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.

Abstract: A method and apparatus for measuring strains in a test object in any of a plurality of directions. The object is illuminated with coherent light so that light is reflected to a focussing lens and a shearing diffraction grating having lines extending in a plurality of directions. The various diffracted orders interfere at the focal plane of the lens and are recorded on a photographic media. The object is then stressed and a second exposure is made on the same media, resulting in interference between the fringes produced on the two exposures. The media is developed as a transparency and subjected to optical processing to detect strain in any direction.

Abstract: Object deformations are analyzed by recording interferometric images using a television camera. The camera's photosensitive recording cathode is successively exposed to interferometric images of the object, respectively before and after a stress is applied to the object, while the camera's scanning beam is blanked out in order to record a composite image having fringe families arrayed as a function of the deformation of the object. Subsequent scanning of the cathode produces video signals representing variations of intensity in the superimposed illumination patterns of the composite image. The video signals may be digitized, analyzed and displayed on a cathode ray tube.

Abstract: A machine for performing double exposure, interferometric analysis of the changes in an object surface that result from changes in the ambient pressure on the object, as by holography, includes a pressure chamber partially formed by a horizontal base operative to support the test object and interferometric camera on its upper surface. A semispherical pressure dome is placed on the base over the test object and camera. A manifold volume bounded by a thin resilient steel disc supported beneath the base plate on a rubber gasket has its pressure equalized with the area beneath the dome by passages formed beneath the base plate. When the pressure is changed beneath the dome a similar pressure change occurs in the manifold volume beneath the base so that no net pressure forces are exerted on the base plate and no deformation of the camera or test object occurs.

Abstract: An adjustable camera is operative to perform interferometric analysis of areas on the surface of an object such as a vehicle tire using light from a coherent source. The camera mechanism includes vertical guides projecting upwardly from a support moveable in the horizontal plane along the base. A slide is adjustable vertically along the guides and carries a camera housing that is adjustable relative to the slide about a horizontal pivot axis. A coherent light source is fixed relative to the base and projects its beam parallel to the adjustment of the guide support. An optical element on the guide support projects the beam upwardly parallel to the guides to a mirror which reflects the beam horizontally about the pivot axis of the housing. A beam splitter divides the beams into an object beam and a reference beam. The object beam is projected out of the housing to illuminate a surface of the tire and cause light to be reflected to a film section supported in the housing.

Abstract: Holder and spreader fixturing for spreading and positioning the bead portions of tire casings to enable unobstructed holographic inspection of the interior of tire casings for manufacturing defects, including holder fixtures comprised of a pair of spreader rings insertable into the rim opening of the tire casing and engaging opposite bead portions of the tire casings. A plurality of U-shaped externally positioned props assembled to each of the spreader rings position the bead portions in the spread-apart position and provide an unobstructed view from the rim opening. Various configurations of the spreader rings include a split one-piece ring; a one-piece ring having trimmed side flanges; and a collapsible hinged spreader ring configuration.