Monday, April 11, 2016

Material and process information for design

Materials selection enters each stage of the design (Figure 3.1, left-hand side). The nature of the data needed in the early stages differs greatly in its level of precision and breadth from that needed later on. At the concept stage, the designer requires only approximate property values, but for the widest possible range of materials. All options are open: a polymer may be the best choice for one concept, a metal for another. The problem, at this stage, is not precision and detail, it is breadth and speed of access: how can the vast range of data be presented to give the designer the greatest freedom in considering alternatives? At the embodiment stage the landscape has narrowed. Here we need data for a subset of materials, but at a higher level of precision and detail. These are found in more specialized handbooks and software that deal with a single class or subclass of materials—metals, or just aluminum alloys, for instance. The risk now is that of losing sight of the bigger spread of materials to which we must return if the details don’t work out; it is easy to get trapped in a single line of thinking when others have potential to offer better solutions. The final stage of detailed design requires a still higher level of precision and detail, but for only one or a very few materials. Such information is best found in the data sheets issued by the material producers themselves and in detailed databases for restricted material classes. A given material (polyethylene, for instance) has a range of properties that derive from differences in the ways different producers make it. At the detailed design stage, a supplier must be identified and the properties of his product used in the design calculations; that from another supplier may have slightly different properties. And sometimes even this is not good enough. If the component is a critical one (meaning that its failure could, in some sense or another, be disastrous) then it may be prudent to conduct in-house tests to measure the critical properties, using a sample of the material that will be used to make the product itself. The process is one of narrowing the materials search space by screening out materials that cannot meet the design requirements, ranking those that remain and identifying the most promising choice (Figure 3.4). The materials input does not end with the establishment of production. Products fail in service and failures contain information. It is an imprudent manufacturer who does not collect and analyze data on failures. Often this points to the misuse of a material, one that redesign or re-selection can eliminate. The selection of a material cannot be separated from that of process and of shape. To make a shape, a material is subjected to processes that, collectively, we shall call manufacture. Figure 2.5 of Chapter 2 introduced them. The selection of process follows a route that runs parallel to that of material (Figure 3.1, right-hand side). The starting point is a catalog of all processes, which is then narrowed by screening out those that fail to make the desired shape or are incompatible with the choice of material. Material, shape and process interact (Figure 3.5). Process choice is influenced by the material: by its formability, machinability, weldability, heat treatability and so on. Process choice is influenced by the requirements for shape—the process determines the shape, the size, the precision and, to a large extent, the cost of a component. The interactions are twoway: specification of shape restricts the choice of material and process, but equally the specification of process limits the materials you can use and the shapes they can take. The more sophisticated the design, the tighter the specifications and the greater the interactions. The interaction between material, shape and process lies at the heart of the selection process. To tackle it we need a strategy. 

Materials
Engineering, Science,
Processing and Design
Michael Ashby, Hugh Shercliff and David Cebon
University of Cambridge,
UK
AMSTERDAM • BOSTON • HEIDELBERG • LONDON • NEW YORK • OXFORD
PARIS • SAN DIEGO • SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO
Butterworth-Heinemann is an imprint of Elsevier

Saturday, December 21, 2013

Jasa Desain Apartemen Minimalis

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Monday, April 22, 2013

SMART (INTELLIGENT) GELS (HYDROGELS)

In the literature you can find these smart materials under a variety of names, as reflected by
the title of this section. The concept of smart gels is a combination of the simple concept
of solvent-swollen polymer networks in conjunction with the material being able to respond
to other types of stimuli. A partial list of these stimuli includes temperature, pH, chemicals,
concentration of solvents, ionic strength, pressure, stress, light intensity, electric fields, magnetic
fields, and different types of radiation.35–39 The founding father of these smart gels,
Toyochi Tanaka, first observed this phenomenon in swollen clear polyacrylamide gels. Upon
cooling, these gels would cloud up and become opaque. Upon warming these gels regained
their clarity. Upon further investigation to explain this behavior, it was found that some gel
systems could expand to hundreds of times their original volume or could collapse to expel
up to 90% of its fluid content with a stimulus of only a 1 C change in temperature. Similar
behavior was observed with a change of 0.1 pH unit.
These types of behaviors led to the development of gel-based actuators, values, sensors,
control-led release systems for drugs and other substances, artificial muscles for robotic
devices, chemical memories, optical shutters, molecular separation systems, and toys. Other
potential systems for the development of products with smart (intelligent) gels (hydrogels)
include paints, adhesives, recyclable absorbents, bioreactors, bioassay systems, and display.
Numerous examples of the commercialization of these smart gels can be found in Ref.
35. This chapter will only include a few examples of smart gels. One such smart gel consists
of an entangled network of two polymers, a poly(acrylic acid) (PAA) and a triblock copolymer
of poly(propylene oxide) (PPO) and poly(ethylene oxide) (PEO) with a sequence of
PEO–PPO–PEO. The PAA portion is a bioadhesive and is pH responsive, the PPO moieties
are hydrophobic substances that assist in solubilizing lipophilic substances in medical applications,
and the PEO functionalities tend to aggregate, resulting in gelation at body temperatures.
Another smart gel system with a fairly complex composition consists of citosan,
a hydrolyzed derivative of chitin (a polymer of N-acetylglucosamine that is found in shrimp
and crab shells), a copolymer of poly(nisopropylacrylamide) and poly(acrylic acid), and a
graft copolymer of poly(methacrylic aid) and poly(ethylene glycol). This gel system was
developed for the controlled release of insulin in diabetics.
Polyampholytic smart hydrogels swell to their maximum extent at neutral pH values.
When such gels, copolymers of methacrylic acid 2-(N,N-dimethylamino)ethyl methacrylate,
are subjected to either acidic or basic media, they undergo rapid dehydration.39
One very unusual smart gel is based upon the polymerization of N-isopropylacrylamide,
a derivative of tris(2,2 -bipyridyl)ruthenium(II) that has a polymerizable vinyl group, and
N,N -methylenebisacrylamide. It is a self-oscillating gel that simulates the beating of the
heart with color changes.
Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition.
Edited by Myer Kutz
2006 by John Wiley & Sons, Inc.