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

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

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

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

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

An Ejection Mechanism Design Method for AIM Tools

One of the key advantages of AIM tooling is time savings when producing small batch production quality parts. However, designing suitable ejection mechanisms is becoming a bottleneck. There are two goals of this paper. First, a model is presented that effectively characterizes the stresses on the mold core and part during injection molding. Second, a method is described for ejection system design. Our approach consists of a combination of analytical, computational, and physical experiments. The ejection system design method will first determine the feasibility of ejection for a particular part geometry, then will determine the number, sizes, and locations of ejector pins. Each phase of the method will be formulated into a Compromise Decision Support Problem, a multi-objective optimization problem formulation. An example will be presented to provide an idea of the robustness and the limitations of the method. Preliminary results indicate that this methodology is sound for a simple geometry.Mechanical Engineerin