Long Life Durability of Electrodes of Electrical Resistance Change Method for Damage Monitoring of CFRP Composite Structures; Final rept. Apr 2007-Mar 2008

摘要

Investigated the applicability of the electrical resistance change method through experiments of CFRP laminates (6-18). Instead of using two or four electrodes, this research adopted multiple electrodes mounted on the surface of the target structure to identify delamination location and dimension. Orthotropic electric conductivity was also measured experimentally for three types of fiber volume fractions, and the paper revealed that electric conductivity in thickness direction of CFRP was approximately one thousandth of conductivity of fiber direction. The large difference brings difficulty of identifications of delamination location from the measured electrical resistance changes. For these studies, a response surface method was adopted as a tool to solve inverse problems delamination location and dimension were obtained from measured electric resistance changes of multiple segments between electrodes. The previous study (20) used FEM analyses of various delamination lengths and locations of beam-type specimens to investigate the reason of the large estimation errors of delamination locations; furthermore an improvement to obtain higher estimation performance was proposed, which used the data normalization method before making response surfaces. The normalized method provides highly precise estimations of location and size: 7mm error in size and 10mm error in location experimentally for CFRP laminates. Other researchers attached electrodes on the edges of the specimens (1-15). The method does not cause damages of the electrical contact at the electrodes during loading. The method, however, does not monitor the location of the damages instead. The important point is to mount multiple electrodes on the surface of the target CFRP structure in our method although mounting electrodes on the surface may cause degradation of electrical contact during loading. In.