shearography

ShearographyPresented By :

DEEPA RAM

DEEPAK LAMBA

ARUN SHARMA

SIDDHANT

PRABHAT PACHAURI

Introduction…..

•Originally developed as a strain measurement technique Y Y Hung (1974)

• Shearography is a laser based interferometric technique that is sensitive to the out-of-plane deformation of a surface. Under the action of a small load, the structure is deformed and the presence of defects are revealed by local strain singularities.

Principle

• Interferometry

• Digital Image Correlation

InterferometryInterferometry is determination of fractional relative phase difference between light waves traversing different paths. Phenomena which can

be measured are those which influence the phase of the light beams. In practice this is e. g. surface deformation

Digital Image CorrelationDigital Image Correlation is a data analysis method, which uses a

proprietary mathematical correlation method to analyse digital image data taken while samples are subjected to mechanical stresses. Consecutive image captures taken during the testing phase will “show” a change in surface characteristics as the specimen is effected by the mechanical

stresses imposed upon it.

Steps:

• Fringe Formation

• Fringe Interpretation

Fringe Formation

• A shearographic image of an object may be mathematically represented as: I=I0 [1+ γ cos∅ ]

• After deformed I’ =I0 [1+ γ cos(∅+∆)

• Computing the difference of the two speckle patterns before and after deformation yields

Id= 2I0[ γsin(∅+∆/2) sin(∆/2)]

• Dark fringe lines corresponds to ∆=2(pie)n, n is fringe order.

• The computerized shearography allows ∆, the phase change due to deformation, to be automatically determined using a phase determination technique.

Fringe interpretation

• The phase ∆ is induced by the relative optical path length change between the light scattered from two neighboring points, P(x,y,z) and P’(x+∆x, y,z) on the object surface.

• In this case the shearing direction is assumed parallel to x axis and the amount is δx. It can be shown that ∆ is related to the relative displacement δu, δv, δw of two neighboring points separated by

∆ = 2(pie)/λ [A δu + B δv +C δw]

Where u,v,w are displacement vectors , λ wavelength and A,B,C are sensitivity factors related to the position of the illumination point and the camera position.

Applications

The use of Shearograph allows Non-Destructive-Inspection of:

• Disbondings

• Delaminations

• Dents

• Impacts

• Cracks

• Water & air inclusions

Advantages:

• No contact with the surface

• Global method (able to inspect surfaces up to 50x50 cm2 in one shot)

• High-resolution detection method (fractions of micrometers).

• Reduce inspection time and costs

• whole component inspection viable

• “real-time”, in-situ, in service inspections of components (measurement of gradients makes the system less sensitive to environmental noise)

• surface preparation requirements eliminated

• Produce real-time data during inspection

• permanent computer based records

• “Fitness for purpose information”

• Identify significant defects

• .

Optical NDT

Benefits

•Reduce inspection time and costs• whole component inspection viable• “real-time”, in-situ, in service inspections of components• surface preparation requirements eliminated

•Produce real-time data during inspection• permanent computer based records

•“Fitness for purpose information”• Identify significant defects

THANK YOU