Mechanical Engineering
McGraw−Hill Primis
ISBN: 0−390−76487−6
Text:
Shigley’s Mechanical Engineering Design,
Eighth Edition
Budynas−Nisbett
Shigley’s Mechanical Engineering Design,
Eighth Edition
Budynas−Nisbett
McGraw-Hill
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Shigley's Mechanical Engineering Design - 8th Edition with Solution of Problems, Notas de estudo de Design
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Mechanical Engineering
McGraw−Hill Primis
ISBN: 0−390−76487−
Text:
Shigley’s Mechanical Engineering Design, Eighth Edition Budynas−Nisbett
Shigley’s Mechanical Engineering Design, Eighth Edition
Budynas−Nisbett
McGraw-Hill abc
Mechanical Engineering
http://www.primisonline.com
Copyright ©2006 by The McGraw−Hill Companies, Inc. All rights reserved. Printed in the United States of America. Except as permitted under the United States Copyright Act of 1976, 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 prior written permission of the publisher.
This McGraw−Hill Primis text may include materials submitted to McGraw−Hill for publication by the instructor of this course. The instructor is solely responsible for the editorial content of such materials.
111 0192GEN ISBN: 0−390−76487−
This book was printed on recycled paper.
- Front Matter Budynas−Nisbett • Shigley’s Mechanical Engineering Design, Eighth Edition
- Preface
- List of Symbols
- I. Basics
- Introduction
- Introduction to Mechanical Engineering Design
- Materials
- Load and Stress Analysis
- Deflection and Stiffness
- II. Failure Prevention
- Introduction
- Failures Resulting from Static Loading
- Fatigue Failure Resulting from Variable Loading
- III. Design of Mechanical Elements
- Introduction
- 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
- IV. Analysis Tools
- Introduction
- Finite−Element Analysis
- Statistical Considerations
- Back Matter
- Appendix A: Useful Tables
- Appendix B: Answers to Selected Problems
- Index
Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition
Front Matter Preface © The McGraw−Hill^1 Companies, 2008
Objectives This text is intended for students beginning the study of mechanical engineering design. The focus is on blending fundamental development of concepts with practi- cal specification 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 components. 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 me- chanics and materials, failure prevention under static and variable loading, and char- acteristics of the principal types of mechanical elements.
- Offer a practical approach to the subject through a wide range of real-world applica- tions and examples.
- Encourage readers to link design and analysis.
- Encourage readers to link fundamental concepts with practical component specification.
New to This Edition This eighth edition contains the following significant enhancements:
- New chapter on the Finite Element Method. In response to many requests from reviewers, this edition presents an introductory chapter on the finite element method. The goal of this chapter is to provide an overview of the terminology, method, capa- bilities, and applications of this tool in the design environment.
- New transmission case study. The traditional separation of topics into chapters sometimes leaves students at a loss when it comes time to integrate dependent topics in a larger design process. A comprehensive case study is incorporated through stand- alone example problems in multiple chapters, then culminated with a new chapter that discusses and demonstrates the integration of the parts into a complete design process. Example problems relevant to the case study are presented on engineering paper background to quickly identify them as part of the case study.
- Revised and expanded coverage of shaft design. Complementing the new transmis- sion case study is a significantly revised and expanded chapter focusing on issues rel- evant to shaft design. The motivating goal is to provide a meaningful presentation that allows a new designer to progress through the entire shaft design process – from gen- eral shaft layout to specifying dimensions. The chapter has been moved to immedi- ately follow the fatigue chapter, providing an opportunity to seamlessly transition from the fatigue coverage to its application in the design of shafts.
- Availability of information to complete the details of a design. Additional focus is placed on ensuring the designer can carry the process through to completion.
Preface
xv
Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition
Front Matter Preface © The McGraw−Hill^3 Companies, 2008
Part 3: Design of Mechanical Elements Part 3 covers the design of specific machine components. All chapters have received general cleanup. The shaft chapter has been moved to the beginning of the section. The arrangement of chapters, along with any significant changes, is described below:
- Chapter 7, Shafts and Shaft Components. This chapter is significantly expanded and rewritten to be comprehensive in designing shafts. Instructors that previously did not specifically cover the shaft chapter are encouraged to use this chapter immediately following the coverage of fatigue failure. The design of a shaft provides a natural pro- gression from the failure prevention section into application toward components. This chapter is an essential part of the new transmission case study. The coverage of setscrews, keys, pins, and retaining rings, previously placed in the chapter on bolted joints, has been moved into this chapter. The coverage of limits and fits, previously placed in the chapter on statistics, has been moved into this chapter.
- Chapter 8, Screws, Fasteners, and the Design of Nonpermanent Joints. The sec- tion on setscrews, keys, and pins, has been moved from this chapter to Chapter 7. The coverage of bolted and riveted joints loaded in shear has been returned to this chapter.
- Chapter 9, Welding, Bonding, and the Design of Permanent Joints. The section on bolted and riveted joints loaded in shear has been moved to Chapter 8.
- Chapter 10, Mechanical Springs.
- Chapter 11, Rolling-Contact Bearings.
- Chapter 12, Lubrication and Journal Bearings.
- Chapter 13, Gears – General. New example problems are included to address design of compound gear trains to achieve specified gear ratios. The discussion of the rela- tionship between torque, speed, and power is clarified.
- Chapter 14, Spur and Helical Gears. The current AGMA standard (ANSI/AGMA 2001-D04) has been reviewed to ensure up-to-date information in the gear chapters. All references in this chapter are updated to reflect the current standard.
- Chapter 15, Bevel and Worm Gears.
- Chapter 16, Clutches, Brakes, Couplings, and Flywheels.
- Chapter 17, Flexible Mechanical Elements.
- Chapter 18, Power Transmission Case Study. This new chapter provides a complete case study of a double reduction power transmission. The focus is on providing an ex- ample for student designers of the process of integrating topics from multiple chap- ters. Instructors are encouraged to include one of the variations of this case study as a design project in the course. Student feedback consistently shows that this type of project is one of the most valuable aspects of a first course in machine design. This chapter can be utilized in a tutorial fashion for students working through a similar design.
Part 4: Analysis Tools Part 4 includes a new chapter on finite element methods, and a new location for the chapter on statistical considerations. Instructors can reference these chapters as needed.
- Chapter 19, Finite Element Analysis. This chapter is intended to provide an intro- duction to the finite element method, and particularly its application to the machine design process.
Preface xvii
Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition
(^4) Front Matter Preface © The McGraw−Hill Companies, 2008
xviii Mechanical Engineering Design
- Chapter 20, Statistical Considerations. This chapter is relocated and organized as a tool for users that wish to incorporate statistical concepts into the machine design process. This chapter should be reviewed if Secs. 5–13, 6–17, or Chap. 11 are to be covered.
Supplements The 8th^ edition of Shigley’s Mechanical Engineering Design features McGraw-Hill’s ARIS (Assessment Review and Instruction System). ARIS makes homework meaningful—and manageable—for instructors and students. Instructors can assign and grade text-specific homework within the industry’s most robust and versatile homework management sys- tem. Students can access multimedia learning tools and benefit from unlimited practice via algorithmic problems. Go to aris.mhhe.com to learn more and register! The array of tools available to users of Shigley’s Mechanical Engineering Design includes:
Student Supplements
- Tutorials—Presentation of major concepts, with visuals. Among the topics covered are pressure vessel design, press and shrink fits, contact stresses, and design for static failure.
- MATLAB ®^ for machine design. Includes visual simulations and accompanying source code. The simulations are linked to examples and problems in the text and demonstrate the ways computational software can be used in mechanical design and analysis.
- 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.
- Algorithmic Problems. Allow step-by-step problem-solving using a recursive com- putational procedure (algorithm) to create an infinite number of problems.
Instructor Supplements (under password protection)
- Solutions manual. The instructor’s manual contains solutions to most end-of-chapter nondesign problems.
- PowerPoint ®^ slides. Slides of important figures and tables from the text are provided in PowerPoint format for use in lectures.
Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition
(^6) Front Matter List of Symbols © The McGraw−Hill Companies, 2008
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 k variate, unit vector in the z -direction L Length, life, fundamental dimension length LN Lognormal distribution l Length M Fundamental dimension mass, moment M Moment vector, moment variate m Mass, slope, strain-strengthening exponent N Normal force, number, rotational speed N Normal distribution n Load factor, rotational speed, safety factor 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 R Vector reaction force r Correlation coefficient, radius r Distance vector S Sommerfeld number, strength S S variate s Distance, sample standard deviation, stress T Temperature, tolerance, torque, fundamental dimension time T Torque vector, torque variate t Distance, Student’s t-statistic, time, tolerance U Strain energy U Uniform distribution u Strain energy per unit volume V Linear velocity, shear force v Linear velocity W Cold-work factor, load, weight W Weibull distribution w Distance, gap, load intensity w Vector distance X Coordinate, truncated number x Coordinate, true value of a number, Weibull parameter x x variate Y Coordinate y Coordinate, deflection y y variate Z Coordinate, section modulus, viscosity z Standard deviation of the unit normal distribution z Variate of z
xxiv Mechanical Engineering Design
Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition
Front Matter List of Symbols © The McGraw−Hill^7 Companies, 2008
List of Symbols xxv
α Coefficient, coefficient of linear thermal expansion, end-condition for springs, thread angle β Bearing angle, coefficient Change, deflection δ Deviation, elongation ǫ Eccentricity ratio, engineering (normal) strain Normal distribution with a mean of 0 and a standard deviation of s ε True or logarithmic normal strain Ŵ Gamma function γ Pitch angle, shear strain, specific weight λ Slenderness ratio for springs L Unit lognormal with a mean of l and a standard deviation equal to COV μ Absolute viscosity, population mean ν Poisson ratio ω Angular velocity, circular frequency φ Angle, wave length ψ Slope integral ρ Radius of curvature σ Normal stress σ ′^ Von Mises stress S Normal stress variate σ ˆ Standard deviation τ Shear stress Shear stress variate θ Angle, Weibull characteristic parameter ¢ Cost per unit weight $ Cost
Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition
I. Basics 1. Introduction to Mechanical Engineering Design
© The McGraw−Hill^9 Companies, 2008
3
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 12 1–8 Safety and Product Liability 15 1–9 Stress and Strength 15 1–10 Uncertainty 16 1–11 Design Factor and Factor of Safety 17 1–12 Reliability 18 1–13 Dimensions and Tolerances 19 1–14 Units 21 1–15 Calculations and Significant Figures 22 1–16 Power Transmission Case Study Specifications 23
Introduction to Mechanical
Engineering Design
Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition
I. Basics 1. Introduction to Mechanical Engineering Design
(^10) © The McGraw−Hill Companies, 2008
4 Mechanical Engineering Design
Mechanical design is a complex undertaking, requiring many skills. Extensive relation- ships need to be subdivided into a series of simple tasks. The complexity of the subject 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. The design engineer needs not only to develop competence in their field but 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 component is often related through stress and strength. Matters of uncertainty are ever-present in engineer- ing 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. The book consists of four parts. Part 1, Basics, begins by explaining some differ- ences 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 key principles nec- essary 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 fail- ure are difficult questions, and so we take two chapters to answer them, one on pre- venting 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 material of Parts 1 and 2 is 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, Analysis Tools, provides introductions to two important methods used in mechanical design, finite element analysis and statistical analysis. 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 use- ful 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 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, occasion- ally 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 adjust as more becomes known. The point is that the engineering designer has to be personally comfortable with a decision-making, problem-solving role.
Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition
I. Basics 1. Introduction to Mechanical Engineering Design
(^12) © The McGraw−Hill Companies, 2008
6 Mechanical Engineering Design
adverse circumstance or a set of random circumstances that arises almost simultaneously. For example, the need to do something about a food-packaging machine may be indi- cated 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 spec- ifications for the object that is to be designed. The specifications are the input and out- put 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 specifications 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 lim- itations, 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 processes 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 specifica- tions. It may be that a small plant, for instance, does not own cold-working machin- ery. Knowing this, the designer might select other metal-processing methods that can be performed in the plant. The labor skills available and the competitive situa- tion 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 materials and sizes. An example of a specification is given in Sec. 1–16. 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 impor- tant step in the synthesis task. Various schemes must be proposed, investigated, and
Figure 1– The phases in design, acknowledging the many feedbacks and iterations.
Identification of need
Definition of problem
Synthesis
Analysis and optimization
Evaluation
Presentation
Iteration
Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition
I. Basics 1. Introduction to Mechanical Engineering Design
© The McGraw−Hill^13 Companies, 2008
Introduction to Mechanical Engineering Design 7
quantified 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.g., 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 specifica- tions in order to determine the forces that will be transmitted to the shaft. But stock gears come with certain bore sizes, requiring knowledge of the necessary shaft diame- ter. 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 models of the system that will admit some form of mathematical analysis. We call these mod- els 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, evaluation is a significant phase of the total design process. Evaluation is the final proof of a success- ful 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? 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 explain their accomplishments to others. Presentation is a selling job. The engineer, when presenting a new solution to administrative, management, or supervisory persons, is attempting to sell or to prove to them that this solution is a better one. Unless this can be done successfully, the time and effort spent on obtaining the 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 solutions to management, they begin to receive salary increases and promotions; in fact, this is how anyone succeeds in his or her profession.
(^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.
Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition
I. Basics 1. Introduction to Mechanical Engineering Design
© The McGraw−Hill^15 Companies, 2008
Introduction to Mechanical Engineering Design 9
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 sub- set of CAE. Some computer software packages perform specific engineering analysis 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 integrated within a CAD system—include finite-element analysis (FEA) programs for analysis of stress and deflection (see Chap. 19), vibration, and heat transfer (e.g., Algor, ANSYS, and MSC/NASTRAN); computational fluid dynamics (CFD) programs for fluid-flow analy- sis and simulation (e.g., CFD++, FIDAP, and Fluent); and programs for simulation of dynamic force and motion in mechanisms (e.g., ADAMS, DADS, and Working Model). Examples of non-engineering-specific computer-aided applications include soft- ware for word processing, spreadsheet software (e.g., Excel, Lotus, and Quattro-Pro), and mathematical solvers (e.g., Maple, MathCad, Matlab, 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 caution, however: Computer software is no substitute for the human thought process. You 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 solu- tions, and monitor the software company and user-group newsletters.
Acquiring Technical Information We currently live in what is referred to as the information age, where information is gen- erated 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 encyclo- pedias, textbooks, monographs, handbooks, indexing and abstract services, journals, translations, technical reports, patents, and business sources/brochures/catalogs.
- Government sources. Departments of Defense, Commerce, Energy, and Transportation; NASA; Government Printing Office; U.S. 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.^3
(^3) Some helpful Web resources, to name a few, include www.globalspec.com, www.engnetglobal.com, www.efunda.com, www.thomasnet.com, and www.uspto.gov.
Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition
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10 Mechanical Engineering Design
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 (man- agement, clients, consumers, etc.) and is expected to do so in a competent, responsi- ble, 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 cul- tivate 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 (achieve- ments, promotions, raises, etc.) may in large part be due to competence but if you can- not communicate your ideas clearly and concisely, your technical proficiency 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 companies 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 chrono- logical records will make it easier to explain your decisions at a later date. Many engineering students see themselves after graduation as practicing engineers 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 make any presenta- tion, 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 problem statement.
- Identify the known. From the refined problem statement, describe concisely what information is known and relevant.
- Identify the unknown and formulate the solution strategy. State what must be deter- mined, in what order, so as to arrive at a solution to the problem. Sketch the compo- nent or system under investigation, identifying known and unknown parameters. 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; equations