Microstructure and damage of the interlaminar interface of carbon fiber polymer-matrix composites, monitored by contact electrical resistivity measurement

The microstructure and damage of the interlaminar interface of continuous carbon fiber polymer-matrix structural composites were monitored during dynamic changes in temperature, humidity and stress by contact electrical resistivity measurement. The stress was compressive, in the direction perpendicular to the interface. Temperature, humidity and stress had reversible effects on the resistivity, due to the effects on the interfacial microstructure, such as the extent of contact between fibers of adjacent laminae. These parameters had irreversible effects on the resistivity, due to relaxation and damage of the interface. The effects differed between composites with thermoplastic and thermoset matrices. The reversible effects allow the use of the contact resistivity as an indicator of temperature, humidity and stress.