| 1. |
- Ringsberg, Jonas, 1971, et al.
(författare)
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Sheet metal fatigue near nuts welded to thin sheet structures
- 2008
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Ingår i: International Journal of Fatigue. - : Elsevier BV. - 0142-1123. ; 30:5, s. 877-887
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Tidskriftsartikel (refereegranskat)abstract
- One of the fatigue design processes of a car body is stress-based sheet metal fatigue near nuts welded to thin sheets (weld nuts). In this investigation, the influence from nut geometry and dimension, as well as sheet material and thickness on sheet metal fatigue life was studied by fatigue experiments and numerical analyses. The fatigue experiments were force-controlled and carried out on a weld nut specimen which, during the reversed loading that was applied, was designed to result in bending fatigue loading conditions of the sheet metal near the weld nut. The results from the experiments were Fa–N curves for various combinations of nut geometry and dimension, sheetmaterial and thickness. Numerical analyses of the experiments were carried out by linear elastic finite element (FE) analyses, in order to transform the Fa–N curves to Wöhler (sig_a–N) curves. A simplified FE model of the weld nut, which is suitable for structural analysis of car body structures, was used. The structural stresses calculated using the FE model showed good agreement with the structural stresses calculated using an analytical model that is based on plate theory. The conclusion was that the simplified representation of the weld nut, and the mesh density used in the FE model, was appropriate for computation of the stress response near a weld nut subjected to bending fatigue loading conditions. Finally, ra–N curves were computed for each weld nut configuration using its experimental data set. A sig_a–N curve fitted to all data sets resulted in the relation sig_a = 9888N^0.312. The sig_a–N curves for the 21 weld nut configurations tested were gathered within a factor of three in fatigue life from this curve.
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| 2. |
- Heiskari, Janne, et al.
(författare)
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On the thickness determination of rectangular glass panes in insulating glass units considering the load sharing and geometrically nonlinear bending
- 2022
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Ingår i: Thin-Walled Structures. - : Elsevier BV. - 0263-8231. ; 171
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Tidskriftsartikel (refereegranskat)abstract
- The number and size of windows has increased in large cruise ships, especially on the top decks. They have therefore become a weight and stability-critical component of the structure. Their thickness is determined according to the classification rules which are generalized for all type of passenger ships. That is, the provided formulae are based on linear-elastic, small deformation, plate theory and therefore more suitable for smaller windows in non-weight critical applications. However, majority of the windows are large insulating glass units (IGUs) that exhibit two e ects that the rules do not currently consider: development of membrane stresses in the glass panes at large deflections due to the von Karman strains (geometric nonlinearity) and interaction of the glass panes due to the internal cavity pressure between them (load sharing). Both increase the load bearing capacity of the IGUs. Therefore, extension to the thickness determination is needed for achieving the lightweight design. This paper uses nonlinear Finite Element Method to study the IGUs static response under uniformly distributed load considering the e ects. The response consists of principal stress and deflection of the panes, and the cavity pressure. Validation is carried out by experimental results from scientific literature. Case study on typical panes from cruise ships indicate that considering the two beneficial effects, the thickness of the glass panes in the IGUs may potentially be reduced between 26-54 % with respect to the classification rule-based design. That is, by using the same allowable principal stress criterion between the linear and nonlinear predictions.
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| 3. |
- Hogström, Per, 1979, et al.
(författare)
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Analysis of a struck ship with damage opening - influence from model and material properties uncertainties
- 2010
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Ingår i: Proceedings of The ASME 2010 29th International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2010). - 9780791849101 ; 2, s. 51-58
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Konferensbidrag (refereegranskat)abstract
- The conditions for damage stability and survivability of a ship struck by collision in arbitrary sea-state are, from a structural point of view, determined by the size and shape of the damage opening in its side shell. In the current investigation, explicit finite element analyses (FEA) are presented of a ship-to-ship collision scenario where the damage opening of a struck ship is calculated for a selection of damage degradation models and realistic material properties; here referred to as model and material properties uncertainties. The model uncertainty is considered as a possible (user-related) insecurity in the selection of the most appropriate damage degradation model for the analysis: the shear failure and the forming limit diagram (FLD) criteria. The uncertainty in material properties is accounted for in the constitutive material model description and the material parameters used in the two criteria. The size and shape of the damage openings predicted by the FEA are used in damage stability analyses in which the struck ship is subjected to wave motions in arbitrary sea-state and flooding into the damage opening.
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| 4. |
- Ringsberg, Jonas, 1971, et al.
(författare)
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Structural response analysis of slamming impact on free fall lifeboats
- 2017
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Ingår i: Marine Structures. - : Elsevier BV. - 0951-8339. ; 54:1, s. 112-126
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Tidskriftsartikel (refereegranskat)abstract
- The evaluation of impact induced slamming loads experienced by ships and offshore structures using advanced fluid structure interaction methods may be a challenging task involving complex and time consuming engineering solutions. This is the reason why to date the application of well understood and validated quasi-response approaches remains the most rational alternative used by experts for preliminary design assessment. Based on a benchmark study carried out by the International Ship and Offshore Structures Congress Technical Committee II.1 on Quasi-Static Response this paper demonstrates the practical use of quasi response prediction methods for the assessment of impact loads on modern free fall lifeboats. The case study presented is considered relevant in terms of technical background and ship design for safety. Following a brief review rationalising the practical relevance of the engineering solutions examined, the influence of high speed impact is evaluated using linear-elastic and nonlinear beam models, as well as a nonlinear transient dynamic finite element analysis idealisation. Comparisons of the methods presented against experimental results led to the conclusion that the nonlinear quasi-dynamic beam approach accounts for the influence of the dynamic effects of strain by suitably idealising the effects of nonlinear geometric stiffness. It may therefore be more appropriate to employ this approach at preliminary stage, especially when conducting comparisons against simplistic linear methods used for rigid structures (e.g. stiffened steel and aluminium panels), or advanced nonlinear finite element analysis, and other multi-physics methods that may be computationally complex and time consuming.
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| 5. |
- Sanchez Heres, Luis Felipe, 1984, et al.
(författare)
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Effective use of composite marine structures: reducing weight and acquisition cost
- 2018
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Ingår i: Marine Composites - Design and Performance. - 9780081022641 ; , s. 161-184
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Composite structures are a way to reduce the operational costs of a vessel or to increase its potential revenue. However, depending on the design of the vessel, its operational profile, and the business model of the owner, the benefits brought by a composite structure may not justify its acquisition cost. This paper presents a number of investigations aimed at reducing the acquisition cost of marine composite structures and maximizing their benefits through a more effective use of composite materials (in other words, weight reduction of the composite structure). The investigations cover three areas of opportunity for doing so: material safety factors, material characterization, and numerical optimization of large composite structures. The following conclusions are drawn from the investigations: motivating a reduction of material safety factors through probabilistic analyses is unpractical at best, and questionable at worst; improving the material characterization of textile composites is easy, relatively costless, and can modestly reduce structural weight through better material property values; numerical optimization of large composite structures is cumbersome, but feasible, and holds the greatest potential increasing the economical attractiveness of composite marine structures.
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| 6. |
- Josefson, Lennart, 1954, et al.
(författare)
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Assessment of uncertainties in life prediction of fatigue crack initiation in rails – influence of residual stresses from manufacturing
- 2007
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Ingår i: Proceedings of The 8th International Conference on Multiaxial Fatigue & Fracture (ICMF&M8). ; , s. 1-8
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Konferensbidrag (refereegranskat)abstract
- The risk for initiation of fatigue cracks in the web in the weld zone of a rail is studied. The interaction between the welding residual stress field and the stress field caused by service loads is simulated in a nonlinear finite element (FE) analysis where the welding residual stress distribution (shape) and magnitude, the service load magnitude, and the material parameters used in the fatigue life estimation are varied. The initiation of fatigue cracks is assessed using the shear-stress-based multiaxial fatigue criterion proposed by Dang Van. In addition, the accuracy in the fatigue life assessment is evaluated by statistical uncertainty analysis where the variances according to the Gauss approximation formula are studied. It is seen that the welding residual stress enhances the risk for fatigue crack initiation in the rail web, and that the uncertainty in load level dominates the uncertainty in the fatigue assessment.
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| 7. |
- Karlsson, Ulf, 1965, et al.
(författare)
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Experimental and numerical investigation of bulb impact with a ship side-shell structure
- 2009
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Ingår i: Marine Technology. - 0025-3316. ; 46:1, s. 16-26
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Tidskriftsartikel (refereegranskat)abstract
- The finite element (FE) method is suitable as a numerical tool in the numerical analysis of, for example, ship collision scenarios. It is feasible to simulate and compare different collision scenarios by parameter variations. The objective with this investigation was to establish a reliable and robust FE modeling procedure for ship-ship collision simulations, using the commercial FE software Abaqus/Explicit, by means of parameter sensitivity and experimental analyses. Four types of experiments are presented that have supported the development of the FE models and simulations with sufficient information for representation of material characteristics and for validation of models: (i) uniaxial tensile tests, (ii) friction tests, (iii) bulb impact with a steel-sheet test and, finally (iv) a bulb impact with a side-shell ship structure. The outcome of the parameter study after calibration against test results was two validated FE models: one of the bulb-sheet test and one of the bulb-structure test.
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| 8. |
- Lee, Dong Hun, et al.
(författare)
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Computational models for the ultimate compressive strength analysis of a steel stiffened plate structure at cryogenic condition
- 2019
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The aim of the present study is to develop computational models for the ultimate strength analysis of steel stiffened plate structures under axial compressive loading and cryogenic condition. As the number of vessels fueled by liquefied natural gas (LNG) are increasing, there are potential hazards that LNG leaks to hull structures, leading to cryogenic condition with a temperature of -160 deg. C. Under extreme compressive loading, steel stiffened plate structures under cryogenic condition can exhibit brittle fracture before and after ultimate strength is reached. The authors have shown such an evidence through a physical model testing on a large scale steel stiffened plate structures, which was presented in a separate paper. In the present paper, computational models using nonlinear finite element method are developed to simulate the ultimate compressive strength behavior of steel stiffened plate structures at cryogenic condition, involving brittle fracture. The numerical computations are compared with test database obtained from the physical model testing.
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| 9. |
- Paik, Jeom Kee, et al.
(författare)
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Full-scale collapse testing of a steel stiffened plate structure under cyclic axial-compressive loading
- 2020
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Ingår i: Structures. - : Elsevier BV. - 2352-0124. ; 26, s. 996-1009
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Tidskriftsartikel (refereegranskat)abstract
- Plate panels of ships and floating offshore structures are likely subjected to cyclic loads arising from waves at sea. Depending on sea states, e.g., whipping in harsh sea states, the maximum amplitude of the cyclic loads may reach over 70% of ultimate loads. Of concerns is how the cyclic loads will affect the ultimate strength compared to a case of monotonically increasing loads. The aim of this paper is to experimentally investigate the ultimate strength characteristics of a steel stiffened plate structure under cyclic axial-compressive loading. A full-scale collapse testing in association with bottom structures of an as-built 1,900 TEU containership was conducted. It is concluded that the effects of cyclic loading on the ultimate compressive strength of steel stiffened plate structures are small as far as fatigue damages are not suffered due to the small number of load cycles and/or local structural members do not reach the ultimate strength during cyclic axial-compressive loading. Details of the test database are documented, which will be useful to validate computational models for the ultimate strength analysis.
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| 10. |
- Xu, Ying, et al.
(författare)
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An ice material model for assessment of strain rate, temperature and confining pressure effects using finite element method
- 2019
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Ingår i: Ships and Offshore Structures. - : Informa UK Limited. - 1754-212X .- 1744-5302. ; 14:S1, s. 34-44
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Tidskriftsartikel (refereegranskat)abstract
- This paper addresses an investigation of ice constitutive laws modeling with strain rate, temperature and confining pressure effects of interest in modeling ice compressive behaviour. For the proposed phenomenological model consisting of elastic, delayed elastic and viscous components, strain rate is taken into account by introducing a viscous term based on Glen’s law. The effects of temperature and confining pressure are also included in the ice model. With the consideration that the viscous term and delayed elastic term are affected by temperature, the pressure hardening and pressure softening phenomena are embedded in the constitutive model. The proposed three-dimensional constitutive model is implemented in explicit LS-DYNA as a user-defined material model, and the numerical simulations of constant strain rate and creep experiments are conducted to verify the proposed ice material model. Ice strength and strain-time curves at different strain rates, temperatures and confining pressures are obtained and compared with experimental results.
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