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X Y Cheng - One of the best experts on this subject based on the ideXlab platform.

  • the influence of hydrogen on deformation under the elastic stress in Mooring Chain steel
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2018
    Co-Authors: X Y Cheng, X. Zhang, Hong Zhang
    Abstract:

    Abstract The cyclic deformation was investigated under cyclic stress with different maxima in seawater or simultaneously charging hydrogen for a tempered Mooring Chain steel. The loss of fatigue life in seawater is similar as that charged hydrogen, suggesting that the deterioration in lifetime caused by harsh seawater should mainly result from hydrogen evolution rather than anodic dissolution. Hydrogen can enhance bowing mobility of mobile dislocation and hence increase the recoverable displacement although local plastic is not obvious. In the meantime, hydrogen can promote the diminution of elastic modulus, which is always accompanied by an extra of internal friction.

  • effect of copper alloy element on corrosion properties of high strength Mooring Chain steel
    hsla, 2016
    Co-Authors: H P Shen, X Y Cheng, Hui Li, S Y Zhang, L C Su
    Abstract:

    The effect of copper on the corrosion properties of Mooring Chain steel in synthetic seawater at room temperature were investigated by weight loss tests, electrochemical methods and corrosion product analysis. The results indicated that the Mooring Chain steel exhibited active dissolution behavior in synthetic seawater. Corrosion potential shifted to noble direction and corrosion current decreased with copper contents. Therefore, the weight loss reduced and the polarization resistance was increased with increasing copper addition. The improvement of corrosion with copper was attributed to the change of corrosion rust that became smaller granules with higher adhesion strength as well as thicker layer when the steel was added more copper content. Meanwhile, the microcrack of inner rust was prevented to grow.

  • effect of boron microalloying element on susceptibility to hydrogen embrittlement in high strength Mooring Chain steel
    hsla, 2016
    Co-Authors: Hui Li, H P Shen, X Y Cheng, L C Su, S Y Zhang
    Abstract:

    The susceptibility to hydrogen embrittlement in high strength Mooring Chain steel with different boron content (0, 0.003 %, 0.008 %) were investigated by electrochemical hydrogen charging technique and tensile test. The results revealed that appropriate boron content can effectively depress hydrogen induced embrittlement. Precharged with a low current density, this effect seemed to be unobvious. It gradually became clearly with the increasing current density. The increase of resistance to the hydrogen embrittlement for 3B and 8B after adding appropriate boron was attributed to three facts. The first was that the segregation of boron atoms along grain boundaries reduced the grain boundary segregation of phosphorus, which prohibited hydrogen concentration at the grain boundaries, depressing the possibility of the intergranular fracture due to H. The second was that the segregation of boron increased intergranular cohesion, enhanced grain boundary strength, and refined the final microstructure. The third was that the addition of boron changed the state of hydrogen traps, leading to the small amount of diffusible hydrogen. That is to say, hydrogen transferred to these defects by dislocations was accordingly decreased, which led to the low sensitive of hydrogen induced cracking.

  • HSLA Steels 2015, Microalloying 2015 & Offshore Engineering Steels 2015 - Effect of Boron Microalloying Element on Susceptibility to Hydrogen Embrittlement in High Strength Mooring Chain Steel
    HSLA Steels 2015 Microalloying 2015 & Offshore Engineering Steels 2015, 2015
    Co-Authors: Hui Li, H P Shen, X Y Cheng, L C Su, S Y Zhang
    Abstract:

    The susceptibility to hydrogen embrittlement in high strength Mooring Chain steel with different boron content (0, 0.003 %, 0.008 %) were investigated by electrochemical hydrogen charging technique and tensile test. The results revealed that appropriate boron content can effectively depress hydrogen induced embrittlement. Precharged with a low current density, this effect seemed to be unobvious. It gradually became clearly with the increasing current density. The increase of resistance to the hydrogen embrittlement for 3B and 8B after adding appropriate boron was attributed to three facts. The first was that the segregation of boron atoms along grain boundaries reduced the grain boundary segregation of phosphorus, which prohibited hydrogen concentration at the grain boundaries, depressing the possibility of the intergranular fracture due to H. The second was that the segregation of boron increased intergranular cohesion, enhanced grain boundary strength, and refined the final microstructure. The third was that the addition of boron changed the state of hydrogen traps, leading to the small amount of diffusible hydrogen. That is to say, hydrogen transferred to these defects by dislocations was accordingly decreased, which led to the low sensitive of hydrogen induced cracking.

  • effect of tempering temperature on the microstructure and mechanical properties in Mooring Chain steel
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2015
    Co-Authors: X Y Cheng, Hui Li, Hong Zhang, H P Shen
    Abstract:

    Abstract The tensile behavior of a Mooring Chain steel was investigated after tempering at 560 °C, 600 °C, 640 °C temperatures. With increasing tempering temperature, the steel displayed not only a decrease in strength, but also a slight increase in strain-hardening ability between the proof and ultimate stress. In the meantime, an upper yield point appeared at 640 °C tempered samples. The susceptibility to hydrogen-induced embrittlement reduced on the same precharging hydrogen condition as tempering temperature elevated. These changes of tensile behavior were elucidated from their microstructure variation observed by transmission electron microscopy (TEM) and electron back-scattered diffraction (EBSD).

Nian-zhong Chen - One of the best experts on this subject based on the ideXlab platform.

  • Mooring Fatigue Assessment Evaluating Chain Twist and Out-of-Plane Bending for a Semi-submersible
    Journal of Offshore Mechanics and Arctic Engineering-transactions of The Asme, 2020
    Co-Authors: Nian-zhong Chen, Yongchang Pu
    Abstract:

    Abstract A Mooring fatigue assessment for Mooring Chain links of a semi-submersible in Offshore West Africa (OWA) is presented. Three cases that Mooring Chain links are subjected to pure tension, out-of-plane bending (OPB), and torque are considered in the assessment. For the case that Mooring Chain links are subjected to pure tension, a comparative study on S–N curves, T–N curves, and fracture mechanics (FM)-based Mooring system fatigue analyses is made, and the results show that the fatigue lives predicted by these three approaches are generally comparable if the safety factors suggested by API and DNVGL are applied to T–N curves and S–N curves based approaches. For the cases that Mooring Chain links are subjected to the OPB and torque, the investigation shows that fatigue lives of Mooring Chain links are decreased significantly due to the OPB effects, while the decline of fatigue lives of Mooring Chain links happens when the twist angles are more than 10 deg.

  • fracture mechanics analysis for Mooring Chain links subjected to out of plane bending opb
    Marine Structures, 2020
    Co-Authors: Nian-zhong Chen, Yongchang Pu
    Abstract:

    Abstract A fracture mechanics (FM) based investigation on the mechanism of out-of-plane bending (OPB) between Mooring Chain links and its effects on fatigue lives of Mooring Chain links are conducted. Four types of OPB problems that Mooring Chain links laying on the Chain wheel, Chain links passing over the bending shoe, Chain links constraint provided by the Chain hawse, and Chain links constraint provided by the Chain stopper are considered. Tension ranges of Mooring lines are calculated based on the combined loading process induced by the motions of wave frequency (WF) and low frequency (LF). Initial cracks are assumed to propagate from surfaces of Chain links and stress intensity factors are calculated in terms of stress ranges determined by a finite element (FE) analysis. The results show that fatigue lives of Mooring Chain links are decreased significantly due to OPB effects. In addition, the increase of the number of pockets of Chain wheel mitigates OPB effects on fatigue lives of Mooring Chain links laying on the Chain wheel, and the increase of the track diameter would reduce OPB effects on fatigue lives of Mooring Chain links passing over the bending shoe as well. However, for Chain links constraint provided by the Chain hawse, the diameter of Mooring Chain hawse has no significant effect on fatigue lives of the Mooring Chain links subject to OPB if without the abrupt change of the contact conditions between Chain links and Chain hawse. For Mooring links constraint provided by Chain stoppers considering the effect of proof loading test, fatigue lives of Mooring Chain links would drop significantly with the increase of interlink angles and friction coefficient.

  • Fracture Mechanics Based Mooring Fatigue Analysis for a Semi-Submersible Subjected to Triple Narrow-Band Loading Processes
    Volume 3: Structures Safety and Reliability, 2019
    Co-Authors: Nian-zhong Chen, Yongchang Pu
    Abstract:

    Abstract In the general offshore operating locations, Mooring systems are normally considered to be primarily affected by environmental loadings induced by waves, wind and current. WF motion induced by first-order waves, LF motion induced by second-order waves and wind would make the most contribution to the fatigue damage of Mooring lines. However, it was reported recently that in the Gulf of Mexico (GoM), the fatigue life of Mooring lines can be significantly affected by the vortex induced motion (VIM) induced by loop current. The aim of this presented paper is to address the influence of VIM on fatigue life of the Mooring system operating at the central of the GoM through performing a fracture mechanics (FM) based fatigue analysis for an offshore Mooring system. A frequency-domain Mooring analysis for the semi-submersible is conducted where WF motion induced by first-order waves, LF motion induced by second-order waves and wind, and VIM induced by loop current are taken into account. WF motion, LF motion and VIM are treated as three independent loading processes. A wide-band loading combination method is then used for predicting the loading processes acting on the Mooring system combining WF motion, LF motion and VIM. A fracture mechanics based analysis is performed to examine the fatigue life of Mooring system, in which initial surface cracks in previous existence are assumed to grow from the surfaces of Mooring Chain links connecting to the fairleads. The stress intensity factor ranges to estimate the crack growth in the FM based analysis are obtained from a finite element (FE) analysis.

  • Fracture Mechanics Based Mooring Chain Fatigue Analysis for a Semi-Submersible Subjected to Tension and Torque
    Volume 11B: Honoring Symposium for Professor Carlos Guedes Soares on Marine Technology and Ocean Engineering, 2018
    Co-Authors: Nian-zhong Chen
    Abstract:

    Mechanism of torque induced by Chain twist and its effects on the predicting fatigue lives of Mooring Chains of a semi-submersible operated in OWA (Offshore Western Africa) are investigated in this paper. The fatigue lives of Mooring Chains are estimated based on a fracture mechanics analysis. Stress ranges on the Mooring Chains induced by tension ranges acting on the twisted Chains are achieved by a finite element analysis. The low frequency (LF) and wave frequency (WF) tension processes induced by the motions of LF and WF are regarded as two random loading processes and the combined tension process of LF and WF is predicted by a dual narrow-band method. The Mooring Chains are treated as round bars and initial surface cracks are assumed to propagate at the surface of Mooring Chains. The influence of the Chain twist on the fatigue lives of Mooring Chains is investigated and the results show that when the twist angle is less than 20 degree, fatigue lives of Mooring Chains are increased with the increase of the twist angle. However, when the twist angle approaches lock-up angle of 30 degree, fatigue lives of Mooring Chains are significantly decreased due to the torque effects induced by the Chain twist.

  • Mooring system fatigue analysis for a semi submersible
    Ocean Engineering, 2018
    Co-Authors: Nian-zhong Chen, Yongyan Wu, Yeping Xiong
    Abstract:

    Abstract T-N curves, S-N curves, and fracture mechanics (FM) based Mooring system fatigue analyses for a semi-submersible are presented. Stress ranges are calculated based on the tension ranges of Mooring lines subjected to the combined loading process induced by the motions of wave frequency (WF) and low frequency (LF). A comparison between T-N curves, S-N curves, and FM based Mooring fatigue analyses for the semi-submersible is made and the results show that the fatigue lives predicted by the three approaches are in general comparable if the safety factors suggested by API and DNVGL are considered in the T-N and S-N curves based approaches. In addition, the crown section of a Mooring Chain is prone to fatigue damage compared to bend and weld sections without considering the SCF. A parametric study to investigate the impact of initial crack shape, critical crack depth, and initial crack sizes on fatigue life of a Mooring Chain is also conducted and the results show that fatigue life of a Mooring Chain predicted by the FM approach is generally sensitive to initial crack shape and initial crack sizes, however, it is relatively insensitive to the critical crack depth.

H P Shen - One of the best experts on this subject based on the ideXlab platform.

  • effect of copper alloy element on corrosion properties of high strength Mooring Chain steel
    hsla, 2016
    Co-Authors: H P Shen, X Y Cheng, Hui Li, S Y Zhang, L C Su
    Abstract:

    The effect of copper on the corrosion properties of Mooring Chain steel in synthetic seawater at room temperature were investigated by weight loss tests, electrochemical methods and corrosion product analysis. The results indicated that the Mooring Chain steel exhibited active dissolution behavior in synthetic seawater. Corrosion potential shifted to noble direction and corrosion current decreased with copper contents. Therefore, the weight loss reduced and the polarization resistance was increased with increasing copper addition. The improvement of corrosion with copper was attributed to the change of corrosion rust that became smaller granules with higher adhesion strength as well as thicker layer when the steel was added more copper content. Meanwhile, the microcrack of inner rust was prevented to grow.

  • effect of boron microalloying element on susceptibility to hydrogen embrittlement in high strength Mooring Chain steel
    hsla, 2016
    Co-Authors: Hui Li, H P Shen, X Y Cheng, L C Su, S Y Zhang
    Abstract:

    The susceptibility to hydrogen embrittlement in high strength Mooring Chain steel with different boron content (0, 0.003 %, 0.008 %) were investigated by electrochemical hydrogen charging technique and tensile test. The results revealed that appropriate boron content can effectively depress hydrogen induced embrittlement. Precharged with a low current density, this effect seemed to be unobvious. It gradually became clearly with the increasing current density. The increase of resistance to the hydrogen embrittlement for 3B and 8B after adding appropriate boron was attributed to three facts. The first was that the segregation of boron atoms along grain boundaries reduced the grain boundary segregation of phosphorus, which prohibited hydrogen concentration at the grain boundaries, depressing the possibility of the intergranular fracture due to H. The second was that the segregation of boron increased intergranular cohesion, enhanced grain boundary strength, and refined the final microstructure. The third was that the addition of boron changed the state of hydrogen traps, leading to the small amount of diffusible hydrogen. That is to say, hydrogen transferred to these defects by dislocations was accordingly decreased, which led to the low sensitive of hydrogen induced cracking.

  • HSLA Steels 2015, Microalloying 2015 & Offshore Engineering Steels 2015 - Effect of Boron Microalloying Element on Susceptibility to Hydrogen Embrittlement in High Strength Mooring Chain Steel
    HSLA Steels 2015 Microalloying 2015 & Offshore Engineering Steels 2015, 2015
    Co-Authors: Hui Li, H P Shen, X Y Cheng, L C Su, S Y Zhang
    Abstract:

    The susceptibility to hydrogen embrittlement in high strength Mooring Chain steel with different boron content (0, 0.003 %, 0.008 %) were investigated by electrochemical hydrogen charging technique and tensile test. The results revealed that appropriate boron content can effectively depress hydrogen induced embrittlement. Precharged with a low current density, this effect seemed to be unobvious. It gradually became clearly with the increasing current density. The increase of resistance to the hydrogen embrittlement for 3B and 8B after adding appropriate boron was attributed to three facts. The first was that the segregation of boron atoms along grain boundaries reduced the grain boundary segregation of phosphorus, which prohibited hydrogen concentration at the grain boundaries, depressing the possibility of the intergranular fracture due to H. The second was that the segregation of boron increased intergranular cohesion, enhanced grain boundary strength, and refined the final microstructure. The third was that the addition of boron changed the state of hydrogen traps, leading to the small amount of diffusible hydrogen. That is to say, hydrogen transferred to these defects by dislocations was accordingly decreased, which led to the low sensitive of hydrogen induced cracking.

  • effect of tempering temperature on the microstructure and mechanical properties in Mooring Chain steel
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2015
    Co-Authors: X Y Cheng, Hui Li, Hong Zhang, H P Shen
    Abstract:

    Abstract The tensile behavior of a Mooring Chain steel was investigated after tempering at 560 °C, 600 °C, 640 °C temperatures. With increasing tempering temperature, the steel displayed not only a decrease in strength, but also a slight increase in strain-hardening ability between the proof and ultimate stress. In the meantime, an upper yield point appeared at 640 °C tempered samples. The susceptibility to hydrogen-induced embrittlement reduced on the same precharging hydrogen condition as tempering temperature elevated. These changes of tensile behavior were elucidated from their microstructure variation observed by transmission electron microscopy (TEM) and electron back-scattered diffraction (EBSD).

Xiaoying Cheng - One of the best experts on this subject based on the ideXlab platform.

  • the character of hydrogen embrittlement in Mooring Chain steel
    JOM, 2020
    Co-Authors: Xiaoying Cheng, Xiaoyan Zhang, Yuhao Wu, Li Wang, Peiwen Zhao, Li Yang
    Abstract:

    The digital image correlation method has been applied to directly observe the local strain and crack formation in Mooring Chain steel during tensile tests in air or when simultaneously charging hydrogen in different ways, viz. including/excluding the notch root. Interestingly, hydrogen accumulation promoted crack initiation on the surface when the local strain reached approximately 0.9%, while strain of 19% to 20% was reached in the hydrogen-free specimens before visible crack formation. Even through the stress–strain curves prior to the sudden drop indicate a negligible effect of hydrogen, its presence can greatly reduce the stress-induced crack initiation. In addition, hydrogen introduced while avoiding the notch root can disorganize the regular distribution of strain produced by the notch before crack initiation. Therefore, hydrogen-induced embrittlement below the critical stress criterion can be explained by hydrogen-enhanced localized plasticity, while above the critical stress criterion, hydrogen-enhanced decohesion provides a better explanation.

  • the influence of hydrogen on fatigue fracture in Mooring Chain steel
    Fracture Fatigue and Wear, 2018
    Co-Authors: Xiaoying Cheng, Xiaoyan Zhang
    Abstract:

    The effect of hydrogen on every stress-strain hysteresis loop, fatigue life and fracture surfaces after fatigue test performed below yield strength in R5 Mooring Chain steel tempered at 560 and 600 ℃ temperature respectively was studied. The fatigue life was greatly reduced by hydrogen when fatigue tests carried on at simultaneously charging with different hydrogen content. This phenomenon is similar to uniaxial tensile test under same environment, illustrating that both fatigue and uniaxial tensile may have same mechanism of hydrogen-induced embrittlement. In addition, hydrogen can increase the recoverable displacement although local plastic deformation is not obvious, declaring that hydrogen may enhance mobility of dislocation and promote the microplastic deformation. At the same time, hydrogen decreases the elastic modulus and increases the internal friction. The accompanied changes indicate another reason for the decreased modulus except hydrogen-enhanced decohesion. Furthermore, the increment of internal friction caused by hydrogen may promote crack initiation and accelerate the crack growth.

  • hydrogen diffusion and trapping in v microalloyed Mooring Chain steels
    Materials Letters, 2018
    Co-Authors: Xiaobing Cheng, Xiaoying Cheng, Chaowei Jiang, Xiaoyan Zhang
    Abstract:

    Abstract In this paper, three different microalloyed steels were designed to investigate the effect of V on hydrogen trapping and diffusion in Mooring Chain steel by electrochemical hydrogen permeation technique and Atom Probe Tomography (APT). According to the results, the addition of V in Mooring Chain steel can decrease the hydrogen diffusion coefficient, and the calculated activation energy for hydrogen revealed that vanadium carbide nanoparticles in steel can trap hydrogen effectively.

  • influence of Mooring Chain steel strength on stress corrosion cracking
    Applied Mechanics and Materials, 2013
    Co-Authors: Xiaoying Cheng, Hong Yuan Chen, Zhi Juan Zhang
    Abstract:

    Two strength Mooring Chain steels were used to investigate the stress corrosion cracking (SCC) in synthetic seawater. The resistance of both strength steels to SCC was similar in neutral synthetic seawater. But the failure mechanism was different. For lower strength steel, it is mainly induced by anodic dissolution, while for higher strength steel, by hydrogen embrittlement. The reason was elucidated from their microstructures and corrosion characteristics.

  • direct observation of hydrogen trapping sites in newly developed high strength Mooring Chain steel by atom probe tomography
    Progress in Natural Science: Materials International, 2013
    Co-Authors: Xiaoying Cheng, Zhi Juan Zhang, Xiaojiao Wang
    Abstract:

    Hydrogen-trapping sites were directly observed by using a three-dimensional atom probe (3DAP) in high-strength Mooring Chain steel. Three typical 3DAP datasets show that trapping hydrogen is mainly enriched in retained austenite, and secondarily in carbides. In addition, these interfaces between ferrite and carbide are segregated by phosphorus, but do not admit hydrogen.

Philippe Bastid - One of the best experts on this subject based on the ideXlab platform.

  • Computational fatigue assessment of Mooring Chains under tension loading
    Engineering Failure Analysis, 2019
    Co-Authors: Imanol Martinez Perez, Yan-hui Zhang, Philippe Bastid, Andrei Constantinescu, Vengatesan Venugopal
    Abstract:

    Abstract This paper presents a computational fatigue assessment method of Mooring Chains under tensile loading, it is composed of a mechanical analysis followed by a fatigue analysis. The mechanical analysis is performed in two steps: residual stress prediction and service loading. From this analysis, the shakedown cycle is extracted at the critical points, ie: the asymptotically stabilized stress-strain cycles. As the Mooring Chain under service loading is under elastic shakedown, the Dang Van fatigue criterion is applied for the fatigue analysis. The accuracy of the proposed fatigue assessment method is proved by comparing with the experimental results from full-scale fatigue testing of Mooring Chain in seawater. The numerical results match both the experimental observations with respect to the localization of the damage zone and the lifetime.

  • Effect of seawater environment on the fracture toughness of Mooring Chain link material under cathodic protection
    Procedia structural integrity, 2019
    Co-Authors: Fokion Oikonomidis, Philippe Bastid, Marcelo Fonseca Dos Santos
    Abstract:

    Abstract High strength C-Mn Mooring Chains are used to keep floating offshore oil and gas platforms in position and as structural components in oil and gas subsea production systems. Cathodic protection (CP) can effectively prevent general corrosion of the Chains from the surrounding seawater. However, hydrogen atoms in the water can be liberated at the surface of the links because of the cathodic reaction and diffuse into the steel, causing hydrogen embrittlement of the material. As a result, the fracture toughness of the Chain link material drops. There is a dearth of knowledge about the fracture toughness of Chain link material when subjected to the operating environment. This paper presents and discusses results from full-scale fracture toughness testing of a studless Mooring Chain link grade R5 in NaCl solution under CP. The Chain link was subjected to tensile step loading while being completely submerged in the environment. There was evidence of crack extension beyond the fatigue pre-crack that was imposed on the Chain link. However, there was no definitive quantitative evidence at which step load the crack extension began. The post-test metallographic analysis showed that the crack extension due to hydrogen embrittlement has taken place in two steps. Taking into account the compressive residual stress caused by manufacturing at the crack tip, the maximum stress intensity factor (K) value that came from the second step load of 7035kN was 2735N/mm1.5. The average fracture toughness of the material in the same environment measured from small scale testing was 2372N/mm1.5. This value is acceptably near the full-scale value considering the difference in the notch depth ratio, and the design of small-scale specimens having higher constraint, expected to give lower toughness. The results at this stage suggest that small-scale specimens can give conservative predictions of full-scale behaviour of Mooring Chain links.

  • Multiaxial Fatigue Analysis of Mooring Chain Links Under Tension Loading: Influence of Mean Load and Simplified Assessment
    Volume 3: Structures Safety and Reliability, 2018
    Co-Authors: Imanol Martinez Perez, Philippe Bastid, Andrei Constantinescu, Vengatesan Venugopal
    Abstract:

    Current standards (as an example, DNV-OS-E301[1] and API-RP-2SK[2]) do not account for mean load in the fatigue assessment of Mooring Chains. Both standards, provide S-N curves derived from experimental work without specifying the mean load for which they have been obtained or proposing a mean load correction function. This paper reports a fatigue analysis study of Mooring Chains under Tension Loading using a multiaxial fatigue criterion for two different mean loads. Multiaxial fatigue criteria enable to account directly for complex phenomena, such as residual stresses, non-proportionality of the stress tensor, among others. This paper presents an example of the implementation of the Dang Van fatigue criterion for studying the fatigue behavior of Mooring Chains under tension. It quantifies the effect of the mean load on the fatigue lifetime and the failure location. Furthermore, it also proposes a simplified approach to reduce the complexity and the computational time of the fatigue analysis using Dang Van fatigue criterion. The paper is organized as follows: in the first part an example of the fatigue assessment is reported. Two different loading conditions with the same load amplitude but different mean loads are studied. The assessment method is based on two steps: a mechanical analysis and a fatigue analysis. In the second part, a simplified fatigue assessment method is proposed. As part of this method, a ratio between the fatigue lifetimes of two loading conditions, which have the same load amplitude but different mean load, is formulated. This ratio has been obtained analytically using the geometric representation of the Dang Van fatigue Criterion. Finally, the paper ends with a discussion, based on recent works, regarding the formulation of the locus of the Dang Van criterion and the fatigue properties used for the calibration of this criterion.

  • numerical analysis of contact stresses between Mooring Chain links and potential consequences for fatigue damage
    ASME 2013 32nd International Conference on Ocean Offshore and Arctic Engineering, 2013
    Co-Authors: Philippe Bastid, Simon D Smith
    Abstract:

    Design codes for offshore Mooring systems recommend proof loading Chain links to around 70% of the specified breaking load of the Chain (API RP 2FP1, Lloyd’s Register). This is primarily to check that the Chain will safely resist the service loads and will not excessively elongate. It is assumed that the proof load also generates compressive residual stresses at the interlink contact region and also at the point of the intrados (KT point) where a high stress concentration occurs during tensile loading. Tests have shown that proof loading improves the fatigue performance of Chain under cyclic axial loads.Elastic-plastic finite element analyses of the proof loading have been performed. These analyses have shown that the proof loading also generates very high tensile residual stresses in the region surrounding the interlink contact zone. This region also experiences significant in-service cyclic stresses under cyclic tension or out-of-plane bending. The combination of the cyclic stresses and high tensile residual stress is of concern and it is proposed that the periphery of the interlink contact zone should be carefully reviewed. It is understood that Chain link fatigue at present is only based on the risk of fatigue damage at the KT point.This paper presents and discusses results of finite element stress analyses of studless Chains of different sizes and grades, and show the relative fatigue sensitivity of the KT and contact regions. The Chain grade, dimensions and loading regime are shown to be important.© 2013 ASME