| 1. |
- 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
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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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| 2. |
- Busse, Christian, et al.
(författare)
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Crystallographic crack propagation rate in single-crystal nickel-base 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
- Single-crystal nickel-base superalloys are often used in the hot sections of gas turbines due to their good mechanical properties at high temperatures such as enhanced creep resistance. However, the anisotropic material properties of these materials bring many difficulties in terms of modelling and crack growth prediction. Cracks tend to switch cracking mode from Mode I cracking to crystallographic cracking. Crystallographic crack growth is often associated with a decrease in crack propagation life compared to Mode I cracking and this must be taken into account for reliable component lifing. In this paper a method to evaluate the crystallographic crack propagation rate related to a crystallographic crack driving force parameter is presented. The crystallographic crack growth rate is determined by an evaluation of heat tints on the fracture surface of a specimen subjected to fatigue loading. The complicated crack geometry including two crystallographic crack fronts is modelled in a three dimensional finite element context. The crack driving force parameter is determined by calculating anisotropic stress intensity factors along the two crystallographic crack fronts by finite-element simulations and post-processing the data in a fracture mechanics tool that resolves the stress intensity factors on the crystallographic slip planes in the slip directions. The evaluated crack propagation rate shows a good correlation for both considered crystallographic cracks fronts.
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| 3. |
- 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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| 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. |
- Kolmert, Johan, et al.
(författare)
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Urinary Leukotriene E-4 and Prostaglandin D-2 Metabolites Increase in Adult and Childhood Severe Asthma Characterized by Type 2 Inflammation A Clinical Observational Study
- 2021
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Ingår i: American Journal of Respiratory and Critical Care Medicine. - NEW YORK, USA : AMER THORACIC SOC. - 1073-449X .- 1535-4970. ; 203:1, s. 37-53
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Tidskriftsartikel (refereegranskat)abstract
- Rationale: New approaches are needed to guide personalized treatment of asthma. Objectives: To test if urinary eicosanoid metabolites can direct asthma phenotyping. Methods: Urinary metabolites of prostaglandins (PGs), cysteinyl leukotrienes (CysLTs), and isoprostanes were quantified in the U-BIOPRED (Unbiased Biomarkers for the Prediction of Respiratory Diseases Outcomes) study including 86 adults with mild-to-moderate asthma (MMA), 411 with severe asthma (SA), and 100 healthy control participants. Validation was performed internally in 302 participants with SA followed up after 12-18 months and externally in 95 adolescents with asthma. Measurement and Main Results: Metabolite concentrations in healthy control participants were unrelated to age, body mass index, and sex, except for the PGE(2) pathway. Eicosanoid concentrations were generally greater in participants with MMA relative to healthy control participants, with further elevations in participants with SA. However, PGE(2) metabolite concentrations were either the same or lower in male nonsmokers with asthma than in healthy control participants. Metabolite concentrations were unchanged in those with asthma who adhered to oral corticosteroid treatment as documented by urinary prednisolone detection, whereas those with SA treated with omalizumab had lower concentrations of LTE4 and the PGD(2) metabolite 2,3-dinor-11 beta-PGF(2 alpha). High concentrations of LTE4 and PGD(2) metabolites were associated with lower lung function and increased amounts of exhaled nitric oxide and eosinophil markers in blood, sputum, and urine in U-BIOARED participants and in adolescents with asthma. These type 2 (T2) asthma associations were reproduced in the follow-up visit of the U-BIOPRED study and were found to be as sensitive to detect T2 inflammation as the established biomarkers. Conclusions: Monitoring of urinary eicosanoids can identify T2 asthma and introduces a new noninvasive approach for molecular phenotyping of adult and adolescent asthma.
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| 6. |
- Sparve, Erik, et al.
(författare)
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Prediction and Modeling of Effects on the QTc Interval for Clinical Safety Margin Assessment, Based on Single-Ascending-Dose Study Data with AZD3839
- 2014
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Ingår i: Journal of Pharmacology and Experimental Therapeutics. - : American Society for Pharmacology & Experimental Therapeutics (ASPET). - 0022-3565 .- 1521-0103. ; 350:2, s. 469-478
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Tidskriftsartikel (refereegranskat)abstract
- Corrected QT interval (QTc) prolongation in humans is usually predictable based on results from preclinical findings. This study confirms the signal from preclinical cardiac repolarization models (human ether-a-go-go-related gene, guinea pig monophasic action potential, and dog telemetry) on the clinical effects on the QTc interval. A thorough QT/QTc study is generally required for bioavailable pharmaceutical compounds to determine whether or not a drug shows a QTc effect above a threshold of regulatory interest. However, as demonstrated in this AZD3839 [(S)-1-(2-(difluoromethyl)pyridin-4-yl)-4-fluoro-1-(3-(pyrimidin-5-yl)phenyl)-1H-isoindol-3-amine hemifumarate] single-ascending-dose (SAD) study, high-resolution digital electrocardiogram data, in combination with adequate efficacy biomarker and pharmacokinetic data and nonlinear mixed effects modeling, can provide the basis to safely explore the margins to allow for robust modeling of clinical effect versus the electrophysiological risk marker. We also conclude that a carefully conducted SAD study may provide reliable data for effective early strategic decision making ahead of the thorough QT/QTc study.
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