| 1. |
- Ahadi, Aylin, et al.
(författare)
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Indentation of thin copper film using molecular dynamics and peridynamics
- 2016
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Ingår i: Procedia Structural Integrity. - : Elsevier BV. - 2452-3216. ; 2, s. 1343-1350
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Tidskriftsartikel (refereegranskat)abstract
- In this study we investigate the efficiency of peridynamics to reproduce results from molecular dynamic simulations of nanoindentation of thin single-crystal fcc copper layers by calibration of material parameters in the peridynamic model. The free-ware LAMMPS supports both molecular dynamic and peridynamics approaches, and has been used as the common framework. Nanoindentation response for two different crystallographic orientations has been simulated using both numerical approaches and the force-displacement curves from the simulations have been compared between the different approaches. The conclusion is that proper chose of the peridynamic material parameters results in proper reproduction of the molecular dynamic results for the nanoindentationtest. This opens for peridynamic simulations of geometrically more complicated structures to a much lower computational cost, retaining the mechanical response from the atomic scale.
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| 2. |
- Azeez, Ahmed, et al.
(författare)
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Low Cycle Fatigue Modelling of Steam Turbine Rotor Steel
- 2019
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Ingår i: 9th International Conference Materials Structure & Micromechanics of Fracture (MSMF9). - : Elsevier. ; , s. 149-154, s. 149-154
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Konferensbidrag (refereegranskat)abstract
- Materials in steam turbine rotors are subjected to cyclic loads at high temperature, causing cracks to initiate and grow. To allow for more flexible operation, accurate fatigue models for life prediction must not be overly conservative. In this study, fully reversed low cycle fatigue tests were performed on a turbine rotor steel called FB2. The tests were done isothermally, within temperature range of room temperature to 600 °C, under strain control with 0.8-1.2 % total strain range. Some tests included hold time to calibrate the short-time creep behaviour of the material. Different fatigue life models were constructed. The life curve in terms of stress amplitude was found unusable at 600 °C, while the life curve in terms of total strain or inelastic strain amplitudes displayed inconsistent behaviour at 500 °C. To construct better life model, the inelastic strain amplitudes were separated into plastic and creep components by modelling the deformation behaviour of the material, including creep. Based on strain range partitioning approach, the fatigue life depends on different damage mechanisms at different strain ranges. This allowed the formulation of life curves based on plasticity or creep domination, which showed creep domination at 600 °C, while at 500 °C, creep only dominates for higher strain range.
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| 3. |
- Azeez, Ahmed, 1991-, et al.
(författare)
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Stress intensity factor solution for single-edge cracked tension specimen considering grips bending effects
- 2023
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Ingår i: Procedia Structural Integrity. - 2452-3216. ; 47, s. 195-204
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Tidskriftsartikel (refereegranskat)abstract
- Using the stress intensity factor to describe the stress field around a crack has become widely adopted due to its simplicity. The stress intensity factor depends on the applied nominal stress, the crack length, and a geometrical factor. Geometrical factors can be obtained from handbook solutions or, for complicated cases, through finite element simulations. Carefully defining the geometrical factor with realistic boundary conditions is vital to obtain accurate values for the stress intensity factor. For fatigue life predictions, even a small error in the stress intensity factor may get amplified as the total fatigue life is computed through integration over thousands of crack growth increments. A commonly used specimen geometry for fatigue crack growth testing is the single-edge cracked specimen. For such a specimen, the crack on one side of the geometry introduces bending, which, to some degree, is constrained by the grips that hold the specimen in the testing rig. The effect of bending on the geometrical factor, and consequently on the stress intensity factor, is generally overlooked due to the assumption that the test rig grips are infinitely stiff. Not considering the bending effects could lead to an inaccurate evaluation of the stress intensity factor, especially for long crack lengths. This work investigated the effect of bending on the stress intensity factor for a single-edge cracked specimen. Different grip dimensions were studied to understand the degree of bending and its impact on the stress intensity factor. The work resulted in recommendations for accurately evaluating the stress intensity factor for single-edge cracked specimens.
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| 4. |
- Babu, Ramesh, et al.
(författare)
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Additive manufactured marine component - Ni Al bronze propeller
- 2021
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Ingår i: Procedia Structural Integrity. - : Elsevier. - 2452-3216. ; , s. 20-25
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Konferensbidrag (refereegranskat)abstract
- Seaworthiness, also known as Fitness For Service (FFS), assessment of marine structures and machinery components is performed in accordance with the actual ship classification society’s Rules and/or Standards. The maritime industry is for the time being taking an interest into Additive Manufacturing (AM) for the sake of design and manufacturing cost optimization. Components of particular interest appear to be valves, heat exchangers and propellers. For conventional manufactured materials, for example cast, forged, rolled, and extruded copper alloys there are well established marine classification rules and standards. Recently, Ship Classification Rules and Standards for AM materials has been published. The seaworthiness or FFS of a Ni Al bronze (NAB) marine propeller constructed by Wire Arc Additive Manufacturing (WAAM) has been scrutinized by a novel approach of combining conventional material qualification procedures with identification and data acquisition (DAQ) of essential WAAM process parameters. A 520 kg heavy marine propeller, with a diameter of 2 m, was manufactured by the South Korean company SY Metal under strict observation of DNV South Korea. In this report the authors are presenting essential WAAM process parameters and authentic mechanical properties of the Ni Al bronze WAAM marine propeller; benchmarked toward authentic NAB cast propeller data. © 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0)
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| 5. |
- Berthellemy, Jacques, et al.
(författare)
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Fatigue reinforcement during repainting for two motorway bridges
- 2019
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Ingår i: Procedia Structural Integrity. - : Elsevier BV. - 2452-3216. ; 19, s. 49-63
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Konferensbidrag (refereegranskat)abstract
- A large number of metallic structures have already reached or even exceeded the limit of their initial design fatigue life. All this paper reports and investigates about the various works carried out in order to extend the fatigue life of existing motorway bridges located in the north of France. The studied bridge is composed with two independent decks of a French motorway carrying heavy traffics for 40 years. The slabs of both bridge decks are very fine: steel-concrete composite slabs associating 8 mm steel plate and 100 mm concrete layer according to the original design of Charles Brignon, who was also a pioneer in France of modern fatigue design for bridges, using rounded gussets to attach transverse beams, which reduces the stress concentration factor at the crossing point of the flanges. The structures of the bridges were recently strengthened to extend their fatigue resistance by three different methods which are: Addition of a continuous welded steel plate inclined outside of the edge girders to increase the safety at the Ultimate Limit State (ULS) and the robustness in fatigue of the bottom steel flanges. The inclined additional plate supported by the webs and the free bottom flanges Post weld treatment with Tungsten Inert Gas (TIG) dressing of the welded cross-beams connection gussets were performed. Bonding of CFRP carbon fibres on the bottom steel flanges of the main beams at the extremities of the welded existing cover-plates. These fibres need a high elastic modulus of 400 GPa. The interactions between both fatigue and anticorrosion life extension works are discussed. An innovative option of mixed complete-partial sandblasting methods was proved more economic than the usual complete sandblasting method and performed. The initial conception with two independent decks carrying the highway showed itself particularly relevant for the implementation of heavy repairs. The traffic deviation on the other deck allowed to work on each deck without stopping the traffic.
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| 6. |
- Blixt, Kevin, et al.
(författare)
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Molecular dynamics simulations of nanometric cutting of single crystal copper sheets using a diamond tool
- 2023
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Ingår i: Materials Structure & Micromechanics of Fracture. - : Elsevier BV. - 2452-3216. ; 43, s. 9-14
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Konferensbidrag (refereegranskat)abstract
- Nanometric cutting of a single crystal copper workpiece of different crystallographic orientations by a stiff cylindrical cubic diamond tool has been investigated by MD simulations using the freeware LAMMPS. The chip evolves during the cutting process and forms depending on crystal orientation, cutting velocity and tool geometry. It was found that no significant difference in the cutting force magnitude was observed for different crystallographic orientations despite significant differences in deformation patterns. After tool passage the surface is smooth and no elastic recovery was detected. Instead, a grain structure with areas surrounded by dislocation clusters form in the tool wake. Increasing the cutting velocity promotes chip formation and chip folding, thus increasing the chip thickness.
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| 7. |
- Bödeker, Felix, et al.
(författare)
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A novel FFT-based homogenization scheme for cohesive zones
- 2022
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Ingår i: Procedia Structural Integrity. - : Elsevier. - 2452-3216. ; 42, s. 490-497
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Tidskriftsartikel (refereegranskat)abstract
- Cohesive Zone Models with finite thickness are widely used for the fracture mechanical modeling of layers of material, e.g., adhesives. Within this approach, the whole layer is modeled as a Cohesive Zone. Moreover, computational homogenization techniques are crucial for the development of advanced engineering materials, which are often heterogeneous. Compared to the classical Finite Element Method (FEM), computationally more efficient solvers based on the Fast Fourier Transform (FFT) are expected to reduce the computational effort needed for the homogenization. Originated from an existing method for the computational homogenization of Cohesive Zones using FEM, a novel FFT-based homogenization scheme for Cohesive Zone Models was developed. Our implementation of the FFT solver uses the Barzilai-Borwein scheme and a non-local ductile damage model for the fracture behavior. Finally, the method is applied to the core material of HybrixTM metal sandwich plates, and the good agreement with experimental results in opening mode I is shown.
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| 8. |
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| 9. |
- Calmunger, Mattias, 1986-, et al.
(författare)
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Thermomechanical Fatigue of Heat Resistant Austenitic Alloys
- 2023
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Ingår i: Procedia Structural Integrity. - : Elsevier. - 2452-3216. ; 43, s. 130-135
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Tidskriftsartikel (refereegranskat)abstract
- Rising global energy consumption and the increase in emissions of greenhouse gases (e.g. CO2) causing global warming, make need for more sustainable power generation. This could be accomplished by increasing the efficiency of the biomass-fired power plants, which is achieved by increasing the temperature and pressure. In addition, flexible generation of power is critical if only renewable power generation is to be achieved and this will increase the number of start-and stop cycles. Cyclic condition in a long-term high temperature environment is an operation process that such materials must withstand, in order to satisfy the needs for future power generation.Commonly austenitic stainless steel are used for critical components of power plants. Because of future change in operating conditions, further investigations are needed to verify that the demands on safety for cyclic long-term usage is fulfilled. This work includes investigation of two commercial austenitic steels: Esshete 1250 and Sanicro 25. The materials were exposed to thermomechanical fatigue (TMF) in strain control under In-Phase and Out-of-Phase conditions and main testing temperature ranges of 100-650°C and 100-800°C respectively. Some of the specimens were pre-aged to simulate prolonged service condition. Mechanical test data were obtained and analysed in order to define the TMF performance of the investigated alloys. The differences in performance were discussed in relation to mechanical and microstructural characterization.
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| 10. |
- Edgren, Martin, et al.
(författare)
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Evaluation of HFMI as a Life Extension Technique for Welded Bridge Details
- 2019
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Ingår i: Procedia Structural Integrity. - : Elsevier BV. - 2452-3216. ; 19, s. 73-80
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Konferensbidrag (refereegranskat)abstract
- Published by Elsevier B.V. In this current study, HFMI technique is used to study the possibility to extend the fatigue life of pre-fatigued flange gusset welds typically found in girder bridges. The results from the study are also compared with results found in the literature for other more conventional techniques for retrofitting, e.g. cut-outs. The study also aims to investigate if the IIW HFMI recommendations could be applied for existing steel structures and that equal fatigue strength improvement could be claimed for prefatigued structures. Furthermore, new recommendations for structural hot spot stress type B are suggested for HFMI treated welds, applicable to flange guest welds. The results indicate that the HFMI could be used for welded bridge details rehabilitation as a competing technology with conventional cut-out. Furthermore, the results indicate that the IIW recommendations for HFMI fatigue strength improvement could also be applied for pre-fatigued welded details. © 2019 The Authors.
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