 NDTnetWCNDT '96 - New Delhi Table of Contents |  |
  | Full Paper Not Received |  |
| NDTnet WCNDT '96 - New Delhi Table of Contents | |
| | Full Paper Not Received | |
The electromagnetic field induced by a suspended exciter coil over a flawed conducting magnetic half-space is studied. The fundamental information about the system being examined can be obtained by studying the regularities of the distribution of EC density vector in the vicinity of a crack as one of the primary sources of the field of defect, and by studying the topographical features of the magnetic field distribution in the region examined.
For most practical problems a geometry of the region is too complicated for analytical solution and the numerical method must be used. The numerical analysis technique such as a finite element method has been successfully developed for modelling EC NDT phenomena [1]. We have used the three-dimensional finite element formulation in terms of the magnetic vector potential.
The analysis of the numerical results allows us to separate the two responsible mechanisms of electromagnetic field formation in the vicinity of a crack. The first one relates to the specific behaviour of the distribution of EC in the region and resembles the field induced by the two current-carrying wires. The second one relates to the distortion of the primary magnetic flux in the vicinity of a crack. The results obtained and those which have been presented in the early analytical model [2] are compared.
The theory which explains the nature of the mechanisms and relationship between them is discussed. A summary of the governing equations, assumptions and a qualitative description of the mechanisms are presented. The efficiencies of the mechanisms in the formation of the field of the defect are compared with taking into account the dimensions of the exciter coil, crack sizes, frequencies of excitation and macroscopic media properties. REFERENCES
| | Full Paper Not Received | |