What type of material can NOT be inspected using eddy current testing?

Answer: C — Non-metallic materials

Eddy current testing is a non-destructive testing method primarily utilized for conductive materials, particularly metals. This technique works by inducing an electrical current in the material being tested, which then generates secondary currents (eddy currents) that can be measured to detect flaws, measure conductivity, and assess overall material properties. Non-metallic materials, such as plastics, composites, and ceramics, do not conduct electricity and lack the necessary properties to be evaluated through eddy current testing. As a result, they do not generate eddy currents, rendering this testing method ineffective for inspecting them. On the other hand, ferrous metals, painted surfaces (as long as the paint does not significantly insulate the surface), and coated metals can all be effectively inspected using eddy current testing, as they possess conductive properties that allow for the generation and detection of eddy currents.