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Photoelasticity

Photoelasticity. Sukit Yindeesuk. Outline. Theory of Photoelasticity The application of photoelasticity Products GFP2000 for real-time photoelasticity PhotoStress Measurement Limitations Conclusions. Theory of Photoelasticity. Photoelasticity

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Photoelasticity

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  1. Photoelasticity Sukit Yindeesuk

  2. Outline • Theory of Photoelasticity • The application of photoelasticity • Products GFP2000 for real-time photoelasticity PhotoStress Measurement • Limitations • Conclusions

  3. Theory of Photoelasticity • Photoelasticity 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

  4. e Transparent material o Different refractive indices Theory of Photoelasticity • Birefringence A transparent material is birefringent if a ray of light passing through it experiences two refractive indices. The effect of this is to change the polarization state of the transmitted light to form interference fringes Double Refraction Optic Mechanics :” the refractive indices are depended on the existing stress state in transparent material” Phase Angle is

  5. Theory of Photoelasticity Isochromatic fringes are lines of constant principal stress difference, (s P – s Q). Isoclinic fringes happens when principal stress direction coincides with the axis of polarisation of the polariser. “Photoelasticity can provide both magnitude and direction of principal stress and strain”

  6. Theory of Photoelasticity • Basic Instrumentation Simplest , but no light pass through The analyzer

  7. Colors Theory of Photoelasticity • Circular Polariscope for Stress Opticon Specimen induced stressed Light source Circular Polarizer Analyzer Circular Polarizer Polarizer

  8. 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

  9. Products • GFP2000 for real-time photoelasticity (www.viseng.com) 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 • 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

  10. Products • GFP2000 for real-time photoelasticity Remote Light Source and Projection Head GFP2000 Test Setup Compact Camera Head • Orientation of ellipse measures direction of e1 • Ellipticity measures magnitude

  11. Products • PhotoStress Measurement: • “ full field solution for stress-analysis based on • photoelasticity (www.vishay.com)” Verification of FEA model by photoelasticity Principal stress direction and magnitude measurement

  12. Products Sets of Photoelastic Instruments (www.vishay.com) Coating kit LF/Z reflection polariscope system Hand-held portable operation Tripod mounted

  13. Limitations • Data Acquisition for principal stress magnitude and direction • Coating 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)

  14. 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.

  15. Question ?

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