Flexible graphite as a strain/stress sensor

Flexible graphite sandwiched by copper, after stabilization by two cycles of compressive stress, is an effective piezoresistive compressive strain/stress sensor for stresses up to 4 MPa and strains up to 25%. The stress sensitivity (fractional change in resistance per unit stress) is up to 5.4 MPa^-1 and strain sensitivity (fractional change in resistance per unit strain) is up to 6.2 in the direction perpendicular to the sheet. The electrical resistance decreases reversibly upon compression, due mainly to reversible decrease in the contact resistivity between graphite and copper. Stabilization removes most of the irreversible effects. The strain/stress sensitivities decrease with increasing strain/stress.