Method and device for visually measuring structural fatigue using a temperature sensitive coating
First Claim
1. A visual structural fatigue crack length measurement device comprising:
- a test structure having a temperature responsive paint coating;
a test structure mechanical excitation means for resonance and narrowband random excitation, said resonance and narrowband random excitation increasing a rate of fatigue crack generation in said test structure wherein, said test structure mechanical excitation means comprises;
a signal generator, an excitation signal waveform filter and power amplifier connected to said signal generator, an electrodynamic shaker, and a test structure receiving fixture attaching said test structure to said electrodynamic shaker;
a test structure mechanical excitation means signal recorder;
a video system for viewing and acquiring images of thermal sensitivity variations of the temperature responsive paint coating and for measuring the fatigue crack length in the test structure based on said acquired images wherein, the intensity variations in said temperature responsive paint coating correspond to variations in local temperature of said test structure; and
wherein, the variations in the local temperature correspond to said test structure fatigue crack.
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Abstract
A method and device for visually detecting crack length of a temperature sensitive paint coated test structure during excitation of the test structure. The method and device of the invention capitalizes on surface temperature changes of the test structure as structural fatigue increases. Test structure surface temperature changes are realized in corresponding fluorescence intensity changes in the temperature sensitive paint and recorded with a CCD camera. Improvements over conventional structural fatigue systems include the ability to detect fatigue during flight testing, to record fatigue without stopping the electrodynamic excitation and the ability to detect crack onset and crack length resulting in more accurate cycles-to-fatigue analysis.
41 Citations
16 Claims
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1. A visual structural fatigue crack length measurement device comprising:
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a test structure having a temperature responsive paint coating;
a test structure mechanical excitation means for resonance and narrowband random excitation, said resonance and narrowband random excitation increasing a rate of fatigue crack generation in said test structure wherein, said test structure mechanical excitation means comprises;
a signal generator, an excitation signal waveform filter and power amplifier connected to said signal generator, an electrodynamic shaker, and a test structure receiving fixture attaching said test structure to said electrodynamic shaker;
a test structure mechanical excitation means signal recorder;
a video system for viewing and acquiring images of thermal sensitivity variations of the temperature responsive paint coating and for measuring the fatigue crack length in the test structure based on said acquired images wherein, the intensity variations in said temperature responsive paint coating correspond to variations in local temperature of said test structure; and
wherein, the variations in the local temperature correspond to said test structure fatigue crack.- View Dependent Claims (2, 3, 4, 5, 6, 7)
a blue light;
a CCD; and
video processing software.
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4. The visual structural fatigue crack length measurement device of claim 1 further comprising a temperature sensitive paint coating receiving and stabilizing white base coat applied to said test structure.
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5. The visual structural fatigue crack length measurement device of claim 4 wherein said test structure paint coating further comprises a probe doped active sol-gel temperature sensitive paint.
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6. The visual structural fatigue crack length measurement device of claim 4 wherein said test structure paint coating further comprises a luminescent probe containing sol-gel temperature sensitive paint.
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7. The visual structural fatigue crack length measurement device of claim 4 wherein said probe doped active sol-gel temperature sensitive paint comprises platinum meso tetra (pentafluorophenyl)porphine.
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8. A visual structural fatigue crack length measurement method comprising the steps:
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coating a test structure with a fluorescent intensity varying fatigue-responsive temperature sensitive paint coating, generating a test structure excitation signal by using a test structure mechanical excitation means capable of resonance and narrowband random excitation, said resonance and narrowband random excitation increasing a rate of fatigue crack generation in said test structure;
wherein, said test structure mechanical excitation means comprises;
a signal generator, an excitation signal waveform filter and power amplifier connected to said signal generator, an electrodynamic shaker, a test structure receiving fixture to said electrodynamic shaker;
applying said test structure excitation signal to said test structure;
applying said test structure excitation signal to said test structure;
acquire images of a fatigue induced test structure crack using a video system for viewing thermal sensitivity variations of the temperature responsive paint coating and measuring the length of the test structure crack based on acquired images wherein, the intensity variations in said temperature responsive paint coating correspond to variations in local temperature of said test structure; and
wherein, the variations in the local temperature are corresponding to said test structure fatigue crack.- View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16)
sensing a waveform filtered and amplified output signal from said generating step and;
recording a time history output from said sensing step.
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14. The visual structural fatigue crack length measurement method of claim 8 wherein said generating step further includes the steps of:
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generating an electrical signal;
filtering and amplifying said electrical signal; and
vibrating a test structure using an electrical signal activating electrodynamic shaker responsive to said filtered and amplified electrical signal.
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15. The visual structural fatigue crack length measurement method of claim 8 wherein said recording step further comprises:
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measuring test structure motion using test structure mounted first and second accelerometers;
communicating a signal from said test structure mounted accelerometers to a recorder; and
recording an output signal incorporating data from said communicating step.
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16. The visual structural fatigue crack length measurement method of claim 8 wherein said video recording step further comprises the steps of:
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illuminating the test structure using output energy from a blue light-emitting diode; and
acquiring an image comprising pixels of said illuminated test structure using a CCD camera; and
determining amplitude of pixels obtained in said acquiring step;
analyzing image from said acquiring step by dividing the amplitude of each pixel in an image by an amplitude of each pixel in an initial image acquired before applying said excitation signal to said test structure to determine the test structure intensity change from said vibrating step.
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Specification