TV fatigue crack monitoring system

• US 4,063,282 A
• Filed: 07/20/1976
• Issued: 12/13/1977
• Est. Priority Date: 07/20/1976
• Status: Expired due to Term

• Current Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Exton, Reginald J.
• Primary Examiner(s): Murray, Richard
• Application Number:
  US05/707,125
• Time in Patent Office: 511 Days
• Field of Search: 358/106, 358/107, 358/100, 358/93, 358/108
• US Class Current: 348/132
• CPC Class Codes: G01L 1/24 by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
• CPC Class Codes: G01N 2203/0064 Initiation of crack
• CPC Class Codes: G01N 2203/0066 Propagation of crack
• CPC Class Codes: G01N 2203/027 Specimens with holes or notches
• CPC Class Codes: G01N 3/32 by applying repeated or pulsating forces

Abstract

An apparatus is disclosed for monitoring the development and growth of fatigue cracks in a test specimen subjected to a pulsating tensile load. A plurality of television cameras photograph a test specimen which is illuminated at the point of maximum tensile stress. The television cameras have a modified vidicon tube which has an increased persistence time thereby eliminating flicker in the displayed images.

Claims

1. A fatigue crack monitoring apparatus comprising a specimen which is subjected to a pulsating tensile load which varies from a maximum to a minimum;

a strobe light means for illuminating said specimen;

a video means for taking television pictures of said specimen;

a display means for displaying said television pictures; and

a recording means for recording said television pictures.

2. The apparatus of claim 1 wherein said strobe light means comprises a plurality of strobe lights which are directed toward said specimen and which illuminates said specimen only when the maximum tensile load is applied to said specimen.

3. The apparatus of claim 1 wherein said video means comprises a plurality of television cameras positioned to photograph said specimen.

4. The apparatus of claim 3 wherein said television cameras are equipped with a vidicon tube having a persistence time which is longer than the time required from the pulsating tensile load to move through one cycle.

5. The apparatus of claim 3 wherein said plurality of strobe lights are positioned relative to said specimen and said cameras such that very little light from said strobe lights are reflected toward the lens of said television cameras whereby whenever a fatigue crack develops and grows the crack scatters light toward the lens of said cameras causing the crack to appear white against a black background in the photographs produced by said cameras.

6. The apparatus of claim 3 wherein said display means comprises a special effects generator and a television monitor;

said special effects generator being capable of allocating a portion of said monitor for the simultaneous display of the pictures from said plurality of cameras.

7. The apparatus of claim 3 wherein said recording means is a video tape recorder.