Quality control plasma monitor for laser shock processing

• US 20010045416A1
• Filed: 06/29/2001
• Published: 11/29/2001
• Est. Priority Date: 02/19/1999
• Status: Active Grant

• Current Assignee: LSP Technologies Incorporated
• Original Assignee: LSP Technologies Incorporated
• Inventors: Epstein, Harold M., Clauer, Allan H., Sokol, David W., Walters, Craig T., Dulaney, Jeffrey L., OʼLoughlin, Mark
• Granted Patent: US 6,554,921 B2
• Time in Patent Office: Days
• US Class Current: 219/121.62
• CPC Class Codes: C21D 10/005 by laser shock processing
• CPC Class Codes: G01N 2291/0237 Thin materials, e.g. paper, membranes, thin films
• CPC Class Codes: G01N 2291/0251 Solidification, icing, curing composites, polymerisation
• CPC Class Codes: G01N 2291/0426 Bulk waves, e.g. quartz crystal microbalance, torsional waves
• CPC Class Codes: G01N 23/20 by using diffraction of the radiation by the materials, e.g. for investigating crystal structure; by using scattering of the radiation by the materials, e.g. for investigating non-crystalline materials; by using reflection of the radiation by the materials
• CPC Class Codes: G01N 29/14 using acoustic emission techniques echo of particles G01N29/046; measuring mechanical vibrations or acoustic waves in solids in general G01H1/00
• CPC Class Codes: G01N 29/2418 using optoacoustic interaction with the material, e.g. laser radiation, photoacoustics photoacoustic cells G01N21/1702; measuring characteristics of vibrations by using radiation-sensitive means G01H9/00; acousto-optical conversion techniques for short-range imaging G01S15/8965; sound-producing devices using laser bundle G10K15/046

Abstract

A method and apparatus for quality control of laser shock processing. The method includes measuring emissions and characteristics of a workpiece when subjected to a pulse of coherent energy from a laser. These empirically measured emissions and characteristics of the workpiece are correlated to theoretical shock pressure, residual stress profile, or fatigue life of the workpiece. The apparatus may include a radiometer or acoustic detection device for measuring these characteristics.

Claims

1. An apparatus for monitoring laser shock processing of a workpiece, comprising:

a material applicator for applying an energy absorbing material onto the workpiece;

a transparent overlay applicator for applying a transparent overlay onto the workpiece over said energy absorbing layer;

a laser operatively associated with said energy absorbing layer; and

at least one radiometer.

2. The apparatus of

claim 1

further comprising a second radiometer, said radiometers detecting energy at different wavelengths.

3. The apparatus of

claim 1

wherein said energy absorbing material contains a dopant.

4. The apparatus of

claim 3

wherein the presence of said dopant results in a detectable optical signal when said dopant is subjected to pressure.

5. The apparatus of

claim 3

wherein the presence of said dopant results in a detectable optical signal when said dopant is heated.

6. The apparatus of

claim 1

wherein said energy absorbing material fluoresces when said energy absorbing material is subjected to heat.

7. The apparatus of

claim 1

wherein said energy absorbing material fluoresces when said energy absorbing material is subjected to pressure.

8. The apparatus of

claim 1

wherein said energy absorbing material emits optical energy detectable by said radiometer.

9. The apparatus of

claim 3

wherein said dopant consists of micro-spheres filled with a marker.

40. The apparatus of

claim 6

, further comprising:

a laser pulse of coherent energy; and

said laser pulse produces said heat.

10. A method for real time laser shock processing of a workpiece comprising the steps of:

applying an opaque overlay to the workpiece;

directing a beam of coherent energy to the workpiece to vaporize a portion of the opaque overlay and create a plasma which emits energy therefrom; and

monitoring a portion of the energy emitted from the plasma.

11. The method for real time monitoring laser shock processing of a workpiece according to

claim 10

wherein the step of monitoring a portion of the energy emitted from the plasma further comprises the steps of:

detecting spectral emissions from said emitted energy.

12. The method for real time monitoring laser shock processing of a workpiece according to

claim 10

wherein the step of monitoring a portion of the energy emitted from the plasma further comprises the steps of:

detecting acoustic emissions from said emitted energy.

16. The method of

claim 11

, wherein said step of detecting spectral emissions further comprises the step of:

correlating a feature of said spectral emissions to the shock pressure applied to the workpiece.

17. The method of

claim 12

, wherein said step of detecting acoustic emissions further comprises the step of:

correlating a feature of said acoustic emissions to the shock pressure applied to the workpiece.

20. The method of

claim 11

, further comprises the step of

correlating a feature of said detected spectral emissions to a residual stress profile produced in the workpiece.

21. The method of

claim 12

, wherein said step of detecting acoustic emissions further comprises the step of:

correlating a feature of said acoustic emissions to a residual stress profile produced in the workpiece.

24. The method of

claim 11

, wherein said step of detecting spectral emissions further comprises the step of:

correlating a feature of said spectral emissions to the fatigue life of the workpiece.

25. The method of

claim 12

, wherein said step of detecting acoustic emissions further comprises the step of:

correlating a feature of said acoustic emissions to the fatigue life of the workpiece.

28. The method of

claim 11

, wherein said step of detecting spectral emissions further comprises the step of:

correlating a feature of said spectral emissions to the presence of a transparent overlay on the workpiece.

29. The method of

claim 12

, wherein said step of detecting acoustic emissions further comprises the step of:

correlating a feature of said acoustic emissions to the presence of a transparent overlay on the workpiece.

30. The method of

claim 11

, wherein said step of detecting spectral emissions further comprises the step of:

correlating a feature of said spectral emissions to the presence of an opaque overlay on the workpiece.

31. The method of

claim 12

, wherein said step of detecting acoustic emissions further comprises the step of:

correlating a feature of said acoustic emissions to an opaque overlay on the workpiece.

13. A method for real-time monitoring the laser shock peening of a workpiece comprising the steps of:

applying a transparent overlay to the workpiece;

directing a beam of coherent energy to a workpiece through said transparent overlay and create a plasma which emits energy therefrom; and

monitoring a portion of the energy emitted from said plasma.

14. The method of

claim 13

, wherein said step of monitoring a portion of energy further comprises the step of:

detecting spectral emissions from said plasma emitted energy.

15. The method of

claim 13

, wherein said step of monitoring the plasma further comprises the step of:

detecting acoustic emissions from said emitted energy.

18. The method of

claim 14

, wherein said step of detecting spectral emissions further comprises the step of:

correlating a feature of said spectral emissions to the shock pressure applied to the workpiece.

19. The method of

claim 15

, wherein said step of detecting the acoustic emissions further comprises the step of:

correlating a feature of said acoustic emissions to the shock pressure applied to the workpiece.

22. The method of

claim 14

, wherein said step of detecting spectral emissions further comprises the step of:

correlating a feature of said spectral emissions to a residual stress profile produced in the workpiece.

23. The method of

claim 15

, wherein said step of detecting acoustic emissions further comprises the step of:

correlating a feature of said acoustic emissions to a residual stress profile produced in the workpiece.

26. The method of

claim 14

, wherein said step of detecting the spectral emissions further comprises the step of:

correlating a feature of said spectral emissions to the fatigue life of the workpiece.

27. The method of

claim 15

, wherein said step of detecting acoustic emissions further comprises the step of:

correlating a feature of said acoustic emissions to the fatigue life of the workpiece.

41. The method of

claim 14

, wherein said step of detecting spectral emissions further comprises the step of:

correlating a feature of said spectral emissions to the presence of a transparent overlay on the workpiece.

42. The method of

claim 15

, wherein said step of detecting acoustic emissions further comprises the step of:

correlating a feature of said acoustic emissions to the presence of a transparent overlay on the workpiece.

43. The method of

claim 14

, wherein said step of detecting spectral emissions further comprises the step of:

correlating a feature of said spectral emissions to the presence of an opaque overlay on the workpiece.

44. The method of

claim 15

, wherein said step of detecting acoustic emissions further comprises the step of:

correlating a feature of said acoustic emissions to an opaque overlay on the workpiece.

32. A method for real-time monitoring the laser shock peening of a workpiece comprising the steps of:

applying an opaque overlay to a workpiece;

directing a beam of coherent energy to a workpiece to vaporize a portion of said opaque overlay and create a plasma thereon; and

monitoring the temperature of said plasma.

33. The method of

claim 32

, further comprises the step of creating a shock pressure on the workpiece:

and correlating the plasma temperature to the shock pressure on the workpiece.

34. The method of

claim 32

, further comprising the steps of creating a residual stress profile in the workpiece;

and

correlating the plasma temperature to the residual stress profile provided in the workpiece.

35. The method of

claim 32

, wherein said step of monitoring the plasma temperature further comprises the step of:

correlating the plasma temperature to the fatigue life of the workpiece.

36. A method for real-time monitoring the laser shock processing of a workpiece comprising the steps of;

applying a transparent overlay to a workpiece;

directing a beam of coherent energy to a workpiece through said transparent overlay and create a plasma thereon; and

monitoring the temperature of said plasma.

37. The method of

claim 36

, wherein said step of monitoring the plasma temperature further comprises the step of:

correlating the plasma temperature to the shock pressure on the workpiece.

38. The method of

claim 36

, wherein said step of monitoring the plasma temperature further comprises the step of:

correlating the plasma temperature to the residual stress profile provided in the workpiece.

39. The method of

claim 36

, wherein said step of monitoring the plasma temperature further comprises the step of:

correlating the plasma temperature to the fatigue of life of the workpiece.