Cyclic Loading Effect on Electrical Resistance Change of CFRP Laminates

摘要

The Electrical Resistance Change Method (ERCM) is useful as the damage detection for CFRP (Carbon Fiber Reinforced Plastic) structures, using the characteristic of high electrical conductivity of carbon fiber. Fatigue damages of CFRP should be detected because these damages lead to decreasing the strength and the reliability of CFRP structures. By detecting fatigue damages, the fatigue life of structures can be estimated and the reliability of CFRP structures are expected to improve. Some researchers have been investigated to detect fatigue damages using the ERCM so far. However, the effect of the damage of electrodes has not been clarified in the existing research. The damage of electrodes may have effects on the performance of damage detection.In this study, firstly, the effect of the damage of electrodes was investigated experimentally by cyclic loading tests for CFRP laminates using the ERCM. As a result, the electrical resistance of CFRP laminates with stacking sequence of [0/±45/90]s decreased with the increase of number of cycles from the beginning of the cyclic test. The contact resistance at the electrode was calculated and began to increase when the number of cycles became over 10 . This result indicates that the electrodes were damaged by the cyclic loading and the contact resistance was changed by its damage. However, the damage of electrodes did not have an effect on the resistance change of CFRP laminates because the electrical resistance change of CFRP laminates continue to decrease, in spite of the fact that the contact resistance were increased over 10 cycles. The resistance of CFRP laminates was measured by 4-probe method which can ignore contact resistance theoretically. The 4-probe method should be used to detect fatigue damages of CFRP during the cyclic loading.In addition to that, the mechanism of the electrical resistance change of CFRP laminates is investigated. The issue of decreasing the electrical resistance of quasi-isotropic laminates under cyclic loading can not be explained by the existing research. In this study, the additional test was conducted for this issue. The electrical resistance change of CFRP laminates with stacking sequence of [0_2/90_2]s was investigated. As a result, the electrical resistance increased from the beginning of the cyclic test. This result suggests that ±45° plies have an effect on the mechanism of decreasing the electrical resistance of CFRP laminates. The residual strain of ±45° plies cause contraction in the fiber orthogonal direction of 0° ply. This deformation causes increasing fiber-fiber contact and decreases the electrical resistance of CFRP laminates.