1,721,086 research outputs found
Selection of appropriate numerical models for modelling the stresses in mooring chains
No full textMooring chains are key components for floating platforms. The failure of these components can be catastrophic in terms of the economic and environmental impacts, especially when dealing with the potential failure of FPSOs. However, mooring failures have been regularly occurring much earlier in their service lives than expected, with almost 50% of the reported failures happening in the first 3 years of 20-year design lives. Although the operating stresses play a major role in determining the failure mechanisms of mooring chains, the methods of predicting the operating stresses in mooring chains vary in the openly available literature, and the accuracy of these different numerical methods for predicting types of mooring failures is unknown. There is currently little evidence provided for when one model is appropriate for a particular scenario. Therefore, this paper benchmarks the different available methods for modelling mooring chains under tension, including FE models found in the literature. These models are calibrated and verified against previous studies and compared with experiments and a developed FE explicit model. There is a significant difference in the way that the numerical models behave, which are discussed in terms of their applicability and limitations in modelling mooring chains. The results of this study show that the explicit modelling approach should be utilised for accurate assessment of mooring lines, as it provides the most realistic response, with a substantial reduction in the computational cost and without any convergence problems
Microstructural modelling of fatigue initiation in aluminium-bearing alloys
No full textMicrostructural fatigue initiation in Al-Sn-Si-Cu-Ni bearing lining alloys is reported and investigated. The secondary phases of such alloys comprise fine and relatively few Sn and Si particles as well as a large number of hard AlNi3-type intermetallics, frequently encapsulated within soft Sn layers. During fatigue tests, these particles were observed to initiate short fatigue cracks. Through elasto-plastic finite element analysis of ideal microstructures but with realistic geometric and mechanical property data, critical values of key stress and strain components within the matrix, the Sn layers, and the particles were predicted and linked to microstructural features associated with observed fatigue initiation. These modelling results indicate the extent to which either the hydrostatic stresses or plastic shear strains may be responsible for fatigue crack initiation in the Sn layers, as well as the optimum microstructural characteristics that would minimise tensile stresses, which are responsible for brittle particle fracture
Fatigue approaches for mooring chains subjected to wear degradation
No full textThere are currently 365 FPSOs in service around the world. These vessels all use mooring lines to maintain position and provide stability, keeping the vessel and cargo safe. However, more than 21 failures have occurred between 2001 and 2011 and approximately 50% of the reported failures occurred in the first 3 years of 20-year design life. Each mooring line failure represents the potential for serious environmental and economic consequences. Based on industry surveys, the most common failure mode is fatigue failure. In the current offshore standards, the surface degradation due to wear and corrosion is modelled as a diameter loss at a standards rate. To assess whether the uniform reduction in chain diameter suggested in the offshore standards is able to explain the early chain failures seen in service, this paper incorporates two wear rates into a fatigue life calculation; one wear rate is taken from DNV-OS-E301 and is compared against one taken from NORSOK M-001. Three fatigue life estimation approaches: tension, nominal stress and hotspot, are used to compare the differences in fatigue method. The stress in the chain is calculated using an analytical model, which is verified against an FE model. The effect of wear degradation on the ultimate strength of the chain is calculated based on the minimum breaking load. The results show that the diameter loss rates suggested in the offshore standards are not able to explain the early mooring chain failures seen in the past and that the reduction of diameter cannot solely explain the early failures seen in service. The hotspot approach, not often used in mooring line predictions, is best able to predict these shorter lives, as it offers more accurate fatigue predictions by considering high peak stresses compared to standard methods such as tension and nominal stress approaches
Influence of orientation-dependent grain boundary oxidation on fatigue cracking behaviour in an advanced Ni-based superalloy
Full text linkFatigue tests have been conducted on an advanced disc Ni-based superalloy [low solvus, high refractory (LSHR) alloy] at 650°C in air under three-point bend loading to investigate the role of orientation-dependent grain boundary (GB) oxidation in crack initiation and early propagation. It is found that crack initiation occurs mainly from bulged GB oxides, and cracks then predominantly propagate along the oxidised grain boundaries. These bulged oxides are extremely enriched in Co and preferentially form at the boundaries between high and low Schmid factor grains which are inclined normal to the applied tensile stress direction. Meanwhile, relatively flat/thin Ni/ Ti/Al-rich oxide complexes also form at other grain boundaries, but they appear to be much less detrimental in fatigue crack initiation and propagation compared with the bulged GB Co-rich oxide complexes
A numerical study of the effects of shot peening on crack growth in notch geometries under bending fatigue tests
No full textDataset: Effect on overall fatigue performance of varying thickness of an intermetallic sublayer within a soft multilayer coating
No full textEach sheet in the file shows raw data corresponding to different figures in the paper which has been accepted on 2021.1.13 Lu, S., Cook, R., Zhang, Y., & Reed, P. (2021). Effect on overall fatigue performance of varying thickness of an intermetallic sublayer within a soft multilayer coating. International Journal of Fatigue.</span
Oxidation induced crack closure in a nickel base superalloy: a novel phenomenon and mechanism assessed via combination of 2D and 3D characterization
No full textUnderstanding the mechanism of oxidation induced crack closure (OICC) is of great importance in understanding the fatigue resistance of materials operating at intermediate or high temperatures subjected to oxidation. Current work reveals that the occurrence of OICC is most closely related to the test frequencies and temperatures rather than the microstructure in a directionally solidified (DS) superalloy. Characterization techniques in three dimensions - X-ray scanning tomography (CT) and two dimensions - scanning electron microscopy (SEM) with attached energy-dispersive Xray spectroscopy (EDX) are combined to capture the oxides formed within the crack wake. These data are then incorporated into modified models to provide quantitative measurements of oxidation induced crack closure. Both the experimental and modelling results show that the external oxides forming close to the crack tip, result in a high crack tip opening displacement and thereby significant crack closure
Low-cycle fatigue assessment of offshore mooring chains under service loading
No full textThe integrity of mooring chains is essential to the safety of a range of offshore platforms. However, mooring line failures are occurring earlier than their design lives, with a high number of these failures occurring due to fatigue. Early in the fatigue life of the component fatigue initiation processes occur, where the fatigue hotspot is sensitive to the mean load and there is plastic strain accumulation from the multiaxial stress-strain responses of the material, leading to cyclic plastic damage accumulation. The traditional SN approach suggested by mooringstandards does not consider these effects, and it is proposed that this lack of consideration under low-cycle fatigue conditions is the reason for the current non-conservative fatigue assessments of mooring chains. This paper aims to develop a fatigue approach based on a critical plane multiaxial fatigue criterion for mooring chains that can consider the damage-induced by the cyclic plasticity and the mean load effect, to investigate the importance of incorporating low-cycle fatigue into the mooring chain life prediction. To develop the criticalplane approach, the multiaxial stress-strain states are extracted for the critical plane at the fatigue hotspot from a finite element model of a mooring chain. This is then correlated with a fatigue life prediction provided by conventional fatigue design data. It uses a simulation of an FPSO as a case study to demonstrate the importance of low cycle fatigue, which shows that the mean load effect is significant in reducing the fatigue life for mooring chain applications, while the effect of fatigue damage-induced cyclic plasticity is limited. The fatigue damageaccumulation predicted by the critical plane approach is significantly higher than that of the traditional SN approach and should be accounted for in mooring line design
Dataset for the publication 'Oxidation induced crack closure in a nickel base superalloy: a novel phenomenon and mechanism assessed via combination of 2D and 3D characterization'
No full textDataset supporting the publication by Y Tan, N Gao, P Reed,
"Oxidation induced crack closure in a nickel base superalloy: A novel phenomenon and mechanism assessed via combination of 2D and 3D characterization",
Materials Science and Engineering: A, Volume 861, 2022, 144311,
ISSN 0921-5093,
https://doi.org/10.1016/j.msea.2022.144311.
The data is derived from three dimensions - X-ray scanning tomography (CT) and two dimensions - scanning electron microscopy (SEM) with attached energy-dispersive Xray spectroscopy (EDX). The data was incorporated into modified models to provide quantitative measurements of oxidation induced crack closure.
The data is presented as:
COD_final.opju
L_and_T_650_1_1_1_and_sinewaveform.opju
Resharp_data.opju
The project was funded by EPSRC (Grant no:EP/M000710/1) and the China Scholarship Council.</span
Research data management education for future curators
Full text linkScience has progressed by “standing on the shoulders of giants” and for centuries research and knowledge have been shared through the publication and dissemination of books, papers and scholarly communications. Moving forward, much of our understanding builds on (large scale) datasets, which have been collected or generated as part of the scientific process of discovery. How will this be made available for future generations? How will we ensure that, once collected or generated, others can stand on the shoulders of the data we produce?Educating students about the challenges and opportunities of data management is a key part of the solution and helps the researchers of the future to start to think about the problems early on in their careers. We have compiled a set of case studies to show the similarities and differences in data between disciplines, and produced a booklet for students containing the case studies and an introduction to the data lifecycle and other data management practices. This has already been used at the University of Southampton within the Faculty of Engineering and is now being adopted centrally for use in other faculties. In this paper, we will provide an overview of the case studies and the guide, and reflect on the reception the guide has had to date
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