Instrumentation and method for monitoring change in electric potential to detect crack growth

A method for monitoring crack growth in a specimen having a first specimen surface, the first specimen surface including a starter crack of predetermined size formed therein, the starter crack having opposite sides, the method comprising the steps of:

• applying a layer of insulating material on a portion of the first specimen surface on each of opposite sides of the starter crack;
• applying a layer of conductive material over each layer of insulating material, a portion of each layer of conductive material in electrical contact with the first specimen surface in at least one location;
• providing a pair of sensing leads, each sensing lead having opposed ends;
• attaching an end of each sensing lead to each layer of conductive material and attaching an opposed end of each sensing lead to a means for measuring electric potential, the sensing leads configured to measure a change in electric potential across the starter crack;
• providing at least two current leads, each current lead having opposed ends;
• attaching an end of the least two current leads to the specimen, the opposed end of each lead connected to a current source;
• passing an electric current through the current leads;
• and
• measuring a change in electric potential across the starter crack to monitor changes in the electric potential indicative of growth in the starter crack.

Instrumentation for monitoring crack growth comprising:

• a specimen of a material to be analyzed for crack growth propagation, the specimen having a first specimen surface with a starter crack formed therein, the starter crack having a width of less than or equal to 8 mils and a depth of less than or equal to 4 mils;
• a plurality of current leads attached to the specimen, the current leads configured to pass electric current through the specimen;
• a layer of insulating material disposed on each of opposite sides of the starter crack on the first specimen surface;
• a layer of conductive material disposed on each layer of insulating material, wherein a portion of each layer of conductive material is in electrical contact with the first specimen surface at a distance of less than or equal to 17 mils from the starter crack;
• and
• a pair of sensing leads, one sensing lead attached to each layer of conductive material at a location that overlies the layer of insulating material.