491 research outputs found
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Effect of Processing Parameters on the Density and Microstructure of Direct Laser Sintered Al-12Si Powders
The effect of processing parameters on the sintering behaviour of gas atomised Al-12Si
powders has been investigated. Laser power, scanning rate, scan spacing and layer
thickness are found to control the densification and the resultant microstructural
characteristics of the laser sintered parts. It was found that sintered density increased as
the energy density increased reaching a maximum of 80.2% at an energy input per unit
volume of 67 J mm-3. For parts produced with a slightly lower power density (50 J mm-3), the microstructure consisted of fine dendrites with interconnected porosity while parts
fabricated with a slightly higher power density (100 J mm-3) were noted to have a
preponderance of coarse dendrites with a discontinuous network of irregular shaped pores
surrounded by a fully dense aluminium-silicon matrix.Mechanical Engineerin
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Mass Customization of Foot Orthosis for Rheumatoid Arthritis
Rheumatoid arthritis (RA) is an inflammatory disease, which can cause pain, stiffness, and
swelling in the joints of hands and feet. The foot is a major site for RA involvement and a
major source of disability resulting from this disease. This paper introduces research which
aims to create a mass customisation process for customised orthoses for patients with RA.
3D laser scanning, and gait analysis will be used to generate the orthosis geometry and
rapid manufacturing, namely the selective laser sintering (SLS) process, will be used to
produce the orthoses. The SLS process enables the incorporation of compositional
functional elements, such as locally adjusted stiffness or flexibility, into the orthosis
design.
The process involved two central elements. The first was a literature survey to identify
orthotic design rules for foot impairments in RA. This survey will form a platform for the
design rule development and will be complemented by data obtained from two patient
trials. The second is a virtual three-segment foot model, created in Anybody dynamics
modelling software which can be motivated by data measured from patients using 3D
motion capture and force plate systems. Once the measured data has been applied to the
model, a virtual insole can be used to simulate the effects of various features in the
orthosis.
Considerable variation was noted in the literature for types of material, design and
methods of orthotic construction. Pressure redistribution using cushioning materials was
consistently mapped to painful deformed joints. Orthoses with contoured surfaces, either
custom- or mass produced in thermoplastic materials of varying stiffness and density were
mapped to joint motion control and deformity prevention. The paper will also describe
applying patient gait data to the Anybody model, and then altering the gait pattern by
applying the insole model. Future work will also be discussed.Mechanical Engineerin
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Selective Laser Sintering of Polymer Nanocomposites
This paper describes the fabrication and characterization of polymer nanocomposite (PNC)
materials for use in the selective laser sintering (SLS) process. PNC materials are of great
interest generally because of their excellent physical properties, and offer excellent potential
in rapid manufacturing of structural polymeric parts. Three different nano additive materials
have been used: cerium oxide IV, yttrium stabilized zirconia, and layered Hectorite clay.
These materials have been used to reinforce PA6 polymer using solution blending and spray
drying to create powder with particle sizes in the range of 5-40 µm. The mechanical
properties and microstructure of the PNC materials have been evaluated and the results
compared to those of unfilled polymer.Mechanical Engineerin
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Strength of the DTM RapidSteel 1.0 Material
This paper reports the results of a study into the strength of the DTM RapidSteel 1.0 material.
Elastic modulus and strength of the metal/copper composite material was investigated as a
function of the distance from the point of copper infiltration, the furnace cycle duration, and the
furnace type. The microstructure of the RapidSteel material was also examined in an attempt to
understand the science behind the infiltration process. The results have implications for the
design of tools to be made using the RapidTool process in situations where the tool will be used
as a production tool, rather than a prototype tool.Mechanical Engineerin
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Mechanical Properties and Biological Responses of Bioactive Glass Ceramics Processed using Indirect SLS
This paper will report on research which aims to generate bone replacement components by
processing bioactive glass-ceramic powders using indirect selective laser sintering. The indirect
SLS route has been chosen as it offers the ability to tailor the shape of the implant to the
implantation site, and two bioactive glass ceramic materials have been processed through this
route: apatite-mullite and apatite-wollostanite. The results of bend tests, to investigate
mechanical properties, and in vitro and in vivo experiments to investigate biological responses of
the materials will be reported, and the suitability of completed components for implant will be
assessed.Mechanical Engineerin
Ab initio determination of polarizabilities and van der Waals coefficients of Li atoms using the relativistic CCSD(T) method
We report a new technique to determine the van der Waals coeffcients of
lithium (Li) atoms based on the relativistic coupled-cluster theory. These
quantities are determined using the imaginary parts of the scalar dipole and
quadrupole polarizabilities, which are evaluated using the approach that we
have proposed in [1]. Our procedure is fully ab initio, and avoids the
sum-over-the-states method. We present the dipole and quadrupole
polarizabilities of many of the low-lying excited states of Li. Also, the
off-diagonal dipole and quadrupole polarizabilites between some of the
low-lying states of Li are calculated.Comment: 8 pages, 4 figure
Generalized Supersymmetric Perturbation Theory
Using the basic ingredient of supersymmetry, we develop a simple alternative
approach to perturbation theory in one-dimensional non-relativistic quantum
mechanics. The formulae for the energy shifts and wave functions do not involve
tedious calculations which appear in the available perturbation theories. The
model applicable in the same form to both the ground state and excited bound
states, unlike the recently introduced supersymmetric perturbation technique
which, together with other approaches based on logarithmic perturbation theory,
are involved within the more general framework of the present formalism.Comment: 13 pages article in LaTEX (uses standard article.sty). No Figures.
Sent to Ann. Physics (2004
Synthesis of bioinspired collagen/alginate/fibrin based hydrogels for soft tissue engineering
Hydrogels based on natural polymers offer a range of properties to mimic the native extracellular matrix, and provide microenvironments to preserve cellular function and encourage tissue formation. A tri-component hydrogel using collagen, alginate and fibrin (CAF) was developed and investigated at three collagen concentrations for application as a functional extracellular matrix analogue. Physical-chemical characterization of CAF hydrogels demonstrated a thermo-responsive crosslinking capacity at physiological conditions with stiffness similar to native soft tissues. CAF hydrogels were also assessed for cytocompatibility using L929 murine fibroblasts, pancreatic MIN6 β-cells and human mesenchymal stem cells (hMSCs); and demonstrated good cell viability, proliferation and metabolic activity after 7 days of in vitro culture. CAF hydrogels, especially with 2.5% w/v collagen, increased alkaline phosphatase production in hMSCs indicating potential for the promotion of osteogenic activity. Moreover, CAF hydrogels also increased metabolic activity of MIN6 β-cells and promoted the reconstitution of spherical pseudoislets with sizes ranging between 50 and 150 μm at day 7, demonstrating potential in diabetic therapeutic applications
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