Photoelasticity Sukit Yindeesuk Outline Theory of - PowerPoint PPT Presentation

Title: Photoelasticity Sukit Yindeesuk Outline Theory of


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Photoelasticity

• Sukit Yindeesuk

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Outline

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

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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
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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
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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
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Theory of Photoelasticity

• Basic Instrumentation

Simplest , but no light pass through The analyzer
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Theory of Photoelasticity

• Circular Polariscope for Stress Opticon

Specimen induced stressed
Light source
Circular Polarizer
Analyzer
Circular Polarizer
Polarizer
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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
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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

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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

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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
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Products
Sets of Photoelastic Instruments (www.vishay.com)
Coating kit
LF/Z reflection polariscope system
Hand-held portable operation
Tripod mounted
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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 poissons
  ratio ( local effect from coating process)

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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.

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Question ?