Machine Elements in Mechanical Design

Citation

Mott, R. L., Vavrek, E. M., & Wang, J. (2017). Machine Elements in Mechanical Design (6th ed.). Pearson.

Chapter Summary

The sixth edition has 23 chapters in three parts, followed by 19 appendices of data and design aids. Part 1 reviews stress analysis and loading for design; Part 2 is organised around the design of a single mechanical drive; Part 3 covers further machine elements and ends with a chapter of design projects. Pearson's description notes that two new coauthors joined Mott for this edition, which strengthens the stress-analysis material and widens the range of technical topics.

Chapter 1: The Nature of Mechanical Design

The opening chapter sets out what mechanical design involves and how the book approaches it, as the start of Part 1, "Principles of Design and Stress Analysis".

Chapter 2: Materials in Mechanical Design

A survey of engineering materials and their design properties. It prepares the reader to use the property tables in the appendices, which cover carbon, alloy, heat-treated, carburized, stainless and structural steels, cast iron, aluminum, zinc, magnesium, nickel and titanium alloys, copper alloys and plastics.

Chapter 3: Stress and Deformation Analysis

Pearson's free sample of this chapter shows its shape. It opens with "The Big Picture", a discussion prompt asking readers to think about how familiar products fail, and "You Are the Designer", a utility-crane scenario used to review statics and free-body analysis. Its 23 sections then review direct axial and shear stress, torsion (including non-circular sections and thin-walled tubes), bending stress and shear stress in beams, the flexural center, beam deflection, curved beams, superposition, stress concentrations and notch sensitivity. The text states plainly that it assumes a completed course in strength of materials.

Chapter 4: Combined Stresses

Treats members carrying more than one kind of stress at the same time, extending the single-load cases reviewed in Chapter 3.

Chapter 5: Design for Different Types of Loading

Covers how the type of loading, static or varying, governs the design approach. Together with Chapters 3 and 4, it forms the analysis base that the component chapters draw on.

Chapter 6: Columns

Closes Part 1 with compression members, where stability rather than stress limits the design.

Chapters 7–10: Belt Drives and Chain Drives; Kinematics of Gears; Spur Gear Design; Helical Gears, Bevel Gears, and Wormgearing

Part 2, "Design of a Mechanical Drive", begins with flexible drives and then moves through gearing: first gear kinematics, then the design of spur gears, then helical, bevel and worm gearing. Appendix 19 supplies the pitting geometry factor for spur gears.

Chapters 11–14: Keys, Couplings, and Seals; Shaft Design; Tolerances and Fits; Rolling Contact Bearings

The elements that connect and support the rotating parts: keys, couplings and seals, then shafts, then tolerances and fits, then rolling bearings. The Chapter 3 sample already points forward to this material, with an example on the deflection of gear shafts that refers ahead to the gear-force chapters.

Chapter 15: Completion of the Design of a Power Transmission

The capstone of Part 2, which brings the separately designed elements together into a complete power transmission.

Chapters 16–19: Plain Surface Bearings; Linear Motion Elements; Springs; Fasteners

Part 3, "Design Details and Other Machine Elements", turns to components outside the drive: sliding bearings, elements for linear motion, springs and fasteners.

Chapters 20–22: Machine Frames, Bolted Connections, and Welded Joints; Electric Motors and Controls; Motion Control: Clutches and Brakes

The structure that holds a machine together and the components that power and control it: frames and joints, electric motors with their controls, and clutches and brakes.

Chapter 23: Design Projects

The final chapter collects design projects that draw on the whole book.

Key Concepts

Part 1: Principles of Design and Stress Analysis (Chapters 1–6)

• Design for safety: the stresses and deflections a component experiences must stay acceptable under reasonably foreseeable conditions; Chapter 3 opens with this philosophy.
• Stress element: a small element used to represent the normal and shear stresses acting at a point.
• Stress concentration and notch sensitivity: the local rise in stress at geometric changes, and how much of it a given material actually feels.
• Combined stresses: the state of stress when several loads act together.
• Column stability: the failure of compression members by buckling rather than by overstress.

Part 2: Design of a Mechanical Drive (Chapters 7–15)

• Gear kinematics: the geometry and speed relationships of meshing gears, studied before gear strength.
• Shaft design: sizing a shaft that carries gears, pulleys or sprockets and is supported by bearings.
• Tolerances and fits: specifying the size limits of mating parts.
• System integration: completing a power transmission by combining the separately designed elements (Chapter 15).

Part 3: Design Details and Other Machine Elements (Chapters 16–23)

• Bearing types: rolling contact bearings (Chapter 14) and plain surface bearings (Chapter 16) as alternative ways to support moving parts.
• Joints: bolted connections and welded joints in machine frames.
• Motion control: clutches and brakes, and the electric motors and controls that drive machines.

Critical Analysis

Strengths

• Elements designed in context. Pearson describes the book's emphasis as applying machine elements while always considering them within the larger machine they belong to. The structure carries this out: Part 2 is organised around designing one mechanical drive, from belts and gears through shafts and bearings, and closes with a chapter that completes the power transmission.
• Clear, consistent worked examples. In the Chapter 3 sample, about twenty example problems follow the same Objective, Given, Analysis, Results and Comment layout, and more than eighty end-of-chapter problems follow. Examples use both U.S. Customary and SI units, which matters for readers who will meet either system.
• Practical design data. Nineteen appendices cover section properties, preferred sizes and screw threads, property tables for many metals and plastics, beam-deflection formulas, standard structural shapes, conversion factors, hardness conversion and stress-concentration factors. The sample chapter also lists references and Internet resources, such as educational stress-analysis software and an online source of stress-concentration data.
• A review built in. Chapters 3–5 review stress analysis before any component is designed, so students whose strength-of-materials course was some time ago can catch up without a separate text.

Limitations

• Breadth over depth. Twenty-three chapters on a wide range of elements leave less space per topic than in the more analytical machine-design texts. The book is a practical course text rather than a reference on failure theory.
• Prerequisites are real. Although the review chapters help, the sample says plainly that it assumes a completed course in strength of materials and that statics is already familiar; the material is a review, not a first course.
• A large book to select from. The Open Library record for this hardcover gives 880 pages; most courses will need to choose chapters, particularly from Part 3.

Where It Fits in the Course

Among the machine-design books in this course, Mott is the most directly practical: it reviews the stress analysis a student needs, then walks through the design of a complete drive. Juvinall and Marshek's Fundamentals of Machine Component Design and Norton's Machine Design: An Integrated Approach give more space to failure theories, fatigue and surface damage, and Norton follows recurring case studies with computer-aided calculation. Shigley's Mechanical Engineering Design is the reference-level treatment for upper-level courses. Mott works well as the first machine-design text, with one of these as the next step when a course needs more theory.

The design-methodology books play a different role. Nigel Cross's Engineering Design Methods and Pahl and Beitz's Engineering Design: A Systematic Approach deal with how a product concept is developed, not with sizing gears, shafts and bearings. They are worth reading alongside Mott's Chapter 23 design projects, where students must define and develop a design rather than solve a set problem.

How to Use This Book

The book is for mechanical engineering and engineering technology students taking their first machine-design course after statics and strength of materials, and for practising engineers who want a readable reference with design data. Pearson presents it as a course text for machine design.

A practical one-semester plan:

• Core analysis: Chapters 1–5. Work through Chapter 3 even if strength of materials feels fresh, because later chapters use its notation and its treatment of stress concentrations. Chapter 6 on columns can be taken when compression members come up.
• Core design sequence: Chapters 7–15 in order. The chapters build towards Chapter 15, so keep a running file of decisions (speeds, loads, materials, sizes) as each element is designed.
• Optional and project-dependent: choose from Chapters 16–22 to match the course or a project, for example springs and fasteners for a mechanism, or frames, bolted and welded joints for a structure.
• Integration: use a Chapter 23 design project as the term project.

For each chapter, read "The Big Picture" and the scenario first, then work the example problems yourself before reading the solutions. Get used to the appendices early, since realistic design depends on looking up material properties, preferred sizes and stress-concentration factors rather than assuming them.