15 research outputs found
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An Evaluation of the Mechanical Behavior of Bronze-NI Composites Produced by Selective Laser Sintering
Mechanical properties of Bronze-Nickel composites produced by Selective Laser Sintering (SLS)
were evaluated by constant displacement tension tests. These were studied as a function of SLS
process parameters - laser power density, scan speed, scan spacing, scan direction and layer
thickness. The strength data was then correlated to the microstructure and the part bulk density. To
further enhance the part densities and the mechanical properties, post-SLS sintering was studied.
The relationships between SLS process parameters, post-SLS sintering parameters and the
resulting microstructures, part bulk density and the mechanical properties will be described.Mechanical Engineerin
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Densification of Selective Laser Sintered Metal Part by Hot Isostatic Pressing
Metal matrix alloy composite parts were made from powders by Selective Laser Sintering (SLS).
In this study, partially dense (60%-80%) metal parts made by SLS were densified to full density
(>98%) by hot isostatic pressing (HIPping) without any loss of shape. HIPping was done by
vacuum sealing SLS samples in glass capsules. HIPping parameters, such as, temperature,
pressure, and time, were studied with respect to density, linear shrinkage, and microstructures.
Anisotropy in linear shrinkage was correlated to the SLS processing parameters. Densification
resulting from HIPping was correlated to microstructures and theoretical HIP densification maps.
A detailed analysis of such maps is presented.Mechanical Engineerin
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Listening for change: quantifying the impact of ecological restoration on soundscapes in a tropical dry forest
Ecological restoration is crucial to mitigate climate change and conserve biodiversity, and accurately monitoring responses to restoration is imperative to guide current and future efforts. This study examines the impact of ecological restoration of a tropical dry forest in Central India. Here, the state forest department and a nongovernmental organization work with local communities to remove an invasive shrub, Lantana camara, in the forest, to assist natural regeneration, primarily for the purpose of improving access to forest resources for forest-dependent people. We used acoustic technology to examine the bird community composition and the acoustic space used (ASU) across comparable restored, unrestored (with L. camara), and naturally low L. camara density (LLD) sites. We found no significant difference in the cumulative number of bird species detected between the site types (median in restored and LLD = 38, unrestored = 41). We found a significant difference in bird community composition across sites (r2 = 0.049, p ≤ 0.001). ASU differs between site types (r2 = 0.023, p ≤ 0.10), with restored sites positively associated with ASU compared to unrestored and LLD sites, which could represent a temporary increase in ASU as animal communities are reorganized after the complete removal of L. camara. Our results suggest that small-scale restoration efforts that aim to help meet livelihood needs have the potential to contribute to ecological goals in this landscape. However, it is necessary to continue to monitor the regeneration trajectory in restored sites and the possible changes in the ASU
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Part Quality Prediction Tools for Fused Deposition Processing
Fused Deposition process fabricates requested part geometries by sequentially depositing
discrete curvilinear beads ofmaterial next to and on top of each other. The part integrity
depends strongly on the bonding quality at the bead interfaces. Since diffusion bonding of
thermoplastic components in the material system is thermally driven, temperature history
ofinterfaces determine the bonding quality. Detailed thermal analysis of deposition region
and layer building simulation for a model geometry have been performed to investigate
local and global material behavior during processing. A simple transport property
prediction model has also been developed for the determination of thermal transport
properties of the particle loaded systems used in Fused Deposition. Based on the
information obtained from thermal models, a computationally efficient part building
model has been developed to predict bonding quality in the whole part. The model is
driven by the same command file, sml file, that drives the Fused Deposition hardware;
and hence is capable of replicating the building process. The model has been tested for a
model geometry, spur gear, and three dimensional bonding quality distribution has been
predicted for the part.Mechanical Engineerin
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Gelcast Molding with Rapid Prototyped Fugitive Molds
A technique for the rapid manufacture ofceramic components has been developed
using rapid prototyping to generate molds for the required components. The process
entails the fabrication offugitive tooling using rapid prototyping techniques from which
ceramic articles are formed using gelcasting. In the gelcasting process, the mold cavities
are filled with a fluid suspension of ceramic powder which sets to a solid form through
the polymerization of gelling additives and application of heat. The mold is carefully
removed by dissolution or heat treatment leaving the intact gelcast part. The "green"
gelcast part is subsequently dried and sintered to full density. Computer aided
manufacturing of the tooling using solid freeform fabrication techniques allows for
complex shapes to be manufactured with minimal tooling cost. The technique is idealfor
the manufacture of ceramic parts in small batch conditions or for prototyping of
functional parts in design cycles. Cost and time reduction of a magnitude can be
achieved.Mechanical Engineerin
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Direct Fabrication of Polymer Composite Structures with Curved LOM
This report describes the application of Curved LOM to the direct fabrication of polymer matrix
composites (PMCs). The overall methodology of directly fabricating PMC parts involved the use of the
Curved LOM machine to lay-up and shape "green" composite laminates from prepreg feedstocks,
followed by vacuum bag / oven cure and consolidation. The conventional Curved LOM laminator was
replaced with a vacuum thermoforming apparatus to better accommodate the bonding of commercially
available prepregs. The study also demonstrated that it is possible to interface a general composite design
sofiware package with the Curved LOM machine via the curved slice file (.CSF) format. Taken together,
these two improvements allow for improved flexibility in manufacturing PMC components, from both a
material handling and a design point-of-view. A simple C-shaped panel was fabricated and tested to
demonstrate the overall feasibility of the process for PMCs. A glass fiber 1 epoxy prepreg obtained from a
commercial supplier was used as a model material system. It was found that the cumulative accuracy of
the overall process was good, and the mechanical properties of the laminates were acceptable for nonstructural applications for which the material is normally used.Mechanical Engineerin
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Synthesis, Selective Laser Sintering and Infiltration of High Super Tc Dual Phase Ag-YBa2Cu307-x Superconductor Composites
Fine, homogeneous dual phase Ag-YBa2Cu307-x composite powders were prepared by a simple
colloidal sol-gel co-precipitation technique. Silver did not react with or degrade YBa2Cu307-x.
Bulk porous samples of pure YBa2Cu307-x and Ag-YBa2Cu307-x were made from powders by
Selective Laser Sintering. The porous parts were further densified by infiltrating silver into pores,
resulting in a dense, structurally sound dual phase superconducting composite. Laser processing
parameters were varied to obtain optimum microstructure. The laser sintered parts required oxygen
annealing after infiltration to restore the orthorhombic, superconducting structure. X-ray
diffraction and Tc measurements indicate some impurity phases present in samples processed
under aggressive laser conditions.Mechanical Engineerin
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Improved household living standards can restore dry tropical forests
Despite multiple approaches over the last several decades to harmonize conservation and development goals in the tropics, forest-dependent households remain the poorest in the world. Durable housing and alternatives to fuelwood for cooking are critical needs to reduce multi-dimensional poverty. These improvements also potentially reduce pressure on forests and alleviate forest degradation. We test this possibility in dry tropical forests of the Central Indian Highlands where tribal and other marginalized populations rely on forests for energy, construction materials, and other livelihood needs. Based on a remotely sensed measure of forest degradation and a 5000 household survey of forest use, we use machine learning (causal forests) and other statistical methods to quantify treatment effects of two improved living standards—alternatives to fuelwood for cooking and non-forest-based housing material—on forest degradation in 1, 2, and 5 km buffers around 500 villages. Both improved living standards had significant treatment effects (−0.030 ± 0.078, −0.030 ± 0.023, 95% CI), respectively, with negative values indicating less forest degradation, within 1 km buffers around villages. Treatment effects were lower with increasing distance from villages. Results suggest that improved living standards can both reduce forest degradation and alleviate poverty. Forest restoration efforts can target improved living standards for local communities without conflicts over land tenure or taking land out of production to plant trees