Patent US3911733A successfully refreshed from Google Patents.
US3911733A
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US
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Optical signature method and apparatus for structural integrity verification
Assignee: Northrop Grumman Space and Mission Systems Corp
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Filing: 1974-04-01
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Granted: 1975-10-14
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Expires: 1994-04-01
Abstract
Abstract The structural integrity of a load bearing structure is periodically evaluated by recording on the same holographic recording medium two successive holograms of the structure while the latter is in two different stress conditions, respectively, to produce a holographic interferogram which may be reconstructed to create a deformation fringe pattern representing the deformations in the structure resulting from the change in the stress conditions. This deformation pattern is compared with an earlier deformation pattern of the structure resulting from the same stress conditions to determine differences, if any, between the two patterns, such differences being indicative of a reduction in the stiffness and hence structural integrity of the structure due to weakening of the latter by fatigue damage, stress corrosion cracking, and/or other causes.
Inventors
- 👤 Pravin G Bhuta
- 👤 David A Evensen
- 👤 Edmund K Burchman
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 19:07
CPC Classifications
G; G01; G01M; G01M11/00; G01M11/08; G01M11/081; G01B; G01B9/00; G01B9/02; G01B9/021; G01M5/00; G01M5/0016; G01M5/0033; G01M5/0075; G01M5/0091
Claims Analysis
Total Claims: 24
Claim 1
Independent Claim
165 words
The method of nondestructively evaluating the structural integrity of a load bearing structure comprising the steps of: recording on a first holographic recording medium a first hologram of said structure while the latter is in a first stress condition and a second hologram of said structure while the latter is in a second stress condition to produce a first holographic interferogram for reconstructing a first holographic deformation pattern of the structure; and thereafter recording on a second holographic recording medium a first hologram of said structure while the latter is in said first stress condition and a second hologram of said structure while the latter is in said second stress condition to produce a second holographic interferogram for reconstructing a second holographic deformation pattern of the structure which may be compared with said first deformation pattern to detect differences, if any, in the patterns, such differences being indicative of changes in the structural integrity of said structure in the interval between recording of said interferograms.
Claim 2
Independent Claim
165 words
The method of nondestructively evaluating the structural integrity of a load bearing structure comprising the steps of: recording on a first holographic recording medium a first hologram of said structure while the latter is in a first stress condition and a second hologram of said structure while the latter is in a second stress condition to produce a first holographic interferogram for reconstructing a first holographic deformation pattern of the structure; and thereafter recording on a second holographic recording medium a first hologram of said structure while the latter is in said first stress condition and a second hologram of said structure while the latter is in said second stress condition to produce a second holographic interferogram for reconstructing a second holographic deformation pattern of the structure which may be compared with said first deformation pattern to detect differences, if any, in the patterns, such differences being indicative of changes in the structural integrity of said structure in the interval between recording of said interferograms.
Claim 3
Dependent Claim
21 words
The method of claim 1 including the additional step of: stressing said structure in the interval between recording of said interferograms.
Claim 4
Dependent Claim
24 words
The method of claim 1 including the additional step of: subjecting said structure to variable stress in the interval between recording of said interferograms.
Claim 5
Dependent Claim
17 words
The method of claim 1 wherein: said stress conditions are created by static loading of said structure.
Claim 6
Dependent Claim
38 words
The method of claim 1 wherein: said stress conditions are created by subjecting said structure to a first static load during recording of each first hologram and to a second static load during recording of each second hologram.
Claim 7
Dependent Claim
17 words
The method of claim 1 wherein: said stress conditions are created by impulsive loading of said structure.
Claim 8
Dependent Claim
75 words
The method of claim 1 wherein: said stress conditions are created by applying an impulsive load to said structure in such a way as to propagate stress waves through said structure, and recording each set of first and second holograms in rapid succession, whereby said stress waves establish said first stress condition on the structure during recording of the first hologram and said second stress condition in the structure during recording of the second hologram.
Claim 9
Dependent Claim
20 words
The method of claim 1 wherein: said stress conditions are created by combined static and impulsive loading of the structure.
Claim 10
Dependent Claim
75 words
The method of claim 8 wherein: said structure is impulsively loaded by applying an impulsive load to said structure in such a way as to propagate stress waves through said structure, and recording each set of first and second hologram in rapid succession, whereby said stress waves establish said first stress condition on the structure during recording of the first hologram and said second stress condition in the structure during recording of the second hologram.
Claim 11
Dependent Claim
35 words
The method of claim 1 wherein: said structure is an aircraft structure; and said method comprises the additional step of subjecting said structure to variable stress cycles in the interval between recording of said interferograms.
Claim 12
Dependent Claim
21 words
The method of claim 10 wherein: said structure is subjected to said stress cycles by flying the aircraft during said intErval.
Claim 13
Dependent Claim
17 words
The method of claim 10 wherein: said stress conditions are created by static loading of said structure.
Claim 14
Dependent Claim
38 words
The method of claim 10 wherein: said stress conditions are created by subjecting said structure to a first static load during recording of each first hologram and to a second static load during recording of each second hologram.
Claim 15
Dependent Claim
17 words
The method of claim 10 wherein: said stress conditions are created by impulsive loading of said structure.
Claim 16
Dependent Claim
75 words
The method of claim 10 wherein: said stress conditions are created by applying an impulsive load to said structure in such a way as to propagate stress waves through said structure, and recording each set of first and second holograms in rapid succession, whereby said stress waves establish said first stress condition in the structure during recording of the first hologram and said second stress condition in the structure during recording of the second hologram.
Claim 17
Dependent Claim
20 words
The method of claim 10 wherein: said stress conditions are created by combined static and impulsive loading of the structure.
Claim 18
Dependent Claim
75 words
The method of claim 16 wherein: said structure is impulsively loaded by applying an impulsive load to said structure in such a way as to propagate stress waves through said structure, and recording each set of first and second holograms in rapid succession, whereby said stress waves establish said first stress condition in the structure during recording of the first hologram and said second stress condition in the structure during recording of the second hologram.
Claim 19
Dependent Claim
108 words
The method of claim 10 wherein: said stress conditions are created by combined static and impulsive loading of the aircraft structure to simulate the stress on said structure at the instant of touchdown of the aircraft during landing; and said structure is impulsively loaded by applying an impulsive load to said structure in such a way as to propagate stress waves through said structure, and recording each set of first and second holograms in rapid succession, whereby said stress waves establish said first stress condition in the structure during recording of the first hologram and said second stress condition in the structure during recording of the second hologram.
Claim 20
Dependent Claim
88 words
Apparatus for nondestructively evaluating the structural integrity of a structure comprising: a holographic system including a laser for recording on the same holographic recording medium successive holograms of the structure; means for impulsively loading said structure; and means for operating said system and loading means in timed relation in such a way as to record on said medium a first hologram of said structure while the latter is in one stress condition and a second hologram of said structure while the latter is in a second stress condition.
Claim 21
Dependent Claim
88 words
Apparatus for nondestructively evaluating the structural integrity of a structure comprising: a holographic system including a laser for recording on the same holographic recording medium successive holograms of the structure; means for impulsively loading said structure; and means for operating said system and loading means in timed relation in such a way as to record on said medium a first hologram of said structure while the latter is in one stress condition and a second hologram of said structure while the latter is in a second stress condition.
Claim 22
Dependent Claim
13 words
Apparatus according to claim 19 including: a wheeled vehicle carrying said holographic system.
Claim 23
Dependent Claim
16 words
Apparatus according to claim 20 wherein: said vehicle includes an adjustable boom mounting said holographic system.
Claim 24
Dependent Claim
20 words
Apparatus according to claim 21 wherein: said vehicle further includes an adjustable platform on said boom supporting said holographic system.
References Cited (Backward Citations)
US3136154A
Cited
US3631713A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-10-13 | 1979-04-14 | 1979-10-14 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-10-13 | 1983-04-14 | 1983-10-14 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-10-13 | 1987-04-14 | 1987-10-14 | $7700.00 | Window Closed / Lapsed |