An Introduction to Mechanical Engineering - Web Education

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P URPOSE

A PPROACH AND C ONTENT

Third, you will learn some of the calculations, estimates, and approximations that mechanical engineers can make when solving technical problems and communicating their results. You won't be an expert in mechanical engineering after reading this textbook, but that's not our intention and it shouldn't be yours.

A PPROACH

O BJECTIVES

Collectively, these courses included lectures, computer-aided design and manufacturing projects, product analysis labs (examples of which are discussed in Section 2.1), and team design projects (examples of which are described in Sections 2.4 and 2.5 in the context of design conceptualization). We also discuss many vignettes and case studies to show students the reality of what they are learning, including the “Top Ten” list of accomplishments developed by the American Society of Mechanical Engineers (Section 1.3), fourteen “Grand Challenges” from the National Academy of Engineering (NAE) (Section 2.1), Design Innovation and Patents (Section 2.2), Urban Energy Infrastructures (Section 2.5), Integrated Computer-Aided Engineering (Section 2.6), The Loss of the Mars Climate Orbiter and the Air Canada Flight Refueling Failure 143 (section 3.1), the Deepwater Horizon oil spill disaster (section 3.6), the Challenger disaster (section 3.7), the Kansas City Hyatt disaster (section 4.5), the design of Masdar City (section 5.2), the design of advanced materials (section 5.5), microfluidic devices (Section 6.2), blood flow in the human body (Section 6.5), sports technology (Sections 6.6 and 6.7), renewable energy sources (Section 7.5), internal combustion engines (Section 7.6), solar energy generation (Section 7.7 ) and nanomachines (Section 8.3).

C ONTENT

Match the background, maturity, and interests of students early in their study of engineering
Expose students to the signifi cance of mechanical design principles in the development of innovative solutions to technical challenges that
Help students think critically and learn good problem-solving skills, particularly with respect to formulating sound assumptions, making
Convey aspects of mechanical engineering science and empiricism that can be applied at the freshman and sophomore levels
Expose students to a wide range of hardware, innovative designs, engineering technology, and the hands-on nature of mechanical
Generate excitement through applications encompassing urban infrastructure development, nanomachines, aircraft, space fl ight,

This textbook reflects our experiences and philosophy for introducing students to the vocabulary, skills, applications, and excitement of the mechanical engineering profession. Convey aspects of the science and empiricism of mechanical engineering that can be applied at the freshman and sophomore levels can be applied at the freshman and sophomore levels.

N EW IN THE T HIRD E DITION

Additionally, in Chapter 1, we present an updated figure illustrating the organization of mechanical engineering topics in this edition and in a typical mechanical engineering curriculum. This figure is used in each chapter to graphically show how the content of the chapter fits into the overall study of mechanical engineering.

S UPPLEMENTS

C OURSE M ATE

A CKNOWLEDGMENTS

O VERVIEW

In this introductory chapter, we describe who mechanical engineers are, what they do, what their challenges and rewards are, what their global impact can be, and what their notable achievements have been. They also create a host of other products that you don't necessarily see or hear about because they are used in business and industrial settings.

The Elements of Mechanical Engineering

Rather, engineering is a driver of social and economic growth and an integral part of the business cycle. They analyze the impact of the products they develop or the systems they design on the environment and on the people who use them.

Figure 1.6 Percentages of engineers working in the traditional engineering ﬁ elds and their specializations

The discipline is closely related to the engineering fields of industrial (240,500 people), aerospace (71,600), and nuclear (16,900) engineering, as each of those fields has evolved historically as a spin-off of mechanical engineering. While mechanical engineering is often considered the broadest of the traditional engineering fields, there are many opportunities for specialization in the industry or technology that interests you.

Mechanical Engineering’s Top Ten Achievements

The automobile. The development and commercialization of the automobile were judged as the profession’s most signifi cant achievement
Power generation. One aspect of mechanical engineering involves designing machinery that can convert energy from one form to another
Agricultural mechanization. Mechanical engineers have developed technologies to improve signifi cantly the effi ciency in the agricultural
Integrated-circuit mass production. The electronics industry has developed remarkable technologies for miniaturizing integrated

C AREER P ATHS
T YPICAL P ROGRAM OF S TUDY

The development of the aircraft and related technologies for safe powered flight has also been recognized by the American Society of Mechanical Engineers as a key achievement of the profession. Jobs historically labeled as "mechanical engineer" now include a number of diverse titles that reflect the changing nature of the profession.

Figure 1.11 Mechanical engineers design machines for producing energy from a variety of renewable sources, such as (a) wave energy power plants, (b) solar power towers, and (c) innovative wind turbines.

S UMMARY

Some of the computer-aided design and manufacturing tools discussed in Chapter 2 are also relevant to outcome (k). In Chapter 3, we focus directly on preparing you to achieve outcomes (e) and (g), which are critical to preparing you to become a successful engineering professional ready to design, create, innovate, study, analyze , production and impact. lives in a dynamic and global society.

Self-Study and Review

What is engineering?
What are the differences among engineers, mathematicians, and scientists?
What is mechanical engineering?
Compare mechanical engineering to the other traditional engineering fi elds
Describe a half dozen products that mechanical engineers design, improve, or produce, and list some technical issues that must be solved
Describe several of the top ten achievements of the mechanical engineering profession listed in Section 1.3
Discuss the career options and job titles that are available to mechanical engineers
Describe some of the main subjects that comprise a typical mechanical engineering curriculum

Outcomes (c), (h) and (j) are addressed in Chapters 1 and 2 and will also be part of other mechanical engineering courses, including higher level design courses.

PROBLEMS

Problem P1.1

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O VERVIEW

The purpose of this chapter is to introduce you to some of the issues that arise when a new product is designed, manufactured, and patented. Once the details of the product have been determined, the hardware must be built economically.

Figure 2.1 Relationship of the topics emphasized in this chapter (shaded boxes) relative to an overall program of study in mechanical engineering.

In the lower right corner is the Low-Style/High-Tech version of FINIS' SwiMP3 player. In the upper left corner, the High-Style/Low-Tech product is the Fashion Bottle filter system from Clear2O®.

Requirements Development

As mentioned in section 1.4, engineers must be able to communicate with a wide variety of stakeholders in a design process as they read patents issued for related technologies, consult with suppliers of components that can be used in the product, attend trade shows , presenting product proposals to management and meeting with potential customers.

Conceptual Design

The list of requirements from the first stage is used to eliminate unfeasible or inferior designs and to identify the concepts with the greatest potential to fulfill the requirements. Computer models and hardware prototypes can also be produced at this stage to aid in the selection process.

Detailed Design

However, the design patent would not protect the functional characteristics of the body, such as reducing wind drag or providing improved crash protection. A specification is a written description of the invention's purpose, construction, and operation.

Production

M ANUFACTURING P ROCESSES

The drill press shown in Figure 2.15 (see on page 54) is used to drill circular holes in a workpiece. Some of the same technologies used to create rapid product prototypes for design review are starting to be used for custom manufacturing.

C ASE S TUDY IN C ONCEPTUAL D ESIGN : M OUSETRAP -P OWERED V EHICLES

The team will then record progress as prototypes are built and tested to document the outcome of their iterative efforts.

First Concept: String and Lever Arm

The team records these questions and discussion topics in their notebook, but they leave them for future consideration. However, if this concept eventually emerges as a promising candidate, the team will need to address these issues before constructing a viable prototype.

Second Concept: Compound Geartrain

To prevent skidding, weight can be added to the vehicle to improve contact between the drive wheels and the ground. On the other hand, a heavier vehicle would be slower because the potential energy of the mousetrap spring is converted into the kinetic energy of the vehicle.

Third Concept: Sector-Shaped Gear

C ASE S TUDY IN U RBAN P OWER I NFRASTRUCTURES
C ASE S TUDY : C OMPUTER -A IDED D ESIGN : N ONINVASIVE M EDICAL I MAGING
What are the major stages of a mechanical design process?
Discuss the importance of innovation in the design process
What are the categories of system requirements that design engineers must consider when they start a design process?
To what extent should detailed decisions be made early in the design process regarding dimensions, materials, and other factors?
Discuss some of the interpersonal and communication issues that arise when engineers work together in a cross-disciplinary team on a design
Explain how simplicity, iteration, and documentation play signifi cant roles in a design process
What are some differences between design and utility patents?
How long is a recently issued utility patent valid?

A computer generated drawing of the design concept for the syringe and its interface to the electronically controlled injection system. Mechanical engineers designed each component of the mold to be used to manufacture the injection interface.

Problem P2.1

For problems P2.1–P2.6, the product happens to not have a certain shape or color; by regulation and/or basic function, it must be of a certain shape or color.

Problem P2.2

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Problem P2.32

O VERVIEW

List the base units in the United States customary system and the Système International d’Unités, and list some derived units used in mechanical engineering. Before takeoff, it was determined that the aircraft had 7,682 liters (L) of fuel in its tanks.

G ENERAL T ECHNICAL P ROBLEM -S OLVING A PPROACH

The point of this step is to make sure you have a plan of attack in mind to solve the problem. For example, if gravity is assumed to be present, the weight of all components in the problem may need to be taken into account.

Solution. Your solution to an engineering analysis problem will generally include text and diagrams along with your calculations to explain the

U NIT S YSTEMS AND C ONVERSIONS

Write a brief outline of the problem and explain the general approach you plan to take and list the key concepts, assumptions, equations, and conversion factors you expect to use. By being clear about the objective, you can ignore extraneous information and focus on solving the problem efficiently.

Base and Derived Units

Of course, you should always check the calculations and make sure they are dimensionally consistent. Finally, underline, circle, or outline your final result so there is no ambiguity about the answer you are communicating.

International System of Units

The SI base and derived units are often combined with a prefix so that the numerical value of a physical quantity does not have an exponent that is a power of ten that is either too large or too small. Except for derived units that are named after individuals, dimensions in SI are written in lowercase letters.

United States Customary System of Units

Another difference between USCS and SI is that USCS uses two different dimensions of mass: pound mass and slug mass. On the other hand, pound mass is defined as the amount of mass that weighs one pound.

Converting Between the SI and USCS

S IGNIFICANT D IGITS

The precision of a number is half the place of the last significant digit in the number. The accuracy of the numerical value is ±0.005 mN, a variation that could be present in the force reading and still result in a rounded value of 43.01 mN.

D IMENSIONAL C ONSISTENCY

Then we will use the difference in weight to determine the acceleration of the elevator. Finally, we solve for the acceleration, noting that the mass of the person must be converted to slugs.

E STIMATION IN E NGINEERING

The remaining usable oil may have been sealed off with cement, or the flow rate may have been limited by flow restrictions in the well • Approximate time of actual containment. Estimate the force exerted on the aircraft's main cabin door by this pressure imbalance.

Figure 3.8 Fluid ﬂ ow modeling and prediction.

C OMMUNICATION S KILLS IN E NGINEERING

By virtue of their work, engineers interact daily with other engineers, customers, business executives, marketers, and members of the public. As you begin your study of mechanical engineering, you should begin to develop some of the problem-solving and technical communication skills that meet the standards of what other engineers and the public will expect of you.

Written Communication

The body of the report reviews previous work, brings the reader up to speed, and then describes in detail the design, the supporting decisions, the results of testing, performance calculations, and other technical information. Engineers must carefully consider which type of graph or chart to use; the choice depends on the nature of the data and the type of insights to be understood by the reader.

Technical Presentations

An engineer is tasked with developing a professional table and graph that communicates the data and explains the Hooke's Law relationship for the spring. The number of significant digits in each column is now the same. • Titles are written in capital letters and bold.

Problem P3.1

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Problem P3.27

Calculate, in units of kilotons, the kinetic energy of an asteroid that has the size (boxy shape, km) and composition (density, 2.4 g/cm3) of our solar system's asteroid Eros. Objects passing through the inner solar system typically have speeds in the range of 20 km/s.

Problem P3.28

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O VERVIEW

Successful design is supported by effective engineering analysis; Effective engineering analysis relies on an understanding of the forces in structures and machines. This chapter introduces you to the subject of mechanics, a subject that involves the forces acting on structures and machines and their tendency either to remain stationary or to move.

Every object remains in a state of rest or uniform motion of constant velocity unless an external unbalanced force acts upon it

The forces of action and reaction between two objectives are equal, opposite, and collinear

F ORCES IN R ECTANGULAR AND P OLAR F ORMS

The topics on force systems and machine components discussed in this chapter fit naturally into the hierarchy of mechanical engineering topics shown in Figure 4.2. In this chapter and subsequent chapters, we will use conversion tables with this type of notation for other engineering quantities.

Rectangular Components

In fact, the number pair (Fx, Fy) is just the coordinates of the peak of the force vector. Just as Fx and Fy provide information about the magnitudes of the horizontal and vertical components, the unit vectors provide information about the directions of these components.

Polar Components

R ESULTANT OF S EVERAL F ORCES

Each force is combined with the others to describe their net effect, and the resulting R measures the cumulative action. This summation can be performed using the vector algebra or vector polygon approaches described below.

Vector Algebra Method

Vector Polygon Method

The magnitude of a moment depends on the force applied and on the lever arm separating the force from the point of rotation.

Perpendicular Lever Arm Method

The distance d is called the perpendicular lever arm and extends from the line of action of the force to point O. The moment is calculated from both the magnitude of F and the perpendicular offset d between the line of action of the force and point O.

Moment Components Method

E QUILIBRIUM OF F ORCES AND M OMENTS

With groundwork for the properties of forces and moments now in place, we next move on to the task of calculating (unknown) forces acting on structures and machines in response to other (known) forces present. This process involves applying the principles of static equilibrium from Newton's first law to structures and machines that are either stationary or moving at constant velocity.

Particles and Rigid Bodies

The summations in the equilibrium equations cover all forces and moments present, whether their directions and magnitudes are known in advance or not. Mathematically speaking, the equilibrium equations for a rigid body consist of a system of three linear equations involving the unknown forces.

Free Body Diagrams

D ESIGN A PPLICATION : R OLLING -E LEMENT B EARINGS

Calculate the magnitude and direction of the forces exerted by the shaft on the two bearings. Assuming that the forces are equally balanced between the four wheels, calculate the magnitude of the resultant force acting on the tapered roller bearings that support each wheel.

Make a cross-sectional drawing of a tapered roller bearing

How to calculate the resultant of a force system using the vector algebra and vector polygon methods. How to calculate a moment using the perpendicular lever arm and moment components methods.