College of Engineering
Department of Mechanical Engineering
MATERIAL IN DESIGN
DR: MOHAMMAD ELSHAYEB
Submitted By:
Abdullah A. AL-Shubaiki, ….. # 200801368
Zaki S. Al-Qarni, …………….……. # 200801484
Fasial Ansari, ……………………... # 200800635
Nadeem Khan, ……………………. # 200900147
Nawaf Al Bassam, ……………….. # 200801200
FALL SEMESTER 2012/2013
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Table of Contents
Chapter 1:
1.1
1.2
1.3
1.4
1.5
1.6
Materials Selection
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Performance Requirements of materials
. . . . .. . . . . . . . . . . . . . . . . . . . .
The materials selection process . . . . . . . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
Source of information on material properties
. . . . . . . .. .. .. ... ... ... ... ... ... ... .. .. .. . . . .
Cost of materials . . . . . . . . . . . . . . . . . . . . . . . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
Overview of methods of materials selection
. . . . . . ........ .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
03
04
07
08
09
11
1.7
1.8
1.9
1.10
1.11
Materials performance indices . . . . . . . . . . . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
Materials selection with decision matrices . . . ... ... ... .. .. .. .. .. .. .. .. .. .. .. . .
Selection with computer-aided databases .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
Design examples . . . . . . . . . . . . . . . . . . . . . .. .. .. .. .. .. ... ... ... ... ... ... ... .. .. .. .. .. ..
Summary . . . . . . . . . . . . . . . . . . . . . .. .. .. .. .. .. .. .. .. . .. .. .. .. .. .. .. .. .. .. .. . . . .
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23
24
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1.1 Introduction:
 Relation of materials selection to design
 General Criteria for selection:
o
Performance characteristics (Properties)
o
Processing (manufacturing) characteristics
o
Environmental profile
o
Business considerations
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1.2 Performance Requirements of materials
 Classification of materials
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 Properties of materials
The first task in materials selection is to determine which material properties
are relevant to the application.
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 Mechanical properties
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 Ashby Charts
It displays elastic modulus of polymers, metals, ceramics, and composites
plotted against density
1.3 The materials selection process
 Material choices governed by:
 Material properties
 Manufacturing issues
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 Materials selection for a new product or new design:
 Define the function that the design must perform
 Define the manufacturing parameters
 Compare the needed properties and parameters against a large material
data
 Investigate the candidate
 Develop design data and/or a design specification
 Materials substitution in an existing design:
 Characterize the currently used material in terms of performance,
manufacturing and cost.
 Determine which properties must be improved
 Search for alternative materials and/ or manufacturing routes.
 Compile a short list of materials and processing routes.
 Two different approaches to materials selection
 Selecting a material class
 Manufacturing process
1.4 Source of information on material properties
 Conceptual design
 Embodiment design
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 metals
 Ceramics
 Polymers
 Composites
 Electronic materials
 Thermal properties
 Chemical properties
 Internet
 Detail design
 Needs very precise data.
 Wide range of material information is required.
1.5 Cost of materials
 Cost of materials
The cost of a material depends upon:
 Scarcity, as determined by either the concentration of the metal in the
ore or the cost of feedstock for making a polymer.
 The cost and amount of energy required to process the material
 The basic supply and demand for the material.
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Example: Increase in the strength of steel are achieved by:
 Expensive alloy additions such as nickel.
 Heat treatment such as quenching and tempering
 Vacuum treatment of the liquid steel to remove gaseous impurities.
 Cost structure of materials
 True value can be obtained through quotations from vendors.
 Reference sources typically give only the nominal or baseline price.
 The actual price depends upon a variety of price extras in addition to
the base price.
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1.6 Overview of methods of materials selection
 A variety of approaches to materials selection are followed by designer
and materials engineers:
 Common path is to critically examine the service of existing designs in
environments similar to the one of the new design.
 Experience with a pilot plant provide valuable input.
 Often a minimum innovation path is followed.
 Analytical methods of materials selection are:
 Performance indices
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 Decision materials
 Pugh selection method
 Weighted property index
 Computer-aided databases
 Rational way to select materials:
 Using a material performance index
 Determine the way in which actual parts, or parts similar to a new
design, fail in service. Then, on the basis of that knowledge, materials
that are unlikely to fail are selected.
1.7 Material Performance Indices
 A material performance index is a group of material properties that
governs some aspect of the performance of a component.
 The performance of an engineering component is limited by the
properties of the material of which it is made, along with the shapes to
which the material can be formed.
 When the performance index is maximized, it gives the best solution of
the design requirement.
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1.8 Material selection with decision matrices
 Selection of materials is divided into three groups:
1. Go/no-go parameters
2. Non discriminating parameters
3. Discriminating parameters
The 3 parameters
1. Go/no-go parameters: Such a parameter in which requirements must
meet a certain fixed minimum value.
2. Non-discriminating parameters: Requirement must be met if the
material is to be used at all.
3. Discriminating parameters: Those requirements to which the
quantitative values can be assigned.
Pugh Selection Method
 This is the simplest decision method used for selection of any material.
This method involves comparison of each alternative to a reference or
alternative. Go/no-go parameter is not used, but non discriminating and
discriminating parameters are used.
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Weighted property index
 It is a method of evaluating competing concepts by ranking the design
criteria with the weighting factors and scoring the degree to which each
design concept meets the criterion.
 The weighted property index is given by,
γ≈∑βiwi
βi: Is summed over all the properties.
Wi: Is the weighing factor for the ith property.
Selection with computer aided database
 Developing and using well defined standards for electronic information
sharing to enable selective protection of organizational private data,
company’s proprietary data and industry restricted data from the
public domain data.
 Reviving contact between researcher, designer and supplier or design
Advantages of using computer aided database
 Minimizes the material selection information overload.
 Over 100 material databases are available worldwide.
 It is useful to employ limits on properties.
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 Most existing databases provide numerical material properties as
opposed to quantitative ranking.
 Some data bases have the ability to weight the importance of various
properties.
Design Examples
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Material performance indices:
The performance of an engineering component is limited by the properties of
the material of which it is made, and by the shapes to which this material can
be formed. Under some circumstances a material can be selected satisfactorily
by specifying ranges for individual properties. More often, however,
performance depends on a combination of properties, and then the best
material is selected by maximizing one or more ‘performance indices’. An
example is the specific stiffness E/r (E is Young’s modulus and r is the
density). Performance indices are governed by the design objectives. One is
derived later in this paper and many others are tabulated elsewhere [1, 2].
Component shape is also an important consideration. Hollow tubular beams
are lighter than solid ones for the same bending stiffness and I–section beams
may be better still. Information about section shape can be included in the
performance index to enable simultaneous selection of material and shape.
Performance Indices
A performance index is a group of material properties which governs some
aspect of the performance of a component [1, 2]. They are derived from
simple models of the function of the component, as illustrated by the following
example.
A material is required for a light, stiff beam. The aim is to achieve a specified
bending stiffness at minimum weight. The beam has a length L and a square,
solid, cross–section as shown in Figure
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1a. The mass of the beam is
where A is the area of the cross–section and r is the density of the material of
which the beam is made. The stiffness S of a simply–supported beam with
modulus E, second moment of area I, central load F, and central deflection d,
is
with C1 = 48 for 3-point bending. Other supports, or other distributions of
load, change C1, but nothing else. Assume that the beam has a square section,
of side b. The second moment of area is
Substituting for I in equation (2) and eliminating A between this and (1) gives
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The mass of the beam can be minimized (and performance maximized) by
seeking the material with the largest value of the performance index
The same performance index holds for square–section beams with any value
of the design stiffness S, any boundary conditions and distributions of load
(defined by C1), and any length L. The cross–section shape of the beam (like
the I–section shown in Figure 1b) can be included in the performance index by
introducing a dimensionless shape factor f, defined [3] by
The value of f measures the bending efficiency of the section shape. For the
solid section of Figure 1(a), f @ 1; that for the I-section of Figure 1(b) is about
5. Real I-sections have efficiencies, f , as high as 40. The maximum value of f is
limited by manufacturing constraints or by local buckling of the component,
and, for this reason, it can be considered to be a material property. Shape
factors can also be defined for design against yield or fracture, and for shafts
as well as beams. Using equation (6) in place of equation (3) to eliminate A in
equation (1) gives the new index:
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For a constant shape ( f constant) the criterion reduces to the earlier one; the
best selection is then the material with the largest value of M1 (equation (5)).
In comparing materials with different shapes, the best choice is that with the
greatest value of M2 (equation (7)).
Material Property Charts
Material selection using performance indices is best achieved by plotting one
material property (or mathematical combination of properties) on each axis of
a materials selection chart [1,2]. In the example shown in Figure 2, the axes are
Young's modulus and density. The logarithmic scales span a range so wide
that all materials are included. When data for a given material class such as
metals are plotted on these axes, it is found that they occupy a field which
can be enclosed in a ‘balloon’. Ceramics also occupy a field, and so do
polymers, elastomers, composites, and so on. The fields may overlap, but are
nonetheless distinct. Individual materials or sub–classes (like steels, or
polypropylenes, PP) appear as little ‘bubbles’ which define the ranges of their
properties. Hardcopy charts relating many mechanical and thermal
properties are now available [1] (two appear in this article). Others can be
constructed with the software described in a moment.
The subset of materials with the greatest value of M1 can be identified
rapidly by taking logarithms of equation (5) (Log E = 2 Log r + 2 Log M1),
and plotting the resulting selection line of slope 2 on the chart. The
construction is illustrated in Figure 2, from which it can be seen that woods,
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fiber reinforced composites and some ceramics are the best choices for a light
stiff beam with square cross–section. When section shape is included in the
selection criterion, (as in equation (7)) woods become considerably less
attractive, because they cannot be manufactured in thin sections with large
shape factors, like metals.
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Materials selection with decision matrices:
The values of material properties or performance indices for each candidate
material are expressed in a material property matrix as
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where, A1,..., Am are the kinds of candidate materials and X1,..., Xn are the
material properties or performance indices. Hence, xi j is the value or degree
of the j-th property or index Xj for the i-th material Ai.
Selection of materials is divided into three groups:
1. Go/no-go parameters
2. Non discriminating parameters
3. Discriminating parameters
1. Go/no-go parameters: Such a parameter in which requirements must
meet a certain fixed minimum value.
2. Non-discriminating parameters: Requirement must be met if the
material is to be used at all.
3. Discriminating
parameters:
Those
requirements
to
which
the
quantitative values can be assigned.
Pugh Selection Method:
This is the simplest decision method used for selection of any material.
This method involves comparison of each alternative to a reference. Go/no-go
parameter is not used, but non discriminating and discriminating parameters
are used.
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Weighted property index:
The weighted property index is given by,
γ≈∑βiwi
βi: Is summed over all the properties.
Wi: Is the weighing factor for the ith property
Selection with computer aided databases:
The selection of the proper materials for a structural component is a
critical engineering activity. It is governed by many, often conflicting factors
that typically include service requirements, design life, materials availability,
database accessibility, manufacturing constraints, repair and replacement
strategies, client preferences, and cost.
The incorporation of computer-aided materials selection systems into
computer-aided design and computer-aided manufacturing operations could
assist designers by suggesting potential manufacturing processes for
particular products to facilitate concurrent engineering, recommending
various materials for a specific part based on a given set of characteristics, or
proposing possible modifications of a design if suitable materials for a
particular part do not exist.
This report reviews the structural design process, determines the
elements and capabilities required for a computer-aided materials selection
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system to assist design engineers, and recommends the research and
development areas of materials database, knowledge base, and modeling
required to develop a computer-aided materials selection system.
1.9 Design Examples:
1- Bathing device for pets:An animal-containment device that enables quick and easy containment, such
as bathing, of a household pet. The device includes a basin that may be easily
manufactured in a unitary piece. The basin includes at least one adjustable
strap attached between the sides of the basin. The strap is secured in
elongated slots along the sides of the basin over the back of the pet being
bathed. A central hump is formed on the basin floor that conforms
substantially to the underbelly of the pet. The hump prevents the pet from
sitting down during the bathing process. An adjustable collar restraint strap
is attached to an additional slot. The collar restraint strap is attachable to a
standard pet collar. The pet is immobilized by way of the hump and
adjustable straps. A drain with a removable plug is included at the bottom of
the basin that is attachable to a standard garden hose for removal of bath
water. Assorted bathing accessories are also included for attachment around
the lip of the basin.
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2- Apparatus and method for enhancing the efficiency of liquid-fuelburning systems:-
A cold-steam atomizer designed to use ultrasonics to produce mist to be
mixed with a combustible fluid. The device is designed to transfer that
mist/combustible fluid mixture into a combustion system in order to enhance
internal and external combustion. The mist generator utilizes an immersed
vibrating element to atomize a liquid such as water to create the mist. The
atomizer is housed in a chamber having a baffle that is designed to prevent
large droplets of the liquid from entering the combustion chamber. The
system alternatively includes a tank for storing the liquid prior to
atomization.
3- Shoulder-strap retainer apparatus:-
A shoulder-strap retainer attachable to a shoulder strap for preventing a
shoulder strap from slipping off the user's shoulder. The shoulder strap
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retainer includes a main retainer body, a first retainer end, and a second
retainer end. The first retainer end is axially connected to one end of the main
retainer body and includes a first tongue end operatively associated with a
first securing means. The second retainer end is axially connected to a second
end of the main retainer body and includes a second tongue end operatively
associated with a second securing means. The first retainer end is attached to
one leg of the shoulder strap and the second retainer end is attached to a
second leg of the shoulder strap. The shoulder-strap retainer is used such that
the shoulder strap is placed on top of the shoulder while the shoulder-strap
retainer is positioned underneath the arm and adjusted to securely fit the
shoulder strap to the shoulder.
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1.11 Summary:
This chapter has shown that there are no magic formulas for materials
selection. Rather, the solution of a materials selection problem is every bit a
challenging as any other aspect of the design process and follows the dame
general approach of problem.
The steps in material selection are:
1- Define the function that the design must perform and translate these
into required material properties and to business factors such as cost
and availability.
2- Define the manufacturing parameters such as number of parts
required, size and complexity of the part, tolerances, quality level, and
fabric ability of the material.
3- Compare the need properties and process parameter with large
material databases to select a few material that look promising for the
application.
4- Investigate the candidates’ material in greater detail, particularly in
terms of trade-offs in performance. Cost and manufacturing. Make a
final selection of material.
5- Develop design data and a design specification.
Life cycle issues should always be considered, especially those having to
do with recycling and disposal material.
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