Double exposure interferometric analysis of structures and emplo

Details Double exposure interferometric analysis of structures and emplo Double exposure interferometric analysis of structures and emplo

1982-11-15

1987-10-27

McGraw, Vincent P.

Optics: measuring and testing

Material strain analysis

By light interference detector

356348, G01B 9025, G01B 1116

Patent

active

047025948

ABSTRACT:
In order to detect subsurface defects in a vehicle tire the tire is placed in a sealed pressure chamber and the pressure is rapidly reduced to a very low level, and maintained at that level for a period of time. The body of the tire creeps for a period of time following the pressure change as a result of the stresses imposed by the pressure change. During this creep period a section on the surface of the tire is illuminated with coherent light and two separate exposures of interferograms are made using the reflected light and recorded on either a photographic media or the cathode of a television image tube. The exposure may either be holographic, in which case the interferogram is produced by using a reference beam of light derived from the same source that illuminates the object surface, or shearography, in which case two focused images of the tire surface section are formed on the photosensitive media, displaced with respect to one another and overlapping one another. The resultant hologram or shearogram is processed in the normal manner to derive an image of the object surface containing fringes arrayed as a function of the deformation of the surface between the two exposures. These fringes are analyzed either by a computer or an operator, to detect anomalous fringe families related to subsurface defects in the tire section.

REFERENCES:
patent: 3828126 (1974-08-01), Ramsey, Jr.
patent: 3911733 (1975-10-01), Bhuta et al.
patent: 4139302 (1979-02-01), Hung et al.

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