There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

The Design and Analysis of Experiments

Friction stir welding (FSW) is a relatively new solid-state joining process. This joining technique is energy efficient, environment friendly, and versatile. In particular, it can be used to join high-strength aerospace aluminum alloys and other metallic alloys that are hard to weld by conventional fusion welding. FSW is considered to be the most significant development in metal joining in a decade. Recently, friction stir processing (FSP) was developed for microstructural modification of metallic materials. In this review article, the current state of understanding and development of the FSW and FSP are addressed. Particular emphasis has been given to: (a) mechanisms responsible for the formation of welds and microstructural refinement, and (b) effects of FSW/FSP parameters on resultant microstructure and final mechanical properties. While the bulk of the information is related to aluminum alloys, important results are now available for other metals and alloys. At this stage, the technology diffusion has significantly outpaced the fundamental understanding of microstructural evolution and microstructure–property relationships.

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Friction Stir Welding and Processing

An introduction to heat transfer

Recent advances in friction-stir welding : Process, weldment structure and properties

Air-texturisation is a process that adds bulkiness to bundles of fibres. In this study, the permeability and compaction behaviour of air-texturised glass fibre rovings are experimentally characteri...

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Permeability and compaction behaviour of air-texturised glass fibre rovings: A characterisation study:

A 1-D analytical model for the thermally induced stresses in the mold surface during die casting

The required accuracy for the final dimensions of the molded lenses in wafer-based precision glass molding as well as the need for elimination of costly experimental trial and error calls for numerical simulations. This study deals with 3D thermo-mechanical modeling of the wafer-based precision glass lens molding process. First, a comprehensive 3D thermo-mechanical model of glass is implemented into a FORTRAN user subroutine (UMAT) in the FE program ABAQUS, and the developed FE model is validated with both a well-known sandwich seal test and experimental results of precision molding of several glass rings. Afterward, 3D thermo-mechanical modeling of the wafer-based glass lens manufacturing is performed to suggest a proper molding program (i.e., the proper set of process parameters including preset force-time and temperature-time histories) for molding a wafer to a desired dimension and quality. Moreover, the effect of some important process parameters such as cooling rate and pressing temperature on the final size and residual stress inside the wafer is evaluated. Finally, it is noted that the suggested molding program minimizes the costly empirical efforts and raises the process efficiency.

Three-Dimensional Modeling of Glass Lens Molding

This work summarizes the findings of multi-objective optimization of a gravity sand-cast steel part for which an increase of casting yield via riser optimization was considered. This was accomplished by coupling a casting simulation software package with an optimization module. The benefits of this approach, recently adopted in the foundry industry worldwide and based on fully automated computer optimization, were demonstrated. First, analyses of filling and solidification of the original casting design were conducted in the standard simulation environment to determine potential flaws and inadequacies. Based on the initial assessment, the gating system was redesigned and the chills rearranged to improve the solidification pattern. After these two cases were evaluated, the adequate optimization targets and constraints were defined. One multi-objective optimization case with conflicting objectives was considered in which minimization of the riser volume together with minimization of shrinkage porosity and limitation of centerline porosity were performed.

A Casting Yield Optimization Case Study: Forging Ram

In this study, the planar extrudate swelling of power-law and Oldroyd-B fluids are investigated. Our numerical predictions are in good agreement with the other results available in the literature. In addition, a simplified two-dimensional model of fused filament fabrication that provides details of the flow in the gap between the printing head and the substrate is presented. The numerical simulations use the streamfunction/log-conformation and the volume-of-fluid methods. INTRODUCTION The simulation of non-Newtonian freesurface flows is an important topic of computational rheology. The free-surface flow simulations of non-Newtonian fluids have several applications in polymer processing. Extrusion and fused filament fabrications are two examples of these applications related to the manufacturing of plastic parts. Fused filament fabrication is a popular 3D-printing technique, based on the extrusion of a molten filament deposited on a moving substrate. In this technology, the size of printed filament is a key fabrication parameter, as it both determines the fabrication time and the precision of the 3D print. The optimal processing parameter often depends on the rheology of the material. Numerical simulations can help understanding the flow mechanism. Shape optimization algorithms and sensitivity analysis built on numerical simulations have successfully been applied to develop computer-aided design strategies for extrusion dies1,2,3. Generally, non-Newtonian fluids are either characterized by a non-constant viscosity that depends on the flow conditions (shear-thinning and pseudoplastic liquids), or by a time-dependent stress response that includes an elastic stress component representing the recoverable deformations coming from the stretching of polymer chains (viscoelastic liquids). Extrudate swelling is a typical phenomenon influenced by shear-thinning and viscoelasticity. This conference paper presents numerical results of two-dimensional simulations of the extrudate swelling and the fused filament fabrication of non-Newtonian fluids. The models focus on the flow regions near the die exits. The results are computed with a novel non-Newtonian flow solver, based on the streamfunction/logconformation method of Comminal et al.4,5. GOVERNING EQUATIONS The isothermal creeping flows of the incompressible non-Newtonian fluids are governed by the conservation of mass and momentum: 0 ∇⋅ = u (1) Numerical Simulations of Planar Extrusion and Fused Filament Fabrication of Non-Newtonian Fluids Raphaël Comminal, Jesper H. Hattel, and Jon Spangenberg Department of Mechanical Engineering, Technical University of Denmark, Kgs. Lyngby, Denmark ANNUAL TRANSACTIONS OF THE NORDIC RHEOLOGY SOCIETY, VOL. 25, 2017

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Jesper Henri Hattel

Papers

Permeability and compaction behaviour of air-texturised glass fibre rovings: A characterisation study:

A 1-D analytical model for the thermally induced stresses in the mold surface during die casting

Three-Dimensional Modeling of Glass Lens Molding

A Casting Yield Optimization Case Study: Forging Ram

Numerical Simulations of Planar Extrusion and Fused Filament Fabrication of Non-Newtonian Fluids