Holographic nondestructive testing techniques, holographic interferometry

Holographic Nondestructive Testing of Materials

TECHNICAL

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
Field	Applications
Aerospace	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
Automobiles	Testing of oil pressure sections Testing of welding methods Research in construction of automobile bodies 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
Civil Engineering	Analysis of constructions Design of pipes Research in concrete.
Chemical industry	Measurement of mixed fluids. Tyre, rubber and NDT of tyres, plastics Testing of molded products Measurement of adhesion defects
Medicine	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.
Musical instruments	Measurement of vibration modes
Cultural articles and paintings	NDT and restoration.

Holographic Nondestructive Testing of Materials 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.