What happens to the eddy current amplitude when a defect is present?

When a defect is present in a conductive material and assessed using eddy current testing, the eddy current amplitude typically decreases. This decrease occurs because the defect, such as a crack or void, disrupts the flow of the eddy currents within the material. The eddy currents are generated by an alternating magnetic field, and when the material is homogeneous and free of defects, the currents can flow freely, resulting in a stronger signal or higher amplitude.

However, when a defect is introduced, it alters the conductivity and permeability of the material in that localized area. This alteration can lead to less efficient eddy current flow, causing the amplitude to drop. Therefore, a decrease in amplitude is interpreted as an indication of a defect's presence. This principle is critical in nondestructive testing, allowing technicians to identify potential faults in materials through the analysis of eddy current signals.

Thus, recognizing that a decrease in eddy current amplitude signifies a defect is fundamental in the effective application of eddy current testing.