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Material Selection

Senior Design

ME

Fall 2017

Dr. Bardia Konh

Materials Selection in Design

This Lecture:

• Importance of material selection in design
• Exploring materials using materials property charts
• Materials selection process
• Selecting materials: materials indices
• Case studies

Material selection is critical part of almost all engineering designs

So many factors to consider:

strength, stiffness, durability, corrosion, cost, formability, etc.

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”,

Materials selection is a key step for a successful design

A large number of materials to select from

Recently, there has been more emphasis on the role of materials

Discovery of new and advanced materials

The Role of Materials Selection in Design

Function

Mechanical

Properties Failure

Mode

Manufacturability

Cost

Environmental

Considerations

Advanced new materials can introduce

new products with more efficiencies,

lower manufacturing costs

Exhibit desired behavior

An ability to select materials that best meet requirements of a design

Access to information and tools for comparison and selection

Need for a new product and new materials

Development of a new materials

http://hleelabhome.wixsite.com/mysite/research http://hleelabhome.wixsite.com/mysite

• Soft active materials
• Biologically inspired design principles

Soft robotics

Dr. Howon Lee

Rutgers University

Soft multi-material actuators

Dr. Conor Walsh

Harvard University

https://biodesign.seas.harvard.edu/soft-robotics

• Large bending motions

Material Properties Physical

• Density
• Melting point
• Vapor pressure
• Viscosity
• Porosity
• Permeability
• Reflectivity
• Transparency
• Optical properties
• Dimensional stability Chemical - Corrosion - Oxidation - Thermal stability - Biological stability - Stress Corrosion - …. Electrical - Conductivity - Dielectric constant - Coersive force - Hysteresis Thermal - Conductivity - Specific Heat - Thermal expansion - Emissivity Mechanical - Hardness - Elastic constants - Yield strength - Ultimate strength - Fatigue - Fracture Toughness - Creep - Damping - Wear resistance - Spalling - Ballistic performance - …….

http://www.matweb.com/

What do we expect from a design

The products should perform their functions effectively, safely, at acceptable cost”

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. Elastic Limit 40 - 45 MPa Endurance Limit 24 - 27 MPa Fracture Toughness 2.3 - 2.6 MPa.m1/ Hardness 100 - 140 MPa Loss Coefficient 0.009- 0. Modulus of Rupture 50 - 55 MPa Poisson's Ratio 0.38 - 0. 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

Material stiffness

Metals

Metal Examples of application

Ferrous Metals 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

Light Alloys Aluminum Alloys Aerospace, construction, transport, packaging,

electrical conductors

Magnesium Alloys Aerospace, automotive, sporting equipment

Titanium Alloys Aerospace, chemical industry

Copper Alloys Copper Electrical conductors

Bronze Heat exchangers, chemical industry, maritime

industry

Brass Pressure vessels, fittings

Nickel Alloys Aerospace, currency

Material selection [ASHBY99] - Materials Selection In Mechanical Design

First Step: Translation “Express design requirements as constraints and objectives” Using design requirements, analyze four items:

1. Function: What does the component do? 2. Objective : What essential conditions must be met? 3. Constraints : What is to be maximized or minimized? 4. Free variables: Which design variables are free? - Which can be modified? - Which are desirable?

Example: Materials for a Light, Strong Tie Objective : Constraints: Rearrange to eliminate free variable: Minimizing weight by minimizing

Second Step: Screening Eliminate materials that cannot do the job Need effective way of evaluating large range of material classes and properties Metals Steels Cast irons Al-alloys Cu- alloys Ti-alloys Ceramics Alumina Si-carbide Si-nitride Ziconia Hybrids Composites Sandwiches Lattices Segmented Polymers PE, PP, PC, PS, PET, PVC, PA (Nylon) Polyester Epoxy Glasses Soda glass Borosilicate Silica glass Glass ceramic Elastomers Isoprene Butyl rubber Natural rubber Silicones EVA

Screening Example Function: Heat Sink Constraints:

1. Max service temp > 200 C
2. Electrical insulator R > 10 20 μohm cm
3. Thermal conductor T-conduct. λ > 100 W/m K
4. Not heavy Density < 3 Mg/m 3 Free Variables: Materials and Processes

Heat Sink for Power Electronics

Heat Sink Screening: Bar Chart 200 ºC λ > 100 W/mK R > 10^20 μ ohm cm

temp > 200 C