Preface for Hamrock - Fundamentals of Machine Elements

		Fundamentals of Machine Elements Bernard Hamrock
		About the Book

PREFACE

This book is intended to provide the undergraduate student with a clear and thorough understanding of both the theory and application of the fundamentals of machine elements. It is expected that this book will also be used as a reference by practicing engineers. Familiarity with differential and integral calculus is needed to comprehend the material presented. The design of machine elements involves a great deal of geometry as well. Therefore, the ability to sketch the various configurations that arise, as well as to draw a free-body diagram of the loads acting on a component, is also needed. The material covered in this text is appropriate as a third- or fourth-year engineering course for students who have studied basic engineering sciences, including physics, engineering mechanics, and materials and processes.

The book is divided into two parts. Part 1 (Chapters 1 to 8) presents the fundamentals, and Part 2 (Chapters 9 to 19) uses the fundamentals in considering the design of various machine elements. The material in Part 1 is sequential; material presented in early chapters is needed in subsequent chapters. This building-block approach provides the foundation necessary to design the various machine elements considered in Part 2.

LEARNING TOOLS

The following pedagogical devices are used in each chapter to improve understanding and motivate the student:

• Symbol list-defines the symbols used within the chapter and gives their units for use in unit checks within equations.

• Quotation and photograph-open each chapter as an introduction to the topics in the chapter

• Introduction-previews the material covered in the chapter.

• Key words-presented in bold when first used and listed along with definitions at the end of the chapter.

• Worked examples-presented when a new concept is developed to reinforce student understanding. There are over 200 worked examples, and each one uses a consistent problem-solving format.

• Consistent problem-solving methodology-each example and problem is solved according to a consistent methodology. Students are encouraged to follow these four steps in solving examples and problems:

1. Sketch-gives graphical description of problem.

2. Given-presents the information from the problem statement in symbol form.

3. Find-states what needs to be determined.

4. Solution-indicates the method, procedure, and equations used to solve the problem.

• Case studies-presented in select chapters, the case studies are design oriented and combine multiple concepts from the chapter. Many of the case studies involve situations encountered by practicing engineers. There are 25 case studies total. In addition there are three system design projects at the end of Chapter 19 in complete solution form, as well as 19 additional design projects to assign.

• Summary-recapitulates the information from the chapter.

• Recommended readings and references-these lists are located at the end of each chapter as sources of further information and greater detail. The author-date system is used for reference citations.

• End-of-chapter problems-over 600 homework problems to solidify understanding of the chapter material and stimulate creativity. The problems range from simple to complex and many provide design-related opportunities for the student. Solutions to the homework problems can be found in the Instructor's Solutions Manual, available to professors who adopt the text.

MACHINE DESIGN CD-ROM

The publisher and authors researched the types of teaching and learning aids that would be useful to users of Fundamentals of Machine Elements. Based on that research, a CD-ROM containing various tools was developed and packaged with every copy of this text. The CD-ROM contains the following items:

• PowerPoint files containing all the figures and tables from the text. These PowerPoint files can be used for the creation of print transparencies, or they can be loaded into an instructor's PowerPoint presentation for electronic use in lecture.

• Video clips and brief animations from industry to highlight concepts from the text such as gears, failure analysis, and bearings.

• Design tutorials to serve as interactive case studies. These tutorials will provide real-world design situations, along with exercises to test problem-solving and design skills.

• Full-color animations of select machine elements to help the student better visualize the motion and dynamics of the element being studied.

• Additional rolling element bearing data to allow more flexible design problems to be examined.

WEB SITE

A web site containing other book-related resources can be found at http://www.mhhe. com/hamrock. The web site provides reported errata, web links to related sites of interest, password-protected solutions to homework problems for instructors, a bulletin board, and information about ordering books and supplements.

CONTENTS

Chapter 1 introduces machine design and machine elements and covers a number of topics, such as safety factors, statistics, units, unit checks, and significant figures. In designing a machine element it is important to evaluate the kinematics, loads, and stresses at the critical section. Chapter 2 describes the applied loads (normal, torsional, bending, and transverse shear) acting on a machine element with respect to time, the area over which the load is applied, and the location and method of application. The importance of support reaction, application of static force and moment equilibrium, and proper use of free-body diagrams is highlighted. Shear and moment diagrams applied to beams for various types of singularity function are also considered. Chapter 2 then describes stress and strain separately.

Chapter 3 focuses on the properties of solid engineering materials, such as the modulus of elasticity. (Appendix A gives properties of ferrous and nonferrous metals, ceramics, polymers, and natural rubbers. Appendix B explores the stress-strain relationships for uniaxial, biaxial, and triaxial stress states.) Chapter 4 describes the stresses and strains that result from the types of load described in Chapter 2, while making use of the general Hooke's law relationship developed in Appendix B. Chapter 4 also considers straight and curved members under these four types of load.

Certainly, ensuring that the design stress is less than the yield stress for ductile materials and less than the ultimate stress for brittle materials is important for a safe design. However, attention must also be paid to displacement (deformation), since a machine element can fail by excessive elastic deformation. Chapter 5 attempts to quantify the deformation that might occur in a variety of machine elements. Some approaches investigated are the integral method, the singularity function, the method of superposition, and Castigliano's theorem. These methods are applicable for distributed loads.

Stress raisers, stress concentrations, and stress concentration factors are investigated in Chapter 6. An important cause of machine element failure is cracks within the microstructure. Therefore, Chapter 6 covers stress levels, crack-producing flaws, and crack propagation mechanisms and also presents failure prediction theories for both uniaxial and multiaxial stress states. The loading throughout Chapter 6 is assumed to be static (i.e., load is gradually applied and equilibrium is reached in a relatively short time). However, most machine element failures involve loading conditions that fluctuate with time. Fluctuating loads induce fluctuating stresses that often result in failure by means of cumulative damage. These topics, along with impact loading, are considered in Chapter 7.

Chapter 8 covers lubrication, friction, and wear. Not only must the design stress be less than the allowable stress and the deformation not exceed some maximum value, but lubrication, friction, and wear (tribological considerations) also must be properly understood for machine elements to be successfully designed. Stresses and deformations for concentrated loads, such as those that occur in rolling-element bearings and gears, are also determined in Chapter 8. Simple expressions are developed for the deformation at the center of the contact as well as for the maximum stress. Chapter 8 also describes the properties of fluid film lubricants used in a number of machine elements. Viscosity is an important parameter for establishing the load-carrying capacity and performance of fluid-film lubricated machine elements. Fluid viscosity is greatly affected by temperature, pressure, and shear rate. Chapter 8 considers not only lubricant viscosity but also pour point and oxidation stability, greases and gases, and oils.

Part 2 (Chapters 9 to 19) relates the fundamentals to various machine elements. Chapter 9 deals with columns, which receive special consideration because yielding and excessive deformation do not accurately predict the failure of long columns. Because of their shape (length much larger than radius) columns tend to deform laterally upon loading; and if deflection becomes critical, they fail catastrophically. Chapter 9 establishes failure criteria for concentrically and eccentrically loaded columns.

Chapter 10 considers cylinders, which are used in many engineering applications. The chapter covers tolerancing of cylinders; stresses and deformations of thin-walled, thick-walled, internally pressurized, externally pressurized, and rotating cylinders; and press and shrink fits.

Chapter 11 considers shafting and associated parts, such as keys and flywheels. A shaft design procedure is applied to static and cyclic loading; thus, the material presented in Chapters 6 and 7 is directly applied to shafting. Chapter 11 also considers critical speeds of rotating shafts.

Chapter 12 presents the design of hydrodynamic bearings-both thrust and journal configurations-as well as design procedures for the two most commonly used slider bearings. The procedures provide an optimum pad configuration and describe performance parameters, such as normal applied load, coefficient of friction, power loss, and lubricant flow through the bearing. Similar design information is given for plain and nonplain journal bearings. The chapter also considers squeeze film and hydrostatic bearings, which use different pressure-generating mechanisms. The last section of the chapter presents the design of gas-lubricated bearings.

Rolling-element bearings are presented in Chapter 13. Statically loaded radial, thrust, and preloaded bearings are considered, as well as loaded and lubricated rolling-element bearings, fatigue life, and dynamic analysis. The use of the elastohydrodynamic lubrication film thickness is integrated with the rolling-element bearing ideas developed in this chapter.

Chapter 14 covers the design of spur gears and briefly describes helical gears. Stress failures are also considered. The transmitted load is used to establish the design bending stress in a gear tooth, which is then compared with an allowable stress to establish whether failure will occur. Chapter 14 also considers fatigue failures. The Hertzian contact stress with modification factors is used to establish the design stress, which is then compared with an allowable stress to determine whether fatigue failure will occur. If an adequate protective elastohydrodynamic lubrication film exists, gear life is greatly extended.

Chapter 15 covers threaded, riveted, welded, and adhesive joining of members, as well as power screws. Riveted and threaded fasteners in shear are treated alike in design and failure analysis. Four failure modes are presented: bending of member, shear of rivet, tensile failure of member, and compressive bearing failure. Fillet welds are highlighted, since they are the most frequently used type of weld. A brief stress analysis for lap and scarf adhesively bonded joints is also given.

Chapter 16 treats the design of springs, especially helical compression springs. Because spring loading is most often continuously fluctuating, Chapter 16 considers the design allowance that must be made for fatigue and stress concentration. Helical extension springs are also covered in Chapter 16. The chapter ends with a discussion of torsional and leaf springs.

Brakes and clutches are covered in Chapter 17. The brake analysis focuses on the actuating force, the torque transmitted, and the reaction forces in the hinge pin. Two theories relating to clutches are studied: the uniform pressure model and the uniform wear model.

Chapter 18 deals with flexible machine elements. Flat belts and V-belts, ropes, and chains are covered. Methods of effectively transferring power from one shaft to another while using belts, ropes, and chains are also presented. Failure modes of these flexible machine elements are considered.

Chapter 19 presents three system design projects in complete solution form. When possible, some of the design engineer's reasons for pursuing alternatives are discussed in detail. This chapter is the culmination of machine element design. At the end of the chapter 26 additional projects are suggested.

Bernard J. Hamrock Bo O. Jacobson Steven R. Schmid

Ohio State University Lund University The University of Notre Dame

Lund, Sweden