Effects of process variants on residual stresses in wire arc additive manufacturing of aluminium alloy 5183

Development of residual stress of high magnitude, to the extent of material yield strength and in some cases higher than yield strength, is one of the major challenges faced by components produced using wire arc additive manufacturing (WAAM). This study focuses on aluminium alloy 5183 with respect to the residual stress formation and distribution in WAAM builds. Residual stresses were determined using the contour method. The effects of processing conditions, such as substrate thickness, interlayer temperature and deposit height on the magnitude and distribution of residual stresses were investigated. Substrate thickness was found to have a major influence on the residual stress distribution along the sample height. Tensile residual stress up to the value of the material yield strength was present. Majority part of deposit showed tensile stress while substrate showed compensating compressive residual stress. Lower interlayer temperature samples exhibited residual stresses of higher degree of magnitude compared sample produced using higher interlayer temperature. Deposit height i.e. total number of layers affected stress distribution pattern similar to substrate thickness.

Predictors of Visual outcome in Post Fever Retinitis: A Retrospective Analysis

Purpose: To identify the predictors of final visual outcome in cases with post fever retinitis (PFR).Methods : This is a retrospective study of cases with diagnosis of post fever retinitis. Color fundus photograph and optical coherence tomography (OCT) parameters at presentation and final visit were analysed. Various factors at presentation [age, systemic illness, best corrected visual acuity (BCVA), area of retinitis and hard exudates, OCT parameters], at final visit (optic disc pallor, OCT parameters) and the treatment modalities used were correlated with BCVA at final visit.Results : Twenty four eyes of 16 patients with PFR were included in the study. Median BCVA at presentation was 6/60 and at final visit was 6/9. By multiple linear regression after adjusting for other variables, for every 1 unit increase in height of SRF at fovea at presentation, the value of final BCVA decreased by 0.001 unit. For every 1 unit increase in extent of EZ loss and subfoveal deposit height, the value of final BCVA decreased by 0.0001unit and 0.004 unit respectively.Conclusion: Height of SRF at presentation, extent of EZ loss and subfoveal deposit height at final visit were associated with poor final BCVA in PFR.

Desferrioxamine-Related Pseudo-Vitelliform Dystrophy and the Effect of Anti-Vascular Endothelial Growth Factor

We report a case of a 72-year-old female who developed bilateral pseudo-vitelliform dystrophy after taking desferrioxamine for the treatment of chronic iron overload. The patient then developed a right superior hemiretinal vein occlusion associated with intraretinal fluid in the right eye and was treated with monthly intravitreal aflibercept injections for 3 months followed by as required treatment. In addition to the intraretinal fluid responding to anti-VEGF treatment, there was a reduction in the size of the pseudo-vitelliform subfoveal deposit height, which was not seen in the untreated eye. Our case of an uncommon presentation of desferrioxamine-related maculopathy associated with a vein occlusion and the changes associated with intravitreal anti-VEGF treatment may help with the potential hypotheses of the pathophysiology of desferrioxamine-related pseudo-vitelliform retinal lesions and help with the potential future treatments of the condition.

The mechanical origin of snow avalanche dynamics and flow regime transitions

Snow avalanches cause fatalities and economic damage. Key to their mitigation is the understanding of snow avalanche dynamics. This study investigates the dynamic behavior of snow avalanches, using the material point method (MPM) and an elastoplastic constitutive law for porous cohesive materials. By virtue of the hybrid Eulerian–Lagrangian nature of the MPM, we can handle processes involving large deformations, collisions and fractures. Meanwhile, the elastoplastic model enables us to capture the mixed-mode failure of snow, including tensile, shear and compressive failure. Using the proposed numerical approach, distinct behaviors of snow avalanches, from fluid-like to solid-like, are examined with varied snow mechanical properties. In particular, four flow regimes reported from real observations are identified, namely, cold dense, warm shear, warm plug and sliding slab regimes. Moreover, notable surges and roll waves are observed peculiarly for flows in transition from cold dense to warm shear regimes. Each of the flow regimes shows unique flow characteristics in terms of the evolution of the avalanche front, the free-surface shape, and the vertical velocity profile. We further explore the influence of slope geometry on the behavior of snow avalanches, including the effect of slope angle and path length on the maximum flow velocity, the runout angle and the deposit height. Unified trends are obtained between the normalized maximum flow velocity and the scaled runout angle as well as the scaled deposit height, reflecting analogous rules with different geometry conditions of the slope. It is found that the maximum flow velocity is mainly controlled by the friction between the bed and the flow, the geometry of the slope, and the snow properties. We reveal the crucial effect of both flow and deposition behaviors on the runout angle. Furthermore, our MPM modeling is calibrated and tested with simulations of real snow avalanches. The evolution of the avalanche front position and velocity from the MPM modeling shows reasonable agreement with the measurement data from the literature. The MPM approach serves as a novel and promising tool to offer systematic and quantitative analysis for mitigation of gravitational hazards like snow avalanches.

The mechanical origin of snow avalanche dynamics and flow regime transitions

Snow avalanches cause fatalities and economic damages. Key to their mitigation entails the understanding of snow avalanche dynamics. This study investigates the dynamic behaviors of snow avalanches, using the Material Point Method (MPM) and an elastoplastic constitutive law for porous cohesive materials. By virtue of the hybrid Eulerian-Lagrangian nature of MPM, we can handle processes involving large deformations, collisions and fractures. Meanwhile, the elastoplastic model enables us to capture the mixed-mode failure of snow, including tensile, shear and compressive failure. Using the proposed numerical approach, distinct behaviors of snow avalanches, from fluid-like to solid-like, are examined with varied snow mechanical properties. In particular, four flow regimes reported from real observations are identified, namely, cold dense, warm shear, warm plug and sliding slab regimes. Moreover, notable surges and roll-waves are observed peculiarly for flows in transition from cold dense to warm shear regimes. Each of the flow regimes shows unique flow characteristics in terms of the evolution of the avalanche front, the free surface shape, and the vertical velocity profile. We further explore the influence of slope geometry on the behaviors of snow avalanches, including the effect of slope angle and path length on the maximum flow velocity, the $\\alpha$ angle and the deposit height. Unified trends are obtained between the normalized maximum flow velocity and the scaled $\\alpha$ angle as well as the scaled deposit height, reflecting analogous rules with different geometry conditions of the slope. It is found the maximum flow velocity is mainly controlled by the friction between the bed and the flow, the geometry of the slope, and the snow properties. In addition to the flow behavior before reaching the deposition zone, which has long been regarded as the key factor governing the $\\alpha$ angle, we reveal the crucial effect of the stopping behavior in the deposition zone. Furthermore, our MPM model is benchmarked with simulations of real snow avalanches. The evolution of the avalanche front position and velocity from the MPM modeling shows reasonable agreement with the measurement data from literature. The MPM approach serves as a novel and promising tool to offer systematic and quantitative analysis for mitigation of gravitational hazards like snow avalanches.

Towards the third dimension in direct electron beam writing of silver

Carboxylates constitute an extremely promising class of precursor compounds for the electron beam induced deposition of silver. In this work both silver 2,2-dimethylbutyrate and silver pentafluoropropionate were investigated with respect to their dwell-time-dependent deposition behavior and growth characteristics. While silver 2,2-dimethylbutyrate showed a strong depletion in the center of the impinging electron beam profile hindering any vertical growth, silver pentafluoropropionate indicated a pronounced dependency of the deposit height on the dwell time. Truly three-dimensional silver structures could be realized with silver pentafluoropropionate. The pillars were polycrystalline with silver contents of more than 50 atom % and exhibit strong Raman enhancement. This constitutes a promising route towards the direct electron beam writing of three-dimensional plasmonic device parts from the gas phase.

Fundamental edge broadening effects during focused electron beam induced nanosynthesis

The present study explores lateral broadening effects of 3D structures fabricated through focused electron beam induced deposition using MeCpPt(IV)Me3 precursor. In particular, the scaling behavior of proximity effects as a function of the primary electron energy and the deposit height is investigated through experiments and validated through simulations. Correlated Kelvin force microscopy and conductive atomic force microscopy measurements identified conductive and non-conductive proximity regions. It was determined that the highest primary electron energies enable the highest edge sharpness while lower energies contain a complex convolution of broadening effects. Moreover, it is demonstrated that intermediate energies lead to even more complex proximity effects that significantly reduce lateral edge sharpness and thus should be avoided if desiring high lateral resolution.

Thermal Accumulation in Metal Micro-Parts Fabricated by Micro Droplet Deposition Manufacturing Technique

Thermal accumulation in micro droplet deposition manufacturing (MDDM) has a significant influence on geometric profile and microstructure of the fabricated metal micro-parts. In this paper, thermal behavior of a new aluminum droplet on the deposit surface was investigated using one-dimensional heat transfer model. Then several thin-walled aluminum cubic pipes were fabricated by MDDM to verify the numerical analysis result. The result shows that the thermal accumulation would increase gradually with the increase of the deposit height. It associated with thermal input and output on the top surface of the deposit, which could be controlled or eliminated by optimizing processing parameters such as deposition frequency.