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L14 - MAE 486 Design of Mechanical Systems Lecture 14 Fall...

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Unformatted text preview: MAE 486 Design of Mechanical Systems Lecture 14 Fall 2011 Today s topics: Material Selection (Chapter 11); Review: Use of AHP: Are we done? •  What is next when using AHP in design? •  How to apply AHP to design selec=ons? Review: Use of AHP: Are we done? •  How to apply AHP to design selec=ons? Review: AHP in Design: Consistency Check Material Selec=on (Chapter 11) •  •  •  •  •  •  •  •  •  •  Why is it important in design? Rela=on to Design What are the Criteria in General? Material Selec=on Process: Overview Performance Characteris=cs Concept of Structure What are the basic types? What are structural materials? What are the characteris=cs of engineering materials? What are the criteria? Review: •  •  •  •  •  •  •  •  •  •  •  •  •  •  Mechanical Proper=es Ul#mate tensile strength: Modulus of elas#city (Young modulus): Duc#lity: Fracture toughness: Fa#gue proper#es: Damping capacity Creep: Impact resistance: Hardness: Wear rate: Metal : Ceramics: Glass: Polymer: Material Performance Indices •  Performance Index vs. Material Proper=es: Difference? •  Example of Objec#ve Func#on: –  Mass per unit length •  Op=miza=on of performance index: What is the catch? •  First constraint: What is the No. 1 concern? I σe Mb = r Op=miza=on of the Objec=ve Func=on •  Other constraints? •  With the constraints, the mass now becomes: •  Performance metrics: General expression Op=miza=on of the Material Index •  Separa=on of material selec=on in the Mat. Index: Common Material Performance Index Case Study #1: Radiator Cooling Fan •  Problem Statement: –  Driven: –  Issue: –  Results: –  Objec=ve: Case Study #1: Radiator Cooling Fan •  Boundaries of the problem: –  Cost –  Performance requirement: •  Available Informa=on: CES, www.grantadesign.com.uk Case Study #1: Radiator Cooling Fan •  What are the basic Physical Laws/ Assump1ons? –  Radius of the fan:  Size of Fan hub and blade –  Which material property to look at? •  Construct the model for the material performance index –  The centrifugal force –  The stress at the root of the blade Case Study #1: Radiator Cooling Fan •  Analysis: –  Cause of blade failure –  Cri=cal value of stress •  Bound func=on Case Study #1: Radiator Cooling Fan •  Performance metric •  What is the materials performance index? •  Analysis of material performance index: –  How to make it easier to quan=fy/compare? Case Study #1: Radiator Cooling Fan • HDPE ­ High ­density polyethylene • Cast iron • Nylon • Aluminum or magnesium alloys Case Study #1: Radiator Cooling Fan •  What is the second most important concern in selec=on? •  Second Material Performance Index •  Assump=ons in manufacturing and volume Case Study #1: Material Selec=on Analysis •  Which one is best choice? •  What is the main concern? •  •  What is(are) the second choice(s)? Case Study #1: How to make the selec=on? •  What are the tools we can use? •  What are the important factors? Pugh Selec=on Method – Helical Steel Spring Example Recycling and Material Selec=on Design for Recycling •  What things we need should do? Material Selec=on for Eco ­a[ributes •  Energy and emission associated with material produc=on Material Performance Index for Recycling •  Environmental issues material performance index –  Minimize mass beam E1/ 2 M= ρ –  Modify to accommodate produc=on energy –  Select a material with minimum CO2 produc=on for a beam of given strength Important Informa1on to Know •  Is there an economically viable recycling market for the material? •  It is important to know how readily the material can be added to virgin material without deleterious effects on proper=es. Some materials can only be recycled into lower ­grade materials. •  Some materials can be disposed of by biodegrada=on in landfills, while the bulk of materials that are not recycled go to landfills. However, some materials like lead, cadmium, and some of the heavy metals are toxic, and must be disposed of by methods used for hazardous materials. ...
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