Fracture Toughness Measurement of Adhesively Bonded Joints at Cryogenic Temperatures

A sharp initial crack tip is required for measuring the fracture toughness or energy release rate of adhesive joints, especially at cryogenic temperatures because a blunt initial crack tip in the adhesive may lead to a higher value of fracture toughness than a sharp initial crack tip. Although ASTM D3433 standard specifies how to measure the fracture toughness of adhesive layers in bonded joints, it does not state the way to generate crack tips. In this work, the fracture toughness of adhesive joints was measured at the cryogenic temperature of −150°C with respect to the crack generation method and location of the initial crack, and compared to that at 25°C. From the experimental results, it was concluded that an initial sharp crack tip should be generated in the adhesive region to measure accurately the energy release rate of the adhesively bonded joint. Also, the fracture toughness of the adhesive joint at the cryogenic temperature of −150°C should be measured with respect to crack tip location.