Fracture toughness improvement of polyurethane adhesive joints with chopped glass fibers at cryogenic temperatures

Polyurethane (PU) adhesive is widely used for bonding the secondary barrier of cryogenic containment systems (CCS) of liquefied natural gas (LNG) ships due to its ductility at room temperature, although it can become brittle at the cryogenic temperature below its glass transition temperature. To evaluate the reliability of PU adhesive at the cryogenic temperature of −150°C, the fracture toughness of double-cantilever-beam (DCB) adhesive joints composed of stainless steel and aluminum adherends was measured. Because the fracture toughness of the PU adhesive was found to be very low at the cryogenic temperature, the adhesive was reinforced with chopped glass fibers. The fracture toughness with respect to the length and volume fraction of the chopped glass fibers was then measured. Based on the experimental results, an optimal reinforcement method is suggested for the reliable application of PU adhesive at cryogenic temperatures.