| 1. |
- Andersson Hagiwara, Magnus, et al.
(författare)
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A shorter system delay for haemorrhagic stroke than ischaemic stroke among patients who use emergency medical service
- 2018
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Ingår i: Acta Neurologica Scandinavica. - : Hindawi Limited. - 0001-6314 .- 1600-0404. ; 137:5, s. 523-530
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Tidskriftsartikel (refereegranskat)abstract
- ObjectivesWe compare various aspects in the early chain of care among patients with haemorrhagic stroke and ischaemic stroke. Materials & methodsThe Emergency Medical Services (EMS) and nine emergency hospitals, each with a stroke unit, were included. All patients hospitalised with a first and a final diagnosis of stroke between 15 December 2010 and 15 April 2011 were included. The primary endpoint was the system delay (from call to the EMS until diagnosis). Secondary endpoints were: (i) use of the EMS, (ii) delay from symptom onset until call to the EMS; (iii) priority at the dispatch centre; (iv) priority by the EMS; and (v) suspicion of stroke by the EMS nurse and physician on admission to hospital. ResultsOf 1336 patients, 172 (13%) had a haemorrhagic stroke. The delay from call to the EMS until diagnosis was significantly shorter in haemorrhagic stroke. The patient's decision time was significantly shorter in haemorrhagic stroke. The priority level at the dispatch centre did not differ between the two groups, whereas the EMS nurse gave a significantly higher priority to patients with haemorrhage. There was no significant difference between groups with regard to the suspicion of stroke either by the EMS nurse or by the physician on admission to hospital. ConclusionsPatients with a haemorrhagic stroke differed from other stroke patients with a more frequent and rapid activation of EMS.
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| 2. |
- Balachandramurthi, Arun Ramanathan, 1989-, et al.
(författare)
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Anisotropic fatigue properties of Alloy 718 manufactured by Electron Beam Powder Bed Fusion
- 2020
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Ingår i: International Journal of Fatigue. - : Elsevier. - 0142-1123 .- 1879-3452. ; 141
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Tidskriftsartikel (refereegranskat)abstract
- In this study, Alloy 718 specimens manufactured by Electron Beam Powder Bed Fusion process are subjected to two different post-treatments to have different microstructural features. Low cycle fatigue testing has been performed both parallel and transverse to the build direction. EB-PBF Alloy 718 exhibits anisotropic fatigue behaviour; the fatigue life is better along the parallel direction compared to the transverse direction. The anisotropy in fatigue life is related to the anisotropy in the Young’s modulus. The pseudo-elastic stress vs. fatigue life approach is presented as a potential solution to handle anisotropy in fatigue life assessment of additively manufactured engineering components. © 2020 The Authors
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| 3. |
- Balachandramurthi, Arun Ramanathan, 1989-, et al.
(författare)
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On the microstructure of laser beam powder bed fusion alloy 718 and its influence on the low cycle fatigue behaviour
- 2020
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Ingår i: Materials. - : MDPI AG. - 1996-1944 .- 1996-1944. ; 13:22
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Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing of Alloy 718 has become a popular subject of research in recent years. Understanding the process-microstructure-property relationship of additively manufactured Alloy 718 is crucial for maturing the technology to manufacture critical components. Fatigue behaviour is a key mechanical property that is required in applications such as gas turbines. Therefore, in the present work, low cycle fatigue behaviour of Alloy 718 manufactured by laser beam powder bed fusion process has been investigated. The material was tested in as-built condition as well as after two different thermal post-treatments. Three orientations with respect to the building direction were tested to evaluate the anisotropy. Testing was performed at room temperature under controlled amplitudes of strain. It was found that defects, inclusions, strengthening precipitates, and Young’s modulus influence the fatigue behaviour under strain-controlled conditions. The strengthening precipitates affected the deformation mechanism as well as the cycle-dependent hardening/softening behaviour. The defects and the inclusions had a detrimental effect on fatigue life. The presence of Laves phase in LB-PBF Alloy 718 did not have a detrimental effect on fatigue life. Young’s modulus was anisotropic and it contributed to the anisotropy in strain-life relationship. Pseudo-elastic stress vs. fatigue life approach could be used to handle the modulus-induced anisotropy in the strain-life relationship. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
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| 4. |
- Hansson, Per-Olof, 1958, et al.
(författare)
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Prehospital identification of factors associated with death during one-year follow-up after acute stroke
- 2018
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Ingår i: Brain and Behavior. - : Wiley. - 2162-3279. ; 8:6
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: In acute stroke, the risk of death and neurological sequelae are obvious threats. The aim of the study was to evaluate the association between various clinical factors identified by the emergency medical service (EMS) system before arriving at hospital and the risk of death during the subsequent year among patients with a confirmed stroke. Material and Methods: All patients with a diagnosis of stroke as the primary diagnosis admitted to a hospital in western Sweden (1.6 million inhabitants) during a four-month period were included. There were no exclusion criteria. Results: In all, 1,028 patients with a confirmed diagnosis of stroke who used the EMS were included in the analyses. Among these patients, 360 (35%) died during the following year. Factors that were independently associated with an increased risk of death were as follows: (1) high age, per year OR 1.07; 95% CI 1.05-1.09; (2) a history of heart failure, OR 2.08; 95% CI 1.26-3.42; (3) an oxygen saturation of < 90%, OR 8.05; 95% CI 3.33-22.64; and (4) a decreased level of consciousness, OR 2.19; 95% CI 1.61-3.03. Conclusions: Among patients with a stroke, four factors identified before arrival at hospital were associated with a risk of death during the following year. They were reflected in the patients' age, previous clinical history, respiratory function, and the function of the central nervous system.
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| 5. |
- Kjellsson, Henrik, et al.
(författare)
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High Temperature Fatigue Performance of Electron Beam Powder Bed Fusion Manufactured Alloy 718
- 2022
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer Nature. - 1073-5623 .- 1543-1940. ; 53, s. 2496-2514
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure and mechanical properties of additively manufactured (AM) parts have been shown to be different from that of cast and wrought counterparts. In this study, electron beam powder bed fusion (EB-PBF) fabricated Alloy 718 was exposed to three different heat treatment routes followed by strain-controlled fatigue testing at 550 degrees C. The fatigue tests were performed with specimens built with their center axis parallel and transverse relative to the build direction. The microstructure showed saturated precipitation of delta-Ni3Nb after repeated solution treatment at 954 degrees C. In contrast, no delta-Ni3Nb precipitates could be observed after a single-step solution treatment at 1025 degrees C. However, the disparity of secondary phases showed no noticeable influence on the fatigue life. A significant difference in fatigue behavior was noted between the parallel and transverse directions. The specimens loaded parallel to the elongated grains showed on average similar to 5x greater life in comparison to the perpendicularly loaded specimens. Compared to corresponding heat-treated material conditions tested at ambient temperature, the specimens showed lower life at high strain amplitude and superior life at low strain amplitude. Moreover, competitive internal and surface failure modes were observed at the lower strain amplitudes while for the higher strain ranges, surface failure modes dominated. (C) The Author(s) 2022
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| 6. |
- Sadeghi, Esmaeil, 1985-, et al.
(författare)
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Fatigue crack initiation and propagation in Alloy 718 with a bimodal grain morphology built via electron beam-powder bed fusion
- 2021
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Ingår i: Materials Science & Engineering. - : Elsevier Ltd. - 0921-5093 .- 1873-4936. ; 827
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Tidskriftsartikel (refereegranskat)abstract
- A unique melting strategy was implemented in electron beam-powder bed fusion (EB-PBF) of Alloy 718, resulting in the formation of a bimodal grain morphology consisting of fine equiaxed and columnar grains. The microstructure was preserved following various thermal post-treatments. The post-treated specimens were exposed to low cycle fatigue (LCF), and fatigue crack growth (FCG) tests in ambient air at 600 °C under pure and dwell-time (120 s) fatigue cycles. Clustered inclusions spanned a region of 100-600 µm in length acted as the crack initiation site, reducing the specimens' total fatigue life. When compared to pure fatigue cycles, dwell-time fatigue cycles reduced LCF life by approximately 35%, regardless of the thermal post-treatments. Due to a high fraction of grain boundary area in the as-built EB-PBF specimens, oxygen diffusion across the grain boundaries was enhanced. The intergranular fracture mode was favored in the plastic zone ahead of the crack tip, leading to rapid crack growth. No unbroken ligaments behind the crack front were found by high-resolution X-ray computed tomography, which was consistent with a large crack opening displacement linked to severe deformation around the crack tip.
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