METHOD AND APPARATUS FOR THERMOGRAPHIC NONDESTRUCTIVE EVALUATION OF AN OBJECT

• US 20080317090A1
• Filed: 06/20/2007
• Published: 12/25/2008
• Est. Priority Date: 06/20/2007
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Tralshawala, Nilesh, Howard, Donald Robert, Ringermacher, Harry Israel, Knight, Bryon Edward
• Granted Patent: US 7,549,789 B2
• Time in Patent Office: Days
• US Class Current: 374/43
• CPC Class Codes: G01N 25/72 Investigating presence of flaws

Abstract

A method and system for determining thermal diffusivity and porosity of an article are provided. The method comprises heating a surface of the article, capturing image data corresponding to an evolution of lateral heat flow from the surface of the article, applying a thermal time of flight analysis on the image data and determining thermal diffusivity and porosity values of the article using the thermal time of flight analysis for the lateral heat flow.

Claims

1. A method for determining porosity of an article, the method comprising:

heating a surface of the article;

capturing image data corresponding to an evolution of lateral heat flow from the surface of the article;

applying a thermal time of flight analysis on the image data; and

determining thermal diffusivity and porosity values of the article using the thermal time of flight analysis for the lateral heat flow.

2. The method of claim 1, wherein the thermal time of flight analysis comprises generating a curve for the time of flight as a function of a distance from a heat source edge, wherein the curve comprises at least three regions, wherein a first one of the regions has a slope 1, wherein a third one of the regions has a slope 2, and wherein an intermediate one of the regions is bounded by a first and a second time point t₁ and t₂, and

wherein the thermal diffusivity is calculated from the slopes 1 and 2 and the time points t₁ and t₂.

3. The method of claim 2, wherein determining the thermal diffusivity comprises determining an in-plane thermal diffusivity α

_p using an equation for the slope 1;

$\mathrm{Slope}<br><br><br><br>1=\frac{1}{{\mathrm{\pi <br><br>}}^2<br><br>{\mathrm{\alpha <br><br>}}_p}.$

4. The method of claim 2, wherein determining the thermal diffusivity comprises determining an in-plane thermal diffusivity α

_p using an equation for the slope 2;

$\mathrm{Slope}<br><br><br><br>2=\frac{1}{6<br><br>{\mathrm{\alpha <br><br>}}_p}.$

5. The method of claim 2, wherein the article comprises a plurality of layers including a plurality of surface layers, the method further comprising determining a thermal diffusivity α

_p of the surface layers using an equation;

$\mathrm{Slope}<br><br><br><br>1=\frac{1}{{\mathrm{\pi <br><br>}}^2<br><br>{\mathrm{\alpha <br><br>}}_p}.$

6. The method of claim 2, wherein the article comprises an isotropic material, the method further comprising determining a thermal diffusivity a of the article using an equation:

$\mathrm{Slope}<br><br><br><br>1=\frac{1}{{\mathrm{\pi <br><br>}}^2<br><br>\mathrm{\alpha <br><br>}}.$

7. The method of claim 2, wherein determining the thermal diffusivity of the article of thickness d comprises determining a through-thickness thermal diffusivity at using an equation for the time t₁:

$t_1=\frac{1.5<br><br><br><br>d^2}{{\mathrm{\pi <br><br>}}^2<br><br>{\mathrm{\alpha <br><br>}}_t}.$

8. The method of claim 2, wherein determining the thermal diffusivity comprises determining a through-thickness thermal diffusivity at using an equation for the time t₂:

$t_2=\frac{4<br><br>d^2}{{\mathrm{\pi <br><br>}}^2<br><br>{\mathrm{\alpha <br><br>}}_t}.$

wherein d is the thickness of the article.

9. The method of claim 2, wherein the article comprises an isotropic material characterized by a thermal diffusivity α

, the method further comprising independently determining both thermal diffusivity, α

, and thickness d of the article by using equations,

$t_1=\frac{1.5<br><br>d^2}{{\mathrm{\pi <br><br>}}^2<br><br>\mathrm{\alpha <br><br>}}<br><br><br><br>\mathrm{or}<br><br><br><br>t_2=\frac{4<br><br>d^2}{{\mathrm{\pi <br><br>}}^2<br><br>\mathrm{\alpha <br><br>}},<br><br>\mathrm{and}$ $\mathrm{Slope}<br><br><br><br>1=\frac{1}{{\mathrm{\pi <br><br>}}^2<br><br>\mathrm{\alpha <br><br>}}<br><br><br><br>\mathrm{or}<br><br><br><br>\mathrm{Slope}<br><br><br><br>2=\frac{1}{6<br><br>\mathrm{\alpha <br><br>}}.$

10. The method of claim 1 further comprising spatially modulating the heating using a shutter.

11. The method of claim 1 further comprising spatially modulating the heating using a mask to create a pattern on the surface of the composite article.

12. The method of claim 1, wherein the heating comprises applying one or more flash-pulses.

13. The method of claim 1, wherein the heating is performed using a step-heat source.

14. The method of claim 1, wherein the porosity values are determined using the thermal diffusivity values.

15. A non-destructive evaluation system for inspecting an object, the system comprising:

a heat source configured for heating a surface of the object;

a focal plane array camera configured to capture a plurality of images corresponding to an evolution of lateral heat flow from the surface;

an image acquisition system configured for capturing data corresponding to the plurality of images from the focal plane array camera; and

a time of flight analysis system configured to perform a thermal time of flight analysis on the data, and determine diffusivity and porosity values using the thermal time of flight analysis for the lateral heat flow in the object.

16. The system of claim 15, wherein the heat source comprises a flash-pulse source.

17. The system of claim 16 further comprising a shutter configured to create a stripe of finite width on the surface of the object.

18. The system of claim 15, wherein the heat source comprises a step-heat source.

19. The system of claim 18 further comprising a mask configured to create a pattern on the surface of the object.

20. The system of claim 15, wherein the focal plane array camera is configured to capture a plurality of images from one side of the object.

21. The system of claim 15, wherein the plurality of images comprise temperature-time responses at plurality of points in the object.