Method for analyzing a separation in a deformable structure

• US 6,088,101 A
• Filed: 06/30/1999
• Issued: 07/11/2000
• Est. Priority Date: 04/17/1996
• Status: Expired due to Fees

• Current Assignee: Michelin Recherche et Technique SA (Compagnie Generale DES Etablissements Michelin SCA)
• Original Assignee: Michelin North America Incorporated (Compagnie Generale DES Etablissements Michelin SCA)
• Inventors: Newman, John W.
• Primary Examiner(s): Kim, Robert H.
• Application Number:
  US09/345,637
• Time in Patent Office: 377 Days
• Field of Search: 356/345, 356/35.5, 356/353
• US Class Current: 356/520
• CPC Class Codes: G01B 11/162 by speckle- or shearing interferometry
• CPC Class Codes: G01B 9/025 Double exposure technique
• CPC Class Codes: G01M 17/027 using light, e.g. infrared, ultraviolet or holographic techniques

Abstract

A deformable structure is subjected to a plurality of reduced pressures, causing a bulge in the surface of the deformable structure above a separation in the deformable structure. The cross sectional area of the bulge is measured for each reduced pressure in a plane parallel to the surface of the deformable structure. When the cross sectional area of the bulge does not increase with a reduction in the pressure, the cross sectional area of the bulge approximates the area of the separation. The depth of the separation is calculated using the change in cross sectional area of the bulge per change in pressure.

Claims

1. A method of determining depth of a defect in a test object, the method comprising the steps of:

(a) varying pressure in a vicinity of the test object, while simultaneously obtaining a plurality of interferograms of the object, so as to generate defect indication areas, on said interferograms, the defect indication areas having diameters which depend on pressure;

(b) measuring a rate of change in said diameters relative to changes in pressure; and

(c) determining depth of the defect according to the result of step (b).

2. The method of claim 1, wherein the interferograms comprises shearograms.

3. The method of claim 1, wherein step (b) is preceded by the step of electronically analyzing each interferogram to determine the diameters of indicated defect areas.

4. A method of determining depth of a defect in a test object, the method comprising the steps of:

(a) generating a plurality of interferograms of the object, while simultaneously varying pressure in a vicinity of the object,

(b) storing said plurality of interferograms electronically,

(c) identifying defect areas indicated on said interferograms, the defect areas having diameters,

(d) measuring a rate of change of the diameters of said defect areas, relative to a change in pressure, and

(e) determining a depth of the defect according to the rate of change measured in step (d).

5. The method of claim 4, wherein the interferograms are produced by electronic shearography.

6. The method of claim 5, wherein step (d) comprises the step of measuring a rate of change of the diameters of said defect areas, relative to a change in pressure, electronically.