Apparatus and method for detecting fatigue cracks using infrared thermography

Claim 1

A method for detecting a defect in a workpiece, comprising the steps of: (a) positioning a surface of the workpiece to be inspected in an optical path of an infrared radiation detector; (b) generating a graph of irradiance versus distance along a selected portion of the workpiece to establish an original irradiance intensity level; (c) heating the selected portion of the workpiece by electromagnetic radiation for a selected duration to cause an increase in radiance from any defect present at the workpiece surface in the selected portion, the radiation detector operating in a different spectral band than the electromagnetic radiation wherein any defect has a substantially higher emissivity relative to the workpiece surface surrounding the defect to cause an enhanced signal-to-noise ratio so as to allow distinction of a flaw which may cause a failure of the workpiece from another minor surface anomaly; (d) generating a series of graphs of irradiance versus distance along the selected portion as the irradiance decays from a peak intensity level back to the original intensity level after the heat is removed, the series of graphs representing a transient response of the irradiance from the selected portion; and (e) detecting defects in the selected portion of the workpiece by comparing the graphs to one another to analyze the transient response of the radiance received from the selected portion by the infrared radiation detector and to distinguish any flaw which may cause a failure of the workpiece from another minor surface anomaly.

Claim 2

A method for detecting a defect in a workpiece, comprising the steps of: (a) positioning a surface of the workpiece to be inspected in an optical path of an infrared radiation detector; (b) generating a graph of irradiance versus distance along a selected portion of the workpiece to establish an original irradiance intensity level; (c) heating the selected portion of the workpiece by electromagnetic radiation for a selected duration to cause an increase in radiance from any defect present at the workpiece surface in the selected portion, the radiation detector operating in a different spectral band than the electromagnetic radiation wherein any defect has a substantially higher emissivity relative to the workpiece surface surrounding the defect to cause an enhanced signal-to-noise ratio so as to allow distinction of a flaw which may cause a failure of the workpiece from another minor surface anomaly; (d) generating a series of graphs of irradiance versus distance along the selected portion as the irradiance decays from a peak intensity level back to the original intensity level after the heat is removed, the series of graphs representing a transient response of the irradiance from the selected portion; and (e) detecting defects in the selected portion of the workpiece by comparing the graphs to one another to analyze the transient response of the radiance received from the selected portion by the infrared radiation detector and to distinguish any flaw which may cause a failure of the workpiece from another minor surface anomaly.

Claim 14

A method for detecting a fatigue crack in a component, comprising the steps of: (a) positioning a surface of the component to be inspected in an optical path of an infrared imaging radiometer; (b) generating a graph of irradiance versus distance along a selected portion of the surface to establish an original irradiance intensity level; (c) selectively heating the selected surface area of the component by scanning with a laser beam to cause an increase in radiance from the selected surface area, the infrared imaging radiometer operating in a different spectral band than the laser beam; (d) generating a series of video images of the heated surface area from the irradiance received by the infrared radiometer during and immediately after scanning with the laser beam; (e) generating a series of graphs of irradiance versus distance along the selected surface area from the video images, the graphs corresponding to a transient response of the irradiance during and immediately after scanning with the laser beam; and (f) distinguishing between a minor surface anomaly and a crack which may cause a failure of the component by analyzing an intensity level of the irradiance and a decay rate from a peak intensity level to the original irradiance intensity level after laser scanning, the decay rate for a crack which may cause a failure of the component being more than about 2 times as long as the decay time for a minor surface anomaly.

Claim 15

A method for detecting a fatigue crack in a component, comprising the steps of: (a) positioning a surface of the component to be inspected in an optical path of an infrared imaging radiometer; (b) generating a graph of irradiance versus distance along a selected portion of the surface to establish an original irradiance intensity level; (c) selectively heating the selected surface area of the component by scanning with a laser beam to cause an increase in radiance from the selected surface area, the infrared imaging radiometer operating in a different spectral band than the laser beam; (d) generating a series of video images of the heated surface area from the irradiance received by the infrared radiometer during and immediately after scanning with the laser beam; (e) generating a series of graphs of irradiance versus distance along the selected surface area from the video images, the graphs corresponding to a transient response of the irradiance during and immediately after scanning with the laser beam; and (f) distinguishing between a minor surface anomaly and a crack which may cause a failure of the component by analyzing an intensity level of the irradiance and a decay rate from a peak intensity level to the original irradiance intensity level after laser scanning, the decay rate for a crack which may cause a failure of the component being more than about 2 times as long as the decay time for a minor surface anomaly.

Claim 21

An apparatus for detecting a crack in a component, comprising: means for generating a graph of irradiance versus distance along a selected surface area of the component to establish an original irradiance intensity level; means for heating the selected surface area of the component to cause an increase in radiance from any crack present at the component surface, wherein any crack which may cause a failure of the component has a substantially higher emissivity relative to the component surface surrounding the crack to cause an enhanced signal-to-noise ratio so as to allow distinction of any crack which may cause a failure from other minor surface anomalies; means for receiving the radiance from the selected surface area; and means for generating a series of graphs corresponding to the radiance received from the selected area immediately after heating as the irradiance decays from a peak intensity level back to said original intensity level, said series of graphs providing a transient response of the radiance received to distinguish between a minor surface anomaly and a crack which may cause a failure of the component.

Claim 22

An apparatus for detecting a crack in a component, comprising: means for generating a graph of irradiance versus distance along a selected surface area of the component to establish an original irradiance intensity level; means for heating the selected surface area of the component to cause an increase in radiance from any crack present at the component surface, wherein any crack which may cause a failure of the component has a substantially higher emissivity relative to the component surface surrounding the crack to cause an enhanced signal-to-noise ratio so as to allow distinction of any crack which may cause a failure from other minor surface anomalies; means for receiving the radiance from the selected surface area; and means for generating a series of graphs corresponding to the radiance received from the selected area immediately after heating as the irradiance decays from a peak intensity level back to said original intensity level, said series of graphs providing a transient response of the radiance received to distinguish between a minor surface anomaly and a crack which may cause a failure of the component.