Durability of anticorrosive-coated steel–carbon fiber reinforced polymer structural adhesive joint at high temperature and humidity

Limited information on the long-term reliability of structural adhesive joints hinders their practical application. Moreover, performance improvement in transportation equipment and the solution of concrete problems, such as high strengthening, vibration reduction, and weight saving, are expected by increasing the availability of materials in the shipbuilding industry using highly functional materials that are not welded. This study evaluated the durability of second-generation acrylic (SGA) structural adhesives. The strength of SGA was higher than that of epoxy-based adhesives in the case of thick adhesive layers, and few fluctuations were observed in the strength owing to variations in the adhesive-layer thickness. The static strength following environmental degradation was evaluated using a tensile lap shear structural adhesive joint coated with an anticorrosive coating, assuming application to the exposed part. The acceptable design adhesive strength in shipbuilding was evaluated using the strength retention rate η _d (mean strength after deterioration/initial mean strength) and coefficient of variation CV (standard deviation/mean strength) after deterioration. η _d for each test was greater than 72 %. The CV value for each test was <0.16; this is equivalent to a coefficient of dispersion of deterioration D _y ≥ 0.41 on percent defects allowed = 1/10,000 (upper limit of the defect rate assumed at the design stage). This result indicates that the adhesive joint is available even for the exposure section, if the adhesive joint is protected similar to adherend steel with anticorrosive paint, which is common in the field of shipbuilding.