18,326 research outputs found
Study made of mechanics of deformation and fracture of fibrous composites
Report summarizes the findings of studies made of the influence of both fiber and matrix characteristics upon the mechanics of deformation and fracture of fibrous composites. The major portion of the report is devoted to a study of the mechanics of tensile failure of a fibrous composite
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Design for Additive Manufacturing: A Method to Explore Unexplored Regions of the Design Space
Additive Manufacturing (AM) technologies enable the fabrication of parts and devices that
are geometrically complex, have graded material compositions, and can be customized. To take
advantage of these capabilities, it is important to assist designers in exploring unexplored regions
of design spaces. We present a Design for Additive Manufacturing (DFAM) method that
encompasses conceptual design, process selection, later design stages, and design for
manufacturing. The method is based on the process-structure-property-behavior model that is
common in the materials design literature. A prototype CAD system is presented that embodies
the method. Manufacturable ELements (MELs) are proposed as an intermediate representation
for supporting the manufacturing related aspects of the method. Examples of cellular materials
are used to illustrate the DFAM method.Mechanical Engineerin
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On the Use of Angled, Dynamic Laser Beams to Improve Stereolithography Surface Finish
Improved surface finish of Stereolithography (SLA) parts is an important goal for furthering
the resolution of the technology. In order to improve the surface finish, a dynamic laser beam
with changing angle, beam size, beam shape, and irradiance distribution is proposed. In this
paper, an analytical irradiance model of an angled, dynamic laser beam in the SLA process is
presented. This model is used to simulate cured shapes of SLA builds. Simulated build shapes
are compared to established SLA analytical models and conclusions are drawn on the accuracy
of the developed model.Mechanical Engineerin
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Use of Parameter Estimation for Stereolithography Surface Finish Improvement
In order to improve Stereolithography (SLA) surface finish, a systematic approach based on
estimation of process parameters is needed. In this paper, the exposure on a desired SLA build
surface is formulated as a function of process parameters. The deviation of exposure on this
surface from the critical exposure, which is the threshold that determines curing in the SLA
process, is formulated using least squares minimization. By applying inverse design techniques,
SLA process parameters that satisfy this least squares minimization are determined. Application
of parameter estimation formulation to important SLA geometries is presented and the results,
including surface finish improvement, are discussed.Mechanical Engineerin
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Compensation Zone Approach to Avoid Z Errors in Mask Projection Stereolithography Builds
Print-through results in unwanted polymerization occurring beneath a part cured using
Mask Projection Stereolithography (MPSLA) and thus creates error in its Z dimension. In this
paper, the "Compensation zone approach" is proposed to avoid this error. This approach entails
modifying the geometry of the part to be cured. A volume (Compensation zone) is subtracted
from underneath the CAD model in order to compensate for the increase in the Z dimension that
would occur due to Print-through. Three process variables have been identified: Thickness of
Compensation zone, Thickness of every layer and Exposure distribution across every image used
to cure a layer. Analytical relations have been formulated between these process variables in
order to obtain dimensionally accurate parts. The Compensation zone approach is demonstrated
on an example problem.Mechanical Engineerin
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Process Planning Based on User Preferences
Typical approaches to adaptive slicing in previous literature have typically used surface finish
requirements to control the slicing process. As a result, slice schemes improve the part's surface
quality, but do not enable explicit trade-offs between finish and build time. The purpose of this
article is to present a process planning method that enables the preferences of the user for surface
finish, build time, and accuracy to control how trade-offs are made in a process plan. A multiobjective goal formulation is used by this method to evaluate how well user preferences are met by
a process plan. This method consists of three modules, for determining part orientation, for slicing
the part, and for determining other parameter values. An example with several scenarios
representing different user preferences is provided to illustrate the process planning method.Mechanical Engineerin
Human Trafficking and Foreign Policy: An Introduction
[Excerpt] Human trafficking (also known as trafficking in persons) refers to the subjection of men, women, or children to exploitative conditions that may be tantamount to modern-day slavery. From a foreign policy perspective, human trafficking can be viewed as a human rights problem, a manifestation of transnational organized crime, and a violation of core international labor standards. Human trafficking also raises economic development, international migration, and global governance and security issues, and disproportionately victimizes vulnerable populations.
The Trafficking Victims Protection Act of 2000 (TVPA, Division A of P.L. 106-386; 22 U.S.C. 7101 et seq.) defined “severe forms of trafficking in persons” to include sex trafficking induced by force, fraud, or coercion, child sex trafficking (under 18 years of age), and forced labor trafficking. The latter involves the recruitment, harboring, transportation, provision, or obtaining of a person—induced by force, fraud, or coercion—for the purpose of subjecting that person, including a child, to involuntary servitude, peonage, debt bondage, or slavery
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Manufacturing Metallic Parts with Designed Mesostructure via Three-Dimensional Printing of Metal Oxide Powder
Cellular materials, metallic bodies with gaseous voids, are a promising class of materials that offer
high strength accompanied by a relatively low mass. In this paper, the authors investigate the use of ThreeDimensional Printing (3DP) to manufacture metallic cellular materials by selectively printing binder into a
bed of metal oxide ceramic powder. The resulting green part undergoes a thermal chemical post-process in
order to convert it to metal. As a result of their investigation, the authors are able to create cellular
materials made of maraging steel that feature wall sizes as small as 400 µm and angled trusses and channels
that are 1 mm in diameter.Mechanical Engineerin
A concept for improving the dimensional stability of filamentary composites in one direction
Investigation of filamentary composites having high strength and stiffness and a zero thermal coefficient of expansion in one direction shows that advanced filament materials, such as boron, have substantial advantages over conventional filamentary composites. Various other results are discussed, including guidelines and analysis methods for further evaluation
Testing filamentary composites
NOL ring split-dee tensile test has the advantages that the specimen is readily fabricated by winding and the test is performed in a conventional testing machine without special fixtures. Strain gages cannot be mounted, however, and substantial bending moments are introduced
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