Key Takeaways & Executive Findings
- •• Fatigue crack growth rate increases with stress ratio while fatigue threshold decreases. • Crack closure and dual-parameter driving force both contribute to stress ratio effects. • A new prediction model incorporating near-threshold and destabilization stages was developed. • The model shows excellent predictive ability validated against literature data and existing models.
Abstract
As a typical steel, the fatigue of marine high-strength steels has been emphasized by scholars. In this paper, the fatigue performance and crack growth mechanism of a high-strength steel for ships are investigated by experimental methods. First, the fatigue threshold test and fatigue crack growth rate test of this high-strength steel under different stress ratios were carried out. The influence of stress ratio on the fatigue properties of this steel was analyzed. Secondly, scanning electron microscope was used to analyze the crack growth specimen section of this steel. The crack growth and failure mechanism of this steel were revealed. Finally, based on the above research results, the stress ratio effect of high-strength steel was investigated from the perspectives of crack closure and driving force. Considering the fatigue behavior in the near-threshold stage and the destabilization stage, a fatigue crack growth behavior prediction model of high-strength steel was established. The accuracy of the model was verified by test data. Moreover, the applicability of the modified model to various materials and its excellent predictive ability were verified through comparison with literature data and existing models.
1. Introduction
With the development of modern engineering technology, the application of high-strength steel has become more and more widespread. Compared with ordinary steel, high-strength steel has significant advantages in terms of stress performance, processing and economic benefits. The increase in yield strength leads to an insignificant strain-strengthening effect during loading, which makes the fatigue performance of high-strength steel poor [1]. Fatigue damage is particularly prominent on ships, accounting for 80%−90% of its damage forms [2], causing great harm to the safe use of ships. Therefore, it is very important to conduct fatigue tests on high-strength steel and predict its fatigue performance in conjunction with the fracture of specimens.
The application of high-strength steel in the field of marine has been mainly reflected in the construction of offshore platforms and ships. Liu et al [3] conducted an experimental study on the fatigue performance of DH36 steel, an offshore steel. It was found that an increase in the load ratio would lead to an elevation of the crack growth rate, while the fatigue threshold value would decrease accordingly. Wang et al [4] found the existence of significant differences in the crack growth behavior of EH36 under different load ratios. Not coincidentally, Zhong et al [5] also found that the load ratio has a remarkable effect on the fatigue behavior of EH36. Most scholars attribute this difference to crack closure during crack growth. Wang [6] investigated the crack closure behavior of 10Ni5CrMoV and found that the level of crack closure was enhanced with the increase of R, which led to the difference in crack growth behavior. However, on the other hand, some scholars believed that crack closure was not the main reason for the differences in crack growth behavior of steels. They began to ignore crack closure and turned to explain the fatigue behavior of steels from a completely new perspective. Kujawski [7] proposed the dual-parameter-driving force. He believed that both ΔK and Kmax drive crack growth. Martelo et al [8] found that the dual-parameter-driving force could better explain the crack growth behavior of AISI 301 LN. The same conclusion was obtained by Wei [9]. Up to now, no scholar has given definite evidence to prove which of the two, crack closure theory or dual-parameter driving force, can better explain the crack growth behavior of steels.
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LEI Yin-hui, WANG Ke, ZHANG Ruo-nan, LI Yong-zheng, QIN Chuang, WEI Peng-yu (2025). Fatigue Crack Growth Behavior of High-strength Steel for Ships. SinoTechIntel Verified Research. https://doi.org/10.3969/j.issn.1007-7294.2025.06.009
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Frequently Asked Questions
What is the effect of stress ratio on fatigue crack growth rate?
The study found that an increase in stress ratio leads to an elevation of the crack growth rate and a decrease in the fatigue threshold value.
What mechanisms explain the stress ratio effect in high-strength steel?
The stress ratio effect is attributed to both crack closure and dual-parameter driving force (ΔK and Kmax). The paper investigates both perspectives.
How was the fatigue crack growth prediction model developed?
The model was developed by considering the fatigue behavior in the near-threshold stage and the destabilization stage, and it incorporates the dual-parameter driving force concept.
Was the prediction model validated?
Yes, the model's accuracy was verified by test data, and its applicability to various materials and excellent predictive ability were confirmed through comparison with literature data and existing models.
What is the significance of this research for shipbuilding?
High-strength steel is widely used in ships and offshore platforms, and fatigue damage accounts for 80-90% of ship damage forms. This research provides a better understanding and prediction of fatigue crack growth, which is crucial for safe design and maintenance.
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