Study On The Failure Behavior Of CFRP Unidirectional Pultruded Composites By Electrical Resistance Method

The damage behaviors of CFRP unidirectional pultruded composites were monitored by an electrical resistance method. The project is a basic research on structure health monitoring of CFRP composite.An electrical resistance method was set up to monitor the failure behaviors of CFRP unidirectional pultruded composites. The sensitivity of the method was studied. The results showed that the lower the contact electrical resistance of introduced electrodes and a loading speed were, the more sensitive the electrical resistance method was. The failure behaviors of the pultruded carbon fiber/ vinyl ester composites and carbon fiber tows were monitored by the electrical resistance measurement during tensile loading. Infrared thermograph was performed in real time during tensile test of composites to non-destructive evaluate the change of microstructure in the materials. Experiment results demonstrated that composite and the carbon fiber tows were damaged by different mechanisms. The damage mechanism for composites is mainly attributable to the debonding between matrix and fibers, while that for the carbon fiber tows being in the form of fiber fracture. The correlation between the infrared thermographs and the variation in the electrical resistance could be considered as an evidence of the damage mechanisms of composites.The variation in the longitudinal electrical resistance and transverse electrical resistance of carbon fiber/ vinyl ester composites during three-point bending and interlaminar shear loadings were investigated in detail. It has been shown that during three-point–bending loading, the main damage form was the simultaneous fracture of matrix and fibers, while during the interlaminar shear loading, the variation in the electrical resistance was related to the damage degree of interface structure between the resin and carbon fibers. The electrical resistance measurement was more sensitive to the damage behaviors of the CFRP composites than the stress/time curve. In addition, the variation in the electrical resistance of a pultruded carbon fiber/epoxy composite was compared with that of the pultruded carbon fiber/ vinyl ester composites during tensile loading. Experiment results demonstrated that the variation in the electrical resistance of the pultruded carbon fiber/epoxy composite was resulted from the fracture of carbon fibers, while that of the carbon fiber/ vinyl ester composites from the debonding between the vinyl ester resin and carbon fibers, indicating that the two kinds of composites exhibit different damage mechanisms.