INFLUENCES OF PLASTICITY -INDUCED CRACK CLOSURE ON FATIGUE CRACK HEALING OF CARBON STEEL WITH HEAT TREATMENT

Healing technology for metallic materials is an important subject in terms of long-term reliability and durability of structural members, a healing technology to heal fatigue crack by applying heat treatment at annealing temperature level has been discovered. In this study, the influences of plasticity induced crack closure on healing were evaluated by obtaining the crack opening load during the pre-crack introduction and evaluating the fatigue crack propagation characteristics before and after the healing heat treatment, using compact tension specimens made of carbon steel with different test conditions. As a result, the specimen with high crack opening load showed high healing effect and were able to heal up to 95% of the pre crack length. This suggested that the residual compressive stress due to the plasticity-induced crack closure accelerates the solidstate diffusion bonding during the crack healing process and this leads to the improvement of the healing effect.