Effect of Section Thickness and Build Orientation on Tensile Properties and Material Characteristics of Laser Sintered Nylon-12 Parts

It has been suggested that different section thicknesses in Laser Sintered parts may cause variations in mechanical properties, and this has previously been demonstrated for some properties (e.g. fracture toughness). The research presented here investigates whether the same is true of tensile properties, and whether the orientation of parts within the build volume has any effect on this. Results are presented for three different orientations of tensile specimens, at a range of thicknesses from 2mm to 6mm, showing that, at any of the orientations tested, the section thickness had no significant effect on any of the main tensile properties. These results are in direct contradiction with related research investigating the effect of section thickness on Fracture Toughness, where an increase in thickness also increased the toughness of the parts. This highlights the importance to Additive Manufacturing users of identifying the correct properties to assess when choosing a suitable process or material, and when designing complex parts.Mechanical Engineerin

Powder Pre-Conditioning for the LS Process

It has previously been shown that the use of recycled Nylon-12 powder leads to increased Elongation at Break (EaB) of Laser Sintered (LS) parts, possibly due to elevated powder temperature in the part bed causing increases in molecular weight. However, this increase in EaB often corresponds to a decrease in repeatability, likely to be through variations in powder history. The research presented here has shown that thermal pre-conditioning of virgin powder can increase EaB of LS parts, with no significant loss of repeatability. Materials analysis of the conditioned powder batches is also presented in order to quantify the differences in powder properties and to help explain the mechanisms involved.Mechanical Engineerin

Controlled Multi-Scale Turbulence through the Use of Laser Sintered Sierpinski Pyramids

The research presented here is the result of a new collaboration between the Centre for Advanced Additive Manufacturing (AdAM) and the Thermofluids group at The University of Sheffield, regarding the use of fractal geometries for the control and influence of fluid flow. It is believed that the use of multiscale objects can be used to introduce many different orders of turbulence into a flow. However, whilst substantial simulations have been carried out in this area, the complexity of the physical geometries means that to date these have not been validated via physical testing. In this work, varying orders of Sierpinski pyramids were produced using Laser Sintered PA2200 and analysed in a wind tunnel with regards to their effects on air flow through the structures. As predicted by theoretical analyses, the coarsest pyramids induced large vortices into the air-stream, whereas the more complex orders induced vortices at a number of different scales, rapidly developing into a standard turbulent flow. Further investigations are planned to isolate the effects of the smaller-scale turbulence in this situation.Mechanical Engineerin

Effect of infra‐red power level on the sintering behaviour in the high speed sintering process

This is a journal article. It was published in the journal, Rapid prototyping journal, [© Emerald]. The definitive version is available at: http://www.emeraldinsight.com/1355-2546.htmPurpose: To investigate the effects of the infra-red power level on sintering behaviour in the High Speed Sintering process. Design/methodology/approach: Single-layer parts were produced using the High Speed Sintering process, in order to determine the effect of the infra-red power level on the maximum achievable layer thickness, and the degree of sintering. The parts were examined using both optical microscopy and contact methods. Findings: Whilst it was expected that an increase in the infra-red lamp powder might allow an increase in the depth of sintering that could be achieved, as a result of increased thermal transfer through the powder, results in fact indicated that there is a maximum layer thickness that can be achieved, as a result of part shrinkage in the z direction. Optical microscopy images have shown that a greater degree of sintering occurs at higher power levels, which would be expected to correspond to an improvement in the mechanical properties of the parts produced. These images also indicate that the RAM forms in small ‘islands’ on the powder bed surface. However, these islands begin to merge as sintering progresses, to a greater degree as the infra-red lamp power is increased. Research limitations/implications: These results are based only on single layer parts. Further work will examine the sintering characteristics of multiple layer parts. Practical implications: Results have shown that, whilst it is not possible to increase the achievable layer thickness of the parts produced by modifying the infra-red lamp power, the degree of sintering can be improved greatly by increasing the power. Originality/value: High Speed Sintering is an entirely new process which is currently still under development; the results presented here will directly impact the direction of further development and research into this process

Projected WIMP sensitivity of the LUX-ZEPLIN dark matter experiment

LUX-ZEPLIN (LZ) is a next-generation dark matter direct detection experiment that will operate 4850 feet underground at the Sanford Underground Research Facility (SURF) in Lead, South Dakota, USA. Using a two-phase xenon detector with an active mass of 7 tonnes, LZ will search primarily for low-energy interactions with weakly interacting massive particles (WIMPs), which are hypothesized to make up the dark matter in our galactic halo. In this paper, the projected WIMP sensitivity of LZ is presented based on the latest background estimates and simulations of the detector. For a 1000 live day run using a 5.6-tonne fiducial mass, LZ is projected to exclude at 90% confidence level spin-independent WIMP-nucleon cross sections above 1.4 × 10-48cm2 for a 40 GeV/c2 mass WIMP. Additionally, a 5σ discovery potential is projected, reaching cross sections below the exclusion limits of recent experiments. For spin-dependent WIMP-neutron(-proton) scattering, a sensitivity of 2.3 × 10−43 cm2 (7.1 × 10−42 cm2) for a 40 GeV/c2 mass WIMP is expected. With underground installation well underway, LZ is on track for commissioning at SURF in 2020

Measurement of the View the tt production cross-section using eμ events with b-tagged jets in pp collisions at √s = 13 TeV with the ATLAS detector

This paper describes a measurement of the inclusive top quark pair production cross-section (σtt¯) with a data sample of 3.2 fb−1 of proton–proton collisions at a centre-of-mass energy of √s = 13 TeV, collected in 2015 by the ATLAS detector at the LHC. This measurement uses events with an opposite-charge electron–muon pair in the final state. Jets containing b-quarks are tagged using an algorithm based on track impact parameters and reconstructed secondary vertices. The numbers of events with exactly one and exactly two b-tagged jets are counted and used to determine simultaneously σtt¯ and the efficiency to reconstruct and b-tag a jet from a top quark decay, thereby minimising the associated systematic uncertainties. The cross-section is measured to be: σtt¯ = 818 ± 8 (stat) ± 27 (syst) ± 19 (lumi) ± 12 (beam) pb, where the four uncertainties arise from data statistics, experimental and theoretical systematic effects, the integrated luminosity and the LHC beam energy, giving a total relative uncertainty of 4.4%. The result is consistent with theoretical QCD calculations at next-to-next-to-leading order. A fiducial measurement corresponding to the experimental acceptance of the leptons is also presented

Search for strong gravity in multijet final states produced in pp collisions at √s=13 TeV using the ATLAS detector at the LHC

A search is conducted for new physics in multijet final states using 3.6 inverse femtobarns of data from proton-proton collisions at √s = 13TeV taken at the CERN Large Hadron Collider with the ATLAS detector. Events are selected containing at least three jets with scalar sum of jet transverse momenta (HT) greater than 1TeV. No excess is seen at large HT and limits are presented on new physics: models which produce final states containing at least three jets and having cross sections larger than 1.6 fb with HT > 5.8 TeV are excluded. Limits are also given in terms of new physics models of strong gravity that hypothesize additional space-time dimensions

Search for TeV-scale gravity signatures in high-mass final states with leptons and jets with the ATLAS detector at sqrt [ s ] = 13TeV

A search for physics beyond the Standard Model, in final states with at least one high transverse momentum charged lepton (electron or muon) and two additional high transverse momentum leptons or jets, is performed using 3.2 fb−1 of proton–proton collision data recorded by the ATLAS detector at the Large Hadron Collider in 2015 at √s = 13 TeV. The upper end of the distribution of the scalar sum of the transverse momenta of leptons and jets is sensitive to the production of high-mass objects. No excess of events beyond Standard Model predictions is observed. Exclusion limits are set for models of microscopic black holes with two to six extra dimensions

Measurement of the correlation between flow harmonics of different order in lead-lead collisions at √sNN = 2.76 TeV with the ATLAS detector

Correlations between the elliptic or triangular flow coefficients vm (m=2 or 3) and other flow harmonics vn (n=2 to 5) are measured using √sNN=2.76 TeV Pb+Pb collision data collected in 2010 by the ATLAS experiment at the LHC, corresponding to an integrated luminosity of 7 μb−1. The vm−vn correlations are measured in midrapidity as a function of centrality, and, for events within the same centrality interval, as a function of event ellipticity or triangularity defined in a forward rapidity region. For events within the same centrality interval, v3 is found to be anticorrelated with v2 and this anticorrelation is consistent with similar anticorrelations between the corresponding eccentricities, ε2 and ε3. However, it is observed that v4 increases strongly with v2, and v5 increases strongly with both v2 and v3. The trend and strength of the vm−vn correlations for n=4 and 5 are found to disagree with εm−εn correlations predicted by initial-geometry models. Instead, these correlations are found to be consistent with the combined effects of a linear contribution to vn and a nonlinear term that is a function of v22 or of v2v3, as predicted by hydrodynamic models. A simple two-component fit is used to separate these two contributions. The extracted linear and nonlinear contributions to v4 and v5 are found to be consistent with previously measured event-plane correlations