Magnetic field characterization of stresses and properties in materials

Abstract

Described are methods for monitoring of stresses and other material properties. These methods use measurements of effective electrical properties, such as magnetic permeability and electrical conductivity, to infer the state of the test material, such as the stress, temperature, or overload condition. The sensors, which can be single element sensors or sensor arrays, can be used to periodically inspect selected locations, mounted to the test material, or scanned over the test material to generate two-dimensional images of the material properties. Magnetic field or eddy current based inductive and giant magnetoresistive sensors may be used on magnetizable and/or conducting materials, while capacitive sensors can be used for dielectric materials. Methods are also described for the use of state-sensitive layers to determine the state of materials of interest. These methods allow the weight of articles, such as aircraft, to be determined.

1 . A method for determining weight of an article, said method comprising: 
 disposing a sensor array comprising at least one linear drive conductor with a plurality of sense elements proximate to a surface of a magnetizable test material, the magnetizable material transferring a load from the article;    passing a time-varying electric current through the drive conductor to create a magnetic field;    measuring the response from each sense element to determine magnetic permeability; and, using a correlation between this magnetic permeability and article weight to determine the article weight.    
   
   
       2 . The method as claimed in  claim 1  wherein the article is an aircraft.  
   
   
       3 . The method as claimed in  claim 1  wherein the properties are monitored at selected locations on the article.  
   
   
       4 . The method as claimed in  claim 1  wherein the sensor is scanned over the surface of the article.  
   
   
       5 . The method as claimed in  claim 1  wherein the sensor is mounted to the surface of the article.  
   
   
       6 . The method as claimed in  claim 1  wherein the sensor is oriented to measure the response parallel to the maximum principal stresses.  
   
   
       7 . The method as claimed in  claim 2  wherein the correlation to weight is determined by performing measurements as the aircraft is loaded.  
   
   
       8 . The method as claimed in  claim 1  wherein the magnetizable test material is a landing gear component.  
   
   
       9 . A weight monitor for determining the weight of an article, the weight monitor comprising: 
 a sensor array, the sensor array comprising at least one drive conductor with a plurality of sense elements, a time-varying current being passed through the drive conductor to create a magnetic field;    a magnetizable test material, the plurality of sense elements being proximate to a surface of the magnetizable test material, and the magnetizable test material transferring a load from the article; and    correlation electronics using a measured response from each sense element to determine a magnetic permeability and correlate the magnetic permeability to determine the article weight.    
   
   
       10 . The weight monitor of  claim 9  wherein the article is an aircraft.  
   
   
       11 . The weight monitor of  claim 10  wherein the correlation to weight is determined by performing measurements as the aircraft is loaded.  
   
   
       12 . The weight monitor of  claim 9  wherein the magnetizable test material is a loading gear component.  
   
   
       13 . The weight monitor of  claim 9  wherein the sensor is oriented to measure the response parallel to maximum principal stresses.  
   
   
       14 . A weight monitor for determining the weight of an article, the weight monitor comprising: 
 a magnetizable receiving means for receiving a load from an article, the load changing a magnetic permeability of the magnetizable receiving means;    a sensing means for sensing the magnetic permeability of the magnetizable receiving means; and    a correlation means for correlating the magnetic permeability to the weight of the article.