Chapter 1
Introduction
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
Materials in Design
Design is the process of translating a new
idea or a market need into the detailed
information from which a product can be
manufactured
Each of its stages requires decisions about
the materials of which the product is to be
made and the process for making it
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
Material development is
driven by the desire for
ever greater performance
Today, over 160,000
materials are available to
engineers
Figure 1.1
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
The development of
materials to meet
demands on strength
and density is
illustrated by these
material property
charts
Similar time plots
show this progressive
filling for all materials
properties
Figure 1.2
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
Evolution of Materials in Products
Figure 1.3
Early kettles, heated directly over a fire, were
made of materials that could conduct heat well
and withstand exposure to an open flame
Today almost all kettles are made of plastic,
allowing economic manufacture with great
freedom of form and color
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
The development of vacuum cleaners has been
rapid and driven by the use of new materials
Hand-powered cleaners made mostly of natural
materials have been replaced with high powered
motors and centrifugal filtration
Figure 1.4
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
Early cameras were made of wood and constructed
with the care and finish of a cabinetmaker; they had
well-ground glass lenses manufactured by
techniques developed for watch and clock making
Figure 1.5
High-end cameras are now manufactured with the
precision and electronic sophistication of scientific
instruments; lower-end models are made with
molded polypropylene or ABS bodies
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
Early planes were made of low-density
woods, steel wire, and silk
Figure 1.6
The aluminum airframe provided high stiffness
and strength to allow planes to be bigger and
fly further
The future of airframes is exemplified by
Boeings 787 Dreamliner (80% carbon-fiber
reinforced plastic), claims to be 30% lighter per
seat than competing aircraft
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
Chapter 2
The Design Process
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
Design-Led Approach
We aim to develop a methodology for
selecting materials and processes that is
design led;
The methodology for selecting materials
uses, as inputs, the functional requirements
of the design
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
The starting point of a design is a market need
or a new idea that can be expressed as a set of
design requirements the end point is the full
specification of a product that fills the need
Design Flow Chart
Figure 2.1
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
The product itself is
called a technical
system which consists
of subassemblies and
components
Material and process
selection is at the
component level
Figure 2.2
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
Function Structure
Figure 2.3
Systems approach to the analysis of a
technical system considers the inputs,
flows, and outputs of information, energy,
and materials
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
Convoluted Path of Design
Cs: Concepts
Es: Embodiments of Cs
Ds: Detailed realizations of Es
The design process is
complete when a compatible
path from need to
specification can be identified
Figure 2.4
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
Design Flow Chart
Figure 2.5
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
Figure 2.6
The central problem of materials
selection in mechanical design: the
interaction between function, material,
process, and shape
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
Case Study
Device to Open Corked Bottles
Left
The market need; a
device to allow access
to wine contained in a
corked bottle
Right
Five possible concepts
(C), illustrating physical
principles, to fill the
need
Figure 2.7
Figure 2.7
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
Working principles for implementing
three concept (C)designs
Figure 2.8
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
Device to Open Corked Bottles
The embodiments (E) identify the functional
requirements of each component of the device,
which might be expressed in statements such as
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
a)
b)
a)
b)
Embodiments
Direct pull
Lever-assisted pull
Gear-assisted pull
Spring-assisted pull
Detailed design of the
lever of embodiment with
material choice
Figure 2.9
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
Figure 2.10
The function structure and working
principles of cork removers
Materials Selection in Mechanical Design, 4th Edition 2010 Michael Ashby
Chapter 3
Engineering
Materials and
Their Properties
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Material Selection
It is not necessarily a material
that we seek, but a certain
profile of properties the one
that best meets the needs of
the design
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Menu of Engineering Materials
The members of a
material family have
certain features in
common: similar
properties, similar
processing routes,
and, often, similar
applications
Figure 3.1
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Ceramics
Stiff high E
Hard
Abrasion resistant
Good high temperature strength
Good corrosion resistance
Brittle
Glasses
Hard
Corrosion resistant
Electrically insulating
Transparent
Brittle low KIC
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Fracture Toughness vs E
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Qual o melhor compromisso?
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Polymers
Light low
Easily shaped
High strength per unit weight (/)
Lack stiffness low E (50X less than metals)
Properties highly sensitive to temperature
Elastomers
Lack stiffness low E (500 5000X less than
metals)
Able to retain initial shape after being stretched
Relatively strong and tough
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Metals
Tough high KIC
Stiff high E
Ductile
Wide range of strengths depending on composition and
processing
Thermally and electrically conductive
Reactive low corrosion resistance
Hybrids
Expensive
Difficult to shape and join
Properties dependent on combination of
materials
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
What type of materials information do
you need for design?
Figure 3.2
We are interested in the data in the center of the
schematic; structured data for design allowables and
information concerning the materials ability to be
formed, joined, and finished
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Material Properties and Their Units
Each material can be
thought of as having a
set of attributes or
properties
The combination that
characterizes a given
material is its property
profile
Figure 3.3
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Mechanical Properties
The stress-strain curve for a metal,
showing the modulus, E, the 0.2% yield
strength, y, and the ultimate strength, ts
The strain at the
point of failure
indicates the ductility
of a material
Figure 3.4
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Figure 3.5
The tensile response of a
polymer varies with
temperature here the
response is shown with
respect to the glass
transition temperature, Tg
The compressive
strength of a ceramic is
10-15 times greater than
the tensile strength
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Figure 3.6
The modulus of rupture (MOR) is the
surface stress at failure in bending it is
equal to, or slightly larger than, the failure
stress in tension
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Figure 3.7
For many materials there exists a fatigue or
endurance limit, e, illustrated by the Nf
curve; it is the stress amplitude below which
fracture does not occur, or only occurs after a
very large number (Nf >107) cycles
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Hardness is measured as the load, F,
divided by the projected area of contact,
A, when a diamond-shaped indenter is
forced into the surface
Figure 3.8
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Commonly used scales of hardness
related to each other and to the yield
strength
Figure 3.9
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Figure 3.10
The fracture toughness, KIC, measures the
resistance to the propagation of a crack; the
test specimen containing a crack of length 2c
fails at stress *; the fracture toughness is
then KIC = Y*(c)1/2
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Figure 3.11
The loss tangent measures the
fractional energy dissipated in a stressstrain cycle
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Figure 3.12
Wear is the loss of material from surfaces
when they slide; the wear resistance is
measured by the Archard wear constant, KA
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Thermal Properties
Figure 3.13
The heat capacity the energy to
raise the temperature of 1 kg of
material by 1C
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Figure 3.14
The thermal conductivity
measures the flux of heat driven
by a temperature gradient
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Figure 3.15
The linear-thermal expansion coefficient
measures the change in length, per unit
length, when the sample is heated
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Electrical Properties
Figure 3.16
Electrical resistivity, e, is measured as the
potential gradient, V/L, divided by the current
density, i/A; it is related to the resistance, R, by
e = AR/L
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Dielectric Constant
Figure 3.17
Dielectric Loss
Figure 3.18
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Chapter 4
Material Property Charts
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Bar Charts One Property
Figure 4.1
Each property of an engineering material has a
characteristic range of values; the bar chart
shows the modulus for a family of solids
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Bubble Charts Multiple Properties
Figure 4.2
Youngs modulus plotted against density
on log scales; each material class
occupies a characteristic field
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Youngs Modulus - Density
Figure 4.3
The guide lines of constant E/, E1/2/, and
E1/3/ allow selection of materials for minimum
weight, deflection-limited, design
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Strength - Density
Figure 4.4
The guide lines of constant f/, f2/3/, and
f1/2/ are used in minimum weight, yieldlimited design
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Strength Modulus: The design guide lines help
with the selection of materials for springs, pivots,
knife-edges, diaphragms, and hinges
Figure 4.5
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Specific modulus E/ plotted against specific strength
f/; the design guide lines help with the selection of
materials for lightweight springs and energy-storage
systems
Figure 4.6
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Figure 4.7
Plot of fracture toughness vs. Youngs
modulus helps in design against fracture
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Material selection for damage-tolerant design
should utilize the fracture toughness vs. strength
property chart
Figure 4.8
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Loss Coefficient Youngs Modulus
Figure 4.9
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Thermal Conductivity
Electrical Resistivity
Figure 4.10
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Thermal Conductivity
Thermal Diffusivity
Figure 4.11
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Thermal Expansion
Thermal Conductivity
Figure 4.12
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Thermal Expansion
Youngs Modulus
Figure 4.13
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Maximum Service Temperature
Above this temperature, the
material becomes unusable
Figure 4.14
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Figure 4.15
Bar chart of the friction coefficient
of materials sliding on an
unlubricated steel counterface
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Figure 4.16
The normalized wear rate plotted against the
hardness; the chart gives an overview of the
way in which common engineering materials
behave
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
The cost of a
material can be
expressed in two
ways:
$/kg
or
$/m3
Figure 4.17
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Youngs Modulus
Cost Per Unit Volume
Chart helps
the selection
to maximize
stiffness per
unit cost
Figure 4.18
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Strength Cost Per Unit Volume
Design guide lines help selection to
maximize strength per unit cost
Figure 4.19
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Chapter 5
Material Index
(without shape)The Basics
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
This chapter sets out
the basic procedure
for selection,
establishing the link
between material and
function
Figure 5.1
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Figure 5.2
The universe of materials is divided into
families, classes, subclasses, and
members; each member is characterized
by a set of attributes: its properties
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Selection Strategies
Figure 5.3
Required features are constraints; they are
used to screen out unsuitable cars. The
survivors are ranked by cost of ownership
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Restries e Objectivos tpicos
Restries
rigidez
resistncia
tenacidade fractura
condutividade trmica
resistividade elctrica
limitaes magnticas
transparncia ptica
custo
massa
resistncia corroso
resistncia abraso
Objectivos
minimizao
custo
massa
volume
impacte ambiental
perda trmica
maximizao
armazenamento energtico
fluxo trmico
ndice do Material a propriedade, ou conjunto de propriedades,
que maximizam o desempenho
5
Choosing a Material
Figure 5.14
1. Design requirements are first expressed as constraints and objectives.
2. The constraints are used for screening.
3. The survivors are ranked by the objective, expressed as a material index.
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Strategy for Materials Selection
The four main steps:
1. Translation
2. Screening - restrictions
3. Ranking - objectives
4. Documentation
Figure 5.5
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Translating Design Requirements
Soft constraints
Hard constraints
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Figure 5.14
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Material Indices
Constraints set property limits.
Objectives define material indices, for
which we seek extreme values (Max or
min).
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Minimizing Mass:
A light, strong tie
Objective Function: equation
describing the quantity to be
maximized or minimized.
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
We can reduce the mass by reducing the
cross-section, but there is a constraint: A must
be sufficient to carry F*, requiring that:
Eliminating A between these two
equations gives:
Material indices are generally expressed so that a
maximum value is sought, so the material index
for a light, strong tie is:
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Minimizing Mass
A light, stiff panel
Objective Function
Constraint on Stiffness
Second Moment of Area
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Material index for a light, stiff panel
Material index with a constraint of
strength rather than stiffness
Fiquei aqui 2013-03-06
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Try it!
Minimizing Mass
A light, stiff beam
Objective Function
Constraint on Stiffness
Second Moment of Area
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Material index for a light, stiff beam
Material index with a constraint of
strength rather than stiffness
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Performance Equation
Structural Efficiency Index
The performance of a structural element is
determined by three things:
the functional requirements, the geometry,
and the properties of the material of which it
is made.
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Figure 5.7
The specification of function, objective,
and constraint leads to a materials index.
The combination in the highlighted boxes
leads to the index E1/2/.
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Translating and Deriving the Index
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Figure 5.8
A schematic E- chart showing a lower
limit for E and an upper limit for .
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Ranking: Indices on Charts
Figure 5.9
A schematic E- chart showing guide lines for the
three material indices for stiff, lightweight design.
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Figure 5.10
A schematic E- chart showing a grid of
lines for the material index M=E1/3/.
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Figure 5.11
A selection based on the index M=E1/3/ > 2(GPa)1/3 (Mg/m3)
together with the property limit E > 50 GPa. The materials
contained in the search region become the candidates for the
next stage of the selection process
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
Figure 5.12
Computer-aided selection using the CES software. The
schematic shows the three types of selection window.
They can be used in any order and any combination.
The selection engine isolates the subset of materials
that passes all the selection stages.
Materials Selection in Mechanical Design, 4th Edition, 2010 Michael Ashby
