Acoustic emission source location by reverse ray tracing

• US 5,528,557 A
• Filed: 08/07/1995
• Issued: 06/18/1996
• Est. Priority Date: 08/07/1995
• Status: Expired due to Fees

• Current Assignee: Vought Aircraft Industries, Inc. (Triumph Group, Inc.)
• Original Assignee: Northrop Grumman Corporation
• Inventors: Horn, Michael
• Primary Examiner(s): Lobo, Ian J.
• Application Number:
  US08/512,249
• Time in Patent Office: 316 Days
• Field of Search: 367/118, 367/124, 367/127, 367/129, 367/907, 73/583, 73/587, 364/507, 364/508, 364/550
• US Class Current: 367/129
• CPC Class Codes: G01N 2291/0258 Structural degradation, e.g. fatigue of composites, ageing of oils
• CPC Class Codes: G01N 2291/0289 Internal structure, e.g. defects, grain size, texture
• 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 2291/0428 Mode conversion
• CPC Class Codes: G01N 2291/2632 flat
• CPC Class Codes: G01N 2291/2638 Complex surfaces
• 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: G01S 3/8083 determining direction of source
• CPC Class Codes: Y10S 367/907 Coordinate determination

Abstract

A method of locating an acoustic emission source in a structure by reverse ray tracing. An azimuth acoustic emission sensor is utilized which has an array of individual elemental detectors which independently and sequentially respond to the passage of an acoustic stress wave. The response of each element of the array is electronically monitored, and individual responses to the acoustic stress wave are analyzed to determine the azimuth approach angle of the wave to the azimuth acoustic emission sensor. An accurate measurement of the true location of the acoustic emission signal source is then provided by reverse ray tracing by using a parallel processing arrangement having a plurality of parallel processing elements. The structure is modeled in the computer on a one to one basis, with each parallel processing element simulating and having structural data on one discrete area of the structure. The determined azimuth approach angle is an input to the parallel processing arrangement, such that a simulated wave propagation takes place in the computer model as if it were propagating in the structure, and the actual location of the acoustic emission source is determined by reverse ray tracing by taking into account the structure of the intervening path of the wave and the most probable perturbations of the wave therein. The present invention has particular applicability to aircraft structures, and the method is utilized to locate structural defects therein.

Claims

1. A method of locating an acoustic emission source in a structure by reverse ray tracing comprising:

a. utilizing an azimuth acoustic emission sensor having an array of individual elemental detectors which independently and sequentially respond to the passage of an acoustic stress wave, electronically monitoring the response of each element of the array, and analyzing the individual responses to the acoustic stress wave to determine the azimuth approach angle of the wave to the azimuth acoustic emission sensor; and

b. providing an accurate measurement of the true location of the acoustic emission signal source by reverse ray tracing by using a parallel processing arrangement having a plurality of parallel processing elements in which the structure is modeled in a computer on a one to one basis, with each parallel processing element simulating and having structural data on one discrete area of the structure in a database, and the determined azimuth approach angle is an input to the parallel processing arrangement, such that a simulated wave propagation takes place in the computer model as if it were propagating in the structure, and the actual location of the acoustic emission source is determined by reverse ray tracing by taking into account the structure of the intervening path and the most probable perturbations of the wave therein.

2. A method of locating an acoustic emission source in a structure by reverse ray tracing as claimed in claim 1, wherein the structure is an aircraft, and the method is utilized to locate structural defects therein.

3. A method of locating an acoustic emission source in a structure by reverse ray tracing as claimed in claim 1, wherein the response of each element of the array is measured with a resolution of at least 100 nsec, with a clock which is triggered at the moment that the first of the elements output signal reaches a peak, and the clock runs until another element produces a signal peak, and the time difference between the peak signals is utilized as a measurement of the azimuth approach angle of the wave.

4. A method of locating an acoustic emission source in a structure by reverse ray tracing as claimed in claim 1, wherein the displacement magnitudes and propagation directions of received signals are measured and digitized, and the digitized signals are inputs to the parallel processing arrangement.

5. A method of locating an acoustic emission source in a structure by reverse ray tracing as claimed in claim 1, wherein the complexity and size of the structure which is modeled in the computer is based upon considerations including frequency, velocity range, the smallest physical detail, and the total size of the structure being modeled, and the considerations are matched to the total number of processors of the parallel processing arrangement and the number of processors required per wavelength.

6. A method of locating an acoustic emission source in a structure by reverse ray tracing as claimed in claim 1, wherein the detection element which is opposite to the detection element first actuated is deactuated to provide greater signal processing accuracy, and reduce wasted processing time and error in responding to the passage of two or more coincidental but separate waves.

7. A method of locating an acoustic emission source in a structure by reverse ray tracing as claimed in claim 1, including utilizing more than one azimuth acoustic sensor to determine the azimuth approach location in two or more dimensions.