Experimental and numerical investigation of fracture toughness in the heat-affected zone of FH36 steel for LCO₂ vessels

With increasing decarbonisation demands, the structural safety of liquefied carbon dioxide (LCO₂) carriers in low-temperature environments has gained attention. Cracks significantly reduce structural service life, and fracture toughness is an essential material property for assessing the crack stability. Cracks tend to form in welded regions due to stress concentration. While some fracture toughness tests on the heat-affected zone (HAZ) at low temperatures have been conducted, numerical simulation studies remain limited. Firstly, this study experimentally evaluates the fracture toughness of FH36 steel base material and HAZ specimens under both room and low temperatures. To further investigate the experimental process and establish a constitutive model, finite element simulations of the testing process are performed, which incorporates a stress-modified fracture strain (SMFS) model to account for material damage. Furthermore, a new method for determining material parameters in the SMFS model is proposed, and a numerical approach for simulating fracture in the HAZ at low temperatures is developed. The resulting fracture toughness data and damage model are expected to provide reliable support for structural safety assessments in low-temperature environments.