Shigleys mechanical engineering design 10th edition solutions

The tenth edition of Shigley’s Mechanical Engineering Design maintains the approach that has made this book the standard in machine design for nearly 50 years. Students will find that the text inherently

directs them into familiarity with both the basics of design decisions and the standards of industrial components. It combines the straightforward focus on fundamentals that instructors have come to

expect, with a modern emphasis on design and new applications.

Salient Features:

- practical approach to the subject through a wide range of real-world applications and problems.

- Authoritative coverage of the design considerations for major machine elements like gears, brakes

and clutches.

- New Chapter on Geometrical Design & Tolerancing to enable students to better read and

understand design specifications. Part 1 Basics

• Introduction to Mechanical Engineering Design
• Materials
• Load and Stress Analysis
• • Deflection and Stiffness

Part 2 Failure Prevention

• Failures Resulting from Static Loading

• Fatigue Failure Resulting from Variable Loading

Part 3 Design of Mechanical Elements

• Shafts and Shaft Components

• Screws, Fasteners, and the Design of Nonpermanent Joints

• Welding, Bonding, and the Design of Permanent Joints

• Mechanical Springs

• Rolling-Contact Bearings

• Lubrication and Journal Bearings

• Gears-General

• Spur and Helical Gears

• Bevel and Worm Gears

• Clutches, Brakes, Couplings, and Flywheels

• Flexible Mechanical Elements

• Power Transmission Case Study

Part 4 Special Topics

• Finite-Element Analysis

• Geometric Dimensioning and Tolerancing

Appendix A Useful Tables

Appendix B Answers to Selected Problems

Index

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Shigley’s

Mecha nical

Engineering

Design

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Shigley’s

Mechanical

Engineering

Design

Tenth Edition

Richard G. Budynas Professor Emeritus, Kate Gleason College of Engineering, Rochester Institute of Technology

J. Keith Nisbett Associate Professor of Mechanical Engineering, Missouri University of Science and Technology

SHIGLEY’S MECHANICAL ENGINEERING DESIGN, TENTH EDITION

Published by McGraw-Hill Education, 2 Penn Plaza, New York, NY 10121. Copyright © 2015 by McGraw-Hill Education. All rights reserved. Printed in the United States of America. Previous editions © 2011 and 2008. No part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written consent of McGraw-Hill Education, including, but not limited to, in any network or other electronic storage or transmission, or broadcast for distance learning.

Some ancillaries, including electronic and print components, may not be available to customers outside the United States.

This book is printed on acid-free paper.

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ISBN 978-0-07-339820- MHID 0-07-339820-

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Library of Congress Cataloging-in-Publication Data

Budynas, Richard G. (Richard Gordon) Shigley’s mechanical engineering design.—Tenth edition / Richard G. Budynas, professor emeritus, Kate Gleason College of Engineering, Rochester Institute of Technology, J. Keith Nisbett, associate professor of mechanical engineering, Missouri University of Science and Technology. pages cm—(Mcgraw-Hill series in mechanical engineering) Includes index. ISBN-13: 978-0-07-339820-4 (alk. paper) ISBN-10: 0-07-339820-9 (alk. paper)

1. Machine design. I. Nisbett, J. Keith. II. Shigley, Joseph Edward. Mechanical engineering design. III. Title. TJ230 2014 621 9 15—dc 2013035900

The Internet addresses listed in the text were accurate at the time of publication. The inclusion of a website does not indicate an endorsement by the authors or McGraw-Hill Education, and McGraw-Hill Education does not guarantee the accuracy of the information presented at these sites.

mhhe

Dedication

To my wife, Joanne, my family, and my late brother,

Bill, who advised me to enter the field of mechanical

engineering. In many respects, Bill had considerable

insight, skill, and inventiveness.

Richard G. Budynas

To my wife, Kim, for her unwavering support.

J. Keith Nisbett

vi

Joseph Edward Shigley (1909–1994) is undoubtedly one of the most well-known and respected contributors in machine design education. He authored or coauthored eight books, including Theory of Machines and Mechanisms (with John J. Uicker, Jr.), and Applied Mechanics of Materials. He was coeditor-in-chief of the well-known Standard Handbook of Machine Design. He began Machine Design as sole author in 1956, and it evolved into Mechanical Engineering Design , setting the model for such textbooks. He contributed to the first five editions of this text, along with coauthors Larry Mitchell and Charles Mischke. Uncounted numbers of students across the world got their first taste of machine design with Shigley’s textbook, which has literally become a classic. Nearly every mechanical engineer for the past half century has referenced terminology, equations, or procedures as being from “Shigley.” McGraw-Hill is honored to have worked with Professor Shigley for more than 40 years, and as a tribute to his lasting contribution to this textbook, its title officially reflects what many have already come to call it— Shigley’s Mechanical Engineering Design. Having received a bachelor’s degree in Electrical and Mechanical Engineering from Purdue University and a master of science in Engineering Mechanics from the University of Michigan, Professor Shigley pursued an academic career at Clemson College from 1936 through 1954. This led to his position as professor and head of Mechanical Design and Drawing at Clemson College. He joined the faculty of the Department of Mechanical Engineering of the University of Michigan in 1956, where he remained for 22 years until his retirement in 1978. Professor Shigley was granted the rank of Fellow of the American Society of Mechanical Engineers in 1968. He received the ASME Mechanisms Committee Award in 1974, the Worcester Reed Warner Medal for outstanding contribution to the permanent literature of engineering in 1977, and the ASME Machine Design Award in 1985. Joseph Edward Shigley indeed made a difference. His legacy shall continue.

Dedication to Joseph Edward Shigley

vii

Richard G. Budynas is Professor Emeritus of the Kate Gleason College of Engineering at Rochester Institute of Technology. He has more than 50 years experience in teach- ing and practicing mechanical engineering design. He is the author of a McGraw-Hill textbook, Advanced Strength and Applied Stress Analysis, Second Edition; and coau- thor of a McGraw-Hill reference book, Roark’s Formulas for Stress and Strain, Eighth Edition. He was awarded the BME of Union College, MSME of the University of Rochester, and the PhD of the University of Massachusetts. He is a licensed Professional Engineer in the state of New York.

J. Keith Nisbett is an Associate Professor and Associate Chair of Mechanical Engineering at the Missouri University of Science and Technology. He has more than 30 years of experience with using and teaching from this classic textbook. As demon- strated by a steady stream of teaching awards, including the Governor’s Award for Teaching Excellence, he is devoted to finding ways of communicating concepts to the students. He was awarded the BS, MS, and PhD of the University of Texas at Arlington.

About the Authors

viii

Brief Contents

Brief Contents ix

Part 4 Special Topics 944

19 Finite-Element Analysis 945

20 Geometric Dimensioning and Tolerancing 969

Appendixes

A Useful Tables 1011

B Answers to Selected Problems 1067

Index 1073

x

Contents

xii Mechanical Engineering Design

8 Screws, Fasteners, and the

9 Welding, Bonding, and

xiv Mechanical Engineering Design

• Part 1 Basics Preface xv
• 1 Introduction to Mechanical Engineering Design
• 2 Materials
• 3 Load and Stress Analysis
• 4 Deflection and Stiffness
• Part 2 Failure Prevention
• 5 Failures Resulting from Static Loading
• 6 Fatigue Failure Resulting from Variable Loading
• Part 3 Design of Mechanical Elements
• 7 Shafts and Shaft Components
  • of Nonpermanent Joints 8 Screws, Fasteners, and the Design
  • of Permanent Joints 9 Welding, Bonding, and the Design
• 10 Mechanical Springs
• 11 Rolling-Contact Bearings
• 12 Lubrication and Journal Bearings
• 13 Gears—General
• 14 Spur and Helical Gears
• 15 Bevel and Worm Gears
• 16 Clutches, Brakes, Couplings, and Flywheels
• 17 Flexible Mechanical Elements
• 18 Power Transmission Case Study
• Part 1 Basics Preface xv
  • Engineering Design 1 Introduction to Mechanical
• 1–1 Design
• 1–2 Mechanical Engineering Design
  • Process 1–3 Phases and Interactions of the Design
• 1–4 Design Tools and Resources
  • Responsibilities 1–5 The Design Engineer’s Professional
• 1–6 Standards and Codes
• 1–7 Economics
• 1–8 Safety and Product Liability
• 1–9 Stress and Strength
• 1–10 Uncertainty
• 1–11 Design Factor and Factor of Safety
• 1–12 Reliability and Probability of Failure
• 1–13 Relating the Design Factor to Reliability
• 1–14 Dimensions and Tolerances
• 1–15 Units
• 1–16 Calculations and Significant Figures
• 1–17 Design Topic Interdependencies
  • Specifications 1–18 Power Transmission Case Study
• Problems
• 2 Materials
• 2–1 Material Strength and Stiffness
  • Properties 2–2 The Statistical Significance of Material
• 2–3 Strength and Cold Work
• 2–4 Hardness - 2–5 Impact Properties - 2–6 Temperature Effects - 2–7 Numbering Systems - 2–8 Sand Casting - 2–9 Shell Molding - 2–10 Investment Casting - 2–11 Powder-Metallurgy Process - 2–12 Hot-Working Processes - 2–13 Cold-Working Processes - 2–14 The Heat Treatment of Steel - 2–15 Alloy Steels - 2–16 Corrosion-Resistant Steels - 2–17 Casting Materials - 2–18 Nonferrous Metals - 2–19 Plastics - 2–20 Composite Materials - 2–21 Materials Selection - Problems - Analysis 3 Load and Stress - 3–1 Equilibrium and Free-Body Diagrams - Beams 3–2 Shear Force and Bending Moments in - 3–3 Singularity Functions - 3–4 Stress - 3–5 Cartesian Stress Components - 3–6 Mohr’s Circle for Plane Stress - 3–7 General Three-Dimensional Stress - 3–8 Elastic Strain - 3–9 Uniformly Distributed Stresses - 3–10 Normal Stresses for Beams in Bending - 3–11 Shear Stresses for Beams in Bending - 3–12 Torsion - 3–13 Stress Concentration
• 3–14 Stresses in Pressurized Cylinders Contents xi
• 3–15 Stresses in Rotating Rings
• 3–16 Press and Shrink Fits
• 3–17 Temperature Effects
• 3–18 Curved Beams in Bending
• 3–19 Contact Stresses
• 3–20 Summary
• Problems
  • Stiffness 4 Deflection and
• 4–1 Spring Rates
• 4–2 Tension, Compression, and Torsion
• 4–3 Deflection Due to Bending
• 4–4 Beam Deflection Methods
• 4–5 Beam Deflections by Superposition
  • Functions 4–6 Beam Deflections by Singularity
• 4–7 Strain Energy
• 4–8 Castigliano’s Theorem
• 4–9 Deflection of Curved Members
• 4–10 Statically Indeterminate Problems
• 4–11 Compression Members—General
• 4–12 Long Columns with Central Loading
  • Loading 4–13 Intermediate-Length Columns with Central
• 4–14 Columns with Eccentric Loading
• 4–15 Struts or Short Compression Members
• 4–16 Elastic Stability
• 4–17 Shock and Impact
• Problems
• Part 2 Failure Prevention
  • Static Loading 5 Failures Resulting from
• 5–1 Static Strength
• 5–2 Stress Concentration
• 5–3 Failure Theories
  • Materials 5–4 Maximum-Shear-Stress Theory for Ductile - Materials 5–5 Distortion-Energy Theory for Ductile - Materials 5–6 Coulomb-Mohr Theory for Ductile - Summary 5–7 Failure of Ductile Materials - Brittle Materials 5–8 Maximum-Normal-Stress Theory for - Brittle Materials 5–9 Modifications of the Mohr Theory for
    • 5–10 Failure of Brittle Materials Summary
    • 5–11 Selection of Failure Criteria
    • 5–12 Introduction to Fracture Mechanics
    • 5–13 Important Design Equations
    • Problems
      • from Variable Loading 6 Fatigue Failure Resulting
    • 6–1 Introduction to Fatigue in Metals
      • and Design 6–2 Approach to Fatigue Failure in Analysis
    • 6–3 Fatigue-Life Methods
    • 6–4 The Stress-Life Method
    • 6–5 The Strain-Life Method
      • Method 6–6 The Linear-Elastic Fracture Mechanics
    • 6–7 The Endurance Limit
    • 6–8 Fatigue Strength
      • Factors 6–9 Endurance Limit Modifying
      • Sensitivity 6–10 Stress Concentration and Notch
    • 6–11 Characterizing Fluctuating Stresses
      • Stress 6–12 Fatigue Failure Criteria for Fluctuating
      • Stresses 6–13 Torsional Fatigue Strength under Fluctuating
    • 6–14 Combinations of Loading Modes
      • Fatigue Damage 6–15 Varying, Fluctuating Stresses; Cumulative
    • 6–16 Surface Fatigue Strength
      • for the Stress-Life Method 6–17 Road Maps and Important Design Equations
    • Problems
  • Elements Part 3 Design of Mechanical
  • Components 7 Shafts and Shaft
• 7–1 Introduction
• 7–2 Shaft Materials
• 7–3 Shaft Layout
• 7–4 Shaft Design for Stress
• 7–5 Deflection Considerations
• 7–6 Critical Speeds for Shafts
• 7–7 Miscellaneous Shaft Components
• 7–8 Limits and Fits
• Problems
  • Joints Design of Nonpermanent
• 8–1 Thread Standards and Definitions
• 8–2 The Mechanics of Power Screws
• 8–3 Threaded Fasteners
• 8–4 Joints—Fastener Stiffness
• 8–5 Joints—Member Stiffness
• 8–6 Bolt Strength
• 8–7 Tension Joints—The External Load
• 8–8 Relating Bolt Torque to Bolt Tension
  • Preload 8–9 Statically Loaded Tension Joint with
• 8–10 Gasketed Joints
• 8–11 Fatigue Loading of Tension Joints
  • Shear 8–12 Bolted and Riveted Joints Loaded in
• Problems
  • Joints the Design of Permanent
• 9–1 Welding Symbols
• 9–2 Butt and Fillet Welds
• 9–3 Stresses in Welded Joints in Torsion
• 9–4 Stresses in Welded Joints in Bending - 9–5 The Strength of Welded Joints - 9–6 Static Loading - 9–7 Fatigue Loading - 9–8 Resistance Welding - 9–9 Adhesive Bonding - Problems - 10 Mechanical Springs - 10–1 Stresses in Helical Springs - 10–2 The Curvature Effect - 10–3 Deflection of Helical Springs - 10–4 Compression Springs - 10–5 Stability - 10–6 Spring Materials - Service 10–7 Helical Compression Spring Design for Static - 10–8 Critical Frequency of Helical Springs - Springs 10–9 Fatigue Loading of Helical Compression - Fatigue Loading 10–10 Helical Compression Spring Design for - 10–11 Extension Springs - 10–12 Helical Coil Torsion Springs - 10–13 Belleville Springs - 10–14 Miscellaneous Springs - 10–15 Summary - Problems - Bearings 11 Rolling-Contact - 11–1 Bearing Types - 11–2 Bearing Life - 11–3 Bearing Load Life at Rated Reliability - Distribution 11–4 Reliability versus Life—The Weibull - 11–5 Relating Load, Life, and Reliability - 11–6 Combined Radial and Thrust Loading - 11–7 Variable Loading - Bearings 11–8 Selection of Ball and Cylindrical Roller - 11–9 Selection of Tapered Roller Bearings - Contact Bearings 11–10 Design Assessment for Selected Rolling-
• 11–11 Lubrication Contents xiii
• 11–12 Mounting and Enclosure
• Problems
  • Bearings 12 Lubrication and Journal
• 12–1 Types of Lubrication
• 12–2 Viscosity
• 12–3 Petroff’s Equation
• 12–4 Stable Lubrication
• 12–5 Thick-Film Lubrication
• 12–6 Hydrodynamic Theory
• 12–7 Design Considerations
• 12–8 The Relations of the Variables
  • Bearings 12–9 Steady-State Conditions in Self-Contained
• 12–10 Clearance
• 12–11 Pressure-Fed Bearings
• 12–12 Loads and Materials
• 12–13 Bearing Types
• 12–14 Thrust Bearings
• 12–15 Boundary-Lubricated Bearings
• Problems
• 13 Gears—General
• 13–1 Types of Gears
• 13–2 Nomenclature
• 13–3 Conjugate Action
• 13–4 Involute Properties
• 13–5 Fundamentals
• 13–6 Contact Ratio
• 13–7 Interference
• 13–8 The Forming of Gear Teeth
• 13–9 Straight Bevel Gears
• 13–10 Parallel Helical Gears
• 13–11 Worm Gears
• 13–12 Tooth Systems
• 13–13 Gear Trains
• 13–14 Force Analysis—Spur Gearing
• 13–15 Force Analysis—Bevel Gearing
• 13–16 Force Analysis—Helical Gearing - 13–17 Force Analysis—Worm Gearing - Problems - 14 Spur and Helical Gears - 14–1 The Lewis Bending Equation - 14–2 Surface Durability - 14–3 AGMA Stress Equations - 14–4 AGMA Strength Equations - 14–5 Geometry Factors I and J ( ZI and YJ ) - 14–6 The Elastic Coefficient C p ( ZE ) - 14–7 Dynamic Factor Kv - 14–8 Overload Factor Ko - 14–9 Surface Condition Factor Cf ( ZR ) - 14–10 Size Factor Ks - 14–11 Load-Distribution Factor Km ( KH ) - 14–12 Hardness-Ratio Factor CH ( ZW ) - 14–13 Stress-Cycle Factors YN and ZN - 14–14 Reliability Factor KR ( YZ ) - 14–15 Temperature Factor KT ( Y u) - 14–16 Rim-Thickness Factor KB - 14–17 Safety Factors SF and SH - 14–18 Analysis - 14–19 Design of a Gear Mesh - Problems - 15 Bevel and Worm Gears - 15–1 Bevel Gearing—General - 15–2 Bevel-Gear Stresses and Strengths - 15–3 AGMA Equation Factors - 15–4 Straight-Bevel Gear Analysis - 15–5 Design of a Straight-Bevel Gear Mesh - 15–6 Worm Gearing—AGMA Equation - 15–7 Worm-Gear Analysis - 15–8 Designing a Worm-Gear Mesh - 15–9 Buckingham Wear Load - Problems - and Flywheels 16 Clutches, Brakes, Couplings, - 16–1 Static Analysis of Clutches and Brakes - Brakes 16–2 Internal Expanding Rim Clutches and
  • Brakes 16–3 External Contracting Rim Clutches and
• 16–4 Band-Type Clutches and Brakes
• 16–5 Frictional-Contact Axial Clutches
• 16–6 Disk Brakes
• 16–7 Cone Clutches and Brakes
• 16–8 Energy Considerations
• 16–9 Temperature Rise
• 16–10 Friction Materials
• 16–11 Miscellaneous Clutches and Couplings
• 16–12 Flywheels
• Problems
  • Elements 17 Flexible Mechanical
• 17–1 Belts
• 17–2 Flat- and Round-Belt Drives
• 17–3 V Belts
• 17–4 Timing Belts
• 17–5 Roller Chain
• 17–6 Wire Rope
• 17–7 Flexible Shafts
• Problems
  • Case Study 18 Power Transmission
• 18–1 Design Sequence for Power Transmission
• 18–2 Power and Torque Requirements
• 18–3 Gear Specification
• 18–4 Shaft Layout
• 18–5 Force Analysis
• 18–6 Shaft Material Selection
• 18–7 Shaft Design for Stress
• 18–8 Shaft Design for Deflection
• 18–9 Bearing Selection
• 18–10 Key and Retaining Ring Selection
• 18–11 Final Analysis
• Problems - Part 4 Special Topics - 19 Finite-Element Analysis - 19–1 The Finite-Element Method - 19–2 Element Geometries - 19–3 The Finite-Element Solution Process - 19–4 Mesh Generation - 19–5 Load Application - 19–6 Boundary Conditions - 19–7 Modeling Techniques - 19–8 Thermal Stresses - 19–9 Critical Buckling Load - 19–10 Vibration Analysis - 19–11 Summary - Problems - and Tolerancing 20 Geometric Dimensioning - Systems 20–1 Dimensioning and Tolerancing - and Tolerancing 20–2 Definition of Geometric Dimensioning - 20–3 Datums - 20–4 Controlling Geometric Tolerances - 20–5 Geometric Characteristic Definitions - 20–6 Material Condition Modifiers - 20–7 Practical Implementation - 20–8 GD&T in CAD Models - 20–9 Glossary of GD&T Terms - Problems - A Useful Tables Appendixes - Problems B Answers to Selected - Index

xv

Objectives

This text is intended for students beginning the study of mechanical engineering design. The focus is on blending fundamental development of concepts with practical specifi- cation of components. Students of this text should find that it inherently directs them into familiarity with both the basis for decisions and the standards of industrial com- ponents. For this reason, as students transition to practicing engineers, they will find that this text is indispensable as a reference text. The objectives of the text are to:

• Cover the basics of machine design, including the design process, engineering mechanics and materials, failure prevention under static and variable loading, and characteristics of the principal types of mechanical elements.

• Offer a practical approach to the subject through a wide range of real-world appli- cations and examples.

• Encourage readers to link design and analysis.

• Encourage readers to link fundamental concepts with practical component specification.

New to This Edition

Enhancements and modifications to the tenth edition are described in the following summaries:

• A new Chap. 20, Geometric Dimensioning and Tolerancing, has been added to intro- duce an important topic in machine design. Most of the major manufacturing companies utilize geometric dimensioning and tolerancing (GD&T) as a standardized means of accurately representing machine parts and assemblies for the purposes of design, man- ufacture, and quality control. Unfortunately, many mechanical engineers do not have sufficient exposure to the notation and concepts of GD&T to interpret the drawings. During the time when GD&T was becoming most prevalent in manufacturing, many engineering schools were phasing out comprehensive drafting courses in favor of computerized CAD instruction. This was followed by another transition to 3D solid modeling, where the part was drawn with ideal dimensions. Unfortunately, this ability to draw a perfect part in three dimensions is all too often accompanied by a neglect of focus on how to accurately and uniquely represent the part for manufacture and inspection. A full understanding of GD&T is usually obtained through an intensive course or training program. Some mechanical engineers will benefit from such a rigorous training. All mechanical engineers, however, should be familiar with the basic con- cepts and notation. The purpose of the coverage of GD&T in this new chapter is to provide this foundational exposure that is essential for all machine designers. It is always a challenge to find time to include additional material in a course. To facilitate this, the chapter is arranged and presented at a level appropriate for students

Preface

xvi Mechanical Engineering Design

to learn in an independent study format. The problems at the end of the chapter are more like quiz questions, and are focused on checking comprehension of the most fundamental concepts. Instructors are encouraged to consider using this chapter as a reading assignment, coupled with even a minimal lecture or online discussion. Of course, there is ample material for expanded presentation and discussion as well.

• Chapter 1, Introduction to Mechanical Engineering Design, has been expanded to provide more insight into design practices. Further discussion of the development of the design factor is presented, as well as the statistical relationships between reliability and the probability of failure, and reliability and the design factor. Sta- tistical considerations are provided here rather than in a chapter at the end of the text as in past editions. The section on Dimensions and Tolerances has been expanded to emphasize the designer’s role in specifying dimensions and tolerances as a critical part of machine design.
• The chapter of the previous edition, Statistical Considerations, has been eliminated. However, the material of that chapter pertinent to this edition has been integrated within the sections that utilize statistics. The stand-alone section on stochastic methods in Chap. 6, Fatigue Failure Resulting from Variable Loading, has also been eliminated. This is based on user input and the authors’ convictions that the excessive amount of development and data provided in that section was far too involved for the simple class of problems that could be solved. For instructors who still want access to this material, it is available on McGraw-Hill’s Online Learning Center at mhhe/shigley.
• In Chap. 11, Rolling-Contact Bearings, the Weibull probability distribution is defined and related to bearing life.
• In conjunction with the Connect Engineering resource, the end-of-chapter problems have been freshly examined to ensure they are clearly stated with less room for vague interpretations. Approximately 50 percent of the problems are targeted for Connect implementation. With the problem parameterization available in this Web- based platform, students can be assigned basic problems with minimal duplication from student to student and semester to semester. For a good balance, this edition maintains many end-of-chapter problems that are open-ended and suitable for exploration and design.

Connect Engineering The tenth edition continues to feature McGraw-Hill Connect Engineering, a Web- based assignment and assessment platform that allows instructors to deliver assign- ments, quizzes, and tests easily online. Students can practice important skills at their own pace and on their own schedule.

McGraw-Hill LearnSmart ®

McGraw-Hill LearnSmart is an adaptive learning system designed to help students learn faster, study more efficiently, and retain more knowledge for greater success. Through a series of adaptive questions, Learnsmart pinpoints concepts the student does not understand and maps out a personalized study plan for success. It also lets instructors see exactly what students have accomplished, and it features a built-in assessment tool for graded assignments. Ask your McGraw-Hill Representative for more information, and visit mhlearnsmart for a demonstration.

Preface xvii

McGraw-Hill SmartBook™

Powered by the intelligent and adaptive LearnSmart engine, SmartBook is the first and only continuously adaptive reading experience available today. Distinguishing what students know from what they don’t, and honing in on concepts they are most likely to forget, SmartBook personalizes content for each student. Reading is no lon- ger a passive and linear experience but an engaging and dynamic one, where students are more likely to master and retain important concepts, coming to class better pre- pared. SmartBook includes powerful reports that identify specific topics and learning objectives students need to study. These valuable reports also provide instructors insight into how students are progressing through textbook content and are useful for identifying class trends, focusing precious class time, providing personalized feedback to students, and tailoring assessment. How does SmartBook work? Each SmartBook contains four components: Preview, Read, Practice, and Recharge. Starting with an initial preview of each chap- ter and key learning objectives, students read the material and are guided to topics for which they need the most practice based on their responses to a continuously adapting diagnostic. Read and practice continue until SmartBook directs students to recharge important material they are most likely to forget to ensure concept mastery and retention.

Electronic Textbooks

This text is available as an eBook at CourseSmart. At CourseSmart your students can take advantage of significant savings off the cost of a print textbook, reduce their impact on the environment, and gain access to powerful web tools for learning. CourseSmart eBooks can be viewed online or downloaded to a computer. The eBooks allow students to do full text searches, add highlighting and notes, and share notes with classmates. CourseSmart has the largest selection of eBooks available anywhere. Visit CourseSmart to learn more and to try a sample chapter.

McGraw-Hill Create™

With McGraw-Hill Create, you can easily rearrange chapters, combine material from other content sources, and quickly upload content you have written, like your course syllabus or teaching notes. Find the content you need in Create by searching through thousands of leading McGraw-Hill textbooks. Arrange your book to fit your teaching style. Create even allows you to personalize your book’s appearance by selecting the cover and adding your name, school, and course information. Order a Create book and you’ll receive a complimentary print review copy in 3–5 business days or a complimentary electronic review copy (eComp) via e-mail in minutes. Go to mcgrawhillcreate today and register to experience how McGraw-Hill Create empowers you to teach your students your way. Additional media offerings available at mhhe/shigley include:

Student Supplements

• Fundamentals of Engineering (FE) exam questions for machine design. Interactive problems and solutions serve as effective, self-testing problems as well as excellent preparation for the FE exam.

xviii Mechanical Engineering Design

Instructor Supplements (under password protection)

• Solutions manual. The instructor’s manual contains solutions to most end-of- chapter nondesign problems.
• PowerPoint ® slides. Slides outlining the content of the text are provided in Power- Point format for instructors to use as a starting point for developing lecture presentation materials. The slides include all figures, tables, and equations from the text.
• C.O.S.M.O. A complete online solutions manual organization system that allows instructors to create custom homework, quizzes, and tests using end-of-chapter problems from the text.

Acknowledgments The authors would like to acknowledge those who have contributed to this text for over 50 years and nine editions. We are especially grateful to those who provided input to this tenth edition: Expanded Connect Implementation Peter J. Schuster, California Polytechnic State University Drawings for GD&T Chapter Glenn Traner, Tech Manufacturing, LLC CAD Model Used in Cover Design Jedrzej Galecki, University of the West of England Reviewers Kenneth Huebner, Arizona State Gloria Starns, Iowa State Tim Lee, McGill University Robert Rizza, MSOE Richard Patton, Mississippi State University Stephen Boedo, Rochester Institute of Technology Om Agrawal, Southern Illinois University Arun Srinivasa, Texas A&M Jason Carey, University of Alberta Patrick Smolinski, University of Pittsburgh Dennis Hong, Virginia Tech

xix

List of Symbols

This is a list of common symbols used in machine design and in this book. Specialized use in a subject-matter area often attracts fore and post subscripts and superscripts. To make the table brief enough to be useful, the symbol kernels are listed. See Table 14–1, pp. 727–728 for spur and helical gearing symbols, and Table 15–1, pp. 781–782 for bevel-gear symbols.

A Area, coefficient a Distance B Coefficient Bhn Brinell hardness b Distance, Weibull shape parameter, range number, width C Basic load rating, bolted-joint constant, center distance, coefficient of variation, column end condition, correction factor, specific heat capacity, spring index c Distance, viscous damping, velocity coefficient COV Coefficient of variation D Diameter, helix diameter d Diameter, distance E Modulus of elasticity, energy, error e Distance, eccentricity, efficiency, Naperian logarithmic base F Force, fundamental dimension force f Coefficient of friction, frequency, function fom Figure of merit G Torsional modulus of elasticity g Acceleration due to gravity, function H Heat, power HB Brinell hardness HRC Rockwell C-scale hardness h Distance, film thickness h # CR Combined overall coefficient of convection and radiation heat transfer I Integral, linear impulse, mass moment of inertia, second moment of area i Index i Unit vector in x -direction J Mechanical equivalent of heat, polar second moment of area, geometry factor j Unit vector in the y -direction K Service factor, stress-concentration factor, stress-augmentation factor, torque coefficient k Marin endurance limit modifying factor, spring rate k Unit vector in the z -direction L Length, life, fundamental dimension length

xx Mechanical Engineering Design

l Life in hours l Length M Fundamental dimension mass, moment M Moment vector m Mass, slope, strain-strengthening exponent N Normal force, number, rotational speed, number of cycles n Load factor, rotational speed, factor of safety nd Design factor P Force, pressure, diametral pitch PDF Probability density function p Pitch, pressure, probability Q First moment of area, imaginary force, volume q Distributed load, notch sensitivity R Radius, reaction force, reliability, Rockwell hardness, stress ratio, reduc- tion in area R Vector reaction force r Radius r Distance vector S Sommerfeld number, strength s Distance, sample standard deviation, stress T Temperature, tolerance, torque, fundamental dimension time T Torque vector t Distance, time, tolerance U Strain energy u Strain energy per unit volume V Linear velocity, shear force v Linear velocity W Cold-work factor, load, weight w Distance, gap, load intensity X Coordinate, truncated number x Coordinate, true value of a number, Weibull parameter Y Coordinate y Coordinate, deflection Z Coordinate, section modulus, viscosity z Coordinate, dimensionless transform variable for normal distributions a Coefficient, coefficient of linear thermal expansion, end-condition for springs, thread angle b Bearing angle, coefficient D Change, deflection d Deviation, elongation P Eccentricity ratio, engineering (normal) strain e True or logarithmic normal strain G Gamma function, pitch angle g Pitch angle, shear strain, specific weight l Slenderness ratio for springs m Absolute viscosity, population mean n Poisson ratio v Angular velocity, circular frequency f Angle, wave length

List of Symbols xxi

c Slope integral r Radius of curvature, mass density s Normal stress s 9 Von Mises stress sˆ Standard deviation t Shear stress u Angle, Weibull characteristic parameter ¢ Cost per unit weight $ Cost

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Shigley’s

Mecha nical

Engineering

Design

Part 1 Basics Preface xv

Chapter Outline 1–1 Design 4 1–2 Mechanical Engineering Design 5 1–3 Phases and Interactions of the Design Process 5 1–4 Design Tools and Resources 8 1–5 The Design Engineer’s Professional Responsibilities 10 1–6 Standards and Codes 12 1–7 Economics 13 1–8 Safety and Product Liability 15 1–9 Stress and Strength 16 1–10 Uncertainty 16 1–11 Design Factor and Factor of Safety 18 1–12 Reliability and Probability of Failure 20 1–13 Relating the Design Factor to Reliability 24 1–14 Dimensions and Tolerances 27 1–15 Units 31 1–16 Calculations and Significant Figures 32 1–17 Design Topic Interdependencies 33 1–18 Power Transmission Case Study Specifications 34

1 Introduction to Mechanical Engineering Design

1 Engineering Design

3

4 Mechanical Engineering Design

Mechanical design is a complex process, requiring many skills. Extensive relation- ships need to be subdivided into a series of simple tasks. The complexity of the process requires a sequence in which ideas are introduced and iterated. We first address the nature of design in general, and then mechanical engineering design in particular. Design is an iterative process with many interactive phases. Many resources exist to support the designer, including many sources of information and an abundance of computational design tools. Design engineers need not only develop competence in their field but they must also cultivate a strong sense of responsibility and professional work ethic. There are roles to be played by codes and standards, ever-present economics, safety, and considerations of product liability. The survival of a mechanical compo- nent is often related through stress and strength. Matters of uncertainty are ever- present in engineering design and are typically addressed by the design factor and factor of safety, either in the form of a deterministic (absolute) or statistical sense. The latter, statistical approach, deals with a design’s reliability and requires good statistical data. In mechanical design, other considerations include dimensions and tolerances, units, and calculations. This book consists of four parts. Part 1, Basics, begins by explaining some dif- ferences between design and analysis and introducing some fundamental notions and approaches to design. It continues with three chapters reviewing material properties, stress analysis, and stiffness and deflection analysis, which are the principles neces- sary for the remainder of the book. Part 2, Failure Prevention, consists of two chapters on the prevention of failure of mechanical parts. Why machine parts fail and how they can be designed to prevent failure are difficult questions, and so we take two chapters to answer them, one on preventing failure due to static loads, and the other on preventing fatigue failure due to time-varying, cyclic loads. In Part 3, Design of Mechanical Elements, the concepts of Parts 1 and 2 are applied to the analysis, selection, and design of specific mechanical elements such as shafts, fasteners, weldments, springs, rolling contact bearings, film bearings, gears, belts, chains, and wire ropes. Part 4, Special Topics, provides introductions to two important methods used in mechanical design, finite element analysis and geometric dimensioning and toleranc- ing. This is optional study material, but some sections and examples in Parts 1 to 3 demonstrate the use of these tools. There are two appendixes at the end of the book. Appendix A contains many useful tables referenced throughout the book. Appendix B contains answers to selected end-of-chapter problems.

1–1 Design

To design is either to formulate a plan for the satisfaction of a specified need or to solve a specific problem. If the plan results in the creation of something having a physical reality, then the product must be functional, safe, reliable, competitive, usable, manufacturable, and marketable. Design is an innovative and highly iterative process. It is also a decision-making process. Decisions sometimes have to be made with too little information, occasionally with just the right amount of information, or with an excess of partially contradictory information. Decisions are sometimes made tentatively, with the right reserved to

Introduction to Mechanical Engineering Design 5

adjust as more becomes known. The point is that the engineering designer has to be personally comfortable with a decision-making, problem-solving role. Design is a communication-intensive activity in which both words and pictures are used, and written and oral forms are employed. Engineers have to communicate effectively and work with people of many disciplines. These are important skills, and an engineer’s success depends on them. A designer’s personal resources of creativeness, communicative ability, and problem- solving skill are intertwined with the knowledge of technology and first principles. Engineering tools (such as mathematics, statistics, computers, graphics, and languages) are combined to produce a plan that, when carried out, produces a product that is functional, safe, reliable, competitive, usable, manufacturable, and marketable, regard- less of who builds it or who uses it.

1–2 Mechanical Engineering Design

Mechanical engineers are associated with the production and processing of energy and with providing the means of production, the tools of transportation, and the techniques of automation. The skill and knowledge base are extensive. Among the disciplinary bases are mechanics of solids and fluids, mass and momentum transport, manufacturing processes, and electrical and information theory. Mechanical engineering design involves all the disciplines of mechanical engineering. Real problems resist compartmentalization. A simple journal bearing involves fluid flow, heat transfer, friction, energy transport, material selection, thermomechan- ical treatments, statistical descriptions, and so on. A building is environmentally con- trolled. The heating, ventilation, and air-conditioning considerations are sufficiently specialized that some speak of heating, ventilating, and air-conditioning design as if it is separate and distinct from mechanical engineering design. Similarly, internal- combustion engine design, turbomachinery design, and jet-engine design are some- times considered discrete entities. Here, the leading string of words preceding the word design is merely a product descriptor. Similarly, there are phrases such as machine design, machine-element design, machine-component design, systems design, and fluid-power design. All of these phrases are somewhat more focused examples of mechanical engineering design. They all draw on the same bodies of knowledge, are similarly organized, and require similar skills.

1–3 Phases and Interactions of the Design Process

What is the design process? How does it begin? Does the engineer simply sit down at a desk with a blank sheet of paper and jot down some ideas? What happens next? What factors influence or control the decisions that have to be made? Finally, how does the design process end? The complete design process, from start to finish, is often outlined as in Fig. 1–1. The process begins with an identification of a need and a decision to do something about it. After many iterations, the process ends with the presentation of the plans for satisfying the need. Depending on the nature of the design task, several design phases may be repeated throughout the life of the product, from inception to termi- nation. In the next several subsections, we shall examine these steps in the design process in detail. Identification of need generally starts the design process. Recognition of the need and phrasing the need often constitute a highly creative act, because the need may be

6 Mechanical Engineering Design

only a vague discontent, a feeling of uneasiness, or a sensing that something is not right. The need is often not evident at all; recognition can be triggered by a particular adverse circumstance or a set of random circumstances that arises almost simultane- ously. For example, the need to do something about a food-packaging machine may be indicated by the noise level, by a variation in package weight, and by slight but perceptible variations in the quality of the packaging or wrap. There is a distinct difference between the statement of the need and the definition of the problem. The definition of problem is more specific and must include all the specifications for the object that is to be designed. The specifications are the input and output quantities, the characteristics and dimensions of the space the object must occupy, and all the limitations on these quantities. We can regard the object to be designed as something in a black box. In this case we must specify the inputs and outputs of the box, together with their characteristics and limitations. The specifica- tions define the cost, the number to be manufactured, the expected life, the range, the operating temperature, and the reliability. Specified characteristics can include the speeds, feeds, temperature limitations, maximum range, expected variations in the variables, dimensional and weight limitations, etc. There are many implied specifications that result either from the designer’s par- ticular environment or from the nature of the problem itself. The manufacturing pro- cesses that are available, together with the facilities of a certain plant, constitute restrictions on a designer’s freedom, and hence are a part of the implied specifications. It may be that a small plant, for instance, does not own cold-working machinery. Knowing this, the designer might select other metal-processing methods that can be performed in the plant. The labor skills available and the competitive situation also constitute implied constraints. Anything that limits the designer’s freedom of choice is a constraint. Many materials and sizes are listed in supplier’s catalogs, for instance, but these are not all easily available and shortages frequently occur. Furthermore, inventory economics requires that a manufacturer stock a minimum number of mate- rials and sizes. An example of a specification is given in Sec. 1–18. This example is for a case study of a power transmission that is presented throughout this text. The synthesis of a scheme connecting possible system elements is sometimes called the invention of the concept or concept design. This is the first and most important

Identification of need

Definition of problem

Synthesis

Analysis and optimization

Evaluation

Presentation

Iteration

Figure 1–1 The phases in design, acknowledging the many feedbacks and iterations.

Introduction to Mechanical Engineering Design 7

step in the synthesis task. Various schemes must be proposed, investigated, and quan- tified in terms of established metrics. 1 As the fleshing out of the scheme progresses, analyses must be performed to assess whether the system performance is satisfactory or better, and, if satisfactory, just how well it will perform. System schemes that do not survive analysis are revised, improved, or discarded. Those with potential are optimized to determine the best performance of which the scheme is capable. Competing schemes are compared so that the path leading to the most competitive product can be chosen. Figure 1–1 shows that synthesis and analysis and optimization are intimately and iteratively related. We have noted, and we emphasize, that design is an iterative process in which we proceed through several steps, evaluate the results, and then return to an earlier phase of the procedure. Thus, we may synthesize several components of a system, analyze and optimize them, and return to synthesis to see what effect this has on the remaining parts of the system. For example, the design of a system to transmit power requires attention to the design and selection of individual components (e., gears, bearings, shaft). However, as is often the case in design, these components are not independent. In order to design the shaft for stress and deflection, it is necessary to know the applied forces. If the forces are transmitted through gears, it is necessary to know the gear specifications in order to determine the forces that will be transmit- ted to the shaft. But stock gears come with certain bore sizes, requiring knowledge of the necessary shaft diameter. Clearly, rough estimates will need to be made in order to proceed through the process, refining and iterating until a final design is obtained that is satisfactory for each individual component as well as for the overall design specifications. Throughout the text we will elaborate on this process for the case study of a power transmission design. Both analysis and optimization require that we construct or devise abstract mod- els of the system that will admit some form of mathematical analysis. We call these models mathematical models. In creating them it is our hope that we can find one that will simulate the real physical system very well. As indicated in Fig. 1–1, evalu- ation is a significant phase of the total design process. Evaluation is the final proof of a successful design and usually involves the testing of a prototype in the laboratory. Here we wish to discover if the design really satisfies the needs. Is it reliable? Will it compete successfully with similar products? Is it economical to manufacture and to use? Is it easily maintained and adjusted? Can a profit be made from its sale or use? How likely is it to result in product-liability lawsuits? And is insurance easily and cheaply obtained? Is it likely that recalls will be needed to replace defective parts or systems? The project designer or design team will need to address a myriad of engi- neering and non-engineering questions. Communicating the design to others is the final, vital presentation step in the design process. Undoubtedly, many great designs, inventions, and creative works have been lost to posterity simply because the originators were unable or unwilling to properly explain their accomplishments to others. Presentation is a selling job. The engineer, when presenting a new solution to administrative, management, or supervi- sory persons, is attempting to sell or to prove to them that their solution is a better one. Unless this can be done successfully, the time and effort spent on obtaining the

1 An excellent reference for this topic is presented by Stuart Pugh, Total Design — Integrated Methods for

Successful Product Engineering, Addison-Wesley, 1991. A description of the Pugh method is also provided in Chap. 8, David G. Ullman, The Mechanical Design Process, 3rd ed., McGraw-Hill, 2003.

8 Mechanical Engineering Design

solution have been largely wasted. When designers sell a new idea, they also sell themselves. If they are repeatedly successful in selling ideas, designs, and new solu- tions to management, they begin to receive salary increases and promotions; in fact, this is how anyone succeeds in his or her profession.

Design Considerations Sometimes the strength required of an element in a system is an important factor in the determination of the geometry and the dimensions of the element. In such a situ- ation we say that strength is an important design consideration. When we use the expression design consideration, we are referring to some characteristic that influences the design of the element or, perhaps, the entire system. Usually quite a number of such characteristics must be considered and prioritized in a given design situation. Many of the important ones are as follows (not necessarily in order of importance): 1 Functionality 14 Noise 2 Strength/stress 15 Styling 3 Distortion/deflection/stiffness 16 Shape 4 Wear 17 Size 5 Corrosion 18 Control 6 Safety 19 Thermal properties 7 Reliability 20 Surface 8 Manufacturability 21 Lubrication 9 Utility 22 Marketability 10 Cost 23 Maintenance 11 Friction 24 Volume 12 Weight 25 Liability 13 Life 26 Remanufacturing/resource recovery Some of these characteristics have to do directly with the dimensions, the material, the processing, and the joining of the elements of the system. Several characteristics may be interrelated, which affects the configuration of the total system.

1–4 Design Tools and Resources

Today, the engineer has a great variety of tools and resources available to assist in the solution of design problems. Inexpensive microcomputers and robust computer software packages provide tools of immense capability for the design, analysis, and simulation of mechanical components. In addition to these tools, the engineer always needs technical information, either in the form of basic science/engineering behavior or the characteristics of specific off-the-shelf components. Here, the resources can range from science/engineering textbooks to manufacturers’ brochures or catalogs. Here too, the computer can play a major role in gathering information. 2

Computational Tools Computer-aided design (CAD) software allows the development of three-dimensional (3-D) designs from which conventional two-dimensional orthographic views with

2 An excellent and comprehensive discussion of the process of “gathering information” can be found in Chap. 4, George E. Dieter, Engineering Design, A Materials and Processing Approach, 3rd ed., McGraw-Hill, New York, 2000.

Introduction to Mechanical Engineering Design 9

automatic dimensioning can be produced. Manufacturing tool paths can be generated from the 3-D models, and in some cases, parts can be created directly from a 3-D database by using a rapid prototyping and manufacturing method (stereolithography)— paperless manufacturing! Another advantage of a 3-D database is that it allows rapid and accurate calculations of mass properties such as mass, location of the center of gravity, and mass moments of inertia. Other geometric properties such as areas and distances between points are likewise easily obtained. There are a great many CAD software packages available such as Aries, AutoCAD, CadKey, I-Deas, Unigraphics, Solid Works, and ProEngineer, to name a few. The term computer-aided engineering (CAE) generally applies to all computer- related engineering applications. With this definition, CAD can be considered as a subset of CAE. Some computer software packages perform specific engineering anal- ysis and/or simulation tasks that assist the designer, but they are not considered a tool for the creation of the design that CAD is. Such software fits into two categories: engineering-based and non-engineering-specific. Some examples of engineering-based software for mechanical engineering applications—software that might also be inte- grated within a CAD system—include finite-element analysis (FEA) programs for analysis of stress and deflection (see Chap. 19), vibration, and heat transfer (e., Algor, ANSYS, and MSC/NASTRAN); computational fluid dynamics (CFD) pro- grams for fluid-flow analysis and simulation (e., CFD++, FIDAP, and Fluent); and programs for simulation of dynamic force and motion in mechanisms (e., ADAMS, DADS, and Working Model). Examples of non-engineering-specific computer-aided applications include soft- ware for word processing, spreadsheet software (e., Excel, Lotus, and Quattro-Pro), and mathematical solvers (e., Maple, MathCad, MATLAB, 3 Mathematica, and TKsolver). Your instructor is the best source of information about programs that may be available to you and can recommend those that are useful for specific tasks. One cau- tion, however: Computer software is no substitute for the human thought process. Yo u are the driver here; the computer is the vehicle to assist you on your journey to a solution. Numbers generated by a computer can be far from the truth if you entered incorrect input, if you misinterpreted the application or the output of the program, if the program contained bugs, etc. It is your responsibility to assure the validity of the results, so be careful to check the application and results carefully, perform benchmark testing by submitting problems with known solutions, and monitor the software com- pany and user-group newsletters.

Acquiring Technical Information

We currently live in what is referred to as the information age, where information is generated at an astounding pace. It is difficult, but extremely important, to keep abreast of past and current developments in one’s field of study and occupation. The reference in footnote 2 provides an excellent description of the informational resources available and is highly recommended reading for the serious design engineer. Some sources of information are:

• Libraries (community, university, and private). Engineering dictionaries and ency- clopedias, textbooks, monographs, handbooks, indexing and abstract services, jour- nals, translations, technical reports, patents, and business sources/brochures/catalogs.

3 MATLAB is a registered trademark of The MathWorks, Inc.

10 Mechanical Engineering Design

• Government sources. Departments of Defense, Commerce, Energy, and Transporta- tion; NASA; Government Printing Office; U. Patent and Trademark Office; National Technical Information Service; and National Institute for Standards and Technology.
• Professional societies. American Society of Mechanical Engineers, Society of Manufacturing Engineers, Society of Automotive Engineers, American Society for Testing and Materials, and American Welding Society.
• Commercial vendors. Catalogs, technical literature, test data, samples, and cost information.
• Internet. The computer network gateway to websites associated with most of the categories listed above. 4 This list is not complete. The reader is urged to explore the various sources of information on a regular basis and keep records of the knowledge gained.

1–5 The Design Engineer’s Professional Responsibilities

In general, the design engineer is required to satisfy the needs of customers (manage- ment, clients, consumers, etc.) and is expected to do so in a competent, responsible, ethical, and professional manner. Much of engineering course work and practical experience focuses on competence, but when does one begin to develop engineering responsibility and professionalism? To start on the road to success, you should start to develop these characteristics early in your educational program. You need to culti- vate your professional work ethic and process skills before graduation, so that when you begin your formal engineering career, you will be prepared to meet the challenges. It is not obvious to some students, but communication skills play a large role here, and it is the wise student who continuously works to improve these skills— even if it is not a direct requirement of a course assignment! Success in engineering (achievements, promotions, raises, etc.) may in large part be due to competence but if you cannot communicate your ideas clearly and concisely, your technical profi- ciency may be compromised. You can start to develop your communication skills by keeping a neat and clear journal/logbook of your activities, entering dated entries frequently. (Many compa- nies require their engineers to keep a journal for patent and liability concerns.) Separate journals should be used for each design project (or course subject). When starting a project or problem, in the definition stage, make journal entries quite frequently. Others, as well as yourself, may later question why you made certain decisions. Good chronological records will make it easier to explain your decisions at a later date. Many engineering students see themselves after graduation as practicing engi- neers designing, developing, and analyzing products and processes and consider the need of good communication skills, either oral or writing, as secondary. This is far from the truth. Most practicing engineers spend a good deal of time communicating with others, writing proposals and technical reports, and giving presentations and interacting with engineering and nonengineering support personnel. You have the time now to sharpen your communication skills. When given an assignment to write or

4 Some helpful Web resources, to name a few, include globalspec, engnetglobal, efunda, thomasnet, and uspto.

Introduction to Mechanical Engineering Design 11

make any presentation, technical or nontechnical, accept it enthusiastically, and work on improving your communication skills. It will be time well spent to learn the skills now rather than on the job. When you are working on a design problem, it is important that you develop a systematic approach. Careful attention to the following action steps will help you to organize your solution processing technique.

• Understand the problem. Problem definition is probably the most significant step in the engineering design process. Carefully read, understand, and refine the prob- lem statement.

• Identify the knowns. From the refined problem statement, describe concisely what information is known and relevant.

• Identify the unknowns and formulate the solution strategy. State what must be determined, in what order, so as to arrive at a solution to the problem. Sketch the component or system under investigation, identifying known and unknown param- eters. Create a flowchart of the steps necessary to reach the final solution. The steps may require the use of free-body diagrams; material properties from tables; equa- tions from first principles, textbooks, or handbooks relating the known and unknown parameters; experimentally or numerically based charts; specific computational tools as discussed in Sec. 1–4; etc.

• State all assumptions and decisions. Real design problems generally do not have unique, ideal, closed-form solutions. Selections, such as the choice of materials, and heat treatments, require decisions. Analyses require assumptions related to the modeling of the real components or system. All assumptions and decisions should be identified and recorded.

• Analyze the problem. Using your solution strategy in conjunction with your deci- sions and assumptions, execute the analysis of the problem. Reference the sources of all equations, tables, charts, software results, etc. Check the credibility of your results. Check the order of magnitude, dimensionality, trends, signs, etc.

• Evaluate your solution. Evaluate each step in the solution, noting how changes in strategy, decisions, assumptions, and execution might change the results, in positive or negative ways. Whenever possible, incorporate the positive changes in your final solution.

• Present your solution. Here is where your communication skills are important. At this point, you are selling yourself and your technical abilities. If you cannot skill- fully explain what you have done, some or all of your work may be misunderstood and unaccepted. Know your audience.

As stated earlier, all design processes are interactive and iterative. Thus, it may be necessary to repeat some or all of the above steps more than once if less than satisfac- tory results are obtained. In order to be effective, all professionals must keep current in their fields of endeavor. The design engineer can satisfy this in a number of ways by: being an active member of a professional society such as the American Society of Mechanical Engineers (ASME), the Society of Automotive Engineers (SAE), and the Society of Manufacturing Engineers (SME); attending meetings, conferences, and seminars of societies, manufacturers, universities, etc.; taking specific graduate courses or pro- grams at universities; regularly reading technical and professional journals; etc. An engineer’s education does not end at graduation.

12 Mechanical Engineering Design

The design engineer’s professional obligations include conducting activities in an ethical manner. Reproduced here is the Engineers’ Creed from the National Society of Professional Engineers (NSPE) 5 : As a Professional Engineer I dedicate my professional knowledge and skill to the advancement and betterment of human welfare. I pledge: To give the utmost of performance; To participate in none but honest enterprise; To live and work according to the laws of man and the highest standards of professional conduct; To place service before profit, the honor and standing of the profession before personal advantage, and the public welfare above all other considerations. In humility and with need for Divine Guidance, I make this pledge.

1–6 Standards and Codes

A standard is a set of specifications for parts, materials, or processes intended to achieve uniformity, efficiency, and a specified quality. One of the important purposes of a standard is to limit the