Materials Selection for Mechanical Design: Exploring the World of Materials
Background: the motivation
History – the evolution of materials
Materials and their attributes
The nature of materials data
Introduction
Design is… “…the process of translating a new idea or a market need into detailed information from which a product can be manufactured.” M. F. Ashby, “Materials Selection in Mechanical Design”,
Idea or Need
Design
Invention
Engineering Design
Market need
Industrial Design
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Product
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Types of Design
Original Design
New idea or working principle e.g. CD replacing magnetic tape
Adaptive or Development Design
Takes existing product and seeks an incremental advance in performance through a refinement in working principle. e.g. beverage cans, automobiles,…
Variant Design
Change in scale/dimension without change of function e.g. desktop to laptop computer
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Vocabulary of Design
Design problems are open ended - no single correct answer
Design is an iterative process
Products are technical systems composed of assemblies and components
The design objective must be formulated as a “need statement” “A device for performing task x is needed”
But must not specify a way of satisfying the need “Must be solution neutral”
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Example Need
Design objective: “A device is needed to pull the cork from wine bottle” Not solution neutral – pulling specifies the solution
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Possible solutions
Revised Design Objective: “a device is required to allow access to wine in a corked bottle with convenience, at modest cost, without contaminating wine…”
Screw to transmit prescribed load to cork
Slender elastic blade that will not buckle when driven between the cork and the bottle-neck
Thin, hollow needle, stiff and strong enough to penetrate cork Concepts
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Possible solutions
Embodiments of one concept
Embodiments
Direct pull
Levered pull
Geared pull
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Spring assisted pull
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One solution
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Other Concepts
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Air pressure cork popper
Air Pressure Bottle Opener Automatic Cork Popper No tugs, no pulls, no corkscrews - no groans! This advanced approach to uncorking wines is almost effortless. Just push the needle into the cork, pump and... pop! The injected air causes the cork to lift itself right out of the bottle
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Butler’s friend
This device consists of a pair of thin, narrow, flexible metal blades mounted in parallel to a flattened loop of a handle.
In storage the blades are protected by a metal or plastic sheath.
Remove the sheath, and you'll notice that one blade is slightly longer than the other.
Insert the longer blade first between cork and glass (about 1/4 inch); then insert the shorter blade opposite.
Rocking the handle back and forth, you gently push down each blade in turn about 1/4 inch at a time until the frame of the handle rests on the top of the cork. Then simply twist and lift.
The cork comes out with ease and can be removed from between the puller's blades in one motion--no need to untwist as from a helix. ME 474-674 Winter 2008
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Why Materials and Process Selection In Design?
Engineers make things to make life better.
They make them out of materials using processes.
Materials have played a role in human life since the beginning of civilization.
The progress of civilization has been recorded by the materials.
Stone age, bronze age, iron age etc.
At this time we have over 160,000 materials available to us.
Materials selection is a systematic elimination of those that are not suitable to arrive at an optimum material for the particular application.
Materials selection is an integral part of any design processes
The transition from the conceptual design to physical reality.
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Materials and Process Selection In Design
What do engineers need to know to do this successfully?
A perspective of the world of materials and processes
An understanding material properties and their origins
An ability to select those that best meet requirements of a design
Access to information and tools for comparison and selection
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General Classification of Materials
Metals
Ceramics
Polyethylene, PVC, Teflon, Nylon, Plexiglas, Bakelite, Epoxy, Polyesters, Melamine, Neoprene, Silicone
Electronic Materials
Porcelain, China, Glass, Silicon Carbide, Boron Nitride, Aluminum Oxide, etc.
Polymers
Iron, Copper, Aluminum, Zinc, Nickel, Titanium, Silver, Gold, etc. and their alloys Steel, Brass, Bronze, etc.
Silicon, Germanium, Gallium-Arsenide
Composites
Concrete, FRP, MMC, CMC, Asphalt, Wood
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The world of structural materials Steels Cast irons Al-alloys
Metals, alloys Cu-alloys Ni-alloys Ti-alloys PE, PP, PC PS, PET, PVC PA (Nylon)
Alumina Si-carbide
Ceramics Si-nitride Ziconia
Polymers
Composites Sandwiches
Polyester Phenolic Epoxy
Hybrids Lattices Segmented
Soda glass Borosilicate
Isoprene Butyl rubber
Glasses
Elastomers
Silica glass Glass ceramic
Natural rubber Silicones EVA
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History – the evolution of materials
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Comparison of Materials
Metals
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Metals Bonding:
Metallic bonds – Delocalized electrons
Structure:
Crystalline Disadvantages
Advantages
Relatively high moduli (stiff)
Failure by fatigue
Can be made strong by alloying or working
Most susceptible to environmental attack
Nominally ductile
Relatively high toughness
Paramagnetic or ferromagnetic
Good electrical conductors
(corrosion and oxidation)
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Metals
Ferrous Metals
Light Alloys
Copper Alloys
Nickel Alloys
Metal
Examples of application
Carbon Steels
Utensils, construction, automotive, transmission towers …
Stainless Steels
Off shore drilling rigs, naval construction, chemical transport, food preparation, medical instruments
Cast Irons
Cylinders, pistons, motor blocks, construction, wear resistant materials
Aluminum Alloys
Aerospace, construction, transport, packaging, electrical conductors
Magnesium Alloys
Aerospace, automotive, sporting equipment
Titanium Alloys
Aerospace, chemical industry
Copper
Electrical conductors
Bronze
Heat exchangers, chemical industry, maritime industry
Brass
Pressure vessels, fittings Aerospace, currency
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Ceramics and Glasses
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Ceramics and Glasses Bonding:
Ionic & Covalent Bonding – Directional & Strong
Structure:
Crystalline or amorphous
Advantages
Disadvantages
High moduli (stiff)
Brittle
High strength
Abrasion resistant
Statistical spread in strength
High melting point
Strength in compression ~ 15x strength in tension
Resist corrosion and oxidation
Notch sensitive
Transparent
More difficult to design with than metals or polymers
Good electrical insulators
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Ceramics and Glasses Ceramics Bulk Ceramics
Ceramic fibers and powders
Industrial Ceramics
Glasses
Examples of application
Hydrated ceramics (cement, plaster…)
Construction
Rocks
Construction
Fired ceramics (pottery, bricks …)
Construction, electrical insulators, hygienic applications, household
Fibers (glass, carbon …)
Reinforcements in polymer composites
Particles (alumina, silicon carbide, magnesia)
Reinforcements in polymer and metal Composites
Abrasive Particles
Cutting wheels, polishing cloths
Alumina, Silicon Nitride, Silicon Carbide…
High temperature furnaces, heat shields Windows, food preparation
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Polymers and Elastomers
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Polymers and Elastomers Bonding:
Covalent and secondary bonding
Structure:
Amorphous or partially crystalline
Advantages
Disadvantages
Can have high strength
Creep at room temp.
High elastic deformation (flexible)
Properties change a great deal with temperature
Low coefficient of friction
Low melting points
Corrosion resistant
Low moduli
Easy to form
Difficult to recycle
Can be colored
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Polymers and Elastomers Thermoplastics
Thermosets
Elastomers
Foams
Polymers
Examples of Applications
Acrylobutadiene styrene (ABS)
Clothing, household appliances
Cellulose Acetate
Overhead transparencies
Polyamide (Nylons)
Clothing, strong fabrics
Polycarbonates
Windows, food storage
Polyether ether ketone (PEEK)
Microwave oven dishes
Polyvinylechloride (PVC)
Credit cards, plumbing, window sashes…
Epoxy
Glue, connectors, molding
Phenols
Electrical components
Polyesters
Fabrics
Polyamides
Integrated circuit supports
Silicone
Electrical applications, structural applications (< 200ºC)
Butyl
Tires, joints
Polyethylene Chloride
Tires
Ethyl vinyl acetate
Medical equipment
Polyurethane
Shock absorbers
Flexible Foams
Automotive interiors
Rigid Foams
Shock absorbers, thermal insulators
Elastomeric Foams
Thermal or acoustic insulators ME 474-674 Winter 2008
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Composites
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Composites Bonding:
Various bonding
Structure:
Inhomogeneous and anisotropic structure
Advantages
Disadvantages
Combine attractive qualities of other materials Properties can be engineered to demand
Expensive
Difficult to join
Often difficult to fabricate
Light Stiff Strong
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Composites
Composites Polymer Matrix
Metal Matrix
Examples of Application
Thermoplastic Matrix
Mechanical components, protection screens
Thermoset Matrix
Aerospace, spoting equipment
Elastomer Matrix
Tires
Aluminum Matrix
Aerospace, sporting equipment, electronic packaging
Titanium Matrix
Aerospace turbines
Copper Matrix
High strength electrical conductors
Ceramic Matrix Alumina Matrix Cermets
High temperature mechanical applications Cutting tools, polishing materials
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Natural Materials
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Natural Materials Variety of bonding at different levels
Advantages
Highly Recyclable
Often high strength
Variety of physical and mechanical properties
Disadvantages
Large variability in properties
Difficult to control
Renewable?
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Summary of Structural materials
Broadly the “material kingdom” has 6 basic families
As designers we need to familiarize ourselves with the range of properties available from each class
Each class of material has advantages and disadvantages
Application of material depend on their properties
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Materials information for design The goal of engineering design: “To create products that perform their function effectively, safely, at acceptable cost”. What do we need to know to do this?
More than just test data.
KNOWLEDGE
INFORMATION
DATA Data capture
Selection of material and process
Statistical analysis
Economic analysis and business case
Mechanical Properties Bulk Modulus Compressive Strength Ductility Elastic Limit Endurance Limit Fracture Toughness Hardness Loss Coefficient Modulus of Rupture Poisson's Ratio Shear Modulus Tensile Strength Young's Modulus
Test
Test data
Characterization
4.1 55 0.06 40 24 2.3 100 0.00950 0.38 0.85 45 2.5 -
4.6 GPa 60 MPa 0.07 45 MPa 27 MPa 2.6 MPa.m 1/2 140 MPa 0.026 55 MPa 0.42 0.95 GPa 48 MPa 2.8 GPa
$ Potential applications
Allowables
Successful applications
Selection and implementation ME 474-674 Winter 2008
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Approaches to Materials Selection
Traditional approach
Most design within an organization, or for a particular class of applications is with a limited number of materials. Materials selection is based on what we are already comfortable with.
This approach is suitable in applications that are highly codified. The introduction of a new material would require approval from governmental or standards organizations. e.g. Critical aircraft components, highway bridges require lengthy approval or certification processes
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Approaches to Materials Selection
Optimization approach
This approach is promoted by Ashby, involves selecting a material based on critical properties, with multiple constraints imposed on the selection process.
The approach requires the definition of a “performance index” for combining and quantifying the various requirements and constraints.
Single properties are rarely the basis of materials selection. Mechanical design may require materials with a combination of strength, stiffness, density, corrosion resistance, weldability, etc.
Master charts showing the properties of all materials, relevant to this performance index, are used to down-select from the tens of thousands of materials that are available down to a few that would work the best ME 474-674 Winter 2008
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Example: Electrical Transmission Wire
Select a material that has lowest transmission losses
Transmission Loss – heat generated due to electrical resistance of the wire W = I 2R
Minimize Resistance R
What about cost?
R=
ρL A
Material
Electrical Density Resistivity, ρ, (Ωm) (kg/m3)
Cost ($/kg)
Cost ($/m3)
Melting Point (°C)
Copper
1.72x10-8
8,890
7.5
66k
1080
Silver
1.47x10-8
10,490
400
4M
962
Aluminum
2.9x10-8
2,700
10
27k
660
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Materials Selection in Product Development
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Factors Involved in Materials Selection
Properties There are literally dozens of properties that a material could have.
Mechanical: Strength, stiffness, ductility, fracture toughness, fatigue strength, creep strength, etc
Thermophysical: Density, thermal conductivity, color, transparency, electrical conductivity, magnetic susceptibility, etc.
Chemical: Corrosion resistance, bonding, composition, etc.
Other: Cost
Availability
An issue that is taken into consideration in material selection is the availability of the material
is it available at hand does it need to be ordered from a warehouse, does it need to be specially made for the application Budinski ME 474-674 Winter 2008
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Factors Involved in Materials Selection
Economics
How many parts are to be made? a few, a few hundred or millions per year The economy of scale may dictate one material over another, or one process over another.
Business and Environmental Issues
Is recycleability an issue?
Are the materials hazardous or subject to environmental and other regulations?
Is there a liability issue related to a particular material?
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Materials Selection
In summary, a designer assumes certain properties when creating a new design or modifying an existing one.
The designer is not is not interested in the material per se, but the properties.
There are thousands of materials, each of which has a specific set of attributes or properties.
Materials selection is the process of identifying the optimum material for a particular design or application
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Finding Information for Materials Selection
Material properties are generally available in a database. These properties may be classified and tabulated in different ways.
If a particular application requires both high impact strength and high stiffness then
Impact strength requirement eliminates ceramics.
The stiffness requirement further eliminates polymers since they have very low elastic moduli.
This may limit the selection to a few metals; copper, titanium, steels, stainless steels or nickel based alloys.
At this point, the engineer may look back at the experience in the company and select an alloy steel, 4140 in particular, for a part that is being designed.
Does this approach give the best material for the application? ME 474-674 Winter 2008
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Finding information
z
Handbooks, compilations (see Appendix D of The Text)
z
Suppliers’ data sheets
z
The Internet : www.matweb.com www.matdata.net
Tables or compilation of data but no comparison or perspective
Finding data using the EduPack z
Browse: locate candidate on MATERIALS or PROCESS TREE and double click,
z
Search: enter name or word string name (trade-name, or application)
z
3 levels of data, with increasing content z
Level 1: 64 materials 75 processes
z
Level 2: 94 materials 107 processes
z
Level 3: 2916 materials 233 processes
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