| 1. |
- Andersson, Håkan, 1970-
(författare)
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A Co-Simulation Approach for Hydraulic Percussion Units
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This Licentiate of Engineering thesis concerns modelling and simulation of hydraulic percussion units. These units are often found in equipment for breaking or drilling in rock and concrete, and are also often driven by oil hydraulics, in which complex fluid-structure couplings are essential for their operation.Current methodologies used today when developing hydraulic percussion units are based on decoupled analyses, which are not correctly capturing the important coupled mechanisms. Hence, an efficient method for coupled simulations is of high importance, since these mechanisms are critical for the function of these units. Therefore, a co-simulation approach between a 1D system simulation model representing the fluid system and a structural 3D FE-model is proposed.This approach is presented in detail, implemented for two well-known simulation tools and evaluated for a simple but relevant model. The Hopsan simulation tool was used for the fluid system and the FE-simulation software LS-DYNA was used for the structural mechanics simulation. The co-simulation interface was implemented using the Functional Mock-up Interface-standard.The approach was further developed to also incorporate multiple components for coupled simulations. This was considered necessary when models for the real application are to be developed. The use of two components for co-simulation was successfully evaluated for two models, one using the simple rigid body representation, and a second where linear elastic representations of the structural material were implemented.An experimental validation of the co-simulation approach applied to an existing hydraulic hammer was performed. Experiments on the hydraulic hammer were performed using an in-house test rig, and responses were registered at four different running conditions. The co-simulation model was developed using the same approach as before. The corresponding running conditions were simulated and the responses were successfully validated against the experiments. A parameter study was also performed involving two design parameters with the objective to evaluate the effects of a parameter change.This thesis consists of two parts, where Part I gives an introduction to the application, the simulation method and the implementation, while Part II consists of three papers from this project.
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| 2. |
- Andersson, Håkan, et al.
(författare)
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A co-simulation method for system-level simulation of fluid-structure couplings in hydraulic percussion units
- 2017
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Ingår i: Engineering with Computers. - : SPRINGER. - 0177-0667 .- 1435-5663. ; 33:2, s. 317-333
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Tidskriftsartikel (refereegranskat)abstract
- This paper addresses a co-simulation method for fluid power driven machinery equipment, i.e. oil hydraulic machinery. In these types of machinery, the fluid-structure interaction affects the end-product performance to a large extent, hence an efficient co-simulation method is of high importance. The proposed method is based on a 1D system model representing the fluid components of the hydraulic machinery, within which structural 3D Finite Element (FE) models can be incorporated for detailed simulation of specific sub-models or complete structural assemblies. This means that the fluid system simulation will get a more accurate structural response, and that the structural simulation will get more correct fluid loads at every time step, compared to decoupled analysis. Global system parameters such as fluid flow, performance and efficiency can be evaluated from the 1D system model simulation results. From the 3D FE-models, it is possible to evaluate displacements, stresses and strains to be used in stress analysis, fatigue evaluation, acoustic analysis, etc. The method has been implemented using two well-known simulation tools for fluid power system simulations and FE-simulations, respectively, where the interface between the tools is realised by use of the Functional Mock-up Interface standard. A simple but relevant model is used to validate the method.
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| 3. |
- Andersson, Håkan, 1970-, et al.
(författare)
-
System level co-simulation of a control valve and hydraulic cylinder circuit in a hydraulic percussion unit
- 2017
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Ingår i: Proceedings of 15:th Scandinavian International Conference on Fluid Power, June 7-9, 2017, Linköping, Sweden. - Linköping : Linköping University Electronic Press. - 9789176853696 ; , s. 225-235
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Konferensbidrag (refereegranskat)abstract
- In this study a previously developed co-simulation method that is based on a 1D system model representing the fluid components of a hydraulic machinery, within which structural 3D Finite Element (FE) models can be incorporated for detailed simulation of specific sub-models or complete structural assemblies, is further developed. The fluid system model consists of ordinary differential equation sub-models that are computationally very inexpensive, but still represents the fluid dynamics very well. The co-simulation method has been shown to work very well for a simple model representing a hydraulic driven machinery. A more complex model was set up in this work, in which two cylinders in the hydraulic circuit were evaluated. Such type of models, including both the main piston and control valves, are necessary as they represent the real application to a further extent than the simple model, of only one cylinder. Two models have been developed and evaluated, from the simple rigid body representation of the structural mechanics model, to the more complex model using linear elastic representation. The 3D FE-model facilitates evaluation of displacements, stresses, and strains on a local level of the model. The results can be utilised for fatigue assessment, wear analysis and for predictions of noise radiation.
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| 4. |
- Ewest, Daniel, et al.
(författare)
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COMPARISON BETWEEN LINEAR AND NON-LINEAR FRACTURE MECHANICS ANALYSIS OF EXPERIMENTAL DATA FOR THE DUCTILE SUPERALLOY HAYNES 230
- 2015
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Ingår i: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2015, VOL 7A. - : ASME Press. - 9780791856765
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Konferensbidrag (refereegranskat)abstract
- Vith increasing use of renewable energy sources, an industrial us turbine is often a competitive solution to balance the power rid. However, life robustness approaches for gas turbine corn9nents operating under increasingly cyclic conditions, is a chalmging task. Ductile superalloys, as Haynes 230, are often used n stationary gas turbine hot parts such as combustors. The main cad for such components is due to non -homogeneous thermal xpansion within or between parts. As the material is ductile Jere is considerable redistribution of stresses and strains due to nelastic deformations during the crack initiation phase. There ore, the subsequent crack growth occurs through a material with :gnificant residual stresses and strains. In this work, fatigue ack propagation experiments, including the initiation phase, ave been performed on a single edge notched specimen under train controlled conditions. The test results are compared to -acture mechanics analyses using the linear AK and the non near AJ approaches, and an attempt to quantify the difference 2 terms of a life prediction is made. For the tested notched gemetry, material and strain ranges, the difference in the results using AKeff or ATeff are larger than the scatter seen when fitting the model to the experimental data. The largest differences can be found for short crack lengths, when the cyclic plastic work is the largest. The AJ approach clearly shows better agreement with the experimental results in this regime.
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| 5. |
- Ewest, Daniel, et al.
(författare)
-
Comparison between linear and non-linear fracture mechanics analysis of experimental data for the ductile superalloy Haynes 230
- 2016
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Ingår i: Journal of engineering for gas turbines and power. - : ASME Press. - 0742-4795 .- 1528-8919. ; 138:6, s. 062101-1-062101-7
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Tidskriftsartikel (refereegranskat)abstract
- With increasing use of renewable energy sources, an industrial gas turbine is often a competitive solution to balance the power grid. However, life robustness approaches for gas turbine components operating under increasingly cyclic conditions are a challenging task. Ductile superalloys, as Haynes 230, are often used in stationary gas turbine hot parts such as combustors. The main load for such components is due to nonhomogeneous thermal expansion within or between parts. As the material is ductile, there is considerable redistribution of stresses and strains due to inelastic deformations during the crack initiation phase. Therefore, the subsequent crack growth occurs through a material with significant residual stresses and strains. In this work, fatigue crack propagation experiments, including the initiation phase, have been performed on a single edge notched specimen under strain controlled conditions. The test results are compared to fracture mechanics analyses using the linear ΔK and the nonlinear ΔJ approaches, and an attempt to quantify the difference in terms of a life prediction is made. For the tested notched geometry, material, and strain ranges, the difference in the results using ΔKeff or ΔJeff is larger than the scatter seen when fitting the model to the experimental data. The largest differences can be found for short crack lengths, when the cyclic plastic work is the largest. The ΔJ approach clearly shows better agreement with the experimental results in this regime.
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| 6. |
- Ewest, Daniel, et al.
(författare)
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Fatigue crack propagation in a ductile superalloy at room temperature and extensive cyclic plastic flow
- 2015
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Ingår i: International Journal of Fatigue. - : ELSEVIER SCI LTD. - 0142-1123 .- 1879-3452. ; 80, s. 40-49
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Tidskriftsartikel (refereegranskat)abstract
- Fatigue crack propagation experiments under both force and displacement control have been performed on the wrought superalloy Haynes 230 at room temperature, using a single edge notched specimen. The force controlled tests are nominally elastic, and the displacement controlled tests have nominally large plastic hysteresis at the beginning of the tests, but saturates towards linear elastic conditions as the crack grows. As some tests are in the large scale yielding regime, a non-linear fracture mechanics approach is used to correlate crack growth rates versus the fracture parameter Delta J. It is shown that crack closure must be accounted for, to correctly model the crack growth seen in all the tests in a unified manner. For the force controlled small scale yielding tests the Newman crack closure model was used. The Newman equation is however not valid for large nominal cyclic plasticity, instead the crack closure in the displacement controlled tests is extracted from the test data. A good agreement between all tests is shown, when closure is accounted for and effective values of Delta J are used.
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| 7. |
- Ewest, Daniel, et al.
(författare)
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Isothermal and thermomechanical fatigue crack propagation in both virgin and thermally aged Haynes 230
- 2019
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Ingår i: International Journal of Fatigue. - : ELSEVIER SCI LTD. - 0142-1123 .- 1879-3452. ; 120, s. 96-106
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Tidskriftsartikel (refereegranskat)abstract
- Fatigue crack propagation tests under both isothermal and non-isothermal thermomechanical fatigue conditions have been performed on wrought Haynes 230, a ductile combustor material. A number of specimens were thermally aged by pre-straining and subsequent furnace exposure for 3000 h at 600 degrees C. The tests were performed both under load and strain control, between room temperature and 600 degrees C. The thermally aged notched specimens show a decrease in the crack initiation life, similar to results previously reported for smooth test specimens at room temperature. For the crack growth rates, the effects of thermal ageing were less pronounced than for crack initiation. Further, the tests have been simulated using the finite element method to calculate the crack driving force, where the plasticity induced crack closure is handled with a full history description. A temperature dependent linear kinematic hardening plasticity law has been adopted for describing the material behaviour between room temperature and 600 degrees C. A post-processing tool was used in which the plasticity induced crack opening level was calculated, followed by a calculation of the effective Delta J range for each crack length. The adopted procedure yields good correlation between the different tests, under both isothermal and non-isothermal conditions.
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| 8. |
- Ewest, Daniel
(författare)
-
Modelling and experimental evaluation of non-linear fatigue crack propagation in a ductile superalloy
- 2016
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fatigue life evaluation is an important part in the design process of an industrial gas turbine. The fatigue life can be divided into crack initiation and crack propagation, and not to address the crack propagation part usually yields a non-conservative and overcomplicated design. Historically a lot of attention has been directed towards the crack initiation, but the crack propagation part in an industrial gas turbine context has not been given the same attention due to limitations in theoretical modelling, lack of test possibilities and that the design requirements have been fulfilled within the initiation life. However, with the need to reduce service down time and to improve performance, the crack propagation life needs to be further accounted for. As an example, cracks that emerge from notches or other stress concentrations grow under non-elastic conditions, which cannot be modelled with linear theories.In this Licentiate of Engineering thesis a non-linear approach is put forward in which the plastic contribution in fatigue crack propagation is addressed and accounted for. The theoretical background is not new, but the finite element implementation done was, to the author knowledge, not available. This numerical post processing tool can calculate the non-linear ΔJ value for an arbitrary 2D-geometry. It was used to produce an expression for a non-linear geometry factor used in a simple expression for estimation of ΔJ in a test evaluation context. Room temperature tests were performed on a single notch specimen, under both displacement and force control. The latter were carried out in order to show the behaviour under small scale yielding conditions, while the displacement controlled testing was to show large scale yielding at the beginning of the tests. It was shown that all the test results could be collected in a Paris law type plot with ΔJ if the crack closure effect is taken into account. Furthermore, a study was performed where both a linear and a non-linear approach are applied on the displacement controlled tests. It was concluded that for the studied test series, the linear fatigue fracture parameter ΔK underestimates the crack growth behaviour if the elasto-plastic stresses from the tests are used, hence yielding non-conservative results.Since this project focuses on non-linear crack propagation at thermo-mechanical conditions a crack length description is put forward, which simplifies and increases the accuracy of crack length measurements in fatigue crack propagation tests. It has also been shown that irrespectively of the crack initiation location in a single edge notch specimen the data fall on one curve, meaning that no care has to be taken regarding this aspect when evaluating crack length with the modified compliance method put forward in Paper III.This Licentiate of Engineering thesis consists of two parts, where Part I gives an introduction to the subject, while Part II consists of three papers.
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| 9. |
- Lindström, Thomas, et al.
(författare)
-
Crack initiation prediction of additive manufactured ductile nickel-based superalloys
- 2018
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Ingår i: 12TH INTERNATIONAL FATIGUE CONGRESS (FATIGUE 2018). - : E D P SCIENCES.
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Konferensbidrag (refereegranskat)abstract
- A model to predict crack initiation life of an additive manufactured nickel-based superalloy similar to Hastelloy X subjected to low-cycle fatigue loading at room temperature has been developed, taking material anisotropy into account. An anisotropic constitutive model based on the Hill yield criterion was developed, with linear kinematic hardening up to a saturation value of the back stress, above which the material behaves perfectly plastic. Low-cycle fatigue experiments has been performed on additive manufactured smooth bars with two different build orientations, with an angle of 0 degrees and 90 degrees relative to the building platform. A total of 20 experiments at room temperature were conducted with different strain ranges and R-values. To predict the crack initiation life of the specimens, a model based on the Smith-Watson-Topper (SWT) parameter has been established, where ten of the specimens were used to calibrate the initiation model, and the remaining specimens were used for validation. Using this model, the obtained crack initiation life agrees well with the experiments.
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| 10. |
- Andersson, Håkan, et al.
(författare)
-
Validation of a co-simulation approach for hydraulic percussion units applied to a hydraulic hammer
- 2019
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Ingår i: Advances in Engineering Software. - : ELSEVIER SCI LTD. - 0965-9978 .- 1873-5339. ; 131, s. 102-115
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Tidskriftsartikel (refereegranskat)abstract
- In this study, a previously developed co-simulation approach has been adopted to simulate the responses of an existing hydraulic hammer product. This approach is based on a 1D system model representing the fluid components and a 3D finite element model representing the structural parts of the hydraulic hammer. The simulation model was validated against four experiments with different running conditions. The corresponding set-ups were analysed using the co-simulation method in order to evaluate the overall responses. A parameter study was also performed involving the working pressure and the restrictor diameter, with the objective to validate that a parameter change in the simulation model will affect the input and output power in the same direction as in the experiments. The experimental responses used in the validation were time history data of fluid pressure, component position and acceleration, and structural stresses. The experiments result in high frequency and high amplitude excitations of the hydraulic hammer and thus require a model with a high resolution of the model dynamics. The conclusion of the validation is that the simulation model is able to replicate the experimental responses with high accuracy including the high frequency dynamics. The favourable outcome of the validation makes the described co-simulation approach promising as an efficient tool for a wide range of other applications where short time duration mechanisms need to be studied.
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| 11. |
- Busse, Christian, et al.
(författare)
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A FINITE ELEMENT STUDY OF THE EFFECT OF CRYSTAL ORIENTATION AND MISALIGNMENT ON THE CRACK DRIVING FORCE IN A SINGLE-CRYSTAL SUPERALLOY
- 2016
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Ingår i: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2016, VOL 7A. - : AMER SOC MECHANICAL ENGINEERS. - 9780791849835
-
Konferensbidrag (refereegranskat)abstract
- The elastic and plastic anisotropy of the single-crystal materials bring many difficulties in terms of modeling, evaluation and prediction of fatigue crack growth. In this paper a single-crystal material model has been adopted to a finite element-environment, which is paired with a crack growth tool. All simulations are performed in a three-dimensional context. This methodology makes it possible to analyze complex finite element-models, which are more application-near than traditional two-dimensional models. The influence of the crystal orientation, as well as the influence of misalignments of the crystal orientation due to the casting process are investigated. It is shown that both the crystal orientation and the misalignment from the ideal crystal orientation are important for the crack driving force. The realistic maximum limit of 10 degrees misalignment is considered. It can be seen that crack growth behavior is highly influenced by the misalignment. This knowledge is of great interest for the industry in order to evaluate the crack growth in single-crystal components more accurately.
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| 12. |
- Busse, Christian, 1989-
(författare)
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Aspects of Crack Growth in Single-Crystal Nickel-Base Superalloys
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This Licentiate of Engineering thesis is a product of the results generated in the research project KME-702, which comprises modelling, microstructure investigations and material testing of cast nickel-base superalloys.The main objective of this work is to model the fatigue crack propagation behaviour in single-crystal nickel-base superalloys. To achieve this, the influence of the crystal orientations on the cracking behaviour is assessed. The results show that the crystal orientation is strongly affecting the material response and must be accounted for. Furthermore, a linear elastic crack driving force parameter suitable for describing crystallographic cracking has been developed. This parameter is based on resolved anisotropic stress intensity factors and is able to predict the correct crystallographic cracking plane after a transition from a Mode I crack. Finally, a method to account for inelastic deformations in a linear elastic fracture mechanics context was investigated. A residual stress field is extracted from an uncracked finite-element model with a perfectly plastic material model and superimposed on the stress field from the cracked model with a linear elastic material model to account for the inelastic deformations during the determination of the crack driving force. The modelling work is validated by material testing on two different specimen geometries at different temperatures.This Licentiate of Engineering thesis consists of two parts, where Part I gives an introduction and background to the research area, while Part II consists of three papers.
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| 13. |
- Busse, Christian, et al.
(författare)
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Evaluation of the crystallographic fatigue crack growth rate in a single-crystal nickel-base superalloy
- 2019
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Ingår i: International Journal of Fatigue. - : ELSEVIER SCI LTD. - 0142-1123 .- 1879-3452. ; 127, s. 259-267
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Tidskriftsartikel (refereegranskat)abstract
- Cracks in single-crystal nickel-base superalloys have been observed to switch cracking mode from Mode I to crystallographic cracking. The crack propagation rate is usually higher on the crystallographic planes compared to Mode I, which is important to account for in crack growth life predictions. In this paper, a method to evaluate the crystallographic fatigue crack growth rate, based on a previously developed crystallographic crack driving force parameter, is presented. The crystallographic crack growth rate was determined by evaluating heat tints on the fracture surfaces of the test specimens from the experiments. Complicated crack geometries including multiple crystallographic crack fronts were modelled in a three dimensional finite element context, The data points of the crystallographic fatigue crack growth rate collapse on a narrow scatter band for the crystallographic cracks indicating a correlation with the previously developed crystallographic crack driving force.
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| 14. |
- Busse, Christian, 1989-
(författare)
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Modelling of Crack Growth in Single-Crystal Nickel-Base Superalloys
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation was produced at the Division of Solid Mechanics at Linköping University and is part of a research project, which comprises modelling, microstructure investigations and material testing of cast nickel-base superalloys. The main objective of this work was to deepen the understanding of the fracture behaviour of single-crystal nickel-base superalloys and to develop a model to predict the fatigue crack growth behaviour. Frequently, crack growth in these materials has been observed to follow one of two distinct cracking modes; Mode I like cracking perpendicular to the loading direction or crystallographic crack growth on the octahedral {111}-planes, where the latter is associated with an increased fatigue crack growth rate. Thus, it is of major importance to account for this behaviour in component life prediction. Consequently, a model for the prediction of the transition of cracking modes and the correct active crystallographic plane, i.e. the crack path, and the crystallographic crack growth rate has been developed. This model is based on the evaluation of appropriate crack driving forces using three-dimensional finite-element simulations. A special focus was given towards the influence of the crystallographic orientation on the fracture behaviour. Further, a model to incorporate residual stresses in the crack growth modelling is presented. All modelling work is calibrated and validated by experiments on different specimen geometries with different crystallographic orientations. This dissertation consists of two parts, where Part I gives an introduction and background to the field of research, while Part II consists of six appended papers.
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| 15. |
- Busse, Christian, 1989-, et al.
(författare)
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Prediction of crystallographic cracking planes in single-crystal nickel-base superalloys
- 2018
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Ingår i: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 196, s. 206-223
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Tidskriftsartikel (refereegranskat)abstract
- The inherent anisotropy of single-crystal nickel-base superalloys brings many difficulties in terms of modelling, evaluation and prediction of fatigue crack growth. Two models to predict on which crystallographic plane cracking will occur is presented. The models are based on anisotropic stress intensity factors resolved on crystallographic slip planes calculated in a three-dimensional finite-element context. The developed models have been compared to experiments on two different test specimen geometries. The results show that a correct prediction of the crystallographic cracking plane can be achieved. This knowledge is of great interest for the industry and academia to better understand and predict crack growth in single-crystal materials.
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| 16. |
- Busse, Christian, et al.
(författare)
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Three-Dimensional LEFM Prediction of Fatigue Crack Propagation in a Gas Turbine Disk Material at Component Near Conditions
- 2016
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Ingår i: Journal of engineering for gas turbines and power. - : ASME. - 0742-4795 .- 1528-8919. ; 138:4
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the possibility to use linear elastic fracture mechanics (LEFM), with and without a superimposed residual stress field, to predict fatigue crack propagation in the gas turbine disk material Inconel 718 has been studied. A temperature of 400 degrees C and applied strain ranges corresponding to component near conditions have been considered. A three-dimensional crack propagation software was used for determining the stress intensity factors (SIFs) along the crack path. In the first approach, a linear elastic material behavior was used when analyzing the material response. The second approach extracts the residual stresses from an uncracked model with perfectly plastic material behavior after one loading cycle. As a benchmark, the investigated methods are compared to experimental tests, where the cyclic lifetimes were calculated by an integration of Paris law. When comparing the results, it can be concluded that the investigated approaches give good results, at least for longer cracks, even though plastic flow was taking place in the specimen. The pure linear elastic simulation overestimates the crack growth for all crack lengths and gives conservative results over all considered crack lengths. Noteworthy with this work is that the 3D-crack propagation could be predicted with the two considered methods in an LEFM context, although plastic flow was present in the specimens during the experiments.
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| 17. |
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| 18. |
- Ekström, Daniel P T, 1976, et al.
(författare)
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Climate impact optimization in concrete bridge construction
- 2017
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Ingår i: IABSE Conference, Vancouver 2017. - : International Association for Bridge and Structural Engineering (IABSE). - 9783857481536 ; , s. 1161-1168, s. 1161-1168
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Konferensbidrag (refereegranskat)abstract
- Estimates indicate that the total climate impact, from a lifecycle perspective, generated by Swedish construction processes reaches the same magnitude as emissions from all passenger cars in Sweden. A large part of the emissions from construction of roads and railways arise from production of steel and concrete used in bridges and other infrastructure structures. In this research, several cases of existing concrete bridges have been investigated. The case studies are in a very firm way analyzed, and then opportunities for reducing climate gas emissions are described and elaborated upon. Accordingly, design and dimensioning through the use of today's technology and material selection are discussed. Without developing new ways to construct bridges, or comparing concrete with other materials, a useful guide on how to use technology and opportunities that are available for constructing climate smarter versions of standard bridges today is developed and described.
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| 19. |
- Ekström, Daniel P T, 1976, et al.
(författare)
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Integrated project teams in early design stages - Key variables influencing cost effectiveness in bridge building
- 2016
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Ingår i: 19th IABSE Congress Stockholm, 21-23 September 2016, Challenges in Design and Construction of an Innovative and Sustainable Built Environment. ; , s. 598-606
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Konferensbidrag (refereegranskat)abstract
- The construction industry is usually regarded as a complex, multidisciplinary and project focused environment. It is also regularly identified as a one-of-a-kind nature, hence focus is on the uniqueness of projects rather than in similarities. The results presented in this article are based on questionnaire addressed to clients, contractors, and designers, mainly active within the Swedish infrastructure sector. The purpose is to highlight key-variables influencing cost effectiveness for the organization of integrated project teams, designing of projects, and construction at site. The results indicate that more attention needs to be paid to the actual project setting if to fully gain the benefits from integrated project teams. Further, the results indicates that it is mainly project culture; collaboration and social relationships, and project competence, the ability to solve mutual issues, that needs to be developed.
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| 20. |
- Eriksson, Robert, et al.
(författare)
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Evaluation of notch effects in low cycle fatigue of alloy 718 using critical distances
- 2018
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Ingår i: 12TH INTERNATIONAL FATIGUE CONGRESS (FATIGUE 2018). - : E D P SCIENCES.
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Konferensbidrag (refereegranskat)abstract
- Gas turbine disks contain many notch-like features acting as stress raisers. The fatigue life based on the notch root stress may be overly conservative as the steep stress gradient in front of the notch may give rise to so-called notch support. In the current work, the theory of critical distances was applied to the prediction of the total fatigue life of low cycle fatigued, notched specimens made from alloy 718. The fatigue tests were performed at 450 degrees C and 550 degrees C. It was found that, for lives shorter than 5000-10000 cycles, the notched specimens had longer lives than would have been expected based on the notch root strain. For lives longer than 5000-10000 cycles, there were no notch support. The life prediction for notched specimens could be significantly improved by basing the prediction on the strain chosen some distance from the notch (the critical distance). An expression for calculating the critical distance based on the notch root strain was suggested.
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| 21. |
- Ewest, D., et al.
(författare)
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A modified compliance method for fatigue crack propagation applied on a single edge notch specimen
- 2016
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Ingår i: International Journal of Fatigue. - London : ELSEVIER SCI LTD. - 0142-1123 .- 1879-3452. ; 92, s. 61-70
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Tidskriftsartikel (refereegranskat)abstract
- Crack length measurements with high accuracy are often difficult to achieve during fatigue crack propagation testing under non-isothermal conditions. In this work a modified approach to the compliance method defined in e.g. ASTM E647 is described, which is better suited for high loads, varying temperatures and for taking the scatter in Youngs modulus into account. A numerical finite element study is performed for a single edge notch specimen, to investigate the influence of initiation locations on the accuracy of the method. The change in cracked area versus change in stiffness for three different cases are numerically shown to collapse to one curve, i.e. the result is not significantly affected by how the crack is initiated. The numerical study is compared to results from two experiments using different materials, with heat tinting during the tests for extracting snapshots of the crack fronts. A good agreement between the experiments and the numerical study is shown. A new compliance curve and a new geometry function for the stress intensity factor is proposed for the single edge notch specimen. (C) 2016 Elsevier Ltd. All rights reserved.
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| 22. |
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| 23. |
- Gunnarsson, Adrian, 1990, et al.
(författare)
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Radiative Heat Transfer Modeling and in Situ Diagnostics of Soot in an 80 kWth Propane Flame with Varying Feed-Gas Oxygen Concentration
- 2018
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 57:36, s. 12288-12295
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Tidskriftsartikel (refereegranskat)abstract
- This work presents experimental measurements of various 80 kWth propane flames, using a swirl burner, and modeling of the radiative heat transfer. The combustion conditions were altered by varying the oxygen concentration in the oxidant within range of 21-32%, while keeping the thermal input and oxygen-to-fuel ratio constant. Temperature, gas composition, and radiative intensity were measured using probes, while the soot volume fraction was quantified using nonintrusive laser-induced incandescence. The radiative intensity and the soot volume fraction increased with an increased oxygen concentration in the flame. When the oxygen concentration exceeded 27% the soot volume fraction was increased more than 14-fold. The results reveal the potential of promoting radiative heat transfer by increasing the oxygen concentration; the total radiative intensity becomes dominated by the soot particle contribution. In addition, laser-induced incandescence was successfully used for instantaneous and spatially resolved soot measurements in this type of furnace being at a technical scale.
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| 24. |
- Gunnarsson, Adrian, 1990, et al.
(författare)
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Soot Formation and Radiative Heat Transfer in Oxy-Fuel and Oxygen-Enhanced Propane Flames
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This work aims to determine radiation-related properties of various propane flames, where the measurements were conducted in a down-fired and cylindrical 100 kW furnace equipped with a swirl burner. The combustion conditions were varied by altering the composition of the oxidant. For six cases, oxygen-enhanced air was used, step-wise varying the oxygen concentration in the oxidant from 21% to 32%. Also for six cases, the furnace was operated in oxy-fuel mode, recirculating dry flue gas and varying the oxygen concentration from 25% to 42%. All measurements were conducted at an axial distance of 384 mm from the burner. Temperature, gas composition and radiative intensity were measured (by intrusive instruments) along the furnace diameter using probes while the soot volume fraction was quantified using non-intrusive laser induced incandescence (LII). An Nd:YAG laser at wavelength 1064 nm was used for the LII measurements, and a diode laser at wavelength 808 nm was used for extinction measurements for absolute calibration of the LII-signal. Two-dimensional images of the LII-signal were captured using an intensified CCD-camera and radial profiles of the soot volume fraction were achieved. The soot volume fraction increased with increasing oxygen concentration in the feed gas, and, when the oxygen concentration exceeded 30 and 42% for the oxygen-enriched air and oxy-fuel cases, respectively, the soot formation was substantially enhanced with volume fractions more than 10 times higher than for lower oxygen concentrations. The higher oxygen concentration required for the increased soot production in the oxy-fuel combustion cases is mainly due to the higher heat capacity of carbon dioxide that lowers the flame temperatures. The data collected from the measurements was used to model the radiative intensity using a discrete transfer model. In this model, gas properties are calculated using a statistical narrow-band model and particle properties are calculated using Rayleigh theory. Good agreement was achieved between the modeled and measured radiative intensity for most flames and the use of an LII-system to measure the soot volume fraction in this type of furnace was successful.
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| 25. |
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| 26. |
- Leidermark, Daniel, et al.
(författare)
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Procedures for handling computationally heavy cyclic load cases with application to a disc alloy material
- 2019
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Ingår i: Materials at High Temperature. - : TAYLOR & FRANCIS LTD. - 0960-3409 .- 1878-6413. ; 36:5, s. 447-458
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Tidskriftsartikel (refereegranskat)abstract
- The computational efficiency in analysing cyclically loaded structures is a highly prioritised issue for the gas turbine industry, as a cycle-by-cycle simulation of e.g. a turbine disc is far too time consuming. Hence, in this paper, the efficiency of two different procedures to handle computational expansive load cases, a numerical extrapolation and a parameter modification procedure, are evaluated and compared to a cycle-by-cycle simulation. For this, a local implementation approach was adopted, where a user-defined material subroutine is used for the cycle jumping procedures with good results. This in contrast to a global approach where the finite element simulation is restarted and mapping of the solution is performed at each cycle jump. From the comparison, it can be observed that the discrete parameter modification procedure is by margin the fastest one, but the accuracy depends on the material parameter optimisation routine. The extrapolation procedure can incorporate stability and/or termination criteria.
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| 27. |
- Nguyen, Duong, 1986, et al.
(författare)
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Cartilage Tissue Engineering by the 3D Bioprinting of iPS Cells in a Nanocellulose/Alginate Bioink
- 2017
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Cartilage lesions can progress into secondary osteoarthritis and cause severe clinical problems in numerous patients. As a prospective treatment of such lesions, human-derived induced pluripotent stem cells (iPSCs) were shown to be 3D bioprinted into cartilage mimics using a nanofibrillated cellulose (NFC) composite bioink when co-printed with irradiated human chondrocytes. Two bioinks were investigated: NFC with alginate (NFC/A) or hyaluronic acid (NFC/HA). Low proliferation and phenotypic changes away from pluripotency were seen in the case of NFC/HA. However, in the case of the 3D-bioprinted NFC/A (60/40, dry weight % ratio) constructs, pluripotency was initially maintained, and after five weeks, hyaline-like cartilaginous tissue with collagen type II expression and lacking tumorigenic Oct4 expression was observed in 3D -bioprinted NFC/A (60/40, dry weight % relation) constructs. Moreover, a marked increase in cell number within the cartilaginous tissue was detected by 2-photon fluorescence microscopy, indicating the importance of high cell densities in the pursuit of achieving good survival after printing. We conclude that NFC/A bioink is suitable for bioprinting iPSCs to support cartilage production in co-cultures with irradiated chondrocytes.
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| 28. |
- Simonsson, J., et al.
(författare)
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In-situ soot characterization of propane flames and influence of additives in a 100 kW oxy-fuel furnace using two-dimensional laser-induced incandescence
- 2019
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 37:1, s. 833-840
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Tidskriftsartikel (refereegranskat)abstract
- In-situ soot characterization has been successfully performed in a 100 kW(th) down-fired oxy-fuel test furnace using laser-induced incandescence (LII) and extinction measurements. Primarily non-premixed propane flames were investigated in oxy-fuel mode with various concentrations of oxygen in the oxidant. The turbulent flame character was manifested through two-dimensional single-shot LII signals from soot showing strong spatial variations as well as local temporal variations. The LII signals were calibrated to soot volume fractions, f(v) , using in-situ extinction in the same spatial regions of the furnace. The results show increased f(v) for increasing oxygen concentration in the oxidant, which is related to increased temperatures as well as decreased mixing inside the furnace due to lowered total flow. For some measurement cases, the influence of additives was studied for flames in oxy-fuel and air environments. The results showed increased f(v) for additions of SO2 and NO for oxy-fuel conditions, while a decrease of f(v) was found for air-fed flames. Also, a large decrease in f(v) was found for water injection in the air-fed flames, and a slightly larger decrease for addition of KCl dissolved in water with the same amount of injected solution. Uncertainties in performing soot volume fraction measurements using LII and extinction in this large-scale furnace are discussed, and mainly considered to be uncertainties in E(m) for soot, the spatial variation of the laser fluence in the large imaged area, and the estimation of the absorption length during extinction calibration.
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