•A high-fidelity Thermal-Fluid Dynamics framework is utilised.•The momentum contribution due to condensing vapour bubbles leads to more mixing.•Preferential element loss due to heterogeneous boiling ...of components is quantified.•Fundamental insights pertaining to L-PBF of multi-component systems are obtained.
In this work a novel mathematical framework, that fully describes the fusion and vapourisation state transitions in multi-component systems, has been applied to assist in understanding the fundamental mechanisms of defect formation and chemical homogenisation in the laser powder bed fusion process (L-PBF). Specifically, the role of vapourisation and condensation of the multi-component metallic substrate is investigated to determine the importance of properly capturing the state transitions when understanding the substrate evolution. The framework is applied to a ternary metallic system; it is revealed that entrained vapour bubbles in chemically dissimilar flows promote greater homogenisation during the condensation and collapse of these bubbles when compared to non-condensing phases. It is further shown that as the laser power density is increased, there is a greater tendency for preferential element evaporation of the lighter elements; this preferential element evaporation is quantified numerically for the first time, and shown to be a non-linear function of power density.
•Thermal-metallurgical-mechanical model for electron beam (EB) welding in SA508 Gr.4N low-alloy steel plate has been developed and validated.•Inter-part gapping occurs when EB weld centre plane is ...not restrained before welding, but the gapping distortion can be mitigated by tack-weld restraint.•High tensile stress is induced at stop-end tack weld during welding, which can be effectively reduced by increasing tack-weld extent.•Tack-weld restraint hardly affects final weld residual stress which exhibits steep gradient across heat affected zone (HAZ) boundary.•Weld-induced martensitic transformation promotes compression and suppresses tension in EB weld and HAZ, and peak tensile residual stress is concentrated in base material immediately outside HAZ.
Electron beam (EB) welding has a low tolerance to inter-part gapping distortion and can generate complicated stresses, which pose challenges to weld quality and integrity. This study investigates welding distortion and stresses in an EB welded plate made from SA508 Grade 4N low-alloy steel. A thermal-metallurgical-mechanical model was developed to predict the temperature, micro-constituents, hardness, distortion and stresses in the EB weldment; the predictions are in good agreement with experimental results. Different restraint conditions on the weld plane were modelled to examine their effects on distortion and stresses. If welding is performed with no restraint, inter-part gapping develops ahead of the beam position that could exceed the tolerance for a sound weld. In contrast, tack welds at the plate ends significantly reduce this gapping, but induce additional tensile stress at the stop-end tack weld. This stress is particularly high as the beam approaches the tack weld. Increasing the extent of the tack weld reduces the tensile stress, while increasing number of distantly distributed narrow tack welds does not help. A full through-length restraint eliminates the opening gap and minimises the development of tensile stresses ahead of the beam that could potentially break the restraint. The applied restraint on the weld plane has little effect on the final residual stress field, since this field mostly develops during cooling after the EB weld is complete. The weld-induced martensitic transformation suppressed tension or promoted compression in the EB weld and heat affected zone (HAZ). A steep gradient of residual stress exists, with high tensile stress concentrated in a narrow region immediately outside the HAZ.
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Iterative mesh-based hardness mapping Brayshaw, W. J.; Roy, M. J.; Sun, T. ...
Science and technology of welding and joining,
07/2017, Letnik:
22, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Hardness mapping permits quantification of the properties of materials over microstructurally significant lengths. A technique has been developed whereby hardness maps can be generated to account for ...specific weld geometry and further refined using an adaptive approach. Once a preliminary map is produced, subsequent indents are placed in high hardness gradient locations to decrease interpolation distances between indentation sites. The method is demonstrated with three test cases: an Al-7010 friction stir weld, an Alloy 600/82 (NeT TG6) weld and an SA508-4N/Alloy 82/316LN dissimilar metal weld. The results show that the method has identified and resolved high regions with elevated hardness gradients. This provides the ability to resolve weld regions rapidly across large areas minimising indent counts.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Introduction: Infection is a detrimental complication of operatively treated
hip fractures. The objective of this retrospective case-control study was
to evaluate the mortality, the physical function ...and the quality of life of hip
fractures complicated with infection and determine risk factors for deep
infection in hip fractures. Patients and methods: All patients with hip
fractures (31A and 31B OTA/AO) that were operatively managed over a 10-year
period that subsequently developed deep infection were included in the
study. Thirty-nine patients met the inclusion criteria. These patients were
compared with a matched control group of 198 patients without infection.
Minimum follow-up was 1 year. Mortality, Barthel index score, EQ-5D-5L,
Parker mobility score and visual analogue scale (VAS) pain score were compared between groups.
Results: Mortality at 1 month was 20.5 % and 43 % at 1 year. Half of
the infections were acute and 28 % were polymicrobial. Mortality was
greater in the infection group (43 % vs. 16.5 %, p<0.0014), and
Barthel index was inferior in the infection group (14 vs. 18, p<0.0017) compared to control group. Logistic regression analysis revealed
that time from admission to surgery was a negative factor that predisposed
to infection. Conclusions: Patients complicated with infection after a hip
fracture have higher mortality and inferior functional results. Delay from
admission to surgery predisposes to infection.
Ferritic steels experience solid-state phase transformation (SSPT), which causes volumetric changes due to differences in the atomic packing density of different phases in the steel. The importance ...of the prior austenite grain size (PAGS) as an input physical variable is assessed, for adequately modelling the anisothermal SSPT during welding of ferritic steels. The knowledge of the PAGS value pre-requires a thorough microstructural study of each particular weld, information that might be difficult to acquire. A relationship between hardness, PAGS and phase fractions is proposed to be used to feed in weld models. The case of a single-pass, autogenous, reduced-pressure electron beam weld is used for this study. The adequacy of the finite-element weld model in predicting the micro-constituents, the hardness and the residual stress is demonstrated via comparing the predicted results of the thermo-metallurgical and stress analyses with the set of corresponding experimental data. This work aims at providing a better understanding of the impact of PAGS on transformation kinetics and best practice guidelines for modelling, using an extensively validated electron beam weld model as baseline.
There are limited data on the association of diabetes mellitus (DM) and levels of glycated hemoglobin (HbA1c) with outcomes in patients with atrial fibrillation (AF).
This retrospective cohort study ...included patients who were recently hospitalized with a primary or secondary diagnosis of AF from December 2015 through June 2018. Kaplan-Meier curves and Cox-regression adjusted hazard ratios (aHR) were calculated for the primary outcome of all-cause mortality and for the secondary outcomes of cardiovascular (CV) mortality and the composite outcome of CV death or hospitalization. Competing-risk regression analyses were performed to calculate the cumulative risk of stroke, major bleeding, AF- or HF-hospitalizations adjusted for the competing risk of all-cause death. Spline curve models were fitted to investigate associations of HbA1c values and mortality among patients with AF and DM.
In total 1109 AF patients were included, of whom 373 (33.6%) had DM. During a median follow-up of 2.6 years, 414 (37.3%) patients died. The presence of DM was associated with a higher risk of all-cause mortality (aHR = 1.40 95% confidence intervals CI 1.11-1.75), CV mortality (aHR = 1.39, 95% CI 1.07-1.81), sudden cardiac death (aHR = 1.73, 95% CI 1.19-2.52), stroke (aHR = 1.87, 95% CI 1.01-3.45) and the composite outcome of hospitalization or CV death (aHR = 1.27, 95% CI 1.06-1.53). In AF patients with comorbid DM, the spline curves showed a positive linear association between HbA1c levels and outcomes, with values 7.6-8.2% being independent predictors of increased all-cause mortality, and values < 6.2% predicting significantly decreased all-cause and CV mortality.
The presence of DM on top of AF was associated with substantially increased risk for all-cause or CV mortality, sudden cardiac death and excess morbidity. HbA1c levels lower than 6.2% were independently related to better survival rates suggesting that optimal DM control could be associated with better clinical outcomes in AF patients with DM.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
OBJECTIVE:The present systematic review and meta-analysis investigated the effects of hydralazine in maternal, perinatal and neonatal outcomes in pregnant women with hypertensive disorders, compared ...with other antihypertensive drugs.
DESIGN AND METHOD:Bibliographic search was performed in medline (PubMed), cochrane central register of controlled trials (CENTRAL), cochrane pregnancy and childbirth groupʼs trial register and clinicaltrials.gov for randomized controlled clinical trials. Two authors independently extracted data and assessed risk of bias for each outcome.
RESULTS:Twenty studies with 1283 participants were included. 626 of them received hydralazine and 657 other antihypertensive treatments such as labetalol, nifedipine, ketanserin, diazoxide, urapidil, isradipine and epoprostenol. Women receiving hydralazine had higher end follow-up heart rate (WMD13.43, 95%CI0.08 to 26.79), while hydralazine was also associated with increased number of side effects (RR1.21, 95%CI1.01 to 1.45). Finally, infants of mothers that had received hydralazine had lower birthweight compared to other treatments (WMD−135.30, 95%CI−260.95 to −9.65).
CONCLUSIONS:These results do not support the use of hydralazine as first line treatment for hypertension in pregnancy. Hydralazine was associated with more maternal side effects, lower birthweight and higher maternal heart rate.
OBJECTIVE:Angiotensin converting enzyme inhibitors (ACEIs) and angiotensin II receptor blockers (ARBs) are widely used for the treatment of hypertension. However, data on their comparative efficacy ...is incomplete. The present systematic review and network meta-analysis investigated the comparative efficacy of these two drug categories in blood pressure reduction, mortality and morbidity of adults with essential hypertension.
DESIGN AND METHOD:Bibliographic search was performed in Medline (PubMed) and Cochrane Central Register of Controlled Trials (CENTRAL) for placebo- and active-controlled, double-blind randomized trials, which had studied for blood pressure reduction, mortality and/or morbidity.
RESULTS:Thirty studies with 7370 participants were included for the blood pressure reduction analysis and eight studies with 25158 participants were included for the mortality/morbidity analysis. The two pharmacological categories did not differ in lowering systolic (WMD0.59, 95%CI−0.21 to 1.38) and diastolic blood pressure (WMD0.62, 95%CI−0,06 to 1.30), all-cause mortality (RR0.96, 95%CI 0.80 to 1.14), cardiovascular mortality (RR0.87, 95%CI 0.67 to 1.14), fatal and non-fatal myocardial infarction (RR1.02, 95%CI 0.75 to 1.37) and stroke (RR1.13, 95%CI 0.87 to 1.46). ACEIs found to be superior in the development and/or hospitalization for heart failure (RR0.71, 95%CI 0.54 to 0.93).
CONCLUSIONS:ACEIs and ARBs do not differ in blood pressure reduction, mortality and morbidity in patients with essential hypertension. ACEIs were superior in the development and/or hospitalization for heart failure.
Rhythm control and rate control are both employed commonly in patients with atrial fibrillation (AF) and heart failure (HF), but limited real-world data exist on them. We aimed to compare outcomes ...between these two strategies across the left ventricular ejection fraction (LVEF) spectrum.
This retrospective cohort study used data from the randomized MISOAC-AF trial, including from patients with AF and coexistent HF who were hospitalized and followed up after discharge. At baseline, the patients were classified into pharmaceutical (or electrical cardioversion) rhythm control strategy or rate control treatment (b-blocker, digoxin, calcium channel blockers) groups. The primary outcome was all-cause mortality. Kaplan-Meier curves and multivariable-adjusted Cox regression were utilized to compare the two strategies. Spline curve models were used to demonstrate the results across the LVEF stratified spectrum.
In total, 199 AF patients with HF were studied (mean age, 77 years). At discharge, 73 (36.7%) patients received rhythm control and 126 (63.3%) rate control treatment. After a median follow-up period of 31 months, 26 (35.6%) patients in the rhythm-control group died, as compared to 43 (33.3%) in the rate-control group (aHR: 1.29; 95% CI: 0.78-2.14; p = 0.31). The spline curves also revealed no difference in all-cause mortality favoring either strategy in any HF subtype across the nominally classified LVEF.
The use of a pharmacological rhythm-control strategy was not associated with a survival advantage compared to the rate control strategy in recently hospitalized patients with AF and comorbid HF. More randomized trials and large studies are needed in the future to explore these results in each subgroup of HF patients.
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