ABSTRACT
This chapter looks at the use of electrical methods for evaluation of materials, particularly the use of eddy currents. Eddy current inspection depends on inducing time-dependent currents in materials, the strength of which depend on permeability and conductivity of a material. Thus, eddy current methods can be used to determine changes in microstructure of a material and any materials properties that are related to microstructure. Therefore, variations in heat treatment, mechanical hardness, impurities or other differences in chemical content, and corrosion damage can all be detected by eddy current inspection. Flaws in a material also interrupt the flow of eddy currents, and so eddy current inspection is also sensitive to these features. Macroscopic cracks in materials can be detected through their effects on eddy currents However, microscopic damage — such as the accumulation of dislocations under fatigue damage — that has effects similar to microstructural changes rather than macroscopic cracks, also affects the eddy current signals.
