Material gauge factor of directional electric potential drop sensors for creep monitoring

Directional electric potential drop measurements can be exploited for in-situ monitoring of creep in metals. The sensor monitors the variation in the ratio of the resistances measured simultaneously in the axial and lateral directions using a square-electrode configuration. This method can efficient...

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Bibliographic Details
Main Authors: Madhi, E., Nagy, P. B.
Format: Conference Proceeding
Language:English
Subjects:
ANISOTROPY
CAVITIES
CHEMISTRY
CRACKS
CREEP
ELECTRIC CONDUCTIVITY
ELECTRIC POTENTIAL
ELECTRICAL PROPERTIES
ELECTROCHEMISTRY
ELECTRODES
ELEMENTS
FAILURES
GRAIN BOUNDARIES
MATERIALS
MATERIALS SCIENCE
MEASURING INSTRUMENTS
MECHANICAL PROPERTIES
METALS
MICROSTRUCTURE
MONITORING
ORGANIC COMPOUNDS
ORGANIC POLYMERS
PETROCHEMICALS
PETROLEUM PRODUCTS
PHYSICAL PROPERTIES
PLASTICS
POLYMERS
RUPTURES
SENSITIVITY
SENSORS
STRAIN GAGES
STRAINS
STRESSES
SYNTHETIC MATERIALS
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Summary:Directional electric potential drop measurements can be exploited for in-situ monitoring of creep in metals. The sensor monitors the variation in the ratio of the resistances measured simultaneously in the axial and lateral directions using a square-electrode configuration. This method 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 (size and shape) and indirect material (resistivity) effects of creep. Similarly to ordinary strain gauges, the relative sensitivity of the sensor is defined as a gauge factor that can be approximated as the sum of geometrical and material parts. Initially, subtle material changes produce weak electric anisotropy via reversible and irreversible piezoresistivity due to elastic and plastic strains, respectively. At high temperature, much stronger irreversible resistivity changes also occur due to preferentially aligned clusters of cavities developing along grain boundaries approximately perpendicular to the applied stress and subsequent cracks forming between these cavities. The ensuing electric anisotropy is detected by the directional sensor. Although the material effects remain smaller than the geometrical ones up to the initiation of preferentially oriented cracks, later the material gauge factor sharply increases and close to rupture can reach a value of more than 10.
ISSN:0094-243X
1551-7616
DOI:10.1063/1.3592075