Materials Selection for Mechanical Design: Exploring the World of - - PowerPoint PPT Presentation

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

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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 Product Design

Invention Market need Engineering Design Industrial Design

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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

Design objective: “A device is needed to pull the cork from wine bottle” Not solution neutral – pulling specifies the solution

Need

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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

Direct pull Levered pull Spring assisted pull Geared pull

Embodiments of one concept

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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

• f 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

• pposite.

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.

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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

• Iron, Copper, Aluminum, Zinc, Nickel, Titanium, Silver, Gold, etc.

and their alloys Steel, Brass, Bronze, etc.

Ceramics

• Porcelain, China, Glass, Silicon Carbide, Boron Nitride, Aluminum

Oxide, etc.

Polymers

• Polyethylene, PVC, Teflon, Nylon, Plexiglas, Bakelite, Epoxy,

Polyesters, Melamine, Neoprene, Silicone

Electronic Materials

• Silicon, Germanium, Gallium-Arsenide

Composites

• Concrete, FRP, MMC, CMC, Asphalt, Wood

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The world of structural materials

Composites Sandwiches

Hybrids

Lattices Segmented PE, PP, PC PS, PET, PVC PA (Nylon)

Polymers

Polyester Phenolic Epoxy Soda glass Borosilicate

Glasses

Silica glass Glass ceramic Isoprene Butyl rubber

Elastomers

Natural rubber Silicones EVA Alumina Si-carbide

Ceramics

Si-nitride Ziconia Steels Cast irons Al-alloys

Metals, alloys

Cu-alloys Ni-alloys Ti-alloys

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History – the evolution of materials

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Comparison of Materials Metals

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Metals

Disadvantages

Failure by fatigue Most susceptible to

environmental attack (corrosion and oxidation) Advantages

Relatively high moduli (stiff) Can be made strong by alloying

• r working

Nominally ductile Relatively high toughness Paramagnetic or ferromagnetic Good electrical conductors

Bonding: Metallic bonds – Delocalized electrons Structure: Crystalline

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Metals

Aerospace, currency Nickel Alloys Pressure vessels, fittings Brass Heat exchangers, chemical industry, maritime industry Bronze Electrical conductors Copper Copper Alloys Aerospace, chemical industry Titanium Alloys Aerospace, automotive, sporting equipment Magnesium Alloys Aerospace, construction, transport, packaging, electrical conductors Aluminum Alloys Light Alloys Cylinders, pistons, motor blocks, construction, wear resistant materials Cast Irons Off shore drilling rigs, naval construction, chemical transport, food preparation, medical instruments Stainless Steels Utensils, construction, automotive, transmission towers … Carbon Steels Ferrous Metals Examples of application Metal

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Ceramics and Glasses

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Ceramics and Glasses

Advantages

High moduli (stiff) High strength Abrasion resistant High melting point Resist corrosion and

• xidation

Transparent Good electrical insulators

Disadvantages

Brittle Statistical spread in

strength

Strength in compression ~

15x strength in tension

Notch sensitive More difficult to design with

than metals or polymers Bonding: Ionic & Covalent Bonding – Directional & Strong Structure: Crystalline or amorphous

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Ceramics and Glasses

Windows, food preparation Glasses High temperature furnaces, heat shields Alumina, Silicon Nitride, Silicon Carbide… Industrial Ceramics Cutting wheels, polishing cloths Abrasive Particles Reinforcements in polymer and metal Composites Particles (alumina, silicon carbide, magnesia) Reinforcements in polymer composites Fibers (glass, carbon …) Ceramic fibers and powders Construction, electrical insulators, hygienic applications, household Fired ceramics (pottery, bricks …) Construction Rocks Construction Hydrated ceramics (cement, plaster…) Bulk Ceramics Examples of application Ceramics

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Polymers and Elastomers

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Polymers and Elastomers

Advantages

Can have high strength High elastic deformation

(flexible)

Low coefficient of friction Corrosion resistant Easy to form Can be colored

Disadvantages

Creep at room temp. Properties change a great

deal with temperature

Low melting points Low moduli Difficult to recycle

Bonding: Covalent and secondary bonding Structure: Amorphous or partially crystalline

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Polymers and Elastomers

Thermal or acoustic insulators Elastomeric Foams Shock absorbers, thermal insulators Rigid Foams Automotive interiors Flexible Foams Foams Shock absorbers Polyurethane Medical equipment Ethyl vinyl acetate Tires Polyethylene Chloride Tires, joints Butyl Elastomers Electrical applications, structural applications (< 200ºC) Silicone Integrated circuit supports Polyamides Fabrics Polyesters Electrical components Phenols Glue, connectors, molding Epoxy Thermosets Credit cards, plumbing, window sashes… Polyvinylechloride (PVC) Microwave oven dishes Polyether ether ketone (PEEK) Windows, food storage Polycarbonates Clothing, strong fabrics Polyamide (Nylons) Overhead transparencies Cellulose Acetate Clothing, household appliances Acrylobutadiene styrene (ABS) Thermoplastics

Examples of Applications Polymers

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Composites

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Composites

Advantages

Combine attractive qualities

• f other materials

Properties can be

engineered to demand Light Stiff Strong Disadvantages

Expensive Difficult to join Often difficult to fabricate

Bonding: Various bonding Structure: Inhomogeneous and anisotropic structure

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Composites

Cutting tools, polishing materials Cermets High temperature mechanical applications Alumina Matrix Ceramic Matrix High strength electrical conductors Copper Matrix Aerospace turbines Titanium Matrix Aerospace, sporting equipment, electronic packaging Aluminum Matrix Metal Matrix Tires Elastomer Matrix Aerospace, spoting equipment Thermoset Matrix Mechanical components, protection screens Thermoplastic Matrix Polymer Matrix Examples of Application Composites

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Natural Materials

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Natural Materials

Advantages

Highly Recyclable Often high strength Variety of physical and

mechanical properties Disadvantages

Large variability in

properties

Difficult to control Renewable?

Variety of bonding at different levels

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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. Test Test data

Data capture Statistical analysis

Allowables

Mechanical Properties

Bulk Modulus 4.1

• 4.6

GPa Compressive Strength 55

• 60

MPa Ductility 0.06 - 0.07 Elastic Limit 40

• 45

MPa Endurance Limit 24

• 27

MPa Fracture Toughness 2.3

• 2.6

MPa.m1/2 Hardness 100 - 140 MPa Loss Coefficient 0.009- 0.026 Modulus of Rupture 50

• 55

MPa Poisson's Ratio 0.38 - 0.42 Shear Modulus 0.85 - 0.95 GPa Tensile Strength 45

• 48

MPa Young's Modulus 2.5

• 2.8

GPa

Successful applications

$

Economic analysis and business case Selection of material and process

Potential applications

Characterization Selection and implementation DATA INFORMATION KNOWLEDGE

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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

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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 Minimize Resistance R What about cost?

R I W

2

= A L R ρ = 660 27k 10 2,700 2.9x10-8 Aluminum 962 4 M 400 10,490 1.47x10-8 Silver 1080 66k 7.5 8,890 1.72x10-8 Copper Melting Point (°C) Cost ($/m3) Cost ($/kg) Density (kg/m3) Electrical Resistivity, ρ, (Ωm) Material

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Materials Selection in Product Development

Dieter

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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

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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?

Budinski

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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?

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Finding information

Handbooks, compilations (see Appendix D of The Text) Suppliers’ data sheets The Internet : www.matweb.com

www.matdata.net Finding data using the EduPack

Browse: locate candidate on MATERIALS or PROCESS TREE and double click,

Search: enter name or word string name (trade-name, or application) 3 levels of data, with increasing content Level 1: 64 materials 75 processes Level 2: 94 materials 107 processes Level 3: 2916 materials 233 processes

Tables or compilation of data but no comparison or perspective