Nondestructive evaluation of non-ferromagnetic materials using magnetostrictively induced acoustic/ultrasonic waves and magnetostrictively detected acoustic emissions

• US 5,457,994 A
• Filed: 03/16/1993
• Issued: 10/17/1995
• Est. Priority Date: 11/06/1992
• Status: Expired due to Term

• Current Assignee: Southwest Research Institute
• Original Assignee: Southwest Research Institute
• Inventors: Kwun, Hegeon, Teller, Cecil M. II
• Primary Examiner(s): Williams, Hezron E.
• Assistant Examiner(s): Finley, Rose M.
• Application Number:
  US08/033,256
• Time in Patent Office: 945 Days
• Field of Search: 73/587, 73/594, 73/643
• US Class Current: 73/587
• CPC Class Codes: G01N 2291/0258 Structural degradation, e.g. fatigue of composites, ageing of oils
• CPC Class Codes: G01N 2291/0422 Shear waves, transverse waves, horizontally polarised waves
• CPC Class Codes: G01N 2291/048 Transmission, i.e. analysed material between transmitter and receiver
• CPC Class Codes: G01N 2291/101 one transducer
• CPC Class Codes: G01N 2291/102 one emitter, one receiver
• CPC Class Codes: G01N 2291/2626 Wires, bars, rods
• 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 29/2412 using the magnetostrictive properties of the material to be examined, e.g. electromagnetic acoustic transducers [EMAT]; investigating the presence of flaws using eddy currents G01N27/90, magnetostrictive transducers B06B1/08, measuring magnetostrictive properties G01R33/18

Abstract

A method and apparatus for the nondestructive evaluation of ferromagnetic and non-ferromagnetic materials, particularly wire ropes, cables, and strands, and pipes utilizing the magnetostrictive effect for measuring minute variations in magnetic fields and characterizing these minute variations as indicative of the acoustic/ultrasonic behavior of fractures, cracks, and other anomalies within a substance under evaluation. The apparatus and method contemplate both an active testing application, wherein a transmitting sensor generates an acoustic/ultrasonic pulse within a material through the magnetostrictive effect and a second receiving sensor detects reflected acoustic/ultrasonic waves within the material, again by the inverse magnetostrictive effect. The advantages of utilizing magnetostrictive sensors as opposed to well known piezoelectric sensors lies in the ability to generate and detect acoustic/ultrasonic waves without a direct physical or acoustical contact to the material. The apparatus and method of the present invention also anticipates the use of a passive monitoring system comprised only of a receiving magnetostrictive sensor that continuously monitors a ferromagnetic or non-ferromagnetic substance for acoustic emissions and either records this monitored information or alerts the appropriate personnel of the existence of an acoustic emission indicating deterioration within the structure.

Claims

1. A method for the non-destructive monitoring of a non-ferromagnetic material for the growth of fractures, cracks, dynamic strains, and delamination, as well as impact damage and other anomalies comprising the steps of:

dispersing a magnetic material throughout a volume of said non-ferromagnetic material subject to said non-destructive monitoring;

detecting changes in a magnetic field about said magnetic material as a result of a passage of acoustic waves within said magnetic material and said non-ferromagnetic material, said changes in said magnetic field caused by an inverse magnetostrictive effect resulting from said passage of said acoustic waves, said acoustic waves being generated by said fractures, cracks, dynamic strains, delaminations, and other anomalies in said non-ferromagnetic material;

analyzing said detected changes in said magnetic field indicative of said acoustic waves, and correlating said detected changes with patterns of changes known to be indicative of said growth of said fractures, cracks, dynamic strains, delaminations, and other anomalies in said non-ferromagnetic material.

2. The method of claim 1 further comprising the step of:

establishing a DC bias magnetic field in a localized area of said non-ferromagnetic material prior to detecting changes in said magnetic field.

3. The method of claim 1, wherein said step of detecting changes in said magnetic field comprises placing an electromagnetic coil proximate to said localized area of said non-ferromagnetic material containing said magnetic material, and detecting variations in a voltage induced in said electromagnetic coil.

5. The method of claim 1, wherein said magnetic material comprises a network of wires dispersed through said non-ferromagnetic material with a density and with a structure sufficient to provide resolution of said growth of said fractures, cracks, delaminations, dynamic strains, and other anomalies.

4. An apparatus for the non-destructive monitoring of non-ferromagnetic material comprising a disperse in network of magnetic material within said non-ferromagnetic material;

receiving coil positioned adjacent to or encompassing a localized area of said non-ferromagnetic material proximate to said network of magnetic material;

bias magnet adjacent said receiving coil, said bias magnet creating a DC magnetic field within and around said localized area of said non-ferromagnetic material;

signal conditioner for amplifying and filtering a voltage from said receiving coil, said amplified and filtered voltage being a signal indicative of fluxuations in said magnetic field; and

recording means for storing said signal and for subsequently allowing a test operator to interpret said signal and thereby interpret said fluxuations in said DC magnetic field;

wherein said fluxuations in said DC magnetic field results from a magnetostrictive effect caused by acoustic waves within said non-ferromagnetic material, said acoustic waves being generated from said fractures, cracks, and other anomalies within said non-ferromagnetic material.