERITE(U.S.A) 87ºC
520 0.024 * 10^6 0.48 4
KRISTON(U.S.A) 20ºC 135ºC
8200680
0.54 * 10^60.0138 * 10^6
--------
806.25
CELLULOSE NITRATE(U.K)
6000 TO 8000
0.25 * 10 ^6 TO 0.32 * 10^6
0.34 220
GELATINE(14% GLYCERINE)
---- 14 0.5 0.17
Products GFP2000 for real-time photoelasticityGFP2000 for real-time photoelasticity
•Ability to work with various types of coating materials
•Dynamic Testing •Possible use in dynamic rigs •Real-time images of stress patterns •Compact size camera head and flexible light source and projection head •Use in production line environment, e.g. monitoring the quality of glass or plastic
Key features System Performance
Typical Strain Resolution
~ 20 microstrain (1/100 fringe order)
Spatial Resolution ~ 320x240
Frame Rate
~ Real-Time Calculation: 10frame/s
Capture Video/Post Process: full
frame rate
Image Acquisition
PCI Frame Grabber Card
ProductsGFP2000 for real-time photoelasticity
Tension
Compression Compact Camera Head
Remote Light Source and Projection Head
GFP2000 Test SetupGFP2000 Test Setup
•Orientation of ellipse measures direction of 1
• Ellipticity measures magnitude
ProductsPhotoStress Measurement: PhotoStress Measurement: “ “ full field solution for stress-analysis based on full field solution for stress-analysis based on photoelasticity.photoelasticity.
Verification of FEA model by photoelasticity
Principal stress direction and magnitude measurement
Sets of Photoelastic Instruments))
LF/Z reflection polariscope system
Coating kit
Hand-held portable operationTripod mounted
LimitationsData Acquisition for principal stress
magnitude and directionCoating material and process for damp
concrete-problem from bond failure and unknown shrinkage stress effects in concrete
The difference between thermal coefficient in coating material and concrete leads to errors to field investigation
Too sensitive to the Young Modulus and poisson’s ratio ( local effect from coating process)
Conclusion Photoelasticity theory and its application are given.
The examples of products from venders are described. The most practical use of photoelasticity is to qualitatively investigate the stress-strain pattern in complex specimen. The limitations of this technology is to measure the direction and magnitude of principal stress of a number of interesting locations is impractical due to the data acquisition process. The unreliability in applying the coating material in the field investigation of reinforced concrete structures due to shrinkage, thermal effect, bond, and local effect of material properties.