Continous carbon fibre epoxy-matrix composite as a sensor of its own strain

Unidirectional continuous carbon fibre reinforced epoxy was found to be able to sense its own strain in the fibre direction, due to its longitudinal electrical resistance decreasing reversibly and its transverse resistance increasing reversibly upon longitudinal tension. The strain sensitivity (gauge factor) is from -35.7 to -37.6 and from +34.2 to +48.7 for the longitudinal and transverse resistances respectively. Both effects originate from resistivity changes associated with the increase in the degree of fibre alignment upon longitudinal tension, Either effect allows strain sensing, Slight irreversibility is associated with the resistance decreasing after the first strain cycle and stems from the decrease in the degree of neatness of the fibre arrangement.