Laser-air, hybrid, ultrasonic testing of railroad tracks

• US 20040003662A1
• Filed: 05/30/2003
• Published: 01/08/2004
• Est. Priority Date: 11/25/2002
• Status: Active Grant

• Current Assignee: Materials And Sensors Technologies, Inc.
• Original Assignee: Johns Hopkins University
• Inventors: Djordjevic, B. Boro, Kenderian, Shant, Cerniglia, Donatella, Green, Robert E. Jr.
• Granted Patent: US 6,945,114 B2
• Time in Patent Office: Days
• US Class Current: 73/579
• CPC Class Codes: G01N 2291/014 Resonance or resonant frequency
• CPC Class Codes: G01N 2291/02854 Length, thickness
• CPC Class Codes: G01N 2291/0421 Longitudinal waves
• CPC Class Codes: G01N 2291/0422 Shear waves, transverse waves, horizontally polarised waves
• CPC Class Codes: G01N 2291/0423 Surface waves, e.g. Rayleigh waves, Love waves
• CPC Class Codes: G01N 2291/044 Internal reflections (echoes), e.g. on walls or defects
• CPC Class Codes: G01N 2291/106 one or more transducer arrays
• CPC Class Codes: G01N 2291/2623 Rails; Railroads
• CPC Class Codes: G01N 29/12 by measuring frequency or resonance of acoustic waves measuring frequency or resonant frequency of mechanical vibrations or acoustic waves in general G01H1/06, G01H3/04, G01H13/00; acoustic resonators G10K11/04; vibration or shock testing of structures G01M7/00
• 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
• CPC Class Codes: G01N 29/46 by spectral analysis, e.g. Fourier analysis or wavelet analysis spectral signal processing per se G06F17/14

Abstract

Formed Laser Sources (FLS) using pulsed laser light for generation of ultrasonic stress waves are combined with air-coupled detection of ultrasound to provide for the hybrid non-contact, dynamic and remote ultrasonic testing of structural materials, especially railroad tracks. Using this hybrid technique, multimode and controlled frequency and wavefront surface acoustic waves, plate waves, guided waves, and bulk waves are generated to propagate on and within the rail tracks. The non-contact, remote nature of this methodology enables high-speed, full access inspections of rail tracks. The flexibility and remote nature of this methodology makes possible the detection of critical cracks that are not easy, or impossible to detect, with current inspection techniques available to the railroad industry. For purpose of field testing, the equipment of the present invention can be located above the top surface of the rail. Cracks of unfavorable positions and orientations at hard to reach geometrical locations can be detected with this Laser-Air Hybrid Ultrasonic approach. By analog amplification, gating, digital signal capture, signal processing and digital data analysis and processing, such rail testing can be performed totally automated.

Claims

1. A remote, non-contact system for detecting a defect in a structural material that is surrounded by a gaseous or vacuum environment, said system comprising:

a remote means, located at a first specified location in said environment and spaced from said structural material, for generating, in a non-contact manner in said structural material, modes of ultrasonic stress waves having a specified, controlled wavefront and frequencies,

a non-contact means, located at a second specified location in said environment and spaced from said structural material, for sensing from said structural material an acoustic signal in said environment that distinguishes the propagation of said modes of ultrasonic stress waves in said structural material, and

a means, responsive to said sensed acoustic signal, for distinguishing in said sensed signal the differences between said modes of said ultrasonic stress waves so as to detect said defect in said structural material.

2. A defect detection system as recited in claim 1, wherein said controlled wavefront is chosen so as to yield said stress waves having frequencies that match the frequency sensing capabilities of said non-contact, sensing means.

3. A defect detection system as recited in claim 1, wherein said controlled frequency is chosen so as to yield said stress waves having frequencies that match the frequency sensing capabilities of said non-contact, sensing means.

4. A defect detection system as recited in claim 2, wherein said controlled frequency is chosen so as to yield said stress waves having frequencies that match the frequency sensing capabilities of said non-contact, sensing means.

5. A defect detection system as recited in claim 1, wherein said defect is of a specified type and said controlled wavefront and frequencies are chosen so as to enhance the sensitivity of said non-contact, sensing means to said specified type of defect.

6. A remote, non-contact method for detecting a defect in a structural material that is surrounded by a gaseous or vacuum environment, said method comprising the steps of:

generating, in a non-contact manner in said structural material, modes of ultrasonic stress waves having a specified, controlled wavefront and frequencies,

sensing from said structural material an acoustic signal in said environment that distinguishes the propagation of said modes of ultrasonic stress waves in said structural material, and

distinguishing in said sensed signal the differences between said modes of said sensed ultrasonic stress waves so as to detect said defect.

7. A defect detection method as recited in claim 6, wherein said controlled wavefront is chosen so as to yield said stress waves having frequencies that match the frequency sensing capabilities encountered in said sensing step.

8. A defect detection method as recited in claim 6, wherein said controlled frequency is chosen so as to yield said stress waves having frequencies that match the frequency sensing capabilities encountered in said sensing step.

9. A defect detection method as recited in claim 7, wherein said controlled frequency is chosen so as to yield said stress waves having frequencies that match the frequency sensing capabilities encountered in said sensing step.

10. A defect detection method as recited in claim 6, wherein said defect is of a specified type and said controlled wavefront and frequencies are chosen so as to enhance the signal sensitivity encountered in said sensing step to said specified type of defect.

11. A remote, non-contact system for detecting a defect in a structural material that is surrounded by a gaseous or vacuum environment, said system comprising:

a pulsed, laser light source, located at a first specified location in said environment and spaced from said structural material, for generating in said structural material, modes of ultrasonic stress waves,

a lens in the path of the light from said light source for focusing said light into a specified illumination pattern to generate a controlled ultrasonic wavefront,

an air-coupled transducer, located at a second specified location in said environment and spaced from said structural material, for sensing from said structural material an acoustic signal in said environment that distinguishes the propagation of said modes of ultrasonic stress waves in said structural material, and

a signal processor, responsive to said sensed acoustic signal, for distinguishing in said sensed signal the differences between said modes of said ultrasonic stress waves so as to detect said defect.

12. A defect detection system as recited in claim 11, wherein said controlled wavefront is chosen so as to yield said stress waves having frequencies that match the frequency sensing capabilities of said transducer.

13. A defect detection system as recited in claim 11, wherein said pulsed laser is modulated so as to yield said stress waves having frequencies that match the frequency sensing capabilities of said transducer.

14. A defect detection system as recited in claim 12, wherein said pulsed laser is modulated so as to yield said stress waves having frequencies that match the frequency sensing capabilities of said transducer.

15. A defect detection system as recited in claim 11, wherein said defect is of a specified type and said controlled wavefront is chosen so as to enhance the sensitivity of said transducer to said specified type of defect.

16. A defect detection system as recited in claim 11, wherein said structural material is a railroad track and said defect is an internal defect in a rail head, said controlled wavefront is a circular area source.

17. A defect detection system as recited in claim 11, wherein said structural material is a railroad track and said defect is a surface defect in a rail base, said controlled wavefront is a rectangular area source.