839 research outputs found
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Fabrication of X-Graded H13 and Cu Powder Mix Using High Power Pulsed Nd:YAG Laser
The manufacturing of Functionally Graded Material (FGM) parts using Solid Free Form
manufacturing technologies has been carried out since early 1980. At present, most of the
powder manufacturing techniques are being focused on layering powder with different
powder blend compositions with Z gradients (graded in direction of layer build). Although,
there are a few researchers working on multi powder feeder and deposition system, the study
of laser fusion of the deposited powder (by a powder deposition system) is minimum or not
known to date. Consequently, the manufacturing of functionally graded structures is still
geometry limited. This work was focused on the manufacturing of X-graded (graded along the
powder bed plane) specimens with H13 tool steel and Cu mix. Five bimodal powder blends
were used with a multi-container feed hopper to spread powder layers for the selective laser
fusion of the powder. The powder was fused using a high power Nd:YAG pulsed laser using a
specific scanning strategy to reduce porosity. Specimens were produced with graded Cu
within the H13 matrix. The specimens were analysed for dimensional accuracy,
microstructure, porosity, cracks and micro hardness of the FGM.Mechanical Engineerin
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Tailoring the Mechanical Properties of Selective Laser Sintered Parts
The ~ÂŁ1 million IMCRC-funded integrated project âPersonalised Sports Footwear: From
Elite to High Streetâ is investigating the use of Rapid Manufacturing to produce personalised
sports shoes, with the aim of enhancing performance, reducing injury, and providing improved
functionality.
Research has identified that, for sprinting, performance benefits can be achieved by
tuning the bending stiffness of a shoe to the characteristics of an individual athlete. This paper
presents research to date on several novel methods of influencing the mechanical properties of
Selective Laser Sintered shoe soles, with a particular focus on stiffness.Mechanical Engineerin
Nâheterocyclic carbene catalyzed photoenolization/DielsâAlder reaction of acid fluorides
The combination of light activation and Nâheterocyclic carbene (NHC) organocatalysis has enabled the use of acid fluorides as substrates in a UVAâlightâmediated photochemical transformation previously observed only with aromatic aldehydes and ketones. Stoichiometric studies and TDâDFT calculations support a mechanism involving the photoactivation of an orthoâtoluoyl azolium intermediate, which exhibits âketoneâlikeâ photochemical reactivity under UVA irradiation. Using this photoâNHC catalysis approach, a novel photoenolization/DielsâAlder (PEDA) process was developed that leads to diverse isochromanâ1âone derivatives
Smoother and stronger high speed sintered elastomers through surface modification process
High speed sintering is a novel additive manufacturing process which creates parts by employing a combination of inkjet printing and infrared heating to sinter successive layers of polymer powder. This paper investigates the effect of a new surface modification method called the PUSh⹠process on the mechanical properties of high speed sintered elastomer. ALM TPE210-S elastomeric powder was used to manufacture specimens, and the PUSh⹠process was subsequently performed on selected specimens. Surface roughness and mechanical properties of TPE210-S specimens were measured. The results show that the PUSh⹠process reduced surface roughness by 50% from 20 to 10 ”m. Finished specimens had 50% higher values of ultimate tensile strength, Young's modulus and elongation at break compared to unfinished specimens, and tear strength was significantly improved by 233%. The process resulted in 3% average part shrinkage while part hardness remains unchanged. Overall, the mechanical properties of high speed sintered TPE210-S elastomer were improved by the PUSh⹠process
On the diffusion of lattice matched InGaAs/InP microstructures
Copyright (2003) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.
The following article appeared in F. Bollet et al., J. Appl. Phys. 93, 3881 (2003) and may be found at http://link.aip.org/link/?jap/93/388
Customised Alloy Blends for In-Situ Al339 Alloy Formation Using Anchorless Selective Laser Melting
The additive manufacturing process Selective Laser Melting (SLM) can generate large
thermal gradients during the processing of metallic powder; this can in turn lead to increased residual
stress formation within a component. Metal anchors or support structures are required to be built
during the process and forcibly hold SLM components to a substrate plate and minimise geometric
distortion/warpage due to the process induced thermal residual stress. The requirement for support
structures can limit the geometric freedom of the SLM process and increase post-processing operations.
A novel method known as Anchorless Selective Laser Melting (ASLM) maintains processed material
within a stress relieved state throughout the duration of a build. As a result, metal components formed
using ASLM do not develop signification residual stresses within the process, thus, the conventional
support structures or anchors used are not required to prevent geometric distortion. ASLM locally
melts two or more compositionally distinct powdered materials that alloy under the action of the laser,
forming into various combinations of hypo/hyper eutectic alloys with a new reduced solidification
temperature. This new alloy is maintained in a semi-solid or stress reduced state for a prolonged
period during the build with the assistance of elevated powder bed pre-heating. In this paper, custom
blends of alloys are designed, manufactured and processed using ASLM. The purpose of this work is
to create an Al339 alloy from compositionally distinct powder blends. The in-situ alloying of this
material and ASLM processing conditions allowed components to be built in a stress-relieved state,
enabling the manufacture of overhanging and unsupported features
Use of tobacco and e-cigarettes among youth in Great Britain in 2022: analysis of a cross sectional survey
Introduction: Although e-cigarettes can be an effective form of nicotine substitution for adults attempting to quit smoking, their use among children and young people is a concern. Accurate data about this are needed to inform debates over policy and regulation in the UK and elsewhere. Methods: Using data from an online survey of 2613 youth aged 11â18 years, conducted by the market research company YouGov in March 2022, we present prevalence estimates of e-cigarette and tobacco use. We use logistic regression models to assess differences in e-cigarette use, tobacco use and use of disposable e-cigarettes across a range of covariates including age, sex, tobacco smoking status, social class, and country. Results: Among the 18.0% of those surveyed who reported ever having smoked a cigarette, 83.9% were not regular (at least once per week) smokers and 16.1% were (15.1% and 2.9% of the total sample, respectively). Among the 19.2% of those surveyed who had ever used an e-cigarette, 79.2% were not regular users, while 20.8% were (15.2% and 4.0% of the total sample, respectively). Regular e-cigarette use was more common than regular tobacco smoking (4.0% vs 2.9%). E-cigarette use was more common among those who also smoked tobacco, with 9.0% of never e-cigarette users ever smoking tobacco, compared with 89.4% of regular e-cigarette users. Both smoking and e-cigarette use were associated with increasing age and use by others within the home, but not with social class. Use of disposable e-cigarettes was reported by 53.8% of those who have ever used an e-cigarette, and more common among females than males. Conclusions: Regular e-cigarette use is now more common than smoking in children and youth, though the majority of this is among those who have also smoked tobacco. Measures to reduce the appeal of both e-cigarettes and tobacco to children and young people are warranted
Photoluminescence spectroscopy of bandgap reduction in dilute InNAs alloys
Photoluminescence (PL) has been observed from dilute InNxAs1âx epilayers grown by molecular-beam epitaxy. The PL spectra unambiguously show band gap reduction with increasing N content. The variation of the PL spectra with temperature is indicative of carrier detrapping from localized to extended states as the temperature is increased. The redshift of the free exciton PL peak with increasing N content and temperature is reproduced by the band anticrossing model, implemented via a (5Ă5) k·p Hamiltonian
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