Defect detection of composite adhesive joints using electrical resistance method

Abstract

Mechanical joint and adhesive bonding are two typical joining methods for composite materials. The bolt fastening method is reliable but increases the weight of the structure and cuts the composite fiber, which may cause stress concentration and strength degradation. The adhesive bonding method has a higher bonding strength than the mechanical fastening, but the bonding strength can deteriorate depending on the various parameters that influence the environmental conditions and manufacturing process. In addition, bonding defects due to the presence of foreign substances on the bonding surface or immature surface treatment is called a Kissing Bond, and can significantly reduce the bonding strength. The electrical resistance method is a very promising technique for detecting kissing bond defects by measuring the electrical characteristics after the dispersion of CNTs in the adhesive. In this study, composite-to-composite single-lap joint specimens with CNTs were fabricated and the defect detection capability and the static strength of composite joints were evaluated using the electrical resistance method. A carbon/epoxy composite was used as an adherend and the electrical resistance of the adhesive joint was measured by varying the content of CNTs to 0.5 wt%, 1.0 wt%, and 2.0 wt%. The AC and DC resistance values of composite adhesive joints with artificial defects were measured using an LCR meter and a high-resistance meter, and their lap shear strengths were evaluated.