71 research outputs found
Making the great transformation, November 13, 14, and 15, 2003
This repository item contains a single issue of the Pardee Conference Series, a publication series that began publishing in 2006 by the Boston University Frederick S. Pardee Center for the Study of the Longer-Range Future. This Conference took place during November 13, 14, and 15, 2003. Co-organized by Cutler Cleveland and Adil Najam.The conference discussants and participants analyze why transitions happen, and why they matter. Transitions are those wide-ranging changes in human organization and well being that can be convincingly attributed to a concerted set of choices that make the world that was significantly and recognizably different from the world that becomes.
Transition scholars argue that that history does not just stumble along a pre-determined path, but that human ingenuity and entrepreneurship have the ability to fundamentally alter its direction. However, our ability to ‘will’ such transitions remains in doubt. These doubts cannot be removed until we have a better understanding of how transitions work
Dynamic Crushing Response of Closed-cell Aluminium Foams during Shock Loading
Understanding the impact response of aluminium foams is essential for assessing their energy absorption capacity under dynamic loading. In this paper, the dynamic compaction behavior of closed-cell aluminium foam (CYMAT â„¢) has been tested using the plate-impact technique. Post-impacted samples have been examined using optical microscopy to observe the microstructural changes with the objective of elucidating the pore-collapse mechanism.The authors
also gratefully acknowledge UNSW Canberra’s Defence Related Research program that part-funded this work
A microstructural study of warm rolled interstitial free steel
published_or_final_versionMechanical EngineeringDoctoralDoctor of Philosoph
The effect of cross-rolling on the growth of goss grains in a grain oriented silicon steel
© 2016, Springer International Publishing AG. All rights reserved. A series of cross-rolled cold rolling experiments, followed by annealing experiments, were carried out on a commercial two-pass cold rolled Fe-Si alloy. Even though no major influence was observed on the primary recrystallized grains after the sheet was subjected to ~10% deformation, its effect on the texture distribution of the sheet (prior to annealing) is noticeable. The texture of the rolled sample showed increases in the {112}<111> orientation and Goss texture within a 5° spread. However, after annealing for 10 and 60 min. at 900°C, abnormal growth of Goss grains does not occur and the Goss texture gradually disappears
An ebsd study of nickel sheets after unidirectional and cross rolling arb processings
Copyright © 2015 MS&T15®.Commercially pure nickel sheets were processed by accumulative roll bonding (ARB) up to six cycles at room temperature in two different routes. In route one ARB was carried out conventionally and it is called U (unidirectional)-ARB. In route two the sample is rotated by 90° around the normal direction (ND) in alternating ARB cycles and it is called C (cross-rolled)-ARB. Both routes produce typical fine lath structures of severe rolling deformations. EBSD study shows that U-ARB produces typical FCC rolling textures containing Copper {112} <111>, S {123} <634> and Brass {110} <112> orientations. In comparison, C-ARB produces diffused orientation distributions with principal components distributing between Brass and {011} <111> orientations. Schmid factor calculation of the sheet around the RD shows less variation in C-ARB sample than the U-ARB sample. This implies that reduced in-plane anisotropics can be achieved by cross rolling in ARB processing
Time and temperature regime of continuous grain coarsening in an ECAP-processed Al(0.1 wt.% Sc) alloy
An equiaxed, submicron grain size distribution was generated in an Al(0.1 wt.% Sc) alloy by processing through equal channel angular pressing followed by a low temperature pre-ageing heat treatment. The alloy was subsequently annealed for various times at 300, 350, 400 and 450 °C for investigating the thermal stability of the deformation microstructure. It was found that up to 400 °C, the submicron grain structure coarsens slowly and uniformly by a process of continuous recrystallization. Within this temperature range, the uniform dispersion of nano-sized Al 3Sc particles generated by the pre-ageing treatment substantially hinders grain coarsening by Zener pinning of the (sub)grain boundaries. At the higher annealing temperature of 450 °C, certain grains were found to grow discontinuously thereby generating a mixed microstructure consisting of both fine and coarse grains. The data in this study was combined with recent data for a higher solute Al(0.3 wt.% Sc) alloy for furthering our understanding of the time and temperature range in which this family of alloys is resistant to rapid, discontinuous grain coarsening (recrystallization). © 2011 Elsevier Ltd. All rights reserved
The initial stages of formation of low angle boundaries within lamellar bands during accumulative roll bonding of aluminum
The nature of newly forming lamellar band boundaries was investigated in accumulative roll bonded aluminum. These boundaries initiate as low angle interfaces parallel to the existing lamellar band boundaries irrespective of the crystallographic orientation of the parent lamellar band. The transverse directions of the divided segments were found to rotate at an angle equal to the degree of misorientation between segments. Such a phenomenon is not sustained when the boundaries become high angle
Composites matching the properties of human cortical bones: The design of porous titanium-zirconia (Ti-ZrO2) nanocomposites using polymethyl methacrylate powders
Bone-like low elastic modulus micro-porous titanium (Ti) and titanium-zirconia (Ti-ZrO2) nanocomposites were fabricated by a pressureless sintering process with biocompatible polymethyl methacrylate (PMMA) powders as the pore-forming agents. A microstructural analysis revealed that the method can successfully make randomly distributed pores in the sintered monolithic and nanocomposite, and the pore-forming agents can be removed by a heat treatment process. The material properties, i.e., the relative density, pore morphology, microhardness and elastic modulus, can be dramatically altered with the pore-forming agent. Moreover, the porous Ti-based nanocomposites produced in this way (50 vol% PMMA) have interconnected pores, higher biocompatibility, better mechanical properties and well controlled the Ti grain size, when compared with the monolithic porous Ti bodies through the second phase strengthening mechanism. The elastic moduli of the highly porous monolithic Ti and Ti-ZrO2 nanocomposites can be controlled to be about 20.0 and 22.4 GPa, respectively, which are almost the same as human cortical bones (7-25 GPa)
Crystallography of the low angle lamellar band boundaries in ARB-processed aluminum sheet
Lamellar bands are the primary structural features in accumulative roll bonding (ARB) of sheet metals. The structural refinement in ARB sheets occur by forming a dense distribution of lamellar band boundaries. The lamellar band boundaries initiate as low angle interfaces, parallel to the existing lamellar band boundaries, irrespective of the crystallographic orientations of the parent lamellar bands. From an extensive investigation it was found that the transverse directions across the lamellar band boundaries are rotated by an angle equal to their misorientations. Such a phenomenon is not sustained when the boundaries turn to high angle. © (2012) Trans Tech Publications, Switzerland
The mode of deformation in a cold-swaged multifunctional Ti-Nb-Ta-Zr-O alloy
Multifunctional titanium alloys, termed Gum Metal™, are ß-phase Ti alloys first developed in 2003. These alloys exhibit many interesting properties including, for example, low rate of work-hardening and superplasticity during cold deformation. The original report described a new plastic deformation mechanism not involving major dislocation activity to explain such deformation behavior. In the current study, a comparable Ti-36.8Nb-2.7Zr-2.0Ta-0.44O (wt pct) alloy to the original investigators was produced by powder sintering, hot forging, solution treatment, and cold swaging with the aim at investigating the microstructural development during swaging. XRD and TEM showed that the forged/solution-treated alloy was ß-phase with a small amount of ?-phase. After cold swaging by up to 96 pct area reduction, TEM/HRTEM revealed the existence of dislocations, deformation twins, ?-phase, nanodisturbances, and lattice bending, with EBSD showing the grains to be highly elongated in the swaging direction, fragmented, and distorted. Most notably, swaging also generated a strong 〈 110âŒo fiber texture, even after moderate strains. The foregoing structural analysis provides substantial evidence that dislocations are present in the alloy after cold swaging. The major support of dislocation glide processes acting as the dominant plastic deformation mode in the swaged alloy is the strong 〈110âŒo fiber texture that develops, which is a characteristic feature of all cold-drawn/swaged body centered cubic metals and alloys. © 2013 The Minerals, Metals & Materials Society and ASM International
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