In-Situ Monitoring of Creep Using Directional Electric Potential Drop Measurements

A directional low-frequency alternating current potential drop (ACPD) sensor was developed for in-situ monitoring of creep in metals. The sensor relies on a modified ACPD technique that measures two resistances in orthogonal directions using a square-electrode configuration. As compared to the more commonly used in-line electrode configuration, the square arrangement used in this sensor is highly directional and thus allows the detection of creep-induced plastic strain and resistivity anisotropy. The technique monitors the variation of the ratio between the measured axial and lateral resistances, therefore can efficiently separate the mostly isotropic common part of the resistivity variation caused by reversible temperature variations from the mostly anisotropic differential part caused by direct geometrical and indirect material effects of creep. Initially, this resistance ratio is mainly sensitive to creep strain, while at later stages the formation of directional discontinuities such as preferentially oriented grain boundary cavities and microcracks become also detectable in the material.

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