Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Three-point bending experiment and numerical study on CTOD of cryogenic high Mn steel
Zhengxin Li, Jianbo Chen, Jingxi Liu
School of Naval Architecture and Ocean Engineering, Huazhong University of Science and Technology
Wuhan, Hubei Province, China

technology has the characteristics of less test limitation and accurate
determination, which can reflect the local performance of structure andthe influence of temperature on fracture toughness. With the continuous
development of optical and electronic technologies, the measurements ofCTOD have become more accurate and faster (Xu & Yan, 2012). Moreand more scholars can observe the real-time CTOD value in theirexperiments.

ABSTRACTIn 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 ofcryogenic 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 andexperiment, 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 isverified as insensitive to the mesh parameters and applicable to differentmaterials.

Fig. 1 The definition of CTOD
To accurately solve the CTOD value of engineering structure with crack,
many researchers have carried out theoretical and numerical calculation
methods of CTOD. Huang (2011) proposed a two-dimensional finite
element method for calculating the CTOD value by studying the central
crack finite plate subjected to uniaxial uniform tensile load, which isapplicable to any material. Liu (2012) studied the two-dimensional
analytical approximation method for calculating CTOD value underrandom cyclic loading and proposed an empirical formula with higher
computational efficiency suitable for simple cracked plates. Antunes(2017, 2018, 2019) quantified the plastic deformation of crack tip, anduse plastic CTOD range (ΔCTODp) instead of classical ΔK (stressintensity factor range) to study fatigue crack growth rate (da/dN), andstudy the effects of different numerical parameters on ΔCTODp andda/dN-ΔCTODp curves. CTOD is extremely helpful for the study offatigue crack propagation in high toughness steel.
Many scholars use two-dimensional model to study the theories about
CTOD, which has some limitations for solving three-dimensional crackproblem. This paper uses the spiderweb mesh along the crack front, asshown in Fig. 2, which consists of concentric element rings (Cordeiro &Leonel, 2018). A typical spiderweb mesh is 8 singular elements aroundthe crack tip and 2 rings of brick elements. The length of each ring alongradial direction is equal, and the total radial length of all rings is 𝑟𝑐𝑡 ,which is referred to as the spiderweb radius. Based on the definition ofCTOD, the CTOD value is calculated by the nodal displacement of theKEY WORDS: crack; CTOD; three-point bending test; cryogenic highMn steel; spiderweb mesh.

INTRODUCTION
With the widely use of clean energy, the global production and trade ofLNG 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 etal. 2019). Due to the great toughness of cryogenic high Mn steel, there isa large range of plastic zone at the crack tip when crack is cracking. TheK (stress intensity factor) criterion is not applicable, but CTOD can beused 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 inFig. 1. The CTOD value reflects the ability of material to resist crack
propagation. The larger value of CTOD, the higher fracture toughness ofmaterial, and vice versa, the poorer fracture toughness of material. TheCTOD assessment criteria has a wide range of application, especially inlarge-scale yield and complete yield conditions. CTOD evaluation

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