Optimum glass fiber volume fraction in the adhesive for the Al-SUS adhesively bonded joints at cryogenic temperatures

The tight control of adhesive thickness in large bonding areas such as the secondary barrier of CCS (cargo containment system) for LNG (Liquefied Natural Gas) carriers or floaters is difficult and expensive although the adhesive thickness is a dominant parameter to determine the bonding performance of adhesively bonded joint, especially at cryogenic temperatures. Therefore, the method for improving bonding strength and fracture toughness for thick adhesive layer was investigated by reinforcing the adhesive layer with glass fiber mat for the robust and sustainable system design for the secondary barrier. Randomly oriented E-glass fiber mat was used as reinforcement for the film type epoxy adhesive. The lap shear strength and fracture behavior were investigated with respect to fiber volume fraction, and compared to those of the adhesive without reinforcement. The effects of repeated thermal shocks on adhesive bonding performances of adhesive joints with reinforced adhesive were also studied. The experimental results revealed that the randomly oriented glass fiber reinforcement improved much the bonding strength and fracture toughness of adhesive even with 1.0 mm thickness at the cryogenic temperature. Also it was found that the enhancement of bonding performances strongly depended on the CTE (Coefficient of Thermal Expansion) differences between the stainless steel foil and reinforced adhesive. Finally an optimum volume fraction of the glass fiber reinforcement was proposed for the newly developed Al-SUS adhesively bonded joint.