Development of magnetic stress detection methods involving a cobalt ferrite composite stress sensing material and a magnetic imaging system

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Paulsen, Jason
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Mechanical Engineering
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The principle of using magnetics to evaluate stress levels has not been as widely investigated as other techniques until recently; however, it can be a very useful method. The magnetic properties of a magnetic material can be greatly affected by the presence of a stress through the magnetoelastic coupling. Because of this, the stress state of a material can be determined by simply measuring some of the magnetic properties of the material. A few methods for doing this have been previously investigated and partially employed. One of these methods involves utilizing the magnetomechanical effect. That is the change in magnetization with stress. The other method is by analysis of the stress dependence of the magnetic hysteresis loop and Barkhausen emission noise. In this work, a magnetic imaging system has been developed to non-destructively measure variations in material conditions or stress concentrations in magnetic materials. This system is capable of producing an image of the special variation of the magnetic properties in materials by measuring the magnetic hysteresis loop and Barkhausen effect noise. Images produced by this system are compared with FEM images which show the system is able to detect defects and stress gradients. This work also involves progress in the development of a new magnetomechanical stress sensing material based off of a metal bonded cobalt ferrite composite. An improvement upon this cobalt ferrite composite has been made by lowering the Curie temperature by substituting other materials into the cobalt ferrite. This will decrease the magnetomechanical hysteresis present at room temperature. A new manganese doped cobalt ferrite material that was recently developed exhibits a lower Curie temperature then the pure cobalt ferrite. Results on this material along with some other materials developed are discussed.

Thu Jan 01 00:00:00 UTC 2004