Strain sensors based on the electrical resistance change accompanying the reversible pull-out of conducting short fibers in a less conducting matrix

A new class of strain sensors has been discovered. These sensors are short-fiber composites. Their sensing ability is based on the electrical resistance change accompanying the reversible pull-out of conducting short fibers in a less conducting matrix. The fiber pull-out is associated with crack opening; the fiber push-in is associated with crack closing. The fiber pull-out, though slight, causes an increase in the fiber-matrix contact resistivity, thereby increasing the overall resistance of the composite. An example of these sensors is carbon fiber reinforced concrete.