1 Step 1: Translation Step 1: Translation Constraints Free - - PowerPoint PPT Presentation

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Steps in Materials Selection:

Step 2 Screening: eliminate materials that cannot do the job Step 3 Ranking: find the materials that do the job best Step 4 Supporting information: explore pedigrees of top-ranked candidates Step 1 Translation: express design requirements as constraints & objectives

Selection has 4 basic steps

More info: “Materials Selection in Mechanical Design”, Chapters 5 and 6

ME 499-699 Fall 2006 Slides 3 -2

The design process and material search space

Market need Product specification Concept Embodiment Detail Design requirements

Material search space

Screen, rank Screen, rank Screen, rank

All materials Material & process needs

Data for all materials and processes, low precision Data for fewer materials

• r processes, higher precision

Data for one material

• r process, highest precision

Final choice

ME 499-699 Fall 2006 Slides 3 -3

Step 1: Translation

Terminology

A “solution” is a material choice that meets all the constraints

Translation: “express design requirements as constraints and objectives” Analyze: Function

What does the component do ?

Constraints

What essential conditions must be met ?

Objectives

What is to be maximized or minimized ?

Free variables

Which design variables are free ?

Design requirements

ME 499-699 Fall 2006 Slides 3 -4

Step 1: Translation

Function

What does the component or structure have to do?

Support a load Contain a pressure Transmit heat, …

Objective

What is to be maximized or minimized?

As cheap as possible As light as possible As strong as possible, …

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ME 499-699 Fall 2006 Slides 3 -5

Step 1: Translation

Constraints

What essential conditions must be met?

Component must be of a certain length Component must carry a certain load Component must operate above a certain temperature,…

Hard Constraints (non-negotiable)

Component MUST meet the specification

The beam must support the weight of a 300 lb person Soft Constraints (negotiable)

Component MAY meet the specification - often aesthetic or cost

related e.g. beam should cost less than $50

If a design can’t meet the soft constraint no one dies

ME 499-699 Fall 2006 Slides 3 -6

Step 1: Translation

Free Variables

Which design variables are free? These variables are under our control to

change in order for the component to perform the function, satisfy the objectives, without violating the constraints

The materials choice (one we will always have!) The cross sectional area The cross sectional shape …

ME 499-699 Fall 2006 Slides 3 -7

Step 2: Screening

Design requirements can be qualitative or yes/no Material must be transparent Design requirements are often quantitative Material must be able to operate above 1000ºC Material must be less dense than water (ρ < 1000 kg/m3) Material must have a Young’s modulus > 100 GPa We can use Property charts to find subset of materials

that satisfy screening criteria

Find a stiff (E>100 GPa), cheap material (<$0.50/kg) for

building and highway construction

ME 499-699 Fall 2006 Slides 3 -8

Screening Graph Stage – Single property

Material

MaterialUniverse:\Ceramics and glasses MaterialUniverse:\Hybrids: composites, foams, natural materials MaterialUniverse:\Metals and alloys MaterialUniverse:\Polymers and elastomers

Price (USD/kg)

0.1 1 10 100

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Screening Graph Stage – Single property

Material

MaterialUniverse:\Ceramics and glasses MaterialUniverse:\Hybrids: composites, foams, natural materials MaterialUniverse:\Metals and alloys MaterialUniverse:\Polymers and elastomers

Young's modulus (Pa)

1e6 1e7 1e8 1e9 1e10 1e11

ME 499-699 Fall 2006 Slides 3 -10

Screening Graph Stage – Two properties

Price (USD/kg)

0.1 1 10 100

Young's modulus (Pa)

1e6 1e7 1e8 1e9 1e10 1e11 Concrete Cement Low carbon steel Sandstone Limestone Marble

Low cost and high stiffness materials for construction

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Screening Graph Stage

Ts>1000ºC and λ<10W/m.K

Thermal conductivity (W/m.K)

0.1 1 10 100

Maximum service temperature (°C)

50 100 200 500 1000

7 of 94 Materials

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Material for a Heat Sink

Need a material to make a heat sink for a power electronics application. The material must not interfere with the functioning of the electronic component and must not allow the temperature to rise above 200ºC.

Selection for this application is demonstrated using the “Limit” stage of the CES Edupack Software

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ME 499-699 Fall 2006 Slides 3 -13

Material for a Heat Sink Translation: “Express the requirement in terms of properties” Screening: “Eliminate materials that can’t do the job”

Example: heat sink for

power electronics

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Material for a Heat Sink

• operate at 200oC
• be electrical insulator
• conduct heat well
• not heavy

Constraints Function Heat sink Free variable

Choice of material and process Retain materials with:

• 1. Max service temp > 200º C
• 2. “Good insulator”, or R > 1020 μohm.cm
• 3. “Good T-conductor” or T-conduct. λ > 100 W/m.K
• 4. Density < 3 Mg/m3

Level 1 Level 2

Translation

ME 499-699 Fall 2006 Slides 3 -15 Mechanical attributes Minimum

Maximum Density Mg/m3 Young’s modulus GPa Elastic limit MPa

Thermal attributes

• Max. service temp. C

T-expansion 10-6/K T-conductivity W/m.K

Electrical attributes

Good insulator Poor insulator Poor conductor Good conductor

A limit stage

Graph stage Limit stage Tree stage

Screening using a LIMIT STAGE

New Browse Select Search Print Search web Toolbar

Materials, Level 1

200 100

b

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2000C λ > 100 W/m.K R > 1020 μΩ.cm

Screening using GRAPH STAGE

Screening using

bar-charts

Max service temperature (K)

Metals Polymers Ceramics Composites PEEK PP PTFE WC Alumina Glass CFRP GFRP Fibreboard Steel Copper Lead Zinc Aluminum 1000 Screening using

property charts

0.1 Metals Polymers & elastomers Composites Foams 1030 1 1010 1020

Electrical resistivity ( μΩ.cm) Thermal conductivity (W/m.s)

Ceramics 10 1 100 0.01

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ME 499-699 Fall 2006 Slides 3 -17

Process Join Shape Surface

Cast Deform Mold Composite Powder Prototype

A tree stage

Graph stage Limit stage Tree stage

Screening using a TREE STAGE

New Browse Select Search Print Search web Toolbar

Select what? Materials, Level 1

ME 499-699 Fall 2006 Slides 3 -18

These are

• ften enough !
• The four steps of selection:
• 1. Translation, giving constraints and objectives
• 2. Screening , using constraints
• 3. Ranking, using objectives
• 4. Supporting information for prime candidates

The main points

• CES allows

screening using limit stages, graph stages and tree stages

• Translation of design requirements into a material prescription: analyse

the function of the component, the constraints must meet, the objective of the design, the free variables of the problem

ME 499-699 Fall 2006 Slides 3 -19

Function

CD enclosure

Homework: Select a new material for a CD case

Translation: “express design requirements as constraints and objectives” Constraints

Strength > PS Toughness > PS Transparency Smoothness Recyclable

Objectives

Minimize cost

Free variable

Choice of material and process

Contain CD Protect without scratching Internal label visible Eco-friendly Cheap

Design requirements

CD cases are made of polystyrene (PS). They crack and scratch the disks. Find a better material.

Translation