Design of Machine Elements, Eighth Edition (2004)

Design of Machine Elements, Eighth Edition M. F. Spotts, T. E. Shoup, L. E. Hornberger, Pearson Prentice Hall, Upper Saddle River, NJ, 2004 (ISBN 0-13-048989-1). The eighth edition of Machine Elements provides tools and techniques to facilitate design calculations for the most frequently encountered machine elements. The book opens with a brief overview of the design process relative to general problem solving approaches and specific ANSI design standards. A condensed but informative overview of statics and failure theories is provided, followed by separate chapters for the design of shafts, springs, screws and transmission elements such as belts, clutches, brakes, chains, bearings, and the most common types of gears. Using a phenomenological approach, each type of machine element and its associated variants are described with respect to function, form, and constraints. The provided performance and failure analysis is accessible, with most mathematical derivations given in full detail to increase the usefulness and adaptability of the provided information. Educators and practitioners currently utilizing the 7th edition will appreciate the important changes to the 8th edition. While the organization of the two books is virtually identical through Chapter 14, a structured approach has been applied to all the design examples. This structured approach includes the enumeration of the problem statement, given information, assumptions, solution method, and solution details. While quite standard, this structured approach does facilitate an understanding of the engineering approach and may assist the development of critical thinking skills. The 8th edition also provides 54 improved spreadsheets that are utilized throughout the text. The spreadsheets are well presented and usually include a schematic, relevant equations, an input section, and a results section. In most cases, the spreadsheets provide drop-down menus for switching between unit systems. Furthermore, the spreadsheets are not protected so that the reader may inspect or modify the equations if desired. Also new in the 8th edition is the 15th chapter on designing with plastics by L. E. Hornberger. This twenty page chapter provides an overview of polymeric materials with respect to morphology and additives, however, I would prefer more substantive instruction for designing with plastics. The two quantitative examples in the chapter are reworked problems from previous chapters with substituted material properties. The two qualitative examples do not provide sufficient analysis or data for adequate guidance to the practicing engineer or engineering student. Issues related to plastics manufacturing processes (e.g. process selection, tolerances, economics, etc.) are not discussed. While I highly recommend this text, I have two concerns. First, the approach is classical and formulaic without significant treatment of uncertainty in the design requirements or parameters. For example, a module on fatigue design of transmission shafts utilizes the Soderberg equation and von Mises-Hencky theory to find an allowable equivalent static stress for fluctuating components, but the spreadsheet implementation provides a simple pass/fail result. No graphs are provided showing the relationships between the results and the critical design variables. Second, a table of material properties would be very helpful. While some properties are listed for metals in a chapter on engineering materials, designers would benefit by the inclusion of a uniform table listing density, modulus, yield strength, Poisson’s ratio, density, strain to failure, coefficient of thermal expansion, and others for metals, plastics, and ceramics. Overall, this 8th edition of Machine Elements is rich with content and examples, and those looking for an undergraduate text on the subject should consider adopting this text. I am also confident that graduate students and practicing engineers will find this to be a valuable reference.