In this paper, a method for estimating the crack-tip opening displacement (CTOD) is proposed, which based on the maximum crack opening displacement (MCOD) and the nodal displacement of the crack surfaces at crack front. The critical CTOD and corresponding MCOD values of cryogenic high Mn steel specimens were obtained by three-point bending test. According to the definition of CTOD, the critical CTOD simulation values of three-point bending specimens at different CTOD calculated positions were calculated. By comparing the results of simulation and experiment, the value range of CTOD calculated position for cryogenic high Mn steel was obtained. The effect of mesh parameters and different materials on the numerical results was discussed, and the method is verified as insensitive to the mesh parameters and applicable to different materials.
With the widely use of clean energy, the global production and trade of LNG is becoming more and more active and the demand for LNG storage tanks is increasing. The traditional LNG storage tanks mainly use expensive invar alloy, 9% nickel steel, aluminum alloy and austenitic stainless steel. In recent years, cryogenic high Mn steel has been attracting attention for its low price and excellent low-temperature toughness, which has a wide range of application prospects (Demin M et al. 2019). Due to the great toughness of cryogenic high Mn steel, there is a large range of plastic zone at the crack tip when crack is cracking. The K (stress intensity factor) criterion is not applicable, but CTOD can be used to characterize the fracture toughness. When the crack is gradually opened after loading, the crack tip will be blunted. Then, the opening displacement at the original crack tip is defined as CTOD, as shown in Fig. 1. The CTOD value reflects the ability of material to resist crack propagation. The larger value of CTOD, the higher fracture toughness of material, and vice versa, the poorer fracture toughness of material. The CTOD assessment criteria has a wide range of application, especially in large-scale yield and complete yield conditions. CTOD evaluation technology has the characteristics of less test limitation and accurate determination, which can reflect the local performance of structure and the influence of temperature on fracture toughness. With the continuous development of optical and electronic technologies, the measurements of CTOD have become more accurate and faster (Xu & Yan, 2012). More and more scholars can observe the real-time CTOD value in their experiments.
