Holographic nondestructive testing techniques (HNDT) are used to locate and evaluate cracks, disbonds, voids, delaminations, inhomogeneity and residual stresses in a test sample without destruction of the sample. The holographic interferometry techniques are applied for nondestructive testing of materials.
The HNDT techniques can be used for the testing of laminated structures, turbine blades, solid propellant rocket motor casings, tyres and air foils. These techniques are also useful in medical and dental research. In HNDT techniques, the test sample is interferometrically compared with the sample after it has been stressed (loaded). A flaw can be detected if by stressing the object it creates an anomalous deformation of the surface around the flaw. The holographic interferogram will show up the anomalous deformation by an abrupt change in the shape of the interference pattern.
The object can be stressed by mechanical stressing, pressure or vacuum stressing, thermal stressing, vibrational stressing and magnetic stressing. The stressing of the object can create gross deformation and rigid body motion of the object. This will produce fine interference fringes in the interferogram if the test area is large. In such a situation, the interference fringes around the flaw will be very fine and it would not be detected by unaided eye. By using fringe control methods, the effects of gross deformation and rigid body motion can be compensated.
Applications of holographic interferometry
Defects in honeycomb plates
Testing of construction materials,
Testing of welding methods
Inspection of rocket bodies
Flow visualization in wind tunnels
Vibration modes of turbine blades
Testing of oil pressure sections
Testing of welding methods
Research in construction of
Construction of engines
Machine tools and precision instruments
Measurement of deformations of machine parts, jigs and tools
Measurement inside cylinders
Measurements of stiffness (heat, static or dynamic)
Analysis of construction of instruments and tools
Electrical and electronic industries
Vibration modes of turbine blades, motors, transformers, loudspeakers
Testing of welding and adhesion
Testing of circuit parts
Analysis of audio equipments
Leak test of batteries
Analysis of constructions
Design of pipes
Research in concrete.
Measurement of mixed fluids. Tyre, rubber and NDT of tyres, plastics
Testing of molded products
Measurement of adhesion defects
Measurement on living bodies
Chest deformation due to inhalation
Measurement on teeth and bones
Testing materials for dental surgery
Testing of urinary track
Measurement on eyes, ears, etc.
Measurement of vibration modes
Cultural articles and paintings
NDT and restoration.
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